1,720,977 research outputs found
Complexation and Extraction of Copper Ions in Ionic Liquids
No full textMany carrier molecules were synthesised in our laboratories and successfully used for the complexation and the transport of copper(II), cadmium(II), lead(II) and mercury(II) ions. In order to minimize the amounts of organic solvents, researches have been directed towards alternative extraction systems, still based on the chelating properties of our carrier molecules but using ionic liquids as membrane. We present here results on the chelating features of simple lipophilic polyamines towards Cu(II) ions; the chelating agents were used in water/ionic liquids biphasic systems to achieve liquid/liquid extraction processes based on imidazolium-type ionic liquids
Acute Tossicity of Some Cationic and Zwitterionic Surfactants to Freshwater Amphipod Echinogammarus tibaldii
No full textQuaternary ammonium compounds (QACs) are an important class of industrial chemicals with a wide range of commercial and consumer uses as detergents, antistatic and softening agents, biocides, germicides, deodorizers and emulsifiers. These substances are now increasingly used all over the world and their annual rates of production and consumption are considerable.The following study was therefore undertaken to evaluate the effect of molecular structure changes on the acute toxicity of cationic and zwitterionic surfactants to Echinogammarus
tibaldii, a benthic shredder amphipod with an important role in the detritus chain of rivers
and streams
Enzyme activity and stability control by amphiphilic self-organizing systems in aqueous solutions
No full textThe interaction of surfactants with proteins in aqueous solutions has been the subject of many investigations to understand the interactions between membrane proteins and lipids, structurally similar to synthetic surfactants. The effect of surfactant on enzyme structure and activity is the result of chemically selective interactions that may be influenced both by the enzyme structure and by the chemistry of the surfactant. For many years, surfactants have been considered as non-specific denaturants of proteins, even if in the literature several of them are reported to enhance activity and/or stability of some enzymes: the detergent can interact with the enzyme and cause a conformational change to a more active form and/or stabilize its native folded structure. Although the surfactant head group seems to have a determining role, other structural features of the detergent are also important in influencing the catalytic properties of an enzyme, i.e. head group size and its hydrophobic/hydrophilic balance. Up to now it is very difficult to predict the molecular features of the surfactant and an extensive investigation on the relationship between the surfactant chemical structure and the catalytic properties of enzyme is still required. (C) 2000 Elsevier Science Ltd. All rights reserved
The Hammett equation and micellar effects on S(N)2 reactions of methyl benzenesulfonates - The role of micellar polarity
No full textSubstituent effects on the reaction of H2O, OH-, and Br- with p-substituted methyl benzenesulfonates in cationic micelles of cetyl trialkylammonium ion surfactants (n-C16H33NR3X, X = OH, Br, R = Me, Et, nPr, nBu) and in water were analyzed by using the Hammett equation. Values of rho in the various media confirm that micellar interfacial regions are less polar than water and polarities decrease with increasing bulk of the surfactant head-group
Effects of Ionic and Zwitterionic Surfactants on the Stabilization of Bovine Catalase
No full textThe activity and stability of beef liver catalase have been investigated in the presence of different ionic and zwitterionic surfactants. Ah cationic and zwitterionic surfactants used in this work have no effect on the initial activity of catalase, but several of them allow the enzyme to retain a high residual activity for longer periods of time than those observed in the absence of any additives. However, the interactions between surfactants and catalase appear to be very peculiar, and certain zwitterionic surfactants have been found to remarkably: slow down enzyme degradation, with the enzyme completely preserving its activity after several weeks at temperatures of up to 30 degrees C. This effect is probably due to an interaction between the surfactant and the intersubunit region of the protein; this interaction could stabilize the quaternary structure of the enzyme
Activation and stabilization of alpha-chymotrypsin by cationic additives
