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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Inorganic nitrate and nitrite from endogenous or dietary sources are metabolized in vivo to nitric oxide (NO) and other bioactive nitrogen oxides. The nitrate-nitrite-NO pathway is emerging as an important mediator of blood flow regulation, cell signaling, energetics and tissue responses to hypoxia. The latest advances in our understanding of the biochemistry, physiology and therapeutics of nitrate, nitrite and NO were discussed during a recent two-day meeting at the Nobel Forum, Karolinska Institutet in Stockholm.

Ferrihemoproteins in buffer solutions bind nitric oxide to yield their nitric oxide adducts. Reversible binding of NO was found for ferricytochrome c (Cyt III ) and metmyoglobin (Mb III ) at pH values lower than ca. 7.0. The equilibrium constants were obtained as (1.6 ( 0.1) × 10 4 M -1 for Cyt III and (1.3 ( 0.1) × 10 4 M -1 for Mb III . At higher pH, the reversible formation of the NO adducts is no longer observed; the NO adduct of Cyt III (Cyt III -NO) undergoes reduction to ferrocytochrome c, Cyt II , and that of Mb III (Mb III -NO) to the nitrosyl adduct of Mb II (Mb II -NO). Methemoglobin (Hb III ) reacts readily with NO even at pH < 6 to give the nitrosyl adduct of hemoglobin (Hb II -NO). The rates for the formation of Cyt II , Mb II -NO, and Hb II -NO were measured as functions of NO and OHconcentrations. Kinetic analysis indicates that Cyt III -NO and Mb III -NO undergo nucleophilic attack by OHat higher pH to yield Cyt II and Mb II , respectively. Mb II thus produced further reacts with NO to give Mb II -NO. For Hb III , the nitrosyl adduct (Hb III -NO) was found to react with both OHand H 2 O to give Hb II -NO in the presence of excess NO. The rate constants for the reaction between the nitrosyl ferrihemoproteins and OHwere determined as (1.5 ( 0.1) × 10 3 M -1 s -1 for Cyt III -NO, (3.2 ( 0.2) × 10 2 M -1 s -1 for Mb III -NO, and (3.2 ( 0.2) × 10 3 M -1 s -1 for Hb III -NO. The reductive nitrosylation of Hb III observed at pH < 6.0 is explained by reaction of H 2 O with Hb III -NO: the rate constant is (1.1 ( 0.1) × 10 -3 s -1 . 5702

Water-soluble iron( 111) porphyrin and ferrihemoproteins (methemoglobin, metmyoglobin, oxidized cytochrome c, and catalase) associate with N O to yield the nitric oxide adducts. The equilibrium constants for association of ferrihemoproteins and N O are 1 order of magnitude larger than that of the water-soluble iron(II1) porphyrin which is free from protein, suggesting that the proteins offset the forward and backward reaction rates in the equilibrium reactions. Nanosecond laser photolysis studies of the nitric oxide adducts of metmyoglobin, oxidized cytochrome c, and catalase, (NO)MblI1, (NO)CytlI1, and (NO)CatlI1, have been carried out. The transient detected after laser flash photolysis of (NO)CatlI1 is identified as Cat"'. However, the transients observed for (NO)MblI1 and (NO)CytlI1 at 50 ns after laser pulsing are ascribed to MVI,, and Cytrrl,,, respectively, with the absorption spectra different from those of uncomplexed MblI1 and Cyt"'. In particular, the absorption spectrum of Cyt1Irtr markedly differs from that of the uncomplexed Cyt"'. The species MVrrtr and Cytrllt, are found to change to MblI1 and CytlI1, respectively, within a few microseconds. The quantum yields for the photodissociation of NO from nitric oxide adducts of ferrihemoproteins are 1 order of magnitude less than that from the N O adduct of the water-soluble iron(II1) porphyrin, probably due to fast geminate recombination reaction of N O and ferrihemoprotein in a heme pocket. The photochemistry of the nitric oxide adducts of hemoproteins and water-soluble iron(I1) porphyrin is also described on the basis of laser phosolysis studies.

The reaction kinetics of nitric oxide autoxidation in aerobic solutions were investigated by direct observation of the nitrite ion product and by trapping the strongly oxidizing and nitrosating intermediates formed in this reaction. The rate behavior observed for nitrite formation [rate = k3[O2][NO]2, k3 = (6 +/- 1.5) x 10(6) M-2 s-1 at 22 degrees C] was the same as found for oxidation of Fe(CN)6(4-) and of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and as for the nitrosation of sulfanilamide. There was a slight decrease in k3 to (3.5 +/- 0.7) x 10(6) M-2 s-1 at 37 degrees C. The second-order dependency for NO was observed at NO concentrations as low as 3 microM. The results of the competitive kinetics studies suggest that the key oxidizing intermediates, species which are both strong oxidants and nitrosating agents, are not one of those commonly proposed (NO2, N2O3, NO+, or O2NO-) but are one or more as yet uncharacterized NOx species.

Efficient methodologies for converting biomass solids to liquid fuels have the potential to reduce dependence on imported petroleum while easing the atmospheric carbon dioxide burden. Here, we report quantitative catalytic conversions of wood and cellulosic solids to liquid and gaseous products in a single stage reactor operating at 300-320 °C and 160-220 bar. Little or no char is formed during this process. The reaction medium is supercritical methanol (sc-MeOH) and the catalyst, a copper-doped porous metal oxide, is composed of earth-abundant materials. The major liquid product is a mixture of C(2)-C(6) aliphatic alcohols and methylated derivatives thereof that are, in principle, suitable for applications as liquid fuels.

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