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Structure-activity relationships for biologically active congeneric compounds were examined by using free-energy-related physicochemical parameters and regression technique. The steric effects involved in such biological activities were expressible and separable from other factors as steric parameters depending upon the situations. In this article, examples for enzyme reactions, enzyme inhibitions, insecticides, fungicides, herbicides, plant growth regulators and synthetic sweetners, mostly from our own laboratory are reviewed. The steric parameters used here are Taft Es, Hancock Esc, Verloop STERIMOL and van der Waals molar volume. [ABSTRACT FROM AUTHOR]

This section reviews the molecular shape descriptors developed by Amoore, Allinger, Simon et al. and Testa and Purcell. The illustrative examples discussed refer to the odour similarity and cardiotoxic aglycones. One has stressed the methods based on the reference structure because, correctly formulated, these methods seem to offer promising perspectives to model the steric effects in biological systems. Finally, a short discussion of possible connections between steric and other substituent constants (relevant in the context of multicollinearity in QSAR) is included. [ABSTRACT FROM AUTHOR]

The definition of steric parameters initially based on Van der Waals raddi (rv) is described. Tables of various sets of rv are given. These different types of rv are shown to be interrelated. The rv values of Bondi are chosen as the standard set. Substituents are classified according to the degree of conformational dependence of their steric effect. Values of the steric parameters v are obtained directly from rv whenever possible. For symmetric MZn groups they are obtained from calculated rv values. For planar π-bonded groups equations are derived which permit the calculation of both v and the corresponding delocalized electrical effect parameters. Values of v for other grups are based on kinetic data scaled by correlation with groups for which v is known. Over 300 values of v are reported. [ABSTRACT FROM AUTHOR]

This chapter deals with the description of the main topological indices and of related indicatros for molecular constitution used in structure-activity relationships (QSAR). The topological indices are numerical quantities based on various invariants or characteristics of molecular graphs. For the convenience of the discussion, these indices are classified according to their logical derivation from topological invariants, rather than according to their chronological development. [ABSTRACT FROM AUTHOR]