Reactions of two platinum(II) complexes
[Pt(dien)Cl]+ and
[Pt(Gly-Met-S,N,N´)Cl],
in which dien is diethylenetriamine and Gly-Met is the dipeptide
glycyl-L-methionine coordinated through the sulfur and two nitrogen atoms,
with N-acetylated dipeptide L-methionyl-L-histidine
(MeCO-Met-His) have been studied by 1H n.m.r.
spectroscopy. All reactions were carried out in 50 mM phosphate buffer at pD
7.4 and at room temperature. In the initial stages of the reactions both
platinum(II) complexes form a kinetically favoured platinum–peptide
complex with unidentate coordination of MeCO-Met-His through the sulfur atom
of the methionine residue. In the second stages of the reaction an
intramolecular migration of a
[Pt(dien)]2+ unit from the sulfur to the
nitrogen atom of imidazole has been observed. This migration reaction is very
slow and strongly selective to the N 1 atom of the imidazole ring of the
histidine side chain. No migration of the platinum(II) complex was observed in
the reaction between
[Pt(Gly-Met-S,N,N´)Cl]
and the dipeptide MeCO-Met-His. It was found that the latter complex, with a
more sterically hindered Gly-Met ligand, reacts more slowly with
thioether-containing molecules than
[Pt(dien)Cl]+ and forms a more stable
platinum–sulfur bond. This study is an important step in the development
of new platinum(II) complexes for selective covalent modification of peptides
and proteins.
Ultraviolet Resonance Raman Study of Side Chain Electrostatic Control of Poly-l-Lysine Conformation
