1
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Jang T, Lee S, Pang Y. Anomalous proton transfer of a photoacid HPTS in nonaqueous reverse micelles. Phys Chem Chem Phys 2024; 26:11283-11294. [PMID: 38456549 DOI: 10.1039/d3cp05710k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2024]
Abstract
The proton transfer reaction is one of the fundamental chemical reactions where the reaction dynamics strongly depend on solvent properties such as acidity or basicity. A photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) shows a sharp decrease of pKa (7.7 → 0.5) upon photoexcitation, and the excited-state proton transfer (ESPT) occurs with ultrafast time constants of 2.5 and 89 ps in bulk aqueous solution. However, the two-step proton transfers via the contact ion pair formation and the proton diffusion are strongly limited inside the nanopools of reverse micelles (RMs). The confinement in small RMs strongly impeded the proton transfer reactions. In this work, we report the ESPT of HPTS confined in methanol-in-oil RMs by steady-state and time-resolved electronic spectroscopy. Interestingly, HPTS shows substantial deprotonation in the excited state only in small RMs, while the ESPT of HPTS does not occur in bulk methanol solution due to the low basicity of aliphatic alcohols. The kinetic analysis of time-resolved fluorescence and transient absorption measurements will compare the proton transfer dynamics of HPTS in the water-in-oil and methanol-in-oil RMs. The ESPT of photoacids, especially in the nonaqueous RMs, can be crucial in understanding many important chemical reactions involving proton transfer in the confined environments of cells and membranes.
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Affiliation(s)
- Taehyung Jang
- Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.
| | - Sebok Lee
- Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.
| | - Yoonsoo Pang
- Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.
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2
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Stemo G, Nishiuchi J, Bhakta H, Mao H, Wiesehan G, Xiong W, Katsuki H. Ultrafast Spectroscopy under Vibrational Strong Coupling in Diphenylphosphoryl Azide. J Phys Chem A 2024; 128:1817-1824. [PMID: 38437187 PMCID: PMC10945483 DOI: 10.1021/acs.jpca.3c07847] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 01/26/2024] [Accepted: 02/13/2024] [Indexed: 03/06/2024]
Abstract
Strong coupling of cavity photons and molecular vibrations creates vibrational polaritons that have been shown to modify chemical reactivity and alter material properties. While ultrafast spectroscopy of vibrational polaritons has been performed intensively in metal complexes, ultrafast dynamics in vibrationally strongly coupled organic molecules remain unexplored. Here, we report ultrafast pump-probe measurement and two-dimensional infrared spectroscopy in diphenylphosphoryl azide under vibrational strong coupling. Early time oscillatory structures indicate coherent energy exchange between the two polariton modes, which decays in ∼2 ps. We observe a large transient absorptive feature around the lower polariton, which can be explained by the overlapped excited-state absorption and derivative-shaped structures around the lower and upper polaritons. The latter feature is explained by the Rabi splitting contraction, which is ascribed to a reduced population in the ground state. These results reassure the previously reported spectroscopic theory to describe nonlinear spectroscopy of vibrational polaritons. We have also noticed the influence of the complicated layer structure of the cavity mirrors. The penetration of the electric field distribution into the layered structure of the dielectric-mirror cavities can significantly affect the Rabi splitting and the decay time constant of polaritonic systems.
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Affiliation(s)
- Garrek Stemo
- Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma 630-0192, Japan
| | - Joel Nishiuchi
- Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma 630-0192, Japan
| | - Harsh Bhakta
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
| | - Haochuan Mao
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
| | - Garret Wiesehan
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
| | - Wei Xiong
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
| | - Hiroyuki Katsuki
- Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma 630-0192, Japan
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3
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Heisler IA, Meech SR. Altered relaxation dynamics of excited state reactions by confinement in reverse micelles probed by ultrafast fluorescence up-conversion. Chem Soc Rev 2021; 50:11486-11502. [PMID: 34661209 DOI: 10.1039/d1cs00516b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Chemical reactions in confined environments are important in areas as diverse as heterogenous catalysis, environmental chemistry and biochemistry, yet they are much less well understood than the equivalent reactions in either the gas phase or in free solution. The understanding of chemical reactions in solution was greatly enhanced by real time studies of model reactions, through ultrafast spectroscopy (especially when supported by molecular dynamics simulation). Here we review some of the efforts that have been made to adapt this approach to the investigation of reactions in confined media. Specifically, we review the application of ultrafast fluorescence spectroscopy to measure reaction dynamics in the nanoconfined water phase of reverse micelles, as a function of the droplet radius and the charge on the interface. Methods of measurement and modelling of the reactions are outlined. In all of the cases studied (which are focused on ultrafast intramolecular reactions) the effect of confinement was to suppress the reaction. Even in the largest micelles the result in the bulk aqueous phase was not usually recovered, suggesting an important role for specific interactions between reactant and environment, for example at the interface. There was no simple one-to-one correspondence with direct measures of the dynamics of the confined phase. Thus, understanding the effect of confinement on reaction rate appears to require not only knowledge of the dynamics of the reaction in solutions and the effect of confinement on the medium, but also of the interaction between reactant and confining medium.
