Lack of reciprocity of proton vicinal coupling constants and chemical shifts in ternary tridentate dipeptidePd(II)-nucleotide complexes

Abstract

In tridentate dipeptide complexes of Pd(II) such as those with glycyltyrosine, the aromatic side chain is directed toward the metal ion. Binding of purine nucleosides or nucleotides at the fourth tetragonal position about Pd(II) results in a marked upfield chemical shift of the H(2) resonance when Pd(II) is at N(7). On the other hand in complexes with st at N(7). On the other hand in complexes with Pd(II) at N(7) neither the chemical shift of the aromatic tyrosyl protons nor the rotamer distribution about the αβ bond in the side chain is affected. Thus there is a lack of reciprocity evidenced by a marked upfield shift of the nucleic base component and the lack of a significant change in chemical shift or coupling constant of the aromatic amino acid side chain in ternary Pd(II) complexes. The results may be accounted for by edge-on binding of the nucleic base so that it is perpendicular to the face of the aromatic amino acid side chain.