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131.
The kinetics of ligand substitution between aquapentacyanoruthenate(II) ion, [Ru(CN)5H2O]3− and 4-cyanopyridine (4-CNpy) has been investigated spectrophotometrically in the presence of anionic surfactant micelle,
namely sodium dodecylsulphate (SDS) at 400 nm (λmax of the intense yellow product [Ru(CN)54-CNpy]3−) under pseudo-first-order conditions using at least 10% excess of 4-CNpy over [Ru(CN)5H2O]3−. The reaction was studied as a function of [Ru(CN)5H2O3−], [4-CNpy], [SDS], pH, ionic strength and temperature, by varying each of these variables one at a time. The reaction exhibited
overall second-order kinetics, being first order each in [4-CNpy] and [Ru(CN)5H2O3−] over a wide concentration range. Variation of ionic strength of the medium had a significant negative effect on the rate.
The SDS micelle, being negatively charged, does not reveal any regular effect except at or near its critical micelle concentration
(c.m.c). The rate of reaction was measured at different temperatures, and the activation parameters were computed using Arrhenius
and Eyring plots. A plausible mechanism consistent with the experimental results has been proposed. 相似文献
132.
Suryawanshi S Mehrotra N Asthana RK Gupta RC 《Rapid communications in mass spectrometry : RCM》2006,20(24):3761-3768
Swertia chirata is a bitter plant, used in the Indian system of medicine (Ayurveda) for various human ailments. The bioactive constituents include the xanthone and secoiridoid glycosides consisting of mangiferin, amarogentin, amaroswerin, sweroside and swertiamarin. Methanolic extracts of S. chirata possess constituents with antidiabetic activities, which was investigated by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Preliminary HPLC analyses were performed on a reversed-phase C18 column using gradient elution. In the LC/ESI-MS spectra, predominant [M+H]+ and [M+Na]+ ions were observed in positive ion mode and provided molecular mass information. The five components of S. chirata were structurally correlated and confirmed based on the fragmentation characteristics and information available in the literature. The fragmentation behavior of [M+H]+/[M+Na]+ ions of these components were deduced from the collision-induced dissociation (CID) spectra obtained from the selective on-column information-dependant acquisition (IDA) approach. Xanthone-C-glycoside showed characteristic fragment ions due to fragmentation in the C-glycosidic unit while iridoid-O-glycosides showed characteristic fragment ions due to cleavage in the glycoside linkage and retro-Diels-Alder (RDA) cleavage within an iridoid aglycone. Furthermore, on the basis of this information, an analytical assay was developed and validated to determine relative concentrations of mangiferin, amarogentin, amaroswerin, sweroside and swertiamarin. The detection was carried out using multiple reaction monitoring (MRM) in positive ionization mode with a total analysis time of 3.5 min. The method was successfully applied to standardize four different batches of herbal preparation on the basis of relative concentration of five bioactive components. 相似文献
133.
Zhou H Wang DA Baldini L Ennis E Jain R Carie A Sebti SM Hamilton AD 《Organic & biomolecular chemistry》2006,4(12):2376-2386
Platelet-derived growth factor (PDGF) and its receptor PDGFR are required for tumor growth and angiogenesis, so disruption of the PDGF-PDGFR interaction should lead to starvation of tumors and reduction of tumor growth. Potent PDGF antagonists have been discovered through the synthesis of a series of calix[4]arene-based compounds that are designed to bind to the three-loop region of PDGF. The effect of lower-rim alkylation, linker and number of interacting head groups on the calix[4]arene scaffold on PDGF affinity and cellular activity has been investigated. 相似文献
134.
The kinetics and mechanism of substitution reaction of [Ru(CN)5H2O]3? anion with two naphthalene‐substituted ligands viz. Ln = nitroso‐R‐salt (NRS) and α‐nitroso‐β‐naphthol (αNβN) have been studied spectrophotometrically by monitoring an increase in absorbance at λmax = 525 nm corresponding to metal to ligand charge transfer (MLCT) transitions due to formation of substituted [Ru(CN)5L]n?3 as a function of pH, ionic strength, temperature, a wide range of ligands concentration, and [Ru(CN)5H2O3?] under pseudo‐first‐order conditions. The experimental observation suggests that [Ru(CN)5H2O]3? ion interacts with both ligands, which finally get converted into corresponding, [Ru(CN)5L]n?3 complexes as a final reaction product. The reaction is found to obey first‐order dependence each in [Ru(CN)5H2O3?] and [Ln]. The substituted products, viz. [Ru(CN)5L]n?3, in each case have strong MLCT transitions in visible region. The substitutional lability of [Ru(CN)5H2O]3? has been discussed in terms of electronic effect on the M? OH2 bond interactions. The kinetic observation suggests that the complexation reaction of [Ru(CN)5H2O]3? with both the ligands, i.e., NRS and αNβN, follows an ion pair dissociative mechanism. The thermal activation parameters ΔH≠ and ΔS≠ have been calculated using Eyring's equation and provided in support for the proposed mechanistic scheme. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 21–30, 2011 相似文献
135.