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Affiliation(s)
- Ismael A Heisler
- Departamento de Física, Universidade Federal do Paraná, Curitiba, Paraná, CEP 81531-980, Brazil
| | - Stephen R Meech
- School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK.
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4
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Mora AK, Singh PK, Nadkarni SA, Nath S. How mobile is the water in the reverse micelles? A 2DIR study with an ultrasmall IR probe. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2020.114819] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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5
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Dunkelberger AD, Fears KP, Davidson II RB, Dressick WJ, Simpkins BS, Owrutsky JC. Vibrational relaxation of small anions in a polymer film. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2018.03.016] [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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6
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Czurlok D, von Domaros M, Thomas M, Gleim J, Lindner J, Kirchner B, Vöhringer P. Femtosecond 2DIR spectroscopy of the nitrile stretching vibration of thiocyanate anions in liquid-to-supercritical heavy water. Spectral diffusion and libration-induced hydrogen-bond dynamics. Phys Chem Chem Phys 2015; 17:29776-85. [DOI: 10.1039/c5cp05237h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Femtosecond two-dimensional infrared (2DIR) spectroscopy was carried out to study the dynamics of vibrational spectral diffusion of the nitrile stretching vibration of thiocyanate.
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Affiliation(s)
- Denis Czurlok
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
| | - Michael von Domaros
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
| | - Martin Thomas
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
| | - Jeannine Gleim
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
| | - Jörg Lindner
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
| | - Barbara Kirchner
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
| | - Peter Vöhringer
- Institut für Physikalische und Theoretische Chemie
- Rheinische Friedrich-Wilhelms-Universität
- 53115 Bonn
- Germany
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7
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Czurlok D, Gleim J, Lindner J, Vöhringer P. Vibrational Energy Relaxation of Thiocyanate Ions in Liquid-to-Supercritical Light and Heavy Water. A Fermi's Golden Rule Analysis. J Phys Chem Lett 2014; 5:3373-3379. [PMID: 26278447 DOI: 10.1021/jz501710c] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The vibrational relaxation dynamics following an ultrafast nitrile stretching (ν3) excitation of thiocyanate anions dissolved in light and heavy water have been studied over a wide temperature and density range corresponding to the aqueous liquid up to the supercritical phase. In both solvents, the relaxation of the ν3 = 1 state of the anion leads to a direct recovery of the vibrational ground state and involves the resonant transfer of the excess vibrational energy onto the solvent. In light water, the energy-accepting states are provided by the bending-librational combination band (νb + νL), while in heavy water, the relaxation is thermally assisted by virtual acceptor states derived from the stretching-librational/restricted translational hot band (νS - νL,T). The relaxation rate is found to strictly obey Fermi's Golden Rule when the density of resonant solvent states is estimated from the linear infrared spectra of the solute and the pure solvents.
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Affiliation(s)
- Denis Czurlok
- Lehrstuhl für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany
| | - Jeannine Gleim
- Lehrstuhl für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany
| | - Jörg Lindner
- Lehrstuhl für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany
| | - Peter Vöhringer
- Lehrstuhl für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany
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8
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Lee J, Jeon J, Kim MS, Lee H, Cho M. Amide I IR probing of core and shell hydrogen-bond structures in reverse micelles. PURE APPL CHEM 2014. [DOI: 10.1515/pac-2014-5016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
The properties of N-methylacetamide (NMA) molecules encapsulated in the reverse micelles (RMs) formed by anionic surfactant aerosol OT (AOT), are studied with vibrational spectroscopy and computation. Vibrational spectra of the amide I′ mode of the fully deuterated NMA-d7 show gradual increase of peak frequencies and line broadening as the size of RMs decreases. Analyses of the spectral features reveal the presence of three states of NMA-d7 that correspond to NMA located in the core of water phase (absorption frequency of 1606 cm–1) and two types of interfacial NMA near the surfactant layer (1620 and 1644 cm–1). In larger RMs with water content w0 = [D2O]/[AOT] ≥ 10, only the first two states are observed, whereas in smaller RMs, the population of the third state grows up to 25 % at w0 = 2. These results indicate the general validity of the two-state core/shell model for the confined aqueous solution of NMA, with small modifications due to the system-dependent solute-interface interaction. However, simulations of small RM systems with w0 ≤ 15 show continuous variations of the population, frequency shifts, and the solute-solvent interaction strengths at solute-interface distance less than 4 Å. Thus, the distinction of solute core/shell states tends to be blurred in small RMs but is still effective in interpreting the average spectroscopic observables.
