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21.
A new and highly sensitive spectrophotometric method is developed for the determination of sub ppm levels of the widely used organophosphorus insecticide dichlorvos. The method is based on alkaline hydrolysis of dichlorvos to dichloroacetaldehyde followed by coupling with diphenyl semicarbazide (DPC) in alkaline medium. The absorption maxima of the wine red dye compound formed is measured at 490 nm. Beer's law is obeyed over the concentration range of 4.3 to 34 μg in a final solution volume of 25 mL (0.18–1.36 ppm). The molar absorptivity, Sandell's sensitivity and correlation coefficient were found to be 2.9 × 105 l mole?1 cm?1, 0.013 μg cm?2 and 0.9999, respectively. The standard deviation and relative standard deviation were found to be ± 0.007 and 1.90%, respectively. The lower limit of detection is 0.04 μg. The method is simple, sensitive and free from interferences of other pesticides and diverse ions. Other organophosphorous pesticides do not interfere with the proposed method. The method has been satisfactorily applied to the determination of dichlorvos in environmental and agricultural samples. 相似文献
22.
Microwave-activated solvent-free Michael addition of 3-imino-1,4,2-dithiazoles to 4-arylidene-5(4H)-oxazolones furnished isolable adducts regio- and diastereoselectively, which underwent ring transformation to yield the target dithiazolopyrimidines. Alternatively, the similar conjugate addition of methanesulfinylmethylisothioureas to 4-arylidene-5(4H)-oxazolones diastereoselectively afforded Michael adducts, which underwent ring transformation followed by heterocyclization via deoxygenative demethylation with thionyl chloride to yield the same products dithiazolopyrimidines regio- and diastereoselectively. 相似文献
23.
Srivastava PK Rai DK Rai SB 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,(7):1283-1289
It is noted that the 1 <-- 0 transition for nuOH shows a blue shift as the relative concentration of n-butanol in a CCl4-n-butanol is reduced. The magnitude of the shift decreases for the 2 <-- 0 transition and there is almost no shift for the 3 <-- 0 transition. These observations are consistent with the observed red shift [Y. Mizugai, F. Takimoto, M. Katayama, Chem. Phys. Lett. 76 (1980) 615] on dilution for the 5 <-- 0 transition in n-butanol. The observations have been interpreted on the basis of formation of O-H....Cl hydrogen bond. 相似文献
24.
S. Raičević Ž. Vuković S. Lazić M. Mandić 《Journal of Radioanalytical and Nuclear Chemistry》1995,198(2):303-309
The coprecipitation of strontium by a calcium phosphate phase formed at an elevated pH 10.8 was investigated. The first phase obtained under these conditions in the amorphous calcium phosphate (ACP) which is transformed into crystalline hydroxyapatite (HA) after the induction period. Is has been shown that this transformation together with morphological changes of the precipitated solid phase, influences the amount of the sorbed strontium significantly. The possible consequences of this finding on practical application of coprecipitation of strontium by calcium phosphate have been discussed. 相似文献
25.
Summary The coagulation concentration for a titania sol decreases if the concentration of a mixture of electrolytes and papain decreases. If the concentration of papain is increased then lesser amount of electrolytes is needed to coagulate the sol. If glycine is added as an additional substance then the value decreases more rapidly. There is no significant change in the pH and the electrical conductance of the sol by the addition of papain or electrolytes. There is a little change, when glycine is added as an additional substance. These observations are explained due to the formation of negative papain ions in a low pH region. The possibility of the adsorption or the release of the counter ions is ruled out.The authors wish to thank Dr.R. C. Mehrotra, Professor and the Head of the Chemistry Department for providing all the facilities for this work. We are also thankful to the Ministry of Education, Government of India, for the award of a research scholarship to one of us (V.K.S.). 相似文献
26.
