Existence and multiplicity of positive solutions for a system of difference equations with coupled boundary conditions

We study the existence and multiplicity of positive solutions for a system of nonlinear second-order difference equations subject to coupled multi-point boundary conditions.     

Convex games with an infinite number of players and sequencing situations

In this paper we study convex games with an infinite countable set of agents and provide characterizations of this class of games. To do so, and in order to overcome some shortcomings related to the difficulty of dealing with infinite orderings, we need to use a continuity property. Infinite sequencing situations where the number of jobs is infinite countable can be related to convex cooperative TU games. It is shown that some allocations turn out to be extreme points of the core of an infinite sequencing game.     

Thermal,spectral and biological characterisation of copper(II) complexes with isoniazid-based hydrazones

Journal of Thermal Analysis and Calorimetry - A series of complexes [Cu(L)(CH3COO)2]·nH2O (L: isonicotinic acid 2-(2-hydroxy-8-substituted-tricyclo[7.3.1.02.7]tridec-13-ylidene)-hydrazones)...     

Magnetic characterization of some nanometric iron oxides

Nanosized magnetite particles embedded in polypyrrole matrix have been studied by Mössbauer and electron magnetic resonance spectroscopy. Comparison with as grown magnetite is made. Hyperfine fields distribution is determined and line shape of resonance curves are discussed in terms of composite structure, sizes and treatments.     

Spectral,thermal and biological characterization of complexes with a Schiff base bearing triazole moiety as potential antimicrobial species

Journal of Thermal Analysis and Calorimetry - A novel series of complexes ML(ClO4)·nH2O (M: Co, Ni, Cu, Zn; HL: 2-[(E)-(1H-1,2,4-triazol-3-ylimino)methyl]phenol) have been synthesized and...     

Fluorescence and Time-Resolved Delayed Luminescence of Porphyrins in Organic Solvents and Polymer Matrices

Porphyrin dyes fulfill an essential function in photosynthesis and are important in photodynamic therapy and in a range of electronic devices. Their spectroscopic characteristics may play a crucial role in these processes. The spectral properties of two porphyrin dyes: tetraphenylporphyrin and tetraphenysulfporphyrin in organic solvents (acetone, chloroform, methyl alcohol, and dimethyl-sulfoxide) and in polyvinyl alcohol and poly(methylmethacrylate) films have been investigated. Absorption, fluorescence, and microsecond time-resolved delayed luminescence spectra have been measured at room temperature. The existence of different aggregated dye forms in the ground and excited states has been demonstrated. The manifold of dye species depends on the solvent/polymer. In the case of the polymers, it also depends on the solvent used to coat the polymer film. Delayed luminescence spectra and decay times of the two porphyrins in the different solutions and in polymeric matrices suggest that different mechanisms of deexcitation of the singlet excited states may be responsible for their generation in these and other porphyrin dyes.     

Theoretical studies of carbocations in ion pairs. 8. Search for anchimeric assistance in the ionization of 2-butyl cation precursors

The structures of carbocations formed in the ionization of 2-butyl precursors were investigated by high level ab initio MO calculations on the reaction of 2-butyl fluoride (1) with borane, which gives a C4H9+ cation paired with trihydrofluoroborate (FBH3-, A). Two conformations of the "open," secondary cation (2) in the ion pair resulted from two conformations of 1, with F gauche and trans to C4 (2-g and 2-t, respectively). No anchimeric assistance by hydrogen (in 1-g) or methyl (in 1-t) was evidenced. In fact, attempts at optimizing the geometry of the H-bridged (3) and methyl-bridged (6) cations at short interionic distances (d) led to the corresponding conformations of 2. Upon ion separation, proton transfer from 2 to the anion occurred at intermediate interionic distances, consonant with experimental observations in trifluoroacetic acid. Elimination was prevented by addition of a lithium cation to the ion pair, i.e., running computations on triple ions (2.A.Li+). Cation 6 became an energy minimum beyond d = 2.5 A and 3 beyond 2.8 A. Cation 2-g was still the most stable isomer at d = 3.2 A, which was greater than the interionic distance in the crystals of the isomeric tert-butyl cation salts (3-3.1 A). Thus, spectral determinations of 2-butyl cations in the solid state should be interpreted with 2-g as the main component of the ion mixture. When the ions became separated (d >/= 4 A), only the bridged ions were energy minima. In this process, bridging did not occur opposite to the leaving group to assist the ionization, but on the same side with it, being controlled by the electrostatic interaction with the anion, as it departed from the vicinity of the cation. Such behavior was also noted in the ionization of the 3-methyl-2-butyl homolog.     

Per-O-methylation of neutral carbohydrates directly from aqueous samples for gas chromatography and mass spectrometry analysis

Per-O-methylation of neutral carbohydrates in one step by adding dimethyl sulfoxide, powdered sodium hydroxide, and methyl iodide directly to aqueous sample is described. The influence of the water on the methylation reaction is investigated. Solid powdered sodium hydroxide is very hygroscopic and can scavenge the water from sample if an additional excess of sodium hydroxide is added. The degree of per-O-methylation of carbohydrates is checked by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Gas chromatography-mass spectrometry analysis of mono- and disaccharides from grape juice is presented.     

Characterization of self-assembled monolayers (SAMs) on silicon substrate comparative with polymer substrate for Escherichia coli O157:H7 detection

This article presents the characterization of two substrates, silicon and polymer coated with gold, that are functionalized by mixed self-assembled monolayers (SAMs) in order to efficiently immobilize the anti-Escherichia coli O157:H7 polyclonal purified antibody.A biosurface functionalized by SAMs (self-assembled monolayers) technique has been developed. Immobilization of goat anti-E. coli O157:H7 antibody was performed by covalently bonding of thiolate mixed self-assembled monolayers (SAMs) realized on two substrates: polymer coated with gold and silicon coated with gold. The F(ab′)₂ fragments of the antibodies have been used for eliminating nonspecific bindings between the Fc portions of antibodies and the Fc receptor on cells. The properties of the monolayers and the biofilm formatted with attached antibody molecules were analyzed at each step using infrared spectroscopy (FTIR-ATR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV). In our study the gold-coated silicon substrates approach yielded the best results.These experimental results revealed the necessity to investigate each stage of the immobilization process taking into account in the same time the factors that influence the chemistry of the surface and the further interactions as well and also provide a solid basis for further studies aiming at elaborating sensitive and specific immunosensor or a microarray for the detection of E. coli O157:H7.     

Shape tailoring of hexagonally ordered triangular gold nanoparticles with nanosecond-pulsed laser light

In this contribution recent results on selective and precise tailoring of triangular gold nanoparticles (NPs) using ns-pulsed laser light are presented. The NPs were prepared by nanosphere lithography and subsequently tailored with ns-pulsed laser light using different fluences and wavelengths. The method is based on the size and shape dependent localized surface plasmon polariton resonance (SPR) of the NPs. We will demonstrate that the gap size between triangular NPs can be tuned from approximately 102±14 nm to 122±11 nm, due to a shape change of the NP from triangular to oblate. These morphological changes are accompanied by a significant shift of the surface plasmon resonance from λ_SPR=730 nm to λ_SPR=680 nm. Most importantly if the laser wavelength is chosen such that the dipolar SPR is excited, the hexagonal order of the NPs remains intact after irradiation, in contrast to excitation via the quadrupole SPR or within the interband transition. A tuneable gap size and the conservation of the hexagonal order of the NP array is the precondition for applications, where the NPs should serve as anchor points, e.g. for functional molecular nanowires, which can be used to utilize molecular devices.