Oil and water do not mix. The disaffinity of oil for water, with its unusual temperature dependence, is called the hydrophobic effect. It is important to understand the factors underlying the hydrophobic effect because they appear to play key roles in membrane and micelle formation, protein folding, ligand-protein and protein−protein binding, chromatographic retention, possibly nucleic acid interactions, and the partitioning of drugs, metabolites, and toxins throughout the environment and living systems. Here, we survey experimental and theoretical studies of nonpolar solute partitioning into water. We note that the hydrophobic effect is not just due to “water ordering” and not merely due to small size effects of water. The properties vary substantially with temperature and solute shape. Also, we discuss the limitations of using oil/water partitioning as the basis for some thermodynamic models in chemistry and biology.

https://pubs.acs.org/doi/pdf/10.1021/jp020104r

A View of the Hydrophobic Effect

Many biochemists would regard pressure as a physical parameter mainly of theoretical interest and of rather limited value in experimental biochemistry. The goal of this overview is to show that pressure is a powerful tool for the study of proteins and modulation of enzymatic activity.

/pdf/high-pressure-effects-on-protein-structure-and-function-18wedkbmnt.pdf

High Pressure Effects on Protein Structure and Function

Novel Process Windows make use of process conditions that are far from conventional practices. This involves the use of high temperatures, high pressures, high concentrations (solvent-free), new chemical transformations, explosive conditions, and process simplification and integration to boost synthetic chemistry on both the laboratory and production scale. Such harsh reaction conditions can be safely reached in microstructured reactors due to their excellent transport intensification properties. This Review discusses the different routes towards Novel Process Windows and provides several examples for each route grouped into different classes of chemical and process-design intensification.

Novel Process Windows for Enabling, Accelerating, and Uplifting Flow Chemistry

Revisiting volume changes in pressure-induced protein unfolding

https://ucanr.edu/datastoreFiles/608-472.pdf

High pressure enhancement of enzymes: A review

The swelling volume of poly(N-isopropylacrylamide) gels in alcohol-water mixtures (C 1 -C 4 ) was measured at 25 o C. The swollen gel in water shrank first with addition of a small amount of alcohol and then reswelled on further addition of alcohol showing a typical reentrant transition. The swelling behavior of the gels was correlated with the properties of the aqueous alcohol mixtures (i.e., the change of alcohol molar volume and thermodynamic activities of alcohol and water). The uptake of ethanol and water in the equilibrated gels was measured at 25 o C. Ethanol was found to be selectively taken up in all aqueous alcohol mixtures

Swelling of poly(N-isopropylacrylamide) gels in water-alcohol (C1-C4) mixed solvents

The solubilities of benzene, toluene, ethylbenzene, and n-propylbenzene in water were measured at 25{degree}C at pressures to 400 MPa (100 MPa for benzene). The maxima in the solubilities are observed at 200, 150, and 140 MPa for toluene, ethylbenzene, and n-propylbenzene, respectively. The volume changes, {Delta}V{degree}, accompanying the solution are estimated at high pressures from the pressure dependences of the solubilities. The compressions of ethylbenzene, n-propylbenzene, and m-xylene were measured at 25{degree}C up to 350 MPa with a mercury-trapped piezometer in order to estimate the molar volumes, V{degree}, of the solutes. The partial molar volumes, V{degree}, of benzene and alkylbenzenes in water at high pressures up to 400 MPa were estimated from the {Delta}V{degree} and V{degree}, and the isothermal partial molar compressibilities, {beta}{sub {tau}}{degree} ({triple bond} 1/V{degree} ({delta}V{degree}/{delta}P){sub {tau}}), were also determined. The {beta}{sub {tau}}{degree} of ethylbenzene and n-propylbenzene at atmospheric pressure were -1.6 {times} 10{sup {minus}4} and {minus}2.1 {times} 10{sup {minus}4} MPa{sup {minus}1}, respectively; these quantities became positive at ca. 50 MPa. The {beta}{sub {tau}}{degree} for the other solutes were positive and decreased with increasing pressure. The compressibilities, {beta}{sub h}, of the hydration shells around the solutes were estimated by a model of the hydration state. The results suggestmore » that the hydration shell is destroyed by compression and disappears above 100 MPa.« less

Effect of pressure on the solubilities of benzene and alkylbenzenes in water

The solubility of toluene, ethylbenzene, and propylbenzene in water was measured over conditions of 0.10−400 MPa and 273.2−323.2 K. Solubility was found to initially increase with increasing pressure and then decrease from a maximum at around 100 or 200 MPa. On the other hand, the solubility−temperature curve at 0.10 MPa exhibited a minimum at around 290 K. The solubility minimum of toluene disappeared at high pressures. The overall solubility−pressure−temperature surface resembles a portion of a distorted hyperboloid. The partial molar volume of these solutes in water was estimated from the pressure coefficient of solubility using the compression of the solutes in the pure liquid state, a property that was also measured in the present study. Expansion coefficient and isothermal compressibility of partial molar volume of hydrophobic groups in water at atmospheric pressure are estimated from literature data. The expansion coefficient of partial molar volume was found to be significantly larger at atmospher...

Effects of Pressure and Temperature on the Solubility of Alkylbenzenes in Water: Volumetric Property of Hydrophobic Hydration

Solubility of α-amino acids in water under high pressure: glycine, l-alanine, l-valine, l-leucine, and l-isoleucine

Excess partial molar enthalpies of 1-propanol, H1PE, in 1-propanol−NaCl−H2O were measured directly, accurately, and in small increments in mole fraction of 1-propanol, x1P, at 25 °C in the range xNaCl < 0.04. xNaCl is the mole fraction of NaCl. The enthalpic interaction function, H1P-1PE, between 1-propanol molecules was then evaluated. H1P-1PE is a convenient, model-free measure for the intermolecular interaction in terms of enthalpy. The behavior of these thermodynamic quantities was compared with that of the binary 1-propanol−H2O. Based on the knowledge accumulated in our laboratory on the binary aqueous 1-propanol, the effect of NaCl on H2O became apparent. Our tentative conclusions are that (1) a NaCl molecule “binds” to seven or eight molecules of H2O on dissolving into H2O, and (2) the reminder of bulk H2O away from solute NaCl is not affected and stays almost the same as pure H2O.

Seiji Sawamura

Papers

Swelling of poly(N-isopropylacrylamide) gels in water-alcohol (C1-C4) mixed solvents

Effect of pressure on the solubilities of benzene and alkylbenzenes in water

Effects of Pressure and Temperature on the Solubility of Alkylbenzenes in Water: Volumetric Property of Hydrophobic Hydration

Solubility of α-amino acids in water under high pressure: glycine, l-alanine, l-valine, l-leucine, and l-isoleucine

Excess Partial Molar Enthalpy of 1-Propanol in 1-Propanol−NaCl−H2O at 25 °C: The Effect of NaCl on Molecular Organization of H2O†