T. Marino et al., Potential energy surfaces for the gas-phase interaction between alpha-alanine and alkali metal ions (Li+, Na+, K+). A density functional study, INORG CHEM, 40(25), 2001, pp. 6439-6443
The conformations of alpha -alanine and those-of the eight most stable addu
cts that it forms with lithium, sodium, and potassium cations were studied
by means of the density functional theory using the hybrid B3LYP exchange c
orrelation potential and the 6-311++G** basis set. Minima and transition st
ates characterizing the energetic paths for the interaction of the three me
tal ions with the free amino acid were explored in detail, and the results
show that they are almost the same in the cases-of lithium and sodium ions.
At the absolute minimum, the Li+ and Na+ cations appear to be contemporane
ously linked to the carbonyl oxygen and nitrogen atoms of alpha -alanine. S
light differences were found for potassium; the most stable adduct has the
cation coordinated to both oxygen atoms of carboxyl function. The influence
of the low-energy conformers in the determination of the gas-phase absolut
e affinities is demonstrated.