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Antoni Czarnecki M, Warchoł J, Orzechowski K, Beć K, Huck CW. Soft confinement of water in aliphatic alcohols: MIR/NIR spectroscopic and DFT studies. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 323:124851. [PMID: 39084017 DOI: 10.1016/j.saa.2024.124851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Revised: 07/12/2024] [Accepted: 07/17/2024] [Indexed: 08/02/2024]
Abstract
Here, we present the first examination of the state of water under a soft confinement in eight aliphatic alcohols including cyclopentanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol, 2-octanol and 3-octanol. Due to relatively large size of the aliphatic part, water has limited solubility in all studied alcohols. Water content in saturated solutions was determined by Karl Fischer titration and correlated with the spectroscopic data. This way, we determined the molar absorptivity of the ν2+ν3 combination mode. The effect of addition of water and temperature variation was monitored by ATR-IR and NIR spectroscopy. Analysis of the experimental results was guided by DFT calculations, which provided the structures, harmonic MIR spectra and binding energies of selected alcohol-water complexes. Our studies demonstrated that the state of water in alcohols is related to its solubility, which depends on structure of solvent molecules. The solubility of water in 1-alcohols decreases on increasing of the chain length, but for long chain alcohols this effect is less evident. More apparent solubility reduction appears in going from the primary to secondary alcohols. The effective shielding of the OH group in the linear alcohols is achieved when on both sides of the OH group are ethyl or longer substituents, while the shielding by methyl groups is less efficient. Water is much better soluble in the cyclic alcohols as compared with the linear ones due to better accessibility of the OH group. The soft confinement of water in aliphatic alcohols allows for flexible structural arrangements and interactions. Even at low water content, we did not observe free molecules of water. At these conditions, the molecules of water are singly or doubly bonded to the OH groups from the alcohol. Increasing solubility of water reduces the number of the free OH groups and leads to formation of water clusters. Obtained results allow concluding that in alcohols with sizable aliphatic part the molecules of water are confined in the vicinity of the OH groups.
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Affiliation(s)
| | - Justyna Warchoł
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - Kazimierz Orzechowski
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - Krzysztof Beć
- Institute of Analytical Chemistry and Radiochemistry, University of Innsbruck, Innrain 80-82, A6020 Innsbruck, Austria
| | - Christian W Huck
- Institute of Analytical Chemistry and Radiochemistry, University of Innsbruck, Innrain 80-82, A6020 Innsbruck, Austria
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2
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Higuchi H, Ikeda-Fukazawa T. Interactions between Water and a Hydrophobic Polymer. J Phys Chem B 2024; 128:1927-1935. [PMID: 38369787 DOI: 10.1021/acs.jpcb.3c07440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
To investigate the mechanisms of interactions between a hydrophobic polymer and water, molecular dynamics calculations and Raman spectroscopic measurements of cis-1,4-polyisoprene (PI)-water systems were performed. The results show that PI in water undergoes a coil-globule transition at around 248 K. The transition is attributed to changes in the density and diffusivity of water. The volume expansion of the supercooled liquid water induces the coil structure of PI. The phase separation of PI from water with an increase in the self-diffusion coefficient of water molecules results in the globule structure of PI. The self-diffusion coefficient of free water with PI is larger than that of pure water because PI has an effect to decrease the hydrogen-bonding strength of water. The result suggests that the effects of the coexisting water are important factors governing the physical and chemical properties of hydrophobic polymers.
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Affiliation(s)
- Hikaru Higuchi
- Department of Applied Chemistry, Meiji University, Kawasaki 214-8571, Japan
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3
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Urbina AS, Slipchenko LV, Ben-Amotz D. Quantifying the Nearly Random Microheterogeneity of Aqueous tert-Butyl Alcohol Solutions Using Vibrational Spectroscopy. J Phys Chem Lett 2023; 14:11376-11383. [PMID: 38078837 DOI: 10.1021/acs.jpclett.3c02603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
The microheterogeneous structure of aqueous tert-butyl alcohol (TBA) solutions is quantified by combining experimental, simulations, and theoretical results. Experimental Raman multivariate curve resolution (Raman-MCR) C-H frequency shift measurements are compared with predictions obtained using combined quantum mechanical and effective fragment potential (QM/EFP) calculations, as well as with molecular dynamics (MD), random mixture (RM), and finite lattice (FL) predictions. The results indicate that the microheterogeneous aggregation in aqueous TBA solutions is slightly less than that predicted by MD simulations performed using either CHARMM generalized force field (CGenFF) or optimized parameters for liquid simulations all atom (OPLS-AA) force fields but slightly more than that in a self-avoiding RM of TBA-like molecules. The results imply that the onset of microheterogeneity in aqueous solutions occurs when solute contact free energies are about an order of magnitude smaller than thermal fluctuations, thus suggesting a fundamental bound of relevance to biological self-assembly.
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Affiliation(s)
- Andres S Urbina
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Lyudmila V Slipchenko
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Dor Ben-Amotz
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
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4
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Robinson Brown DC, Webber TR, Jiao S, Rivera Mirabal DM, Han S, Shell MS. Relationships between Molecular Structural Order Parameters and Equilibrium Water Dynamics in Aqueous Mixtures. J Phys Chem B 2023; 127:4577-4594. [PMID: 37171393 DOI: 10.1021/acs.jpcb.3c00826] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Water's unique thermophysical properties and how it mediates aqueous interactions between solutes have long been interpreted in terms of its collective molecular structure. The seminal work of Errington and Debenedetti [Nature 2001, 409, 318-321] revealed a striking hierarchy of relationships among the thermodynamic, dynamic, and structural properties of water, motivating many efforts to understand (1) what measures of water structure are connected to different experimentally accessible macroscopic responses and (2) how many such structural metrics are adequate to describe the collective structural behavior of water. Diffusivity constitutes a particularly interesting experimentally accessible equilibrium property to investigate such relationships because advanced NMR techniques allow the measurement of bulk and local water dynamics in nanometer proximity to molecules and interfaces, suggesting the enticing possibility of measuring local diffusivities that report on water structure. Here, we apply statistical learning methods to discover persistent structure-dynamic correlations across a variety of simulated aqueous mixtures, from alcohol-water to polypeptoid-water systems. We investigate a variety of molecular water structure metrics and find that an unsupervised statistical learning algorithm (namely, sequential feature selection) identifies only two or three independent structural metrics that are sufficient to predict water self-diffusivity accurately. Surprisingly, the translational diffusivity of water across all mixed systems studied here is strongly correlated with a measure of tetrahedral order given by water's triplet angle distribution. We also identify a separate small number of structural metrics that well predict an important thermodynamic property, the excess chemical potential of an idealized methane-sized hydrophobe in water. Ultimately, we offer a Bayesian method of inferring water structure by using only structure-dynamics linear regression models with experimental Overhauser dynamic nuclear polarization (ODNP) measurements of water self-diffusivity. This study thus quantifies the relationships among several distinct structural order parameters in water and, through statistical learning, reveals the potential to leverage molecular structure to predict fundamental thermophysical properties. In turn, these findings suggest a framework for solving the inverse problem of inferring water's molecular structure using experimental measurements such as ODNP studies that probe local water properties.
