Theoretical study for partial molar volume of amino acids and polypeptidesby the three-dimensional reference interaction site model

We calculate the partial molar volume (PMV) of 20 amino acids in aqueous so lution at infinite dilution by using the Kirkwood-Buff equation and the thr ee-dimensional reference interaction site model (3D-RISM) integral equation theory for molecular liquids. As compared to the conventional, one-dimensi onal (1D-RISM) approach, the results exhibit drastic improvement for the qu antitative agreement with experiments. The deviation from the experimental data seen for the relatively large amino acids is discussed in terms of the "ideal fluctuation volume" introduced in the previous study based on the 1 D-RISM. Robustness of the new approach is further demonstrated by applying it to the PMV of polyglutamic acids in aqueous solution. The method provide s reasonable account for the PMV increase with the chain length, both in al pha -helical and extended structures, whereas the 1D-RISM approach gives an unnatural decrease of the PMV for the alpha helix with a complete turn of the backbone. (C) 2001 American Institute of Physics.