Nitrogen-15 NMR study of complexation of 1-methylimidazole by zinc(II) and cadmium(II) in aqueous solution

The /sup 15/N NMR study of complexation of 1-methylimidazole (1-MeIM) with Zn/sup 2 +/ or Cd/sup 2 +/ was undertaken to predict more accurately the effects of metal complexation on imidazol-ring /sup 15/N shifts in biological systems when the two nitrogens are usually distinguishable. The data indicated that complexation of 1-MeIM by both metals led to a large upfield shift at /sup 15/N/sub 3/ and an order of magnitude smaller downfield shift at /sup 15/N/sub 1/. Also, earlier observations that replacement of a proton by a methyl group at N/sub 1/ does not greatly alter the /sup 15/N NMR properties of the imidazole-ring nitrogens are substantiated. The data for the /sup 15/N/sub 3/ shift in the two systems correlate well with expected relative magnitudes and trends in the stepwise intrinsic formation constants for the complex systems, but the data are not sufficiently precise to establish values or trends for the stepwise formation constants. (BLM)