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Affiliation(s)
| | - Thomas R Webber
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Sally Jiao
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Daniela M Rivera Mirabal
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Songi Han
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - M Scott Shell
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
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5
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Reddy KD, Biswas R. Hydrophobic Hydration: A Theoretical Investigation of Structure and Dynamics. J CHEM SCI 2023. [DOI: 10.1007/s12039-022-02123-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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6
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A subtle interplay between hydrophilic and hydrophobic hydration governs butanol (de)mixing in water. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.140080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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7
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Trabelsi S, Tlili M, Abdelmoulahi H, Bouazizi S, Nasr S, González MA, Bellissent-Funel MC, Darpentigny J. Intermolecular interactions in an equimolar methanol-water mixture: Neutron scattering, DFT, NBO, AIM, and MD investigations. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2021.118131] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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8
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Evidence of Many-Body Interactions in the Virial Coefficients of Polyelectrolyte Gels. Gels 2022; 8:gels8020096. [PMID: 35200477 PMCID: PMC8871429 DOI: 10.3390/gels8020096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 01/19/2022] [Accepted: 02/02/2022] [Indexed: 12/04/2022] Open
Abstract
Simulation studies of aqueous polymer solutions, and heuristic arguments by De Gennes for aqueous polyethylene oxide polymer solutions, have suggested that many-body interactions can give rise to the ‘anomalous’ situation in which the second osmotic virial coefficient is positive, while the third virial coefficient is negative. This phenomenon was later confirmed in analytic calculations of the phase behavior and the osmotic pressure of complex fluids exhibiting cooperative self-assembly into extended dynamic polymeric structures by Dudowicz et al. In the present study, we experimentally confirm the occurrence of this osmotic virial sign inversion phenomenon for several highly charged model polyelectrolyte gels (poly(acrylic acid), poly(styrene sulfonate), DNA, hyaluronic acid), where the virial coefficients are deduced from osmotic pressure measurements. Our observations qualitatively accord with experimental and simulation studies indicating that polyelectrolyte materials exhibit supramolecular assembly in solution, another symptomatic property of fluids exhibiting many-body interactions. We also find that the inversion in the variation of the second (A2) and third (A2) virial coefficients upon approach to phase separation does not occur in uncharged poly(vinyl acetate) gels. Finally, we briefly discuss the estimation of the osmotic compressibility of swollen polyelectrolyte gels from neutron scattering measurements as an alternative to direct, time-consuming and meticulous osmotic pressure measurements. We conclude by summarizing some general trends and suggesting future research directions of natural and synthetic polyelectrolyte hydrogels.
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Bredt AJ, Kim Y, Mendes de Oliveira D, Urbina AS, Slipchenko LV, Ben-Amotz D. Expulsion of Hydroxide Ions from Methyl Hydration Shells. J Phys Chem B 2022; 126:869-877. [PMID: 35077175 DOI: 10.1021/acs.jpcb.1c08420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The affinity of hydroxide ions for methyl hydration shells is assessed using a combined experimental and theoretical analysis of tert-butyl alcohol (TBA) dissolved in pure water and aqueous NaOH and NaI. The experimental results are obtained using Raman multivariate curve resolution (Raman-MCR) and a new three-component total least squares (Raman-TLS) spectral decomposition strategy used to highlight vibrational perturbations resulting from interactions between TBA and aqueous ions. The experiments are interpreted and extended with the aid of effective fragment potential molecular dynamics (EFP-MD) simulations, as well as Kirkwood-Buff calculations and octanol/water partition measurements, to relate TBA-ion distribution functions to TBA solubility changes. The combined experimental and simulation results reveal that methyl group hydration shells more strongly expel hydroxide than iodide anions, whose populations near the methyl groups of TBA are predicted to be correlated with sodium counterion localization near the TBA hydroxyl group.
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Affiliation(s)
- Aria J Bredt
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Yongbin Kim
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | | | - Andres S Urbina
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Lyudmila V Slipchenko
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Dor Ben-Amotz
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
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10
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Zhang X, Wang Y, Yao J, Li H, Mochizuki K. A tiny charge-scaling in the OPLS-AA + L-OPLS force field delivers the realistic dynamics and structure of liquid primary alcohols. J Comput Chem 2021; 43:421-430. [PMID: 34962297 DOI: 10.1002/jcc.26802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/07/2021] [Accepted: 12/10/2021] [Indexed: 11/06/2022]
Abstract
We carry out molecular dynamics simulations for pure liquid primary alcohols ranging from methanol to 1-decanol under ambient conditions. Based on the OPLS-AA force field with the L-OPLS correction, we demonstrate that a few % increases in the partial charges deliver the realistic dynamics (self-diffusion coefficient and shear viscosity) and structure (density and X-ray scattering intensity) as well as enthalpy of vaporization and isothermal compressibility. The validity against thermal expansion coefficient, isobaric heat capacity, and static dielectric constant are also discussed.
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Affiliation(s)
- Xuan Zhang
- Department of Chemistry, Zhejiang University, Hangzhou, People's Republic of China
| | - Yongtao Wang
- Department of Chemistry, Zhejiang University, Hangzhou, People's Republic of China
| | - Jia Yao
- Department of Chemistry, Zhejiang University, Hangzhou, People's Republic of China
| | - Haoran Li
- Department of Chemistry, Zhejiang University, Hangzhou, People's Republic of China
| | - Kenji Mochizuki
- Department of Chemistry, Zhejiang University, Hangzhou, People's Republic of China
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11
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Robalo JR, Mendes de Oliveira D, Ben-Amotz D, Vila Verde A. Influence of Methylene Fluorination and Chain Length on the Hydration Shell Structure and Thermodynamics of Linear Diols. J Phys Chem B 2021; 125:13552-13564. [PMID: 34875166 DOI: 10.1021/acs.jpcb.1c08601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The interplay between the local hydration shell structure, the length of hydrophobic solutes, and their identity (perfluorinated or not) remains poorly understood. We address this issue by combining Raman-multivariate curve resolution (Raman-MCR) spectroscopy, simulation, and quantum-mechanical calculations to quantify the thermodynamics and the first principle interactions behind the formation of defects in the hydration shell of alkyl-diol and perfluoroalkyl-diol chains. The hydration shell of the fluorinated diols contains substantially more defects than that of the nonfluorinated diols; these defects are water hydroxy groups that do not donate hydrogen bonds and which either point to the solute (radial-dangling OH) or not (nonradial-dangling OH). The number of radial-dangling OH defects per carbon decreases for longer chains and toward the interior of the fluorinated diols, mainly due to less favorable electrostatics and exchange interactions; nonradial-dangling OH defects per carbon increase with chain length. In contrast, the hydration shell of the nonfluorinated diols only contains radial-dangling defects, which become more abundant toward the center of the chain and for larger chains, predominantly because of more favorable dispersion interactions. These results have implications for how the folding of macromolecules, ligand binding to biomacromolecules, and chemical reactions at water-oil interfaces could be modified through the introduction of fluorinated groups or solvents.
