ContentsI. Introduction 3625 II. Tetranuclear Cuprous Halide Clusters 3626 A. Cu 4 I 4 Clusters 3627 B. Other Cu 4 X 4 Clusters 3631 C. Rigidochromic Effects 3632 D. Excited State Energy and Electron Transfer 3633 E. Cu 4 X 4 (phosphines) 4 3635 III. Other Cuprous Halide Complexes 3635 IV. Polynuclear Cu(I) and Ag(I) Complexes with Chalcogen Ligands 3636 A. Dynamic Quenching Studies. 3639 B. Copper(I) in Metallothionein Proteins. 3639 V. Cuprous Clusters with Acetylide Ligands 3640 VI. Other Cuprous Polynuclear Systems 3642 VII. Gold(I) Complexes 3645 VIII. Overview and Summary 3645 IX. Acknowledgments 3646 X. List of Abbreviations 3646 A. Ligands 3646 B. Excited-State Labels Used 3646 XI. References 3646

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Synthetic manganese porphyrins and related systems have been used extensively in chemical modeling of biological monooxygenation reactions catalyzed by heme proteins. [1] They are also versatile catalysts for the oxygenation of alkanes, alkenes, and nitrogen-and sulfur-containing compounds using oxygen donors such as iodosylbenzene, sodium hypochlorite, alkyl, aryl, and hydrogen peroxide, amine Noxides, and molecular oxygen. [2] Only recently has the key oxomanganese(v) intermediate been well characterized. [3] Here we report that the oxomanganese(v)-5,10,15,20-tetrakis(N-methyl-2-pyridyl)porphyrin (1) can efficiently transfer its oxo ligand to bromide ion, and that this oxo transfer is rapid and reversible. [Eq.(1)]The forward reaction mimics the halide oxidation reaction catalyzed by haloperoxidases, [4] while the reverse reaction is the catalyst activation step in substrate oxygenation by manganese porphyrins. This well-behaved equilibrium allows the assignment of a free energy change for the reaction depicted in Equation (1).OxoMn V TM-2-PyP (1) has unusual stability in aqueous solution compared to other oxoMn V porphyrin intermediates. [3b] It can be generated by the stoichiometric reaction of Mn III TM-2-PyP [5] (2) with oxidants such as HSO 5 À , m-CPBA (chloroperoxybenzoic acid), and OCl À . We have found that hypobromite, a weaker oxidant, [6] is also able to generate 1 smoothly. Figure 1 a shows the reaction between 5 mm 2 and 50 mm HOBr/OBr À[7] at pH 8.5 monitored by stopped-flow spectrophotometry. [3a,b] Clear isosbestic points were observed at 392, 444, and 558 nm. Remarkably, the identical isosbestic behavior was also found for the reverse reaction, oxoMn V Br À at higher bromide concentration. Typical spectral changes observed for the oxo-transfer reaction from Figure 1. Time-resolved UV/Vis sepctra for the reaction of a) 5 mm Mn III TM-2-PyP (2) and 50 mm HOBr/OBr À ; b) 5mm Mn V TM-2-PyP (1) and 50 mm Br À at pH 8.5 (10 mm Na 2 B 4 O 7 /H 2 SO 4 buffer). For both reactions there were 60 scans in 120 ms. Every fourth scan is shown.1 to Br À are shown in Figure 1 b. The generation of hypobromite, which is favored by excess bromide and lower pH, was confirmed by observing the diagnostic bromination reaction of phenol red. [8] The pH dependence of the rate of oxo transfer to bromide was examined between pH 5.2 and 9.0 (I 0.25 m NaClO 4 ). The reaction was found to be first-order in both oxoMn V and Br À , and independent of the buffer concentration. Kinetic profiles were obtained by monitoring oxoMn V (1) at 433 nm. Pseudo-first-order fitting of the kinetic data to a single exponential was carried out with at least six concentrations of Br À at each pH value. The apparent second-order rate constant k app was calculated from the slope of the linear plot of k obs versus C Br À . Our results show that 1 was nearly as effective an oxygen donor to Br À (3.8 Â 10 5 m À1 s À1 at pH 7.0) as myeloperoxidase compound I (1.1 Â 10 6 m À1 s À1 at pH 7.0), [9] and much more effective than vanadium bromopero...

The quantitative photoreactivities in solution of Roussin's red salt (RRS, Na2[Fe2S2(NO)4]) and of Roussin's black salt (RBS, NH4[Fe4S3(NO)7]) are described. Photolysis of the red Roussinate anion Fe2S2(NO)4 2- in aerobic aqueous solution leads to quantitative formation of the black Roussinate anion Fe4S3(NO)7 -. The quantum yield for disappearance of Fe2S2(NO)4 2- (Φ I = 0.14) is independent of excitation wavelength over a broad range (313−546 nm). Real time detection of nitric oxide by electrochemical sensors in the photolysis solution demonstrated the release of NO with a quantum yield of 0.07. The black Roussinate anion is much less photoactive (Φ II = 1.1 × 10-3) but does undergo photodecomposition in aerobic solution to give, eventually, ferric precipitates plus NO. These studies were initiated with the goal of developing photochemical strategies for delivering NO to biological targets on demand. In this context, the photolability of Fe2S2(NO)4 2- was examined as a possible candidate for exploiting the known nitric oxide sensitization of γ-radiation induced cell killing in V79 cell cultures (Mitchell, J. B.; et al. Cancer Res. 1993, 53, 5845−5848). Hypoxic cell cultures treated with RRS solution (1.0 mM) and then subjected to γ-radiation (15 Gy) demonstrated strikingly lower survival rates when simultaneously exposed to white light irradiation than did control systems treated identically but in the dark. The black salt was similarly probed, but its greater toxicity and lower quantum yields for NO release make this a less likely candidate for such photochemically induced radiation sensitization.