1
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Hunt JR, Hecht J, Goolsby C, Hagihara J, Loza M, del Pozo S. Excited State Proton Transfer from Acidic Alcohols to a Quinoline Photobase Can Be Solvated by Non-Acidic Alcohol Solvents. J Phys Chem A 2024; 128:6199-6207. [PMID: 39034730 PMCID: PMC11299183 DOI: 10.1021/acs.jpca.4c02907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Revised: 06/25/2024] [Accepted: 07/11/2024] [Indexed: 07/23/2024]
Abstract
Photobases are a type of molecule that become more basic upon photoexcitation and can therefore be used to control proton transfer reactions with light. The solvation requirements for excited state proton transfer (ESPT) in photobase systems is poorly understood, which limits their applicability. Here, we investigate the solvation of the ESPT reaction using 5-methoxyquinoline (MeOQ), a well-studied photobase with an excited state pKa (pKa*) of approximately 15.1, as a model system. Previous studies have shown that, in addition to the acidic donor that donates a proton to the photoexcited MeOQ, an additional "auxiliary donor" is necessary to solvate the resulting alkoxide. We investigate whether a nonacidic hydrogen bond donor (an alcohol solvent that MeOQ cannot deprotonate in bulk) can act as the auxiliary donor for the MeOQ ESPT reaction. First, we use steady state spectroscopy, TCSPC, and electronic structure calculations to show that MeOQ can deprotonate the acidic donor 2,2,2-trifluoroethanol (TFE, pKa = 12.5) using ethanol as the auxiliary donor. We show that the degree of ESPT is largely predicted by the degree of ground state hydrogen bonding between the photobase and the acidic donor. Next, we study the deprotonation of the acidic donors TFE and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP, pKa = 9.3) with MeOQ in a variety of nonacidic alcohol solvents of varying chain length and branching. MeOQ ESPT occurs to varying extents in all solvents, suggesting that all studied nonacidic alcohols can function as auxiliary donors. We show that the concentration of the acidic donor is strongly correlated with the degree of ESPT. These results are necessary fundamental steps toward the understanding of the photobase ESPT reaction and its wide application in a variety of chemical systems.
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Affiliation(s)
- Jonathan Ryan Hunt
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Joseph Hecht
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Clara Goolsby
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Jade Hagihara
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Monique Loza
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Samantha del Pozo
- Loyola Marymount University, Los Angeles, California 90045, United States
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2
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Bhide R, Phun GS, Ardo S. Elementary Reaction Steps That Precede or Follow a Unimolecular Reaction Step Can Obfuscate Interpretation of the Driving-Force Dependence to Its Rate Constant. J Phys Chem A 2024; 128:4177-4188. [PMID: 38752741 DOI: 10.1021/acs.jpca.3c08228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2024]
Abstract
Assessing the validity of a driving-force-dependent kinetic theory for a unimolecular elementary reaction step is difficult when the observed reaction rate is strongly influenced by properties of the preceding or following elementary reaction step. A well-known example occurs for bimolecular reactions with weak orbital overlap, such as outer-sphere electron transfer, where bimolecular collisional encounters that precede a fast unimolecular electron-transfer step can limit the observed rate. A lesser-appreciated example occurs for bimolecular reactions with stronger orbital overlap, including many proton-transfer reactions, where equilibration of an endergonic unimolecular proton-transfer step results in a relatively small concentration of reaction products, thus slowing the rate of the following step such that it becomes rate limiting. Incomplete consideration of these points has led to discrepancies in interpretation of data from the literature. Our reanalysis of these data suggests that proton-transfer elementary reaction steps have a nonzero intrinsic free energy barrier, implying, in the parlance of Marcus theory, that there is non-negligible nuclear reorganization. Outcomes from our analyses are generalizable to inner-sphere electron-transfer reactions such as those involved in (photo)electrochemical fuel-forming reactions.
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Affiliation(s)
- Rohit Bhide
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Gabriel S Phun
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Shane Ardo
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
- Department of Chemical & Biomolecular Engineering, University of California Irvine, Irvine, California 92697, United States
- Department of Materials Science & Engineering, University of California Irvine, Irvine, California 92697, United States
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3
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Xie J, Nealon RE, Egan ZT, Takematsu K. Effect of cyano-addition on the photoacidity switch in 5-cyano-8-amino-2-naphthol. Phys Chem Chem Phys 2023. [PMID: 38050989 DOI: 10.1039/d3cp04845d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
Cyano- or CN-additions are often utilized in the design of photoacids to enhance and/or enable excited state proton transfer (ESPT) from the protic site to aqueous and nonaqueous solvents. In diprotic photoacid 8-amino-2-naphthol (8N2OH), the protonation state of the amino group (NH3+/NH2) acts as an on-off switch for ESPT at the OH site in water. This study investigated whether the addition of CN in 5-cyano-8-amino-2-naphthol (5CN8) could override this switch and promote new ESPT pathways. Analysis of the steady-state and time-resolved emission data showed that in the presence of protonated NH3+, CN enhances OH photoacidity (vs. in 8N2OH) and activates the ESPT pathway at NH3+. Both protic sites, OH and NH3+, can also donate a proton to methanol upon excitation. In contrast, in the presence of deprotonated NH2, despite the addition of CN, ESPT is still not observed at the OH site for 5CN8. Thus, the addition of CN cannot override or negate the inhibiting effect of NH2 on OH photoacidity. Potential causes for this inhibition are discussed, including electronic and antiaromaticity effects of CN and NH2 substitution.
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Affiliation(s)
- Jialin Xie
- Department of Chemistry, Bowdoin College, Brunswick, ME 04011, USA.
| | - Rachel E Nealon
- Department of Chemistry, Bowdoin College, Brunswick, ME 04011, USA.
| | - Zelia T Egan
- Department of Chemistry, Bowdoin College, Brunswick, ME 04011, USA.
| | - Kana Takematsu
- Department of Chemistry, Bowdoin College, Brunswick, ME 04011, USA.
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4
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Zika A, Agarwal M, Schweins R, Gröhn F. Double-Wavelength-Switchable Molecular Self-Assembly of a Photoacid and Spirooxazine in an Aqueous Solution. J Phys Chem Lett 2023; 14:9563-9568. [PMID: 37861686 DOI: 10.1021/acs.jpclett.3c02392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
Quadruple-switchable nanoscale assemblies are built by combining two types of water-soluble molecular photoswitches through dipole-dipole interaction. Uniting the wavelength-specific proton dissociation of a photoacid and ring-opening of an anionic spirooxazine results in an assembly that can be addressed by irradiation with two different wavelengths: pH and darkness.
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Affiliation(s)
- Alexander Zika
- Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, Bavarian Polymer Institute, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91058 Erlangen, Germany
| | - Mohit Agarwal
- Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, Bavarian Polymer Institute, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91058 Erlangen, Germany
- DS/LSS Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20 156, 38042 Grenoble CEDEX 9, France
| | - Ralf Schweins
- DS/LSS Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20 156, 38042 Grenoble CEDEX 9, France
| | - Franziska Gröhn
- Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, Bavarian Polymer Institute, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91058 Erlangen, Germany
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5
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Codescu MA, Kunze T, Weiß M, Brehm M, Kornilov O, Sebastiani D, Nibbering ETJ. Ultrafast Proton Transfer Pathways Mediated by Amphoteric Imidazole. J Phys Chem Lett 2023; 14:4775-4785. [PMID: 37186569 DOI: 10.1021/acs.jpclett.3c00595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Imidazole, being an amphoteric molecule, can act both as an acid and as a base. This property enables imidazole, as an essential building block, to effectively facilitate proton transport in high-temperature proton exchange membrane fuel cells and in proton channel transmembrane proteins, enabling those systems to exhibit high energy conversion yields and optimal biological function. We explore the amphoteric properties of imidazole by following the proton transfer exchange reaction dynamics with the bifunctional photoacid 7-hydroxyquinoline (7HQ). We show with ultrafast ultraviolet-mid-infrared pump-probe spectroscopy how for imidazole, in contrast to expectations based on textbook knowledge of acid-base reactivity, the preferential reaction pathway is that of an initial proton transfer from 7HQ to imidazole, and only at a later stage a transfer from imidazole to 7HQ, completing the 7HQ tautomerization reaction. An assessment of the molecular distribution functions and first-principles calculations of proton transfer reaction barriers reveal the underlying reasons for our observations.
