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Mechanistic Implications (mechanistic + implication)
Selected AbstractsChemInform Abstract: Gold-Catalyzed [4C + 3C] Intramolecular Cycloaddition of Allenedienes: Synthetic Potential and Mechanistic Implications.CHEMINFORM, Issue 29 2009Beatriz Trillo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Cationic Ruthenium-Cyclopentadienyl-Diphosphine Complexes as Catalysts for the Allylation of Phenols with Allyl Alcohol; Relation between Structure and Catalytic Performance in O - vs.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009C -Allylation Abstract A new catalytic method has been investigated to obtain either O - or C -allylated phenolic products using allyl alcohol or diallyl ether as the allyl donor. With the use of new cationic ruthenium(II) complexes as catalyst, both reactions can be performed with good selectivity. Active cationic Ru(II) complexes, having cyclopentadienyl and bidentate phosphine ligands are generated from the corresponding Ru(II) chloride complexes with a silver salt. The structures of three novel (diphosphine)Ru(II)CpCl catalyst precursor complexes are reported. It appears that the structure of the bidentate ligand has a major influence on catalytic activity as well as chemoselectivity. In addition, a strong cocatalytic effect of small amounts of acid is revealed. Model experiments are described that have been used to build a reaction network that explains the origin and evolution in time of both O -allylated and C -allylated phenolic products. Some mechanistic implications of the observed structure vs. performance relation of the [(diphosphine)RuCp]+ complexes and the cocatalytic role of added protons are discussed. [source] H2O2 -mediated oxidation of tetrahydrobiopterin: Fourier transform Raman investigations provide mechanistic implications for the enzymatic utilization and recycling of this essential cofactorJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2002Jeremy Moore The oxidation of (6R)- L - erythro -5,6,7,8-tetrahydrobiopterin (6BH4) by H2O2 was examined by Fourier transform Raman spectroscopy. Initial investigations indicated that oxidation proceeds by incorporation of the H2O2 into the 6BH4 molecule without the formation of any additional water. In addition, the pyrimidine ring is affected with the shift of the double bond from the N1,C2 to the C2,N3 position. Such rearrangements of this double bond are observed after the production of either a carbinolamine or quinonoid species. Using deuterium exchange experiments, it was possible to substantiate that the oxidation of 6BH4 initially proceeds by the formation of a 4a-OH-carbinolamine intermediate prior to its spontaneous dehydration yielding the quinonoid dihydro species (qBH2). Furthermore, the hydrogen on the hydroxyl group of the carbinolamine interacts with the oxygen of the carbonyl group at the C4 position of the pyrimidine ring. It is proposed that this interaction facilitates the dehydration of the carbinolamine, thus explaining its instability. Furthermore, a mechanism for the dehydration reaction is suggested, wherein the 4a-hydroxyl group forms an H-bond to the carbonyl group, thus making the oxygen of the hydroxyl group more susceptible to attack by the proton at position N5 of the pyrazine ring, resulting in qBH2 production concomitant with the loss of a water molecule. Upon increasing the concentration of H2O2 the qBH2 converts to 7,8-BH2, which is further oxidized to L -biopterin. Taken together, our results do not support an earlier proposed mechanism implicating a hydroperoxide intermediate in this oxidation reaction. Copyright © 2002 John Wiley & Sons, Ltd. [source] O3 impacts on plant development: a meta-analysis of root/shoot allocation and growthPLANT CELL & ENVIRONMENT, Issue 7 2006D. A. GRANTZ ABSTRACT The mechanism of O3 action on plants remains poorly characterized. Symptoms include visible lesions on the leaf surface, reduced growth and a hypothesized reduction in allocation of carbohydrate to roots. The generality of this latter phenomenon has not been demonstrated. Here, a meta-analysis is performed of all available experimental data, to test the hypotheses that O3 exposure of the shoot inhibits biomass allocation below ground (the root/shoot allometric coefficient, k) and inhibits whole-plant growth rate [relative growth rate (RGR)]. Both k and RGR were significantly reduced by O3 (5.6 and 8.2%, respectively). Variability in k was greater than in RGR, and both exhibited some positive as well as mostly negative responses. The effects on k were distinct from the effects on RGR. In some cases, k was reduced while RGR was unaffected. Slow-growing plants (small RGR) exhibited the largest declines in k. These observations may have mechanistic implications regarding O3 phytotoxicity. There were no effects of type of exposure chamber on sensitivity to O3. The analyses indicate that the O3 inhibition of allocation to roots is real and general, but variable. Further experiments are needed for under-represented plant groups, to characterize exceptions to this generalization and to evaluate O3,environment interactions. [source] | ||||||||||