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Proton Affinity of Canavanine and Canaline, Oxyanalogues of Arginine and Ornithine, from the Extended Kinetic Method
journal contribution
posted on 2006-10-12, 00:00 authored by Erica J. Andriole, Kathryn E. Colyer, Elizabeth Cornell, John C. PoutsmaThe absolute proton affinities of the nonprotein amino acids canavanine and canaline have been determined
using the extended kinetic method in an electrospray ionization quadrupole ion trap instrument. Canavanine
results from the substitution of an oxygen atom for the δ-CH2 group in the side chain of the protein amino
acid arginine, whereas canaline results from a similar substitution at the δ-CH2 group in the side chain of
ornithine. Absolute proton affinities of 1001 ± 9 and 950 ± 7 kJ/mol are obtained for canavanine and canaline,
respectively. For canaline, this proton affinity is in excellent agreement with theoretical predictions obtained
using the hybrid density functional theory method B3LYP/6-311++G**//B3LYP/6-31+G*. For canavanine,
theory predicts a somewhat larger proton affinity of 1015 kJ/mol. Oxygen atom substitution in these nonprotein
amino acids results in a decrease in their proton affinities of 40−50 kJ/mol compared to arginine and ornithine.