Hydroxylation Reaction (hydroxylation + reaction)

Distribution by Scientific Domains


Selected Abstracts


Extended Hartree,Fock theory of chemical reactions.

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008
VIII.
Abstract We have investigated the reaction pathways for the primary hydroxylation reaction of trimethylmethane by a high-valent Fe(IV)O porphyrin ,-cation radical species known as compound I at the B3LYP/CEP-31G level. The isoelectronic analogy of the Fe(IV)O core of compound I to a molecular oxygen (O2) has been successfully used to clarify the important roles of the singlet excited state of the Fe(IV)O core in the alkane hydroxylation, which has hitherto been neglected. The reaction is initiated by the rate-determining hydrogen-atom abstraction from the substrate to give a discrete radical intermediate complex, in accordance with the conventional radical rebound mechanism. Similar to the chemistry of O2, however, one of the singlet excited states, i.e., the diradical component of the 1, state of the Fe(IV)O core intercepts the triplet ground state (the 3, state) in the region of the transition state for the hydrogen abstraction. Our findings strongly indicate that the exchange polarization or intersystem crossing for the nonradiative transition to the locally singlet state is highly important to enhance the reactivity of compound I. 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]


High-performance liquid chromatographic/tandem mass spectrometric identification of the phototransformation products of tebuconazole on titanium dioxide

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2002
Paola Calza
Abstract Tebuconazole is a widely used fungicide. The formation of by-products on irradiated titanium dioxide as a photocatalyst was evaluated. Several species derived from tebuconazole degradation were identified and characterized by HPLC/MSn. A pattern of reactions accounting for the observed intermediates is proposed. Different parallel pathways are operating (and through these pathways the transformation of the molecule proceeds), leading to a wide range of intermediate compounds. All these molecules are more hydrophylic than tebuconazole. The main steps involved are (1) the hydroxylation of the molecule with the formation of three species having [M + H]+ 324; the hydroxylation occurs on the C-1 carbon and on the aromatic ring in the two ortho -positions; (2) the cleavage of a C,C bond with the release of the tert -butyl moiety and the formation of a species having m/z 250; analogously to step 1, also on this species a further hydroxylation reaction occurs; (3) through the loss of the triazole moiety with the formation of a structure with m/z 257. Copyright 2002 John Wiley & Sons, Ltd. [source]


Crystallization and preliminary X-ray analysis of PaaAC, the main component of the hydroxylase of the Escherichia coli phenylacetyl-coenzyme A oxygenase complex

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2010
Andrey M. Grishin
The Escherichia coli paa operon encodes enzymes of the phenylacetic acid-utilization pathway that metabolizes phenylacetate in the form of a coenzyme A (CoA) derivative. The phenylacetyl-coenzyme A oxygenase complex, which has been postulated to contain five components designated PaaABCDE, catalyzes ring hydroxylation of phenylacetyl-CoA. The PaaAC subcomplex shows low sequence similarity to other bacterial multicomponent monooxygenases (BMMs) and forms a separate branch on the phylogenetic tree. PaaAC, which catalyzes the hydroxylation reaction, was purified and crystallized in the absence of a bound ligand as well as in complexes with CoA, 3-hydroxybutyryl-CoA, benzoyl-CoA and the true substrate phenylacetyl-CoA. Crystals of the ligand-free enzyme belonged to space group P212121 and diffracted to 2.65, resolution, whereas complexes with CoA and its derivatives crystallized in space group P41212 and diffracted to ,2.0, resolution. PaaAC represents the first crystallized BMM hydroxylase that utilizes a CoA-linked substrate. [source]


Tyrosinase-Like Reactivity in a CuIII2(,-O)2 Species

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2008
Anna Company
Center stage: Intermolecular phenolate binding to and hydroxylation by a bis(,-oxo) dicopper(III) species demonstrate the ability of this core to perform tyrosinase-like reactivity. Kinetic analysis of the hydroxylation reaction (see scheme) shows remarkable similarities to aromatic hydroxylation reactions performed by side-on peroxo-type dicopper(II) species. [source]


Theory of chemical bonds in metalloenzymes XIII: Singlet and triplet diradical mechanisms of hydroxylations with iron-oxo species and P450 are revisited

