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481.
4,4'-(Dialkylamino)pyridine (DAAP)-based compounds 1-4 catalytically cleave hydrophobic organophosphate and carboxylate esters in various host micellar aggregates at mildly alkaline pH. The role of the micellar reaction medium in such esterolytic reactions has been carefully examined in this work. The cationic gemini surfactant based micellar aggregates provide more than 1 order of magnitude better reaction medium for the above reactions than their conventional single-chain, single-charge, cationic cetyl trimethylammonium bromide (CTABr) micelles. The catalytic turnover behavior of DAAP nucleophiles in the presence of excess substrates is also retained in gemini micellar media. 相似文献
482.
Praveen RS Naidu GR Prasada Rao T;Inorganic Materials Group 《Analytica chimica acta》2007,600(1-2):205-213
This article describes the preparation of dithiocarbamate immobilized/functionalized and diethylammonium dithiocarbamate (DDTC) sorbed Merrifield Chloromethylated Resin (MCR) beads and comparison of these materials for on-line flow injection (FI)–flame atomic absorption spectrometry (FAAS) determination of lead. The above two materials enrich lead quantitatively over an identical optimal pH range (8.0–9.0), a preconcentration/loading time (up to 4 min) and elution with acidified methanol (a minimum of 0.01 mol L−1 HNO3 in methanol). However, the detection limit for lead using dithiocarbamate functionalized MCR beads is 1.3 μg L−1 compared to 3 μg L−1 for DDTC sorbed MCR beads. Again, the sensitivity enhancement over direct FAAS signal is 48- and 27-fold, respectively. In addition, dithiocarbamate functionalized MCR beads offers better precision compared to DDTC sorbed MCR beads as the corresponding relative standard deviation (R.S.D.) values for five successive determinations of 0.20 μg mL−1 are 1.44 and 4.36%, respectively. The accuracy of the developed on-line FI–FAAS procedure employing dithiocarbamate functionalized MCR beads as column material was tested by analyzing Certified Reference Material (CRM) of soil (IAEA soil-7) and marine sediment reference material (MESS-3) supplied by International Atomic Energy Agency (IAEA), Vienna and National Research Council (NRC), Canada, respectively. Furthermore, the developed procedure has been successfully tested for the analysis of surface, pond, ground and effluent water and soil samples collected from the vicinity of lead acid battery industry in India. 相似文献
483.
Daschbach JL Thallapally PK Atwood JL McGrail BP Dang LX 《The Journal of chemical physics》2007,127(10):104703
The interactions of CO(2)H(2) with p-tert-butylcalix[4]arene (TBC4) were studied using potential of mean force (PMF) and free energy perturbation approaches. To the best of our knowledge, the present work is one of the first to employ the constrained mean force approach to evaluate solute selectivity by the TBC4 molecule. The computed PMFs for the interaction of CO(2)H(2) with a single TBC4 molecule establish that the interaction of CO(2) with the open end of the cage structure is attractive while the interaction with H(2) is repulsive. Free energy perturbation calculations were performed for the same two guest molecules with a pair of facing TBC4 molecules used as a representative model as found in the TBC4 molecular solid. At low temperature, both CO(2)H(2) have favorable interactions with the TBC4 pair, with the CO(2) interaction being considerably greater. These results are in agreement with recent experimental data showing considerable CO(2) uptake by TBC4 at moderate pressures. 相似文献
484.
Praveen K. Tandon Alka Mehrotra Manish Srivastava Mamta Dhusia Santosh B. Singh 《Transition Metal Chemistry》2007,32(1):74-80
RuCl3 can further catalyze the reaction between hexacyanoferrate(III) and iodide ions, which is already catalyzed by the hydrogen
ions obtained from perchloric acid. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated graphically
from the rate when ruthenium(III) and H+ ions both catalyze the reaction. Reactions studied separately in the presence as well as in the absence of RuCl3 under similar conditions were found to follow second order kinetics w.r.t. [I−]. While the rate showed direct proportionality w.r.t. [Fe(CN)6]3− and [RuCl3]. At low concentrations the reaction shows direct proportionality with respect to [H+] which tends to become proportional to the square of hydrogen ion concentrations. External addition of [Fe(CN)6]4− ions retards the reaction velocity while change in ionic strength of the medium has no effect on the rate. With the help
of the intercept of the catalyst graph, extent of the reaction, which takes place without adding ruthenium(III) was calculated
and it was in accordance with the values obtained from the separately studied reaction in which only H+ ions catalyze the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate-determining
step. Arrhenius parameters at four different temperatures were also calculated.
相似文献
485.
