Selective hydroxylation of benzene to phenol has been achieved using H2O2 in the presence a catalytic amount nickel complex [NiII(tepa)]2+ (2) (tepa = tris[2-(pyridin-2-yl)ethyl]amine) at 60 °C. The maximum yield was 21% based on without formation quinone or diphenol. In an endurance test catalyst, 2 showed turnover number (TON) 749, which is highest value reported date for molecular catalysts with H2O2. When toluene employed as substrate instead benzene, cresol obtained major product 90%...

Abstract The dinuclear copper enzyme, tyrosinase, activates O 2 to form a (μ‐η :η ‐p eroxido)dicopper(II) species, which hydroxylates phenols catechols. However, the exact mechanism of phenolase reaction in catalytic site tyrosinase is still under debate. We herein report near atomic resolution X‐ray crystal structures active tyrosinases with substrate l ‐tyrosine. At their sites, CuA moved toward ‐tyrosine (CuA1 → CuA2), whose phenol oxygen directly coordinates CuA2, involving movement CuB...

A mononuclear copper(II) superoxo species has been invoked as the key reactive intermediate in aliphatic substrate hydroxylation by copper monooxygenases such peptidylglycine α-hydroxylating monooxygenase (PHM), dopamine β-monooxygenase (DβM), and tyramine (TβM). We have recently developed a end-on complex using N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane tridentate ligand, structure of which is similar to four-coordinate distorted tetrahedral geometry copper-dioxygen adduct found oxy-form...

Redox properties of a mononuclear copper(II) superoxide complex, (L)CuII–OO•, supported by tridentate ligand (L = 1-(2-phenethyl)-5-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane) have been examined as model compound the putative reactive intermediate peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine β-monooxygenase (DβM) (Kunishita et al. J. Am. Chem. Soc. 2009, 131, 2788–2789; Inorg. 2012, 51, 9465–9480). On basis reactivity toward series one-electron reductants, reduction...

Amyloid proteins displaying a copper histidine-brace offer designable scaffolds for efficient and asymmetric chemical reactions.

Copper(II) complexes 1a and 1b, supported by tridentate ligand bpa [bis(2-pyridylmethyl)amine] tetradentate tpa [tris(2-pyridylmethyl)amine], respectively, react with cumene hydroperoxide (CmOOH) in the presence of triethylamine CH3CN to provide corresponding copper(II) cumylperoxo 2a 2b, formation which has been confirmed resonance Raman ESI-MS analyses using 18O-labeled CmOOH. UV-vis ESR spectra as well DFT calculations indicate that a 5-coordinate square-pyramidal structure involving...

Abstract Reaction of a copper(I) complex supported by sterically demanding tripodal tetradentate ligand, HIPT 3 tren, and O 2 gave mononuclear copper(II) end‐on superoxo complex. Spectroscopic (UV/Vis, resonance Raman, ESR, 1 H‐NMR) DFT studies have been performed. The ‐binding process as well the reaction toward external substrates investigated kinetically to demonstrate unique behavior complex, which may occur result existence hydrophobic core around copper coordination sphere created tren ligand.

A new tridentate N3 ligand (TMG3tach) consisting of cis,cis-1,3,5-triaminocyclohexane (tach) and three N,N,N′,N′-tetramethylguanidino (TMG) groups has been developed to prepare copper complexes with a tetrahedral geometry labile coordination site. Treatment the CuIIX2 (X = Cl Br) gave copper(II)-halide complexes, [CuII(TMG3tach)Cl]+ (2Cl) [CuII(TMG3tach)Br]+ (2Br), structures which have determined by X-ray crystallographic analysis. The exhibit four-coordinate structure C3v symmetry, where...

We repurposed the metal-binding site of a cupin superfamily protein into 2-His-1-carboxylate facial triad, which is one common motifs in natural non-heme enzymes, to construct artificial metalloenzymes that can catalyze new-to-nature reactions. The Cu2+-H52A/H58E variant catalyzed stereoselective Michael addition reaction and was found bear flexible high-resolution crystal structure. Furthermore, H52A/H58E/F104W mutant accommodated water molecule, supported by Glu58 Trp104 residues via...

Autocatalytic formation of His-Cys cross-linkage in the enzyme active site tyrosinase from Aspergillus oryzae has been demonstrated to proceed by treatment apoenzyme with Cu(II) under aerobic conditions, where a (μ-η(2):η(2)-peroxo)dicopper(II) species suggested be involved as key reactive intermediate.