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009
Kizashi Yamaguchi
Abstract Electronic structures of the Compound I (CpdI) in P450 are investigated on the basis of spin coupling forms of iron-oxo (Fe(IV)O) cores and radical ligand (,L) groups to generalize previous singlet and triplet diradical (TD) mechanisms for oxygenations of alkanes with Fe( IV)O. Orbital interaction schemes for four lower-lying spin configurations of CpdI with HC bond of substrate are examined to elucidate how magnetic coupling modes correlate with radical reaction pathways for hydroxylation reactions on the basis of the broken symmetry (BS) molecular orbital (MO) model. The configuration correlation diagrams for the four configurations model are depicted on the basis of the isoelectronic analogy among O, O2, and Fe( IV)O, in addition to Coulomb exchange energy on the iron site, which determines its local spin configuration. Important role of ligand spin (,L) of CpdI for regulation of hydroxylation mechanisms is clarified with the aid of the spin coupling forms. Transition states for one quartet and three doublet configurations under the BS MO approximation are examined on the basis of potential curve crossings along reaction pathways. The four transition structures and corresponding radical intermediates for methane and trimethyl methane with CpI are located by the BS hybrid Kohn,Sham density functional theory (DFT) (B3LYP) method to confirm the orbital interaction schemes. Spin density populations obtained by the BS B3LYP calculations are found to be consistent with the theoretical predictions based on the four configurations model. The configuration and state correlation diagrams by BS B3LYP before and after spin projection are also consistent with the BS MO interaction schemes, which provide local SD and TD mechanisms of hydroxylation with CpdI. The present BS MO-theoretical framework is useful for systematic understanding of a lot of recent BS hybrid DFT computational results for hydroxylation reactions with CpdI and configuration correlation diagrams reported by several groups. Implications of the present theoretical and computational results are discussed in relation to several experimental characteristics of hydroxylation reactions with iron-oxo species and P450. 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]


Crystallization and preliminary X-ray diffraction studies of vitamin D3 hydroxylase, a novel cytochrome P450 isolated from Pseudonocardia autotrophica

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2009
Yoshiaki Yasutake
Vitamin D3 hydroxylase (Vdh) is a novel cytochrome P450 monooxygenase isolated from the actinomycete Pseudonocardia autotrophica and consisting of 403 amino-acid residues. Vdh catalyzes the activation of vitamin D3via sequential hydroxylation reactions: these reactions involve the conversion of vitamin D3 (cholecalciferol or VD3) to 25-hydroxyvitamin D3 [25(OH)VD3] and the subsequent conversion of 25(OH)VD3 to 1,,25-dihydroxyvitamin D3 [calciferol or 1,,25(OH)2VD3]. Overexpression of recombinant Vdh was carried out using a Rhodococcus erythropolis expression system and the protein was subsequently purified and crystallized. Two different crystal forms were obtained by the hanging-drop vapour-diffusion method at 293,K using polyethylene glycol as a precipitant. The form I crystal belonged to the trigonal space group P31, with unit-cell parameters a = b = 61.7, c = 98.8,. There is one Vdh molecule in the asymmetric unit, with a solvent content of 47.6%. The form II crystal was grown in the presence of 25(OH)VD3 and belonged to the orthorhombic system P212121, with unit-cell parameters a = 63.4, b = 65.6 c = 102.2,. There is one Vdh molecule in the asymmetric unit, with a solvent content of 46.7%. Native data sets were collected to resolutions of 1.75 and 3.05, for form I and form II crystals, respectively, using synchrotron radiation. The structure solution was obtained by the molecular-replacement method and model refinement is in progress for the form I crystal. [source]


Tyrosinase-Like Reactivity in a CuIII2(,-O)2 Species

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2008
Anna Company
Center stage: Intermolecular phenolate binding to and hydroxylation by a bis(,-oxo) dicopper(III) species demonstrate the ability of this core to perform tyrosinase-like reactivity. Kinetic analysis of the hydroxylation reaction (see scheme) shows remarkable similarities to aromatic hydroxylation reactions performed by side-on peroxo-type dicopper(II) species. [source]