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排序方式: 共有496条查询结果,搜索用时 31 毫秒
1.
1R,2S,5R,8R; 1R,2S,5R,8S; 1S,2S,5R,8R; and 1S,2S,5R,8S-Iridodials have been prepared in five steps from 4aS,7S,7aR and 4aS,7S,7aS-nepetalactones, major components of catnip oil. 1R,2S,5R,8R-Iridodial has been identified as a male-produced male-aggregation pheromone for Chrysopa oculata, the first pheromone of any kind identified for lacewings. 相似文献
2.
Farukh Arjmand Shamima Parveen Mala Chauhan Shaiba Parveen Sartaj Tabassum 《Transition Metal Chemistry》2006,31(2):237-245
New mononuclear and dinuclear complexes [3-hydroxyethyl-1,3,5,8,11pentaazacyclotridecane]copper(II) (1)/nickel(II) (2) perchlorate and O,O ethane bridged bis-copper(II) (3)/nickel(II) (4) macrocycles have been synthesized and characterized by various spectroscopic techniques, viz. i.r., n.m.r., e.p.r., u.v.–vis. and conductance measurements. Spectral data and conductance measurements reveal that all
the complexes are consistent with square-planar geometry and are ionic in nature. The catalytic activity of the dinuclear
Cu(II) complex (3) in the presence of pyrocatechol was determined spectrometrically by monitoring the increase of the o-benzoquinone characteristic absorption band at 25,000 cm−1 with respect to time in DMF saturated with molecular oxygen. The kinetic parameters Vmax (2.8×10−3 M s−1) and KM (1.4×10−3 mm) have been determined by Michaelis–Menten method. Electrochemistry of the dinuclear Cu(II) complex has been studied in the
presence of molecular oxygen with pyrocatechol and without pyrocatechol at a scan rate of 0.1 V s−1 by cyclic voltammetry. On addition of pyrocatechol, complex shows a shift in Epc, Epa and E1/2 values indicating the oxidation of substrate (pyrocatechol). 相似文献
3.
Isocytosine (ICH) exists in solution as two major tautomers, the keto form with N1 carrying a proton (1a) and the keto form with N3 being protonated (1b). In water, 1a and 1b exist in equilibrium with almost equal amounts of both forms present. Reactions with a series of Pd(II) and Pt(II) am(m)ine species such as (dien)Pd(II), (dien)Pt(II), and trans-(NH(3))(2)Pt(II) reveal, however, a distinct preference of these metals for the N3 site, as determined by (1)H NMR spectroscopy. Individual species have been identified by the pD dependence of the ICH resonances. pK(a) values (calculated for H(2)O) for deprotonation of the individual tautomers complexes are 6.5 and 6.4 for the N3 linkage isomers of dienPd(II) and dienPt(II), respectively, as well as 6.2 and 6.0 for the N1 linkage isomers. The dimetalated species [(dienM)(2)(IC-N1,N3)](3+) (M = Pd(II) or Pt(II)) are insensitive over a wide range of pD. The crystal structure analysis of [(dien)Pd(ICH-N3)](NO(3))(2) is reported. Ab initio calculations have been performed for tautomer compounds of composition [(NH(3))(3)Pt(ICH)](2+), cis- and trans-[(NH(3))(2)PtCl(ICH)](+), as well as trans-[(NH(3))(2)Pt(ICH)(2)](2+). Without exception, N3 linkage isomers are more stable, in agreement with experimental findings. As to the reasons for this binding preference, an NBO (natural bond orbital) analysis for [(NH(3))(3)Pt(ICH-N3)](2+)strongly suggests that intramolecular hydrogen bonding between trans-positioned NH(3) ligands and the two exocyclic groups of the ICH is of prime importance. The calculations furthermore show a marked pyramidalization of the NH(2) group of ICH in the complex once the heterocyclic ligand forms a dihedral angle <90 degrees with the Pt coordination plane. 相似文献
4.
