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Russel NS, Kodali G, Stanley RJ, Narayanan M. Screening for Novel Fluorescent Nucleobase Analogues Using Computational and Experimental Methods: 2-Amino-6-chloro-8-vinylpurine (2A6Cl8VP) as a Case Study. J Phys Chem B 2023; 127:7858-7871. [PMID: 37698525 DOI: 10.1021/acs.jpcb.3c03618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/13/2023]
Abstract
Novel fluorescent nucleic acid base analogues (FBAs) with improved optical properties are needed in a variety of biological applications. 2-Amino-6-chloro-8-vinylpurine (2A6Cl8VP) is structural analogue of two existing highly fluorescent FBAs, 2-aminopurine (2AP) and 8-vinyladenine (8VA), and can therefore be expected to have similar base pairing as well as better optical properties compared to its counterparts. In order to determine the absorption and fluorescence properties of 2A6Cl8VP, as a first step, we used TD-DFT calculations and the polarizable continuum model for simulating the solvents and computationally predicted absorption and fluorescence maxima. To test the computational predictions, we also synthesized 2A6Cl8VP and measured its UV/vis absorbance, fluorescence emission, and fluorescence lifetime. The computationally predicted absorbance and fluorescence maxima of 2A6Cl8VP are in reasonable agreement to the experimental values and are significantly redshifted compared to 2AP and 8VA, allowing for its specific excitation. The fluorescence quantum yield of 2A6Cl8VP, however, is significantly lower than those of 2AP and 8VA. Overall, 2A6Cl8VP is a novel fluorescent nucleobase analogue, which can be useful in studying structural, biophysical, and biochemical applications.
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Affiliation(s)
- Nadim Shahriar Russel
- Department of Chemistry, Temple University, 1901 N. Broad Street, Philadelphia, Pennsylvania 19122, United States
| | - Goutham Kodali
- GlowDNA LLC., Malvern, Pennsylvania 19355, United States
| | - Robert J Stanley
- Department of Chemistry, Temple University, 1901 N. Broad Street, Philadelphia, Pennsylvania 19122, United States
| | - Madhavan Narayanan
- Department of Physical Sciences, Benedictine University, 5700 College Rd, Lisle, Illinois 60532, United States
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2
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Comparing ultrafast excited state quenching of flavin 1,N 6-ethenoadenine dinucleotide and flavin adenine dinucleotide by optical spectroscopy and DFT calculations. Photochem Photobiol Sci 2022; 21:959-982. [PMID: 35218554 DOI: 10.1007/s43630-022-00187-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 02/01/2022] [Indexed: 10/19/2022]
Abstract
Flavins are photoenzymatic cofactors often exploiting the absorption of light to energize photoinduced redox chemistry in a variety of contexts. Both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are used for this function. The study of these photoenzymes has been facilitated using flavin analogs. Most of these analogs involve modification of the flavin ring, and there is recent evidence that adenine (Ade)-modified FAD can affect enzyme turnover, but so far this has only been shown for enzymes where the adenine and flavin rings are close to each other in a stacked conformation. FAD is also stacked in aqueous solution, and its photodynamics are quite different from unstacked FAD or FMN. Oxidized photoexcited FAD decays rapidly, presumably through PET with Ade as donor and Fl* as acceptor. Definitive identification of the spectral signatures of Ade∙+ and Fl∙- radicals is elusive. Here we use the FAD analog Flavin 1,N6-Ethenoadenine Dinucleotide (εFAD) to study how different photochemical outcomes depend on the identity of the Ade moiety in stacked FAD and its analog εFAD. We have used UV-Vis transient absorption spectroscopy complemented by TD-DFT calculations to investigate the excited state evolution of the flavins. In FAD*, no radicals were observed, suggesting that FAD* does not undergo PET. εFAD* kinetics showed a broad absorption band that suggests a charge transfer state exists upon photoexcitation with evidence for radical pair formation. Surprisingly, significant triplet flavin was produced from εFAD* We hypothesize that the dipolar (ε)Ade moieties differentially modulate the singlet-triplet energy gap, resulting in different intersystem crossing rates. The additional electron density on the etheno group of εFAD supplies better orbital overlap with the flavin S1 state, accelerating charge transfer in that molecule.
