INVESTIGATION OF HYDRATION OF ALPHA-AMINO-ACIDS BY MEANS OF ABSORPTION MILLIMETER SPECTROSCOPY

The hydration indexes for 19 protein a-amino acids are measured by mea ns of absorption millimeter spectroscopy (AMS) at 31.42 GHz. The plot of the hydration indexes on the area of surface of aliphatic amino aci d molecules accessible fbr water is a straight line located above the points corresponding to aromatic or polar amino acids. The contributio n of nonpolar groups in the hydration index is greater than that of po lar groups provided that their accessible surface areas are equal. The contribution to hydration of -OH and -CONH2 groups in Ser, Gln, and A sn coincides in sign with that of pure hydrophobic hydration but the v alue of the contribution is significantly smaller. The change in mobil ity of water molecules, which is the basis of the AMS method, may serv e as the physicochemical foundation for the construction of a new hydr ophobicity scale for amino acids comparable with the already existing scales.