Gupta D Roitzsch M Lippert B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6643-6652
Isocytosine (ICH; 1) exists in solution in an equilibrium of tautomers 1a and 1b with the N1 and N3 positions carrying the acidic proton, respectively. In the solid state, both tautomers coexist in a 1:1 ratio. As we show, the N3H tautomer 1b can selectively be crystallized in the presence of the model nucleobase 1-methylcytosine (1-MeC). The complex 1b x (1-MeC)2 x H2O (2) forms pairs through three hydrogen bonds between the components; hydrogen bonds between identical molecules are also formed, leading to an infinite tape structure. On the other hand, the N1H tautomer 1a co-crystallizes with protonated ICH to give [1a x ICH2]NO3 (3), again with three hydrogen bonds between the partners, yet the acidic proton is disordered over the two entities. With M(II)(dien) (M=Pt, Pd; dien=diethylenetriamine) preferential coordination of tautomer 1a through the N3 position is observed. DFT calculations, which were also extended to Pt(II)(tmeda) linkage isomers (tmeda=N,N,N',N'-tetramethylethylenediamine), suggest that intramolecular hydrogen bonding between the ICH tautomers and the co-ligands at M, while adding to the preference for N3 coordination, is not the major determining factor. Rather it is the inherently stronger Pt-N3 bond which favors complexation of 1a. With an excess of M(II)(dien), dinuclear species [M2(dien)2(IC-N1,N3)]3+ (M=Pd(II), 4 and Pt(II), 5) also form and were isolated as their ClO4(-) salts and structurally characterized. In strongly acidic medium 5 is converted to [Pt(dien)(ICH-N1)]2+ (6), that is, to the Pt(II) complex of tautomer 1b. 相似文献
5.
Moni Chauhan Claude Chuit Robert J. P. Corriu Catherine Rey Jean-Paul Declercq Antoine Dubourg 《Journal of organometallic chemistry》1996,510(1-2):173-179
The X-ray structure analysis of bis(8-dimethylamino-l-naphthyl)phenylphosphane (3) and of the corresponding sulphide 4 has revealed hexacoordination at phosphorus in both cases, the N … P separations being less than the sum of the van der Waal radii. Furthermore, in both cases the overall geometry corresponds to a distorted bicapped tetrahedron. The optimum geometry calculated for 4 via the
program developed by Autodesk (MM + method) suggests that the structure of the molecule is a function not only of steric requirements but also of electronic effects. 相似文献
6.
7.
Patel RN Singh N Shukla KK Gundla VL Chauhan UK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2603-2610
X-band electron spin resonance (ESR) and UV-vis spectra of a homobinuclear [(Bipy)2Cu-E-Im-Cu(Bipy)2](BF4)3 and a heterobinuclear [(Bipy)2Cu-E-Im-Zn(Bipy)2](BF4)3 complexes, E-Im=2-ethylimidazolate ion have been described as possible models for superoxide dismutase (SOD). Magnetic moment and ESR spectral measurements of the homobinuclear complex have shown an antiferromagnetic exchange interaction. From pH-dependent ESR and UV-vis spectral measurements studies, these complexes have been found to be stable over 8.5-10.5 pH range. These complexes catalyze the dismutation of superoxide (O2-) at biological pH. All the observations indicate that these complexes act as good possible models for superoxide dismutase. 相似文献
8.
The biomimetic reduction of anti-inflammatory drug, nimesulide (1) with sodium borohydride catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides [TAPFe(III)Cl] has been studied in organic solvents under anaerobic and aerobic conditions. 相似文献
9.
10.
Recognizing the potential of combinatorial chemistry to accelerate drug discovery and development, most pharmaceutical and related industries are seriously looking toward combinatorial synthesis of compounds in order to facilitate the identification of 'lead' molecules. In particular, solid phase synthesis is the core technology for combinatorial chemistry and is widely used for generating libraries of structurally related compounds. Since many drugs contain the nitrogen heterocyclic component and since heterocycles possess a high order of structural diversity, a precise overview of recent progress in the combinatorial synthesis of nitrogen heterocycles using solid phase methodology would be useful. Since the progress in solid phase synthesis of organic molecules has been reviewed regularly from 1992 to 1998, only the development of solid phase combinatorial synthetic approaches of small nitrogen heterocycles since 1999 will be reviewed here. This review describes the solid phase synthesis of azepanes, benzodiazepines, benzimidazoles, benzothiazepines, cinnolines, indolizines, beta lactams, oxazepins, oxazoles including benzisooxazoles, hydantoins, piperidines, pyrimidines, pyrazolones, quinolones, trizolopyridazines and thiazoles. 相似文献