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61.
Pulkkinen S Noguera M Rodríguez-Santiago L Sodupe M Bertran J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(23):4393-4399
The intramolecular proton transfer in cationized glycine and chlorine substituted derivatives with M = Na+, Mg2+, Ni+, Cu+, and Cu2+ has been studied with the three parameter B3LYP density functional method. The coordination of metal cations to the oxygens of the carboxylic group of glycine stabilizes the zwitterionic structure. For all monocations the intramolecular proton transfer occurs readily with small energy barriers (1-2 kcalmol(-1)). For the dication Mg2+ and Cu2+ systems, the zwitterionic structure becomes very stable. However, whereas for Mg2+, the proton transfer process takes place spontaneously, for Cu2+ the reaction occurs with an important energy barrier. The substitution of the hydrogens of the amino group by chlorine atoms decreases the basicity of nitrogen, which destabilizes the zwitterionic structure. For monosubstituted glycine complexed with Na+, the zwitterionic structure still exists as a minimum, but for disubstituted glycine no minimum appears for this structure. In contrast, for Mg2+ complexed to mono- and disubstituted glycine, the zwitterionic structure remains the only minimum, since the enhanced electrostatic interaction with the dication overcomes the destabilizing effect of the chlorine atoms. 相似文献
62.
Martínez-Alvarez R Martín N Seoane C Suárez M Pérez R Rodríguez H Kayali N 《Rapid communications in mass spectrometry : RCM》2001,15(10):758-762
The electrospray ionisation (ESI) in negative mode of the pharmacologically significant 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazin-2-thiones, and their subsequent fragmentations using an ion-trap mass spectrometer, have been investigated. Experiments on sequential product ion fragmentations (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. The data presented show that the fragmentation of the even-electron [M - H](-) ions could proceed through an internal nucleophilic substitution displacement. Decarboxylation and extrusion of carbon disulfide are other fragmentations observed. 相似文献
63.
Carmona AT Fuentes J Robina I García ER Demange R Vogel P Winters AL 《The Journal of organic chemistry》2003,68(10):3874-3883
A new route for the preparation of four new indolizidines, (1R,2S,6S,7S,8aS)- and (1R,2S,6R,7R,8aS)-1,2,6,7-tetrahydroxyindolizidine (30 and 32) and (1S,2R,7S,8S,8aR)- and (1S,2R,7R,8R,8aR)-1,2,7,8-tetrahydroxyindolizidine (44 and 46), is reported. The synthesis is based on Knoevenagel homologation of the readily available enantiomerically pure pyrrolidin-carbaldehydes 13 and 37followed by asymmetric dihydroxylation of the subsequent alkenyl pyrrolidines and cyclization of the corresponding imino-octitols. The new indolizidines and their precursors (imino-octitols 20, 25, 26) and indolizidinones 28a and 28b have been tested for inhibitory activities toward 26 glycosidases. The enzymatic inhibition of trans-7-hydroxy-d-(-)-swainsonine (44) toward alpha-mannosidases is similar to that described for trans-7-hydroxy-l-(+)-swainsonine (11b) toward naringinase (alpha-l-rhamnosidase from Penicillium decumbens). 相似文献
64.
Blanco JM Caamaño O Fernández F Rodríguez-Borges JE Balzarini J de Clercq E 《Chemical & pharmaceutical bulletin》2003,51(9):1060-1063
Six new carbocyclic nucleosides were prepared by constructing a purine base (in compounds 9-11) or pyrimidine base (in 6-8) on the amino groups of (+/-)-(1 beta,2 alpha,4 beta)-4-amino-1,2-cyclopentanedimethanol (4) and (+/-)-(1 beta,3 alpha,4 beta)-4-amino-1,3-cyclopentanedimethanol (5), and their activities against a variety of viruses and tumour cell lines were determined. 相似文献
65.
The main objective of this work is to develop a routine quality control method for pesticide residues in cocoa beans, using gas chromatography-mass spectrometry. The investigated pesticides, which are used to control pests in the growing of cacao, are: Acephate, Propoxur, HCH, Heptachlor, Fenitrothion, Pirimiphos-methyl, Aldrin, Dieldrin, pp'-DDE, op-DDE and DDT. Two extraction methods were tested. The first was based on strong attack by concentrated sulphuric acid and later extraction with n-hexane: the investigated residues were Acephate, HCH, Fenitrothion and DDT; recoveries were 68-95% and the detection limits 0.5-10 ppb. The second extraction method was based on the Universal Trace Residue Extractor (UNITREX), which consists of a distillation system for organophosphorus and organochlorine pesticides in fatty samples. The investigated residues were Heptachlor, Pirimiphos-methyl, Aldrin, Propoxur, Dieldrin, op-DDE and pp'-DDE; recoveries were 67-88% and the detection limits 1-10 ppb. 相似文献
66.
