5,5'-Azoxytetrazolates - a new nitrogen-rich dianion and its comparison to 5,5'-azotetrazolate

A modification of the synthesis of sodium 5,5'-azotetrazolate pentahydrate, described by Thiele in 1898, yields the unknown and unexpected corresponding 5N-oxido derivative sodium 5,5'-azoxybistetrazolate pentahydrate (Na(2)zTO·5H(2)O, ). Purification was achieved by recrystallization based on the better solubility of Na(2)zTO·5H(2)O in water. Different nitrogen-rich salts, such as the diammonium (), the dihydroxylammonium (), the bis-diaminoguanidinium (), the bis-triaminoguanidinium () and the diaminouronium salt (), have been prepared using metathesis reactions starting from barium 5,5'-azoxybistetrazolate pentahydrate () and ammonium, hydroxylammonium, diaminoguanidinium or diaminouronium sulfate and triaminoguanidinium chloride, respectively. The nitrogen rich azoxy-derivatives were characterized using NMR, IR and Raman spectroscopy, mass spectrometry and elemental analysis. Additionally the solid state structures of , , and were determined by single crystal X-ray diffraction. The heats of formation of and and their corresponding azo-tetrazolate derivatives were calculated by the atomization method based on CBS-4M enthalpies. With these values and the crystal densities, several detonation parameters such as the detonation velocity, detonation pressure and specific impulse were calculated (EXPLO5) and compared. The sensitivities towards shock (BAM drophammer), friction (BAM friction tester) and electrostatic discharge of the described compounds were determined.     

Effect of Polystyrene Microsphere Surface to Fluorescence Lifetime Under Two-Photon Excitation

Molecular assays such as immunoassays are often performed using solid carriers and fluorescent labels. In such an assay format a question can be raised on how much the fluorescence of the label is influenced by the bio-affinity binding events and the solid carrier surface. Since changes in fluorescence intensity as labels bind to surfaces are notoriously difficult to quantify other approaches are preferred. A good indicator, independent of the fluorescence intensity of the label, is the fluorescence lifetime of the marker fluorophore. Changes in fluorescence lifetime reliably indicate the presence of dynamic quenching, energy transfer or other de-excitation processes. A microsphere based assay system is studied under two-photon excitation. Changes in fluorescence lifetime are studied as labeled protein conjugates bind on microsphere surfaces – both direct on the surface and with a few nanometer distance from the surface. Fluorescence signal is measured from individual polystyrene microspheres and the fluorescence lifetime histogram is simultaneously recorded. The results indicate that self-quenching and quenching by the polystyrene surface are both present in such a system. However, the effect of the surface can be avoided by increasing the distance between the surface and the label. Typical distances achieved by a standard sandwich type of assay, are already sufficient to overcome the surface induced quenching in fluorescence detection.     

Synthesis of highly soluble fluorescent π-extended 2-(2-thienyl)benzothiazole derivatives via oxidative cyclization of 2-thienylthioanilide as the key step

In this Letter, we synthesize highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and evaluate their photophysical properties. The key step is the synthesis of 2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole (2) via oxidative cyclization of 2-thienylthioanilide using PhI(OAc)₂ as the oxidant. The target dyes could be easily synthesized by the Suzuki–Miyaura cross-coupling reaction of 2 and an appropriate π-donor. The photophysical properties of the 2-thienylbenzothiazole chromophore were controlled by the π-donor moiety. It was found that 2 exhibited large Stokes shifts (5345 cm⁻¹) and a high quantum efficiency for fluorescence (Φ_F = 0.94 in CH₂Cl₂). Therefore, it can be expected to be a useful photofunctional material in liquid crystal laser dyes and nonlinear optical materials.     

A Polymer for Application as a Matrix Phase in a Concept of In Situ Curable Bioresorbable Bioactive Load-Bearing Continuous Fiber Reinforced Composite Fracture Fixation Plates

The use of bioresorbable fracture fixation plates made of aliphatic polyesters have good potential due to good biocompatibility, reduced risk of stress-shielding, and eliminated need for plate removal. However, polyesters are ductile, and their handling properties are limited. We suggested an alternative, PLAMA (PolyLActide functionalized with diMethAcrylate), for the use as the matrix phase for the novel concept of the in situ curable bioresorbable load-bearing composite plate to reduce the limitations of conventional polyesters. The purpose was to obtain a preliminary understanding of the chemical and physical properties and the biological safety of PLAMA from the prospective of the novel concept. Modifications with different molecular masses (PLAMA-500 and PLAMA-1000) were synthesized. The efficiency of curing was assessed by the degree of convergence (DC). The mechanical properties were obtained by tensile test and thermomechanical analysis. The bioresorbability was investigated by immersion in simulated body fluid. The biocompatibility was studied in cell morphology and viability tests. PLAMA-500 showed better DC and mechanical properties, and slower bioresorbability than PLAMA-1000. Both did not prevent proliferation and normal morphological development of cells. We concluded that PLAMA-500 has potential for the use as the matrix material for bioresorbable load-bearing composite fracture fixation plates.     

