V. B. Tsvetkov

On the origin of near-IR luminescence in Bi-doped materials (II). Subvalent monocation Bi+ and cluster Bi5(3+) luminescence in AlCl3/ZnCl2/BiCl3 chloride glass

Broadband NIR photoluminescence (from 1000 to 2500 nm) was observed from partially reduced AlCl₃/ZnCl₂/BiCl₃ glass, containing subvalent bismuth species. The luminescence consists of three bands, assigned to Bi⁺ , Bi₂⁴⁺, and Bi₅³⁺ ions. The physical and optical characteristics of these centers and possible contribution to NIR luminescence from bismuth-doped oxide glasses are discussed.

Synthesis, characterization and in vitro activity of thrombin-binding DNA aptamers with triazole internucleotide linkages

A series of DNA aptamers bearing triazole internucleotide linkages that bind to thrombin was synthesized. The novel aptamers are structurally analogous to the well-known thrombin-inhibiting G-quadruplexes TBA15 and TBA31. The secondary structure stability, binding affinity for thrombin and anticoagulant effects of the triazole-modified aptamers were measured. A modification in the central loop of the aptamer quadruplex resulted in increased nuclease resistance and an inhibition efficiency similar to that of TBA15. The likely aptamer-thrombin binding mode was determined by molecular dynamics simulations. Due to their relatively high activity and the increased resistance to nuclease digestion imparted by the triazole internucleotide linkages, the novel aptamers are a promising alternative to known DNA-based anticoagulant agents.

Disordering of human telomeric G-quadruplex with novel antiproliferative anthrathiophenedione.

Linear heteroareneanthracenediones have been shown to interfere with DNA functions, thereby causing death of human tumor cells and their drug resistant counterparts. Here we report the interaction of our novel antiproliferative agent 4,11-bis[(2-{[acetimido]amino}ethyl)amino]anthra[2,3-b]thiophene-5,10-dione with telomeric DNA structures studied by isothermal titration calorimetry, circular dichroism and UV absorption spectroscopy. New compound demonstrated a high affinity (Kass∼106 M−1) for human telomeric antiparallel quadruplex d(TTAGGG)4 and duplex d(TTAGGG)4∶d(CCCTAA)4. Importantly, a ∼100-fold higher affinity was determined for the ligand binding to an unordered oligonucleotide d(TTAGGG TTAGAG TTAGGG TTAGGG unable to form quadruplex structures. Moreover, in the presence of Na+ the compound caused dramatic conformational perturbation of the telomeric G-quadruplex, namely, almost complete disordering of G-quartets. Disorganization of a portion of G-quartets in the presence of K+ was also detected. Molecular dynamics simulations were performed to illustrate how the binding of one molecule of the ligand might disrupt the G-quartet adjacent to the diagonal loop of telomeric G-quadruplex. Our results provide evidence for a non-trivial mode of alteration of G-quadruplex structure by tentative antiproliferative drugs.

Comparison of the 'chemical' and 'structural' approaches to the optimization of the thrombin-binding aptamer.

Noncanonically structured DNA aptamers to thrombin were examined. Two different approaches were used to improve stability, binding affinity and biological activity of a known thrombin-binding aptamer. These approaches are chemical modification and the addition of a duplex module to the aptamer core structure. Several chemically modified aptamers and the duplex-bearing ones were all studied under the same conditions by a set of widely known and some relatively new methods. A number of the thrombin-binding aptamer analogs have demonstrated improved characteristics. Most importantly, the study allowed us to compare directly the two approaches to aptamer optimization and to analyze their relative advantages and disadvantages as well as their potential in drug design and fundamental studies.

Near infrared photoluminescence of the univalent bismuth impurity center in leucite and pollucite crystal hosts

The bismuth doped aluminosilicate phases leucite (KAlSi2O6), gallium leucite (KGaSi2O6) and pollucite (CsAlSi2O6) display broadband NIR photoluminescence. The active center, responsible for this luminescence, is the Bi+ monocation, which substitutes for the large alkali metal cations. The Al,Si-disorder in the aluminosilicate framework of studied crystal phases results in the heterogeneity of Bi+ luminescent center population, which manifests itself in the characteristic dependency of the luminescence spectrum shape on the excitation wavelength. The relation of NIR emission in Bi+-doped leucite and pollucite phases to the luminescent properties of bismuth-doped glasses is also discussed.

