Very-low-pressure pyrolysis (VLPP) of group IV (A) tetramethyls: Neopentane and tetramethyltin

The decomposition of neopentane was studied using the very-low-pressure pyrolysis (VLPP) technique at temperatures from 1000 to 1260 K. The derived Arrhenius parameters are consistent with δH_f⁰(t-butyl) = 8.4 kcal/mol. Using the above A factor, data on the decomposition of tetramethyltin yield DH⁰(Sn(CH₃)₃ - CH₃) = 69 ± 2 kcal/mol.     

Effect of 100 keV N+ ion irradiation on the organic single crystal of hippuric acid for nonlinear optical applications

The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been grown by the slow evaporation solution growth technique using N, N-dimethylformamide as the solvent. Single crystals of pure HA were irradiated at room temperature with 100 keV Nitrogen (N⁺) ions at fluence 1×10¹⁶ and 5×10¹⁶ ions/cm². The pure and irradiated HA single crystals were characterized by different characterization technique. The photoluminescence and UV–visible absorption were performed at room temperature. The crystalline perfection of the pure and irradiated single crystals has been examined by high-resolution X-ray diffraction. Vickers microhardness technique was used to study the effect on the mechanical strength of the crystal at different ion fluences. The structural changes were analyzed by powder X-ray diffraction analysis. The functional groups of the synthesized compound have been identified by Fourier transform infrared spectroscopy. The dielectric constant and dielectric loss as a function of frequency were analyzed at room temperature.     

An Experimental Study for Enhanced Availability of Free-Space Optics Systems over Hybrid Free-Space Optics/Radio Frequency Systems Using Switching Scheme Based on On–Off Keying and Multiple Pulse Position Modulation Schemes with Variable Data Rates

Abstract

Free-space optic links are degraded by such weather conditions as rain, fog, and atmospheric scintillation. The inherent advantages of free-space optic communication—providing higher data rates, security, and easy redeployment ability—motivate the avoidance of switching over free-space optic links to low bandwidth radio frequency links. This article establishes viable alternatives over free-space optics/radio frequency hybrid links to achieve higher capacity operation exploiting on–off keying and multiple pulse position modulation schemes with variable data rates to overcome the effect of fading due to adverse weather conditions. Results of an experimental free-space optical link at 1,550 nm are presented.     

Spectroscopic properties and photophysics of the synthesized compound 5-nitro-benzo[b]thiophene-2-carboxylic acid in non-polar/polar media and in the presence of TiO2 nanoparticles

The present work investigates by electrochemical and steady-state and time-resolved spectroscopic methods a synthesized compound 5-nitro-benzo[b]thiophene-2-carboxylic acid (5NBTC), both in normal solvents and in the presence of TiO₂ nanoparticles to reveal the nature of the photophysical processes involved. From the present experimental observations it is inferred that both in the ground state and the excited electronic state S₁, there exists a strong binding between -COOH functionality of 5NBTC and TiO₂ nanoparticles. However, the rupture of this binding in the presence of excess TiO₂, as apparent from the steady-state and time-resolved spectroscopic measurements, is responsible for the increase in radiative transitions. Formations of aggregations of TiO₂ nanoparticles at higher concentrations appear the cause of such rupturing. The redox potential measurements by cyclic voltammetry and theoretical computations by time-dependent density functional theory (TD-DFT) with B3LYP/6-311 G(d, p) basis function implemented in the Gaussian package confirm the electron accepting nature of 5NBTC and hence no electron transfer is possible between the organic compound and TiO₂ nanoparticles. It is most likely that the interaction model between 5NBTC and TiO₂ nanoparticles should be that the -COOH group of 5NBTC molecule coordinates either directly or through a hydrogen bond to the TiO₂ surface.     

Thermal behaviour of copolymers of methyl methacrylate and iso-octyl/iso-decyl methacrylate

Thermal behaviour of copolymers of methyl methacrylate (MMA) with iso-octyliso-decyl methacrylate was investigated using dynamic thermogravimetry, mass spectroscopy and pyrolysis gas chromatography. The copolymer samples were stable upto 250 °C. Total loss in weight was observed around 400 °C. The degradation in homopolymers as well as copolymers proceeded by predominans loss of monomer.

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Zusammenfassung Mittels dynamischer Thermogravimetrie, Massenspektroskopie und Pyrolysengaschromatographie wurde das thermische Verhalten von Kopolymeren aus Methylmethacrylat (MMA) und Isooktyl/Isodecyl-methacrylat untersucht. Die Kopolymerproben waren bis 250 °C stabil. Ein vollständiger Gewichtsverlust wurde bei 400 °C beobachtet. Der Abbau sowohl der Homopolymere als auch der Kopolymere erfolgt durch eine überwiegende Abgabe von Monomeren.

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, - /- . /- . 250°. 400°. , .