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Affiliation(s)
- João R Robalo
- Department of Theory & Bio-systems, Max Planck Institute for Colloids and Interfaces, Science Park, Potsdam 14476, Germany
| | | | - Dor Ben-Amotz
- Purdue University, Department of Chemistry, West Lafayette, Indiana 47907, United States
| | - Ana Vila Verde
- University of Duisburg-Essen, Faculty of Physics, Lotharstrasse 1, 47057 Duisburg, Germany
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12
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Zupančič B, Grdadolnik J. Solute-induced changes in the water H-bond network of different alcohol-aqueous systems. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.117349] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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13
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Effects of hydrophobic solute on water normal modes. Chem Phys 2021. [DOI: 10.1016/j.chemphys.2021.111303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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14
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Troncoso J. Effect of hydrophobic phenomena over the volumetric behavior of aqueous ionic liquid solutions. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.115962] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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15
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Bredt AJ, Mendes de Oliveira D, Urbina AS, Slipchenko LV, Ben-Amotz D. Hydration and Seamless Integration of Hydrogen Peroxide in Water. J Phys Chem B 2021; 125:6986-6993. [PMID: 34133177 DOI: 10.1021/acs.jpcb.1c03107] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Raman multivariate curve resolution is used to decompose the vibrational spectra of aqueous hydrogen peroxide (H2O2) into pure water, dilute H2O2, and concentrated H2O2 spectral components. The dilute spectra reveal four sub-bands in the OH stretch region, assigned to the OH stretch and Fermi resonant bend overtone of H2O2, and two nonequivalent OH groups on water molecules that donate a hydrogen bond to H2O2. At high concentrations, a spectral component resembling pure H2O2 emerges. Our results further demonstrate that H2O2 perturbs the structure of water significantly less than either methanol or sodium chloride of the same concentration, as evidenced by comparing the hydration-shell spectra of tert-butyl alcohol dissolved in the three aqueous solutions.
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Affiliation(s)
- Aria J Bredt
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | | | - Andres S Urbina
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Lyudmila V Slipchenko
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Dor Ben-Amotz
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
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16
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Mendes de Oliveira D, Ben-Amotz D. Spectroscopically Quantifying the Influence of Salts on Nonionic Surfactant Chemical Potentials and Micelle Formation. J Phys Chem Lett 2021; 12:355-360. [PMID: 33355467 DOI: 10.1021/acs.jpclett.0c03349] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The influence of two salts (NaSCN and Na2SO4) on the micellization of a nonionic surfactant (1,2-hexanediol) is quantified using Raman multivariate curve resolution spectroscopy, combined with a generalized theoretical analysis of the corresponding chemical potential changes. Although the SCN- and SO42- anions are on opposite ends of the Hofmeister series, they are both found to lower the critical micelle concentration. Our combined spectroscopic and theoretical analysis traces these observations to the fact that in both salt solutions the ions have a greater affinity for (or are less strongly expelled from) the hydration shell of the micelle than the free surfactant monomer, as quantified using the corresponding chemical potentials and Wyman-Tanford coefficients. This probe-free experimental and theoretical analysis strategy may readily be extended to micelle formation processes involving other surfactants, salts, and cosolvents, as well as to other sorts of aggregation and binding processes.
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Affiliation(s)
| | - Dor Ben-Amotz
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
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17
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Viscosity study of tert-butyl alcohol aqueous solution by Brownian motion and gravimetric capillaries. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.114170] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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18
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Biswas S, Mallik BS. Negligible Effect on the Structure and Vibrational Spectral Dynamics of Water Molecules Near Hydrophobic Solutes. ChemistrySelect 2020. [DOI: 10.1002/slct.202002449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Sohag Biswas
- Department of Chemistry Indian Institute of Technology Hyderabad Kandi 502285 Sangareddy, Telangana India
- Present address: University of California Riverside CA 92521 USA
| | - Bhabani S. Mallik
- Department of Chemistry Indian Institute of Technology Hyderabad Kandi 502285 Sangareddy, Telangana India
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Roy S, Patra A, Saha S, Palit DK, Mondal JA. Restructuring of Hydration Shell Water due to Solvent-Shared Ion Pairing (SSIP): A Case Study of Aqueous MgCl 2 and LaCl 3 Solutions. J Phys Chem B 2020; 124:8141-8148. [PMID: 32816482 DOI: 10.1021/acs.jpcb.0c05681] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Hydration of ions plays a crucial role in interionic interactions and associated processes in aqueous media, but selective probing of the hydration shell water is nontrivial. Here, we introduce Raman difference with simultaneous curve fitting (RD-SCF) analysis to extract the OH-stretch spectrum of hydration shell water, not only for the fully hydrated ions (Mg2+, La3+, and Cl-) but also for the ion pairs. RD-SCF analyses of diluted MgCl2 (0.18 M) and LaCl3 (0.12 M) solutions relative to aqueous NaCl of equivalent Cl- concentrations provide the OH-stretch spectra of water in the hydration shells of fully hydrated Mg2+ and La3+ cations relative to that of Na+. Integrated intensities of the hydration shell spectra of Mg2+ and La3+ ions increase linearly with the salt concentration (up to 2.0 M MgCl2 and 1.3 M LaCl3), which suggests no contact ion pair (CIP) formation in the MgCl2 and LaCl3 solutions. Nevertheless, the band shapes of the cation hydration shell spectra show a growing signature of Cl--associated water with the rising salt concentration, which is a manifestation of the formation of a solvent-shared ion pair (SSIP). The OH-stretch spectrum of the shared/intervening water in the SSIP, retrieved by second-round RD-SCF analysis (2RD-SCF), shows that the average H-bonding of the shared water is weaker than that of the hydration water of the fully hydrated cation (Mg2+ or La3+) but stronger than that of the anion (Cl-). The shared water displays an overall second-order dependence on the concentration of the interacting ions, unveiling 1:1 stoichiometry of the SSIP formed between Mg2+ and Cl- as well as La3+ and Cl-.
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Affiliation(s)
- Subhadip Roy
- Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Homi Bhabha National Institute, Mumbai 400085, India
| | - Animesh Patra
- School of Chemistry, Centre for Excellence in Basic Sciences, Mumbai 400098, India
| | - Subhamoy Saha
- Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Homi Bhabha National Institute, Mumbai 400085, India
| | - Dipak K Palit
- School of Chemistry, Centre for Excellence in Basic Sciences, Mumbai 400098, India
| | - Jahur Alam Mondal
- Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Homi Bhabha National Institute, Mumbai 400085, India
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Pethes I, Pusztai L, Ohara K, Kohara S, Darpentigny J, Temleitner L. Temperature-dependent structure of methanol-water mixtures on cooling: X-ray and neutron diffraction and molecular dynamics simulations. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113664] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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21
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Sinha S, Gharat PM, Pal H, Dutta Choudhury S. Lumichrome tautomerism in alcohol-water mixtures: Effect of carbon chain length and mole fraction of alcohols. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113621] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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22
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Conti Nibali V, Pezzotti S, Sebastiani F, Galimberti DR, Schwaab G, Heyden M, Gaigeot MP, Havenith M. Wrapping Up Hydrophobic Hydration: Locality Matters. J Phys Chem Lett 2020; 11:4809-4816. [PMID: 32459100 PMCID: PMC8253475 DOI: 10.1021/acs.jpclett.0c00846] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 05/27/2020] [Indexed: 05/17/2023]
Abstract
Water, being the universal solvent, acts as a competing agent in fundamental processes, such as folding, aggregation or biomolecular recognition. A molecular understanding of hydrophobic hydration is of central importance to understanding the subtle free energy differences, which dictate function. Ab initio and classical molecular dynamics simulations yield two distinct hydration water populations in the hydration shell of solvated tert-butanol noted as "HB-wrap" and "HB-hydration2bulk". The experimentally observed hydration water spectrum can be dissected into two modes, centered at 164 and 195 cm-1. By comparison to the simulations, these two bands are attributed to the "HB-wrap" and "HB-hydration2bulk" populations, respectively. We derive a quantitative correlation between the population in each of these two local water coordination motifs and the temperature dependence of the solvation entropy. The crossover from entropy to enthalpy dominated solvation at elevated temperatures, as predicted by theory and observed experimentally, can be rationalized in terms of the distinct temperature stability and thermodynamic signatures of "HB-wrap" and "HB-hydration2bulk".
