Abstract
The NMR spectra of 14N, 15N, and 17O for complexes formed between calcium(II) and glycine, DL-alanine, and β-alanine were measured so that the Ca(II)-binding sites within the complexes were deduced. The addition of Ca 2+ to solutions containing amino acids caused further broadening of the signals due to 14N and 17O nuclei of natural abundance. This may be taken as evidence that Ca 2+ binds to both the amino and carboxylate groups within the complexes. The 17O signals were clearly observed for the amino acids with naturally abundant 17O when dissolved in 16O-enriched water. This implies that the amino acids should not always be enriched with 17O, if 16O-enriched water is used as the solvent. Upon addition of Ca 2+ to the solution containing 15N enriched glycine, no noticeable chemical shift was observed with reference to the 15N signal of the glycine only. This might be due to the fact that Ca 2+ is expected to bind very weakly to the ligand in view of the very small stability constant. This suggests that the routine 14N NMR would make useful contributions to the study of weak metal-nitrogen interactions.
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