How does using a catalyst affect the speed or rate of a reaction?

AB - Catalysts having structures containing the Mo6S8 cluster (crystalline Chevrel phases, amorphous ternary molybdenum sulfides, and ligated molecular clusters) have been discovered to be active for thiol synthesis from methanol and hydrogen sulfide at 250°C and 1 atm. An amorphous lanthanum molybdenum sulfide material was found to be the most selective catalyst (

The catalyst may temporarily changed though!

In other words the catalyst has changed physically BUT NOT chemically.

T1 - Rh 2(II)-catalyzed synthesis of carbazoles from biaryl azides

It does take a crucial part in the reaction and may be temporarily chemically changed, but the original catalyst does reform to perform its task again i.e.

T1 - Tetrahedral Sn-silsesquioxane

collision theory are repeated here, but with extra experimental methods and theoretical details applied to experiments and theories linked to the effect of using a catalyst on the rate of a chemical reaction

T1 - Synthesis of O-Aminodihydroartemisinin via TMS Triflate Catalyzed C-O Coupling Reaction

Lanosterol biosynthesis pathway, introduction.

Planar-chiral diphosphine (,)-4, having a η5-cyclopentadienylrhenium(I) tricarbonyl backbone was prepared by a sequence involving an enantioselective (CBS) reduction of acetylcyrhetrene 5 to give alcohol ()-6, several retentive SN1-type substitution reactions, and a diastereoselective introduction of the phosphino substituent at the cyclopentadienyl ring through directed -lithiation. The application of a palladium complex of (,)-4 in allylic alkylation reactions afforded a product with up to 88% ee. Use of (,)-4 in Rh-catalyzed hydrogenations of dimethyl itaconate and acetamidocinnamic acid gave enantioselectivities of up to 95 and 89% ee, respectively. Thus, in the catalyses cyrhetrenyl diphosphine (,)-4 compares well with its ferrocene-based analogue, Josiphos 1a. The ligand/metal binding mode of ,-cyrhetrene (,)-10 was revealed by the X-ray crystal structure analysis of complex [PdCl2·(,)-10]. The results of this study confirmed the expected structural similarities between the planar-chiral cyrhetrene and the analogous ferrocene and suggested a lower basicity of the former due to the electron-withdrawing property of its Re(CO)3 fragment. This structure-based analysis is in accord with the interpretation of the catalytic properties of metal complexes bearing cyrhetrenyl diphosphine (,)-4.

Ph.D. Organic Chemistry, Chiral Chemistry and Asymmetric Catalysis

The kinetically controlled synthesis of N-benzyloxycarbonyl (Z)-dipeptides was investigated by the use of free amino acids as nucleophiles and a cysteine protease papain as catalyst. The coupling efficiency was significantly improved by the combined use of the carbamoylmethyl (Cam) ester of a Z-amino acid as acyl donor and frozen aqueous solution (ice, -16 or -24 °C) as reaction medium. The yield of peptide synthesis became high when both P1- and P1-positions were occupied by small non-polar amino acids (Z-Gly-Gly-OH, 76%; Z-Gly-Ala-OH, 75%; Z-Ala-Ala-OH, 72%). Similar results were observed by the use of ficin as catalyst instead of papain. Furthermore, this strategy was applied to the papain-catalyzed incorporation of a d-configured amino acid such as d-alanine into the resulting peptides. Although the coupling in aqueous solution (30 °C) afforded the desired Z-dipeptides in low yields, the freezing of reaction medium reduced significantly unfavorable hydrolysis of the acyl donors, resulting in improvement of the coupling efficiency (Z-Gly-d-Ala-OH, 80%; Z-Ala-d-Ala-OH, 45%; Z-d-Ala-Ala-OH, 22%).

ATP synthase is an enzyme that creates the energy storage molecule ..

We investigated the modulation of the geneexpression in human fibroblasts under hypoxic condition usingGeneChip analysis, and found that the expression of prostacyclinsynthase (PGIS) was upregulated. PGIS, a membrane-bound hemeprotein with spectral characteristics of cytochrome p450 (CYP), isalso an enzyme which catalyzes the conversion of prostaglandinH (PGH) to form prostacyclin(PGI). PGIS is localized to the microsomal fractions ofplatelets, vascular endothelial cells, and vascular smooth musclecells (–). PGIS-deficient mice generated by genetargeting are associated with thickening of arterial walls,interstitial fibrosis with nephrosclerosis and kidney infarction(). Interestingly, some groupsreported that PGI, the product of PGIS, promotescolorectal cancer growth probably by activating peroxisomeproliferator-activated receptor δ (PPARδ) (). Inhibition of COX-2-derivedprostacyclin (PGI) induces colon cancer cell apoptosis(). PGI alsoregulates the transcription of VEGF by PPARδ (,).

Menéndez, Synthesis, 2010, 1053-1057.

Murray AW, Elliott DC and Atkinson MR (1970) Nucleotide biosynthesis from preformed purines in mammalian cells: regulatory mechanisms and biological significance. Progress in Nucleic Acid Research and Molecular Biology 10: 87–119.