The present work reports covalent functionalization of single-walled carbon nanotubes (f-SWNTs) to introduce hydrophilicity to the otherwise amphiphobic nanotubes. The charge and spacer length of the functional moiety were varied by using quaternized ethylene diamine, 6-aminocaproate, quaternized (ethylenedioxy)bis(ethylamine), and a poly(ethylene glycol) (PEG) unit (f-SWNT-1 to f-SWNT-4, respectively). These f-SWNTs with varying degrees of hydrophilicity were incorporated within cetyltrimethyl ammonium bromide (CTAB) reverse micelles to develop stable self-assembled nanohybrids. An optimum hydrophilicity on the SWNT surface led to interfacial localization of f-SWNTs resulting in the augmentation of space at the interface. A surface-active enzyme, lipase, localized at this enhanced interface of f-SWNT-containing CTAB reverse micelles exhibited significant activation (2.5-fold) compared to that in the absence of the nanoconstructs. This improvement in lipase activity was mainly due to the smooth occupancy of lipase and also presumably because of the increase in the concentrations of both substrate and the enzyme at the augmented interface. Interestingly, the f-SWNTs that activate lipase in reverse micelles deactivate the same enzyme in water. The dispersion of f-SWNTs in water and its matching integration at the interface of reverse micelles were confirmed through transmission electron microscopic (TEM) investigations. The interfacial localization of these nanoconstructs was also established from the distinct fluorescence behavior of a hydrophobic fluorescent probe, fluorescein isothiocyanate (FITC), adsorbed onto the f-SWNT surface. In concurrence with the observed lipase activity, the corresponding changes in the enzyme conformation within f-SWNTs integrated reverse micelle as well as in aqueous medium were studied by circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy. 相似文献
Two cyclometalated compounds [IrIIICl{(2-biphenylene-1,8-naphthyridine-??C,N}(??5-pentamethylcyclopentadienyl)] (1) and [IrIIICl{(2-(2-N-Methyl-pyrrolyl-1,8-naphthyridine-??C,N}(??5-pentamethylcyclopentadienyl)] (2) containing naphthyridine based ligands have been synthesized in high yield. Insertion of SnCl2 to a terminal Ir?CCl bond of 1 affords the mixed Ir?CSnCl3 compound [IrIIISnCl3{(2-biphenylene-1,8-naphthyridine-??C,N}(??5-pentamethylcyclopentadienyl)] (3). The heterobimetallic compound 3 is shown to be an excellent catalyst for a variety of cyanosilylation reactions. A cooperative mechanism has been proposed which involves the simultaneous activation of aldehyde and cyanide precursor by Sn and unbound naphthyridine nitrogen. 相似文献
Using the Jagla model potential we calculate the potential of mean force (PMF) between hard sphere solutes immersed in a liquid displaying water-like properties. Consistent estimates of the PMF are obtained by (a) umbrella sampling, (b) calculating the work done by the mean force acting on the hard spheres as a function of their separation, and (c) determining the position dependent chemical potential after calculating the void space in the liquid. We calculate the PMF for an isobar along which cold denaturation of a model protein has previously been reported. We find that the PMF at contact varies non-monotonically, which is consistent with the observed cold denaturation. The Henry constant also varies non-monotonically with temperature. We find, on the other hand, that a second (solvent separated) minimum of the PMF becomes deeper as temperature decreases. We calculate the solvent-solvent pair correlation functions for solvents near the solute and in the bulk, and show that, as temperature decreases, the two pair correlation functions become indistinguishable, suggesting that the perturbation of solvent structure by the solute diminishes as temperature decreases. The solvent-solute pair correlation function at contact grows as the temperature decreases. We calculate the cavity correlation function and show the development of a solvent-separated peak upon decrease of temperature. These observations together suggest that cold denaturation occurs when the solvent penetrates between hydrophobic solutes in configurations with favorable free energy. Our results thus suggest that cold denatured proteins are structured and that cold denaturation arises from strong solvent-solute interactions, rather than from entropic considerations as in heat denaturation. 相似文献
The Cp*Si(+) cation acts as a stoichiometric source of silicon in the reaction with the disilenide Tip(2)Si=Si(Tip)Li (Tip = 2,4,6-(i)Pr(3)C(6)H(2)) affording known neutral unsaturated silicon clusters. It thereby provides a conceptually different approach to this novel class of compounds. The proposed mechanism involves a Cp*-substituted cyclotrisilene in which Cp*(-) acts as a leaving group upon single electron reduction or in a nucleophilic substitution step. 相似文献
A convenient and water‐based approach is described for the synthesis of an l ‐lysine‐based zwitterionic polymer, poly(ε−l ‐lysinyl acrylamide) (PLAM), without using protecting group chemistry, chromatographic purifications, and organic solvents as the reaction media. PLAM contains both amine and carboxylic acid groups in each repeating unit, which can either be protonated or deprotonated just by altering the pH of the solution to obtain overall positive or negative charge. PLAM is tested for its applicability as a zwitterionic polymeric buffer in water. Cu(II) ion‐induced aggregation of PLAM as a function of solution pH is studied. Spherical nanogel aggregates are formed at pH 9.5 due to aggregation of PLAM through its complexation with Cu(II) ion. Spherical aggregates appear to dissociate via breaking of the complexation at a pH < 5.5 resulting in molecular dissolution of PLAM. This aggregation process is pH reversible. The Cu(II)–PLAM aggregates are used as a template for fabrication of CuO and CuS nanoparticles.
We calculate both the micromechanical response and bulk elastic constants of composites of rods embedded in elastic media. We find two fixed points for Poisson's ratio with respect to rod density: there is an unstable fixed point for Poisson's ratio =1/2 (an incompressible system) and a stable fixed point for Poisson's ratio =1/4 (a compressible system). We also derive approximate expressions for the elastic constants for arbitrary rod density, which agree with exact results for both low and high density. These results may help to explain recent experiments [Phys. Rev. Lett. 102, 188303 (2009)10.1103/PhysRevLett.102.188303] that reported compressibility for composites of microtubules in filamentous actin networks. 相似文献
Exploiting the effects of quantum interference we put forward an idea of designing three primary logic gates, OR, AND and NOT, using a benzene molecule. Under a specific molecule-lead interface geometry, anti-resonant states appear which play the crucial role for AND and NOT operations, while for OR gate no such states are required. Our analysis leads to a possibility of designing logic gates using simple molecular structure which might be significant in the area of molecular electronics. 相似文献
The concentration levels of 238U, 232 Th, 40K and 137Cs in top soils of State of Punjab located in the North Western part of India were measured using conventional low background gamma ray spectrometric setup as well as Compton suppressed gamma ray spectrometric setup. The radioactivity level of 238U and 232Th was found to vary between 15 Bq/kg and 27 Bq/kg and between 16 Bq/kg and 57 Bq/kg respectively. The radioactivity level of 40K was found to vary between 266 Bq/kg and 799 Bq/kg. The mean radioactivity level of the NORM in general was found to be similar to what is expected as a result of their normal abundance. 相似文献