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The rhodium (III) complexes supported by a di-deprotonated o-phenylenediamido ligand, ([Cp*RhIII(C6H4N2tBu2Ph22−)] ([Cp*RhIII(L2−)], 1), and one-electron and two-electron oxidized ligands, [Cp*RhII...

Maturation processes of dinuclear copper proteins such as tyrosinase, catechol oxidase, and hemocyanin have been a long-standing mystery in copper protein chemistry. Until now, several crystal structures have revealed that these copper proteins share a similar dinuclear copper active site, where each copper ion is ligated by three histidine imidazoles, and binds molecular oxygen in a side-on fashion to form a (µ-η2:η2-peroxido)dicopper(II) species not only as the dioxygen-adduct in oxy-hemocyanins but also as the key reactive intermediate for the hydroxylation of phenols to catechols (phenolase reaction) and the oxidation of catechols to o-quinones (catecholase reaction) in tyrosinases and catechol oxidases. Recently, we have succeeded in determining the high-resolution crystal structures of the recombinant pro-form of yellow koji mold tyrosinase to find the existence of a distinct C-terminal domain containing a –CXXC– unit, that is the common sequence motif of the copper chaperons. Thus, the C-terminal d...

Resonance Raman spectra are measured for copper(II) complexes ([Cu(RL)2]) using a series of β-diketiminate ligands (L) carrying different α-substituents (R = Me, H, CN, and NO2), and quantum chemic...

Nickel(II) complexes supported by a series of tpa {tris[(pyridin-2-yl)methyl]amine} ligand derivatives containing different numbers of phenyl substituent on the 6-position of pyridine donor group (...

A 2-nitrated 3-oxoester reacted with amines or alcohols to afford unsymmetrical malonic acid derivatives as a result of nucleophilic substitution accompanying C–C bond cleavage. The 2-nitrated 3-ox...

The structure and O2-reactivity of the copper(I) complexes supported by bis[(6-phenyl-2-pyridyl)methyl]amine tridentate ligands (L5R) and bis(2-quinolylmethyl)amine tridentate ligands (L6R) have be...

Copper(I) complexes generated by using a series of β-diketiminate ligands (R1,R2LR3−, [(R3)N–C(R2)–C(R1)–C(R2)–N(R3)]−, see Chart 1; “β-diketiminate” denotes enaminone imine analogs) have been stru...

The aerobic oxidation of 3,5-di-tert-butylcatechol (H2dbc) to the corresponding quinone (dbq), catalyzed by di-μ-hydroxo-dicopper(II) complexes [Cu2(OH)2L2](ClO4)2 [L = N,N′-tetramethylethylenediamine (tmeda) (1) and N,N′-tetraethylethylenediamine (teeda) (2)], has been spectroscopically and kinetically studied to gain some insight into the reaction mechanisms. The ESR spectra show that catecholato complexes [Cu(dbc)L] [L = tmeda (3) or teeda (4)] are formed upon reactions of 1 or 2 with H2dbc, respectively. The UV–vis and ESI mass spectra show that 3 is converted to a semiquinonato complex [Cu(dbsq)tmeda]+ (5) in the aerobic oxidation, while [Cu(dbsq)teeda]+ (6) is only a minor species. In the presence of acid, 3 and 4 are aerobically oxidized to dbq quantitatively. Kinetic studies show that rate constants for the catalytic aerobic oxidation of H2dbc are proportional to the second or the first order with 1 or 2, respectively, and to the first-order with the O2-partial pressure. Based on these data, diffe...

Reactions of copper(I) complexes with molecular oxygen have been examined using a series of N-alkyl-bis[2-(2-pyridyl)ethyl]amine tridentate ligands (R′Py2R) and N,N-dialkyl-2-(2-pyridyl)ethylamine ...

Functionalization of 1H-pyrrolo[2,3-b]pyridine (7-azaindole) was studied to provide new compounds directing toward agrochemicals and/or functional materials. Amino groups such as NH2, NH(CH2)2NH2, and NH(CH2)2NH(CH2)2NH2 were introduced onto 6-position of 7-azaindole to form multidentate agents. 6-Amino and 6-iodo derivatives were easily converted to podant-type compounds, N,N′-bis(1H-pyrrolo[2,3-b]pyridin-6-yl)-1,3-benzenedicarboxamide and bis(1H-pyrrolo[2,3-b]pyridin-6-yl)acetylene, respectively. Polyacetylene having 1H-pyrrolo[2,3-b]pyridyl group as a pendant was obtained by polymerization of 6-ethynyl-7-azaindole synthesized by ethynylation of 6-bromo derivative. As functionalization at 3-position of 7-azaindole, syntheses of 3,3′-selenobis[1H-pyrrolo[2,3-b]pyridine] and the corresponding 3,3′-thio compound, as well as 3-carboxyethenyl- and 3-vinyl-7-azaindoles were performed. Some of these products exhibited high fungicidal activity.

The reaction of coenzyme PQQ with aminoguanidine, which is known as an inhibitor of quinoprotein amine oxidases, was investigated in vitro. The redox reaction predominantly proceeded at pH 10.0 to give PQQH2 (quinol), whereas deactivation of PQQ occurred at pH 6.7 to give the triazine adduct. In the case of semicarbazide or acetohydrazide as the substrate, azo adduct formation was mainly observed even at pH 10.0. Importance of the C-5 carbinolamine-type intermediate a is discussed.

Reduced PQQ (PQQH2) is prepared by the reaction of PQQ with thiophenol, 1-benzyl-1,4-dihydronicotinamide (BNAH), sodium dithionite, or sodium borohydride. Oxidation of PQQH2 to PQQ by molecular oxygen in aqueous solutions is investigated kinetically. The oxidation is accelerated gradually with proceeding of the reaction, which may be attributed to the side reaction of PQQH2 and H2O2 produced by the reaction of PQQH2 and O2. As in fact, the yield of H2O2 is found to be 50% based on PQQH2. Initial rate is first-order in oxygen concentration. The pH-rate profile suggests that an active species in the reaction is PQQH−. Autocatalysis of O2\ewdot and PQQ itself is scarcely detected in this reaction. The mechanism of the oxidation is also discussed.

Kinetic studies on the oxidative deamination of amines by coenzyme PQQ are carried out under anaerobic conditions. The reaction is first-order in the appearance of the reduced PQQ and in the total amine concentrations. A large kinetic isotope effect (kH⁄kD=7.24) in the oxidation of α,α-dideuteriobenzylamine indicates that the C–H bond cleavage is a rate-determining step. From the results of formation of two types of reduced PQQ (quinol and aminophenol) and low reactivities of secondary and tertiary amines, we propose the mechanism via covalent addition of the amine to the quinone followed by rate-limiting α-proton removal.

Kinetic studies on the oxidation of thiols by coenzyme PQQ are carried out under anaerobic conditions. A bell shaped pH-rate profile having a maximum rate at around pKa of the thiol is observed. The rate-determining step changes between acidic and basic sides of the profile indicating the existence of at least one intermediate in the course of the reaction.