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9
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Singh PK, Kuroda DG, Hochstrasser RM. An ion's perspective on the molecular motions of nanoconfined water: a two-dimensional infrared spectroscopy study. J Phys Chem B 2013; 117:9775-84. [PMID: 23855349 DOI: 10.1021/jp406725a] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The vibrational population relaxation and hydration shell dynamics of the symmetric tricyanomethanide (TCM) anion are investigated in a sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle as a function of the water pool radius. Two-dimensional infrared (IR) spectroscopy in combination with linear absorption and ultrafast IR pump-probe spectroscopy is utilized in this study. Spectroscopic measurements show that the anion has two bands in the 2160-2175 cm(-1) region, each with its own spectroscopic signatures. Analysis of the vibrational dynamics shows that the two vibrational bands are consistent with the anion located either at the interface or in the water pool. The sensitivity of the TCM anion to the environment allows us to unequivocally monitor the vibrational and hydration dynamics of the anion in those two different environments. A TCM anion located at the interface does not show any significant variation of the vibrational dynamics with the water pool size. On the contrary, the TCM anion inside the water pool exhibits a large and nonlinear variation of the vibrational lifetime and the frequency-frequency correlation time with the pool radius. Moreover, for the solvated anion in water pools of 49 Å in radius (W0 = 30), the vibrational lifetime reaches the values observed for the anion in bulk water while the frequency-frequency correlation time shows a characteristic time higher than that observed in the bulk. In addition, for the first time a model is developed and used to explain the observed nonlinear variation of the spectroscopic observables with the pool size. This model attributes the changes in the vibrational dynamics of the TCM anion in the water pool to the slow and radius-dependent water dynamics present in the confined environment of a reverse micelle.
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Affiliation(s)
- Prabhat K Singh
- Ultrafast Optical Processes Laboratory, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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10
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Compton R, Gerardi HK, Weidinger D, Brown DJ, Dressick WJ, Heilweil EJ, Owrutsky JC. Spectra and relaxation dynamics of the pseudohalide (PS) vibrational bands for Ru(bpy)2(PS)2 complexes, PS=CN, NCS and N3. Chem Phys 2013. [DOI: 10.1016/j.chemphys.2012.11.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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11
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Costard R, Elsaesser T. Femtosecond OH Bending Dynamics of Water Nanopools Confined In Reverse Micelles. J Phys Chem B 2013; 117:15338-45. [DOI: 10.1021/jp403559d] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Rene Costard
- Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2 a,
D-12489 Berlin, Germany
| | - Thomas Elsaesser
- Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2 a,
D-12489 Berlin, Germany
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12
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Guchhait B, Biswas R, Ghorai PK. Solute and Solvent Dynamics in Confined Equal-Sized Aqueous Environments of Charged and Neutral Reverse Micelles: A Combined Dynamic Fluorescence and All-Atom Molecular Dynamics Simulation Study. J Phys Chem B 2013; 117:3345-61. [DOI: 10.1021/jp310285k] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Biswajit Guchhait
- Department
of Chemical, Biological and
Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt
Lake, Kolkata 700098, India
| | - Ranjit Biswas
- Department
of Chemical, Biological and
Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt
Lake, Kolkata 700098, India
| | - Pradip K. Ghorai
- Indian Institute of Science Education and Research, Kolkata, Mohanpur Campus, Nadia 741252,
India
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13
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Son H, Kwon Y, Kim J, Park S. Rotational Dynamics of Metal Azide Ion Pairs in Dimethylsulfoxide Solutions. J Phys Chem B 2013; 117:2748-56. [DOI: 10.1021/jp312055f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Hyewon Son
- Department of Chemistry, Korea University, Seoul 136-701, Korea
| | - YoungAh Kwon
- Department of Chemistry, Korea University, Seoul 136-701, Korea
| | - Jinwoo Kim
- Department of Chemistry, Korea University, Seoul 136-701, Korea
| | - Sungnam Park
- Department of Chemistry, Korea University, Seoul 136-701, Korea
- Multidimensional Spectroscopy
Laboratory, Korea Basic Science Institute, Seoul 136-713, Korea
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14
