PROTON-TRANSFER IN ARGININE-CARBOXYLATE INTERACTIONS

Arginine-carboxylate interactions in proteins have aroused much intere st due to the important role they play in the stability of biological systems. These interactions have usually been interpreted as being ass ociated with a zwitterionic state as opposed to a neutral one. In this work, ab initio (6-31G* basis set) calculations were carried out in vacuo on appropriate models, methylguanidinium-acetate and methylguani dine-acetic acid, to simulate the zwitterionic and neutral forms, resp ectively. The results obtained reveal that the neutral form is more st able than the zwitterion, i.e, proton transfer should occur with the c onsequent annihilation of charge in some environments, possibly hydrop hobic ones.