Prathima N Harini M Rai N Chandrashekara RH Ayappa KG Sampath S Biswas SK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(6):2364-2374
The thermal stability of short alkanethiol CH(3)(CH(2))(7)SH (C(8)) and long C(18) self-assembled monolayers (SAMs) is investigated using grazing angle reflection-absorption infrared spectroscopy, cyclic voltammetry, and molecular dynamics simulation. We track the disordering of SAM by untilting and gauche defect accumulation with increasing temperature in the 300-440 K range, a range of interest to tribology. Molecular dynamics simulation with both fully covered and partially covered C(6), C(8), and C(18) monolayers brings out the morphological changes in the SAM, which may be associated with the observed thermal stability characteristics. The molecular dynamics simulations reveal that short-chain C(6) and C(8) alkanethiols are more defective at lower temperature than the long-chain C(18) alkanethiol. With increasing temperature disorder in the SAM, as reflected in both untilting and gauche defect accumulation, tends to saturate at temperatures below 360 K for short-chain SAMs such that any further increase in temperature, until desorption, does not lead to any significant change in conformational order. In contrast the disorder in the long-chain C(18) SAM increases monotonically with temperature beyond 360 K. Thus, in a practical range of temperature, the ability of a SAM to retain order with increasing thermal perturbations is governed by the state of disorder prior to heat treatment. This deduction derived from molecular dynamics simulation helps to rationalize the significant difference we have observed experimentally between the thermal response of short- and long-chain thiol molecules. 相似文献
27.
The infrared spectra of 4-Cl 2-Me, 4-Cl 3-Me and 6-Cl 3-Me phenols have been recorded. The vibrational spectrum has been analysed
assuming that the molecules belong toC
s
point group and a tentative assignment of the observed frequencies to various modes of vibration has been proposed. The near
ultraviolet absorption spectrum of these compounds has also been recorded. Assuming the transition to be electronically allowed
the strongest band on the longer wavelength side has been assigned as the (0, 0) band in each case. The spectrum has been
analysed in terms of several excited state frequencies which have been correlated with the ground state frequencies observed
in the infrared spectrum. 相似文献
28.
Landa Purushottam Unnikrishnan V. B. Dattatraya Gautam Rawale Mansi Gujrati Surya Dev Mishra Sajeev T. K. Neelesh C. Reddy Srinivasa Rao Adusumalli Ram Kumar Mishra Vishal Rai 《Chemical science》2020,11(48):13137
Analytically pure proteins are indispensable for diverse applications, including therapeutics. Here, we report a methodology where a single amino acid, glycine, enables metal-free protein purification. This robust platform is enabled by a Gly-tag resin for site-specific capture, enrichment, and release through chemically triggered C–C bond dissociation by resonance-assisted electron density polarization.Gly-tag resin precisely captures and releases a protein with one glycine at the N-terminus. The user-friendly protocol delivers analytically pure protein free of metal contaminants. 相似文献
29.
Dhanpat Rai Dean A. Moore Nancy J. Hess Kevin M. Rosso Linfeng Rao Steve M. Heald 《Journal of solution chemistry》2007,36(10):1261-1285
Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies
on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures
of CO2(g) (0.003 or 0.03 atm.), and as functions of K2CO3 concentrations (0.01 to 5.8 mol⋅kg−1) in the presence of 0.01 mol⋅dm−3 KOH and KHCO3 concentrations (0.001 to 0.826 mol⋅kg−1) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions.
A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum
mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used
to interpret the solubility data. Only two aqueous species [Cr(OH)(CO3)22− and Cr(OH)4CO33−] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO2(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support
the existence of these species. The log 10
K° values of reactions involving these species [{Cr(OH)3(am) + 2CO2(g)⇌Cr(OH)(CO3)22−+2H+} and {Cr(OH)3(am) + OH−+CO32−
⇌Cr(OH)4CO33−}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available
for comparisons. 相似文献
30.
Smita Rai 《Tetrahedron》2007,63(11):2455-2465
Three porphyrin building blocks with N4, N3S and N2S2 cores having three meso-furyl groups and one meso-iodophenyl group were synthesized and characterized. The porphyrin building blocks were used to synthesize six porphyrin dyads such as N4-N4, N3S-N3S, N2S2-N2S2, N4-N3S, N4-N2S2 and N3S-N2S2 containing meso-tolyl and meso-furyl porphyrin sub-units under mild Pd(0) mediated coupling conditions. Steady state fluorescence studies indicated an efficient energy transfer from the meso-tolyl porphyrin sub-unit to the meso-furyl porphyrin sub-unit in all six dyads. This study supported the argument that the meso-furyl porphyrins can be used as good energy acceptors when meso-aryl porphyrins act as energy donors in their metal free form. 相似文献