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Bian H, Li J, Zhang Q, Chen H, Zhuang W, Gao YQ, Zheng J. Ion Segregation in Aqueous Solutions. J Phys Chem B 2012. [DOI: 10.1021/jp310153n] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Hongtao Bian
- Department
of Chemistry, Rice University, Houston,
Texas 77005, United States
| | - Jiebo Li
- Department
of Chemistry, Rice University, Houston,
Texas 77005, United States
| | - Qiang Zhang
- State Key Laboratory of Molecular
Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning,
People’s Republic of China
| | - Hailong Chen
- Department
of Chemistry, Rice University, Houston,
Texas 77005, United States
| | - Wei Zhuang
- State Key Laboratory of Molecular
Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning,
People’s Republic of China
| | - Yi Qin Gao
- College of Chemistry and Molecular
Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871, China
| | - Junrong Zheng
- Department
of Chemistry, Rice University, Houston,
Texas 77005, United States
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15
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Singh PK, Nath S. Ultrafast torsional dynamics in nanoconfined water pool: Comparison between neutral and charged reverse micelles. J Photochem Photobiol A Chem 2012. [DOI: 10.1016/j.jphotochem.2012.08.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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16
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Correa NM, Silber JJ, Riter RE, Levinger NE. Nonaqueous Polar Solvents in Reverse Micelle Systems. Chem Rev 2012; 112:4569-602. [DOI: 10.1021/cr200254q] [Citation(s) in RCA: 204] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- N. Mariano Correa
- Departamento de Química, Universidad Nacional de Río Cuarto, Agencia
Postal #3, C.P. X5804BYA Río Cuarto, Argentina
| | - Juana J. Silber
- Departamento de Química, Universidad Nacional de Río Cuarto, Agencia
Postal #3, C.P. X5804BYA Río Cuarto, Argentina
| | - Ruth E. Riter
- Department of Chemistry, Agnes Scott College, Decatur, Georgia 30030-3770, United
States
| | - Nancy E. Levinger
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872,
United States
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17
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Kim H, Park S, Cho M. Rotational dynamics of thiocyanate ions in highly concentrated aqueous solutions. Phys Chem Chem Phys 2012; 14:6233-40. [DOI: 10.1039/c2cp23749k] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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18
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Olschewski M, Knop S, Lindner J, Vöhringer P. Vibrational relaxation of azide ions in liquid-to-supercritical water. J Chem Phys 2011; 134:214504. [DOI: 10.1063/1.3598108] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
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19
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Chowdhary J, Ladanyi BM. Molecular simulation study of water mobility in aerosol-OT reverse micelles. J Phys Chem A 2011; 115:6306-16. [PMID: 21548627 DOI: 10.1021/jp201866t] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In this work, we present results from molecular dynamics simulations on the single-molecule relaxation of water within reverse micelles (RMs) of different sizes formed by the surfactant aerosol-OT (AOT, sodium bis(2-ethylhexyl)sulfosuccinate) in isooctane. Results are presented for RM water content w(0) = [H(2)O]/[AOT] in the range from 2.0 to 7.5. We show that translational diffusion of water within the RM can, to a good approximation, be decoupled from the translation of the RM through the isooctane solvent. Water translational mobility within the RM is restricted by the water pool dimensions, and thus, the water mean-squared displacements (MSDs) level off in time. Comparison with models of diffusion in confined geometries shows that a version of the Gaussian confinement model with a biexponential decay of correlations provides a good fit to the MSDs, while a model of free diffusion within a sphere agrees less well with simulation results. We find that the local diffusivity is considerably reduced in the interfacial region, especially as w(0) decreases. Molecular orientational relaxation is monitored by examining the behavior of OH and dipole vectors. For both vectors, orientational relaxation slows down close to the interface and as w(0) decreases. For the OH vector, reorientation is strongly affected by the presence of charged species at the RM interface and these effects are especially pronounced for water molecules hydrogen-bonded to surfactant sites that serve as hydrogen-bond acceptors. For the dipole vector, orientational relaxation near the interface slows down more than that for the OH vector due mainly to the influence of ion-dipole interactions with the sodium counterions. We investigate water OH and dipole reorientation mechanisms by studying the w(0) and interfacial shell dependence of orientational time correlations for different Legendre polynomial orders.
