PROTON AFFINITIES OF LYSINE AND HISTIDINE - A THEORETICAL CONSIDERATION OF THE DISCREPANCY BETWEEN EXPERIMENTAL RESULTS FROM THE KINETIC AND BRACKETING METHODS

Ab initio quantum chemical computations in conjunction with semiempirical methods have been applied to the proton affinities of the amino acids lysine and histidine. The data obtained show that lysine is much more basic than histidine. The results reported here agree well with recent bracketing measurements of the proton affinities but contradict other measurements made by the kinetic method. The reason for this disagreement is discussed.