Relationships between the biological and physicochemical properties of series of compounds.

An equilibrium model is described for relationships between the biological activity and the physicochemical properties of compounds in a congeneric series. An equation derived from the model is of the form, log C = log (a + 10-alpha) = b, where C is the total molar concentration of drug to produce a standard response, alpha ia a parameter of the form log K where K is an equilibrium constant, and a and b are coefficients. This equation provides a plausible fit to some nonlinear observations which have been studied.