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Affiliation(s)
- Janamejaya Chowdhary
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA
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20
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Eigner AA, Jones BH, Koprucki BW, Massari AM. Ground-State Structural Dynamics in Doped and Undoped Polyaniline Films Probed by Two-Dimensional Infrared Vibrational Echo Spectroscopy. J Phys Chem B 2011; 115:4583-91. [DOI: 10.1021/jp1113009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Audrey A. Eigner
- Department of Chemistry, University of Minnesota—Twin Cities, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - Brynna H. Jones
- Department of Chemistry, University of Minnesota—Twin Cities, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - Bryce W. Koprucki
- Department of Chemistry, University of Minnesota—Twin Cities, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - Aaron M. Massari
- Department of Chemistry, University of Minnesota—Twin Cities, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
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21
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Rosenfeld DE, Schmuttenmaer CA. Dynamics of the Water Hydrogen Bond Network at Ionic, Nonionic, and Hydrophobic Interfaces in Nanopores and Reverse Micelles. J Phys Chem B 2010; 115:1021-31. [PMID: 21182316 DOI: 10.1021/jp109599q] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Daniel E. Rosenfeld
- Department of Chemistry, Yale University, 225 Prospect Street, P.O. Box 208107, New Haven, Connecticut 06520-8107, United States
| | - Charles A. Schmuttenmaer
- Department of Chemistry, Yale University, 225 Prospect Street, P.O. Box 208107, New Haven, Connecticut 06520-8107, United States
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22
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Ferreira JAB, Costa SMB. Electronic Excited-State Behavior of Rhodamine 3B in AOT Reverse Micelles Sensing Contact Ion Pair to Solvent Separated Ion Pair Interconversion. J Phys Chem B 2010; 114:10417-26. [DOI: 10.1021/jp100571t] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- José A. B. Ferreira
- Universidade Técnica de Lisboa, Instituto Superior Técnico, Centro de Química Estrutural, Complexo Interdisciplinar, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - Sílvia M. B. Costa
- Universidade Técnica de Lisboa, Instituto Superior Técnico, Centro de Química Estrutural, Complexo Interdisciplinar, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
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23
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Houchins C, Weidinger D, Owrutsky JC. Vibrational Spectroscopy and Dynamics of the Hydrazoic and Isothiocyanic Acids in Water and Methanol. J Phys Chem A 2010; 114:6569-74. [DOI: 10.1021/jp102397b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Cassidy Houchins
- Chemistry Division, Code 6111, U.S. Naval Research Laboratory, Washington, D.C. 20375-5342
| | - Daniel Weidinger
- Chemistry Division, Code 6111, U.S. Naval Research Laboratory, Washington, D.C. 20375-5342
| | - Jeffrey C. Owrutsky
- Chemistry Division, Code 6111, U.S. Naval Research Laboratory, Washington, D.C. 20375-5342
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Satpati AK, Kumbhakar M, Nath S, Pal H. Influence of Confined Water on the Photophysics of Dissolved Solutes in Reverse Micelles. Chemphyschem 2009; 10:2966-78. [DOI: 10.1002/cphc.200900527] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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26
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Abstract
Recent advances in ultrafast laser technology have spurred investigations of microheterogeneous solutions. In particular, researchers have explored details of reverse micelles (RMs), which present isolated droplets of polar solvent sequestered from a continuous nonpolar phase by a surfactant layer. This review explores recent studies utilizing a variety of ultrafast laser techniques to uncover details about structure and dynamics in various RMs. Using ultrafast vibrational spectroscopy, researchers have probed hydrogen-bond dynamics and vibrational energy relaxation in RMs. These studies have developed our understanding of reverse micellar structure, identifying varying water environments in the RMs. In a plethora of experiments employing probe molecules, researchers have explored the confined environment presented by RMs and their impact on a range of chemical reactions. These studies have shown that confinement, rather than the specific interactions with surfactants, is an important factor determining the impact of the reverse micellar environment on the chemistry.
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Affiliation(s)
- Nancy E Levinger
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
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27
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Owrutsky JC, Pomfret MB, Barton DJ, Kidwell DA. Fourier transform infrared spectroscopy of azide and cyanate ion pairs in AOT reverse micelles. J Chem Phys 2008; 129:024513. [DOI: 10.1063/1.2952522] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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28
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Mitchell-Koch KR, Thompson WH. Infrared spectra of a model phenol-amine proton transfer complex in nanoconfined CH3Cl. J Phys Chem B 2008; 112:7448-59. [PMID: 18517239 DOI: 10.1021/jp076714e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The vibrational spectra of a model phenol-amine proton transfer complex dissolved in CH3Cl solvent confined in a 12 A radius spherical hydrophobic cavity were calculated using mixed quantum-classical molecular dynamics simulations. The reaction free energy of the proton transfer complex was varied in order to explore the contributions to the vibrational absorption band from product and reactant species. The vibrational spectra of the model proton transfer complex resulted in motionally narrowed spectral linewidths with two distinct peaks for products and reactants in cases where the system undergoes chemical exchange. It was found that the n=1 and n=2 vibrational excited states combine to form diabatic states such that the spectra have contributions from both n=0 --> n=1 and n=0 --> n=2 transitions. A strong relationship between the instantaneous vibrational frequency and a collective solvent coordinate was found that assists in understanding the origin of the spectral features.
