1
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Donon J, Bardaud JX, Brenner V, Ishiuchi SI, Fujii M, Gloaguen E. Stepwise dissociation of ion pairs by water molecules: cation-dependent separation mechanisms between carboxylate and alkali-earth metal ions. Phys Chem Chem Phys 2022; 24:12121-12125. [PMID: 35545953 DOI: 10.1039/d2cp01158a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Microhydrated H2-tagged ion pairs (Ca2+, AcO-)(H2O)n=0-8 and (Ba2+, AcO-)(H2O)n=0-5 are investigated by IR photodissociation laser spectroscopy and DFT-D frequency calculations. The detailed picture of the first steps of ion dissociation reveals two mechanisms, where water molecules promote dissociation either directly or indirectly depending on the nature of the cation.
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Affiliation(s)
- Jeremy Donon
- LIDYL, CEA, CNRS, Université Paris Saclay CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Jean-Xavier Bardaud
- LIDYL, CEA, CNRS, Université Paris Saclay CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Valérie Brenner
- LIDYL, CEA, CNRS, Université Paris Saclay CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Shun-Ichi Ishiuchi
- Laboratory for Chemistry and Life Science, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
| | - Masaaki Fujii
- Laboratory for Chemistry and Life Science, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
| | - Eric Gloaguen
- LIDYL, CEA, CNRS, Université Paris Saclay CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
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2
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Mitra S, Denton JK, Kelleher PJ, Johnson MA, Guasco TL, Choi TH, Jordan KD. Water Network Shape-Dependence of Local Interactions with the Microhydrated -NO 2- and -CO 2- Anionic Head Groups by Cold Ion Vibrational Spectroscopy. J Phys Chem A 2022; 126:2471-2479. [PMID: 35418229 DOI: 10.1021/acs.jpca.2c00721] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report the structural evolutions of water networks and solvatochromic response of the CH3NO2- radical anion in the OH and CH stretching regions by analysis of the vibrational spectra displayed by cryogenically cooled CH3NO2-·(H2O)n=1-6 clusters. The OH stretching bands evolve with a surprisingly large discontinuity at n = 6, which features the emergence of an intense, strongly red-shifted band along with a weaker feature that appears in the region assigned to a free OH fundamental. Very similar behavior is displayed by the perdeuterated carboxylate clusters, RCO2-·(H2O)n=5-7 (R = CD3CD2), indicating that this behavior is a general feature in the microhydration of the triatomic anionic domain and not associated with CH oscillators. Electronic structure calculations trace this behavior to the formation of a "book" isomer of the water hexamer that adopts a configuration in which one of the water molecules resides in an acceptor-acceptor-donor (AAD) (A = acceptor, D = donor) H-bonding site. Excitation of the bound OH in the AAD site explores the local network topology best suited to stabilize an incipient -XO2H-OH-(H2O)2 intracluster proton-transfer reaction. These systems thus provide particularly clear examples where the network shape controls the potential energy landscape that governs water network-mediated, intracluster proton transfer. The CH stretching bands of the CH3NO2-·(H2O)n=1-6 clusters also exhibit strong solvatochromic shifts, but in this case, they smoothly blue-shift with increasing hydration with no discontinuity at n = 6. This behavior is analyzed in the context of the solute-ion polarizability response and partial charge transfer to the water networks.
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Affiliation(s)
- Sayoni Mitra
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Joanna K Denton
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Patrick J Kelleher
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Timothy L Guasco
- Department of Chemistry, Millikin University, Decatur, Illinois 62522, United States
| | - Tae Hoon Choi
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Kenneth D Jordan
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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3
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Donon J, Habka S, Mons M, Brenner V, Gloaguen E. Conformational analysis by UV spectroscopy: the decisive contribution of environment-induced electronic Stark effects. Chem Sci 2021; 12:2803-2815. [PMID: 34164044 PMCID: PMC8179363 DOI: 10.1039/d0sc06074g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Accepted: 01/04/2021] [Indexed: 12/14/2022] Open
Abstract
UV chromophores are frequently used as probes of the molecular structure. In particular, they are sensitive to the electric field generated by the molecular environment, resulting in the observation of Stark effects on UV spectra. While these environment-induced electronic Stark effects (EI-ESE) are already used for conformational analysis in the condensed phase, this work explores the potential of such an approach when performed at much higher conformational resolution in the gas phase. By investigating model alkali benzylacetate and 4-phenylbutyrate ion pairs, where the electric field applied to the phenyl ring is chemically tuned by changing the nature of the alkali cation, this work demonstrates that precise conformational assignments can be proposed based on the correlation between the conformation-dependent calculated electric fields and the frequency of the electronic transitions observed in the experimental UV spectra. Remarkably, the sole analysis of Stark effects and fragmentation patterns in mass-selected UV spectra provided an accurate and complete conformational analysis, where spectral differences as small as a few cm-1 between electronic transitions were rationalized. This case study illustrates that the identification of EI-ESE together with their interpretation at the modest cost of a ground state electric field calculation qualify UV spectroscopy as a powerful tool for conformational analysis.
