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181.
The kinetics of oxidation of D-mannose with pyridinium chlorochromate, C5H5NHCrO3Cl, was investigated in aqueous perchloric acid medium. The ionic strength of the medium was maintained constant by adding sodium perchlorate solution. The oxidation process exhibits unit dependence in each of the reactants, namely D-mannose and pyridinium chlorochromate. The reaction is acid catalyzed. A 32 stoichiometry is observed in the oxidation and the reaction did not induce polymerization of acrylonitrile. Activation parameters have been computed by measuring the rates at different temperatures. A reaction mechanism consistent with the experimental observation is proposed. 相似文献
182.
R. S. Tiwari N. Mehta R. K. Shukla A. Kumar 《Journal of Thermal Analysis and Calorimetry》2005,81(1):45-49
Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses.
DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition
and crystallization temperatures. The variation of glass transition temperature Tgwith Ag concentration has been studied. It has been found that Tgdecreases with increase in Ag concentration. The heating rate dependence of Tgis used to evaluate the activation energy of glass transition (DEt). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DEthas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of
Ag. 相似文献
183.
Km Meenu Neeraj Kumar Kautily Rao Tiwari Tara Yadav Radha Tomar Arvind Kumar Gupta 《Phosphorus, sulfur, and silicon and the related elements》2020,195(10):881-888
AbstractIn this study, we have evaluated the performance of novel adsorbent zeolite Linde Type W and modified LTW with AgO metal oxide composite for the decontamination of chemical warfare agent simulant 2-chloroethylphenylsulphide (CEPS). Zeolites are nanoporous aluminosilicate minerals composed of silicon, aluminum and oxygen framework with cations and water molecules within the pores. The synthesized zeolite LTW and its composites Ag-O-LTW was characterized by XRD, FTIR, SEM-EDS and BET analytical techniques. The decontamination study of CWA simulant, CEPS was monitored by using GC-FID technique. The nanocrystalline zeolite LTW and Ag-O-LTW composites were found powerful adsorbents and showed great decontamination potential toward CWA simulant CEPS. The Ag-O-LTW showed better results (~98 % decontamination in 7?hours) than LTW zeolite. 相似文献
184.
This paper deals with anisotropic behavior of thermal expansivity (α) of poly(ether-ether-ketone) (PEEK) sample prepared by compression molding above the melting point of polymer. The α was determined using thermo mechanical analyzer (TMA) for the temperature interval 50-250 °C in expansion mode. It is found that out-of-plane thermal expansivity (αz) is 3.8-fold of the in-plane thermal expansivity (αxy) below the glass transition temperature (Tg) of PEEK while αz is decreased to 1.8-fold of the αxy above the Tg. Moreover, the average αz over the range studied is about 2.2-fold of the αxy. This anisotropic behavior may be attributed to the alignment of polymer spherulites and chains along in-plane direction due to compressive forces under hot compression molding. 相似文献
185.
186.
187.
Neerja Tiwari Akhilesh Kumar Yadav Madan Mohan Gupta 《Journal of separation science》2013,36(14):2373-2378
Vitex trifolia L. is an important Indian medicinal plant with diverse pharmacological properties. In a recent study, we reported the isolation and antitubercular activity evaluation of three new diterpenoids from its leaves; here we have developed a validated rapid, simple, precise, and accurate high‐performance TLC method for the simultaneous quantification of isolated diterpenoids in V. trifolia. Diterpenoids, 6α,7α‐diacetoxy‐13‐hydroxy‐8(9),14‐labdadien ( A ), 13‐hydroxy‐5(10),14‐halimadien‐6‐one ( B ), and 9‐hydroxy‐13(14)‐labden‐16,15‐olide ( C ) were separated on silica gel 60F254 high‐performance TLC plates using chloroform/acetone (98:2, v/v) as mobile phase. The quantitation of diterpenoids was carried out using densitometric reflection/absorption mode at 610 nm after postchromatographic derivatization using a vanillin/sulfuric acid reagent. A precise and accurate quantification can be performed for compounds A and B in the linear working concentration range of 333–1000 ng/band and for C in the range of 670–2000 ng/band with good correlations (r = 0.9984, 0.9991, and 0.9994, respectively). The method was validated for peak purity, precision, accuracy, robustness, LOD, and LOQ, as per the ICH guidelines. The method reported here is simple, reproducible and may be applied for the quantitative analysis of the above diterpenoids in the leaves of V. trifolia. 相似文献
188.
