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排序方式: 共有491条查询结果,搜索用时 31 毫秒
321.
A novel stability-indicating high-performance liquid chromatographic (HPLC) method was developed and validated for assay and determination of impurities of emtricitabine in drug substance. Emtricitabine was found to be degraded under acidic, alkaline, and oxidative stress conditions and to be more labile under oxidative conditions. The drug proved to be stable to dry heat and photolytic degradation. Resolution of major and minor degradation impurities was achieved on an Intersil ODS-3V column utilizing 10 mM sodium phosphate buffer and methanol (85:15) as mobile phase. Detection was at 280 nm. Validation studies were performed as per ICH recommended conditions. The developed method was found to be linear, accurate, specific, selective, precise, and robust. 相似文献
322.
323.
Ramaswamy Murugavel Vadapalli Chandrasekhar 《Angewandte Chemie (International ed. in English)》1999,38(9):1211-1215
A weakly associated hexamer is formed for [GaCp*] (Cp*=C5Me5) in the solid state (see picture). The recent X-ray crystal structure analyses of [GaCp*] as well as the monomeric InI and TlI compounds [M(2,4,6-Trip3C6H2)] (Trip=2,4,6-iPr3C6H2) throw new light on the association and aggregation of monovalent Group 13 elements in the solid state. The synthesis of [Ni0{In[C(SiMe3)3]}4], a complex with terminally bonded InIR ligands, offers alternative σ-donor/π-acceptor ligands to organometallic chemists. The newest results in this area are likely to open up new and intriguing possibilities in the preparation of main group–transition metal clusters. 相似文献
324.
R. V. S. S. N. Ravikumar A. V. Chandrasekhar S. N. Rao N. Madhu B. J. Reddy Y. P. Reddy 《Crystal Research and Technology》1999,34(7):911-914
Spectroscopic investigations of Cr3+ doped ZAPH are carried out. From the nature of optical absorption bands and their splittings at the liquid nitrogen temperature, the site symmetry of the Cr3+ in ZAPH is attributed to orthorhombic distortion. 相似文献
325.
R. V. S. S. N. Ravikumar A. V. Chandrasekhar B. J. Reddy Y. P. Reddy K. Ikeda 《Crystal Research and Technology》2002,37(10):1127-1132
Cadmium Ammonium Phosphate Hexahydrate (CAPH) is analogous to naturally occurring struvite. CAPH crystals are grown by slow evaporation technique. These crystals are characterised by X‐ray, TG‐DTA and Infra‐red studies. Powder X‐ray pattern indicates the orthorhombic crystal structure analogous to struvite. TG‐DTA analysis suggests loss of water of hydration (6H2O) between 113 and 391°C. Later the substance melts and only Cd remains around 780 °C. Infra Red spectrum is characteristic of H2O, PO43‐ and NH4+ radicals. 相似文献
326.
The reaction of manganese(II) salts with organophosphonic acid [t-BuPO(3)H(2) or cyclopentyl phosphonic acid (C(5)H(9)PO(3)H(2))] in the presence of ancillary nitrogen ligands [1,10-phenanthroline (phen) or 2,6-bis(pyrazol-3-yl)pyridine (dpzpy)], afforded, depending on the stoichiometry of the reactants and the reaction conditions, dinuclear, trinuclear, and tetranuclear compounds, [Mn(2)(t-BuPO(3)H)(4)(phen)(2)]·2DMF (1), [Mn(3)(C(5)H(9)PO(3))(2)(phen)(6)](ClO(4))(2)·7CH(3)OH (2), [Mn(3)(t-BuPO(3))(2)(dpzpy)(3)](ClO(4))(2)·H(2)O (3), [Mn(4)(t-BuPO(3))(2)(t-BuPO(3)H)(2)(phen)(6)(H(2)O)(2)](ClO(4))(2) (4), and [Mn(4)(C(5)H(9)PO(3))(2)(phen)(8)(H(2)O)(2)](ClO(4))(4) (5). Magnetic studies on 1, 2, and 4 reveal that the phosphonate bridges mediate weak antiferromagnetic interactions between the Mn(II) ions have also been carried out. 相似文献
327.