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3
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Dziuba D, Didier P, Ciaco S, Barth A, Seidel CAM, Mély Y. Fundamental photophysics of isomorphic and expanded fluorescent nucleoside analogues. Chem Soc Rev 2021; 50:7062-7107. [PMID: 33956014 DOI: 10.1039/d1cs00194a] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Fluorescent nucleoside analogues (FNAs) are structurally diverse mimics of the natural essentially non-fluorescent nucleosides which have found numerous applications in probing the structure and dynamics of nucleic acids as well as their interactions with various biomolecules. In order to minimize disturbance in the labelled nucleic acid sequences, the FNA chromophoric groups should resemble the natural nucleobases in size and hydrogen-bonding patterns. Isomorphic and expanded FNAs are the two groups that best meet the criteria of non-perturbing fluorescent labels for DNA and RNA. Significant progress has been made over the past decades in understanding the fundamental photophysics that governs the spectroscopic and environmentally sensitive properties of these FNAs. Herein, we review recent advances in the spectroscopic and computational studies of selected isomorphic and expanded FNAs. We also show how this information can be used as a rational basis to design new FNAs, select appropriate sequences for optimal spectroscopic response and interpret fluorescence data in FNA applications.
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Affiliation(s)
- Dmytro Dziuba
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France.
| | - Pascal Didier
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France.
| | - Stefano Ciaco
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France. and Department of Biotechnology, Chemistry and Pharmacy, University of Siena, via Aldo Moro 2, 53100 Siena, Italy
| | - Anders Barth
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany
| | - Claus A M Seidel
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany
| | - Yves Mély
- Laboratoire de Bioimagerie et Pathologies, UMR 7021, Université de Strasbourg, 74 route du Rhin, 67401 Illkirch, France.
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4
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Martinez-Fernandez L, Gustavsson T, Diederichsen U, Improta R. Excited State Dynamics of 8-Vinyldeoxyguanosine In Aqueous Solution Studied by Time-Resolved Fluorescence Spectroscopy and Quantum Mechanical Calculations. Molecules 2020; 25:E824. [PMID: 32070032 PMCID: PMC7071107 DOI: 10.3390/molecules25040824] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 02/10/2020] [Accepted: 02/10/2020] [Indexed: 02/08/2023] Open
Abstract
The fluorescent base guanine analog, 8-vinyl-deoxyguanosine (8vdG), is studied in solution using a combination of optical spectroscopies, notably femtosecond fluorescence upconversion and quantum chemical calculations, based on time-dependent density functional theory (TD-DFT) and including solvent effect by using a mixed discrete-continuum model. In all investigated solvents, the fluorescence is very long lived (3-4 ns), emanating from a stable excited state minimum with pronounced intramolecular charge-transfer character. The main non-radiative decay channel features a sizeable energy barrier and it is affected by the polarity and the H-bonding properties of the solvent. Calculations provide a picture of dynamical solvation effects fully consistent with the experimental results and show that the photophysical properties of 8vdG are modulated by the orientation of the vinyl group with respect to the purine ring, which in turn depends on the solvent. These findings may have importance for the understanding of the fluorescence properties of 8vdG when incorporated in a DNA helix.