No full textalpha -Chymotrypsin activity was tested with N-glutaryl-L-phenylalanine p-nitroanilide (GPNA) in aqueous media in the presence of synthetic surfactants, which differ in the flexibility of their bulky head groups. Superactivity can be ascribed to the presence of the tributylammonium residue on the surfactant head group, as in p-octyloxybenzyltributylammonium bromide (pOOTBABr), while in the presence of a more rigid moiety, i.e. a cyclic one, no activation was found. A nonmicellizable quaternary ammonium salt, the tetrabutylammonium bromide (TBABr), which has a head group structure very similar to pOOTBABr, not only induces a remarkable superactivation, at a concentration 80-fold higher than pOOTBABr, but also allows the enzyme to retain a high residual activity for long periods of time. The presence of a lipophilic chain, which by interacting with apolar residues on the enzyme surface, probably penetrates into hydrophobic pockets of the protein and causes a rapid inactivation. In 0.4 m TBABr, a 20-fold increase both in k(cat) and K-m values, with respect to buffer alone, was found. The increase of K-m could be attributed either to a true decrease in affinity between enzyme and substrate or alternatively to the presence of TBA(+) ions near the catalytic region. They could interact with protein residues around the active site and bind to negatively charged GPNA molecules, lowering the local substrate concentration. Spectroscopic experiments (CD and fluorescence) show minor changes of protein conformation in 0.4 m TBABr, while at 1 m a strong modification of both spectra was observed
Effects of temperature on micellar-assisted bimolecular reaction of methylnaphtalene-2-sulphonate with bromide and chloride ions
No full textReactivity of methyl naphthalene-2-sulphonate, MeONs, with H2O, Br and Cl in water and in cationic micelles of etyltrialkylammonium surfactants, n-C16H33N+R3X, R = Me (CTA+), n-Pr (CTPA+), X = Br, Cl, CH3SO3, has been investigated in the temperature range 25–45 C. Micellar rate effects were analysed by using the pseudophase treatment, and the second-order rate constants in the micellar pseudophase were evaluated at the various temperatures. Values of these rate constants increase with temperature, and the effect is less important in micelles than in water and more important for chloride than for bromide ions. Micelles lead to an ion behaviour discrimination, whose extent depends on surfactant type and on temperature, with maximum effect in CTPA+ at 25 C and with bromide being always more reactive
than chloride. Quantitative analysis of the temperature effect by the Eyring equation showed that micelles speed up reaction of MeONs with halide ions by decreasing the activation enthalpies, which is partially offset by decreases in the activation entropies. The rate acceleration by increase in surfactant head group size has only enthalpic origin for bromide and only entropic origin for chloride: this different behaviour was rationalised taking into account both solvation of anions and the hydrophobic effect
Accelerated Decarboxylation of 6‐Nitrobenzisoxazole-3‐Carboxylate in Imidazolium-Based Ionic Liquids and Surfactant Ionic Liquids
No full textWe report the use of the unimolecular, spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate, 6-NBIC, as kinetic probe to investigate properties of aqueous solutions of a series of ILs, 1-alkyl-3-methyl imidazolium derivatives. The ILs are denoted as [Cnmim][X], where n indicates the number of carbon atoms in 1-alkyl chain. We studied [C4mim][X], with X = Cl-, Br- and BF4-, and the surface active ILs, SAILs, [C12mim][Cl], [C12mim][Br], and [C16mim][Br]. We observed a steep increase of values of kobs after a certain salt concentration for all the systems used. Electrical conductivity of various aqueous systems were measured, in an attempt to rationalize the kinetic effects
Modelling of Micellar Effects upon Substitution Reactions with Moderately Concentrated Hydroxyde Ion
No full textCationic micelles of cetyltrimethylammonium chloride and bromide (CTACl and CTABr) speed reactions of 2,4-dinitro-1-naphthyl chloride (DNNC) and p-nitrophenyl diphenyl phosphate (pNPDPP) with OH–. The pseudophase ion-exchange model fits the data for reaction with [OH–] < 0.05 mol dm–3, but the reaction is faster than predicted at higher ratios of [OH–]. The deviations from theory are largest with high ratios of [OH–] to [Cl–] or [Br–] and are larger in CTABr than in CTACl. A mass-action-like model with each anion binding independently to the micelle fits the data for 10–3–0.5 mol dm–3 OH–
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