Glutathione interaction with SNS/S mixed-ligand complexes of oxorhenium(V): Kinetic aspects and characterization of the products

A series of oxorhenium(Ti) SNS/S mixed-ligand complexes [ReO(L-n/L)] carryi ng different types of tridentate ligands (L-n) and the same monodentate col igand (L) [L = C6H5S, L-1 = C2H5N(CH2CH2S)(2) (1), L-2 = (C2H5)(2)-NCH2CH2N (CH2CH2S)(2) (2), L-3 = C2H5SCH2CH2N(CH2CH2S)(2) (3), and L-4 = 2,6-(SCH2)( 2)NC5H3 (4)] have been synthesized and characterized by spectroscopic metho ds and elemental analyses. X-ray structure determination was performed for complexes 3 and 4. Complex 3 adopts the expected distorted trigonal bipyram idal geometry around the metal in a syn configuration, while complex 4, due to the aromatic character of the nitrogen of the SNS donor-atom set, exhib its a distorted square pyramidal geometry. The interaction of complexes 1-4 with glutathione (GSH) was studied by high-performance liquid chromatograp hy, revealing the rapid formation of the respective daughter complexes 5-8, wherein the L coligand has been substituted by GS. The daughter complexes 5-8 have been characterized by ES-MS and 2D NMR spectroscopy. Kinetic aspec ts of the interaction of complexes 1-3 with GSH have been studied by isothe rmal titration microcalorimetry providing direct measurements of the intera ction rate constants as well as of the total enthalpy change. The reaction of complex 1 exhibits the slowest rate and that of complex 2 the fastest. T his is in agreement with previously reported tt ends for analogous Tc-99m c omplexes.