This paper studies Rayleigh-Bénard convection of micropolar fluid layer heated from below with realistic boundary conditions. A specific approach for stability analysis of a convective problem based on variational principle is applied to characterize the Rayleigh number for quite general nature of bounding surfaces. The analysis consists of replacing the set of field equations by a variational principle and the expressions for Rayleigh number are then obtained by using trial function satisfying the essential boundary conditions. Further, the values of the Rayleigh number for particular cases of large and small values of the microrotation coefficient have been obtained. The effects of wave number and micropolar parameter on the Rayleigh numbers for onset of stationary instability for each possible combination of the bounding surfaces are discussed and illustrated graphically. The present analysis establishes that the nature of bounding surfaces combination and microrotation have significant effect on the onset of convection. 相似文献
486.
487.
We report the first implementation of the fiber based microfluidic Raman spectroscopic detection scheme, which can be scaled down to micrometre dimensions, allowing it to be combined with other microfluidic functional devices. This novel Raman spectroscopic detection scheme, which we termed as Waveguide Confined Raman Spectroscopy (WCRS), is achieved through embedding fibers on-chip in a geometry that confines the Raman excitation and collection region which ensures maximum Raman signal collection. This results in a microfluidic chip with completely alignment-free Raman spectroscopic detection scheme, which does not give any background from the substrate of the chip. These features allow a WCRS based microfluidic chip to be fabricated in polydimethylsiloxane (PDMS) which is a relatively cheap material but has inherent Raman signatures in fingerprint region. The effects of length, collection angle, and fiber core size on the collection efficiency and fluorescence background of WCRS were investigated. The ability of the device to predict the concentration was studied using urea as a model analyte. A major advantage of WCRS is its scalability that allows it to be combined with many existing microfluidic functional devices. The applicability of WCRS is demonstrated through two microfluidic applications: reaction monitoring in a microreactor and detection of analyte in a microdroplet based microfluidic system. The WCRS approach may lead to wider use of Raman spectroscopy based detection in microfluidics, and the development of portable, alignment-free microfluidic devices. 相似文献
488.
Praveen Joseph Santhosh Acharya Ganesh Sanjeev N. N. Bhat Y. Narayana 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(1):209-214
In the case of sparsely ionizing radiation such as electron, the dose rate and the pattern of energy deposition of the radiation
are the important physical factors which can affect the amount of damage in living cells. In the present study, the differences
in the cell survival efficiency and dose rate effect in diploid yeast strains Saccharomyces cerevisiae X2180 and Saccharomyces cerevisiae D7 under euoxic and hypoxic condition have been quantified. Irradiation was carried out using 8 MeV pulsed electron beam
from Microtron accelerator. The dose per pulse and pulse width of the beam used was 0.6 Gy and 2.3 μs, respectively, which
correspond to an instantaneous dose rate of 2.6 × 105 Gy s−1. For survival studies doses were delivered at a rate of 50 pulses per second (an average dose rate of 1,800 Gy s−1). Fricke and alanine dosimeters were used to measure the dose delivered to the sample. A significant difference in the dose
response has been observed under euoxic and hypoxic condition. Dose rate effect has been studied by changing the pulse repetition
rate of the Microtron and the dose rate used was from 180 to 1800 Gy min−1. A significant dose rate effect was observed under euoxic condition for Saccharomyces cerevisiae X2180 but the same was absent under hypoxic condition. The dose rate effect was absent for Saccharomyces cerevisiae D7 under both irradiation condition. The survival curves are found to be sigmoidal in shape under both condition but with
a wider shoulder under hypoxic condition. The D0 value and the Oxygen Enhancement Ratio (OER) at that point have been derived. 相似文献
489.
Sharma U Verma PK Kumar N Kumar V Bala M Singh B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(21):5903-5907
Iron phthalocyanine with iron sulfate has been successfully applied for high chemo- and regioselective reduction of aromatic nitro compounds to give the corresponding amines in a green solvent system without using any toxic ligand. The catalytic systems were also compatible with a large range of other reducible functional groups, such as keto, acid, amide, ester, halogen, lactone, nitrile, N-benzyl, O-benzyl, hydroxy, and heterocycles. In the present study, dinitro compounds have been regioselectively reduced to the corresponding amines with high yield. In most of the cases the conversion and selectivity was greater than 99% as determined by GC-MS analysis. 相似文献
490.
Motkuri RK Thallapally PK Nune SK Fernandez CA McGrail BP Atwood JL 《Chemical communications (Cambridge, England)》2011,47(25):7077-7079
A metal-organic framework obtained from a flexible organic linker shows a breathing phenomenon upon adsorption of saturated hydrocarbons. 相似文献