A 160 W single-frequency laser based on an active tapered double-clad fiber amplifier

We present a CW single-frequency laser at 1062 nm (linewidth <3?MHz) with 160?W of total output power based on a two stage fiber amplifier. A GTWave fiber is used for the first stage of the amplifier. A tapered double-clad fiber (T-DCF) is used for the second stage of the amplifier. The high output power is achieved due to the amplified spontaneous emission (ASE) filtering and increased stimulated Brillouin scattering (SBS) threshold inherent to the axially non-uniform geometry.

A Universal Base in a Specific Role: Tuning up a Thrombin Aptamer with 5-Nitroindole

In this study we describe new modified analogs of the thrombin binding aptamer (TBA) containing 5-nitroindole residues. It has been shown that all modified TBAs form an anti-parallel G-quadruplex structure and retain the ability to inhibit thrombin. The most advanced TBA variant (TBA-N8) has a substantially increased clotting time and two-fold lower IC50 value compared to the unmodified prototype. Molecular modelling studies suggest that the improved anticoagulant properties of TBA-N8 result from changes in the binding mode of the analog. A modified central loop in TBA-N8 is presumed to participate in the binding of the target protein. Studies of FAM labelled TBA and TBA-N8 showed an improved binding affinity of the modified aptamer and provided evidence of a direct interaction between the modified central loop and thrombin. Our findings have implications for the design of new aptamers with improved binding affinities.

Terbium gallium garnet for high average power Faraday isolators: modern aspects of growing and characterization

Nowadays, terbium gallium garnet (TGG) single crystals are most popular media for compact Faraday rotators and Faraday isolators for visible and near infrared range. Their main advantages are high Verdet constant, high optical quality and low absorption. The main technique of TGG single crystals growing is still Czochralski method despite efforts directed to the development of new ways of obtaining these crystals. This method allows growing crystals of high optical quality with diameter up to 75 mm and length up to 150 mm (Fig.1). We test crystal lattice defects and optimize crystal growing conditions. As a result high grade optical elements may be manufactured with aperture up to 30 mm and isolation quality up to 50 dB. Investigation of influence of doping and high temperature annealing on TGG spectral characteristics allows reaching absorption as low as 0.0015cm-1at 1.06 mm wavelength.

The systematic approach to describing conformational rearrangements in G-quadruplexes

Conformational changes in DNA G-quadruplex (GQ)-forming regions affect genome function and, thus, compose an interesting research topic. Computer modelling may yield insight into quadruplex folding and rearrangement, particularly molecular dynamics simulations. Here, we show that specific parameters, which are distinct from those commonly used in DNA conformational analyses, must be introduced for adequate interpretation and, most importantly, convenient visual representation of the quadruplex modelling results. We report a set of parameters that comprehensively and systematically describe GQ geometry in dynamics. The parameters include those related to quartet planarity, quadruplex twist, and quartet stacking; they are used to quantitatively characterise various types of quadruplexes and rearrangements, such as quartet distortion/disruption or deviation/bulging of a single nucleotide from the quartet plane. Our approach to describing conformational changes in quadruplexes using the new parameters is exemplified by telomeric quadruplex rearrangement, and the benefits of applying this approach to analyse other structures are discussed.

A compact 1.06/1.32/2.94μm pulsed laser for dentistry

Abstract A three-wavelength pulsed laser for dental application is developed. The laser houses the Nd:YAG resonator ( 1.06/1.32 μm ) for soft-tissue treatment and Er:YAG resonator ( 2.94 μm ) for caries removal and fits and fissure treatment. Two heads share the cooling unit and two identical high-voltage power supply modules in order to achieve compactness. The Nd:YAG laser has 10 W at 1.06 μm and 7 W at 1.32 μm with a pulse duration of 100 μs . An Er:YAG laser of 2.94 μm has 3.5 W , 20 Hz and a pulse duration of 250 μs . The beams are delivered through fibers and the laser size is 75×55×32.5 cm .