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Affiliation(s)
- Marius-Andrei Codescu
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, 12489 Berlin, Germany
| | - Thomas Kunze
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Moritz Weiß
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Martin Brehm
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Oleg Kornilov
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, 12489 Berlin, Germany
| | - Daniel Sebastiani
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Erik T J Nibbering
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, 12489 Berlin, Germany
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6
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Naumova AO, Melnikov PV, Kuzmin VA, Zaitsev NK. Features of photoinduced proton transfer in the presence of a polyelectrolyte. MENDELEEV COMMUNICATIONS 2023. [DOI: 10.1016/j.mencom.2023.02.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
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7
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Knorr J, Sülzner N, Geissler B, Spies C, Grandjean A, Kutta RJ, Jung G, Nuernberger P. Ultrafast transient absorption and solvation of a super-photoacid in acetoneous environments. PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES : OFFICIAL JOURNAL OF THE EUROPEAN PHOTOCHEMISTRY ASSOCIATION AND THE EUROPEAN SOCIETY FOR PHOTOBIOLOGY 2022; 21:2179-2192. [PMID: 36178669 DOI: 10.1007/s43630-022-00287-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 08/08/2022] [Indexed: 12/13/2022]
Abstract
The phenomenon of photoacidity, i.e., an increase in acidity by several orders of magnitude upon electronic excitation, is frequently encountered in aromatic alcohols capable of transferring a proton to a suitable acceptor. A promising new class of neutral super-photoacids based on pyranine derivatives has been shown to exhibit pronounced solvatochromic effects. To disclose the underlying mechanisms contributing to excited-state proton transfer (ESPT) and the temporal characteristics of solvation and ESPT, we scrutinize the associated ultrafast dynamics of the strongest photoacid of this class, namely tris(1,1,1,3,3,3-hexafluoropropan-2-yl)8-hydroxypyrene-1,3,6-trisulfonate, in acetoneous environment, thereby finding experimental evidence for ESPT even under these adverse conditions for proton transfer. Juxtaposing results from time-correlated single-photon counting and femtosecond transient absorption measurements combined with a complete decomposition of all signal components, i.e., absorption of ground and excited states as well as stimulated emission, we disclose dynamics of solvation, rotational diffusion, and radiative relaxation processes in acetone and identify the relevant steps of ESPT along with the associated time scales.
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Affiliation(s)
- Johannes Knorr
- Physikalische Chemie II, Ruhr-Universität Bochum, 44780, Bochum, Germany.,Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Paul-Gordan-Straße 6, 91052, Erlangen, Germany
| | - Niklas Sülzner
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780, Bochum, Germany.,Physikalische Chemie II, Ruhr-Universität Bochum, 44780, Bochum, Germany
| | - Bastian Geissler
- Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstraße 31, 95053, Regensburg, Germany.,Physikalische Chemie II, Ruhr-Universität Bochum, 44780, Bochum, Germany
| | - Christian Spies
- Biophysikalische Chemie, Universität des Saarlandes, 66123, Saarbrücken, Germany.,Physikalische Chemie II, Ruhr-Universität Bochum, 44780, Bochum, Germany
| | - Alexander Grandjean
- Biophysikalische Chemie, Universität des Saarlandes, 66123, Saarbrücken, Germany
| | - Roger Jan Kutta
- Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstraße 31, 95053, Regensburg, Germany
| | - Gregor Jung
- Biophysikalische Chemie, Universität des Saarlandes, 66123, Saarbrücken, Germany
| | - Patrick Nuernberger
- Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstraße 31, 95053, Regensburg, Germany. .,Physikalische Chemie II, Ruhr-Universität Bochum, 44780, Bochum, Germany.
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8
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Joung JF, Jeong M, Park S. Reliable experimental method for determination of photoacidity revealed by quantum chemical calculations. Phys Chem Chem Phys 2022; 24:21714-21721. [PMID: 36074805 DOI: 10.1039/d2cp03308a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photoacids are aromatic acids that exhibit significantly different acidities when they are electronically excited. Three experimental methods have been extensively used to determine the photoacidity, : fluorescence titration, the Förster cycle, and time-resolved experiments. However, the photoacidities determined by these experimental methods are not consistent. In this work, we used a theoretical method to evaluate the reliability of experimentally determined values. In particular, density functional theory (DFT) and time-dependent DFT calculations were used to obtain the changes in Gibbs free energy for acid dissociation reactions which are directly related to values. The Förster cycle, which is frequently used to experimentally determine the photoacidity due to its simplicity, yielded inconsistent results depending on how the transition energy was defined. We evaluated six empirical parameters extracted from the absorption and emission spectra of acidic and basic species of photoacids to adequately define the transition energy in the Förster cycle. And we found that the values obtained using the optical bandgap as the transition energy in the Förster cycle were in the best agreement with the results of quantum chemical calculations.
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Affiliation(s)
- Joonyoung F Joung
- Department of Chemistry and Research Institute for Natural Science, Korea University, Seoul, 02841, Korea.
| | - Minseok Jeong
- Department of Chemistry and Research Institute for Natural Science, Korea University, Seoul, 02841, Korea.
| | - Sungnam Park
- Department of Chemistry and Research Institute for Natural Science, Korea University, Seoul, 02841, Korea.
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9
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Bhide R, Feltenberger CN, Phun GS, Barton G, Fishman D, Ardo S. Quantification of Excited-State Brønsted-Lowry Acidity of Weak Photoacids Using Steady-State Photoluminescence Spectroscopy and a Driving-Force-Dependent Kinetic Theory. J Am Chem Soc 2022; 144:14477-14488. [PMID: 35917469 DOI: 10.1021/jacs.2c00554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photoacids and photobases constitute a class of molecules that upon absorption of light undergoes a reversible change in acidity, i.e. pKa. Knowledge of the excited-state pKa value, pKa*, is critical for predicting excited-state proton-transfer behavior. A reasonable approximation of pKa* is possible using the Förster cycle analysis, but only when the ground-state pKa is known. This poses a challenge for the study of weak photoacids (photobases) with less acidic (basic) excited states (pKa* (pKb*) > 7), because ground-state pKa (pKb) values are >14, making it difficult to quantify them accurately in water. Another method to determine pKa* relies on acid-base titrations with photoluminescence detection and Henderson-Hasselbalch analysis. This method requires that the acid dissociation reaction involving the thermally equilibrated electronic excited state reaches chemical quasi-equilibrium, which does not occur for weak photoacids (photobases) due to slow rates of excited-state proton transfer. Herein, we report a method to overcome these limitations. We demonstrate that liquid water and aqueous hydroxide are unique proton-accepting quenchers of excited-state photoacids. We determine that Stern-Volmer quenching analysis is appropriate to extract rate constants for excited-state proton transfer in aqueous solutions from a weak photoacid, 5-aminonaphthalene-1-sulfonate, to a series of proton-accepting quenchers. Analysis of these data by Marcus-Cohen bond-energy-bond-order theory yields an accurate value for pKa* of 5-aminonaphthalene-1-sulfonate. Our method is broadly accessible because it only requires readily available steady-state photoluminescence spectroscopy. Moreover, our results for weak photoacids are consistent with those from previous studies of strong photoacids, each showing the applicability of kinetic theories to interpret driving-force-dependent rate constants for proton-transfer reactions.