Nickel complexes of a series β-diketiminate ligands (RL–, deprotonated form 2-substituted N-[3-(phenylamino)allylidene]aniline derivatives RLH, R = Me, H, Br, CN, and NO2) have been synthesized structurally characterized. One-electron oxidation the neutral [NiII(RL–)2] by AgSbF6 or [RuIII(bpy)3](PF6)3 (bpy 2,2′-bipyridine) gave corresponding metastable cationic complexes, which exhibit an EPR spectrum due to doublet species (S 1/2) characteristic absorption band in near IR region ascribable...

The reaction of [CuI(TIPT3tren) (CH3CN)]ClO4 (1) and cumene hydroperoxide (C6H5C(CH3)2OOH, ROOH) at −60 °C in CH2Cl2 gave a CuII–alkylperoxide/anilino radical complex 2, the formation which was confirmed by UV–vis, resonance Raman, EPR, CSI-mass spectroscopy. mechanism as well its reactivity, has been explored.

Adding a metal cofactor to protein bearing latent binding site endows the macromolecule with nascent catalytic activity.

Thermally stable TM1459 cupin superfamily protein from Thermotoga maritima was repurposed as an osmium (Os) peroxygenase by metal-substitution strategy employing the metal-binding promiscuity. This novel artificial metalloenzyme bears a datively bound Os ion supported 4-histidine motif. The well-defined center is responsible for not only catalytic activity but also thermodynamic stability of folding, leading to robust biocatalyst (Tm ≈ 120 °C). spectroscopic analysis and atomic resolution...

Abstract The TM1459 protein from Thermotoga maritima is a member of the cupin superfamily and contains mononuclear metal center. Structural information has been obtained using X‐ray crystallography; however, its physiological role remains unknown. metal‐binding site an octahedral coordination geometry ligated by four histidine imidazoles two terminal water molecules present in cis position. This had ability to bind Mn, Fe, Zn ions; additionally, self‐hydroxylation reaction occurred Fe‐TM1459...

Abstract The pro form of melB tyrosinase from the gene Aspergillus oryzae was over‐produced E. coli and formed a homodimer that exhibited spectral features met‐tyrosinase. In presence NH 2 OH (reductant), proenzyme bound dioxygen to give stable (μ‐η :η ‐peroxo)dicopper(II) species (oxy form), thus indicating can function as an oxygen carrier or storage protein like hemocyanin. itself showed no catalytic activity toward external substrates, but proteolytic digestion with trypsin activated it...

Copper(I) complexes supported by a series of N3-tridentate ligands bearing rigid cyclic diamine framework such as 1,5-diazacyclooctane (L8, eight-membered ring), 1,4-diazacycloheptane (L7, seven-membered or 1,4-diazacyclohexane (L6, six-membered ring) with common 2-(2-pyridyl)ethyl side arm were synthesized and their reactivity toward O2 compared. The copper(I) complex L8 preferentially provided mononuclear copper(II) end-on superoxide S reported previously [Itoh, S., et al. J. Am. Chem....

Abstract The dinuclear copper enzyme, tyrosinase, activates O 2 to form a (μ‐η :η ‐p eroxido)dicopper(II) species, which hydroxylates phenols catechols. However, the exact mechanism of phenolase reaction in catalytic site tyrosinase is still under debate. We herein report near atomic resolution X‐ray crystal structures active tyrosinases with substrate l ‐tyrosine. At their sites, CuA moved toward ‐tyrosine (CuA1 → CuA2), whose phenol oxygen directly coordinates CuA2, involving movement CuB...

Copper(II) complexes supported by a series of phenol-containing bis(pyridin-2-ylmethyl)amine N3 ligands (denoted as LoH, LmH, and LpH) have been synthesized, their O2 reactivity has examined in detail to gain mechanistic insights into the biosynthesis TPQ cofactor (2,4,5-trihydroxyphenylalaninequinone, TOPA quinone) copper-containing amine oxidases. The copper(II) complex LoH (ortho-phenol derivative) involves direct phenolate coordination exhibits almost no toward at 60 °C CH3OH. On other...

A new type of non-innocent β-diketiminate ligand having redox active phenol groups (LH33, fully protonated form) has been developed, and the structure, physical properties reactivity supported copper(II) complex [CuII(L3−3−)]− (L3−3−, deprotonated tri-anionic as well one-electron two-electron oxidised complexes, [CuII(L˙2−)] [CuII(L−−)]+, have examined in detail. The form [CuII(L−−)]+ exhibited hydrogen atom abstraction ability from 1,4-cyclohexadiene (CHD), whereas was found to...

Abstract The reaction of copper(I) complexes and cumene hydroperoxides was examined to demonstrate that heterolytic O–O bond cleavage the peroxides proceeds predominantly give corresponding alcohols (cumyl alcohols) as major product, when stoichiometry Cu I /peroxide is 2:1. result in sharp contrast 1:1 between copper(II) hydroperoxide, which provides ketone (acetophenone) product through homolytic cleavage.