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Banno M, Ohta K, Tominaga K. Ultrafast Dynamics of the Carbonyl Stretching Vibration in Acetic Acid in Aqueous Solution Studied by Sub-Picosecond Infrared Spectroscopy. J Phys Chem A 2008; 112:4170-5. [DOI: 10.1021/jp076920m] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Motohiro Banno
- Molecular Photoscience Research Center, Kobe University, Graduate School of Science and Technology, Kobe University, and CREST/JST, Rokkodai-cho 1-1, Nada, Kobe 657-8501, Japan
| | - Kaoru Ohta
- Molecular Photoscience Research Center, Kobe University, Graduate School of Science and Technology, Kobe University, and CREST/JST, Rokkodai-cho 1-1, Nada, Kobe 657-8501, Japan
| | - Keisuke Tominaga
- Molecular Photoscience Research Center, Kobe University, Graduate School of Science and Technology, Kobe University, and CREST/JST, Rokkodai-cho 1-1, Nada, Kobe 657-8501, Japan
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30
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Park S, Moilanen DE, Fayer MD. Water DynamicsThe Effects of Ions and Nanoconfinement. J Phys Chem B 2008; 112:5279-90. [DOI: 10.1021/jp7121856] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sungnam Park
- Department of Chemistry Stanford University, Stanford, California 94305
| | - David E. Moilanen
- Department of Chemistry Stanford University, Stanford, California 94305
| | - M. D. Fayer
- Department of Chemistry Stanford University, Stanford, California 94305
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31
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Dokter AM, Petersen C, Woutersen S, Bakker HJ. Vibrational dynamics of ice in reverse micelles. J Chem Phys 2008; 128:044509. [DOI: 10.1063/1.2826376] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
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32
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Li S, Schmidt JR, Piryatinski A, Lawrence CP, Skinner JL. Vibrational spectral diffusion of azide in water. J Phys Chem B 2007; 110:18933-8. [PMID: 16986886 DOI: 10.1021/jp057568k] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Vibrational spectral diffusion denotes the time-dependent fluctuations of a solute's vibrational frequencies due to local environmental dynamics. Vibrational line shapes are weakly sensitive to spectral diffusion, whereas three-pulse vibrational echoes are much more sensitive. We report here on theoretical studies of spectral diffusion of the asymmetric stretch of the azide anion in heavy water. We run a classical molecular dynamics simulation of rigid azide in rigid water, and at every time step we calculate the azide's anharmonic asymmetric stretch frequency using an optimized quantum mechanics/molecular mechanics method developed earlier. This generates a frequency trajectory, which we use to calculate the absorption line shape and integrated three-pulse echo intensity. Our results for both the line width and the integrated echo intensity are in excellent agreement with experiment. Our calculated frequency time-correlation function is in excellent agreement with experiment for long times (greater than 250 fs) but differs considerably from experiment at short times; our theoretical correlation function has a very pronounced oscillation, presumably due to intermolecular azide-water hydrogen-bond stretching dynamics.
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Affiliation(s)
- Shuzhou Li
- Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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33
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Seth D, Chakraborty A, Setua P, Sarkar N. Interaction of ionic liquid with water with variation of water content in 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF6])/TX-100/water ternary microemulsions monitored by solvent and rotational relaxation of coumarin 153 and coumarin 490. J Chem Phys 2007; 126:224512. [PMID: 17581068 DOI: 10.1063/1.2736378] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The interaction of water with room temperature ionic liquid (RTIL) [bmim][PF6] has been studied in [bmim][PF6]/TX-100/water ternary microemulsions by solvent and rotational relaxation of coumarin 153 (C-153) and coumarin 490 (C-490). The rotational relaxation and average solvation time of C-153 and C-490 gradually decrease with increase in water content of the microemulsions. The gradual increase in the size of the microemulsion with increase in w0 (w0=[water]/[surfactant]) is evident from dynamic light scattering measurements. Consequently the mobility of the water molecules also increases. In comparison to pure water the retardation of solvation time in the RTIL containing ternary microemulsions is very less. The authors have also reported the solvation time of C-490 in neat [bmim][PF6]. The solvation time of C-490 in neat [bmim][PF6] is bimodal with time constants of 400 ps and 1.10 ns.
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Affiliation(s)
- Debabrata Seth
- Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, West Bengal, India
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34
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Li S, Schmidt JR, Corcelli SA, Lawrence CP, Skinner JL. Approaches for the calculation of vibrational frequencies in liquids: comparison to benchmarks for azide/water clusters. J Chem Phys 2007; 124:204110. [PMID: 16774322 DOI: 10.1063/1.2200690] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Ultrafast vibrational spectroscopy experiments, together with molecular-level theoretical interpretation, can provide important information about the structure and dynamics of complex condensed phase systems, including liquids. The theoretical challenge is to calculate the instantaneous vibrational frequencies of a molecule in contact with a molecular environment, accurately and quickly, and to this end a number of different methods have been developed. In this paper we critically analyze these different methods by comparing their results to accurate benchmark calculations on azide/water clusters. We also propose an optimized quantum mechanics/molecular mechanics method, which for this problem is superior to the other methods.
