Search results for " Catalysis"

Cationic mono- and bi-nuclear iron complexes as Lewis acid catalysts in Mukaiyama reactions

1992

Organometallic Lewis acids derived from photolysis of mono- and bi-nuclear cationic iron carbonyl complexes function as excellent catalysts for the Mukaiyama aldol reaction.

Ligands P-stéréogéniques dérivés du calix[4]arène. Synthèses et applications en catalyse asymétrique

2010

We were interested in synthesis of P-stereogenic ligands derived from calix[4]arene and in their application in asymmetric catalysis. Mono et diphosphines were prepared on the upper rim of the macrocyle starting from the mono or dianion of the calix[4]arene and chlorophosphines borane or the oxazaphospholidine borane complex. The best selectivity was obtained by reaction of the dianion with the oxazaphospholidine borane complex leading to a bisaminophosphine borane. After acidolysis with HCl giving the corresponding bischlorophosphine and reaction with organolithium reagents, diphosphines diborane were obtained with good yields (40 à 60 %). X-ray structures of the prepared ligands confirmed…

Calvin-Benson Cycle

2015

A carbon dioxide fixation pathway where a molecule of CO2 condenses with a 5-C compound (ribulose 1,5-bisphosphate) to yield two molecules of a 3-C compound (3-phosphoglycerate). These 3-C molecules serve both as precursors for biosynthesis and, through a cyclic series of enzymatic reactions, to regenerate the 5-C molecule necessary for the first carboxylating step (Fig. 1). The pathway is present in several bacterial lineages (e.g., cyanobacteria), and its acquisition by eukaryotic cells (chloroplast in algae and plants) was through the endosymbiotic association with ancient cyanobacteria.

Multifunctional halloysite and hectorite catalysts for effective transformation of biomass to biodiesel

2023

Halloysite surface was modified with tetrabutylammonium iodide, and then the obtained nanomaterial was used as support for ZnO nanoparticles. After characterization, the nanomaterial was used as a catalyst for fatty acid methyl esters (FAMEs) production. The recyclability of the nanomaterial was also investigated, and the optimization of reaction conditions by the design of experiments approach was performed as well. In addition, the synthesized nanomaterial was tested as a catalyst for FAME production from a series of waste lipids affording biodiesel in moderate to good yields (35–95%), depending on the matrix. To fully exploit the feasibility of clay minerals as catalysts in biodiesel for…

Recent Advances in Photocatalytic Functionalization of Quinoxalin‐2‐ones

2020

Quinoxalin‐2(1H)‐one is an important class of nitrogen heterocycle in medicinal and pharmaceutical industry, which became a synthetic target in organic chemistry in recent years. This review covers the recent advances in the functionalization of this particular nitrogen heterocycle through photocatalysis.

MINDO/3 Study of the Rearrangement of 1-Methylcyclohexyl Cation to 1,2-Dimethylcyclopentyl Cation

1986

The rearrangement of the 1-methylcyclohexyl cation to the 1,2-dimethylcyclopentyl cation has been studied by MINDO/3 calculations, as an application of the branching mechanism model for cycloalkanes. Possible intermediates and transition states have been characterized by diagonalization of their Hessian matrixes. Two nonequivalent pathways, α and β scissions, are relatively close in energy. The calculated transition states are almost equivalent in energy to those found for cyclohexyl cation. Hence, the energy barriers are higher for the rearrangement of the 1-methyl than for cyclohexyl cation, because the former is less stable than the latter.

Novel Imidazolium Based Catalyst for the Chemical Fixation of Carbon Dioxide

2015

Strong Cooperativity and Loose Geometry between CUB Domains Are the Basis for Procollagen C-Proteinase Enhancer Activity

2009

Procollagen C-proteinase enhancers (PCPE-1 and -2) specifically activate bone morphogenetic protein-1 (BMP-1) and other members of the tolloid proteinase family during C-terminal processing of fibrillar collagen precursors. PCPEs consist of two CUB domains (CUB1 and CUB2) and one NTR domain separated by one short and one long linker. It was previously shown that PCPEs can strongly interact with procollagen molecules, but the exact mechanism by which they enhance BMP-1 activity remains largely unknown. Here, we used a series of deletion mutants of PCPE-1 and two chimeric constructs with repetitions of the same CUB domain to study the role of each domain and linker. Out of all the forms teste…

Structural and surface characterization of the polycrystalline system CrxOy · TiO2 employed for photoreduction of dinitrogen and photodegradation of …

1992

The polycrystalline system CrxOy-TiO2, used as a catalyst for photoreactions, was studied by X-ray diffractometric method, visible-ultraviolet diffuse reflectance and infrared spectroscopic methods, surface area determination, and porosimetry to characterize its structural and surface features. Two series of catalysts were prepared by two different methods, namely by coprecipitation and by impregnation. The first series was tested as photocatalysts for the dinitrogen photoreduction in a gas-solid regime and for the phenol photodegradation in a liquid-solid regime. The results indicate that the interaction of chromium ions with OH groups modifies the surface properties of the supports and co…

Influence of the preparative route on the properties of WOx–ZrO2 catalysts: A detailed structural, spectroscopic, and catalytic study

2007

Abstract Two series of tungstated zirconia (WZ) solid acids covering a wide range of tungsten surface densities ( δ, W at/nm2 ) were prepared by nonconventional impregnation and coprecipitation routes, leading to samples with enhanced surface area ( ∼ 70 – 120 m 2 / g ) on annealing at 973–1073 K. The materials were thoroughly characterized by N2 physisorption , XRD, Raman, XPS, H 2-TPR, and DR UV–vis spectroscopy. The catalytic behavior of the Pt-promoted WZ catalysts (1 wt% Pt) was evaluated for the hydroconversion of n-hexadecane used as model feed representative of Fischer–Tropsch waxes. Both series of catalysts displayed a pronounced maximum in the reaction rate and a minimum in the se…