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Affiliation(s)
- Lara Martinez-Fernandez
- Departamento de Química, Facultad de Ciencias and IADCHEM (Institute for Advanced Research in Chemistry) Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain;
| | - Thomas Gustavsson
- Université Paris-Saclay, CEA, CNRS, LIDYL, 91191 Gif-sur-Yvette, France
| | - Ulf Diederichsen
- Univ Goettingen, Inst Organ & Biomol Chem, Tammannstr 2, D-37077 Goettingen, Germany;
| | - Roberto Improta
- Istituto di Biostrutture e Bioimmagini, CNR, Via Mezzocannone 16, I-80134 Napoli, Italy
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5
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Martinez-Fernandez L, Gavvala K, Sharma R, Didier P, Richert L, Segarra Martì J, Mori M, Mely Y, Improta R. Excited-State Dynamics of Thienoguanosine, an Isomorphic Highly Fluorescent Analogue of Guanosine. Chemistry 2019; 25:7375-7386. [PMID: 30882930 DOI: 10.1002/chem.201900677] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 03/15/2019] [Indexed: 12/27/2022]
Abstract
Thienoguanosine (th G) is an isomorphic analogue of guanosine with promising potentialities as fluorescent DNA label. As a free probe in protic solvents, th G exists in two tautomeric forms, identified as the H1, being the only one observed in nonprotic solvents, and H3 keto-amino tautomers. We herein investigate the photophysics of th G in solvents of different polarity, from water to dioxane, by combining time-resolved fluorescence with PCM/TD-DFT and CASSCF calculations. Fluorescence lifetimes of 14.5-20.5 and 7-13 ns were observed for the H1 and H3 tautomers, respectively, in the tested solvents. In methanol and ethanol, an additional fluorescent decay lifetime (≈3 ns) at the blue emission side (λ≈430 nm) as well as a 0.5 ns component with negative amplitude at the red edge of the spectrum, typical of an excited-state reaction, were observed. Our computational analysis explains the solvent effects observed on the tautomeric equilibrium. The main radiative and nonradiative deactivation routes have been mapped by PCM/TD-DFT calculations in solution and CASSCF in the gas phase. The most easily accessible conical intersection, involving an out-of plane motion of the sulfur atom in the five-membered ring of th G, is separated by a sizeable energy barrier (≥0.4 eV) from the minimum of the spectroscopic state, which explains the large experimental fluorescence quantum yield.
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Affiliation(s)
- Lara Martinez-Fernandez
- Departamento de Química, Facultad de Ciencias, Modúlo13, Universidad Autónoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, 28049 Madrid, Spain
| | - Krishna Gavvala
- Laboratoire de Bioimagerie et Pathologies, UMR 7021 CNRS, Université de Strasbourg, Faculté de pharmacie, 74 route du Rhin, 67401, Illkirch, France
| | - Rajhans Sharma
- Laboratoire de Bioimagerie et Pathologies, UMR 7021 CNRS, Université de Strasbourg, Faculté de pharmacie, 74 route du Rhin, 67401, Illkirch, France
| | - Pascal Didier
- Laboratoire de Bioimagerie et Pathologies, UMR 7021 CNRS, Université de Strasbourg, Faculté de pharmacie, 74 route du Rhin, 67401, Illkirch, France
| | - Ludovic Richert
- Laboratoire de Bioimagerie et Pathologies, UMR 7021 CNRS, Université de Strasbourg, Faculté de pharmacie, 74 route du Rhin, 67401, Illkirch, France
| | - Javier Segarra Martì
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, 80 Wood Lane, W12 0BZ, London, UK
| | - Mattia Mori
- Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, 53100, Siena, Italy
| | - Yves Mely
- Laboratoire de Bioimagerie et Pathologies, UMR 7021 CNRS, Université de Strasbourg, Faculté de pharmacie, 74 route du Rhin, 67401, Illkirch, France
| | - Roberto Improta
- Consiglio Nazionale delle Ricerche, Istituto Biostrutture e Bioimmagini, Via Mezzocannone 16, 80134, Napoli, Italy
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6
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Stanley RJ, van Galen CJ. Measuring electronic structure properties of flavins and flavoproteins by electronic Stark spectroscopy. Methods Enzymol 2019; 620:215-250. [PMID: 31072488 PMCID: PMC7301760 DOI: 10.1016/bs.mie.2019.03.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The optical spectrum of a flavoprotein is one of its signature properties. No two flavoprotein absorption spectra are exactly alike as each encodes the details of the interaction of the flavin cofactor electronic structure with the specific protein binding pocket. Electronic Stark spectroscopy has the potential to elucidate these interactions with high sensitivity, at low cost, and requiring minimal technical sophistication. In this chapter we will outline the theoretical basis for Stark spectroscopy and describe the construction of the Stark spectrometer. Step-by-step instructions are given for acquiring and interpreting Stark spectra to retrieve difference moments of the flavin ground versus excited state charge distributions.
