The effect of ligand field on the excitation luminescence spectra of some complex compounds of manganese (II)

The excitation and emission luminescence spectra of the complex compounds of manganese (II) chloride with the hydrochlorides of pyridine, 2-methyl- and 2-ethylpiperidine have been studied. It has been established that the crystals of these complex compounds appear in tetrahedral and octahedral configurations. The excitation spectra in both configurations contain bands originating from the⁴G,⁴P,⁴D and⁴F terms, the position of which is determined by configuration. From the excitation spectra the Racah parametersB andC and the ligand field strength parameter 10Dq have been determined.The emission luminescence spectra also depend on configuration of the complex compound. The character of these spectra is expressed in terms of the following characteristic parameters: the position of the maximum of the functionG(v), the half-width of the emission luminescence band, and the constants andm. From the excitation and emission luminescence spectra it has been established that the emission in both configurations is due to the⁴T₁(G)⁶A₁ transition.     

Equation of state of zero-temperature quark matter

We outline the key elements of a recent calculation aimed at determining the equation of state of deconfined (but unpaired) quark matter at zero temperature and high density, using finite quark masses. The computation is performed in perturbation theory up to three loops, and necessitates the development and application of some novel computational tools. In this talk, we introduce the basic features of these new techniques and review the main sources of motivation for considering finite mass effects in perturbation theory.     

Mechanical and anti‐stabbing properties of modified thermoplastic polymers impregnated multiaxial p‐aramid fabrics

New forms of hybrid multiaxial nanocomposites with enhanced mechanical and stab resisting properties are presented. This study is motivated by the lack of knowledge in the study of the multiaxial fabric nanocomposites with two modified thermoplastic matrices for antiballistic protection. Introduction of 5 wt.% silica nanoparticles in the composite of polyurethane/p‐aramid/poly (vinyl butyral) leads to significant improvement in mechanical properties, and the addition of silane as a coupling agents and glutaraldehyde as a crosslinking agents yielded maximal values of storage modulus, tensile modulus and anti‐stabbing properties for hybrid nanocomposites. Ballistic resistance testing and penetration depth of the hybrid nanocomposites were visualized using image analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

2-Substituted thiazole-4-carboxamide derivatives as tiazofurin mimics: synthesis and in vitro antitumour activity

Tiazofurin analogues bearing a 5-hydroxymethyl-2-methyl-tetrahydrofuro[2,3-d][1,3]dioxol-6-ol moiety as a sugar mimic (2 and 3), and two novel thiazole-based acyclo-C-nucleosides 4 and 16 have been synthesized in multistep sequences starting from d-xylose (compounds 2 and 3) or from d-arabinose (compounds 4 and 16). All synthesized analogues showed potent in vitro antitumour activities against a panel of human tumour cell lines. Flow cytometry data suggest that cytotoxic effects of analogues 2–4 and 16 in the culture of K562 cells might be mediated by apoptosis. It was also found that these analogues induced changes in cell cycle distribution of K562 cells. Results of western blot analysis (upregulation of Bax and downregulation of Bcl-2, activation of caspase-3 and the presence of a PARP cleavage product) suggest that tiazofurin mimics (2–4 and 16) in K562 cells induced apoptosis in a caspase-dependent way.     

Dipyrrylmetheneboron Difluorides as Labels in Two-Photon Excited Fluorometry. Part II–Nucleic Acid Hybridization Assays

Five two-photon excitable dipyrrylmetheneboron difluoride labels (dipyrrylmethene-BF₂ labels) with fluorescence emission maximum between 530 and 590 nm, and a frequently used rhodamine label, TAMRA, were conjugated to aminomodified oligonucleotides. The performance of the labeled oligonucleotides was studied in a separation-free nucleic acid hybridization assay using ArcDia^™ TPX bioaffinity assay technology. The results show that oligonucleotide conjugates of dipyrrylmethene-BF₂ labels provide higher two-photon excited fluorescence yield and better assay sensitivity than corresponding TAMRA conjugate. The effect of conjugation on photophysical properties of the labels and performance of the labeled oligonucleotides in separation-free hybridization assay is discussed.     

