Solvation and Conformation of Proteins

The results obtained by measuring the affinity to oxygen in the presence of various monohydric alcohols (methanol, ethanol, 2-propanol, 1-propanol) 140-144 were interpreted in terms of the Monod-Wyman-Changeux model145), by which the change of the standard free-energy difference between R and T state in the absence of oxygen, due to the addition of alcohol, can be determined, i.e. 

C is the alcohol concentration. The AAG°(C) plots against the inverse dielectric constant of the solvent showed that at low alcohol concentration all points measured are on a single straight line for all the alcohols used. At higher alcohol concentrations, however, the AAG° values are situated on different curves I45 One can conclude that 

1) at low alcohol concentrations contribution to AAG°(C) linearly depending on the inverse dielectric constant of the solvent (bulk electrostatic contributions) are predominant  

2) With increasing alcohol concentration non-bulk electrostatic contributions become relevant. Because these non-bulk electrostatic contributions depend on the concentration of the cosolvent as well on the size of the alkyl-group, one can conclude that there is a relation to the smaller free energy necessary for exposing hydrophobic surfaces to the medium. It yields  

A thermodynamic analysis regarding the relation between enthalpy and entropy values on the one hand and non-bulk electrostatic contributions on the other leads to the same result144). 

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