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Affiliation(s)
- V. Conti Nibali
- Department of Physical Chemistry II, Ruhr University Bochum, 44780 Bochum, Germany
| | - S. Pezzotti
- Department of Physical Chemistry II, Ruhr University Bochum, 44780 Bochum, Germany
- LAMBE
CNRS UMR8587, Université d’Evry
val d’Essonne & Université Paris-Saclay, 91000 Evry, France
| | - F. Sebastiani
- Department of Physical Chemistry II, Ruhr University Bochum, 44780 Bochum, Germany
| | - D. R. Galimberti
- LAMBE
CNRS UMR8587, Université d’Evry
val d’Essonne & Université Paris-Saclay, 91000 Evry, France
| | - G. Schwaab
- Department of Physical Chemistry II, Ruhr University Bochum, 44780 Bochum, Germany
| | - M. Heyden
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - M.-P. Gaigeot
- LAMBE
CNRS UMR8587, Université d’Evry
val d’Essonne & Université Paris-Saclay, 91000 Evry, France
| | - M. Havenith
- Department of Physical Chemistry II, Ruhr University Bochum, 44780 Bochum, Germany
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23
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Bredt AJ, Ben-Amotz D. Influence of crowding on hydrophobic hydration-shell structure. Phys Chem Chem Phys 2020; 22:11724-11730. [PMID: 32409791 DOI: 10.1039/d0cp00702a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The influence of molecular crowding on water structure, and the associated crossover behavior, is quantified using Raman multivariate curve resolution (Raman-MCR) hydration-shell vibrational spectroscopy of aqueous tert-butyl alcohol, 2-butyl alcohol and 2-butoxyethanol solutions of variable concentration and temperature. Changes in the hydration-shell OH stretch band shape and mean frequency are used to identify the temperature at which the hydration-shell crosses over from a more ordered to less ordered structure, relative to pure water. The influence of crowding on the crossover is found to depend on solute size and shape in a way that is correlated with the corresponding infinitely dilute hydration-shell structure (and the corresponding first hydration-shell spectra are invariably very similar to pure water). Analysis of the results using a Muller-like two-state equilibrium between more ordered and less ordered hydration-shell structures implies that crossover temperature changes are dictated primarily by enthalpic stabilization of the more ordered hydration-shell structures.
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Affiliation(s)
- Aria J Bredt
- Purdue University, Department of Chemistry, West Lafayette, IN 47907, USA.
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24
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Monroe J, Barry M, DeStefano A, Aydogan Gokturk P, Jiao S, Robinson-Brown D, Webber T, Crumlin EJ, Han S, Shell MS. Water Structure and Properties at Hydrophilic and Hydrophobic Surfaces. Annu Rev Chem Biomol Eng 2020; 11:523-557. [PMID: 32169001 DOI: 10.1146/annurev-chembioeng-120919-114657] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The properties of water on both molecular and macroscopic surfaces critically influence a wide range of physical behaviors, with applications spanning from membrane science to catalysis to protein engineering. Yet, our current understanding of water interfacing molecular and material surfaces is incomplete, in part because measurement of water structure and molecular-scale properties challenges even the most advanced experimental characterization techniques and computational approaches. This review highlights progress in the ongoing development of tools working to answer fundamental questions on the principles that govern the interactions between water and surfaces. One outstanding and critical question is what universal molecular signatures capture the hydrophobicity of different surfaces in an operationally meaningful way, since traditional macroscopic hydrophobicity measures like contact angles fail to capture even basic properties of molecular or extended surfaces with any heterogeneity at the nanometer length scale. Resolving this grand challenge will require close interactions between state-of-the-art experiments, simulations, and theory, spanning research groups and using agreed-upon model systems, to synthesize an integrated knowledge of solvation water structure, dynamics, and thermodynamics.
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Affiliation(s)
- Jacob Monroe
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA;
| | - Mikayla Barry
- Department of Materials, University of California, Santa Barbara, California 93106, USA
| | - Audra DeStefano
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA;
| | - Pinar Aydogan Gokturk
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Sally Jiao
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA;
| | - Dennis Robinson-Brown
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA;
| | - Thomas Webber
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA;
| | - Ethan J Crumlin
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.,Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Songi Han
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA; .,Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
| | - M Scott Shell
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA;
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25
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Barnett JW, Ashbaugh HS. Evaluation of second osmotic virial coefficients from molecular simulation following scaled-particle theory. MOLECULAR SIMULATION 2019. [DOI: 10.1080/08927022.2019.1639698] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- J. Wesley Barnett
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, LA, USA
| | - Henry S. Ashbaugh
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, LA, USA
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26
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Huang J, Morin FJ, Laaser JE. Charge-Density-Dominated Phase Behavior and Viscoelasticity of Polyelectrolyte Complex Coacervates. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b00036] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Jun Huang
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Frances J. Morin
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Jennifer E. Laaser
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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27
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Abstract
Hydration-shell vibrational spectroscopy provides an experimental window into solute-induced water structure changes that mediate aqueous folding, binding, and self-assembly. Decomposition of measured Raman and infrared (IR) spectra of aqueous solutions using multivariate curve resolution (MCR) and related methods may be used to obtain solute-correlated spectra revealing solute-induced perturbations of water structure, such as changes in water hydrogen-bond strength, tetrahedral order, and the presence of dangling (non-hydrogen-bonded) OH groups. More generally, vibrational-MCR may be applied to both aqueous and nonaqueous solutions, including multicomponent mixtures, to quantify solvent-mediated interactions between oily, polar, and ionic solutes, in both dilute and crowded fluids. Combining vibrational-MCR with emerging theoretical modeling strategies promises synergetic advances in the predictive understanding of multiscale self-assembly processes of both biological and technological interest.
