Structural and optical characteristics of silver/poly(N-vinyl-2-pyrrolidone) nanosystems synthesized by γ-irradiation

Silver nanoparticles (AgNPs) were synthesized in situ by γ-irradiation using poly(N-vinyl-2-pyrrolidone) (PVP) as a capping agent. The concentration, molecular weight and the structure (crosslinked and interpenetrated network) of PVP were varied, in order to determine the influence of the capping agent in the radiolytic synthesis of the Ag/PVP nanosystems. Transmission electron microscopy (TEM) showed that AgNPs obtained from the solutions containing higher PVP concentration and higher molecular weight were spherical in shape, with narrow size distribution and a diameter of～6 nm, while slightly larger rod-shaped silver agglomerates, with bimodal nanoparticle size distribution and diameters of ～10 nm and ～20 nm were obtained from the solutions containing lower PVP concentration and lower molecular weight. Strong plasmon coupling and extending of plasmon resonance was observed by UV–vis spectroscopy, as a result of formation of nanorod-like agglomerates. Crosslinked and interpenetrated network did not affect the structure of synthesized AgNPs. Ag/PVP nanocomposite, in the form of thin film, was obtained by solvent evaporation from Ag/PVP colloid solution with 10 wt% of PVP, and characterized by FTIR spectroscopy. The interactions in Ag/PVP nanocomposite are shown to be the result of the coordination bonding between AgNPs and nitrogen from pyrrolidone ring of PVP. The optical properties of investigated Ag/PVP nanosystems, as measured by the values of optical band gap, E_g, are mainly the consequence of the interparticle distance as a result of the concentration and the structure of surrounding PVP macromolecules.     

Purification method for recombinant proteins based on a fusion between the target protein and the C-terminus of calmodulin

Calmodulin (CaM) was used as an affinity tail to facilitate the purification of the green fluorescent protein (GFP), which was used as a model target protein. The protein GFP was fused to the C-terminus of CaM, and a factor Xa cleavage site was introduced between the two proteins. A CaM-GFP fusion protein was expressed in E. coli and purified on a phenothiazine-derivatized silica column. CaM binds to the phenothiazine on the column in a Ca(2+)-dependent fashion and it was, therefore, used as an affinity tail for the purification of GFP. The fusion protein bound to the affinity column was then subjected to a proteolytic digestion with factor Xa. Pure GFP was eluted with a Ca(2+)-containing buffer, while CaM was eluted later with a buffer containing the Ca(2+)-chelating agent EGTA. The purity of the isolated GFP was verified by SDS-PAGE, and the fluorescence properties of the purified GFP were characterized.     

Inclusion complexes with cyclodextrin and usnic acid

Molecular inclusion complexes of usnic acid (UA) with β-cyclodextrin (β-CD) and 2-hydroxypropyl β-cyclodextrin (HP β-CD) were prepared by the co-precipitation method in the solid state in the molar ratio of 1:1. Structural complexes characterization was based on different methods, FTIR, ¹H NMR, XRD and DSC. Parallel to the complex by the above methods, corresponding physical mixtures of UA with cyclodextrins and complexing agents (β-CD, HP β-CD and UA) were analyzed. The results of DSC analysis showed that, at around 200 °C, the endothermal peak in the complexes with cyclodextrins originating from the UA melting has disappeared. Complex diffractogram patterns do not contain peaks characteristic for the pure UA. They are more appropriate to cyclodextrin diffractogram. This fact points to the molecular encapsulation of UA in the cyclodextrin cavity. Chemical shifts in ¹H NMR spectra after the inclusion of UA into the cyclodextrin cavity, especially H-3 protons (0.0012 and 0.0102 ppm in the β-CD and HP β-CD, respectively) and H-5 and H-6 (0.0134 ppm) and hydrogen from CH₃ (0.0073 ppm) HP β-CD also points to the formation of molecular inclusion complexes. The improved solubility of UA in water was achieved by molecular incapsulation. In the complex with β-CD the solubility is 0.3 mg/cm³, with HP β-CD 4.2 mg/cm³ while the uncomplexed UA solubility is 0.06 mg/cm³. The microbial activity of UA and both complexes was tested against eight bacteria and two fungi and during the test no reduced activity of UA in the complexes was observed.     

