Observation of oxygenated intermediates in functional mimics of aminophenol dioxygenase.

Aminophenol dioxygenases (APDO) are mononuclear nonheme iron enzymes that utilize dioxygen (O) to catalyze the conversion of o-aminophenols to 2-picolinic acid derivatives in metabolic pathways. This study describes the synthesis and O reactivity of two synthetic models of substrate-bound APDO: [Fe(Tp)(APH)] (1) and [Fe(Tp)(APH)] (2), where Tp = hydrotris(3,5-dimethylpyrazole-1-yl)borate, APH = 4,6-di-tert-butyl-2-aminophenolate, and APH = 4-tert-butyl-2-aminophenolate. Both Fe(II) complexes behave as functional APDO mimics, as exposure to O results in oxidative CC bond cleavage of the o-aminophenolate ligand.

Reversible Dioxygen Binding to Co(II) Complexes with Noninnocent Ligands.

A series of mononuclear Co(II) complexes with noninnocent (redox-active) ligands are prepared that exhibit metal-ligand cooperativity during the reversible binding of O. The complexes have the general formula, [Co()(Tp)] (R = Me, Ph), where is a bidentate -aminothiophenolate and Tp is a hydrotris(pyrazol-1-yl)borate scorpionate with R-substituents at the 3- and 5-positions. Exposure to O at room temperature results in one-electron oxidation and deprotonation of .

Nonheme iron-thiolate complexes as structural models of sulfoxide synthase active sites.

Two mononuclear iron(ii)-thiolate complexes have been prepared that represent structural models of the nonheme iron enzymes EgtB and OvoA, which catalyze the O2-dependent formation of carbon-sulfur bonds in the biosynthesis of thiohistidine compounds. The series of Fe(ii) complexes reported here feature tripodal N4 chelates (LA and LB) that contain both pyridyl and imidazolyl donors (LA = (1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine; LB = N,N-bis((1-methylimidazol-2-yl)methyl)-2-pyridylmethylamine). Further coordination with monodentate aromatic or aliphatic thiolate ligands yielded the five-coordinate, high-spin Fe(ii) complexes [FeII(LA)(SMes)]BPh4 (1) and [FeII(LB)(SCy)]BPh4 (2), where SMes = 2,4,6-trimethylthiophenolate and SCy = cyclohexanethiolate.

Spectroscopic and Computational Comparisons of Thiolate-Ligated Ferric Nonheme Complexes to Cysteine Dioxygenase: Second-Sphere Effects on Substrate (Analogue) Positioning.

Parallel spectroscopic and computational studies of iron(III) cysteine dioxygenase (CDO) and synthetic models are presented. The synthetic complexes utilize the ligand tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (TIP), which mimics the facial three-histidine triad of CDO and other thiol dioxygenases. In addition to the previously reported [Fe(CysOEt)(TIP)]BPh (; CysOEt is the ethyl ester of anionic l-cysteine), the formation and crystallographic characterization of [Fe(2-MTS)(TIP)]BPh () is reported, where the methyl 2-thiosalicylate anion (2-MTS) resembles the substrate of 3-mercaptopropionate dioxygenase (MDO).

A synthetic model of the nonheme iron-superoxo intermediate of cysteine dioxygenase.

A nonheme Fe(ii) complex (1) that models substrate-bound cysteine dioxygenase (CDO) reacts with O at -80 °C to yield a purple intermediate (2). Analysis with spectroscopic and computational methods determined that 2 features a thiolate-ligated Fe(iii) center bound to a superoxide radical, mimicking the putative structure of a key CDO intermediate.

Spectroscopic and computational studies of reversible O binding by a cobalt complex of relevance to cysteine dioxygenase.

The substitution of non-native metal ions into metalloenzyme active sites is a common strategy for gaining insights into enzymatic structure and function. For some nonheme iron dioxygenases, replacement of the Fe(ii) center with a redox-active, divalent transition metal (e.g.

Oxygen activation by mononuclear Mn, Co, and Ni centers in biology and synthetic complexes.

The active sites of metalloenzymes that catalyze O-dependent reactions generally contain iron or copper ions. However, several enzymes are capable of activating O at manganese or nickel centers instead, and a handful of dioxygenases exhibit activity when substituted with cobalt. This minireview summarizes the catalytic properties of oxygenases and oxidases with mononuclear Mn, Co, or Ni active sites, including oxalate-degrading oxidases, catechol dioxygenases, and quercetin dioxygenase.

Synthesis, X-ray Structures, Electronic Properties, and O/NO Reactivities of Thiol Dioxygenase Active-Site Models.

Mononuclear non-heme iron complexes that serve as structural and functional mimics of the thiol dioxygenases (TDOs), cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), have been prepared and characterized with crystallographic, spectroscopic, kinetic, and computational methods. The high-spin Fe(II) complexes feature the facially coordinating tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (TIP) ligand that replicates the three histidine (3His) triad of the TDO active sites. Further coordination with bidentate l-cysteine ethyl ester (CysOEt) or cysteamine (CysAm) anions yielded five-coordinate (5C) complexes that resemble the substrate-bound forms of CDO and ADO, respectively.

Controlled hydrogenative depolymerization of polyesters and polycarbonates catalyzed by ruthenium(II) PNN pincer complexes.

Ruthenium(II) PNN complexes depolymerize many polyesters into diols and polycarbonates into glycols plus methanol via hydrogenation. Notably, polyesters with two methylene units between ester linkages depolymerize to carboxylic acids rather than diols. This methodology represents a new approach for producing useful chemicals from waste plastics.