Copper coordinated ligand thioether-S and NO2− oxidation: relevance to the CuM site of hydroxylases†
Abstract
In order to gain insight into the coordination site and oxidative activity of the CuM site of hydroxylases such as peptidylglycine α-hydroxylating monooxygenase (PHM), dopamine β-monooxygenase (DβM), and tyramine β-monooxygenase (TβM), we have synthesized, characterized and studied the oxidation chemistry of copper complexes chelated by tridentate N2Sthioether, N2Osulfoxide or N2Osulfone donor sets. The ligands are those of N-2-methylthiophenyl-2′-pyridinecarboxamide (HL1), and the oxidized variants, N-2-methylsulfenatophenyl-2′-pyridinecarboxamide (HL1SO), and N-2-methylsulfinatophenyl-2′-pyridinecarboxamide (HL1SO2). Our studies afforded the complexes [(L1)CuII(H2O)](ClO4)·H2O (1·H2O), {[(L1SO)CuII(CH3CN)](ClO4)}n (2), [(L1)CuII(ONO)] (3), [(L1SO)CuII(ONO)]n (4), [(L1)CuII(NO3)]n (5), [(L1SO)CuII(NO3)]n (6) and [(L1SO2)CuII(NO3)] (7). Complexes 1 and 3 were described in a previous publication (Inorg. Chem., 2013, 52, 11084). The X-ray crystal structures revealed either distorted octahedral (in 2, 4–6) or square-pyramidal (in 1, 3) coordination geometry around CuII ions of the complexes. In the presence of H2O2, conversion of 1 → 2, 3–5 → 6 and 6 → 7 occurs quantitatively via oxidation of thioether-S and/or Cu(II) coordinated NO2− ions. Thioether-S oxidation of L1 also occurs when [L1]− is reacted with [CuI(CH3CN)4](ClO4) in DMF under O2, albeit low in yield (20%). Oxidations of thioether-S and NO2− were monitored by UV-Vis spectroscopy. Recovery of the sulfur oxidized ligands from their metal complexes allowed for their characterization by elemental analysis, 1H NMR, FTIR and mass spectrometry.