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Affiliation(s)
- Robert J Stanley
- Department of Chemistry, Temple University, Philadelphia, PA, United States.
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7
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Liu H, Qi G, Song Q, Wang H. Benzene expansion Janus GC base analogues: A detailed theoretical study. J Photochem Photobiol A Chem 2018. [DOI: 10.1016/j.jphotochem.2017.08.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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8
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Kochman MA, Pola M, Miller RJD. Theoretical Study of the Photophysics of 8-Vinylguanine, an Isomorphic Fluorescent Analogue of Guanine. J Phys Chem A 2016; 120:6200-15. [DOI: 10.1021/acs.jpca.6b04723] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Michał A. Kochman
- Max Planck Institute for the Structure and Dynamics of Matter and Hamburg Centre for Ultrafast Imaging, Bldg. 99 (CFEL), Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Martina Pola
- Max Planck Institute for the Structure and Dynamics of Matter and Hamburg Centre for Ultrafast Imaging, Bldg. 99 (CFEL), Luruper Chaussee 149, 22761 Hamburg, Germany
- Institut
für Theoretische Physik, Universität Hamburg, Jungiusstraße
9, 20355 Hamburg, Germany
| | - R. J. Dwayne Miller
- Max Planck Institute for the Structure and Dynamics of Matter and Hamburg Centre for Ultrafast Imaging, Bldg. 99 (CFEL), Luruper Chaussee 149, 22761 Hamburg, Germany
- Department
of Chemistry and Physics, University of Toronto, 80 St. George
Street, Toronto, Ontario M5S 3H6, Canada
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9
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Optical absorption and emission properties of benzene-expanded Janus AT nucleobase analogues: A DFT study. Struct Chem 2016. [DOI: 10.1007/s11224-016-0743-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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10
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Zilbershtein-Shklanovsky L, Kafri P, Shav-Tal Y, Yavin E, Fischer B. Development of fluorescent double-strand probes labeled with 8-(p-CF3-cinnamyl)-adenosine for the detection of cyclin D1 breast cancer marker. Eur J Med Chem 2014; 79:77-88. [DOI: 10.1016/j.ejmech.2014.03.081] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 03/24/2014] [Accepted: 03/29/2014] [Indexed: 12/14/2022]
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11
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Pauszek RF, Stanley RJ. A "how-to" guide to the stark spectroscopy of flavins and flavoproteins. Methods Mol Biol 2014; 1146:443-466. [PMID: 24764101 DOI: 10.1007/978-1-4939-0452-5_17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Flavins and flavoproteins have been studied by a plethora of spectroscopic techniques. Beginning with the characterization of DNA photolyases and the discovery of the diversity of roles played by excited-state flavins in photobiology, the characterization of the electronic excited state of flavins has become increasingly important. In this protocol, we provide a guide to using Stark spectroscopy in obtaining the degree of electronic charge redistribution in simple flavins and in flavoproteins. Stark spectroscopy is technically simpler than more common approaches used to explore the structure of the excited state, considerably cheaper to implement, and yet very powerful in its scope. At the end of this guide, we present data taken on non-photobiological flavoproteins, glutathione reductase and lipoamide dehydrogenase, that suggest that Stark spectroscopy is a unique way to elucidate the electrostatic environment that the flavin cofactor experiences bound inside the protein.