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Affiliation(s)
- Jeremy Donon
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay Bât 522 91191 Gif-sur-Yvette France
| | - Sana Habka
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay Bât 522 91191 Gif-sur-Yvette France
| | - Michel Mons
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay Bât 522 91191 Gif-sur-Yvette France
| | - Valérie Brenner
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay Bât 522 91191 Gif-sur-Yvette France
| | - Eric Gloaguen
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay Bât 522 91191 Gif-sur-Yvette France
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4
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Donon J, Habka S, Vaquero-Vara V, Brenner V, Mons M, Gloaguen E. Electronic Stark Effect in Isolated Ion Pairs. J Phys Chem Lett 2019; 10:7458-7462. [PMID: 31647874 DOI: 10.1021/acs.jpclett.9b02675] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Stark spectral shifts of a molecular probe are commonly used to estimate the local electric field in condensed media. The very large fields reported, typically in the 0.1-10 GV m-1 range, are, however, difficult to reproduce in a controlled manner, limiting the calibration of these molecular probes to ranges below 0.1 GV m-1. In this context, we investigated gas-phase, isolated, molecular ion pairs, where a phenyl ring is immersed in the electric field produced by the nearby ionic groups. The intensity of the electric field is chemically tuned in the 1 GV m-1 range by changing the nature of the cations, and the phenyl ring response is monitored by UV spectroscopy. A quadratic Stark effect is observed, demonstrating the possibility to characterize molecular probes in a solvent-free environment and in the very large field range they typically meet in condensed media such as biological environments.
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Affiliation(s)
- Jeremy Donon
- LIDYL, CEA , CNRS, Université Paris Saclay ; CEA Saclay, Bât 522 , 91191 Gif-sur-Yvette , France
| | - Sana Habka
- LIDYL, CEA , CNRS, Université Paris Saclay ; CEA Saclay, Bât 522 , 91191 Gif-sur-Yvette , France
| | - Vanesa Vaquero-Vara
- LIDYL, CEA , CNRS, Université Paris Saclay ; CEA Saclay, Bât 522 , 91191 Gif-sur-Yvette , France
| | - Valérie Brenner
- LIDYL, CEA , CNRS, Université Paris Saclay ; CEA Saclay, Bât 522 , 91191 Gif-sur-Yvette , France
| | - Michel Mons
- LIDYL, CEA , CNRS, Université Paris Saclay ; CEA Saclay, Bât 522 , 91191 Gif-sur-Yvette , France
| | - Eric Gloaguen
- LIDYL, CEA , CNRS, Université Paris Saclay ; CEA Saclay, Bât 522 , 91191 Gif-sur-Yvette , France
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5
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Denton JK, Kelleher PJ, Johnson MA, Baer MD, Kathmann SM, Mundy CJ, Wellen Rudd BA, Allen HC, Choi TH, Jordan KD. Molecular-level origin of the carboxylate head group response to divalent metal ion complexation at the air-water interface. Proc Natl Acad Sci U S A 2019; 116:14874-14880. [PMID: 31278149 PMCID: PMC6660762 DOI: 10.1073/pnas.1818600116] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We exploit gas-phase cluster ion techniques to provide insight into the local interactions underlying divalent metal ion-driven changes in the spectra of carboxylic acids at the air-water interface. This information clarifies the experimental findings that the CO stretching bands of long-chain acids appear at very similar energies when the head group is deprotonated by high subphase pH or exposed to relatively high concentrations of Ca2+ metal ions. To this end, we report the evolution of the vibrational spectra of size-selected [Ca2+·RCO2-]+·(H2O) n=0to12 and RCO2-·(H2O) n=0to14 cluster ions toward the features observed at the air-water interface. Surprisingly, not only does stepwise hydration of the RCO2- anion and the [Ca2+·RCO2-]+ contact ion pair yield solvatochromic responses in opposite directions, but in both cases, the responses of the 2 (symmetric and asymmetric stretching) CO bands to hydration are opposite to each other. The result is that both CO bands evolve toward their interfacial asymptotes from opposite directions. Simulations of the [Ca2+·RCO2-]+·(H2O) n clusters indicate that the metal ion remains directly bound to the head group in a contact ion pair motif as the asymmetric CO stretch converges at the interfacial value by n = 12. This establishes that direct metal complexation or deprotonation can account for the interfacial behavior. We discuss these effects in the context of a model that invokes the water network-dependent local electric field along the C-C bond that connects the head group to the hydrocarbon tail as the key microscopic parameter that is correlated with the observed trends.
