Aqueous Solutions of Nonpolar Gases<sup>1</sup>

Pierotti, Robert A.

doi:10.1021/j100885a043

Cited by 479 publications

(221 citation statements)

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“…The simulation results for liquid hydrocarbons were tested against experiment (21,23) by calculating the heats of vaporization and densities of the liquid hydrocarbons; the estimated and experimental values agreed within 2% for alkanes with six or fewer carbon atoms (23). Lee's goal (14) in 1991 was to test how well scaled particle theory calculates the cavity work, as his 1985 model for the hydrophobicity of water [based on the small size of the water molecule (13)] relied on calculations made with scaled particle theory, as did much of the earlier work on the hydrophobicity of water (24,25). In contrast to scaled particle theory, the solute insertion model (14,15) is not based on the hard sphere assumption.…”

Section: Resultsmentioning

confidence: 99%

Gas-liquid transfer data used to analyze hydrophobic hydration and find the nature of the Kauzmann-Tanford hydrophobic factor

Baldwin

2012

Proc. Natl. Acad. Sci. U.S.A.

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Hydrophobic free energy for protein folding is currently measured by liquid-liquid transfer, based on an analogy between the folding process and the transfer of a nonpolar solute from water into a reference solvent. The second part of the analogy (transfer into a nonaqueous solvent) is dubious and has been justified by arguing that transfer out of water probably contributes the major part of the free energy change. This assumption is wrong: transfer out of water contributes no more than half the total, often less. Liquidliquid transfer of the solute from water to liquid alkane is written here as the sum of 2 gas-liquid transfers: (i) out of water into vapor, and (ii) from vapor into liquid alkane. Both gas-liquid transfers have known free energy values for several alkane solutes. The comparable values of the two different transfer reactions are explained by the values, determined in 1991 for three alkane solutes, of the cavity work and the solute-solvent interaction energy. The transfer free energy is the difference between the positive cavity work and the negative solute-solvent interaction energy. The interaction energy has similar values in water and liquid alkane that are intermediate in magnitude between the cavity work in water and in liquid alkane. These properties explain why the transfer free energy has comparable values (with opposite signs) in the two transfers. The current hydrophobic free energy is puzzling and poorly defined and needs a new definition and method of measurement. solvation free energy | hydrophobicity | protein energetics | Ostwald coefficient | Pratt-Chandler analysis E ver since Kauzmann's revolutionary proposal (1) in 1959, the hydrophobic factor has been widely acknowledged as a major factor in protein folding energetics (1-3). In the widely used Kauzmann-Tanford approach to measuring it, hydrophobic free energy is synonymous with hydrophobic hydration and is measured by the preference of a nonpolar solute for a reference solvent over water, based on the solute's relative solubility in the two solvents. This approach is still the standard one, although it has been criticized. Much of the current research into the nature of the hydrophobic factor is based on computer simulations (4). The basic criticism of the liquid-liquid transfer approach is that gasliquid transfer (which is better understood) is used to determine the solvation free energy of the nonpolar solute. Moreover, the choice of a reference solvent ought not to change the apparent hydrophobic free energy, but it does (5). The purpose here is to investigate these criticisms with the aid of gas-liquid transfer results and their interpretation.The 1971 paper by Nozaki and Tanford (2) is often cited as the starting point of quantitative work on measuring hydrophobic hydration. However, as ref. 2 emphasizes, it was based on the protocol developed in the Cohn and Edsall laboratory at Harvard by McMeekin, et al. (6) who used it to investigate the water solubility of polar as well as nonpolar protein side chains. The latter au...

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Section: Resultsmentioning

confidence: 99%

Gas-liquid transfer data used to analyze hydrophobic hydration and find the nature of the Kauzmann-Tanford hydrophobic factor

Baldwin

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…) and we recover the standard equations for scaled particle theory (SPT) (10,21) in which the solvent (e.g., pure water) is homogeneous with respect to particle size. This form of SPT has been used, for example, to study solvation of apolar solutes in water (21).…”

Section: Theorymentioning

confidence: 99%

“…This form of SPT has been used, for example, to study solvation of apolar solutes in water (21). The other limit,…”

Section: Theorymentioning

confidence: 99%

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Sharp

2015

Proc. Natl. Acad. Sci. U.S.A.

