Nonaqueous Media (nonaqueou + media)

Distribution by Scientific Domains

Selected Abstracts

(S)-Ibuprofen-imprinted polymers incorporating ,-methacryloxypropyl-trimethoxysilane for CEC separation of ibuprofen enantiomers

Qi-Liang Deng
Abstract In this report, a novel preparation method of molecularly imprinted polymers (MIPs) for CEC was developed. Molecularly imprinted monolithic columns for (S)-ibuprofen were prepared and evaluated, in which charged entities responsible for establishing EOF have been derived from ,-methacryloxypropyltrimethoxysilane (,-MAPS), which was hydrolyzed following copolymerization with 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate,(EDMA). The EOF and molecular recognition of the stationary phase were investigated in aqueous and nonaqueous media, respectively. The experimental results indicated that the material showed a reasonably stable EOF and the prepared separation materials were capable of separating racemic ibuprofen, a task that could not be accomplished by MIPs prepared in parallel, using methacrylic acid (MAA) as a functional monomer. The efficiency at pH,3.2 for the first-eluted enantiomer and the last-eluted enantiomer (the imprinted analyte) were 128,700 and 2100,plates/m, respectively. [source]

Correlation analysis of reactivity in the oxidation of anilines by nicotinium dichromate in nonaqueous media

D. S. Bhuvaneshwari
The kinetics of oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate (NDC) in different organic solvent media in the presence of p -toluenesulfonic acid (TsOH) has been investigated. The rate of the reaction is zero order with respect to substrate, first order in NDC, and is found to increase with increase in [TsOH]. The various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species-anilines reaction (k2) correlates with Hammett's substituent constants affording negative reaction constants. The effect of para- and meta-substituents on the oxidation rates confirms to Swain et al.'s substituent constants F and R, both with negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and E while showing satisfactory correlation with Kamlet,Taft's solvatochromic parameters (,, ,, and ,*). 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 657,665, 2006 [source]

Studies on the kinetics of imidazolium fluorochromate oxidation of some meta - and para -substituted anilines in nonaqueous media

D. S. Bhuvaneshwari
The imidazolium fluorochromate (IFC) oxidation of meta - and para -substituted anilines, in seven organic solvents, in the presence of p -toluenesulfonic acid (TsOH) is first order in IFC and TsOH and is zero order with respect to substrate. The IFC oxidation of 15 meta - and para -substituted anilines at 299,322 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species-anilines reaction (k2) correlates with substituent constants affording negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and ENT. A correlation of rate data with Kamlet,Taft solvatochromic parameters (,, ,, ,*) suggests that the specific solute,solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute,solvent complexation. 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 166,175, 2006 [source]

Thermodynamic activity-based enzyme kinetics: Efficient tool for nonaqueous enzymology

AICHE JOURNAL, Issue 3 2001
Georgina C. Sandoval
Lipase-catalyzed synthesis reactions must be performed in nonaqueous media (organic solvents or solvent-free systems). The choice of the optimal solvent is usually a fastidious task that necessitates the determination of kinetic parameters in each solvent. The approach used here, to overcome the lack of a model that can predict the kinetics whatever the solvent, consists in the use of thermodynamic activities instead of concentrations of components, and assumes that activity-based kinetic parameters are the same in all solvents. This assumption is discussed, and a solution is proposed which takes into account some observed residual solvent effects. The reaction chosen to test this approach was the esterification of oleic acid with ethanol catalyzed by an immobilized lipase, Lipozyme. For this reaction, the kinetics predicted in various organic solvents and in solvent-free systems is in agreement with the experimental data. [source]

Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder

Liwu Wang
A novel dispersant,O-(2-aminopropyl)-O,-(2-methoxyethyl)-polypropylene glycol (AMPG),was developed to disperse submicrometer-sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG. [source]

Cellular response mechanisms in Pseudomonas aeruginosa PseA during growth in organic solvents

R. Gaur
Abstract Aims:, Solvent-tolerant bacteria have emerged as a new class of micro-organisms able to grow at high concentrations of toxic solvents. Such bacteria and their solvent-stable enzymes are perceived to be useful for biotransformations in nonaqueous media. In the present study, the solvent-responsive features of a lipase,producing, solvent-tolerant strain Pseudomonas aeruginosa PseA have been investigated to understand the cellular mechanisms followed under solvent-rich conditions. Methods and Results:, The solvents, cyclohexane and tetradecane with differing log P -values (32 and 76 respectively), have been used as model systems. Effect of solvents on (i) the cell morphology and structure (ii) surface hydrophobicity and (iii) permeability of cell membrane have been examined using transmission electron microscopy, atomic force microscopy and other biochemical techniques. The results show that (i) less hydrophobic (low log P -value) solvent cyclohexane alters the cell membrane integrity and (ii) cells adapt to organic solvents by changing morphology, size, permeability and surface hydrophobicity. However, no such changes were observed in the cells grown in tetradecane. Conclusions:, It may be concluded that P. aeruginosa PseA responds differently to solvents of different hydrophobicities. Bacterial cell membrane is more permeable to less hydrophobic solvents that eventually accumulate in the cytoplasm, while highly hydrophobic solvents have lesser tendency to access the membrane. Significance and Impact of the Study:, To the best of our knowledge, these are first time observations that show that way of bacterial solvent adaptability depends on nature of solvent. Difference in cellular responses towards solvents of varying log P -values (hydrophobicity) might prove useful to search for a suitable solvent for carrying out whole-cell biocatalysis. [source]

Comparative performances of selected chiral HPLC, SFC, and CE systems with a chemically diverse sample set

CHIRALITY, Issue S1 2003
Phil Borman
Abstract Pharmaceutical companies have a continuous need to resolve new racemates. Analysis may be required in aqueous and nonaqueous media, or in the presence of several different sets of potentially interfering compounds. There is often a preparative requirement. For these reasons analysts may require a number of different separation systems capable of resolving a given pair of enantiomers. We wished to improve upon existing approaches that address this situation and undertook a program of work to screen over 100 racemates, selected for their chemical diversity, on over 100 different chiral HPLC, SFC, and CE systems. Here we report results of this comparison and illustrate the use of rapid gradient screening as a valuable tool for chiral method development. Chirality 15:S1,S12, 2003. 2003 Wiley-Liss, Inc. [source]