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Affiliation(s)
- Dor Ben-Amotz
- Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , United States
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28
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Overduin SD, Perera A, Patey GN. Structural behavior of aqueous t-butanol solutions from large-scale molecular dynamics simulations. J Chem Phys 2019; 150:184504. [PMID: 31091933 DOI: 10.1063/1.5097011] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Large-scale molecular dynamics simulations are reported for aqueous t-butanol (TBA) solutions. The CHARMM generalized force field (CGenFF) for TBA is combined with the TIP4P/2005 model for water. Unlike many other common TBA models, the CGenFF model is miscible with water in all proportions at 300 K. The main purpose of this work is to investigate the existence and nature of a microheterogeneous structure in aqueous TBA solutions. Our simulations of large systems (128 000 and 256 000 particles) at TBA mole fractions of 0.06 and 0.1 clearly reveal the existence of long-range correlations (>10 nm) that show significant variations on long time scales (∼50 ns). We associate these long-range slowly varying correlations with the existence of supramolecular domainlike structures that consist of TBA-rich and water-rich regions. This structure is always present but continually changing in time, giving rise to long-range slowly varying pair correlation functions. We find that this behavior appears to have little influence on the single particle dynamics; the diffusion coefficients of both TBA and water molecules lie in the usual liquid state regime, and mean square displacements provide no indication of anomalous diffusion. Using our large system simulations, we are able to reliably calculate small angle x-ray scattering and small angle neutron scattering spectra, except at a very low wave vector, and the results agree well with recent experiments. However, this paper shows that simulation of the relatively simple TBA/water system remains challenging. This is particularly true if one wishes to obtain properties such as Kirkwood-Buff factors, or scattering functions at a low wave vector, which strongly depend on the long-range behavior of the pair correlations.
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Affiliation(s)
- S D Overduin
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Aurélien Perera
- Laboratoire de Physique Théorique de la Matière Condensée (UMR CNRS 7600), Université Pierre et Marie Curie, 4 Place Jussieu, F75252 Paris Cedex 05, France
| | - G N Patey
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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29
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Gailus T, Krah H, Kühnel V, Rupprecht A, Kaatze U. Carboxylic acids in aqueous solutions: Hydrogen bonds, hydrophobic effects, concentration fluctuations, ionization, and catalysis. J Chem Phys 2019; 149:244503. [PMID: 30599745 DOI: 10.1063/1.5063877] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In the frequency range between 100 kHz and 2 GHz, ultrasonic absorption spectra have been measured for a series of carboxylic acids from formic to enanthic acid, including constitutional isomers. Also investigated have been the spectra for mixtures with water of short-chain formic, acetic, propionic, butyric, and isobutyric acid, in each case covering the complete composition range. The neat carboxylic acids feature two Debye-type relaxation terms with relaxation times between 5.6 and 260 ns as well as 0.14 and 1.4 ns, respectively, at room temperature. Depending on the composition, mixtures with water reveal an additional Debye relaxation term in the intermediate frequency range (acetic acid) or a term subject to a relaxation time distribution (propionic, butyric, and isobutyric acid). The relaxations of the neat acids are assigned to the equilibrium between monomers and single-hydrogen-bonded linear dimers and between linear and twofold-hydrogen-bonded cyclic dimers. The latter equilibrium is considerably catalyzed by hydronium and carboxylate ions. Several mixtures with water indicate one of the up to three Debye relaxations to reflect the protolysis of the organic acid. The term with underlying relaxation time distribution is due to noncritical fluctuations in the local concentrations. The Debye relaxations are evaluated to yield the parameters of the relevant elementary chemical reactions, such as the rate and equilibrium constants and the isentropic reaction volumes. A comparison of the correlation length of concentration fluctuations with data for other aqueous systems confirms the idea that the hydrophobic part of the organic constituent promotes the formation of a micro-heterogeneous liquid structure, whereas the hydrophilic moiety is of minor importance in this respect. The high-frequency limiting absorption suggests the equilibrium between conformers of linear dimers to contribute to the spectra well above the frequency range of measurements.
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Affiliation(s)
- Torsten Gailus
- Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Holger Krah
- Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Volker Kühnel
- Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Andreas Rupprecht
- Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Udo Kaatze
- Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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30
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Furukawa K, Kuronuma S, Judai K. Water fluctuation in methanol, ethanol, and 1-propanol aqueous-mixture probed by Brownian motion. J Chem Phys 2018; 149:244505. [PMID: 30599750 DOI: 10.1063/1.5064750] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The origin of the driving force in Brownian motion is the collision between the colloidal particle and the molecules of the surrounding fluid. Therefore, Brownian motion contains information on the local solvent structures of the surrounding colloid. The mean square displacement in a water-ethanol mixture is greater than that anticipated from the macroscopic shear viscosity, indicating that the microscopic movement of Brownian motion involves the local information on the water-ethanol mixture on a molecular level, i.e., an inhomogeneity in the Brownian particle size (∼1 μm). Here, the Brownian motion of mixtures of water and methanol, ethanol, and 1-propanol are systematically investigated. Similar discrepancies between the microscopic and macroscopic viscosities are observed at low alcohol molar concentrations, for all the alcohol mixtures. This means that inhomogeneity with water fluctuation is important in explanation of the unusual Brownian diffusions of alcohol aqueous solutions. The Brownian motion also reveals a thermal energy conversion mechanism between translation and rotation.
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Affiliation(s)
- Kazuki Furukawa
- Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
| | - Sumito Kuronuma
- Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
| | - Ken Judai
- Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
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31
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Sun CQ. Aqueous charge injection: solvation bonding dynamics, molecular nonbond interactions, and extraordinary solute capabilities. INT REV PHYS CHEM 2018. [DOI: 10.1080/0144235x.2018.1544446] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Chang Q. Sun
- EBEAM, Yangtze Normal University, Chongqing, People's Republic of China
- NOVITAS, EEE, Nanyang Technological University, Singapore, Singapore
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32
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33
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Wu X, Lu W, Streacker LM, Ashbaugh HS, Ben‐Amotz D. Methane Hydration‐Shell Structure and Fragility. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201809372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Xiangen Wu
- College of Marine Science and Technology China University of Geosciences Wuhan 430074 China
| | - Wanjun Lu
- State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences Wuhan 430074 China
| | | | - Henry S. Ashbaugh
- Department of Chemical and Biomolecular Engineering Tulane University New Orleans Louisiana 70118 USA
| | - Dor Ben‐Amotz
- Purdue University Department of Chemistry West Lafayette IN 47907 USA
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34
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Wu X, Lu W, Streacker LM, Ashbaugh HS, Ben-Amotz D. Methane Hydration-Shell Structure and Fragility. Angew Chem Int Ed Engl 2018; 57:15133-15137. [PMID: 30368997 DOI: 10.1002/anie.201809372] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Indexed: 11/12/2022]
Abstract
The influence of oily molecules on the structure of liquid water is a question of importance to biology and geology and many other fields. Previous experimental, theoretical, and simulation studies of methane in liquid water have reached widely conflicting conclusions regarding the structure of hydrophobic hydration-shells. Herein we address this question by performing Raman hydration-shell vibrational spectroscopic measurements of methane in liquid water from -10 °C to 300 °C (at 30 MPa, along a path that parallels the liquid-vapor coexistence curve). We show that, near ambient temperatures, methane's hydration-shell is slightly more tetrahedral than pure water. Moreover, the hydration-shell undergoes a crossover to a more disordered structure above ca. 85 °C. Comparisons with the crossover temperature of aqueous methanol (and other alcohols) reveal the stabilizing influence of an alcohol OH head-group on hydrophobic hydration-shell fragility.