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Affiliation(s)
- Joanna K Denton
- Sterling Chemistry Laboratory, Yale University, New Haven, CT 06520
| | | | - Mark A Johnson
- Sterling Chemistry Laboratory, Yale University, New Haven, CT 06520;
| | - Marcel D Baer
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352
| | - Shawn M Kathmann
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352
| | - Christopher J Mundy
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352
- Department of Chemical Engineering, University of Washington, Seattle, WA 98195
| | - Bethany A Wellen Rudd
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH 43210
- Department of Chemistry, Ohio Wesleyan University, Delaware, OH 43015
| | - Heather C Allen
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH 43210
| | - Tae Hoon Choi
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260
| | - Kenneth D Jordan
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260
- Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA 15260
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6
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Habka S, Very T, Donon J, Vaquero-Vara V, Tardivel B, Charnay-Pouget F, Mons M, Aitken DJ, Brenner V, Gloaguen E. Identification of ion pairs in solution by IR spectroscopy: crucial contributions of gas phase data and simulations. Phys Chem Chem Phys 2019; 21:12798-12805. [PMID: 30977483 DOI: 10.1039/c9cp00700h] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In a context where structure elucidation of ion pairs in solution remains a contemporary challenge, this work explores an original approach where accurate gas phase spectroscopic data are used to refine high level quantum chemistry calculations of ion pairs in solution, resulting in an unprecedented level of accuracy in vibrational frequency prediction. First, gas phase studies focus on a series of isolated contact ion pairs (M+, Ph-CH2-COO-, with M = Li, Na, K, Rb, Cs) for which conformer-selective IR spectra in the CO2- stretch region are recorded. These experiments reveal the interactions at play in isolated contact ion pairs, and provide vibrational frequencies enabling us to assess the accuracy of the theoretical approach used, i.e., mode-dependent scaled harmonic frequency calculations at the RI-B97-D3/dhf-TZVPP level. This level of calculation is then employed on large water clusters embedding either a free acetate ion or its contact or solvent-shared pairs with a sodium cation in order to simulate the individual vibrational spectra of these species in solution. This study shows that the stretching modes of carboxylate are sensitive to both solvent-shared and contact ion pair formation. FTIR spectra of solutions of increasing concentrations indeed reveal several spectral changes consistent with the presence of specific types of solvent-shared and contact ion pairs. By providing relevant guidelines for the interpretation of solution phase IR spectra, this work illustrates the potential of the approach for the elucidation of supramolecular structures in electrolyte solutions.
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Affiliation(s)
- Sana Habka
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Thibaut Very
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Jeremy Donon
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Vanesa Vaquero-Vara
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Benjamin Tardivel
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Florence Charnay-Pouget
- ICMMO, CNRS, Université Paris Sud, Université Paris Saclay, UMR 8182, Bât. 420, 15 rue Georges Clémenceau, 91405 Orsay cedex, France
| | - Michel Mons
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - David J Aitken
- ICMMO, CNRS, Université Paris Sud, Université Paris Saclay, UMR 8182, Bât. 420, 15 rue Georges Clémenceau, 91405 Orsay cedex, France
| | - Valérie Brenner
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
| | - Eric Gloaguen
- LIDYL, CEA, CNRS, Université Paris Saclay, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
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7
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León I, Lesarri A, Fernández JA. Evaluation of the aggregation process in a mixture of propofol and benzocaine. Phys Chem Chem Phys 2019; 21:3537-3544. [PMID: 30137107 DOI: 10.1039/c8cp04386h] [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
We report on a mass-resolved IR spectrosopic study on propofol-benzocaine aggregates. This is a complex system due to the several conformational isomers that both monomers may adopt and to the combination of functional groups they present, which allow the molecules to interact in many possible ways. However, our results demonstrate that a single conformation is favored for each stoichiometry. In the heterodimer, propofol acts as a proton donor to the ester group of benzocaine, while the whole cluster is stabilized by dispersive forces. These dispersive forces account for an important part of the system's stabilization energy as the calculations suggest. Propofol does not show any affinity for the amino group of benzocaine, even when a second molecule of propofol is introduced. These results demonstrate the difficulty in anticipating the aggregation preferences of even small organic molecules.
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Affiliation(s)
- I León
- Department of Physical Chemistry, Faculty of Science and Technology, University of the Basque Country, Barrio Sarriena s/n, 48940 Leioa, Spain.
