Macromolecular environment effect on : breaking and making of S – S linkages via nucleophilic substitution

A possible scheme for breaking a disulfide bond and making another one with a new cystein side chain based upon a nucleophilic mechanism has been analysed on the basis of-fully optimized 4-31G* ab-initio computations of the reaction : [math] The energy barrier in vacuuo is found to be 0.5 kcal/mol. Under the influence of a solvent and/or a polarizable macromolecular surroundings, the barrier is raised to 3.5 kcal/mol. The case of a mechanism in which the neutral disulfide bond is attacked by an anionic cystein group is expected to be energetically comparable. The influence of the electrostatic interactions with the macromolecule is discussed

Ab-initio SCF calculations on conformational space of peptides models

N-formyl-lycine-amide, N-formyl- D and L- alanine-amide and N-formyl-L- valine-amide were subjected to ab-initio SCF conformational study. The topology of their Potential Energy Hyper-Surface revealed to be somewhat, different from the ideal surfaces predicted by multidimensional conformational analysis, and the introduction of a side-chain as another variable to the system showed its influence. In certain cases the relative stabilization of the minima was found to be reversed, and some of the minima disappeared from the potential surfaces, as a consequence of strong interaction between the amino-acid backbone and the side-chain. It appeared that the effects associated with those attractive and repulsive interactions could be properly described at the ab-initio SCF level of theory