Ternary complex formation between model nucleobases and [Pd(gly-L-met)] 1 (gly-L-met = dianion of glycylmethionine, deprotonated at the amide N and at the met carboxylate terminus) has been studied by 1H NMR spectroscopy and potentiometry. A representative example, [Pd(gly-L-metH)(Hmgua)]NO3·H2O 3 (Hmgua = 9-methylguanine), has been characterized by X-ray crystallography. Co-ordination of Pd is through the terminal amino group of the glycyl entity, the deprotonated amide nitrogen, S of the methionine, and N7 of the purine nucleobase. The carboxylic acid group of methionine is protonated. In aqueous solution binding of Pd to other nucleobases occurs via N3 in the case of 1-methylcytosine (Hmcyt) and of deprotonated 1-methyluracil, N7 of 9-ethylguanine (Hegua) or N1, N7/N1 of the guanine anion (egua). Discrete rotamers form on binding of Pd to N3 of the pyrimidine nucleobases and to N1 of the guanine. The gly-L-metH resonances provide no evidence for the existence of stable diastereomers, suggesting that inversion at the chiral S atom of met is fast. In contrast, both [Pt(gly-L-metH)Cl] and its ternary derivative with Hmcyt appear to be present in solution as diastereomeric mixtures. Stability constants have been determined for ternary complexes formed from 1 and [Pd(gly-L-metH)Cl], respectively, with nucleobases.
|Number of pages||6|
|Journal||Journal of the Chemical Society - Dalton Transactions|
|Publication status||Published - Feb 21 1997|
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