Metal Ion Effects in Isotopic Hydrogen Exchange in Biologically Important Heterocycles

Abstract

The binding of metal ions to heteroatomic centers of biomolecules has been utilized as a probe of metal ion effects in living systems. This article focuses on the effect of N-coordination by transition metals, especially Pt(II), Co(III), Cr(III), on isotopic C(2)-H or C(8)-H exchange of imidazoles, thiazoles, and purines. The usual reactivity trend, protonated >> metalated >> neutral substrate, is excepted for Cr(III)/1-methylimidazole, where Cr(III) activates stronger than H(+). An interplay of factors is considered, including metal-to-ligand back-bonding, electronic structure of metal ions, and differences in crystal field stabilization energy.

Metal-activated histidine carbon donor hydrogen bonds contribute to metalloprotein folding and function

“…This study expands upon our previous work, presenting evidence for another class of strong carbon donor hydrogen bonds in proteins, those donated by imidazole side chains complexed to metals. This is consistent with measured isotopic proton-exchange rates at C-H sites of imidazole, which are enhanced by protonation or metal binding [13,14]. Histidine is a frequent metal ligand in proteins [15], and the importance of metal-activated imidazoles to protein stability and function is worth further examination.…”

“…Later, we compare the strength of these two carbon donors using models of the SOR active site. Previous calculations for neutral and charged imidazole [11,12] and experimentally measured exchange rates in imidazole-metal complexes [13,14] would suggest that interactions at Ce 1 are stronger than at Cd 2 .…”

Metallacrowns as products of the aqueous medium self-assembly of histidinehydroxamic acid-containing polypeptides

“…The deuterium-hydrogen exchange can be analysed as a pseudo-first order process. The kinetics parameter k i (first-order rate constant) of the DHX reaction can be determined as A recent paper 51,52 has demonstrated that binding of metal ions influences the hydrogen-deuterium exchange of the imidazole ring C2-hydrogen in histidine-containing peptides. The k values for the peptide at pH 5.2 and its complex at pH 5.2, 7.2, 7.3, 8.2, and 8.3 are equal to 0 within experimental error limits.…”

(+)-Echinobetaine B: isolation, structure elucidation, synthesis and preliminary SAR studies on a new nematocidal betaine from a southern Australian marine sponge, Echinodictyum sp.

“…2 (+)-Echinobetaine B (6) is a new example of a rare class of naturally occurring imidazole betaine. The first example of this structure class was zooanemonin (12) reported by Ackermann and Menssen in 1960 from the "horse sponge", Hippospongia equina. 7 Although the structure of 12 was revised shortly thereafter (following communication on its synthesis by Woodward and List), 8 few subsequent references have appeared in the scientific literature.…”