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131.
The catalytic activity of Chromobacterium viscosum lipase (CV-lipase) was estimated across varying surfactant tail lengths (C-10-C-18) in water-in-oil (w/o) microemulsions of cationic surfactants containing four different hydroxyethyl-substituted head groups. An attempt to find a correlation, if any, between the activity of interfacially solubilized lipase and the varying surfactant tails was made for the first time in micellar enzymology. The second-order rate constant, k2, in lipase-catalyzed hydrolysis of p-nitrophenyl-n-hexanoate at pH 6.0 and 25 degrees C shows an improvement in enzyme activity (approximately 30-140%) across different head groups of amphiphiles with increasing tail lengths in varying solution compositions. Improvement of enzyme activity is prominent in ascending from C-10 to C-14/C-16, depending on the nature of polar head group. The hydrolytic activity of lipase in different surfactant (50 mM)/water/isooctane/n-hexanol with varying z= [alcohol]/[surfactant] (6.4 or 4.8) was amplified by 25-250% with increment in surfactant tail length in comparison with widely used cationic w/o microemulsions having solution compositions (z=16). As a notable outcome of this research, we found w/o microemulsions of 25 mM tetradecyltrimethylammonium bromide/water/isooctane/n-hexanol (z=8) producing the highest ever activity of lipase in any w/o microemulsions. 相似文献
132.
Kumar S Sharma D Ghosh G Kabir-ud-Din 《Langmuir : the ACS journal of surfaces and colloids》2005,21(21):9446-9450
Hydrophobic interactions control the morphologies of both surfactant aggregates and proteins. Globular proteins "denature" upon addition of excess amounts of denaturants such as urea. Understanding the microscopic basis of the urea effect on proteins or supramolecular aggregates such as micelles has always been a debated issue. Inspired by this need, the effect of urea (U), thiourea (TU), monomethylurea (MMU), dimethylurea(DMU), tetramethylurea (TMU), dimethylthiourea (DMTU), and tetramethylthiourea (TMTU) on the structural transition (spherical micelles to rod-shaped micelles, s --> r) in the sodium dodecylbenzenesulfonate (SDBS)-1-pentanol system has been investigated through dynamic light scattering(DLS) and viscosity measurements at 25 degrees C. 1-Pentanol, at 0.14 M, is found to promote s --> r in this system (0.2 M SDBS). The presence of the additives causes, in almost all cases, a decrease and increase in this 1-pentanol concentration depending upon the concentration and nature of the additive. These effects are explained in terms of an increased dielectric constant of the solvent medium due to the presence of additives and increased micellar hydration due to the repulsion of charged monomers caused by adsorption of the additives. Taken together, the data signal the exposure of biological assemblies to water at higher [additive], which causes a decrease in hydrophobic interactions responsible for compact structure formation (i.e., native protein). 相似文献
133.
Mandal PK Kaluarachchi KK Ogrin D Bott SG McMurray JS 《The Journal of organic chemistry》2005,70(24):10128-10131
[reaction: see text] Azabicyclo[X.Y.0]alkane amino acids are rigid dipeptide mimetics that are useful tools for structure-activity studies in peptide-based drug discovery. Herein, we report an efficient synthesis of three diastereomers of 9-tert-butoxycarbonyl-2-oxo-3-(N-tert-butoxycarbonylamino)-1-azabicyclo[4.3.0]nonane (3S,6S,9S, 3S,6R,9R, and 3S,6R,9S). Methyl N-Boc-pyroglutamate is cleaved with vinylmagnesium bromide to produce an acyclic gamma-vinyl ketone. Michael addition of N-diphenylmethyleneglycine tert-butyl ester produces the N-Boc-delta-oxo-alpha,omega-diaminoazelate intermediate, which, on hydrogenloysis, gives the fused ring system. Acidolytic deprotection followed by Fmoc-protection provided building blocks suitable for solid-phase synthesis. 相似文献
134.
The synthesis of the title spirodione, a new class of auxiliary based chiral synthon using (−)-trans-2-phenylcyclohexanol and its application to the asymmetric Diels-Alder reaction are described. Methodology for detachment of the chiral auxiliary from the cycloadduct has been developed. 相似文献
135.
