Oxidativeortho-C-N Fusion of Aniline by OsO4. Isolation, Characterization of Oxo-Amido Osmium(VI) Complexes, and their Catalytic Activities for Oxidative C−C Bond Cleavage of Unsaturated Hydrocarbons

The reaction of tetrahydrothiophene in a stream of nitrogen was used to study the relations between dehydrogenation and C-S cleavage reactions on sulphided Co-Mo/Al2O3 catalysts. The course of the reaction was compared for Co-Mo catalysts supported on alumina and activated carbon, for alumina alone as well as for a Pt/C catalyst. The effect of substitution of nitrogen for hydrogen, of the addition of water to the feed, of pre-sulphidation of catalysts and their deactivation by coking on the rate and selectivity of the reaction were also investigated. The results showed that hydrogenation-dehydrogenation and dehydrosulphurization activity of the sulphide catalysts have the same origin. Hydrogen accelerates dehydrosulphurization on the sulphide catalysts by removing sulphur and unsaturated hydrocarbons formed on catalyst surface by C-S bond cleavage reactions.

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A general synthesis approach in action: preparation and characterization of polyoxomolybdenum(vi) organophosphonates through oxidative Mo–Mo bond cleavage in {MoV2O4}

CrystEngComm ◽

10.1039/c2ce25093d ◽

2012 ◽

Vol 14 (14) ◽

pp. 4826 ◽

Cited By ~ 9

Author(s):

Lijuan Zhang ◽

Jingmei Sun ◽

Yunshan Zhou ◽

Sadaf ul Hassan ◽

Enbo Wang ◽

...

Keyword(s):

Bond Cleavage ◽

Action Preparation ◽

General Synthesis ◽

Synthesis Approach

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Unveiling the crucial intermediates in androgen production

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1519376113 ◽

2015 ◽

Vol 112 (52) ◽

pp. 15856-15861 ◽

Cited By ~ 42

Author(s):

Piotr J. Mak ◽

Michael C. Gregory ◽

Ilia G. Denisov ◽

Stephen G. Sligar ◽

James R. Kincaid

Keyword(s):

Bond Cleavage ◽

Nucleophilic Attack ◽

Reaction Intermediates ◽

Structural Determinants ◽

Initial Product ◽

Androgen Synthesis ◽

Ferric Peroxo ◽

Enzymatic Mechanisms ◽

Primary Substrate

Ablation of androgen production through surgery is one strategy against prostate cancer, with the current focus placed on pharmaceutical intervention to restrict androgen synthesis selectively, an endeavor that could benefit from the enhanced understanding of enzymatic mechanisms that derives from characterization of key reaction intermediates. The multifunctional cytochrome P450 17A1 (CYP17A1) first catalyzes the typical hydroxylation of its primary substrate, pregnenolone (PREG) and then also orchestrates a remarkable C17–C20 bond cleavage (lyase) reaction, converting the 17-hydroxypregnenolone initial product to dehydroepiandrosterone, a process representing the first committed step in the biosynthesis of androgens. Now, we report the capture and structural characterization of intermediates produced during this lyase step: an initial peroxo-anion intermediate, poised for nucleophilic attack on the C20 position by a substrate-associated H-bond, and the crucial ferric peroxo-hemiacetal intermediate that precedes carbon–carbon (C-C) bond cleavage. These studies provide a rare glimpse at the actual structural determinants of a chemical transformation that carries profound physiological consequences.

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Crystallization and preliminary X-ray characterization of the 2,4′-dihydroxyacetophenone dioxygenase fromAlcaligenessp. 4HAP

Acta Crystallographica Section F Structural Biology Communications ◽

10.1107/s2053230x14009649 ◽

2014 ◽

Vol 70 (6) ◽

pp. 823-826 ◽

Cited By ~ 4

Author(s):

G. Beaven ◽

A. Bowyer ◽

P. Erskine ◽

S. P. Wood ◽

A. McCoy ◽

...