     

Amperometric glycolate sensors based on glycolate oxidase and polymeric electron transfer mediators

Using experiments involving cyclic voltammetry and stationary potential measurements, it was shown that siloxane polymers with covalently attached ferrocene and 1,1'-dimethylferrocene relays efficiently mediate electron transfer from reduced glycolate oxidase to a conventional carbon-paste electrode. Sensors containing these polymeric relay systems and glycolate oxidase respond rapidly to low (< 0.1 mM) glycolate concentrations, with steady-state current responses achieved in less than 1 min. The dependence of the sensor response on the nature of the siloxane polymer backbone, the type of polymer-bound redox mediator used and the amount of redox mediator present is discussed. From these considerations, sensors have been designed which can operate efficiently at low applied potential and can avoid decreased current response due to dissolved oxygen.     

catena‐Poly[[[triaqua­cobalt(II)]‐μ‐2,6‐dioxo‐1,2,3,6‐tetra­hydro­pyrimidine‐4‐carboxyl­ato(2–)] 1.72‐hydrate]

The Co^II ion in the title complex {[Co(C₅H₂N₂O₄)(H₂O)₃]·1.72H₂O}_n, has a distorted octa­hedral coordination geometry comprised of three water ligands, one deprotonated pyrimidine N atom and an adjacent carboxyl­ate O atom of one orotate ligand. The sixth coordination site is occupied by an exocyclic O atom from a neighbouring orotate moiety, and through this inter­action a helicoidal chain is formed. The mol­ecules are linked by intra­molecular O_water—H⋯O and inter­molecular N—H⋯O and O_water—H⋯O hydrogen bonds, forming a three‐dimensional network.     

Attenuating effect of bioactive coumarins from Convolvulus pluricaulis on scopolamine-induced amnesia in mice

Convolvulus pluricaulis Chois. (Convolvulaceae) has been used in Ayurveda as Medhya Rasyana (nervine tonic) to treat various mental disorders. This study was designed to isolate the bioactive compound(s) of this plant and to evaluate their effect against scopolamine-induced amnesia. Column chromatography of the chloroform and ethyl-acetate fractions led to the isolation of three coumarins identified as scopoletin, ayapanin and scopolin. All the three compounds at 2.5, 5, 10 and 15 mg/kg, p.o. were evaluated for memory-enhancing activity against scopolamine-induced amnesia using elevated plus maze and step down paradigms. Effect on acetylcholinesterase activity in mice brain was also evaluated. Scopoletin and scopolin, in both the paradigms, significantly and dose dependently attenuated the scopolamine-induced amnesic effect. Furthermore, these compounds at 10 and 15 mg/kg exhibited activity comparable to that of standard drug, donepezil. The compounds also exhibited significant acetylcholinesterase inhibitory activity.     

Multivariate analysis for forensic characterization,discrimination, and classification of marker pen inks

The multivariate analysis methods have recently gained high popularity within the field of forensic sciences because of their high accuracy and precision. The accurate and unbiased results are the preliminary need for a forensic investigation. The aim of the present work is to examine the marker pen inks which are widely used in various places like documentation in parcels, for photograph attestation, and also as a study material in the classroom. This research is focused on the three important aspects; first is to characterize the marker inks, second, to discriminate permanent marker and whiteboard marker inks using destructive (extracting of ink samples from paper substrate) and nondestructive (without ink extraction) techniques of ultraviolet–visible absorbance combined with peak identification examination as well as chemometric methods, and the third is to build a classification model for permanent and whiteboard marker inks. It is concluded that the chemometric method, that is, principal component analysis provides better discrimination power as compared to visual examination. However, destructive and nondestructive approaches give almost similar discriminating power. The classification model developed using linear discriminant analysis provides 87.5% of correct classification of marker ink samples. The method can further be used to formulate a statistical model for the determination of class/group of the other forensic exhibits.     

Extended-ensemble docking to probe dynamic variation of ligand binding sites during large-scale structural changes of proteins

Proteins can sample a broad landscape as they undergo conformational transition between different functional states. At the same time, as key players in almost all cellular processes, proteins are important drug targets. Considering the different conformational states of a protein is therefore central for a successful drug-design strategy. Here we introduce a novel docking protocol, termed extended-ensemble docking, pertaining to proteins that undergo large-scale (global) conformational changes during their function. In its application to multidrug ABC-transporter P-glycoprotein (Pgp), extensive non-equilibrium molecular dynamics simulations employing system-specific collective variables are first used to describe the transition cycle of the transporter. An extended set of conformations (extended ensemble) representing the full transition cycle between the inward- and the outward-facing states is then used to seed high-throughput docking calculations of known substrates, non-substrates, and modulators of the transporter. Large differences are predicted in the binding affinities to different conformations, with compounds showing stronger binding affinities to intermediate conformations compared to the starting crystal structure. Hierarchical clustering of the binding modes shows all ligands preferably bind to the large central cavity of the protein, formed at the apex of the transmembrane domain (TMD), whereas only small binding populations are observed in the previously described R and H sites present within the individual TMD leaflets. Based on the results, the central cavity is further divided into two major subsites, first preferably binding smaller substrates and high-affinity inhibitors, whereas the second one shows preference for larger substrates and low-affinity modulators. These central subsites along with the low-affinity interaction sites present within the individual TMD leaflets may respectively correspond to the proposed high- and low-affinity binding sites in Pgp. We propose further an optimization strategy for developing more potent inhibitors of Pgp, based on increasing its specificity to the extended ensemble of the protein, instead of using a single protein structure, as well as its selectivity for the high-affinity binding site. In contrast to earlier in silico studies using single static structures of Pgp, our results show better agreement with experimental studies, pointing to the importance of incorporating the global conformational flexibility of proteins in future drug-discovery endeavors.

Functional states of P-glycoprotein formed during its full transition cycle (red to blue), captured by molecular dynamics simulations, form a structural framework for extended-ensemble docking of small-molecule ligands of diverse activities.