ABSTRACT
The construction of liquid crystal compositions consisting of the dimeric liquid crystal, CB_C9_CB (cyanobiphenyl dimer = 1'',9''-bis(4-cyanobiphenyl-4'-yl)nonane), and the range of nematic systems is explored. The materials include a laterally functionalized monomer, which was used to construct a phase diagram with CB_C9_CB, as well as one laterally linked dimer liquid crystal material and two liquid crystal gold nanoparticle (LC-Au-NPs) systems. For the Au-NP-LCs, the NP diameters were varied between ~3.3 nm and 10 nm. Stable mixtures that exhibit a nematic-nematic phase transition are reported and were investigated by POM (polarizing optical microscopy), DSC (differential scanning calorimetry) and X-ray diffraction studies.
ABSTRACT
It is demonstrated that engineered arginase with a single protruded site of cysteine deliberately placed away from its active centre by site-directed mutagenesis can facilitate its attachment on a gold-nanoparticle surface with atomic precision, resulting in no apparent loss in enzymatic activity.
Subject(s)
Antineoplastic Agents/chemical synthesis , Arginase/chemistry , Arginine/metabolism , Bacterial Proteins/chemistry , Enzymes, Immobilized/chemistry , Adsorption , Arginase/genetics , Arginase/metabolism , Bacillus/chemistry , Bacillus/enzymology , Bacillus/genetics , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Cysteine/chemistry , Electrochemistry , Electrophoresis, Polyacrylamide Gel , Enzymes, Immobilized/genetics , Enzymes, Immobilized/metabolism , Gold/chemistry , Kinetics , Microscopy, Atomic Force , Mutagenesis, Site-Directed , Nanotubes, Carbon/chemistry , Protein Engineering , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Surface PropertiesABSTRACT
Confocal fluorescence demonstrates that single molecules of dye-labelled Cytochrome C or B5 containing paramagnetic Fe(III) can be magnetically placed into the interstices of super-crystal which is composed of three dimensional regular arrays of Fe(3)O(4) nanoparticles.
Subject(s)
Cytochromes b5/chemistry , Cytochromes c/chemistry , Ferrosoferric Oxide/chemistry , Magnetics , Silicon Dioxide/chemistry , Microscopy, Confocal , Nanoparticles/chemistry , Nanoparticles/ultrastructureABSTRACT
There has been limited development in catalyst carriers for magnetic separations where superparamagnetic nanoparticles of a high saturation magnetization with no coercivity are required to isolate expensive catalyst reagent that are subjected to repeated magnetic cycles. By using simple stepwise layer-by-layer nanochemistry techniques, we show that an fcc FePt nanomagnet can be created inside each silica particle with tailored dimensions to great precision. Subsequent engineering of the external surface with Ti-O-Si species in an optimum structure to create a unique interface gives high activity and excellent selectivity of the composite material for the trans-stilbene oxidation to the corresponding epoxide in the presence of tert-butyl hydroperoxide. Thus, a new magnetic separable epoxidation catalyst is described. This work clearly demonstrates the significance of nanoengineering of a single catalyst particle by a bottom-up construction approach in modern catalyst design, which could lead to new catalytic properties.
ABSTRACT
In this paper, we report a new method based on supercritical carbon dioxide (scCO(2)) to fill and distribute the porous magnetic nanoparticles with n-octanol in a homogeneous manner. The high solubility of n-octanol in scCO(2) and high diffusivity and permeability of the fluid allow efficient delivery of n-octanol into the porous magnetic nanoparticles. Thus, the n-octanol-loaded magnetic nanoparticles can be readily dispersed into aqueous buffer (pH 7.40) to form a homogenous suspension consisting of nano-sized n-octanol droplets. We refer this suspension as the n-octanol stock solution. The n-octanol stock solution is then mixed with bulk aqueous phase (pH 7.40) containing an organic compound prior to magnetic separation. The small-size of the particles and the efficient mixing enable a rapid establishment of the partition equilibrium of the organic compound between the solid supported n-octanol nano-droplets and the bulk aqueous phase. UV-vis spectrophotometry is then applied to determine the concentration of the organic compound in the aqueous phase both before and after partitioning (after magnetic separation). As a result, logD values of organic compounds of pharmaceutical interest determined by this modified method are found to be in excellent agreement with the literature data.
Subject(s)
1-Octanol/chemistry , Ferric Compounds/chemistry , Nanoparticles/chemistry , Silicon Dioxide/chemistry , Carbon Dioxide/chemistry , Magnetics , Porosity , Thermogravimetry , Water/chemistryABSTRACT
Enzymes are versatile biocatalysts with major advantages of ultrahigh reaction selectivity and specificity under mild conditions, which currently find increasing applications. However, their applications are often hampered by difficulties in recovery and recycling. As a result, we carried out detailed investigations on the synthesis and characterization of silica-encapsulated iron oxide magnetic nanoparticles of controlled dimension as an enzyme carrier. It is shown that the relatively smaller sized silica-coated magnetic nanoparticle prepared by the microemlusion technique can a carry bulky enzyme, beta-lactamase, via chemical linkages on the silica overlayer without severely blocking the enzymatic active center (which is commonly encountered in conventional solid supports). An activity study by Michalis-Menten kinetics reflects that this new type of immobilization allows enzyme isolation with accessibility as good as free enzyme. The recovery and reusability of the nanoparticle-supported enzyme upon application of magnetic separation are also demonstrated.