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Affiliation(s)
- Rohit Bhide
- Department of Chemistry, University of California─Irvine, Irvine, California 92697, United States
| | - Cassidy N Feltenberger
- Department of Chemistry, University of California─Irvine, Irvine, California 92697, United States
| | - Gabriel S Phun
- Department of Chemistry, University of California─Irvine, Irvine, California 92697, United States
| | - Grant Barton
- Department of Chemistry, University of California─Irvine, Irvine, California 92697, United States
| | - Dmitry Fishman
- Department of Chemistry, University of California─Irvine, Irvine, California 92697, United States.,Laser Spectroscopy Laboratories, University of California─Irvine, Irvine, California 92697, United States
| | - Shane Ardo
- Department of Chemistry, University of California─Irvine, Irvine, California 92697, United States.,Department of Chemical & Biomolecular Engineering, University of California─Irvine, Irvine, California 92697, United States.,Department of Materials Science & Engineering, University of California─Irvine, Irvine, California 92697, United States
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10
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Pan X, Han T, Long J, Xie B, Du Y, Zhao Y, Zheng X, Xue J. Excited state proton transfer of triplet state p-nitrophenylphenol to amine and alcohol: a spectroscopic and kinetic study. Phys Chem Chem Phys 2022; 24:18427-18434. [PMID: 35881619 DOI: 10.1039/d2cp02503e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Hydroxyaromatic compounds (ArOHs) have a wide range of applications in catalytic synthesis and biological processes due to their increased acidity upon photo-excitation. The proton transfer of ArOHs via the excited singlet state has been extensively studied. However, there has still been a debate on the unique type of ArOH that can undergo an ultrafast intersystem crossing. The nitro group in p-nitrophenylphenol (NO2-Bp-OH) enhances the spin-orbit coupling between excited singlet states and the triplet manifold, enabling ultrafast intersystem crossing and the formation of the long-lived lowest excited triplet state (T1) with a high yield. In this work, we used time-resolved transient absorption to investigate the excited state proton transfer of NO2-Bp-OH in its T1 state to t-butylamine, methanol, and ethanol. The T1 state of the deprotonated form NO2-Bp-O- was first observed and identified in the case of t-butylamine. Kinetic analysis demonstrates that the formation of the hydrogen-bonded complex with methanol and ethanol as proton acceptors involves their trimers. The alcohol oligomer size required in the excited state proton transfer process is dependent on the excited acidity of photoacid.
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Affiliation(s)
- Xinghang Pan
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China.
| | - Ting Han
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China.
| | - Jing Long
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China.
| | - Binbin Xie
- Hangzhou Institute of Advanced Studies, Zhejiang Normal University, Hangzhou, 310018, China
| | - Yong Du
- Centre for THz Research, China Jiliang University, Hangzhou, 310018, China
| | - Yanying Zhao
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China. .,Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
| | - Xuming Zheng
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China.
| | - Jiadan Xue
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China. .,Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
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11
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Sülzner N, Geissler B, Grandjean A, Jung G, Nuernberger P. Excited‐state Proton Transfer Dynamics of a Super‐Photoacid in Acetone‐Water Mixtures. CHEMPHOTOCHEM 2022. [DOI: 10.1002/cptc.202200041] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Niklas Sülzner
- Ruhr-Universitat Bochum Lehrstuhl für Theoretische Chemie GERMANY
| | - Bastian Geissler
- Universitat Regensburg Institut für Physikalische und Theoretische Chemie GERMANY
| | | | - Gregor Jung
- Universitat des Saarlandes Biophysikalische Chemie GERMANY
| | - Patrick Nuernberger
- Universitat Regensburg Institut für Physikalische und Theoretische Chemie Universitätsstraße 31 93053 Regensburg GERMANY
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12
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Santos EM, Sheng W, Esmatpour Salmani R, Tahmasebi Nick S, Ghanbarpour A, Gholami H, Vasileiou C, Geiger JH, Borhan B. Design of Large Stokes Shift Fluorescent Proteins Based on Excited State Proton Transfer of an Engineered Photobase. J Am Chem Soc 2021; 143:15091-15102. [PMID: 34516091 DOI: 10.1021/jacs.1c05039] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The incredible potential for fluorescent proteins to revolutionize biology has inspired the development of a variety of design strategies to address an equally broad range of photophysical characteristics, depending on potential applications. Of these, fluorescent proteins that simultaneously exhibit high quantum yield, red-shifted emission, and wide separation between excitation and emission wavelengths (Large Stokes Shift, LSS) are rare. The pursuit of LSS systems has led to the formation of a complex, obtained from the marriage of a rationally engineered protein (human cellular retinol binding protein II, hCRBPII) and different fluorogenic molecules, capable of supporting photobase activity. The large increase in basicity upon photoexcitation leads to protonation of the fluorophore in the excited state, dramatically red-shifting its emission, leading to an LSS protein/fluorophore complex. Essential for selective photobase activity is the intimate involvement of the target protein structure and sequence that enables Excited State Proton Transfer (ESPT). The potential power and usefulness of the strategy was demonstrated in live cell imaging of human cell lines.
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Affiliation(s)
- Elizabeth M Santos
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | - Wei Sheng
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | | | - Setare Tahmasebi Nick
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | - Alireza Ghanbarpour
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | - Hadi Gholami
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | - Chrysoula Vasileiou
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | - James H Geiger
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
| | - Babak Borhan
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, United States
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13
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Kaiser C, Halbritter T, Heckel A, Wachtveitl J. Proton-Transfer Dynamics of Photoacidic Merocyanines in Aqueous Solution. Chemistry 2021; 27:9160-9173. [PMID: 33929051 PMCID: PMC8361770 DOI: 10.1002/chem.202100168] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Indexed: 01/22/2023]
Abstract
Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control proton‐release reactions and pH values of solutions. We present the first time‐resolved spectroscopic study of the excited state and proton‐release dynamics of prominent merocyanine representatives. Femtosecond transient absorption measurements of a pyridine merocyanine with two distinct protonation sites revealed dissimilar proton‐release mechanisms: one site acts as a photoacid generator as its pKa value is modulated in the ground state after photoisomerization, while the other functions as an excited state photoacid which releases its proton within 1.1 ps. With a pKa drop of 8.7 units to −5.5 upon excitation, the latter phenolic site is regarded a super‐photoacid. The 6‐nitro derivative exhibits only a phenolic site with similar, yet slightly less photoacidic characteristics and both compounds transfer their proton to methanol and ethanol. In contrast, for the related 6,8‐dinitro compound an intramolecular proton transfer to the ortho‐nitro group is suggested that is involved in a rapid relaxation into the ground state.
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Affiliation(s)
- Christoph Kaiser
- Institute for Physical and Theoretical Chemistry, Goethe University Frankfurt/Main, Max-von-Laue-Str. 7, 60438, Frankfurt/Main, Germany
| | - Thomas Halbritter
- Current address: Department of Chemistry, Science Institute, University of Iceland, Dunhaga 3, Reykjavik, postcode is missing, Iceland.,Institute for Organic Chemistry and Chemical Biology, Goethe University Frankfurt/Main, Max-von-Laue-Str. 7, 60438, Frankfurt/Main, Germany
| | - Alexander Heckel
- Institute for Organic Chemistry and Chemical Biology, Goethe University Frankfurt/Main, Max-von-Laue-Str. 7, 60438, Frankfurt/Main, Germany
| | - Josef Wachtveitl
- Institute for Physical and Theoretical Chemistry, Goethe University Frankfurt/Main, Max-von-Laue-Str. 7, 60438, Frankfurt/Main, Germany
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14
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Codescu MA, Weiß M, Brehm M, Kornilov O, Sebastiani D, Nibbering ETJ. Switching between Proton Vacancy and Excess Proton Transfer Pathways in the Reaction between 7-Hydroxyquinoline and Formate. J Phys Chem A 2021; 125:1845-1859. [PMID: 33651619 PMCID: PMC7957860 DOI: 10.1021/acs.jpca.0c10191] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Bifunctional or amphoteric
photoacids simultaneously present donor
(acidic) and acceptor (basic) properties making them useful tools
to analyze proton transfer reactions. In protic solvents, the proton
exchange between the acid and the base is controlled by the acidity
or basicity strength and typically occurs on two different pathways
known as protolysis and hydrolysis. We report here how the addition
of a formate base will alter the relative importance of the possible
reaction pathways of the bifunctional photoacid 7-hydroxyquinoline
(7HQ), which has been recently understood to predominantly involve
a hydroxide/methoxide transport mechanism between the basic proton-accepting
quinoline nitrogen site toward the proton-donating OH group with a
time constant of 360 ps in deuterated methanol (CD3OD).