142

129

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The aqueous milieu inside cells contains as much as 30-40% dissolved protein and RNA by volume. This large concentration of macromolecules is expected to cause significant deviations from solution ideality. In vivo biochemical reaction rates and equilibria might differ significantly from those measured in the majority of in vitro experiments that are performed at much lower macromolecule concentrations. Consequently crowding, a nonspecific phenomenon believed to arise from the large excluded volume of these macromolecules, has been studied extensively by experimental and theoretical methods. However, the relevant theory has not been applied consistently. When the steric effects of macromolecular crowders and small molecules like water and ions are treated on an equal footing, the effect of the macromolecules is opposite to that commonly believed. Large molecules are less effective at crowding than water and ions. There is also a surprisingly weak dependence on crowder size. Molecules of medium size, ∼5 Å radius, have the same effect as much larger macromolecules like proteins and RNA. These results require a reassessment of observed high-concentration effects and of strategies to mimic in vivo conditions with in vitro experiments. T he milieu inside cells contains a large amount of solutes that include small ions, metabolites, and macromolecules. Typical protein/RNA concentrations range from 300 mg/mL to 400 mg/mL or about 30-40% by weight. These are 10-fold or more higher than the macromolecular concentrations usually encountered in in vitro measurements and could lead to significant nonideality in solution behavior. The possibility that in vivo biochemical reaction rates and equilibria might be quite different from measured values due to this nonideality has stimulated considerable research. Macromolecular crowding in particular has stimulated a large number of studies, which have been extensively reviewed (1-5). Crowding has been variously described as physical occupation of volume by the macromolecules, which is then unavailable to other molecules, as an excluded volume effect, as a nonspecific effect due to steric repulsion, and as eliminating positions at which the protein can be placed (2, 5, 6). The other contribution to nonideality is from interactions between various solution components, either attractive or repulsive-repulsive interactions distinct from the van der Waals core repulsion or steric factor underlying crowding. We know very little about the contribution of intersolute interactions to nonideality in vivo. Crowding has been more extensively studied because the steric or excluded volume of a macromolecule is a welldefined property, it is always present, and its qualitative effect on biochemical reactions seems obvious (2). However, as I demonstrate in this paper, the effect of crowding macromolecules on a biochemical reaction is not obvious, the relevant theory has not been consistently applied, and indeed the effect is opposite to that commonly believed.Analyses of the effect of crowding mac...

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“…It provides an analytically convenient expression for the solvation free energy of hard-sphere solute [13,14]. In this theory, the detailed interaction and structure of the solution are not taken into account explicitly and affect the solvation free energy of the hard-sphere solute only through the solvent density ρ, pressure P , and temperature T of the system.…”

Section: Theory and Methodologymentioning

confidence: 99%

“…We evaluate the free energy of hydration over a wide range of size, and discuss the volume dependence to connect macroscopic and microscopic behaviors. The hydration free energy is calculated using 4 approaches: (1) method of energy representation, [1][2][3][4] (2) information-theoretic approach, [5][6][7] (3) reference interaction site model (RISM), [8][9][10][11][12] and (4) scaled-particle theory [13,14]. (1), (2), and (3) are molecular approaches in the sense that the structural information of the solution needs to be incorporated, while (4) is not a molecular scheme in that sense.…”

Section: Introductionmentioning

confidence: 99%

Hydration free energy of hard-sphere solute over a wide range of size studied by various types of solution theories

Matubayasi¹,

Kinoshita²,

Nakahara³

2007

Condens. Matter Phys.

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The hydration free energy of hard-sphere solute is evaluated over a wide range of size using the method of energy representation, information-theoretic approach, reference interaction site model, and scaled-particle theory. The former three are distribution function theories and the hydration free energy is formulated to reflect the solution structure through distribution functions. The presence of the volume-dependent term is pointed out for the distribution function theories, and the asymptotic behavior in the limit of large solute size is identified. It is indicated that the volume-dependent term is a key to the improvement of distribution function theories toward the application to large molecules.

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Aqueous Solutions of Nonpolar Gases¹

Cited by 479 publications

References 9 publications

Gas-liquid transfer data used to analyze hydrophobic hydration and find the nature of the Kauzmann-Tanford hydrophobic factor

Gas-liquid transfer data used to analyze hydrophobic hydration and find the nature of the Kauzmann-Tanford hydrophobic factor

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Hydration free energy of hard-sphere solute over a wide range of size studied by various types of solution theories

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Aqueous Solutions of Nonpolar Gases1

Cited by 479 publications

References 9 publications

Gas-liquid transfer data used to analyze hydrophobic hydration and find the nature of the Kauzmann-Tanford hydrophobic factor

Gas-liquid transfer data used to analyze hydrophobic hydration and find the nature of the Kauzmann-Tanford hydrophobic factor

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Hydration free energy of hard-sphere solute over a wide range of size studied by various types of solution theories

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Aqueous Solutions of Nonpolar Gases¹