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Affiliation(s)
- Xiangen Wu
- College of Marine Science and Technology, China University of Geosciences, Wuhan, 430074, China
| | - Wanjun Lu
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China
| | - Louis M Streacker
- Purdue University, Department of Chemistry, West Lafayette, IN, 47907, USA
| | - Henry S Ashbaugh
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana, 70118, USA
| | - Dor Ben-Amotz
- Purdue University, Department of Chemistry, West Lafayette, IN, 47907, USA
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35
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Lenton S, Rhys NH, Towey JJ, Soper AK, Dougan L. Temperature-Dependent Segregation in Alcohol-Water Binary Mixtures Is Driven by Water Clustering. J Phys Chem B 2018; 122:7884-7894. [PMID: 30039970 DOI: 10.1021/acs.jpcb.8b03543] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Previous neutron scattering work, combined with computer simulated structure analysis, has established that binary mixtures of methanol and water partially segregate into water-rich and alcohol-rich components. It has furthermore been noted that, between methanol mole fractions of 0.27 and 0.54, both components, water and methanol, simultaneously form percolating clusters. This partial segregation is enhanced with decreasing temperature. The mole fraction of 0.27 also corresponds to the point of maximum excess entropy for ethanol-water mixtures. Here, we study the degree of molecular segregation in aqueous ethanol solutions at a mole fraction of 0.27 and compare it with that in methanol-water solutions at the same concentration. Structural information is extracted for these solutions using neutron diffraction coupled with empirical potential structure refinement. We show that ethanol, like methanol, bi-percolates at this concentration and that, in a similar manner to methanol, alcohol segregation, as measured by the proximity of neighboring methyl sidechains, is increased upon cooling the solution. Water clustering is found to be significantly enhanced in both alcohol solutions compared to the water clustering that occurs for random, hard sphere-like, mixing with no hydrogen bonds between molecules. Alcohol clustering via the hydrophobic groups is, on the other hand, only slightly sensitive to the water hydrogen bond network. These results support the idea that it is the water clustering that drives the partial segregation of the two components, and hence the observed excess entropy of mixing.
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Affiliation(s)
- Samuel Lenton
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , U.K
| | - Natasha H Rhys
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , U.K
| | - James J Towey
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , U.K
| | - Alan K Soper
- ISIS Facility , STFC Rutherford Appleton Laboratory , Harwell Campus , Didcot OX11 0QX , U.K
| | - Lorna Dougan
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , U.K
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36
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Bandyopadhyay D, Kamble Y, Choudhury N. How Different Are the Characteristics of Aqueous Solutions of tert-Butyl Alcohol and Trimethylamine-N-Oxide? A Molecular Dynamics Simulation Study. J Phys Chem B 2018; 122:8220-8232. [DOI: 10.1021/acs.jpcb.8b02411] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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37
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Chen Y, Zhang H, Zhou W, Deng C, Liao J. The solvent effects on dimethyl phthalate investigated by FTIR characterization, solvent parameter correlation and DFT computation. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2018; 199:412-420. [PMID: 29649677 DOI: 10.1016/j.saa.2018.03.051] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Revised: 03/15/2018] [Accepted: 03/16/2018] [Indexed: 06/08/2023]
Abstract
This study set out with the aim of investigating the solvent effects on dimethyl phthalate (DMP) using FTIR characterization, solvent parameter correlation and DFT calculation. DMP exposed to 17 organic solvents manifested varying shift in the carbonyl stretching vibration frequency (νCO). Non-alkanols induced Band I and alkanols produced Band I and Band II. Through correlating the νCO with the empirical solvent scales including acceptor parameter (AN), Schleyer's linear free energy parameter (G), and linear free salvation energy relationships (LSER), Band I was mainly ascribed to non-specific effects from either non-alkanols or alkanol polymers ((alkanol)n). νCO of the latter indicated minor red shift and less variability compared to the former. An assumption was made and validated about the sequestering of hydroxyl group by the bulky hydrophobic chain in (alkanol)n, creating what we refer to as "screening effects". Ab initio calculation, on the other hand, provided insights for possible hydrogen binding between DMP and (ethanol)n or between ethanol monomers. The two components of Band I observed in inert solvents were assigned to the two CO groups adopting differentiated conformations. This in turn prompted our consideration that hydrogen binding was highly selective in favor of lowly associated (alkanol)n and the particular CO group having relatively less steric hindrance and stronger electron-donating capacity. Band II was therefore believed to derive from hydrogen-bond interactions mainly in manner of 1:1 and 1:2 DMP-(alkanol)n complexes.
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Affiliation(s)
- Yi Chen
- Department of Chemistry, Zhejiang Institute of Metrology, Tianmushan Road No. 222, Hangzhou 310007, Zhejiang, PR China.
| | - Hui Zhang
- Department of Chemistry, Zhejiang Institute of Metrology, Tianmushan Road No. 222, Hangzhou 310007, Zhejiang, PR China
| | - Wenzhao Zhou
- Department of Chemistry, Zhejiang Institute of Metrology, Tianmushan Road No. 222, Hangzhou 310007, Zhejiang, PR China
| | - Chao Deng
- Department of Chemistry, Zhejiang Institute of Metrology, Tianmushan Road No. 222, Hangzhou 310007, Zhejiang, PR China
| | - Jian Liao
- Department of Environmental Science and Engineering, Zhejiang University of Technology, Hangzhou 310004, Zhejiang, PR China
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38
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Ashbaugh HS, Barnett JW, Saltzman A, Langrehr M, Houser H. Connections between the Anomalous Volumetric Properties of Alcohols in Aqueous Solution and the Volume of Hydrophobic Association. J Phys Chem B 2018; 122:3242-3250. [PMID: 28968101 DOI: 10.1021/acs.jpcb.7b08728] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The partial molar volumes of alcohols in water exhibit a non-monotonic dependence on concentration at room temperature, initially decreasing with increasing concentration before passing through a minimum and rising to the pure liquid plateau. This anomalous behavior is associated with hydrophobic interactions. We report molecular simulations of short chain alcohols and alkanes in water to examine the volumetric properties of these mixtures at infinite dilution over a range of temperatures. Our simulations find this anomaly disappears at a crossover temperature, above which the solute volume only varies monotonically with concentration. A Voronoi volume analysis of solution configurations finds that solutes in clusters take up less space than individual solutes at low temperature and more space at elevated temperatures. These changes in cluster volumes are subsequently shown to correlate with the derivative of the solute partial molar volume with respect to solute concentration. The changes in solute volume upon nonpolar solute association impact the response of molecular-scale hydrophobic interactions for assembly with increasing pressure.
