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91.
Castro J Pérez RA Miguel E Sánchez-Brunete C Tadeo JL 《Journal of chromatography. A》2002,947(1):119-127
Rapid analytical methods for the determination of endosulfan isomers and endosulfan-sulfate in air and plant samples were developed. The insecticides were trapped from air using a column containing Florisil and extracted with a low volume of ethyl acetate, assisted by sonication. Pesticide residues were determined by gas chromatography with electron-capture detection using a nonpolar capillary column. Residue identities were confirmed by gas chromatography coupled with mass spectrometry. Recoveries of these compounds from air samples were always higher than 78% with an RSD lower than 11% and the detection limits obtained were at least 0.3 ng/l air. Leaf samples were homogenised with ethyl acetate and extracts cleaned-up on an aluminium oxide column. Pesticides were eluted with a hexane-ethyl acetate (80:20, v/v) mixture. Recoveries obtained from plant samples were higher than 78% with an RSD lower than 14% and detection limits in leaves were 0.02 microg/g for each pesticide. These methods were applied to study the volatilisation of endosulfan from tomato leaves under laboratory conditions. A volatilisation rate near 1% of the initial amount of endosulfan per hour was obtained during the first 24 h at room temperature. 相似文献
92.
Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
93.
The individual and simultaneous enzymatic determination of ethanol and acetaldehyde in wine by flow injection analysis is described. Individual determinations of 0.002–0.016% (v/v) ethanol or 1.0–8.0 μg ml?1 acetaldehyde with r.s.d. 0.7% and 0.5%, respectively, are done with a single-beam spectrophotometer, based on the use of alcohol dehydrogenase and aldehyde dehydrogenase. A diode-array detector and dual reagent injections are used for the simultaneous determination of the two compounds. The errors are 〈 3.5% and 〈 2.0% for ethanol and acetaldehyde, respectively, when the method is applied to wine samples. 相似文献
94.
Maria Ana Castro Zulema D. Chaia Oscar E. Piro Fabio D. Cukiernik Eduardo E. Castellano Marcia Rusjan 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):m393-m395
The title compound, tetrakis(μ‐3,4,5‐triethoxybenzoato‐κ2O:O′)bis[(pyrazine‐κN)rhodium(II)](Rh—Rh), [Rh2(C13H17O5)4(C4H4N2)2], crystallizes on an inversion centre in the triclinic space group . The equatorial carboxylate ligands bridge the two RhII atoms, giving a binuclear lantern‐like structure. The pyrazine molecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10° with respect to the attached carboxylate groups. The pyrazine planes have a torsion angle of ca 19° around the Rh—N bond with respect to the plane of the nearer carboxylate group and are not coplanar with the Rh—Rh bond. 相似文献
95.
The electrochemical oxidation of anodic cobalt, nickel, and zinc in acetonitrile containing both 2-pyrrole-[N-(o-hydroxyphenyl)methylimines] (H2L) and a bidentate ligand (1, 10-phenanthroline(phen) or 2,2′-bipyridine(bipy)) yielded compounds of general formula M(HL)2 · phen and M(HL)2 · bipy (M = Co, Ni, Zn). The crystal structure of 2,2′-bipyridine bis{2-[(2-pyrrole)methylimino]5-methylphenolato}nickel(II) was determined by X-ray diffraction. This compound crystallizes in the orthorhombic space group Pccn with a = 19.430(2), b = 28.488(2), c = 17.567(1) Å. The nickel atom has a distorted octahedral geometry, and the pyrrole nitrogen is not coordinated. The IR, 1H-NMR and UV-visible spectra of the complexes are discussed and related to the structure. 相似文献
96.
Jorge Bravo Jesús Castro Soledad García‐Fontn Elvira M. Lamas Pilar Rodríguez‐Seoane 《无机化学与普通化学杂志》2003,629(2):297-302
The manganese carbonyl complex [MnBr(CO)3 L ] ( 1 ), where L = Ph2POCH2CH2OPPh2, was prepared by reacting [MnBr(CO)5] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)2 LL ′], where L ′ = P(OMe)3 ( 2 ) or P(OEt)3 ( 3 ) and [MnBr(CO)3 L ′2], where L ′ =PPh(OEt)2 ( 4 ) or PPh2(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (1H, 13C and 31P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 . 相似文献
97.
Correia I Costa Pessoa J Duarte MT Henriques RT Piedade MF Veiros LF Jakusch T Kiss T Dörnyei A Castro MM Geraldes CF Avecilla F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(9):2301-2317
The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds. 相似文献
98.
M. Mora M. E. Castro A. Nio F. J. Melendez C. Muoz‐Caro 《International journal of quantum chemistry》2005,103(1):25-33
This work presents an analysis of the equivalence of MP2 and DFT (B3LYP functional) conformational populations. As a test case, we select three cholinergic agents (trans‐nicotine, acetylcholine, and the nicotinic analgesic ABT‐594), where the minima on the conformational energy hypersurfaces expand a large range of energies (~0–30 kJ mol?1). From energetic and structural data obtained in vacuo at the MP2 and B3LYP/cc‐pVDZ levels, we build conformational partition functions, including the effect of the conformational kinetic energy and the rotovibrational coupling. Our results at a physiological temperature (37°C) show qualitative agreement in all cases. Quantitative agreement, however, is only found for trans‐nicotine and ABT‐594. In the first case, energy minima differ by <0.2 kJ mol?1. Therefore, the equivalence of structural results translates in the equivalence of the conformational distribution. For ABT‐594, the minima are separated by as much as 8.0 kJ mol?1, and the conformational energy determines the conformational distribution. In this case, the slight relative variation of conformational energy, between B3LYP and MP2, does not affect the population, since the secondary minima are high in energy and very low in population. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
99.
1,2,4-Thiadiazolo[2,3-a]pyridinium chlorides undergo a very facile base promoted transformation to give bispyridilimino-1,2,4-thiadiazolidines. The unequivocal structural assignment of these last compounds was achieved by spectroscopic 1H, 13C and 15N two dimensional methods. 相似文献
100.
German Urbina-Villalba Leonardo J. Rodriguez German R. Castro Fernando Ruette 《Journal of computational chemistry》1992,13(7):867-873
The electronic structure of cobalt silicide clusters Co7Si7 and Si7Co7 was studied in comparison to that of Co19 and Si17 clusters under the scope of the MINDO/SR method. Clusters Co7Si7 and Si7Co7 represent the environment of a cobalt atom and that of a silicon atom in the cobalt monosilicide bulk, respectively. It is found that the Co? Si bond is essentially sp in character with an indirect participation (by electrostatic interaction) of the cobalt d orbitals. Our calculations show a charge transfer from silicon to the d orbitals of cobalt via sp–sp interaction with an internal sp–d hybridization. The theoretical density of states for cobalt silicide clusters are reported and compared with experimental results of surface spectroscopies. © 1992 by John Wiley & Sons, Inc. 相似文献