Conformation of Peptide Model Molecules in Alcohol-Water Mixtures and Its Pressure Dependence

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The present investigation has focused on alcohol-induced protein folding to clarify its mechanism at fee molecular level. Firstly, structure and size of solvent clusters predominantly formed in various alcohol-water mixtures have been investigated by using X-ray and neutron scattering techniques. It has been shown that the larger the hydrophobic group of alcohols, the more the tetrahedral-like structure of water is disrupted at low alcohol concentration, result in that alcohol molecules easily aggregate to form solvent clusters. In particular, the results from small-angel neutron scattering experiments have shown that fluoroalcohols of trifluoroethanol(TFE) and hexafluoroisopropanol(HFIP) significantly form solvent clusters in their aqueous solutions. These findings, together with the fact that the fluoroalcohols more strongly induce protein folding than aliphatic alcohols, such as ethanol(EtOH) and 2-propanol(2-PrOH), suggest the relation between cluster formation and protein folding.Solvation behavior of 1,4-pentanediol molecule, which involves a hydrophobic hydrocarbon chain and two hydrophilic hydroxyl groups, as a model of peptide molecule in various alcohol-water mixtures has been investigated by using infrared spectroscopy and NMR. The results have suggested that addition of ethanol and 2-propanol into aqueous 1,4-pentanediol solution induces to dehydration from the hydroxyl groups of 1,4-pentanediol molecule, whereas TFE and HFIP strongly interact to the hydrocarbon chain. It has also been shown that the hydrophobic interaction between alcohol molecule and the hydrocarbon chain of 1,4-pentanediol molecule is more stronger in the sequence of HFIP>TFE>EtOH【approximately equal】2-PrOH. This sequence is in agreement with that for the effect of alcohol on protein folding. The present investigation has suggested that interaction between alcohol clusters and protein molecule significantly contributes to protein folding.