Affinity chromatography of β-N-acetylhexosaminidases on columns with mixed charge and affinity functions

Analysis was made of the nature of interactions between β-N-acetylhexosaminidase and affinity chromatography gels made by coupling 2-acetamido-N-(6-aminohexanoyl)-2-deoxy-β-D-glucopyranosylamine (ANAG) to CNBr-Sepharose columns. This showed that although specific binding of the enzyme to the immobilized ligand was too weak to cause retention, compound affinity in which charge interactions were involved could be exploited for purification of the enzyme. Evidence is given for the specificity of interaction of the enzyme with immobilized ligand and for biospecific desorption of β-N-acetylhexosaminidases from ANAG-Sepharose columns. A method was developed for the purification of placental β-N-acetylhexosaminidase A in mg amounts starting from crude extracts.     

Structure, surface excess and effective interactions in polymer nanocomposite melts and concentrated solutions

The Polymer Reference Interaction Site Model (PRISM) theory is employed to investigate structure, effective forces, and thermodynamics in dense polymer-particle mixtures in the one and two particle limit. The influence of particle size, degree of polymerization, and polymer reduced density is established. In the athermal limit, the surface excess is negative implying an entropic dewetting interface. Polymer induced depletion interactions are quantified via the particle-particle pair correlation function and potential of mean force. A transition from (nearly) monotonic decaying, attractive depletion interactions to much stronger repulsive-attractive oscillatory depletion forces occurs at roughly the semidilute-concentrated solution boundary. Under melt conditions, the depletion force is extremely large and attractive at contact, but is proceeded by a high repulsive barrier. For particle diameters larger than roughly five monomer diameters, division of the force by the particle radius results in a nearly universal collapse of the depletion force for all interparticle separations. Molecular dynamics simulations have been employed to determine the depletion force for nanoparticles of a diameter five times the monomer size over a wide range of polymer densities spanning the semidilute, concentrated, and melt regimes. PRISM calculations based on the spatially nonlocal hypernetted chain closure for particle-particle direct correlations capture all the rich features found in the simulations, with quantitative errors for the amplitude of the depletion forces at the level of a factor of 2 or less. The consequences of monomer-particle attractions are briefly explored. Modification of the polymer-particle pair correlations is relatively small, but much larger effects are found for the surface excess including an energetic driven transition to a wetting polymer-particle interface. The particle-particle potential of mean force exhibits multiple qualitatively different behaviors (contact aggregation, steric stabilization, local bridging attraction) depending on the strength and spatial range of the polymer-particle attraction.     

A one-step etching method to produce gold nanoparticle coated silicon microwells and microchannels

Gold (Au) nanoparticles (NPs) have large surface areas and novel optical properties and can be readily functionalized using thiol-based chemistry; hence, they are useful in bioanalytical chemistry. Here, we describe a one-step, plasma-etching process that results in the spontaneous formation of Au NP coated recessed microstructures in silicon (Si). Mechanistically, the plasma etch rate of Si was enhanced in the vicinity of 10-100 nm thick Au patterns resulting in the formation of microwells or microchannels uniformly coated with 20-30 nm sized Au NPs. The methodology provides versatility in the types of microstructures that can be formed by varying the shape and dimensions of the Au patterns and the etch time. We also describe selective binding of antibodies to Au NP coated Si microwells using thiol-based surface modification.     

Acid base properties and catalytic activity of vanadium pentoxide supported on cerium oxide

The surface acidity and basicity of vanadium pentoxide supported on CeO₂ were determined using a set of Hammett indicators. The data have been correlated with the catalytic activity of these oxides towards liquid phase acylation of phenol.     

Spectroscopic investigations and computational study of 2‐[acetyl(4‐bromophenyl)carbamoyl]‐4‐chlorophenyl acetate

The Fourier transform Raman (FT‐Raman) and Fourier transform infrared (FT‐IR) spectra of 2‐[acetyl(4‐bromophenyl)carbamoyl]‐4‐chlorophenyl acetate were studied. The vibrational wavenumbers were examined theoretically using the Gaussian03 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution (PED) calculations. The simultaneous Raman and infrared (IR) activations of the CO stretching mode in the carbamoyl moiety show a charge transfer interaction through a π‐conjugated path. From the optimized structure, it is clear that the hydrogen bonding decreases the double bond character of the CO bond and increases the double bond character of the C N bonds. The first hyperpolarizability and predicted IR intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar structures, which makes this compound an attractive object for future studies of nonlinear optics. Optimized geometrical parameters of the compound are in agreement with similar reported structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Isolation and evaluation of cytogenetic effect of Brahmi saponins on cultured human lymphocytes exposed in vitro

Major saponins of Brahmi (Bacopa monniera, Fam: Scrophulariaceae) – bacosides A and B – were isolated from the total methanol extract and characterised based on melting point, TLC, IR, ¹H NMR and ¹³C NMR. They were evaluated for their in vitro cytogenetic effects on human peripheral blood lymphocytes by chromosomal aberration (CA) assay and sister chromatid exchange (SCE) assay. The frequency of chromatid type aberrations and reciprocal interchanges between sister chromatids in the treated cells was scored in comparison to the untreated control. At 30 μg/mL dose, bacoside A showed a statistically significant increase in the frequency of both CA and SCE and bacoside B showed an increase only in SCE. Our report of the genotoxicity of the saponins is significant in view of the reports of anticancer activity of Brahmi extracts.     

Influence of disorder-to-order transition on lattice thermal expansion and oxide ion conductivity in (Ca(x)Gd(1-x))(2)(Zr(1-x)M(x))2O7 pyrochlore solid solutions

The effect of simultaneous substitutions of Ca at A site and Nb or Ta at B site in pyrochlore-type solid solutions: (Ca(x)Gd(1-x))(2)(Zr(1-x)M(x))(2)O(7) (x = 0.1, 0.2, 0.3, 0.4, 0.5 and M = Nb or Ta) were studied by powder X-ray diffraction (XRD), FT NIR Raman spectroscopic techniques and transmission electron microscopy. The solid solutions were prepared by the conventional high-temperature ceramic route. The XRD results and Rietveld analysis revealed that the defect fluorite structure of Gd(2)Zr(2)O(7) progressively changed to a more ordered pyrochlore phase by simultaneous substitutions at A and B sites. Raman spectroscopy reveals the progressive ordering in the anion sublattice with simultaneous doping. High-resolution images and selected-area electron diffraction patterns obtained from TEM confirms the XRD and Raman spectroscopic results. High-temperature XRD studies show that the lattice expansion coefficient in these pyrochlore oxides is of the order of 10(-6) K(-1). Lattice thermal expansion coefficient increases with increase of disorder in pyrochlore oxides, and hence the variation of thermal expansion coefficient with composition is also a good indicator of disordering in pyrochlore-type oxides. The ionic conducting properties of the samples were characterised by impedance spectroscopy, and it was found that Nb-doped compositions show a considerable change in conductivity near the phase boundary of disordered pyrochlore and defect fluorite phases.