Synthesis and Optical Properties of Cinnamylidene Derivatives of Malononitrile Trimer

Russian Journal of Organic Chemistry - Potassium salts of cinnamylidene derivatives of malononitrile trimer were obtained by the reactions of malononitrile trimer with cinnamaldehyde derivatives....     

Activation of color centers in bismuth glass by femtosecond laser radiation

The activation of color centers in the bismuth aluminum-boron-phosphate glass by high-intensity femtosecond laser radiation is experimentally studied. The dynamics of the laser-induced emitting centers in the bulk of sample is characterized. The photoactivation of bismuth glasses is possibly related to the recharging of structural precursors, which serve as effective electron traps and whose possible configuration is discusses. The effect of the femtosecond irradiation involves the initiation of the nonlinear ionization of the glass matrix and the generation of plasma with the concentration of carriers that is sufficiently high to provide almost complete recharging of precursors over several laser pulses.     

Bismuth valence states and emission centers in Mg-Al-silicate glass

Two Al-Mg-silicate glass sample sets with variable Bi₂O₃ content were prepared. One set was sintered by melting in an iridium crucible at 1850°C in nitrogen, the other—in alumina crucibles at 1550°C in air. Their absorption and emission properties were investigated and compared in the 200–1600 nm spectral range. It was determined that the visible range extinctions values of high-temperature melted samples were almost two orders of magnitude higher than those of the low-temperature melted samples with the same doping level. The concentration dependences of the extinction values at 500, 700 and 800 nm were nonlinear. The investigations allowed us to estimate the absolute concentrations of Bi³⁺ ions and NIR-emitting centers as well as the efficiency of the Bi³⁺ ions conversion into these centers. It was concluded that optical centers emitting at 1100 and 1300 nm contain a pair of bismuth ions. Speculations about some possible structures of Bi dimer NIR-emitting centers were made.     

The microscopic investigation of structures of moving flux lines by neutron and muon techniques

We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux lines in low T _c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line lattice (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (μSR) technique gives the distribution of values of magnetic field within the FLL. We have recently succeeded in performing μSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors.     

Activity-based chemical proteomics accelerates inhibitor development for deubiquitylating enzymes

Converting lead compounds into drug candidates is a crucial step in drug development, requiring early assessment of potency, selectivity, and off-target effects. We have utilized activity-based chemical proteomics to determine the potency and selectivity of deubiquitylating enzyme (DUB) inhibitors in cell culture models. Importantly, we characterized the small molecule PR-619 as a broad-range DUB inhibitor, and P22077 as a USP7 inhibitor with potential for further development as a chemotherapeutic agent in cancer therapy. A striking accumulation of polyubiquitylated proteins was observed after both selective and general inhibition of cellular DUB activity without direct impairment of proteasomal proteolysis. The repertoire of ubiquitylated substrates was analyzed by tandem mass spectrometry, identifying distinct subsets for general or specific inhibition of DUBs. This enabled identification of previously unknown functional links between USP7 and enzymes involved in DNA repair.     

Hydroxyl groups in phosphosilicate glasses for fibre optics

IR absorption spectra of phosphosilicate glasses containing 1–19 mol% of P₂O₅ are measured and analyzed. Interaction of hydroxyl groups with the phosphorus centres in the phosphosilicate glass is investigated in cluster models using PM3 and MNDO quantum-chemical methods. An explanation of the experimentally observed change of vibrational absorption bands caused by the hydroxyl groups is proposed.     

Optical fibre-grating pulse compression

Numerical simulation is used to consider non-linear pulse propagation in fibres and subsequent pulse compression in a dispersive delay line. It is shown that for small initial pulse powers the conventional non-linear Schrödinger equation (NSE) is quite accurate to describe the process of pulse propagation in fibres. In this case initially symmetrical pulses undergo squaring and spectral broadening in fibres, and frequency chirp is linearized over most of the pulse, while shapes of the pulse, spectrum and frequency chirp remain symmetrical at the output of the fibre. There is a certain optimum fibre lengthZ _opt which is determined by the initial pulse parameters and fibre characteristics for pulse compression in the dispersive delay line. When the fibre lengthZ>Z _opt the optical wave breaking effect distorts the linearity of the frequency chirp and thus deteriorates the quality of the compressed pulse. The region of NSE approximation accuracy is determined. It is demonstrated that at increase of the initial pulse power (initial pulse width makes no difference) the NSE approximation becomes inaccurate. So the pulse dynamics in the fibre were described by the modified NSE derived in the higher-order approximation of the method of slowly varying amplitudes from Maxwell's equations. In this case the shock wave appears at the trailing edge of the pulse, which accelerates the wave breaking process. This results in a decrease of the optimum fibre length and deterioration of compressed pulse parameters, compared with the NSE case. Spectral windowing of the extreme Stokes components of the pulse spectrum permits significant improvement in the quality of the compressed pulse. The main features of the compression of pulses with asymmetrical initial shape are also considered.