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Affiliation(s)
- Shuzhou Li
- Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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35
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Chaiyasit W, Stanley CB, Strey HH, McClements DJ, Decker EA. Impact of Surface Active Compounds on Iron Catalyzed Oxidation of Methyl Linolenate in AOT–Water–Hexadecane Systems. FOOD BIOPHYS 2007. [DOI: 10.1007/s11483-007-9031-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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36
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Abstract
The effect of confinement on the dynamical properties of liquid water is investigated for water enclosed in cationic reverse micelles. The authors performed mid-infrared ultrafast pump-probe spectroscopy on the OH-stretch vibration of isotopically diluted HDO in D(2)O in cetyltrimethylammonium bromide (CTAB) reverse micelles of various sizes. The authors observe that the surfactant counterions are inhomogeneously distributed throughout the reverse micelle, and that regions of extreme salinity occur near the interfacial Stern layer. The authors find that the water molecules in the core of the micelles show similar orientational dynamics as bulk water, and that water molecules in the counterion-rich interfacial region are much less mobile. An explicit comparison is made with the dynamics of water confined in anionic sodium bis(2-ethythexyl) sulfosuccinate (AOT) reverse micelles. The authors find that interfacial water in cationic CTAB reverse micelles has a higher orientational mobility than water in anionic AOT reverse micelles.
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Affiliation(s)
- Adriaan M Dokter
- FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands
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37
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Sando GM, Dahl K, Owrutsky JC. Vibrational Spectroscopy and Dynamics of Azide Ion in Ionic Liquid and Dimethyl Sulfoxide Water Mixtures. J Phys Chem B 2007; 111:4901-9. [PMID: 17388412 DOI: 10.1021/jp067143d] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Steady-state and time-resolved infrared spectroscopy of the azide (N(3)-) anion has been used to characterize aqueous mixtures both with the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]) and with dimethyl sulfoxide (DMSO). In the DMSO-water mixtures, two anion vibrational bands are observed for low water mole fractions (0 > X(w) > 0.25), which indicates a heterogeneous ion solvation environment. The band at 2000 cm(-1) observed for neat DMSO does not shift but decreases in amplitude as the amount of water is increased. Another band appears at slightly higher frequency at low X(w) (=0.05). As the amount of water is increased, this band shifts to higher frequency and becomes stronger and is attributed to azide with an increasing degree of hydration. At intermediate and high X(w), a single band is observed that shifts almost linearly with water mole fraction toward the bulk water value. The heterogeneity is evident from the infrared pump-probe studies in which the decay times depend on probe frequency at low mole fraction. For the azide spectra in IL-water mixtures, a single azide band is observed for each mole fraction mixture. The azide band shifts almost linearly with mole fraction, indicating nearly ideal mixing behavior. As with the DMSO-water mixtures, the time-resolved IR decay times are probe-frequency-dependent at low mole fraction, again indicating heterogeneous solvation. In both the DMSO and IL mixtures with water, the relaxation times are slower than would be expected from ideal mixing, suggesting that vibrational relaxation of azide is more sensitive than its vibrational frequency to the solvent structure. The results are discussed in terms of preferential solvation and the degree to which the azide shift and vibrational relaxation depend on the degree of water association in the mixtures.
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Affiliation(s)
- Gerald M Sando
- U.S. Naval Research Laboratory, Washington, District of Columbia 20375-5342, USA
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38
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Ohta K, Tominaga K. Vibrational population relaxation of thiocyanate ion in polar solvents studied by ultrafast infrared spectroscopy. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.08.019] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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39
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Abstract
Solvated electrons have been generated in reverse micelles (RMs) through photodetachment of ferrocyanide (Fe(CN)(6)(4-)) in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) RMs. We have measured both bleach recovery of the parent ferrocyanide CN stretch in the infrared and the decay of the solvated electron absorption at 800 nm. The bleach recovery has been fit to a diffusion model for the geminate recombination process. The fit parameters suggest a narrowing of the spatial distribution of ejected electrons due to confinement in the RMs when compared to bulk water. The diffusion coefficient of the solvated electron does not appear to be significantly affected by RM confinement. The decay of the solvated electron absorption exhibits an additional decay component that is not observed in bulk water and is smaller for larger RMs. No corresponding additional component is seen in the parent ferrocyanide IR bleach recovery, which supports our interpretation that the confinement-induced new decay process in RMs is due to electrons reacting with AOT headgroups.
