This paper presents a molecular connectivity model of the atomic charges in amino acids. Despite many crude approximations of the theoretical treatment, that study led to the determination of charge distributions that permitted a fairly quantitative interpretation of the proton chemical shifta of the amino acids. Years ago, Del Re et al.3 presented a systematic study of the electronic structure of a-amino acids. The problem is that charge distributions in an entire class of pharmacological molecules are largely unknown and normally have to be estimated from resonance structures and from electronegativities of particular atoms.

A QSAR (quantitative structure-activity relationship)model of the isoelectricpoints of amino acids has been presented.2 A correlation between connectivity indexes and isoelectric points is appropriate, because this bulk property (i.e., isoelectric point) depends highly on the presence of ionizable groups in the molecule.2 Most of the receptor maps rely strongly on localized charge patterns that mirror the supposed distribution in the molecule to be bound therefore an effort to correlate activity with measured charges on particular atoms of a molecule would be highly rewarding.

Much effort in the realm of structur*activity work has been made in correlating activity with measured bulk molecular properties1 of nonionizable molecules. A similar correlation was found for nucleotide bases. A correlation was found between the valence delta (sy) index from molecular connectivity theory and the charges on atoms that belong to the same class, whereas different classes of carbon atoms had the same slopes on the 0versus a' matrix, where 0 is the calculated charge distribution. Ab8tmct 0 A molecular connectivity model of atomic charges on the second-row atoms in a-amino acids is discussed. October 1992 Volume 81, Number 10 JOURNAL OF PHARMACEUTICAL SCIENCES A publication of the American Pharmaceutical Assodation ARTICLES Molecular Connectivity: Treatment of the Electronic Structure of Amino Acids LIONELLO POGLIANI Received July 23, 1991, from the Dip8rtimento di Chimica, Universith della Calabria, 87030 Rend8 (CS), kaly.

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