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Affiliation(s)
- Henry S Ashbaugh
- Department of Chemical and Biomolecular Engineering , Tulane University , New Orleans , Louisiana 70118 , United States
| | - J Wesley Barnett
- Department of Chemical and Biomolecular Engineering , Tulane University , New Orleans , Louisiana 70118 , United States
| | - Alexander Saltzman
- Department of Chemical and Biomolecular Engineering , Tulane University , New Orleans , Louisiana 70118 , United States
| | - Mae Langrehr
- Department of Chemical and Biomolecular Engineering , University of Delaware , Newark , Delaware 19716 , United States
| | - Hayden Houser
- Department of Chemical and Biomolecular Engineering , Tulane University , New Orleans , Louisiana 70118 , United States
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39
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Koga K, Yamamoto N. Hydrophobicity Varying with Temperature, Pressure, and Salt Concentration. J Phys Chem B 2018; 122:3655-3665. [PMID: 29357255 DOI: 10.1021/acs.jpcb.7b12193] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Temperature-, pressure-, and salt-concentration-induced variations in the solubility of small nonpolar solutes in aqueous solution and the corresponding variations in the solvent-induced pair attraction between such solute molecules are investigated. The variations in the solvation free energy of a solute and those in the solvent-induced pair attraction are well reproduced by a mean-field approximation in which the repulsive cores of solute molecules are treated as hard spheres and the mean-field energy of a solute molecule is taken to be the average potential energy that the solute molecule feels in solution. The mechanisms of variation in the solvation free energy and those of variation in the solvent-induced pair potential, with increasing temperature, pressure, and salt concentration, are clarified. Correlations between the solvation free energy and the solvent-induced pair potential at a contact distance in temperature, pressure, and salt concentration variations are near linear in any mode of variation, but the slope of the linear relation is dependent on the mode of variation and is determined by a ratio of the solvation thermodynamic quantities characteristic of each mode of variation.
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Affiliation(s)
- K Koga
- Research Institute for Interdisciplinary Science , Okayama University , Okayama 700-8530 , Japan.,Department of Chemistry, Faculty of Science , Okayama University , Okayama 700-8530 , Japan
| | - N Yamamoto
- Department of Chemistry, Faculty of Science , Okayama University , Okayama 700-8530 , Japan
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40
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Sanders SE, Vanselous H, Petersen PB. Water at surfaces with tunable surface chemistries. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:113001. [PMID: 29393860 DOI: 10.1088/1361-648x/aaacb5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Aqueous interfaces are ubiquitous in natural environments, spanning atmospheric, geological, oceanographic, and biological systems, as well as in technical applications, such as fuel cells and membrane filtration. Where liquid water terminates at a surface, an interfacial region is formed, which exhibits distinct properties from the bulk aqueous phase. The unique properties of water are governed by the hydrogen-bonded network. The chemical and physical properties of the surface dictate the boundary conditions of the bulk hydrogen-bonded network and thus the interfacial properties of the water and any molecules in that region. Understanding the properties of interfacial water requires systematically characterizing the structure and dynamics of interfacial water as a function of the surface chemistry. In this review, we focus on the use of experimental surface-specific spectroscopic methods to understand the properties of interfacial water as a function of surface chemistry. Investigations of the air-water interface, as well as efforts in tuning the properties of the air-water interface by adding solutes or surfactants, are briefly discussed. Buried aqueous interfaces can be accessed with careful selection of spectroscopic technique and sample configuration, further expanding the range of chemical environments that can be probed, including solid inorganic materials, polymers, and water immiscible liquids. Solid substrates can be finely tuned by functionalization with self-assembled monolayers, polymers, or biomolecules. These variables provide a platform for systematically tuning the chemical nature of the interface and examining the resulting water structure. Finally, time-resolved methods to probe the dynamics of interfacial water are briefly summarized before discussing the current status and future directions in studying the structure and dynamics of interfacial water.
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Affiliation(s)
- Stephanie E Sanders
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States of America
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41
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Wu X, Lu W, Streacker LM, Ashbaugh HS, Ben-Amotz D. Temperature-Dependent Hydrophobic Crossover Length Scale and Water Tetrahedral Order. J Phys Chem Lett 2018; 9:1012-1017. [PMID: 29420897 DOI: 10.1021/acs.jpclett.7b03431] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Experimental Raman multivariate curve resolution and molecular dynamics simulations are performed to demonstrate that the vibrational frequency and tetrahedrality of water molecules in the hydration-shells of short-chain alcohols differ from those of pure water and undergo a crossover above 100 °C (at 30 MPa) to a structure that is less tetrahedral than pure water. Our results demonstrate that the associated crossover length scale decreases with increasing temperature, suggesting that there is a fundamental connection between the spectroscopically observed crossover and that predicted to take place around idealized purely repulsive solutes dissolved in water, although the water structure changes in the hydration-shells of alcohols are far smaller than those associated with an idealized "dewetting" transition.
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Affiliation(s)
- Xiangen Wu
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences , Wuhan 430074, China
| | - Wanjun Lu
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences , Wuhan 430074, China
| | - Louis M Streacker
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
| | - Henry S Ashbaugh
- Department of Chemical and Biomolecular Engineering, Tulane University , New Orleans, Louisiana 70118, United States
| | - Dor Ben-Amotz
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
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Nayar D, van der Vegt NFA. Cosolvent Effects on Polymer Hydration Drive Hydrophobic Collapse. J Phys Chem B 2018; 122:3587-3595. [PMID: 29443520 DOI: 10.1021/acs.jpcb.7b10780] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Water-mediated hydrophobic interactions play an important role in self-assembly processes, aqueous polymer solubility, and protein folding, to name a few. Cosolvents affect these interactions; however, the implications for hydrophobic polymer collapse and protein folding equilibria are not well-understood. This study examines cosolvent effects on the hydrophobic collapse equilibrium of a generic 32-mer hydrophobic polymer in urea, trimethylamine- N-oxide (TMAO), and acetone aqueous solutions using molecular dynamics simulations. Our results unveil a remarkable cosolvent-concentration-dependent behavior. Urea, TMAO, and acetone all shift the equilibrium toward collapsed structures below 2 M cosolvent concentration and, in turn, to unfolded structures at higher cosolvent concentrations, irrespective of the differences in cosolvent chemistry and the nature of cosolvent-water interactions. We find that weakly attractive polymer-water van der Waals interactions oppose polymer collapse in pure water, corroborating related observations reviewed by Ben-Amotz ( Annu. Rev. Phys. Chem. 2016, 67, 617-638). The cosolvents studied in the present work adsorb at the polymer/water interface and expel water molecules into the bulk, thereby effectively removing the dehydration energy penalty that opposes polymer collapse in pure water. At low cosolvent concentrations, this leads to cosolvent-induced stabilization of collapsed polymer structures. Only at sufficiently high cosolvent concentrations, polymer-cosolvent interactions favor polymer unfolding.
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Affiliation(s)
- Divya Nayar
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Center of Smart Interfaces , Technische Universität Darmstadt , Alarich-Weiss-Strasse 10 , 64287 , Darmstadt , Germany
| | - Nico F A van der Vegt
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Center of Smart Interfaces , Technische Universität Darmstadt , Alarich-Weiss-Strasse 10 , 64287 , Darmstadt , Germany
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Morawietz T, Marsalek O, Pattenaude SR, Streacker LM, Ben-Amotz D, Markland TE. The Interplay of Structure and Dynamics in the Raman Spectrum of Liquid Water over the Full Frequency and Temperature Range. J Phys Chem Lett 2018; 9:851-857. [PMID: 29394069 DOI: 10.1021/acs.jpclett.8b00133] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems.
