Comparison of ¹³C NMR chemical shifts of 2-aminovaleric acid, L-methionine and DL-selenomethionine and their interactions with aurothiomalate in aqueous solution

The¹³C NMR chemical shifts of DL-selenomethionine were measured and compared with L-methionine and 2-aminovaleric acid in neutral and basic aqueous solutions. The Cγ and Cδ carbons which are directly attached to the sulphur atom of L-methionine experience a shielding effect compared to the Cγ and Cδ of 2-amonivaleric acid resonances. However, shielding effects were observed on Cγ and Cδ resonances when S was substituted by Se, i.e., on going from L-methionine to DL-selenomethionine. The interaction of L-methionine and DL-selenomethionine with aurothiomalate was also studied. The results show that L-methionine does not bind to gold(I) at any pH. However, there is a weak binding observed with DL-selenomethionine in basic aqueous solutions, as seen by ¹³C NMR spectroscopy.