The [Ag]+‐catalyzed exchange of coordinated cyanide in [Fe(CN)6]4? by phenylhydrazine (PhNHNH2) has been studied spectrophotometrically at 488 nm by monitoring increase in the absorbance for the formation of cherry red colored complex [Fe(CN)5PhNHNH2]3?. The other reaction conditions were pH 2.80±,0.02, temperature = 30.0 ± 0.1°C, and ionic strength (I) = 0.02 M (KNO3). The reaction was followed as a function of pH, ionic strength, temperature, [Fe(CN)4?6], [PhNHNH2], [Ag+] by varying one variable at a time. The initial rates were evaluated for each variation using the plane mirror method. The initial rates evaluated as a function of [Fe(CN)4?6] clearly indicate that the initial rate increases with the increase in [Fe(CN)4?6] and finally reaches to a limiting value when [Fe(CN)4?6]/[AgNO3] ? 1000. It indicates the formation of a strong adduct between [Fe(CN)6]4? and AgNO3 prior to the abstraction of CN?. The variation in initial rates with [PhNHNH2] also showed limiting values at [Fe(CN)4?6]/[PhNHNH2] ? 8.30. The complex behavior due to pH and [Ag+] variations on the rate has been explained in detail. The composition of the final reaction product [Fe(CN)5PhNHNH2] formed during the course of reaction has been found to be 1:1 using the mole ratio method. The evaluated values of activation parameters for the catalyzed reaction are Ea = 53.85 kJ mol?1, Δ H≠, = 51.33 kJ mol?1, and Δ S≠ = ?134.63 J K?1 mol?1, which suggest an interchange dissociative mechanism. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 447–456, 2007 相似文献
189.
Bhim Bali Prasad Khushaboo Tiwari Meenakshi Singh Piyush Sindhu Sharma Amit Kumar Patel Shrinkhala Srivastava 《Biomedical chromatography : BMC》2009,23(5):499-509
Main inborn errors of metabolism diagnosable through uracil (Ura) analysis and the therapeutic monitoring of toxic 5‐fluorouracil (5FU) in dihydro pyrimidine dehydrogenase (DPD) deficient patients require a sensitive, reproducible, selective and accurate method. In this work, an artificial receptor in the format of molecularly imprinted polymer (MIP) brush ‘grafted to’ the surface of sol–gel immobilized on cost‐effective homemade solid‐phase microextraction (SPME) fibers, individually imprinted with either of Ura and 5FU, was used in combination with a voltammetric sensor duly modified with the same MIP. This combination provided up to 10‐ and 8.4‐fold preconcentrations of Ura and 5FU, respectively, which was more than sufficient for achieving stringent detection limits in the primitive diagnosis of uracil disorders and fluoropyrimidine toxicity in DPD‐deficient patients. The proposed method permits the assessment of Ura and 5FU plasma concentrations with detection limits pf 0.0245 and 0.0484 ng mL?1 (RSD = 1.0–2.5%, S/N = 3), respectively, without any problems of non‐specific false‐positives and cross‐reactivities in complicated matrices of biological samples. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
190.
Anil K. Singh Ram Kishan Vijay Bahadur Narayanasamy Vijayan Vadivelu Balachandran Hemandra K. Tiwari Brajendra K. Singh Brijesh Rathi 《Journal of Physical Organic Chemistry》2014,27(6):490-497
Novel phthalimides ( 1 , 2 , 3 ) possessing variability of cyclic amines have been synthesized and characterized by analytical and spectroscopic techniques. Phthalimide 1 and 2 crystallized in a triclinic system with space group Pī; however, an orthorhombic system with a chiral space group of P212121 was observed for 3 possessing piperidine cyclic amine. The hydrogen atoms attached to the central chiral carbon were oriented anti to each other resulting in minimum steric repulsion. The occurrence of C–H···O hydrogen bonds in 1 , 2 , 3 enabled the building of several supramolecular structures. Hyperpolarizability 197.6096 Debye Å2 calculated for 1 was found to be higher than the hyperpolarizabilities, 138.0836 and 165.2521 Debye Å2 measured for 2 and 3 , respectively. Subsequently, phthalimides ( 1 , 2 , 3 ) were assessed for second harmonic generation (SHG) response, and a negligible response was recorded for 1 and 2 ; however, 3 showed a significant response of 14.2 mV. In addition to acentric structure, helical structural motifs identified in 3 could be responsible for its enhanced SHG response. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献