Chandrasekhar V Nagarajan L Hossain S Gopal K Ghosh S Verma S 《Inorganic chemistry》2012,51(10):5605-5616
A multicomponent synthetic strategy involving copper(II) ions, tert-butylphosphonic acid (t-BuPO(3)H(2)) and 3-substituted pyrazole ligands has been adopted for the synthesis of soluble molecular copper(II) phosphonates. The use of six different 3-substituted pyrazoles, 3-R-PzH [R = H, Me, CF(3), Ph, 2-pyridyl (2-Py), and 2-methoxyphenyl (2-MeO-C(6)H(4))] as ancillary ligands afforded nine different decanuclear cages, [Cu(5)(μ(3)-OH)(2)(O(3)P-t-Bu)(3)(3-R-Pz)(2)(X)(2)](2)·(Y) where R = H, X = t-BuPO(3)H, and Y = (Et(3)NH(+))(4)(solvent) (1); R = Me, X = 3-MePzH, and Y = solvent (2); R = Me, X = t-BuPO(3)H, and Y = (Et(3)NH(+))(4)(solvent) (3); R = CF(3), X = t-BuPO(3)H, and Y = (Et(3)NH(+))(4)(solvent) (4); R = Ph, X = 3-PhPzH, and Y = solvent (5); R = 2-Py, X = 0.5 MeOH, and Y = solvent (6); R = 2-Py, X = none, and Y = solvent (7); R = 2-Py, X = H(2)O, and Y = (Et(3)NH(+)·PF(6)(-))(2)(solvent) (8); R = 2-MeO-C(6)H(4), X = MeOH or 0.5:0.5 MeOH/H(2)O, and Y = solvent (9). Compounds 1-6, 8, and 9 were isolated using a direct synthetic method which involves the reaction of copper(II) salts and the ligands, while 7 was obtained from an indirect route involving the reaction of preformed copper-pyridylpyrazolate precursor complexes and t-BuPO(3)H(2). The decametallic compounds 1-9 possess a butterfly shaped core. The core of the cages 1, 3, and 4 are tetraanionic and contain more phosphonates than pyrazole ligands, while the other cages are neutral and contain more pyrazoles than phosphonate ligands. Compounds 1-6 have been studied by electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The decanuclear cage 6 was shown to be a good plasmid modifier. 相似文献
328.
N.R. Patil R.M. Melavanki S.B. Kapatkar K. Chandrasekhar N.H. Ayachit Siva Umapathy 《Journal of luminescence》2012,132(3):558-565
The fluorescence quenching studies of carboxamide namely (E)-N-(3-Chlorophenyl)-2-(3,4,5-trimethoxybenzylideneamino)-4,5,6,7 tetrahydrobenzo[b]thiophene-3-carboxamide [ENCTTTC] by aniline and carbon tetrachloride in six different solvents namely toluene, cyclohexane, n-hexane, n-heptane, n-decane and n-pentane have been carried out at room temperature with a view to understand the quenching mechanisms. The Stern–Volmer (S–V) plots have been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximation model, it was possible to check these bimolecular reactions as diffusion-limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes Einstein relation. 相似文献
329.
Molecular transition-metal phosphonates 总被引:2,自引:0,他引:2
Chandrasekhar V Senapati T Dey A Hossain S 《Dalton transactions (Cambridge, England : 2003)》2011,40(20):5394-5418
Molecular transition-metal phosphonates are of relatively recent origin and can be assembled by several synthetic strategies. The nuclearity and the structure of the metal aggregates can be modulated by several factors including the stoichiometry of the reactants, nature of the metal precursor and the type of phosphonic acid used. This perspective summarizes some of the recent work carried out on copper(II)-, zinc(II)- and cadmium(II) phosphonates with particular emphasis on their synthesis and structure. 相似文献
330.