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Affiliation(s)
- Gerald M Sando
- Code 6111, US Naval Research Laboratory, Washington D.C. 20375-5342, USA
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40
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Chakraborty A, Seth D, Setua P, Sarkar N. Dynamics of Solvent and Rotational Relaxation of Glycerol in the Nanocavity of Reverse Micelles. J Phys Chem B 2006; 110:5359-66. [PMID: 16539469 DOI: 10.1021/jp056650c] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The dynamics of solvent and rotational relaxation of Coumarin 480 and Coumarin 490 in glycerol containing bis-2-ethyl hexyl sulfosuccinate sodium salt (AOT) reverse micelles have been investigated with steady-state and time-resolved fluorescence spectroscopy. We observed slower solvent relaxation of glycerol confined in the nanocavity of AOT reverse micelles compared to that in pure glycerol. However, the slowing down in the solvation time on going from neat glycerol to glycerol confined reverse micelles is not comparable to that on going from pure water or acetonitrile to water or acetonitrile confined AOT reverse micellar aggregates. While solvent relaxation times were found to decrease with increasing glycerol content in the reverse micellar pool, rotational relaxation times were found to increase with increase in glycerol content.
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Affiliation(s)
- Anjan Chakraborty
- Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, WB, India
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41
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Sando GM, Dahl K, Owrutsky JC. Vibrational relaxation in ionic liquids and ionic liquid reverse micelles. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2005.11.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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42
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Sando GM, Dahl K, Zhong Q, Owrutsky JC. Vibrational Relaxation of Azide in Formamide Reverse Micelles. J Phys Chem A 2005; 109:5788-92. [PMID: 16833912 DOI: 10.1021/jp050930a] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Static and ultrafast infrared spectroscopy have been used to measure absorption spectra and vibrational energy relaxation (VER) times for the antisymmetric stretching vibrational band of azide, N(3)(-), in formamide-containing reverse micelles (RMs). RMs were formed in n-heptane using the surfactant AOT, sodium bis(2-ethylhexyl) sulfosuccinate. The VER times were found to be significantly longer than in bulk formamide. The VER times became longer as the molar ratio of formamide to AOT, omega(F), was decreased. Decreasing omega(F) also resulted in substantial blue shifts of the azide static absorption band compared to the frequency in bulk formamide. The omega(F) dependent studies are consistent with expected size trends, where a larger RM results in more bulklike polar solvent and faster VER rates. These results are in contrast to aqueous AOT RMs where VER times were indistinguishable from those in the bulk and the static spectral shifts were much smaller. The differences between the static and dynamic behavior in aqueous and formamide RMs are related to differences in structural changes upon confinement in RMs.
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Affiliation(s)
- Gerald M Sando
- Code 6111, United States Naval Research Laboratory, Washington, D.C. 20375-5342, USA
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Tan HS, Piletic IR, Fayer MD. Orientational dynamics of water confined on a nanometer length scale in reverse micelles. J Chem Phys 2005; 122:174501. [PMID: 15910039 DOI: 10.1063/1.1883605] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The time-resolved orientational anisotropies of the OD hydroxyl stretch of dilute HOD in H(2)O confined on a nanometer length scale in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles are studied using ultrafast infrared polarization and spectrally resolved pump-probe spectroscopy, and the results are compared to the same experiments on bulk water. The orientational anisotropy data for three water nanopool sizes (4.0, 2.4, and 1.7 nm) can be fitted well with biexponential decays. The biexponential decays are analyzed using a wobbling-in-a-cone model that involves fast orientational diffusion within a cone followed by slower, full orientational relaxation. The data provide the cone angles, the diffusion constants for motion within the cones, and the final diffusion constants as a function of the nanopool size. The two processes can be interpreted as a local angular fluctuation of the OD and a global hydrogen bond network rearrangement process. The trend in the relative amplitudes of the long and short exponential decays suggest an increasing rigidity as the nanopool size decreases. The trend in the long decay constants indicates a longer hydrogen bond network rearrangement time with decreasing reverse micelle size. The anisotropy measurements for the reverse micelles studied extrapolate to approximately 0.33 rather than the ideal value of 0.4, suggesting the presence of an initial inertial component in the anisotropy decay that is too fast to resolve. The very fast decay component is consistent with initial inertial orientational motion that is seen in published molecular-dynamics simulations of water in AOT reverse micelles. The angle over which the inertial orientational motion occurs is determined. The results are in semiquantitative agreement with the molecular-dynamics simulations.
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Affiliation(s)
- Howe-Siang Tan
- Department of Chemistry, Stanford University, California 94305, USA.
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