Herein, we report the effect of gold nanoparticles (GNPs) in enhancing lipase activity in reverse micelles of cetyltrimethylammonium bromide (CTAB)/water/isooctane/n‐hexanol. The size and concentration of the nanoparticles were varied and their specific roles were assessed in detail. An overall enhancement of activity was observed in the GNP‐doped CTAB reverse micelles. The improvement in activity becomes more prominent with increasing concentration and size of the GNPs (0–52 μM and ca. 3–30 nm, respectively). The observed highest lipase activity (k2=1070±12 cm3 g?1 s?1) in GNP‐doped CTAB reverse micelles ([GNP]: 52 μm, ca. 20 nm) is 2.5‐fold higher than in CTAB reverse micelles without GNPs. Improvement in the lipase activity is only specific to the GNP‐doped reverse micellar media, whereas GNP deactivates and structurally deforms the enzyme in aqueous media. The reason for this activation is probably due to the formation of larger‐sized reverse micelles in which the GNP acts as a polar core and the surfactants aggregate around the nanoparticle (‘GNP pool’) instead of only water. Lipase at the augmented interface of the GNP‐doped reverse micelle showed improved activity because of enhancement in both the substrate and enzyme concentrations and increased flexibility in the lipase conformation. The extent of the activation is greater in the case of the larger‐sized GNPs. A correlation has been established between the activity of lipase and its secondary structure by using circular dichroism and FTIR spectroscopic analysis. The generalized influence of GNP is verified in the reverse micelles of another surfactant, namely, cetyltripropylammonium bromide (CTPAB). TEM, dynamic light scattering (DLS), and UV/Vis spectroscopic analysis were utilized to characterize the GNPs and the organized aggregates. For the first time, CTAB‐based reverse micelles have been found to be an excellent host for lipase simply by doping with appropriately sized GNPs. 相似文献
The effect of compressed CO2 on the solubilization capacity of water in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in longer chain n-alkanes was studied at different temperatures and pressures. It was found that the amount of solubilized water is increased considerably by CO2 in a suitable pressure range. The suitable CO2 pressure range in which the solubilization capacity of water could be enhanced decreased with increasing W0 (water-to-AOT molar ratio). The microenvironments in the CO2-stabilized reverse micelles were investigated by UV/Vis adsorption spectroscopy with methyl orange (MO) as probe. The mechanism by which the reverse micelles are stabilized by CO2 is discussed in detail. The main reason is likely to be that CO2 has a much smaller molecular volume than the n-alkane solvents studied in this work. Therefore, it can penetrate the interfacial film of the reverse micelles and stabilize them by increasing the rigidity of the micellar interface and thus reducing the attractive interaction between the droplets. However, if the CO2 pressure is too high, the solvent strength of the solvents is reduced markedly, and this induces phase separation in the micellar solution. 相似文献
The effect of compressed CO2 on the solubilization of bovine serum albumin (BSA) in water/sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/isooctane reverse micelles was studied by observing phase behavior and recording UV-visible spectra under different conditions. The pH values within the water cores of reverse micelles at different CO2 pressures were also determined. The solubilization capacity of the reverse micelles for the protein increased considerably as CO2 pressure increased within the low-pressure range, but decreased at higher CO2 pressures, so that the micelles eventually lost their ability to solubilize the protein. The effect of CO2 on the stability of the reverse micelles played an important role in the relationship between pressure and protein solubility. A "multicomplex" model was proposed to explain these effects. The different solublization capacities within different pressure ranges demonstrates the unique advantage of using compressed CO2 in the extraction of proteins with reverse micelles. 相似文献
Both CO 2 and ethanol are nonsolvents for poly(methyl methacrylate) (PMMA) at 303 K, but PMMA dissolves in CO2‐expanded ethanol (red spectrum, see figure). The dissolution process consists of swelling of the PMMA by the CO2, which allows the ethanol to penetrate the PMMA and interact with the polymer through carbonyl–hydroxyl hydrogen bonds to separate the polymer chains.
A series of multiblock poly(ether urethane)s comprising poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) segments were synthesized. Their aqueous solutions exhibited thermogelling behavior at critical gelation concentrations (CGC) ranging from 8 to 12 wt%. The composition and structural information of the copolymers were studied by GPC and 1H NMR. The critical micellization concentration (CMC) and thermodynamic parameters for micelle formation were determined at different temperatures. The temperature response of the copolymer solutions were studied and found to be associated with the composition of the copolymers. 相似文献
Silver and silver iodide nanocrystals have been synthesized in the water-in-CO(2) reverse microemulsions formed by the commonly used surfactant, sodium bis(2-ethylhexyl)sulfosuccinate (AOT), in the presence of 2,2,3,3,4,4,5,5-octafluoro-1-pentanol as cosurfactant. The nanometer-sized aqueous domains in the microemulsion cores not only act as nanoreactors, but the surfactant interfacial monolayer also helps the stabilization of the metal and semiconductor nanoparticles. The transmission electron microscopy results show that silver and silver iodide nanocrystals with average diameters of 6.0 nm (standard deviation, SD=1.3 nm) and 5.7 nm (SD=1.4 nm), respectively, were formed. The results indicate that the method can be utilized as a general and economically viable approach for the synthesis of metal and semiconductor quantum dots in environmentally benign supercritical carbon dioxide. 相似文献
The study of the micelle‐to‐vesicle transition (MVT) is of great importance from both theoretical and practical points of view. Herein, we studied the effect of compressed CO2 on the aggregation behavior of dodecyltrimethylammonium bromide (DTAB)/sodium dodecyl sulfate (SDS) mixed surfactants in aqueous solution by means of direct observation, turbidity and conductivity measurements, steady‐state fluorescence, time‐resolved fluorescence quenching (TRFQ), fluorescence quantum yield, and template methods. Interestingly, all these approaches showed that compressed CO2 could induce the MVT in the surfactant system, and the vesicles returned to the micelles simply by depressurization; that is, CO2 can be used to switch the MVT reversibly by controlling pressure. Some other gases, such as methane, ethylene, and ethane, could also induce the MVT of the surfactant solution. A possible mechanism is proposed on the basis of the packing‐parameter theory and thermodynamic principles. It is shown that the mechanism of the MVT induced by a nonpolar gas is different from the MVT induced by polar and electrolyte additives. 相似文献
An apparatus to determine the vapor-liquid equilibria of CO(2)/ionic liquid (IL)/organic solvent multisystems and the viscosity of the liquid phase at elevated pressures has been constructed. The solubility of CO(2) in 3-butyl-1-methyl-imidazolium hexafluorophosphate ([C(4)mim][PF(6)]) and the viscosity of CO(2)-saturated [C(4)mim][PF(6)] have been studied at 313.15, 323.15, and 333.15 K and at pressures up to 12.5 MPa. The phase behavior of CO(2)/[C(4)mim][PF(6)]/methanol ternary mixture and the viscosity of the liquid phases at equilibrium condition have also been determined at 313.15 K and at 7.15 and 10.00 MPa. The partition coefficients of the components in the ternary system are calculated. Peng-Robinson equation of state and some thermodynamic functions are combined to calculate the fugacity coefficients of the components in the system. It demonstrates that the viscosity of the IL-rich phase decreases significantly with increasing pressure of CO(2), and the effect of temperature on the viscosity of CO(2)/IL mixture is not noticeable at high pressure, although the viscosity of the CO(2)-free IL decreases dramatically with increasing temperature. Compressed CO(2) may become an attractive reagent for reducing the viscosity of ILs in many applications. The mole fraction of methanol in the CO(2)-rich phase is much lower than that in the IL-rich phase; this indicates that the interaction between the IL and methanol is stronger than that between CO(2) and methanol. The fugacity coefficient of CO(2) in IL-rich phase is larger than unity, while that of methanol is much small than unity, which further suggests that methanol-IL interaction is much stronger than CO(2)-IL interaction. However, the CO(2)-IL interaction is stronger than the CO(2)-methanol interaction. 相似文献
The oxidation of styrene with molecular oxygen catalyzed by PdCl2 CuCl2 has been investigated in supercritical CO2 with a batch reactor. The oxidative system of styrene contains four components at the beginning and seven components during the reaction. The critical temperature, critical pressure, and critical density at different conversions are determined by using a high-pressure view cell. The effect of phase behavior on the conversion and selectivity were studied. Experimental results showed that the critical parameters of the reaction mixture at fixed initial molar ratio changed with the conversion of reactant. The conversion of styrene reached maximum near the critical density of the reaction mixture. Product selectivity also varied with density of reaction mixture and could be tuned to some degree. 相似文献
We present two organometallic precursor approaches leading to the hitherto-unknown dioxo monocarbodiimides (Ln(2)O(2)CN(2)) of the late lanthanides Ho, Er, and Yb as well as yttrium. One involves insertion of CO(2), and the other one is a straightforward route using a molecular single-source precursor. To this end the reactivity of the activated amido lanthanide compound [(Cp(2)ErNH(2))(2)] towards carbon dioxide absorption under supercritical conditions was studied. Selective insertion of CO(2) into the amido complex yielded the single-source precursor [Er(2)(O(2)CN(2)H(4))Cp(4)], which was characterized by vibrational spectroscopy and thermal and elemental analyses. Ammonolysis of this amorphous compound at 700 degrees C affords Er(2)O(2)CN(2). To gain deeper insight into the structural characteristics of the amorphous precursor, a similar molecular carbamato complex was synthesized and fully characterized. X-ray structure analysis of the dimeric complex [Cp(4)Ho(2){mu-eta(1):eta(2)-OC(OtBu)NH}] shows an unusual bonding mode of the tert-butylcarbamate ligand, which acts as both a bridging and side-on chelating group. Ammonolysis of this compound also yielded dioxo monocarbodiimides, and therefore the crystalline carbamato complex turned out to be an alternative precursor for the straightforward synthesis of Ln(2)O(2)CN(2). Analogously, the dioxo monocarbodiimides of Y, Ho, Er, and Yb were synthesized by this route. The crystal structures were determined from X-ray powder diffraction data and refined by the Rietveld method (Ln=Ho, Er). Further spectroscopic characterization and elemental analysis evidenced the existence of phase-pure products. The dioxo monocarbodiimides of holmium and erbium crystallize in the trigonal space group P[over]3m1. According to X-ray powder diffraction, they adopt the Ln(2)O(2)CN(2) (Ln=Ce-Gd) structure type. 相似文献