Hydrophilic Labeling Reagents of Dipyrrylmethene-BF2 Dyes for Two-Photon Excited Fluorometry: Syntheses and Photophysical Characterization

Recently introduced bioaffinity assay technology, ArcDia TPX, is based on two-photon excited fluorescence (TPE) and it enables separation-free ultra-sensitive immunoassays from microvolumes. Here we present syntheses of novel two-photon excitable fluorescent labeling reagents which have been specially designed to be used as label molecules in the ArcDia TPX assay technique. The labeling reagents are based on dipyrrylmetheneboron difluoride (dipyrrylmethene-BF2) chromophore, which have been substituted with aryl, heteroaryl or arylalkenyl chemical groups to extend the pi-electron conjugation. These substitutions results in a series of dipyrrylmethene-BF2 fluorophores with different photophysical properties. Dipyrrylmethene-BF2 fluorophores have been further substituted with a dipeptide linker unit and finally activated as succinimidyl esters to enable specific coupling with primary amino groups. The dipeptide linker serves as a spacer arm between the label and a target, and enhances the solubility of the label in aqueous solutions. Study of the chemical and photophysical performance of the new labeling reagents is described. The new labeling reagents exhibit high fluorescence quantum yields, and molar absorption coefficients. The results show that the new labels with the hydrophilic dipeptide linker unit provide large two-photon excitation cross-sections, high fluorescence quantum efficiency and good solubility in aqueous solutions. The results suggest that the novel dipyrrylmethene-BF2 labels are highly applicable to bioaffinity assays based on two-photon excitation of fluorescence.     

Anomalous lateral beam shift and total absorption due to excitation of surface waves in materials with negative refraction

We studied electromagnetic beam reflection from layered structures that include materials with negative refraction. Excitation of leaky surface waves leads to the formation of anomalous lateral shifts in the reflected beams with single or double peak structures. The presence of reasonable losses within material with negative refraction, besides significant influence on manifestation of the giant lateral shifts, can lead to their total suppression and anomalously high absorption of the incident radiation. If, in addition to the resonant excitation of leaky surface waves, radiation inflow exactly compensates their irreversible damping, total absorption of the incoming radiation can be achieved for moderately wide beams.     

Antitumour tiazofurin analogues embedded with an amide moiety at the C-2′ position

Synthesis of four new tiazofurin analogues has been accomplished starting from d-glucose. The key step of the synthesis was the three-step cascade that enabled an efficient hydrogen sulfide mediated one-pot conversion of 2-azido-3-O-acyl-ribofuranosyl cyanides to the corresponding 2-alkylamido ribofuranosyl thiocarboxamides. The resulting key intermediates were first converted to protected tiazofurin derivatives by cyclocondensation with ethyl bromopyruvate, and finally to target C-nucleosides by treatment with ammonia in methanol. In vitro cytotoxicities of tiazofurin analogues against a number of human tumour cell lines were recorded and compared with those observed for the parent molecule (tiazofurin), as well as the commercial antitumour agent doxorubicin (DOX). Analogues 2b-d have shown a potent in vitro cytotoxic activity against human myelogenous leukaemia K562. Among solid tumour cell lines, HT29 was sensitive only to 2d, while HeLa cells were sensitive to 2a, 2b and 2d. Only analogue 2a was highly cytotoxic against MCF-7 cells. No tiazofurin analogue exhibits any significant cytotoxicity towards normal foetal lung MRC-5 cells. Downregulation of Bcl-2, activation of caspase-3 and presence of cleavage product of PARP suggest that the cytotoxic effects of tiazofurin analogues 2a-d in K562 might be mediated by apoptosis in a caspase-dependent way. On the contrary, tiazofurin did not induce apoptosis of K562 cells, which suggests a different mechanism of action, most probably through the inhibition of IMPDH. Flow cytometry and Western blot analysis data agreed well with the results of MTT assay, and enabled identification of analogue 2c as the most promising antitumour agent that preferentially target cancer cells over normal cells and thus represents a new lead for further optimization.     

Further results on the least eigenvalue of connected graphs

In this paper, we identify within connected graphs of order n and size n+k (with and ) the graphs whose least eigenvalue is minimal. It is also observed that the same graphs have the largest spectral spread if n is large enough.