Extraction of cesium-137 from nitric acid medium in the presence of macrocyclic polyethers 总被引:2,自引:0,他引:2
A. Kumar P. K. Mohapatra V. K. Manchanda 《Journal of Radioanalytical and Nuclear Chemistry》1998,229(1-2):169-172
Extraction behavior of137Cs was studied from nitric acid medium using dibenzo 18 crown 6 (DB18C6), 4,4'(5')di-acetylbenzo 18 crown 6 (DAB18C6), 4,
4'(5')di-hexanoylbenzo 18 crown 6 (DHB18C6), 4,4'(5')di-nonanoylbenzo 18 crown 6 (DNB18C6) and 4,4'(5')di-t-butylbenzo 18
crown 6 (DTBB18C6) in nitrobenzene medium. The stoichiometry of the species extracted with dibenzo 18 crown 6 (L) conformed
to ML+. NO3
− TheD
Cs values were found not to be affected by the presence of aluminium nitrate in the aqueous phase. The separation behavior of
fission products obtained from an irradiated natural uranium target was also studied. Presence of 0.004M phosphotungstic acid
found to enhance theD
Cs
values at lower acidities. 相似文献
136.
Nandy JP Prabhakaran EN Kumar SK Kunwar AC Iqbal J 《The Journal of organic chemistry》2003,68(5):1679-1692
A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereoselectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d6, and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction. 相似文献
137.
An optimized semi-automatic protocol for parallel synthesis of up to 96 peptide nucleic acids (PNA) or PNA-peptide conjugates using Boc-protection strategy has been developed using a robotic system. The approach is illustrated by synthesizing PNA and PNA-peptide libraries varying between 15 and 27 amino acid units. The peptides (NLS (nuclear localization signal) or Tat-peptide) were attached to N-terminus of the PNA. The method was found to be far superior to that based on the SPOT/Fmoc protocol by which PNA oligomers are synthesized on a modified cellulose membrane. On a 0.5 micromole scale the method typically yielded 2 mg product of 90% purity by HPLC/MALDI-TOF analysis. This approach is suitable for screening of a large number of PNA and/or peptide sequences for biochemical and biological studies. 相似文献
138.
Keda Zhang G. Sudesh Kumar D. C. Neckers 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1293-1305
We report herein studies of Co(OAc)2 and related transition metal compounds which serve as catalysts for aldol condensations when complexed with bipyridine, triphenyl phosphine, and crown ether. A comparison has been made with polymeric complexes of cobalt(II), which serve the same purpose. Cobalt complexes of built-in polyureas based on bipyridine and crown ether as well as those immobilized to polystyrene by triphenylphosphine and poly(4-vinyl pyridine) are also reported. 相似文献
139.
Nizakat Bib Misal Khan Amal Badshah Muhammad Ashraf Chaudry 《Radiation Physics and Chemistry》2005,73(6):362-364
Minimally processed cauliflower samples were irradiated, stored at 5 °C for 2 weeks and analyzed for sensory, physicochemical and microbiological qualities at 0th, 7th and 14th days. The data showed highest mean values of 7.93 and 7.57 for appearance and flavor, respectively, for 1.0 kGy treated samples. The D10 values of contaminating microorganisms on cauliflower were 0.20 (Escherischia coli) and 0.24 kGy (Salmonella paratyphae A.) and the resulting 5D10 value was 1.2 kGy. The study revealed that a dose of 1.5 kGy is enough for retention of quality and reduction of microbial load to 5D10 values in cauliflower during 2 weeks storage at refrigerated temperature. 相似文献
140.
Liu SG Liu H Bandyopadhyay K Gao Z Echegoyen L 《The Journal of organic chemistry》2000,65(11):3292-3298
The synthesis and electrochemistry of a series of tetrathiafulvalene (TTF) and dithia-crown-TTF derivatives attached with one or two disulfide group(s) 7a-f are reported. The self-assembled monolayers (SAMs) of these TTF disulfides on gold were prepared and characterized by reflection-absorption infrared spectroscopy. The SAMs are extremely stable under a wide variety of conditions and over extended periods of time and show remarkable electrochemical stability upon repeated potential scans. SAMs of the crown-TTF disulfides 7c,d,f can recognize alkali metal ions, and the process can be monitored following the electrochemical potential shift of the surface-confined TTF group. 相似文献