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Affiliation(s)
- Raymond F Pauszek
- Department of Chemistry, Temple University, 250B Beury Hall, 1901N. 13th Street, Philadelphia, PA, 19122, USA
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12
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13
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Liu H, Song Q, Liu J, Li Y, Wang H. Theoretical study on absorption and emission spectra of size-expanded Janus-type AT nucleobases and effect of base pairing. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2013; 121:670-677. [PMID: 24368287 DOI: 10.1016/j.saa.2013.11.100] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 11/13/2013] [Accepted: 11/17/2013] [Indexed: 06/03/2023]
Abstract
Fluorescent nucleoside analogues have attracted much attention in studying the structure and dynamics of nucleic acids in recent years. In the present work, we design benzo- and naphtha-expanded Janus AT base analogues, using DFT, TDDFT, and CIS methods to investigate the structural and optical properties of the Janus AT base analogues (termed as J-AT, xJ-AT, yyJ-AT, BF, xBF and yyBF), and also consider the effect of base pairing. The results show that the Janus AT base analogues can pair with T and A simultaneously to form stable H-bonded WC base pairs. The ground state structure of J-AT is similar to BF, the size expansion is 2.42Å for the x-Janus AT bases and 4.86Å for the yy-Janus AT bases. The excited state geometries of J-AT and BF change dramatically, while the other bases are similar to the ground state geometries. The lowest excited singlet transitions of the Janus AT base analogues are predicted to be of ππ(*) character and mainly dominated by the configuration HOMO-LUMO. The maximum absorption wavelengths of size expansion Janus AT base analogues are greatly red shifted compared with J-AT (or BF). BF, xBF and yyJ-AT have larger oscillator strengths than J-AT, xJ-AT and yyBF. The emission wavelengths of the Janus AT base analogues also exhibit red shifts from x-Janus AT bases to yy-Janus AT bases. However, the emission wavelengths of J-AT and BF change greatly, which are coincident with the structures observed in the excited state geometries. With regard to the WC base pairs, the B3LYP functional reveals that the lowest energy transitions of some base pairs are charge transfer excitation, while the other base pairs are local excitation. The CAM-B3LYP functional predicts that all the lowest transitions are localized on the Janus AT bases, and show good agreement with the results of the M062X functional.
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Affiliation(s)
- Hongxia Liu
- School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China; Chemical and Biological Engineering College, Yancheng Institute of Technology, Yancheng, Jiangsu 214122, China
| | - Qixia Song
- School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Jianhua Liu
- School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Yan Li
- School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Haijun Wang
- School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China.
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14
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Zilbershtein-Shklanovsky L, Weitman M, Major DT, Fischer B. Rules for the Design of Highly Fluorescent Nucleoside Probes: 8-(Substituted Cinnamyl)-Adenosine Analogues. J Org Chem 2013; 78:11999-2008. [DOI: 10.1021/jo402050x] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Lital Zilbershtein-Shklanovsky
- Department of Chemistry, Gonda-Goldschmied Medical Research Center and the Lise-Meitner-Minerva
Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Michal Weitman
- Department of Chemistry, Gonda-Goldschmied Medical Research Center and the Lise-Meitner-Minerva
Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Dan Thomas Major
- Department of Chemistry, Gonda-Goldschmied Medical Research Center and the Lise-Meitner-Minerva
Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Bilha Fischer
- Department of Chemistry, Gonda-Goldschmied Medical Research Center and the Lise-Meitner-Minerva
Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
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15
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TDDFT Investigation of the Electronic Structures and Photophysical Properties of Fluorescent Extended Styryl Push-Pull Chromophores Containing Carbazole Unit. J Fluoresc 2013; 23:1121-38. [DOI: 10.1007/s10895-013-1241-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Accepted: 05/22/2013] [Indexed: 10/26/2022]
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16
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Oxidation and reduction potentials of 8-vinyladenosine measured by cyclic voltammetry: Implications for photoinduced electron transfer quenching of a fluorescent adenine analog. J Photochem Photobiol A Chem 2012. [DOI: 10.1016/j.jphotochem.2012.08.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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17
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Ottiger P, Leutwyler S, Köppel H. Vibrational quenching of excitonic splittings in H-bonded molecular dimers: the electronic Davydov splittings cannot match experiment. J Chem Phys 2012; 136:174308. [PMID: 22583231 DOI: 10.1063/1.4705119] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The S(1)/S(2) state exciton splittings of symmetric doubly hydrogen-bonded gas-phase dimers provide spectroscopic benchmarks for the excited-state electronic couplings between UV chromophores. These have important implications for electronic energy transfer in multichromophoric systems ranging from photosynthetic light-harvesting antennae to photosynthetic reaction centers, conjugated polymers, molecular crystals, and nucleic acids. We provide laser spectroscopic data on the S(1)/S(2) excitonic splitting Δ(exp) of the doubly H-bonded o-cyanophenol (oCP) dimer and compare to the splittings of the dimers of (2-aminopyridine)(2), [(2AP)(2)], (2-pyridone)(2), [(2PY)(2)], (benzoic acid)(2), [(BZA)(2)], and (benzonitrile)(2), [(BN)(2)]. The experimental S(1)/S(2) excitonic splittings are Δ(exp) = 16.4 cm(-1) for (oCP)(2), 11.5 cm(-1) for (2AP)(2), 43.5 cm(-1) for (2PY)(2), and <1 cm(-1) for (BZA)(2). In contrast, the vertical S(1)/S(2) energy gaps Δ(calc) calculated by the approximate second-order coupled cluster (CC2) method for the same dimers are 10-40 times larger than the Δ(exp) values. The qualitative failure of this and other ab initio methods to reproduce the exciton splitting Δ(exp) arises from the Born-Oppenheimer (BO) approximation, which implicitly assumes the strong-coupling case and cannot be employed to evaluate excitonic splittings of systems that are in the weak-coupling limit. Given typical H-bond distances and oscillator strengths, the majority of H-bonded dimers lie in the weak-coupling limit. In this case, the monomer electronic-vibrational coupling upon electronic excitation must be accounted for; the excitonic splittings arise between the vibronic (and not the electronic) transitions. The discrepancy between the BO-based splittings Δ(calc) and the much smaller experimental Δ(exp) values is resolved by taking into account the quenching of the BO splitting by the intramolecular vibronic coupling in the monomer S(1) ← S(0) excitation. The vibrational quenching factors Γ for the five dimers (oCP)(2), (2AP)(2), (2AP)(2), (BN)(2), and (BZA)(2) lie in the range Γ = 0.03-0.2. The quenched excitonic splittings Γ[middle dot]Δ(calc) are found to be in very good agreement with the observed splittings Δ(exp). The vibrational quenching approach predicts reliable Δ(exp) values for the investigated dimers, confirms the importance of vibrational quenching of the electronic Davydov splittings, and provides a sound basis for predicting realistic exciton splittings in multichromophoric systems.
