Secondary deuterium isotope effects on the acidity of glycine

Secondary deuterium isotope effects (IE) on the acidity (pKa) of glycine were measured by 13C NMR titration. It was found that deuteration decreases the pKa by 0.034 ± 0.002. The experimental data are supported by theoretical calculations, which, in turn, allowed to relate the acidity decrease to the lowering of glycine vibrational frequencies upon deuteration.