The tripeptide glutathione binds to the platinum(II) atom via the thiolato anion in the cysteine side chain. Conformation of the complex [Pt(trpy)GS]+ dissolved in a mixture of dimethylformamide-d7 and water at −15°C is determined by a combination of molecular-mechanics calculations, molecular-dynamics calculations, and two-dimensional cross-relaxation 1H NMR spectroscopy. The viscous solvent and low temperature bring the complex into the spin-diffusion regime, so that cross-relaxation rates can accurately be determined. Interproton distances obtained from these rates serve as constraints in the minimization of molecular potential energy by standard methods. There are hydrophobic interactions between the glutamyl methylene groups in the glutathionato ligand and a terminal pyridine ring in the terpyridine ligand. This interaction excludes the most hydrophobic part of the glutathionato ligand from the polar solvent. Similar interactions may be responsible for the useful dependence of the UV-visible spectroscopic features of the [Pt(trpy)L]2+/+ chromophore, attached to the side chain L in proteins, on the environment of this side chain. Conformation of the glutathionato ligand in [Pt(trpy)GS]+ differs from the conformation of free glutathione in solution. This finding may be relevant to binding of glutathione to many enzymes that depend on it. This is an early, and promising, application of two-dimensional cross-relaxation NMR spectroscopy to stereochemistry of metal complexes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry