1,720,987 research outputs found
Recognition and Complexation of Heavy Metal Ions in Ionic Liquids and Sol-Gel Materials
No full textMetal ion extraction from aqueous solutions is of great concern in a number of different applications. In the past, our research group was extensively interested in carrier-mediated transport through bulk liquid membranes, i.e. organic solvents separating two immiscible aqueous solutions. Many 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 employed as membrane, further researches have been directed towards alternative extraction systems, still based on the chelating properties of our carrier molecules, that is ionic liquids and sol-gel materials.
We present here results on the chelating features of simple lipophilic polyamines towards Cu(II) and Hg(II) ions; the chelating agents were (i) used in water/ionic liquids biphasic systems to achieve liquid/liquid extraction processes based on imidazolium-type ionic liquids2 and (ii) immobilized on sol-gel materials to be used as stationary phases in chromatographic systems for in column metal ion extraction3. Interestingly, chelating properties of the selected molecules seemed to be deeply affected by the different employed settings
Alfa-Chymotrypsin Superactivity in Cetyltrialkylammonium Bromide Rich Media
No full texta-Chymotrypsin (a-CT) activity was tested with N-glutaryl-L-phenylalanine p-nitroanilide in buffered media with added cationic surfactants. The effect of the commercial cetyltrimethylammonium bromide (CTABr) was compared with that of three other surfactants with ethyl (CTEABr), propyl (CTPABr), and butyl (CTBABr) head groups. These were synthesized and purified in this laboratory. Surfactant head groups provided distinct environments that largely modulated the catalytic performance. Larger alkyl head group hydrophobicity led to a marked enhancement of ?-CT activity. CTBABr-rich media induced the highest superactivity. Kinetic measurements were performed in Tris-HCl buffer at a surfactant concentration either below or above CMC, and ?-CT superactivity occurred in both media. Positive interactions between the enzyme and surfactants happened independently of the supramolecular organization of the medium. The reaction followed the Michaelis-Menten kinetics. The substrate to micelle aggregates binding constant was used to calculate the substrate concentration available for catalysis. The k(cat) to K(m) ratio was in CTBABr-rich media always higher than in pure buffer and depended on the surfactant concentration. ?-CT superactivity depended on the pH value of buffer solution. Enzyme inactivation followed a single-step mechanism in pure buffer and a series mechanism in the presence of a surfactant. The rate of activity decay obeyed a first-order kinetics
Ionic and covalent crosslinking in chitosan-succinic acid membranes: Effect on physicochemical properties
No full textIn this work, chitosan-succinic acid membranes were prepared by casting method and the physicochemical and mechanical properties of non-neutralized and neutralized with NaOH films were compared. Mechanical strength, flexibility, thermal stability and water-vapor permeability of chitosan membranes are significantly improved after neutralization. These improvements could be partly ascribed to the use of a dicarboxylic acid, which decreases the spacing between chitosan chains as a consequence of ionic crosslinking. Moreover, the addition of the strong base to the hydrogel promotes the formation of amide bonds, as suggested by FTIR analysis and demonstrated by acid-base titration. The favorable features of chitosan-succinic acid films as well as the possibility to easily incorporate drugs, enzymes, essential oils or other additives in the hydrogel, make such membranes suitable for many applications
SN2 Displacement by Bromide Ions in Dichloromethane. The role of Reverse Micelles
No full textReverse micellar systems are of interest as reaction media because they are powerful models for biological compartmentalization, enzymatic catalysis and separation of biomolecules. Solutions of ionic surfactants in apolar solvents may
contain reverse micelles, but they may also contain ion pairs,
or small clusters, with waters of hydration. We studied the bimolecular reaction in CH2Cl2 solutions of cationic tetraalkylammonium bromide salts (onium salts), such as cetyltrimethylammonium bromide (CTABr), cetyltripropylammonium bromide (CTPABr) and tetra-n-butylammonium bromide (TBABr). Methylnaphthalene-2-sulfonate (β-MeONs), its 6-sulfonate derivative (β-MeONsS–) as the 2,6-lutidinium salt and methyl-5-N,N,N,trimethylammonium naphthalene1-sulfonate (α-MeONsNT+) as the trifluoromethanesulfonate salt react with Br– in CH2Cl2. First-order rate constants, kobs, increase linearly and similarly for the three substrates with increasing concentrations of the onium salts. Reactions are faster with TBABr than they are with CTPABr and CTABr, and the reactivity of the three substrates is in the order: α-MeONsNT+ >> β-MeONsS– > β-MeONs. The reactions are
inhibited by the addition of H2O, but CTABr tolerates H2O in large excess. At [H2O]/[CTABr] = w0 = 6, “water-pool” reverse micelles form, and kobs for all three substrates is then
independent of w0
in water–organic solvent mixtures
Full text linkBackground: The addition of organic solvents to an aqueous medium for enzymatic reactions offers several advantages, as they can increase the solubility of substrates but can also lead to enzyme inactivation and/or aggregation.Results: The effect of adding 30% of several water-soluble organic solvents on the catalytic activity of lipase B from Candida antarctica (CalB) was studied and the results showed that the highest activity was obtained with the addition of t-butanol. t-Butanol and acetonitrile were selected and the kinetic parameters, determined to deepen their effect on CalB activity, showed that the addition of acetonitrile improved the enzyme-substrate affinity, while water-t-butanol mixtures led to a more than ninefold increase in k(cat). To rationalize at a molecular level the kinetic results, molecular dynamic simulations were performed. Analysis of the accessibility of the active-site cavity, solvent occupancy in the site and in the oxyanion hole, and the stability of the catalytic triad in the two solvent mixtures, provided insight into their effects on the catalytic properties of CalB.Conclusion: The lower occupancy in the oxyanion hole of water molecules and a shorter residence time in the active site of acetonitrile molecules in the acetonitrile-water mixture contribute to the higher enzyme-substrate affinity found experimentally. Conversely, the higher k(cat) in the t-butanol mixture is explained by the higher stability of the catalytic triad and by an increase in the nucleophilicity of the catalytic serine due to the persistent presence of t-butanol molecules in the active site. (c) 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI)
Kinetics and stability of alpha-chymotrypsin in surfactant-rich media and in water-butyl acetate two-phase systems
No full text1H-NMR-relaxation and colorimetry for evaluating nanopolymeric dispersions as stone protective coatings
No full textNon-destructive and non-invasive assessment of new nanopolymeric dispersions for protecting stone materials was accomplished; the effectiveness of five formulations was tested regarding commercial products widely used in conservation on Lecce, Montescaglioso and Matera stones. We observed the specimens’ wettability during capillary water absorption up to saturation by nuclear magnetic transverse relaxation time measurements, using a surface and portable probe. The comparison between treated and the untreated ones, concerning their specific hydration behavior, allowed establishing the effects of the polymer films. Finally, color evaluations were performed to inspect differences induced by treatments. The data analysis enabled to select the most satisfactory protective coating for each lithotype
Understanding the role of temperature in structural changes of choline chloride/glycols deep eutectic solvents
No full textDeep eutectic solvents (DESs) represent a new “green” alternative to classic organic solvents; however, their high viscosity often limits their utilization. The physicochemical properties of DESs can be tuned by adding cosolvents, by varying the operating temperature, or both, but their structure has to be preserved. In this work, three pure DESs based on choline chloride (ChCl) mixed with diethylene glycol (DEG), triethylene glycol (TEG) or polyethylene glycol 200 (PEG 200), as well as ChCl/TEG/water mixtures were studied. Particular attention was paid to the effect of temperature on some properties, i.e. density, conductivity, and viscosity, and on the structural characteristics of pure DESs and DES/water blends in the range 303–353 K. All the pure eutectic solvents followed both Arrhenius law and Walden's rule and showed very similar activation energy and poor ionicity, indicating the formation of intimate ion pairs. Multinuclear NMR analysis, such as the determination of the chemical shift of 1H, 13C, 35Cl and linewidths at half height of 14N and 35Cl, as a function of temperature highlighted the conservation of the characteristic supramolecular interactions up to 353 K. However, the temperature effects on the physicochemical properties of DES/water mixtures changed differently depending on the water content. Excess properties and NMR investigations highlighted the strengthening of the hydrogen bond interactions up to a 10% level of added water and their progressive weakening at a higher degree of hydration. These results also showed that temperature only slightly affects the structure of both DES and DES/water systems but can drastically increase their transport properties
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