Electroformation in a flow chamber with solution exchange as a means of preparation of flaccid giant vesicles

A recently described technique [Estes and Mayer, Biochim. Biophys. Acta 1712 (2005) 152-160] for the preparation of giant unilamellar vesicles (GUVs) in solutions with high ionic strength is examined. By observing a series of osmotic swellings followed by vesicle bursts upon a micropipette transfer of a single POPC GUV from a sucrose solution into an iso-osmolar glycerol solution, a value for the permeability of POPC membrane for glycerol, P=(2.09+/-0.82) x 10(-8)m/s, has been obtained. Based on this result, an alternative mechanism is proposed for the observed exchange of vesicle interior. With modifications, the method of Estes and Mayer is then applied to preparation of flaccid GUVs.     

X-ray luminescence of disperse SiO2 and porous silicon

We carry out a comparison between the luminescence spectra (photo-and x-ray luminescence) of porous silicon and disperse SiO₂, which by its physical characteristics is most similar to oxide films on porous silicon. The photoluminescence of porous silicon was also investigated using fluorescence (excitation by a nitrogen laser) and metallographic microscopes. We found that the natures of the luminescence centers of porous silicon and disperse SiO₂ are identical. A porous layer on single-crystal silicon ensures the creation of a highly branched surface of oxide film. Luminescence centers are located on its inner (as viewed from the porous silicon) surface. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 247–251, March–April, 1998.     

Reactions of Nucleosides with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU). Syntheses of N(3)-Methylene-Bridged Bis-uridines and Secouridine-Dinucleoside Analogs

Diasteroisomeric secouridine derivatives, appropriately protected and activated, served as starting compounds in the reactions with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in various solvents (CH₂Cl₂, MeCN, or dimethylformamide (DMF)). Reactions with DBU/CH₂Cl₂ gave N(3)-methylene-bridged bis-secouridines and bis-uridines (Scheme 3), while the reactions with DBU in non-alkylating solvents resulted in formation of secdinucleosides as the result of intermolecular ‘dimerizations’ (Scheme 2).     

Observation of parity violating effects in the polarized thermal neutron total and radiative capture cross sections of 117Sn and 139La

Parity violating effects in the transmission and radiative capture of longitudinally polarized thermal neutrons have been observed for ¹¹⁷Sn and ¹³⁹La targets. Helicity dependent asymmetries a = 10⁶ (σ⁺-? σ^?)/(σ⁺ + σ^?) were found in the total cross section of ¹¹⁷Sn (a = 6.2 ± 0.7) and ${}^{139}\text{La}\text{(a = 9.0 ± 1.4)}$, and also in the (n, γ) cross section of ¹¹⁷Sn (a = 22.6 ± 1.9) and of ¹³⁹La (a = 16.1 ± 2.0).     

Constructibility Classes for Triangle Location Problems

Straightedge-and-compass construction problems are well known for different reasons. One of them is the difficulty to prove that a problem is not constructible: it took about two millennia to prove that it is not possible in general to cut an angle into three equal parts by using only straightedge and compass. Today, such proofs rely on algebraic tools difficult to apprehend by high school student. On the other hand, the technique of problem reduction is often used in theory of computation to prove other kinds of impossibility. In this paper, we adapt the notion of reduction to geometric constructions in order to have geometric proofs for unconstructibility based on a set of problems known to be unconstructible. Geometric reductions can also be used with constructible problems: in this case, besides having constructibility, the reduction also yields a construction. To make the things concrete, we focus this study to a corpus of triangle location problems proposed by William Wernick in the eighties.     

Kinetics of inhibition of peroxidase activity of myeloperoxidase by quercetin

The inhibition of myeloperoxidase (MPO), isolated from human neutrophils, by quercetin was investigated by following peroxidase activity of the enzyme using o-dianisidine as the substrate. The inhibition parameters (IC₅₀) were obtained by graphical analysis of the inhibition curves. A reaction mechanism, which involved the enzyme inhibition by quercetin and H₂O₂ in excess, was proposed. The rate and equilibrium constants for the proposed reaction path were calculated from experimental data. Kinetic analysis in noninhibiting H₂O₂ concentration range in the absence and the presence of quercetin revealed that the reaction mechanism underwent Michaelis–Menten kinetics. K and V values indicated that quercetin was a mixed inhibitor of MPO activity. The initial reaction rates were recalculated using the obtained results. Calculated curves fitted the experimental results within the range of experimental error. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 384–394, 2008