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8
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Asami H, Kawabata R, Kawauchi N, Kohno JY. Photodissociation Spectroscopy of Hydrated Myoglobin Ions Isolated by IR-laser Ablation of a Droplet Beam: Recovery from pH-denatured Structure by Gas-phase Isolation. CHEM LETT 2019. [DOI: 10.1246/cl.180884] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Hiroya Asami
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
| | - Rina Kawabata
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
| | - Norishi Kawauchi
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
| | - Jun-ya Kohno
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
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9
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Luo C, Ji X, Chen J, Gaskell KJ, He X, Liang Y, Jiang J, Wang C. Solid‐State Electrolyte Anchored with a Carboxylated Azo Compound for All‐Solid‐State Lithium Batteries. Angew Chem Int Ed Engl 2018; 57:8567-8571. [DOI: 10.1002/anie.201804068] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Indexed: 11/06/2022]
Affiliation(s)
- Chao Luo
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Xiao Ji
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
- School of Optical and Electronic Information Huazhong University of Science and Technology Wuhan Hubei 430074 China
| | - Ji Chen
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Karen J. Gaskell
- Department of Chemistry and Biochemistry University of Maryland College Park MD 20740 USA
| | - Xinzi He
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Yujia Liang
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Jianjun Jiang
- School of Optical and Electronic Information Huazhong University of Science and Technology Wuhan Hubei 430074 China
| | - Chunsheng Wang
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
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10
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Luo C, Ji X, Chen J, Gaskell KJ, He X, Liang Y, Jiang J, Wang C. Solid‐State Electrolyte Anchored with a Carboxylated Azo Compound for All‐Solid‐State Lithium Batteries. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201804068] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Chao Luo
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Xiao Ji
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
- School of Optical and Electronic Information Huazhong University of Science and Technology Wuhan Hubei 430074 China
| | - Ji Chen
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Karen J. Gaskell
- Department of Chemistry and Biochemistry University of Maryland College Park MD 20740 USA
| | - Xinzi He
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Yujia Liang
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
| | - Jianjun Jiang
- School of Optical and Electronic Information Huazhong University of Science and Technology Wuhan Hubei 430074 China
| | - Chunsheng Wang
- Department of Chemical and Biomolecular Engineering University of Maryland College Park MD 20740 USA
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11
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Comitani F, Rossi K, Ceriotti M, Sanz ME, Molteni C. Mapping the conformational free energy of aspartic acid in the gas phase and in aqueous solution. J Chem Phys 2017; 146:145102. [DOI: 10.1063/1.4979519] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Affiliation(s)
- Federico Comitani
- Department of Physics, King’s College London, Strand, London WC2R 2LS, United Kingdom
| | - Kevin Rossi
- Department of Physics, King’s College London, Strand, London WC2R 2LS, United Kingdom
| | - Michele Ceriotti
- Laboratory of Computational Science and Modeling, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - M. Eugenia Sanz
- Department of Chemistry, King’s College London, Britannia House, 7 Trinity Street, London SE1 1DB, United Kingdom
| | - Carla Molteni
- Department of Physics, King’s College London, Strand, London WC2R 2LS, United Kingdom
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12
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DePalma JW, Kelleher PJ, Tavares LC, Johnson MA. Coordination-Dependent Spectroscopic Signatures of Divalent Metal Ion Binding to Carboxylate Head Groups: H 2- and He-Tagged Vibrational Spectra of M 2+·RCO 2¯ (M = Mg and Ca, R = -CD 3, -CD 2CD 3) Complexes. J Phys Chem Lett 2017; 8:484-488. [PMID: 28060510 DOI: 10.1021/acs.jpclett.6b02964] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We explore the intramolecular distortions present in divalent metal ion-carboxylate ion pairs using vibrational spectroscopy of the cryogenically cooled, mass-selected species isolated in the gas phase. The spectral signatures of the C-O stretching modes are identified using the perdeutero isotopologues of the acetate and propionate anions to avoid congestion arising from the CH2 fundamentals. Both Ca2+ and Mg2+ are observed to bind in a symmetrical, so-called "bidentate" arrangement to the -CO2¯ group. The very strong deformations of the head groups displayed by the binary complexes dramatically relax when either neutral water molecules or counterions are attached to the Mg2+RCO2¯ cation. These results emphasize the critical role that local coordination plays when using the RCO2¯ bands to deduce the metal ion complexation motif in condensed media.
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Affiliation(s)
- Joseph W DePalma
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Patrick J Kelleher
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Laís C Tavares
- Instituto de Química, Universidade de São Paulo , Caixa Postal 26077, São Paulo, CEP 05508-900, Brazil
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States
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