Transport of alkyl homologs across synthetic and biological membranes: A new model for chain length‐activity relationships

The ability of each member of a biologically active homologous series to reach the receptor site can often be equated with its relative ability to permeate biological barriers. This paper presents a structure‐activity model based entirely on firmly established diffusional theories as well as solubility relationships generally applicable to aqueous systems. The equations derived and presented here were previously experimentally verified using synthetic membranes. These equations are generally applicable for transport across membranes and can be of use in describing a variety of passive absorption or permeation phenomena. Since true equilibrium is rarely attained in biological systems, a kinetic model provides an appropriate description of the physiological situation. Furthermore, a kinetic model offers considerable practical utility, because it can readily be incorporated into the overall pharmacokinetic treatment.