Carlos Rodríguez-Abreu Massimo Lazzari Dharmesh Varade Masaya Kaneko Kenji Aramaki Manuel Arturo López Quintela 《Colloid and polymer science》2007,285(6):673-680
The structure and rheological properties of a poly(dimethylsiloxane)-graft-poly(oxyethylene) copolymer at high concentrations
in block-selective solvents were studied by small-angle X-ray scattering (SAXS) and rheometry. Analysis of SAXS data indicates
that quasispherical, reverse micellar aggregates (with no ordered packing) are present in concentrated solutions of the copolymer
in nonpolar solvents, and that upon addition of water, the size of such aggregates increases due to the solubilization inside
the micellar cores. The viscosity of concentrated polymer solutions increases exponentially as water is added, and finally,
viscoelastic, gel-like behavior is found in the vicinity of the phase separation limit. It was found that small silver nanoparticles
with an average diameter of ≈3 nm can be synthesized inside the copolymer aggregates without the need of a reducing agent;
namely, particles embedded in a viscoelastic matrix are obtained. The synthesis seems to follow first-order kinetics.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
67.
Fandos R Hernández C Otero A Rodríguez A Ruiz MJ Terreros P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(3):671-677
Titanium complexes with chelating alkoxide ligands [TiCp*(O(2)Bz)(OBzOH)] (1) and [TiCp*(Me)((OCH(2))(2)Py)] (2) were synthesised by reaction of [TiCp*Me(3)] (Cp*=eta(5)-C(5)Me(5)) with 2-hydroxybenzyl alcohol ((HO)(2)Bz) and 2,6-pyridinedimethanol ((HOCH(2))(2)Py), respectively. Complex 1 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) to yield the early-late heterobimetallic complexes [TiCp*(O(2)Bz)(2)M(cod)] [M=Rh (3), Ir (4)]. Carbon monoxide readily replaces the COD ligand in 3 to give the rhodium dicarbonyl derivative [TiCp*(O(2)Bz)(2)Rh(CO)(2)] (5). Compound 2 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) with protonolysis of a Tibond;Me bond to give [TiCp*((OCH(2))(2)Py)(mu-O)M(cod)] [M=Rh (6), Ir (7)]. The molecular structures of complexes 3, 5 and 7 were established by single-crystal X-ray diffraction studies. 相似文献
68.
J. Doménech E. Brillas J. A. Garrido R. M. Rodríguez 《Monatshefte für Chemie / Chemical Monthly》1987,118(2):197-202
Viscosities and densities of lithium perchlorate solutions in different ethylene glycol-water compositions have been measured at 25.0 and 35.0 °C. From these data, the correspondingB-coefficients of theJones-Dole equation have been determined. TheB-value depends on the solvent composition and it reaches a maximum in the water-rich region. This behaviour is analysed in terms of ionic solvation and solvent structure.
Viskositäts-B-Koeffizienten für Lösungen von Lithiumperchlorat in Ethylenglykol-Wasser-Mischungen
Zusammenfassung Es wurden die Dichten und Viskositäten für Lösungen von Lithiumperchlorat in verschieden zusammengesetzten Ethylenglykol-Wasser-Mischungen bei 25 °C und 35 °C gemessen. Auf Grund der erhaltenen Daten wurden dieB-Koeffizienten in den entsprechendenJones-Dole-Gleichungen für die relative Viskosität bestimmt. DieB-Werte hängen von der Zusammensetzung des Lösungsmittels ab und erreichen im wasserreichen Konzentrationsgebiet ein Maximum. Dieses Verhalten wird in Hinblick auf die Ionensolvatation und die Struktur des Lösungsmittels analysiert.相似文献
69.
Cabaleiro-Lago EM Rodríguez-Otero J Varela-Varela SM Peña-Gallego A Hermida-Ramón JM 《The Journal of organic chemistry》2005,70(10):3921-3928
[reactions: see text] Electrocyclization reactions of (3Z)-1,3,5-hexatrienone and nitrogen derivatives were studied by performing density functional theory (DFT) calculations together with the 6-31+G* basis set. Reactants, products, and transition states for each reaction were localized and the IRC connecting reactants and products was also obtained. Magnetic properties were evaluated along the reaction path to elucidate the characteristics of the reactions studied. As obtained from the calculations, electrocyclization of (3Z)-1,3,5-hexatrienone is a pericyclic process, as indicated by a variety of indexes, such as Nucleus Independent Chemical Shift (NICS), anisotropy of the magnetic susceptibility, or anisotropy of the current-induced density (ACID). This reaction presents characteristics of pericyclic reactions despite the activation energy lowering relative to the electrocyclization of (4Z)-1,2,4,6-heptatetraene, and the relatively small NICS values observed in the transition state. Magnetic properties indicate that an enhancement of the aromaticity relative to reactants and products occurs revealing the absence of orbital disconnections on the cyclic loop of interacting orbitals. Only two reactions among those studied exhibit pseudopericyclic character due to the in-plane attack of the lone pair on nitrogen. In these cases, the reactions showed no barrier for the electrocyclization process, and no aromaticity enhancement was observed. 相似文献
70.
Canosa P Morales S Rodríguez I Rubí E Cela R Gómez M 《Analytical and bioanalytical chemistry》2005,383(7-8):1119-1126
The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive
determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry
detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments
were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges
respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation
pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well
as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts
of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water
samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one
to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis
of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products
(2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when
products containing triclosan are mixed with chlorinated tap water. 相似文献