136.
Ajay Singh Karakoti Ritesh Shukla Rishi Shanker Sanjay Singh 《Advances in colloid and interface science》2015
Quantum dots are a group of inorganic nanomaterials exhibiting exceptional optical and electronic properties which impart distinct advantages over traditional fluorescent organic dyes in terms of tunable broad excitation and narrow emission spectra, signal brightness, high quantum yield and photo-stability. Aqueous solubility and surface functionalization are the most common problems for QDs employed in biological research. This review addresses the recent research progress made to improve aqueous solubility, functionalization of biomolecules to QD surface and the poorly understood chemistry involved in the steps of bio-functionalization of such nanoparticles. 相似文献
137.
Rishi Kumar 《Liquid crystals》2013,40(5):694-700
Guest–host polymer stabilised ferroelectric liquid crystal (PSFLC) composite films have been prepared by polymerisation-induced phase separation process. A small quantity (0.1, 0.25 and 0.5 wt %) of anthraquinone dye in PSFLC host matrix was homogeneously dispersed to create molecular ordering in fibrils network of guest–host composite film. Ordered twisted fibril morphology was clearly observed through optical polarising microscope and thus we determined the order parameter from the dichroism measurements with the help of polarised fluorescence spectroscopy, which impacts the significant contribution of dye molecules into the smectic layers of the host polymer stabilised ferroelectric matrix. 相似文献
138.
Neetu Tiwari Anupama Asthana Kanchan Upadhyay 《Research on Chemical Intermediates》2013,39(6):2867-2879
A sensitive analytical procedure based on solid phase extractive-spectrophotometry has been established for the determination of the widely used herbicide atrazine .The method is based on the Konig reaction in which atrazine reacts with pyridine reagent to form a quaternary pyridinium halide, which further forms glutaconic aldehyde in the presence of alkali. Glutaconic aldehyde is subsequently coupled with 4-aminoacetanilide in the micellar medium of anionic surfactant sodium dodecyl sulphate to give a yellow-orange dye. The produced dye was enriched on a C18 cartridge and is measured spectrophotometrically at 460 nm. The sensitivity and selectivity of the method was largely enhanced in the micellar media and SPE on the C18 cartridge and avoids the use of toxic solvents. Beer’s law was obeyed in the range 0.012–0.12 μg mL?1. Molar absorptivity and Sandell’s sensitivity were found to be 1.52 × 106 L mol? 1 cm?1 and 0.0002 μg cm?2, respectively. The limit of detection and quantification were 0.001 and 0.003 μg mL?1, respectively. The proposed method was applied successfully for the determination of atrazine in environmental and biological samples with a recovery range of 96–101 %. The method was found to be free from interference of a large number of foreign species. The accuracy and reliability of the method was further established by parallel determination by the reference method, and by recovery studies. 相似文献
139.
Kanchan Upadhyay Anupama Asthana Neetu Tiwari Snitha B. Mathew 《Research on Chemical Intermediates》2013,39(8):3553-3563
A simple and sensitive spectrophotometric method for the determination of nimesulide in bulk, in pharmaceutical dosage form, and in biological fluids was developed. The method is based on the reduction of the nitro group of nimesulide by zinc and hydrochloric acid followed by diazotization, and coupling with orcinol in basic medium to form a stable chromophore, which absorbs at 465 nm. The method showed a good linearity in the range 0.4–4.0 μg mL?1. Partial least square modeling as a powerful multivariate statistical tool is also applied, compiled, and compared for determination of nimesulide. The experimental matrix for the partial least square calibration method was designed with 24 samples. The cross-validation was used for selecting the number of factors. The root mean square error prediction (RMSEP) and the relative error of prediction (REP %) were 0.089 and 3.95, respectively. The developed method is free from the interference of common excipients used in pharmaceutical dosages. The method was also used for the determination of nimesulide in pharmaceutical dosages as well as in human serum and urine samples. 相似文献
140.