Entropy of Hydrophobic Hydration: A New Statistical Mechanical Formulation

1992 ◽  
Vol 278 ◽  
Author(s):  
Themis Lazaridis ◽  
Michael E. Paulaitis
Keyword(s):  
Correlation Functions ◽  
Water Structure ◽  
Hydrophobic Hydration ◽  
Dilute Solution ◽  
Hydrophobic Behavior ◽  
Mechanical Formulation ◽  
Polyatomic Fluids ◽  
Statistical Mechanical ◽  
Simple Molecules ◽  
Solute Water

AbstractA statistical mechanical formulation is presented for the entropy of solution of simple molecules in water. The formulation is based on the Green-Wallace expansion for the entropy in terms of multiparticle correlation functions, which is derived here for rigid polyatomic fluids and for mixtures. With a factorization assumption for the solute-water correlation function we have been able to separate the translational and orientational contributions to the entropy of solution. This approach is applied to an infinitely dilute solution of methane in water. The required correlation functions are obtained by Monte Carlo simulation. The orientational contribution, which is due directly to the orientational asymmetry of water-water interactions, is found to be comparable to the translational contribution. We find that the large entropies and heat capacities of hydrophobic hydration can be accounted for by solute-water correlations alone and that large perturbations in water structure are not required to explain hydrophobic behavior.

Comment on "Entropy of hydrophobic hydration: a new statistical mechanical formulation"

1993 ◽  
Vol 97 (21) ◽  
pp. 5788-5788 ◽  
Author(s):  
David E. Smith ◽  
Brian B. Laird ◽  
A. D. J. Haymet
Keyword(s):  
Hydrophobic Hydration ◽  
Mechanical Formulation ◽  
Statistical Mechanical

Motions of water molecules in dilute aqueous solutions of tertiary butyl alcohol; a neutron scattering study of hydrophobic hydration

1970 ◽  
Vol 319 (1537) ◽  
pp. 189-208 ◽  
Keyword(s):  
Aqueous Solutions ◽  
Water Structure ◽  
Hydrophobic Hydration ◽  
Step Length ◽  
Solute Concentration ◽  
Butyl Alcohol ◽  
Tertiary Butyl ◽  
Self Diffusion ◽  
Dilute Aqueous Solutions ◽  
Neutron Scattering Study

Cold neutron inelastic scattering experiments have been performed on dilute aqueous solutions of (CD 3 ) 3 COH and of solutions of (CH 3 ) 3 COH in D 2 O at 21 °C. From the broadening of the quasi-elastic peak and independently determined self-diffusion coefficients ( D ), diffusive lifetimes ( c ) of H 2 O molecules have been calculated as functions of solute concentration. The product Dc is insensitive to concentration, giving a mean diffusion step length of 0.14 nm. The inelastic portion of the spectrum, reflecting lattice-like hydrogen bonding modes indicates that the solute enhances the water ‘structure’ but that such structure bears no resemblance to ice.

Statistical-mechanical formulation of the Willshaw model with local inhibition

1991 ◽  
Vol 43 (12) ◽  
pp. 7012-7018 ◽  
Author(s):  
G. M. Shim ◽  
D. Kim ◽  
M. Y. Choi
Keyword(s):  
Local Inhibition ◽  
Mechanical Formulation ◽  
Statistical Mechanical

scholarly journals Water structure changes in oxime-mediated reactivation process of phosphorylated human acetylcholinesterase

2018 ◽  
Vol 38 (3) ◽  
Author(s):  
Irina V. Zueva ◽  
Sofya V. Lushchekina ◽  
Patrick Masson
Keyword(s):  
Ammonium Sulphate ◽  
Water Structure ◽  
Free Water ◽  
Hydrophobic Hydration ◽  
Nucleophilic Attack ◽  
Water Molecules ◽  
Neutral Salt ◽  
Salting Out ◽  
Hi 6 ◽  
Structure Changes

The role of water in oxime-mediated reactivation of phosphylated cholinesterases (ChEs) has been asked with recurrence. To investigate oximate water structure changes in this reaction, reactivation of paraoxon-inhibited human acetylcholinesterase (AChE) was performed by the oxime asoxime (HI-6) at different pH in the presence and absence of lyotropic salts: a neutral salt (NaCl), a strong chaotropic salt (LiSCN) and strong kosmotropic salts (ammonium sulphate and phosphate HPO42−). At the same time, molecular dynamic (MD) simulations of enzyme reactivation under the same conditions were performed over 100 ns. Reactivation kinetics showed that the low concentration of chaotropic salt up to 75 mM increased the percentage of reactivation of diethylphosphorylated AChE whereas kosmotropic salts lead only to a small decrease in reactivation. This indicates that water-breaker salt induces destructuration of water molecules that are electrostricted around oximate ions. Desolvation of oximate favors nucleophilic attack on the phosphorus atom. Effects observed at high salt concentrations (>100 mM) result either from salting-out of the enzyme by kosmotropic salts (phosphate and ammonium sulphate) or denaturing action of chaotropic LiSCN. MDs simulations of diethylphosphorylated hAChE complex with HI-6 over 100 ns were performed in the presence of 100 mM (NH4)2SO4 and 50 mM LiSCN. In the presence of LiSCN, it was found that protein and water have a higher mobility, i.e. water is less organized, compared with the ammonium sulphate system. LiSCN favors protein solvation (hydrophobic hydration) and breakage of elelectrostricted water molecules around of oximate ion. As a result, more free water molecules participated to reaction steps accompanying oxime-mediated dephosphorylation.

scholarly journals Sum frequency generation, calculation of absolute intensities, comparison with experiments, and two-field relaxation-based derivation

2020 ◽  
Vol 117 (6) ◽  
pp. 2805-2814 ◽  
Author(s):  
Kai Niu ◽  
Rudolph A. Marcus
Keyword(s):  
Sum Frequency Generation ◽  
Water Interface ◽  
Sum Frequency ◽  
Single Term ◽  
Mechanical Formulation ◽  
Air Water Interface ◽  
Statistical Mechanical ◽  
The Absolute ◽  
Frequency Generation ◽  
Motional Narrowing

The experimental sum frequency generation (SFG) spectrum is the response to an infrared pulse and a visible pulse and is a highly surface-sensitive technique. We treat the surface dangling OH bonds at the air/water interface and focus on the absolute SFG intensities for the resonant terms, a focus that permits insight into the consequences of some approximations. For the polarization combinations, the calculated linewidths for the water interface dangling OH SFG band at 3,700 cm−1 are, as usual, too large, because of the customary neglect of motional narrowing. The integrated spectrum is used to circumvent this problem and justified here using a Kubo-like formalism and theoretical integrated band intensities rather than peak intensities. Only relative SFG intensities are usually reported. The absolute integrated SFG intensities for three polarization combinations for sum frequency, visible, and infrared beams are computed. We use molecular dynamics and the dipole and the polarizability matrix elements obtained from infrared and Raman studies of H2O vapor. The theoretical expressions for two of the absolute susceptibilities contain only a single term and agree with experiment to about a factor of 1.3, with no adjustable parameters. The Fresnel factors are included in that comparison. One of the susceptibilities contains instead four positive and negative terms and agrees less well. The expression for the SFG correlation function is normally derived from a statistical mechanical formulation using a time-evolving density matrix. We show how a derivation based on a two-field relaxation leads to the same final result.

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