We follow the reaction dynamics by probing the IR-active marker modes
of the different charged forms of photoexcited 7HQ, and of formic
acid (HCOOD) in CD3OD solution. A comparison of the transient
IR spectra as a function of formate concentration, and classical molecular
dynamics simulations enables us to identify distinct contributions
of “tight” (meaning “contact”) and “loose”
(i.e., “solvent-separated”) 7HQ–formate reaction
pairs in our data. Our results suggest that depending on the orientation
of the OH group with respect to the quinoline aromatic ring system,
the presence of the formate molecule in a proton relay pathway facilitates
a net proton transfer from the proton-donating OH group of 7HQ-N*
via the methanol/formate bridge toward the quinoline N site.
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Affiliation(s)
- Marius-Andrei Codescu
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, 12489 Berlin, Germany
| | - Moritz Weiß
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle Saale, Germany
| | - Martin Brehm
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle Saale, Germany
| | - Oleg Kornilov
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, 12489 Berlin, Germany
| | - Daniel Sebastiani
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle Saale, Germany
| | - Erik T J Nibbering
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, 12489 Berlin, Germany
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15
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Zika A, Gröhn F. Multiswitchable photoacid-hydroxyflavylium-polyelectrolyte nano-assemblies. Beilstein J Org Chem 2021; 17:166-185. [PMID: 33564327 PMCID: PMC7849232 DOI: 10.3762/bjoc.17.17] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Accepted: 12/16/2020] [Indexed: 02/05/2023] Open
Abstract
Light- and pH-responsive nano-assemblies with switchable size and structure are formed by the association of a photoacid, anthocyanidin, and a linear polyelectrolyte in aqueous solution. Specifically, anionic disulfonated naphthol derivatives, neutral hydroxyflavylium, and cationic poly(allylamine) are used as building blocks for the ternary electrostatic self-assembly, forming well-defined supramolecular assemblies with tunable sizes of 50 to 500 nm. Due to the network of possible chemical reactions for the anthocyanidin and the excited-state dissociation of the photoacid upon irradiation, different ways to alter the ternary system through external triggering are accessible. The structure and trigger effects can be controlled through the component ratios of the samples. Dynamic and static light scattering (DLS, SLS) and ζ-potential measurements were applied to study the size and the stability of the particles, and information on the molecular structure was gained by UV-vis spectroscopy. Isothermal titration calorimetry (ITC) provided information on the thermodynamics and interaction forces in the supramolecular assembly formation.
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Affiliation(s)
- Alexander Zika
- Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM) and Bavarian Polymer Institute (BPI), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen, Germany
| | - Franziska Gröhn
- Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM) and Bavarian Polymer Institute (BPI), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen, Germany
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16
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Sittig M, Tom JC, Elter JK, Schacher FH, Dietzek B. Quinoline Photobasicity: Investigation within Water-Soluble Light-Responsive Copolymers. Chemistry 2021; 27:1072-1079. [PMID: 32986286 PMCID: PMC7839697 DOI: 10.1002/chem.202003815] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 09/14/2020] [Indexed: 01/13/2023]
Abstract
Quinoline photobases exhibit a distinctly higher pKa in their electronically excited state than in the ground state, thereby enabling light-controlled proton transfer reactions, for example, in molecular catalysis. The absorption of UV light translates to a pKa jump of approximately 10 units, as established for small-molecule photobases. This contribution presents the first synthesis of quinoline-based polymeric photobases prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization. The integration of quinolines as photobase chromophores within copolymers offers new possibilities for light-triggered proton transfer in nanostructured materials, that is, in nanoparticles, at surfaces, membranes and interfaces. To exploit the light-triggered reactivity of photobases within such materials, we first investigated how the ground- and excited-state properties of the quinoline unit changes upon polymer integration. To address this matter, we combined absorption and emission spectroscopy with time-resolved transient-absorption studies to reveal photoinduced proton-transfer dynamics in various solvents. The results yield important insights into the thermodynamic and kinetic properties of these polymeric quinoline photobases.
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Affiliation(s)
- Maria Sittig
- Department of Functional InterfacesLeibniz Institute of Photonic Technology JenaAlbert-Einstein-Strasse 907745JenaGermany
- Institute of Physical Chemistry and Abbe Center of PhotonicsFriedrich-Schiller-University JenaHelmholtzweg 407743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Jessica C. Tom
- Institute of Organic Chemistry and Macromolecular Chemistry (IOMC)Friedrich Schiller University JenaHumboldtstrasse 1007743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Johanna K. Elter
- Institute of Organic Chemistry and Macromolecular Chemistry (IOMC)Friedrich Schiller University JenaHumboldtstrasse 1007743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Felix H. Schacher
- Institute of Organic Chemistry and Macromolecular Chemistry (IOMC)Friedrich Schiller University JenaHumboldtstrasse 1007743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Benjamin Dietzek
- Department of Functional InterfacesLeibniz Institute of Photonic Technology JenaAlbert-Einstein-Strasse 907745JenaGermany
- Institute of Physical Chemistry and Abbe Center of PhotonicsFriedrich-Schiller-University JenaHelmholtzweg 407743JenaGermany
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17
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Lee C, Chung S, Song H, Rhee YM, Lee E, Joo T. Excited State Proton Transfer of Quinone Cyanine 9: Implications on the Origin of Super‐Photoacidity. CHEMPHOTOCHEM 2020. [DOI: 10.1002/cptc.202000254] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Changmin Lee
- Department of Chemistry Pohang University of Science and Technology (POSTECH) Pohang 37673 Republic of Korea
| | - Seyoung Chung
- Department of Chemistry Pohang University of Science and Technology (POSTECH) Pohang 37673 Republic of Korea
| | - Hayoung Song
- Department of Chemistry Pohang University of Science and Technology (POSTECH) Pohang 37673 Republic of Korea
| | - Young Min Rhee
- Department of Chemistry Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
| | - Eunsung Lee
- Department of Chemistry Pohang University of Science and Technology (POSTECH) Pohang 37673 Republic of Korea
| | - Taiha Joo
- Department of Chemistry Pohang University of Science and Technology (POSTECH) Pohang 37673 Republic of Korea
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18
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Zika A, Bernhardt S, Gröhn F. Photoresponsive Photoacid-Macroion Nano-Assemblies. Polymers (Basel) 2020; 12:E1746. [PMID: 32764323 PMCID: PMC7464814 DOI: 10.3390/polym12081746] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2020] [Revised: 07/27/2020] [Accepted: 07/31/2020] [Indexed: 01/01/2023] Open
Abstract
In this study, light-responsive nano-assemblies with light-switchable size based on photoacids are presented. Anionic disulfonated napthol derivates and cationic dendrimer macroions are used as building blocks for electrostatic self-assembly. Nanoparticles are already formed under the exclusion of light as a result of electrostatic interactions. Upon photoexcitation, an excited-state dissociation of the photoacidic hydroxyl group takes place, which leads to a more highly charged linker molecule and, subsequently, to a change in size and structure of the nano-assemblies. The effects of the charge ratio and the concentration on the stability have been examined with absorption spectroscopy and ζ-potential measurements. The influence of the chemical structure of three isomeric photoacids on the size and shape of the nanoscale aggregates has been studied by dynamic light scattering and atomic force microscopy, revealing a direct correlation of the strength of the photoacid with the changes of the assemblies upon irradiation.
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Affiliation(s)
| | | | - Franziska Gröhn
- Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, Friedrich-Alexander Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen, Germany; (A.Z.); (S.B.)
