Comparison of the Proton(H+)and Alkali Metal Ion (Li+,Na+and K+)Binding Affinities of Pyruvate and Oxamate Anions in the Gas Phase.Quantum-Chemical Studies

摘要

Proton affinity(PA),lithium,sodium and potassium cation affinities(CA)in the gas phase were estimated by Gaussian-2(G2),Moller-Plesset(MP2)methods and/or hybrid density functional theory calculations(B3LYP)for pyruvate and oxamate anions.Comparison of these affinities shows that the COO~-groups of both anions have similar basicities.Differences between their calculated PAs as well as between their calculated CAs are not larger than 3 kcal mol~(-1).Somewhat larger differences are evidenced for the formations of the alkali metal complexes with the cation located between the oxygen atoms of the ~(alpha)C=O and COO~-groups for which the lithium,sodium and potassium cation affinities are larger for oxamate than for pyruvate(by 4+0.5 kcal mol~(-1)at the G2 level and by 6±0.5 kcal mol"1 at the DFT(B3LYP)/6-31++G** level).This is a consequence of the chelate effect on the cation binding seen on the calculated most stable structures of the ad-ducts.