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51.
Erben MF Geronés M Romano RM Della Védova CO 《The journal of physical chemistry. A》2006,110(3):875-883
Site-specific fragmentations following S 2p and O 1s photoexcitation of thioacetic acid, CH3C(O)SH, have been studied by means of synchrotron radiation. Total ion yield (TIY) spectra were measured and multicoincidence techniques, which include photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO) time-of-flight mass spectrometry, were applied. The equivalent-core approximation was employed in order to estimate ionization transition values, and the observed peaks were tentatively assigned. A site-specific fragmentation is moderately observed by comparing the mass spectra collected at resonant energies around the inner and shallow inner shell S 2p and O 1s ionization edges. Beside H+ ion, the most abundant ions observed at the S 2p edge excitation were CH3CO+, SH+, S+, and CH3+. At the O 1s region the large CH3CO+ fragment was depressed, and small CHx+ (x = 0, 1, 2, 3), S+, and SH+ fragments were dominant. The dissociation dynamic for the main ion-pair production has been discussed. Two- and three-body dissociation channels have been observed in the PEPIPICO spectra, and the dissociation mechanisms were proposed. 相似文献
52.
Domínguez M Alvarez R Borràs E Farrés J Parés X de Lera AR 《Organic & biomolecular chemistry》2006,4(1):155-164
(R)-all-trans-3-hydroxyretinal 1, (S)-all-trans-4-hydroxyretinal and (R)-all-trans-4-hydroxyretinal have been synthesized stereoselectively by Horner-Wadsworth-Emmons and Stille cross-coupling as bond-forming reactions. The CBS method of ketone reduction was used in the enantioface-differentiation step to provide the precursors for the synthesis of the 4-hydroxyretinal enantiomers. The kinetic constants of Xenopus laevis ADH8 with these retinoids have been determined. 相似文献
53.
54.
Baracat-Pereira MC Coelho JL Minussi RC Chaves-Alves VM Brandio RL Silva DO 《Applied biochemistry and biotechnology》1999,76(2):129-141
Pectin lyase (PL) induction by organic and inorganic components of yeast extract (YE) was evaluated in Penicillium griseoroseum, cultured in a mineral medium containing sucrose, by determining PL activity (A235) and mycelial growth (mycelial dry weight). The lowest YE concentration that promoted significant PL induction without acting as a carbon source for the fungus corresponded to 0.0075%. Neither calcined YE nor a nutrient solution containing micronutrients induced PL production, indicating that the inducer was an organic compound. Vitamins, phospholipid components, amino acids, and nitrogenous bases were tested in place of YE and promoted no significant PL induction. A PL inducer compound was found to be soluble in the nucleotide fraction obtained during extraction of YE. The inducer was shown to be a thermostable polar substance dialyzable at 2000 Daltons, hydrolyzable by HCl, and activated by boiling for up to 60 min. Cyclic AMP (cAMP) exogenously added to the culture medium at 5 and 10 mM was capable of inducing PL in P. griseoroseum grown on sucrose, suggesting that at least one compound may be present in YE acting in a cooperative fashion for the maintenance of high levels of cAMP into the cell. PL activity and the level of cAMP inside the fungal cells increased after the addition of YE to the culture medium, suggesting the participation of this messenger in this enzyme's synthesis. 相似文献
55.
[reaction: see text] We report herein a very efficient and synthetically useful 1,4-anti-1,5-anti boron-mediated aldol reaction of a chiral alpha-methyl-beta-alkoxy methyl ketone with achiral aldehydes. 相似文献
56.
Lucía Guillade Paula Mora Pedro Villar Rosana Alvarez Angel R. de Lera 《Chemical science》2021,12(45):15157
Inspired by the biogenetic proposal of an intramolecular Diels–Alder (IMDA) cycloaddition, the total synthesis of natural product nahuoic acid A, a cofactor-competitive inhibitor of the epigenetic enzyme lysine methyl transferase SETD8, has been carried out. A non-conjugated pentaenal precursor was synthesized with high levels of stereoselectivity at seven stereogenic centers and with the appropriate control of double bond geometries. Although the IMDA reaction of the non-conjugated pentaenal using Me2AlCl for catalysis at −40 °C selectively afforded the trans-fused diastereomer corresponding to the Re-endo mode of cycloaddition, under thermal reaction conditions it gave rise to a mixture of diastereomers, that preferentially formed through the exo mode, including the cis-fused angularly-methylated octahydronaphthalene diastereomer precursor of nahuoic acid A. The natural product could be obtained upon oxidation and overall deprotection of the hydroxyl groups present in the Si-exo IMDA diastereomer.The total synthesis of natural product nahuoic acid A, a cofactor-competitive inhibitor of the epigenetic enzyme lysine methyl transferase SETD8, has been carried out based on the biogenetic proposal of an intramolecular Diels–Alder (IMDA) cycloaddition. 相似文献
57.
Rosana Rodríguez-Lpez 《Fuzzy Sets and Systems》2008,159(11):1384-1409
The peculiarity of the Hukuhara derivative makes it impossible to find periodic solutions for fuzzy differential equations with the exception of very restrictive situations. In this work, we consider a boundary value problem associated with an impulsive fuzzy differential equation and approximate the extremal solutions in a fuzzy functional interval using the monotone method. Fuzzy comparison results are useful in our procedure and the expression of the solution for some impulsive periodic ‘linear’ differential problems is also provided. 相似文献
58.
We describe a new calamitic smectogen and some of its esters with a three-block molecular architecture (polar oxyethylene chain, rigid biphenyl and non-polar aliphatic chain) which were characterised by a combination of optical, thermical, X-ray and computational techniques. The title compound is a valuable smectogenic building block for amphipathic functional organic materials. 相似文献
59.
Druzhko AB Pirutin SK de Lera AR Alvarez R Weetall HH 《Applied biochemistry and biotechnology》2005,120(2):121-132
Photoinduced transformation in gelatin films made with 14-fluoro bacteriorhodopsin derivatives, both wild-type (WT) and D96N
mutant, were studied. Spectral and kinetic peculiarities for these two types of samples were compared over a wide range of
relative humidity (9–92%). Analysis of the results considered two existing photoinduced processes that occur in suspensions
and films of corresponding pigments. It was demonstrated that there is a range of humidity in which the performance of fluorine
WT bacteriorhodopsin gelatin films may offer a technological advantage compared with fluorine D96N bacteriorhodopsin. 相似文献
60.