A Physicochemical Approach to Interpret the Biological Activities of some Dipeptide Systems

Abstract

The biological activities for four-Iso-nicotinoyl dipepetide systems are attributed to some physiochemical parameters. The semi-empirical MNDO together with the AMI methods, were applied to define these parameters by optimizing the structural energy of the four systems with respect to incremental variation of their backbone dihedral angles. The lowest energetic structures are determined by generating two ECD maps by plotting j11 vs Y1I and Y1 vs +j11 dihedral angles for each of the four systems. The comparison between the lowest energetic structures reveals that these systems have permanent dipole moments. Based on the different susceptibilities of the dipeptide tails to rotate as bonded charged masses around the X-axis of the molecular frame, the Gaussian cylinders characteristic by nine different charged zones could be speculated. The sign of the residual charges on the zones corresponding to the backbone's bonds and side chain residues, which are labelled section 2, are determined as the required physicochemical parameters. It appears that the biological activity of each system is affected by the sign of the charges allocated on the above section of each system. If the charge is +ve then the corresponding dipeptide system(s) should posses biological activities, otherwise the system(s) are biologically inactive.