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Affiliation(s)
- Philipp Ottiger
- Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
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18
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Saha G, Sarkar KK, Mondal TK, Sinha C. Synthesis, spectra, structure, redox properties and DFT computation of copper(I)–triphenylphosphine–pyridyl Schiff bases. Inorganica Chim Acta 2012. [DOI: 10.1016/j.ica.2012.01.030] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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19
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Kodali G, Narayanan M, Stanley RJ. Excited-state electronic properties of 6-methylisoxanthopterin (6-MI): an experimental and theoretical study. J Phys Chem B 2012; 116:2981-9. [PMID: 22276652 DOI: 10.1021/jp2110083] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
6-Methylisoxanthopterin (6-MI) is a pteridine-based guanine analog that has a red-shifted absorption and high fluorescence quantum yield. Its Watson-Crick base-pairing and base stacking properties are similar to guanine. The fluorescence quantum yield of 6-MI is sensitive to its nearest neighbors and base stacking, making it a very useful real-time probe of DNA structure. The fundamental photophysics underlying this fluorescence quenching by base stacking is not well understood. We have explored the excited-state electronic structure of the 6-MI in frozen 77 K LiCl glasses using Stark spectroscopy. These measurements yielded the direction and degree of charge redistribution for the S(0)→S(1) transition as manifested in the difference dipole moment, Δμ(01), and difference static polarizability, TrΔα. TDDFT (time-dependent density functional theory) was employed to calculate the transition energy, oscillator strength, and the dipole moments of the ground and lowest optically bright excited state of 6-MI (S(0)→S(1)). The direction of Δμ(01) was assigned in the molecular frame based on the Stark data and calculations. These results suggest that the C4═O and C2-NH(2) groups are electron-deficient in the excited state, a very different outcome compared with guanine. This implies that Watson-Crick hydrogen bonding in 6-MI may be modulated by absorption of a photon so as to strengthen base pairing, if only transiently. Solvatochromism was also obtained for the absorption and emission spectra of 6-MI in various solvents and compared with the Stark spectroscopic results using both the Lippert-Mataga and Bakhshiev models.
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Affiliation(s)
- Goutham Kodali
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA
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20
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Dement’eva OV, Rudoy VM. Colloidal synthesis of new silver-based nanostructures with tailored localized surface plasmon resonance. COLLOID JOURNAL 2011. [DOI: 10.1134/s1061933x11060032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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21
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Zilbershtein L, Silberman A, Fischer B. 8-(p-CF3-cinnamyl)-modified purine nucleosides as promising fluorescent probes. Org Biomol Chem 2011; 9:7763-73. [PMID: 21960279 DOI: 10.1039/c1ob05681f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Natural nucleotides are not useful as fluorescent probes because of their low quantum yields. Therefore, a common methodology for the detection of RNA and DNA is the application of extrinsic fluorescent dyes coupled to bases in oligonucleotides. To overcome the many limitations from which fluorescent nucleotide-dye conjugates suffer, we have developed novel purine nucleosides with intrinsic fluorescence to be incorporated into oligonucleotide probes. For this purpose we synthesized adenosine and guanosine fluorescent analogues 7-25, conjugated at the C8 position with aryl/heteroaryl moieties either directly, or via alkenyl/alkynyl linkers. Directly conjugated analogues 7-14, exhibited high quantum yields, φ >0.1, and short λ(em) (<385 nm). Alkynyl conjugated analogues 22-25, exhibited low quantum yields, φ <0.075, and λ(em)<385 nm. The alkenyl conjugated analogues 15-21, exhibited λ(em) 408-459 nm. While analogues 15,16, and 20 bearing an EDG on the aryl moiety, exhibited φ <0.02, analogues 17, and 21 with EWG on the aryl moiety, exhibited extremely high quantum yields, φ ≈ 0.8, suggesting better intramolecular charge transfer. We determined the conformation of selected adenosine analogues. Directly conjugated analogue 8 and alkynyl conjugated analogue 22, adapted the syn conformation, whereas alkenyl conjugated analogue 15 adapted the anti conformation. Based on the long emission wavelengths, high quantum yields, anti conformation and base-paring compatibility, we suggest analogues 17 and 21 for further development as fluorescent probes for the sensitive detection of genetic material.
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Affiliation(s)
- Lital Zilbershtein
- Department of Chemistry, Gonda-Goldschmied Medical Research Center, Bar-Ilan University, Ramat-Gan, 52900, Israel
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22
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Melnichuk A, Bartlett RJ. Gas phase solvatochromic effects of phenol and naphthol photoacids. J Chem Phys 2011; 134:244303. [DOI: 10.1063/1.3603456] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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