Keyword(s):

Synchrotron Radiation ◽

Formic Acid ◽

Molecular Oxygen ◽

Aromatic Ring ◽

Bond Cleavage ◽

Its Sequence ◽

Hydroxybenzoic Acid ◽

X Ray

The enzyme 2,4′-dihydroxyacetophenone dioxygenase (or DAD) catalyses the conversion of 2,4′-dihydroxyacetophenone to 4-hydroxybenzoic acid and formic acid with the incorporation of molecular oxygen. Whilst the vast majority of dioxygenases cleave within the aromatic ring of the substrate, DAD is very unusual in that it is involved in C—C bond cleavage in a substituent of the aromatic ring. There is evidence that the enzyme is a homotetramer of 20.3 kDa subunits each containing nonhaem iron and its sequence suggests that it belongs to the cupin family of dioxygenases. By the use of limited chymotrypsinolysis, the DAD enzyme fromAlcaligenessp. 4HAP has been crystallized in a form that diffracts synchrotron radiation to a resolution of 2.2 Å.

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Novel class of glutathione transferases from cyanobacteria exhibit high catalytic activities towards naturally occurring isothiocyanates

Biochemical Journal ◽

10.1042/bj20070328 ◽

2007 ◽

Vol 406 (1) ◽

pp. 115-123 ◽

Cited By ~ 37

Author(s):

Eric Wiktelius ◽

Gun Stenberg

Keyword(s):

Catalytic Properties ◽

Structural Features ◽

Glutathione Transferases ◽

Substrate Specificities ◽

Catalytic Activities ◽

Genome Databases ◽

Naturally Occurring ◽

Physiological Relevance ◽

Associated Proteins

In the present paper, we report a novel class of GSTs (glutathione transferases), called the Chi class, originating from cyanobacteria and with properties not observed previously in prokaryotic enzymes. GSTs constitute a widespread multifunctional group of proteins, of which mammalian enzymes are the best characterized. Although GSTs have their origin in prokaryotes, few bacterial representatives have been characterized in detail, and the catalytic activities and substrate specificities observed have generally been very modest. The few well-studied bacterial GSTs have largely unknown physiological functions. Genome databases reveal that cyanobacteria have an extensive arsenal of glutathione-associated proteins. We have studied two cyanobacterial GSTs which are the first examples of bacterial enzymes that are as catalytically efficient as the best mammalian enzymes. GSTs from the thermophile Thermosynechococcus elongatus BP-1 and from Synechococcus elongatus PCC 6301 were found to catalyse the conjugation of naturally occurring plant-derived isothiocyanates to glutathione at high rates. The cyanobacterial GSTs studied are smaller than previously described members of this enzyme family, but display many of the typical structural features that are characteristics of GSTs. They are also active towards several classical substrates, but at the same moderate rates that have been observed for other GSTs derived from prokaryotes. The cloning, expression and characterization of two cyanobacterial GSTs are described. The possible significance of the observed catalytic properties is discussed in the context of physiological relevance and GST evolution.

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In-Exchanged CHA Zeolites for Selective Dehydrogenation of Ethane: Characterization and Effect of Zeolite Framework Type

Catalysts ◽

10.3390/catal10070807 ◽

2020 ◽

Vol 10 (7) ◽

pp. 807

Author(s):

Zen Maeno ◽

Xiaopeng Wu ◽

Shunsaku Yasumura ◽

Takashi Toyao ◽

Yasuharu Kanda ◽

...

Keyword(s):

Active Sites ◽

Temperature Programmed Desorption ◽

X Ray Diffraction ◽

Zeolite Framework ◽

X Ray ◽

Catalytic Activities ◽

Ethane Dehydrogenation ◽

Temperature Programmed

In this study, the characterization of In-exchanged CHA zeolite (In-CHA (SiO2/Al2O3 = 22.3)) was conducted by in-situ X-ray diffraction (XRD) and ammonia temperature-programmed desorption (NH3-TPD). We also prepared other In-exchanged zeolites with different zeolite structures (In-MFI (SiO2/Al2O3 = 22.3), In-MOR (SiO2/Al2O3 = 20), and In-BEA (SiO2/Al2O3 = 25)) and different SiO2/Al2O3 ratios (In-CHA(Al-rich) (SiO2/Al2O3 = 13.7)). Their catalytic activities in nonoxidative ethane dehydrogenation were compared. Among the tested catalysts, In-CHA(Al-rich) provided the highest conversion. From kinetic experiments and in-situ Fourier transform infrared (FTIR) spectroscopy, [InH2]+ ions are formed regardless of SiO2/Al2O3 ratio, serving as the active sites.

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