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Affiliation(s)
- Tobias Morawietz
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Ondrej Marsalek
- Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
| | - Shannon R Pattenaude
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
| | - Louis M Streacker
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
| | - Dor Ben-Amotz
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
| | - Thomas E Markland
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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Dutta R, Pyne A, Mondal D, Sarkar N. Effect of Microheterogeneity of Different Aqueous Binary Mixtures on the Proton Transfer Dynamics of [2,2'-Bipyridyl]-3,3'-diol: A Femtosecond Fluorescence Upconversion Study. ACS OMEGA 2018; 3:314-328. [PMID: 31457894 PMCID: PMC6641458 DOI: 10.1021/acsomega.7b01833] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 12/28/2017] [Indexed: 06/10/2023]
Abstract
In this article, we have investigated the excited-state intramolecular double proton transfer dynamics of [2,2'-bipyridyl]-3,3'-diol, BP(OH)2, in three alcohol-water binary mixtures, namely, ethanol (EtOH)-water, n-propanol (PrOH)-water, tert-butyl alcohol (TBA)-water, and dimethyl sulfoxide (DMSO)-water utilizing the femtosecond fluorescence upconversion technique. We have found that in alcohol-water binary mixtures the proton transfer (PT) pathway of BP(OH)2 is sequential and the anomalous slowdown in PT dynamics is observed in mole fraction (χ) ranges χEtOH = 0.04-0.07, χEtOH = 0.23-0.28, χPrOH = 0.17-0.30, χTBA = 0.12-0.21, and χTBA = 0.40-0.46. Our study sheds light on the involvement of water network in the PT dynamics. Reduction in water accessibility due to the involvement of water molecules in cluster formation results in hindered PT dynamics, and this retardation is more for the TBA-water binary mixture compared to that for the other two mixtures. Additionally, we have found two anomalous regions for the DMSO-water binary mixture in ranges χDMSO = 0.12-0.16 and χDMSO = 0.26-0.34. However, most interestingly, beyond χDMSO = 0.40, we do not find any growth component in the femtosecond fluorescence upconversion trace, which may be due to the change in the PT mechanism from a sequential water-mediated pathway to a concerted intramolecular pathway.
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Banik D, Bhattacharya S, Datta PK, Sarkar N. Anomalous Dynamics in tert-Butyl Alcohol-Water and Trimethylamine N-Oxide-Water Binary Mixtures: A Femtosecond Transient Absorption Study. ACS OMEGA 2018; 3:383-392. [PMID: 31457899 PMCID: PMC6641418 DOI: 10.1021/acsomega.7b01595] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Accepted: 12/27/2017] [Indexed: 05/17/2023]
Abstract
In this article, we have investigated the unusual dynamics of tert-butyl alcohol (TBA)-water and trimethylamine N-oxide (TMAO)-water binary mixtures using solvation dynamics as a tool. For this purpose, femtosecond transient absorption spectroscopy has been employed. Although these two molecules are isosteres to each other, a significant difference in water dynamics has been observed. The solvation times in TBA-water binary mixtures are found to be between 1.5 and 15.5 ps. On the contrary, we have observed very fast dynamics in TMAO-water binary mixtures (between 210 and 600 fs). Interestingly, unusual retardation in dynamics is observed at 0.10 mole fraction of TBA and TMAO in both the binary mixtures.
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Affiliation(s)
- Debasis Banik
- Department
of Chemistry and Department of Physics, Indian Institute
of Technology, Kharagpur 721302, West Bengal, India
| | - Sayantan Bhattacharya
- Department
of Chemistry and Department of Physics, Indian Institute
of Technology, Kharagpur 721302, West Bengal, India
| | - Prasanta Kumar Datta
- Department
of Chemistry and Department of Physics, Indian Institute
of Technology, Kharagpur 721302, West Bengal, India
- E-mail: (P.K.D.)
| | - Nilmoni Sarkar
- Department
of Chemistry and Department of Physics, Indian Institute
of Technology, Kharagpur 721302, West Bengal, India
- E-mail: . Phone: +91-3222-283332. Fax: 91-3222-255303 (N.S.)
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Tang D, Delpo C, Blackmon O, Ashbaugh HS. Note: Second osmotic virial coefficients of short alkanes and their alcohol counterparts in water as a function of temperature. J Chem Phys 2018; 148:016101. [DOI: 10.1063/1.5008573] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Affiliation(s)
- Du Tang
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA
| | - Courtney Delpo
- Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, USA
| | - Odella Blackmon
- Department of Chemistry, William Carey University, Hattiesburg, Mississippi 39401, USA
| | - Henry S. Ashbaugh
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA
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Furukawa K, Judai K. Brownian motion probe for water-ethanol inhomogeneous mixtures. J Chem Phys 2017; 147:244502. [DOI: 10.1063/1.5007813] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Kazuki Furukawa
- Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
| | - Ken Judai
- Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
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Abstract
This review focuses on papers published since 2000 on the topic of the properties of solutes in water. More specifically, it evaluates the state of the art of our understanding of the complex relationship between the shape of a hydrophobe and the hydrophobic effect. To highlight this, we present a selection of references covering both empirical and molecular dynamics studies of small (molecular-scale) solutes. These include empirical studies of small molecules, synthetic hosts, crystalline monolayers, and proteins, as well as in silico investigations of entities such as idealized hard and soft spheres, small solutes, hydrophobic plates, artificial concavity, molecular hosts, carbon nanotubes and spheres, and proteins.
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Affiliation(s)
- Matthew B Hillyer
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118;
| | - Bruce C Gibb
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118;
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Troncoso J, Zemánková K, Jover A. Dynamic light scattering study of aggregation in aqueous solutions of five amphiphiles. J Mol Liq 2017. [DOI: 10.1016/j.molliq.2017.06.022] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abstract
Whisky is distilled to around 70% alcohol by volume (vol-%) then diluted to about 40 vol-%, and often drunk after further slight dilution to enhance its taste. The taste of whisky is primarily associated with amphipathic molecules, such as guaiacol, but why and how dilution enhances the taste is not well understood. We carried out computer simulations of water-ethanol mixtures in the presence of guaiacol, providing atomistic details on the structure of the liquid mixture. We found that guaiacol is preferentially associated with ethanol, and, therefore, primarily found at the liquid-air interface in mixtures that contain up to 45 vol-% of ethanol. At ethanol concentrations of 59 vol-% or higher, guaiacol is increasingly surrounded by ethanol molecules and is driven to the bulk. This indicates that the taste of guaiacol in the whisky would be enhanced upon dilution prior to bottling. Our findings may apply to other flavour-giving amphipathic molecules and could contribute to optimising the production of spirits for desired tastes. Furthermore, it sheds light on the molecular structure of water-alcohol mixtures that contain small solutes, and reveals that interactions with the water may be negligible already at 89 vol-% of ethanol.
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