THEORETICAL-STUDY OF PROTON AFFINITIES OF SOME N-BASES OF BIOLOGICAL IMPORTANCE

Ab initio SCF (MINI-1 base) and AM1 methods have been used to calculat e the vapour phase proton affinities of substituted methylamines. Our calculations have shown that the MINI-1 proton affinities are superior to those calculated using another minimum basis set (STO-3G). As rega rds the AM1 results, the absolute values of the proton affinities are about 5 % lower than the corresponding vapour phase experimental entha lpies. However, the agreement with experiments is much better for the AM1 method in comparison with the MINI-1 ab initio calculations. Moreo ver, the AM1 quantum-chemical method has been used for the determinati on of the proton affinities of some local anaesthetics.