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19
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Capobianco A, Di Donato M, Caruso T, Centore R, Lapini A, Manfredi C, Velardo A, Volino S, Peluso A. Phototautomerism of triazolo-triazole scaffold. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2019.127368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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20
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Hunt JR, Dawlaty JM. Kinetic Evidence for the Necessity of Two Proton Donor Molecules for Successful Excited State Proton Transfer by a Photobase. J Phys Chem A 2019; 123:10372-10380. [PMID: 31710812 DOI: 10.1021/acs.jpca.9b08970] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Photobases are molecules that convert light to proton transfer drive and therefore have potential applications in many areas of chemistry. Previously, we studied the photobasicity of quinolines and explored their applications. While it is possible to tether a photobase near a target proton donor, for the sake of versatility it is desirable to explore their capability to deprotonate molecules dispersed in a solution. Previous evidence suggested that in this scenario at least two proton donors were necessary for successful excited state proton transfer: one to donate a proton and the second to stabilize the photogenerated donor anion. Here we report kinetic evidence from transient absorption (TA) and time-correlated single photon counting (TCSPC) in support of this hypothesis. We used 5-methoxyquinoline as the photobase and 2,2,2-trifluoroethanol (TFE), a low pKa alcohol, as the proton donor. A constant concentration of the photobase was used for a range of proton-donor dilutions spanning several orders of magnitude in an aprotic background solvent. Absorption spectra confirm that over most of the studied range the majority of the photobase population is hydrogen bonded to at least one donor. Short-pulse TA was used to measure the faster (2-500 ps) dynamics, while TSCPC was used to measure the slower (>500 ps) dynamics. The measured proton transfer time constants varied as a function of donor concentration over a wide range. A log-log plot of the proton transfer rate constant as a function of proton-donor concentration shows two regimes: nondiffusive at high donor concentrations where multiple proton donors are near the photobase and diffusive at low donor concentrations where proton donors are more dilute. The nondiffusive regime has a slope of approximately one, suggesting that the proton transfer process is dependent on one donor molecule in addition to the donor molecule already hydrogen bonded with the photobase. The diffusive regime reasonably follows diffusion kinetics. We propose a model for how the second proton-donor molecule may interact with the photogenerated alkoxide to stabilize it. This work highlights the importance of inducing irreversible changes, in this case solvation of the alkoxide, after proton transfer. Understanding of such details is likely to be important in applications of photobases.
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Affiliation(s)
- Jonathan Ryan Hunt
- Department of Chemistry , University of Southern California , 920 Bloom Walk SSC 702 , Los Angeles , California 90089-0482 , United States
| | - Jahan M Dawlaty
- Department of Chemistry , University of Southern California , 920 Bloom Walk SSC 702 , Los Angeles , California 90089-0482 , United States
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21
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Nelson KJ, Brown PJ, Rudel HE, Takematsu K. Divergent excited state proton transfer reactions of bifunctional photoacids 1-ammonium-2-naphthol and 3-ammonium-2-naphthol in water and methanol. Phys Chem Chem Phys 2019; 21:24383-24392. [PMID: 31663559 DOI: 10.1039/c9cp05269k] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This paper highlights the challenge of predicting the excited state proton transfer (ESPT) reactions of small organic compounds with multiple proton transfer sites. Aminonaphthols, naphthalene compounds with both hydroxyl and amino substituents, can be viewed as a combination of two monoprotic photoacids, naphthol and naphthylammonium. Here, the ESPT reactions of 3-ammonium-2-naphthol (3N2OH) and 1-ammonium-2-naphthol (1N2OH) were studied in water and methanol using a combination of steady-state and time-correlated single-photon counting emission spectroscopy. For 3N2OH, ESPT was observed at the OH site in water but at neither of the sites in methanol; for 1N2OH, ESPT was observed at both the OH and NH3+ sites in water but only at the NH3+ site in methanol. Evidence of ESPT at the NH3+ site is limited for aminonaphthols. The divergent dynamics of 3N2OH and 1N2OH in water and methanol are discussed; dependent on the substitution and solvent, the ESPT reactions were analysed within the frameworks of reference photoacids 2-naphthol and 1-naphthylammonium. The application of crown ether and salt to control the release of select protons in non-aqueous media is also discussed.
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Affiliation(s)
- Kacie J Nelson
- Department of Chemistry, Bowdoin College, Brunswick, ME 04011, USA.
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22
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Aminov D, Pines D, Kiefer PM, Daschakraborty S, Hynes JT, Pines E. Intact carbonic acid is a viable protonating agent for biological bases. Proc Natl Acad Sci U S A 2019; 116:20837-20843. [PMID: 31570591 PMCID: PMC6800339 DOI: 10.1073/pnas.1909498116] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Carbonic acid H2CO3 (CA) is a key constituent of the universal CA/bicarbonate/CO2 buffer maintaining the pH of both blood and the oceans. Here we demonstrate the ability of intact CA to quantitatively protonate bases with biologically-relevant pKas and argue that CA has a previously unappreciated function as a major source of protons in blood plasma. We determine with high precision the temperature dependence of pKa(CA), pKa(T) = -373.604 + 16,500/T + 56.478 ln T. At physiological-like conditions pKa(CA) = 3.45 (I = 0.15 M, 37 °C), making CA stronger than lactic acid. We further demonstrate experimentally that CA decomposition to H2O and CO2 does not impair its ability to act as an ordinary carboxylic acid and to efficiently protonate physiological-like bases. The consequences of this conclusion are far reaching for human physiology and marine biology. While CA is somewhat less reactive than (H+)aq, it is more than 1 order of magnitude more abundant than (H+)aq in the blood plasma and in the oceans. In particular, CA is about 70× more abundant than (H+)aq in the blood plasma, where we argue that its overall protonation efficiency is 10 to 20× greater than that of (H+)aq, often considered to be the major protonating agent there. CA should thus function as a major source for fast in vivo acid-base reactivity in the blood plasma, possibly penetrating intact into membranes and significantly helping to compensate for (H+)aq's kinetic deficiency in sustaining the large proton fluxes that are vital for metabolic processes and rapid enzymatic reactions.
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Affiliation(s)
- Daniel Aminov
- Department of Chemistry, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
| | - Dina Pines
- Department of Chemistry, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
| | - Philip M Kiefer
- Department of Chemistry, University of Colorado Boulder, Boulder, CO 80309-0215
| | | | - James T Hynes
- Department of Chemistry, University of Colorado Boulder, Boulder, CO 80309-0215;
- PASTEUR, Départmente de Chimie, Ecole Normale Supérieure, PSL Research University, Sorbonne Université, UPMC Université Paris 06, CNRS, 75005 Paris, France
| | - Ehud Pines
- Department of Chemistry, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel;
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23
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Ekimova M, Hoffmann F, Bekçioğlu-Neff G, Rafferty A, Kornilov O, Nibbering ETJ, Sebastiani D. Ultrafast Proton Transport between a Hydroxy Acid and a Nitrogen Base along Solvent Bridges Governed by the Hydroxide/Methoxide Transfer Mechanism. J Am Chem Soc 2019; 141:14581-14592. [PMID: 31446754 PMCID: PMC8168916 DOI: 10.1021/jacs.9b03471] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Aqueous
proton transport plays a key role in acid–base neutralization
and energy transport through biological membranes and hydrogen fuel
cells. Extensive experimental and theoretical studies have resulted
in a highly detailed elucidation of one of the underlying microscopic
mechanisms for aqueous excess proton transport, known as the von Grotthuss
mechanism, involving different hydrated proton configurations with
associated high fluxional structural dynamics. Hydroxide transport,
with approximately 2-fold-lower bulk diffusion rates compared to those
of excess protons, has received much less attention. We present femtosecond
UV/IR pump–probe experiments and ab initio molecular dynamics
simulations of different proton transport pathways of bifunctional
photoacid 7-hydroxyquinoline (7HQ) in water/methanol mixtures. For
7HQ solvent-dependent photoacidity, free-energy–reactivity
correlation behavior and quantum mechanics/molecular mechanics (QM/MM)
trajectories point to a dominant OH–/CH3O– transport pathway for all water/methanol mixing
ratios investigated. Our joint ultrafast infrared spectroscopic and
ab initio molecular dynamics study provides conclusive evidence for
the hydrolysis/methanolysis acid–base neutralization pathway,
as formulated by Manfred Eigen half a century ago. Our findings on
the distinctly different acid–base reactivities for aromatic
hydroxyl and aromatic nitrogen functionalities suggest the usefulness
of further exploration of these free-energy–reactivity correlations
as a function of solvent polarity. Ultimately the determination of
solvent-dependent acidities will contribute to a better understanding
of proton-transport mechanisms at weakly polar surfaces and near polar
or ionic regions in transmembrane proton pump proteins or hydrogen
fuel cell materials.
