PPSA1– partial positively charged molecular surface area
TMSA- total molecular surface area
D.T. Stanton, P.C. Jurs, Anal. Chem., 1990 62, 2323; D.T. Stanton, L.M. Egolf, P.C. Jurs, M.G. Hicks, J. Chem. Inf. Comput. Sci., 1992 32, 306.