Contacts Between Alcohols in Water Are Random Rather than Hydrophobic

Rankin, Blake M.; Ben‐Amotz, Dor; Post, Sietse T. van der; Bakker, Huib J.

doi:10.1021/jz5027129

Cited by 89 publications

(138 citation statements)

References 39 publications

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“…To address this, Raman-MCR and polarization-resolved femtosecond IR experiments were combined with random mixing and molecular dynamics simulations. (53) The conclusion of these studies was that from methanol to tertiary butyl alcohol there is no association driven by the HE.…”

Section: Positive Curvaturementioning

confidence: 92%

Molecular Shape and the Hydrophobic Effect

Hillyer

Gibb

2016

Annu. Rev. Phys. Chem.

115

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This review focuses in 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 a selection of references covering both empirical and molecular dynamics studies of small (molecular-scale) solutes are presented. These include empirical studies of small molecules, synthetic hosts, crystalline monolayers, and proteins, as well as in silico investigations of entities including idealized hard and soft spheres, small solutes, hydrophobic plates, artificial concavity, molecular hosts, carbon nanotubes and spheres, and proteins. KeywordsWater; non-covalent interactions; supramolecular chemistry; Hydrophobic Effect; hydration ExordiumWater is found in many parts of the universe, but planet Earth truly is a water-world. All four spheres consist to some extent of water: the hydrosphere, biosphere, atmosphere and lithosphere all contain (respectively decreasing) proportions of water. This review pertains to the hydrosphere and biosphere. More specifically, this review concerns the complex relationship between hydrophobic solutes and the solvent of life.(1) For understanding how solute shape and functionality control solvation, and how this solvation folds into measurable spectroscopic and thermodynamic changes, is key to understanding our world.The ubiquity of water is reflected in a massive literature and consequently boundaries must be set for any review. First, although there is a continuum between a hydrophobe and a hard ion, and cases where the Hydrophobic effect (HE) and the Hofmeister effect(2-4) meet,(5; 6) where possible the latter is avoided. Second, this review focuses on the molecular-scale HE(7) and avoids the micro-scale.(8) Third, temperature and pressure can have a considerable effect on the HE,(9) but with only a few exceptions this review concerns ambient conditions. Fourth, bio-membranes are not discussed.(10) Finally, the bulk of this review concerns work performed since 2000.The layout of this review follows the broad types of curvature as defined by mathematics: positive curvature (convex), zero curvature (flat surface) and negative curvature (concave).

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Section: Positive Curvaturementioning

confidence: 92%

Molecular Shape and the Hydrophobic Effect

Hillyer

Gibb

2016

Annu. Rev. Phys. Chem.

115

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“…[36][37][38][39][40][41] Using Raman spectroscopy, Ben-Amotz et al have concluded that the observed clustering in alcohol-water mixtures is a result of random, rather than hydrophobic, interactions. 42,43 In contrast, some femtosecond midinfrared spectroscopy experiments have shown that water surrounding the aliphatic groups of the alcohols displays significantly slowed dynamics relative to the bulk, lending support to the model in which the measured negative excess entropy is attributed to water forming clathrate-like structure around the hydrophobic groups of the alcohols. 44 Here, we present a study of methanol-, ethanol-, and isopropanol-water mixtures via liquid microjet X-ray absorption spectroscopy (XAS).…”

Section: -17mentioning

confidence: 92%

Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy

Lam

Smith

Saykally

2016

The Journal of Chemical Physics

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While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atomspecific probe providing details of both inter-and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interactions, resulting in additional ordering in the liquid structures and leading to a reduction in entropy and a negative enthalpy of mixing, consistent with existing thermodynamic data. In contrast, the spectra of the isopropanol-water mixtures exhibit an increase in the number of broken alcohol hydrogen bonds for mixtures containing up to 0.5 water mole fraction, an observation consistent with existing enthalpy of mixing data, suggesting that the measured negative excess entropy is a result of clustering or micro-immiscibility. Published by AIP Publishing. [http://dx

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“…The overall conclusion of their study indicates that the hydrophobic interactions between tert-butyl groups are responsible for selfaggregation of TBA molecules. 55 Very recently, Ben-Amotz 56 and Rankin 57 have shown that there are no more hydrophobic contacts in aqueous solutions of alcohols ranging from methanol to TBA than in random mixtures of the same concentration. Therefore, hydrophobic interactions between small hydrophobic groups are weaker than thermal energy fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Picosecond Solvation and Rotational Dynamics: An Attempt to Reinvestigate the Mystery of Alcohol–Water Binary Mixtures

et al. 2015

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In this article, we have investigated the anomalous behavior of two alcohol-water (tert-butyl alcohol (TBA)-water and ethanol-water) binary mixtures using femtosecond fluorescence upconversion technique. Recently, Gupta and Patey (Gupta, R.; Patey, G. N. J. Chem. Phys. 2012, 137, 034509(1)-034509(12)) have used four force fields to simulate TBA-water binary mixtures. Surprisingly, two of them do not identify any aggregation of TBA molecules. We have calculated average solvation time of Coumarin 480 (C480) using two different methods. Our results indicate slowdown in solvation time in the mole fraction ranges XT = 0.09-0.15, XT = 0.40-0.46 and XE = 0.06-0.08, XE = 0.20-0.25 for TBA-water and ethanol-water binary mixtures, respectively. Additionally, we have detected another anomalous region at XT ∼ 0.03. Slow solvation responses in the ranges XT = 0.40-0.46 and XE = 0.20-0.25 are probably due to the higher shear viscosity of the medium. However, XT = 0.09-0.15 and XE = 0.06-0.08 are the manifestation of aggregation induced structural transition of alcohol molecules. Hindered rotation of C480 in the ranges XT = 0.04-0.09 and XE = 0.03-0.07 corroborates our solvation dynamics results. From temperature dependent anisotropy measurements, we have shown that aggregation of alcohol molecules increases with increase in temperature.

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Contacts Between Alcohols in Water Are Random Rather than Hydrophobic

Cited by 89 publications

References 39 publications

Molecular Shape and the Hydrophobic Effect

Molecular Shape and the Hydrophobic Effect

Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy

Picosecond Solvation and Rotational Dynamics: An Attempt to Reinvestigate the Mystery of Alcohol–Water Binary Mixtures

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