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Affiliation(s)
- Maria Ekimova
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , Max Born Str. 2A , 12489 Berlin , Germany
| | - Felix Hoffmann
- Institut für Chemie , Martin-Luther-Universität Halle-Wittenberg , Von-Danckelmann-Platz 4 , 06120 Halle , Saale , Germany
| | - Gül Bekçioğlu-Neff
- Institut für Chemie , Martin-Luther-Universität Halle-Wittenberg , Von-Danckelmann-Platz 4 , 06120 Halle , Saale , Germany
| | - Aidan Rafferty
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , Max Born Str. 2A , 12489 Berlin , Germany
| | - Oleg Kornilov
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , Max Born Str. 2A , 12489 Berlin , Germany
| | - Erik T J Nibbering
- Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , Max Born Str. 2A , 12489 Berlin , Germany
| | - Daniel Sebastiani
- Institut für Chemie , Martin-Luther-Universität Halle-Wittenberg , Von-Danckelmann-Platz 4 , 06120 Halle , Saale , Germany
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24
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Cotter LF, Brown PJ, Nelson RC, Takematsu K. Divergent Hammett Plots of the Ground- and Excited-State Proton Transfer Reactions of 7-Substituted-2-Naphthol Compounds. J Phys Chem B 2019; 123:4301-4310. [PMID: 31021637 DOI: 10.1021/acs.jpcb.9b01295] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The rational design of photoacids requires accessible predictive models of the electronic effect of functional groups on chemical templates of interest. Here, the effect of substituents on the photoacidity and excited-state proton transfer (PT) pathways of prototype 2-naphthol (2OH) at the symmetric C7 position was investigated through photochemical and computational studies of 7-amino-2-naphthol (7N2OH) and 7-methoxy-2-naphthol (7OMe2OH). Time-resolved emission experiments of 7N2OH revealed that the presence of an electron-withdrawing versus electron-donating group (EWG vs EDG, NH3+ vs NH2) led to a drastic decline in photoacidity: p Ka* = 1.1 ± 0.2 vs 9.6 ± 0.2. Time-dependent density functional theory calculations with explicit water molecules confirmed that the excited neutral state (x = NH2) is greatly stabilized by water, with equation-of-motion coupled cluster singles and doubles calculations supporting potential mixing between the La and Lb states. Similar suppression of photoacidity, however, was not observed for 7OMe2OH with EDG OCH3, p Ka* = 2.7 ± 0.1. Hammett plots of the ground- and excited-state PT reactions of substituted 7-x-2OH compounds (x = CN, NH3+, H, CH3, OCH3, OH, and NH2) vs Hammett parameters σp showed breaks in the linearity between the EDG and EWG regions: ρ ∼ 0 vs 1.14 and ρ* ∼ 0 vs 3.86. The divergent acidic behavior most likely arises from different mixing mechanisms of the lowest Lb state with the La and possible Bb states upon substitution of naphthalene in water.
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Affiliation(s)
- Laura F Cotter
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
| | - Paige J Brown
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
| | - Ryan C Nelson
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
| | - Kana Takematsu
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
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25
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Amoruso G, Taylor VCA, Duchi M, Goodband E, Oliver TAA. Following Bimolecular Excited-State Proton Transfer between Hydroxycoumarin and Imidazole Derivatives. J Phys Chem B 2019; 123:4745-4756. [DOI: 10.1021/acs.jpcb.9b01475] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Giordano Amoruso
- School of Chemistry, Cantock’s Close, University of Bristol, Bristol BS8 1TS, United Kingdom
| | - Victoria C. A. Taylor
- School of Chemistry, Cantock’s Close, University of Bristol, Bristol BS8 1TS, United Kingdom
- Bristol Centre for Functional Nanomaterials, School of Physics, University of Bristol, Bristol BS8 1TH, United Kingdom
| | - Marta Duchi
- School of Chemistry, Cantock’s Close, University of Bristol, Bristol BS8 1TS, United Kingdom
| | - Emma Goodband
- School of Chemistry, Cantock’s Close, University of Bristol, Bristol BS8 1TS, United Kingdom
| | - Thomas A. A. Oliver
- School of Chemistry, Cantock’s Close, University of Bristol, Bristol BS8 1TS, United Kingdom
- Bristol Centre for Functional Nanomaterials, School of Physics, University of Bristol, Bristol BS8 1TH, United Kingdom
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26
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Ekimova M, Hoffmann F, Bekcioglu-Neff G, Rafferty A, Nibbering ETJ, Sebastiani D. Ultrafast proton transport in water-methanol mixtures. EPJ WEB OF CONFERENCES 2019. [DOI: 10.1051/epjconf/201920509004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Femtosecond UV/IR pump-probe experiments and ab initio molecular dynamics simulations of 7-hydroxyquinoline in water-methanol mixtures demonstrate an unexpectedly dominant OH-/CH3O- transport pathway but consistent with a solvent-dependent photoacidity free energy-reactivity correlation behaviour.
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27
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Hunt JR, Tseng C, Dawlaty JM. Donor-acceptor preassociation, excited state solvation threshold, and optical energy cost as challenges in chemical applications of photobases. Faraday Discuss 2019; 216:252-268. [PMID: 31025987 DOI: 10.1039/c8fd00215k] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Photobases are molecules with increased pKa in the excited state that can serve to transduce light energy into proton removal capability. They can be used to control chemical reactions using light, such as removing protons from a catalytic site in reactions that are rate-limited by proton transfer. We identify and explore several major challenges toward their practical applications. Two important challenges are the need for pre-association (or ground state hydrogen bonding) between the proton donor and the photobase, and the need for excited state solvation of the photogenerated products. We investigate these two challenges with the photobase 5-methoxyquinoline as the proton acceptor and a low-pKa alcohol, 2,2,2-trifluoroethanol, as the proton donor. We vary the concentration of the donor in a background non-hydrogen-bonding solvent. Using absorption spectroscopy, we have identified that the donor-acceptor concentration ratio must exceed 100 : 1 to achieve appreciable ground state hydrogen bonding. Interestingly, emission spectroscopy reveals that the onset of ground state hydrogen bonding does not guarantee successful excited state proton transfer. It takes an additional order of magnitude increase in donor-acceptor ratio to achieve that goal, revealing that it is necessary to have excess donor molecules to reach the solvation threshold for the photogenerated products. The next challenge is reducing the large ground-excited state energy gap, which often requires UV photons to drive proton transfer. We show experimental and computational data comparing the photobasicity and optical energy gap for a few N-aromatic heterocyclic photobases. In general, we find that reducing the energy gap by increasing the conjugation size necessarily reduces photobasicity, while adding substituents of varying electron-withdrawing strength allows some fine-tuning of this effect. The combination of these two factors provide a preliminary design space for creating new photobasic molecules.
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Affiliation(s)
| | - Cindy Tseng
- University of Southern California, 920 Bloom Walk, Los Angeles, USA.
| | - Jahan M Dawlaty
- University of Southern California, 920 Bloom Walk, Los Angeles, USA.
