MOLECULAR CONNECTIVITY MODEL FOR DETERMINATION OF PHYSICOCHEMICAL PROPERTIES OF ALPHA-AMINO-ACIDS

A molecular connectivity model for the calculation of some physicochemical properties of a-amino acids such as molecular weights, molecular volumes, isoelectric points, relaxation times, crystal densities, solubilities, specific rotations, and atom charges is presented. The given model, based on a set of six molecular connectivity indexes, MCI = {D, D(V), 0X, 0X(V), 1X, 1X(V)} gives a good description of all these physicochemical properties, except atom charges. While calculation of isoelectric points and of solubilities requires a connectivity model centered on the connectivity indexes of the functional fragments of the a-amino acids, other properties, with the exception of the atomic charges, are centered on the molecular connectivity indexes of the whole amino acid. A subset composed of three indexes from this set gives also a rather good description of these properties. The molecular connectivity model of the atom charges shows a simple linear correlation between atomic, delta(V) (and delta for sp3 carbons) index and atom charges, broadening thus the meaning of delta and valence delta numbers used to describe the given set of physicochemical properties in alpha-amino acids.