Quantum dots as simultaneous acceptors and donors in time-gated Förster resonance energy transfer relays: characterization and biosensing

The unique photophysical properties of semiconductor quantum dot (QD) bioconjugates offer many advantages for active sensing, imaging, and optical diagnostics. In particular, QDs have been widely adopted as either donors or acceptors in F?rster resonance energy transfer (FRET)-based assays and biosensors. Here, we expand their utility by demonstrating that QDs can function in a simultaneous role as acceptors and donors within time-gated FRET relays. To achieve this configuration, the QD was used as a central nanoplatform and coassembled with peptides or oligonucleotides that were labeled with either a long lifetime luminescent terbium(III) complex (Tb) or a fluorescent dye, Alexa Fluor 647 (A647). Within the FRET relay, the QD served as a critical intermediary where (1) an excited-state Tb donor transferred energy to the ground-state QD following a suitable microsecond delay and (2) the QD subsequently transferred that energy to an A647 acceptor. A detailed photophysical analysis was undertaken for each step of the FRET relay. The assembly of increasing ratios of Tb/QD was found to linearly increase the magnitude of the FRET-sensitized time-gated QD photoluminescence intensity. Importantly, the Tb was found to sensitize the subsequent QD-A647 donor-acceptor FRET pair without significantly affecting the intrinsic energy transfer efficiency within the second step in the relay. The utility of incorporating QDs into this type of time-gated energy transfer configuration was demonstrated in prototypical bioassays for monitoring protease activity and nucleic acid hybridization; the latter included a dual target format where each orthogonal FRET step transduced a separate binding event. Potential benefits of this time-gated FRET approach include: eliminating background fluorescence, accessing two approximately independent FRET mechanisms in a single QD-bioconjugate, and multiplexed biosensing based on spectrotemporal resolution of QD-FRET without requiring multiple colors of QD.     

Computing weighted Szeged and PI indices from quotient graphs

The weighted (edge-)Szeged index and the weighted (vertex-)PI index are modifications of the (edge-)Szeged index and the (vertex-)PI index, respectively, because they take into account also the vertex degrees. As the main result of this article, we prove that if G is a connected graph, then all these indices can be computed in terms of the corresponding indices of weighted quotient graphs with respect to a partition of the edge set that is coarser than the Θ^*-partition. If G is a benzenoid system or a phenylene, then it is possible to choose a partition of the edge set in such a way that the quotient graphs are trees. As a consequence, it is shown that for a benzenoid system, the mentioned indices can be computed in sublinear time with respect to the number of vertices. Moreover, closed formulas for linear phenylenes are also deduced.     

Quasiconformality, homeomorphisms between metric measure spaces preserving quasiminimizers, and uniform density property

We characterize quasiconformal mappings as those homeomorphisms between two metric measure spaces of locally bounded geometry that preserve a class of quasiminimizers. We also consider quasiconformal mappings and densities in metric spaces and give a characterization of quasiconformal mappings in terms of the uniform density property introduced by Gehring and Kelly.     

Ultrasonic spectroscopy of pure cyclic compounds

Ultrasonic studies of the group of halogens of benzene and particularly dependence of acoustic parameters on the structure of organic liquids, demonstrate some interesting regularities in the group of these compounds in gas and liquid states. In this paper results for five cyclic liquids: bromo-, chloro-, fluoro- and jodobenzene are discussed and compared to benzene. Vibrational relaxation was observed in all the compounds. The studies reported here as well as other experimental for great number of compounds support the conclusion that almost all vibrational relaxation processes in liquids can be described using a single relaxation time. It also seems that all vibrational degrees of freedom of the molecule take part in this vibrational process. It seems that differences in transition probabilities between molecules studied could be caused by additional attraction between of molecules having a significant dipole moments.     

From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task

Background  

Phase-locked gamma oscillations have so far mainly been described in relation to perceptual processes such as sensation, attention or memory matching. Due to its very short latency (≈90 ms) such oscillations are a plausible candidate for very rapid integration of sensory and motor processes.     

On the magnetic properties of some industrial metal aerosols

The magnetic properties of some dusts and fumes collected from different work environments are studied. The specific magnetic remanent and saturation moments, pulse coercive forces and iron contents of the dusts are given and regression equations for the relation between the results are calculated. Some examples of the remanent magnetization curves of the dust are illustrated. A change in the magnetizing time from 0.4 ms to 1 s was not found to affect the remanent moment of stearin embedded dust. When loaded filters were used as a sample, the specific remanent moment was not found to depend on the amount of dust. The variations of the remanent moments among magnetite samples mixed with viscose media is shown to be much higher than that of samples with stearin.