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28
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Gajst O, Pinto da Silva L, Esteves da Silva JCG, Huppert D. Enhanced Excited-State Proton Transfer via a Mixed Methanol–Water Molecular Bridge of 1-Naphthol-3,6-disulfonate in Methanol–Water Mixtures. J Phys Chem A 2018; 123:48-58. [DOI: 10.1021/acs.jpca.8b10374] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Oren Gajst
- Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
| | - Luís Pinto da Silva
- Chemistry Research Unit (CIQUP), Department of Chemistry and Biochemistry, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
- LACOMEPHI, GreenUP, Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
| | - Joaquim C. G. Esteves da Silva
- LACOMEPHI, GreenUP, Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
- Chemistry Research Unit (CIQUP), Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
| | - Dan Huppert
- Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
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29
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Hunt JR, Dawlaty JM. Photodriven Deprotonation of Alcohols by a Quinoline Photobase. J Phys Chem A 2018; 122:7931-7940. [DOI: 10.1021/acs.jpca.8b06152] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Jonathan Ryan Hunt
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Jahan M. Dawlaty
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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30
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Alazaly AM, Amer AS, Fathi AM, Abdel-Shafi AA. Photoacids as singlet oxygen photosensitizers: Direct determination of the excited state acidity by time-resolved spectroscopy. J Photochem Photobiol A Chem 2018. [DOI: 10.1016/j.jphotochem.2018.07.019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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31
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Panja S, Khatua DK, Pramanik P, Halder M. Insights into the effect of different reverse micellar confinements on the photo-induced acidity of water soluble naphthol sulfonates: A detailed spectroscopic account. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2018.04.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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32
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Gajst O, Pinto da Silva L, Esteves da Silva JCG, Huppert D. Enhanced Excited-State Proton Transfer via a Mixed Water–Methanol Molecular Bridge of 1-Naphthol-5-Sulfonate in Methanol–Water Mixtures. J Phys Chem A 2018; 122:4704-4716. [DOI: 10.1021/acs.jpca.8b00957] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Oren Gajst
- Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
| | | | | | - Dan Huppert
- Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
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33
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Joung JF, Kim S, Park S. Cationic Effect on the Equilibria and Kinetics of the Excited-State Proton Transfer Reaction of a Photoacid in Aqueous Solutions. J Phys Chem B 2018; 122:5087-5093. [DOI: 10.1021/acs.jpcb.8b00588] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
| | - Sangin Kim
- Department of Chemistry, Korea University, Seoul 02841, Korea
| | - Sungnam Park
- Department of Chemistry, Korea University, Seoul 02841, Korea
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34
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Groves MS, Nelson KJ, Nelson RC, Takematsu K. pH switch for OH-photoacidity in 5-amino-2-naphthol and 8-amino-2-naphthol. Phys Chem Chem Phys 2018; 20:21325-21333. [DOI: 10.1039/c8cp03984d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
pH switch for OH-photoacidity in 5-amino-2-naphthol and 8-amino-2-naphthol Switching of the amino protonation state turns on and off the OH-photoacidity.
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35
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Driscoll EW, Hunt JR, Dawlaty JM. Proton Capture Dynamics in Quinoline Photobases: Substituent Effect and Involvement of Triplet States. J Phys Chem A 2017; 121:7099-7107. [DOI: 10.1021/acs.jpca.7b04512] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Eric William Driscoll
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Jonathan Ryan Hunt
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Jahan M. Dawlaty
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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36
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Ultrafast photo-induced charge transfer of 1-naphthol and 2-naphthol to halocarbon solvents. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.03.080] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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37
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Xie Y, Ilic S, Skaro S, Maslak V, Glusac KD. Excited-State Hydroxide Ion Release From a Series of Acridinol Photobases. J Phys Chem A 2017; 121:448-457. [DOI: 10.1021/acs.jpca.6b10980] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Yun Xie
- Department
of Chemistry, Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States
| | - Stefan Ilic
- Department
of Chemistry, Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States
| | - Sanja Skaro
- Faculty
of Chemistry, University of Belgrade, Studentski Trg 12-16, Belgrade 11000, Serbia
| | - Veselin Maslak
- Faculty
of Chemistry, University of Belgrade, Studentski Trg 12-16, Belgrade 11000, Serbia
| | - Ksenija D. Glusac
- Department
of Chemistry, Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States
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38
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Joung JF, Kim S, Park S. Ionic effects on the proton transfer mechanism in aqueous solutions. Phys Chem Chem Phys 2017; 19:25509-25517. [DOI: 10.1039/c7cp04392a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Proton dissociation (PD) reactions of weak acids and proton transfer (PT) processes in aqueous solutions are strongly influenced by ions.
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Affiliation(s)
| | - Sangin Kim
- Department of Chemistry
- Korea University
- Seoul
- Korea
| | - Sungnam Park
- Department of Chemistry
- Korea University
- Seoul
- Korea
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39
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Kumpulainen T, Lang B, Rosspeintner A, Vauthey E. Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution. Chem Rev 2016; 117:10826-10939. [DOI: 10.1021/acs.chemrev.6b00491] [Citation(s) in RCA: 249] [Impact Index Per Article: 31.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Tatu Kumpulainen
- Department of Physical Chemistry,
Sciences II, University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland
| | - Bernhard Lang
- Department of Physical Chemistry,
Sciences II, University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland
| | - Arnulf Rosspeintner
- Department of Physical Chemistry,
Sciences II, University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland
| | - Eric Vauthey
- Department of Physical Chemistry,
Sciences II, University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland
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40
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Park SY, Kim TG, Ajitha MJ, Kwac K, Lee YM, Kim H, Jung Y, Kwon OH. The critical size of hydrogen-bonded alcohol clusters as effective Brønsted bases in solutions. Phys Chem Chem Phys 2016; 18:24880-9. [PMID: 27337993 DOI: 10.1039/c6cp01650b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The alkyl oxonium ion, which is a protonated alcohol, has long been proposed as a key reaction intermediate in alcohol dehydration. Nonetheless, the dynamics and structure of this simple but important intermediate species have not been adequately examined due to the transient nature of the oxonium ion. Here, we devised a model system for the key step in the alcohol dehydration reaction, in which a photoacid transfers a proton to alcohols of different basicity in the acetonitrile solvent. Using time-resolved spectroscopy and computation, we have found that the linkage of at least two alcohol molecules via hydrogen bonding is critical for their enhanced reactivity and extraction of the proton from the acid. This finding addresses the cooperative role of the simplest organic protic compounds, namely alcohols, in nonaqueous acid-base reactions.
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Affiliation(s)
- Sun-Young Park
- Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
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41
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Eisenhart TT, Howland WC, Dempsey JL. Proton-Coupled Electron Transfer Reactions with Photometric Bases Reveal Free Energy Relationships for Proton Transfer. J Phys Chem B 2016; 120:7896-905. [DOI: 10.1021/acs.jpcb.6b04011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Thomas T. Eisenhart
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States
| | - William C. Howland
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States
| | - Jillian L. Dempsey
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States
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42
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Safko TM, Faleiros MM, Atvars TDZ, Weiss RG. Intramolecular, Exciplex-Mediated, Proton-Coupled, Charge-Transfer Processes in N,N-Dimethyl-3-(1-pyrenyl)propan-1-ammonium Cations: Influence of Anion, Solvent Polarity, and Temperature. J Phys Chem A 2016; 120:3983-91. [PMID: 27268751 DOI: 10.1021/acs.jpca.6b01519] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation O) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pKa*) has been estimated to be ca. -3.4 in tetrahydrofuran. The ratios between the intensities of emission from the exciplex and the locally excited state (IEx/ILE) appear to be much more dependent on the nature of the anion than are the rates of exciplex formation and decay, although the excited state data do not provide a quantitative measure of the anion effect on the C-O equilibrium. The activation energies associated with exciplex formation in THF are calculated to be 0.08 to 0.15 eV lower than for the neutral amine, N,N-dimethyl-3-(1-pyrenyl)propan-1-amine. Decay of the exciplexes formed from the deprotonation of PyS is hypothesized to occur through charge-recombination processes. To our knowledge, this is the first example in which photoacidity and intramolecular exciplex formation (i.e., a PCCT reaction) are coupled.
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Affiliation(s)
- Trevor M Safko
- Department of Chemistry and cInstitute for Soft Matter Synthesis and Metrology, Georgetown University , 37th and O Streets NW, Washington, DC 20057-1227, United States
| | - Marcelo M Faleiros
- Instituto de Química, Universidade Estadual de Campinas , Caixa Postal 6154, Campinas, Sao Paulo13083-970, Brasil
| | - Teresa D Z Atvars
- Instituto de Química, Universidade Estadual de Campinas , Caixa Postal 6154, Campinas, Sao Paulo13083-970, Brasil
| | - Richard G Weiss
- Department of Chemistry and cInstitute for Soft Matter Synthesis and Metrology, Georgetown University , 37th and O Streets NW, Washington, DC 20057-1227, United States
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43
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Laptenok SP, Conyard J, Page PCB, Chan Y, You M, Jaffrey SR, Meech SR. Photoacid Behaviour in a Fluorinated Green Fluorescent Protein Chromophore: Ultrafast Formation of Anion and Zwitterion States. †. Chem Sci 2016; 7:5747-5752. [PMID: 28066538 PMCID: PMC5207226 DOI: 10.1039/c6sc02031c] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Accepted: 06/02/2016] [Indexed: 11/21/2022] Open
Abstract
The photophysics of the chromophore of the green fluorescent protein in Aequorea victoria (avGFP) are dominated by an excited state proton transfer reaction. In contrast the photophysics of the same chromophore in solution are dominated by radiationless decay, and photoacid behaviour is not observed. Here we show that modification of the pKa of the chromophore by fluorination leads to an excited state proton transfer on an extremely fast (50 fs) time scale. Such a fast rate suggests a barrierless proton transfer and the existence of a pre-formed acceptor site in the aqueous solution, which is supported by solvent and deuterium isotope effects. In addition, at lower pH, photochemical formation of the elusive zwitterion of the GFP chromophore is observed by means of an equally fast excited state proton transfer from the cation. The significance of these results for understanding and modifying the properties of fluorescent proteins are discussed.
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Affiliation(s)
- S. P. Laptenok
- School of Chemistry
, University of East Anglia
,
Norwich NR4 7TJ
, UK
.
| | - J. Conyard
- School of Chemistry
, University of East Anglia
,
Norwich NR4 7TJ
, UK
.
| | - P. C. Bulman Page
- School of Chemistry
, University of East Anglia
,
Norwich NR4 7TJ
, UK
.
| | - Y. Chan
- School of Chemistry
, University of East Anglia
,
Norwich NR4 7TJ
, UK
.
| | - M. You
- Department of Pharmacology Weill Medical College
, Cornell University
,
1300 York Avenue, Box 70
, New York
, NY 10065
, USA
| | - S. R. Jaffrey
- Department of Pharmacology Weill Medical College
, Cornell University
,
1300 York Avenue, Box 70
, New York
, NY 10065
, USA
| | - S. R. Meech
- School of Chemistry
, University of East Anglia
,
Norwich NR4 7TJ
, UK
.
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44
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Driscoll EW, Hunt JR, Dawlaty JM. Photobasicity in Quinolines: Origin and Tunability via the Substituents' Hammett Parameters. J Phys Chem Lett 2016; 7:2093-2099. [PMID: 27195691 DOI: 10.1021/acs.jpclett.6b00790] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Affiliation(s)
| | - Jonathan Ryan Hunt
- University of Southern California , Los Angeles, California 90089, United States
| | - Jahan M Dawlaty
- University of Southern California , Los Angeles, California 90089, United States
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45
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Wide-dynamic-range kinetic investigations of deep proton tunnelling in proteins. Nat Chem 2016; 8:874-80. [PMID: 27554414 DOI: 10.1038/nchem.2527] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Accepted: 04/14/2016] [Indexed: 11/08/2022]
Abstract
Directional proton transport along 'wires' that feed biochemical reactions in proteins is poorly understood. Amino-acid residues with high pKa are seldom considered as active transport elements in such wires because of their large classical barrier for proton dissociation. Here, we use the light-triggered proton wire of the green fluorescent protein to study its ground-electronic-state proton-transport kinetics, revealing a large temperature-dependent kinetic isotope effect. We show that 'deep' proton tunnelling between hydrogen-bonded oxygen atoms with a typical donor-acceptor distance of 2.7-2.8 Å fully accounts for the rates at all temperatures, including the unexpectedly large value (2.5 × 10(9) s(-1)) found at room temperature. The rate-limiting step in green fluorescent protein is assigned to tunnelling of the ionization-resistant serine hydroxyl proton. This suggests how high-pKa residues within a proton wire can act as a 'tunnel diode' to kinetically trap protons and control the direction of proton flow.
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46
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Anstöter C, Caine BA, Popelier PLA. The AIBLHiCoS Method: Predicting Aqueous pKa Values from Gas-Phase Equilibrium Bond Lengths. J Chem Inf Model 2016; 56:471-83. [PMID: 26818245 DOI: 10.1021/acs.jcim.5b00580] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The proposed AIBLHiCoS method predicts a given compound's pKa in aqueous solution from a single ab initio bond length only, after geometry optimization in the gas phase. Here we provide simple and predictive equations for naphthols and chemically similar biomolecules. Each linear equation corresponds to a High-Correlation Subset (HiCoS) that expresses the novel type of linear free energy relationship discovered here. The naphthol family exhibits a clear and strong relationship with the phenol family, with the "active" C-O bond always producing the highest correlations. The proposed method can isolate erroneous experiments and operate in non-aqueous solution and at different temperatures. Moreover, the existence of "active fragments" is demonstrated in a variety of sizable biomolecules for which the pKa is successfully predicted.
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Affiliation(s)
- Cate Anstöter
- Manchester Institute of Biotechnology (MIB) , 131 Princess Street, Manchester M1 7DN, United Kingdom.,School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom
| | - Beth A Caine
- Manchester Institute of Biotechnology (MIB) , 131 Princess Street, Manchester M1 7DN, United Kingdom.,School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom
| | - Paul L A Popelier
- Manchester Institute of Biotechnology (MIB) , 131 Princess Street, Manchester M1 7DN, United Kingdom.,School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom
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47
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Finkler B, Riemann I, Vester M, Grüter A, Stracke F, Jung G. Monomolecular pyrenol-derivatives as multi-emissive probes for orthogonal reactivities. Photochem Photobiol Sci 2016; 15:1544-1557. [DOI: 10.1039/c6pp00290k] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Chameleons in a test tube: up to four easily distinguishable emission colors result from conversion by two hydrolytic enzymes at opposite reaction sites.
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Affiliation(s)
- Björn Finkler
- Biophysical Chemistry
- Saarland University
- 66123 Saarbrücken
- Germany
| | | | - Michael Vester
- Biophysical Chemistry
- Saarland University
- 66123 Saarbrücken
- Germany
| | - Andreas Grüter
- Biophysical Chemistry
- Saarland University
- 66123 Saarbrücken
- Germany
| | | | - Gregor Jung
- Biophysical Chemistry
- Saarland University
- 66123 Saarbrücken
- Germany
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48
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Ditkovich J, Pines D, Pines E. Controlling reactivity by remote protonation of a basic side group in a bifunctional photoacid. Phys Chem Chem Phys 2016; 18:16106-15. [DOI: 10.1039/c5cp07672b] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ultrafast reactivity-switch is achieved by remote-protonation caused by protons diffusing from acidic to basic side-groups of bifunctional photoacids.
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Affiliation(s)
- Julia Ditkovich
- Department of Chemistry
- Ben-Gurion University of the Negev
- Beer-Sheva 84105
- Israel
| | - Dina Pines
- Department of Chemistry
- Ben-Gurion University of the Negev
- Beer-Sheva 84105
- Israel
| | - Ehud Pines
- Department of Chemistry
- Ben-Gurion University of the Negev
- Beer-Sheva 84105
- Israel
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49
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Solntsev KM, Popov AV, Solovyeva VA, Al-Ainain SA, Il’ichev YV, Hernandez R, Kuzmin MG. Kinetics of intra- and intermolecular excited-state proton transfer ofω-(2-hydroxynaphthyl-1)-decanoic acid in homogeneous and micellar solutions. Methods Appl Fluoresc 2015. [DOI: 10.1088/2050-6120/4/1/014001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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50
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Pines D, Nibbering ETJ, Pines E. Monitoring the Microscopic Molecular Mechanisms of Proton Transfer in Acid-base Reactions in Aqueous Solutions. Isr J Chem 2015. [DOI: 10.1002/ijch.201500057] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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