Proton transfer and N(+)-H...S(-) hydrogen bonds in the crystal structure of 4-aminothiophenol

4-Aminothiophenol exists as 4-ammonio-1-benzenethiolate in the solid and liquid state. The crystal structure is characterised by a tetrahedral beta-As type network which is the driving force for the proton transfer.     

Transition metal-catalyzed regio- and stereoselective aminobromination of olefins with TsNH2 and NBS as nitrogen and bromine sources

[reaction: see text] A new synthetic procedure for aminohalogenation of olefins has been developed for the preparation of vicinal haloamine derivatives in high yields by using Cu, Mn, or V catalysts with p-toluenesulfonamide (TsNH(2)) and N-bromosuccinimide (NBS) as nitrogen and bromine sources, respectively. Unprecedented regio- and stereoselectivity (anti:syn > 99:1) toward the aminohalogenation process is shown for olefinic substrates as well as transition metal catalysts.     

TLC Based Method for Standardization of Pongamia pinnata (Karanj) Using Karanjin as Marker

Pongamia pinnata Linn. (Papilionaceae) seeds have gained great commercial and industrial importance owing to their high oil content. Presently, there is no appropriate TLC based method available for standardization of P. pinnata. A simple, robust and reproducible TLC method for the determination of Karanjin is reported in the seeds of P. pinnata. The method involves separation of components by TLC on pre-coated silica gel G 60 F₂₅₄ plates developed on toluene: ethyl acetate (7:3 v/v) and detection at 260 nm in absorbance mode. The sensitivity of the method was found to be 100 ng. The linearity range was 50–300 ng. Four samples of P. pinnata from different geographical locations were tested for their karanjin content using the developed method. The proposed method was found to be robust, precise, and accurate, it therefore holds potential for detection, monitoring and quantification of karanjin in Pongamia pinnata.

     

Dielectric properties of PbSrWO4 and PbBaWO4 compounds

PbSrWO₄ and PbBaWO₄ have been synthesised by the solid state reaction technique XRD patterns show them to be tetragonal. Dielectric constant (K^/) and Dielectric loss (K ^//) of PbSrWO₄ and PbBaWO₄ have been measured at 1 kHz in the temperature range of 300 to 1050 K. The log K^/ vs T as well as log K ^// vs T plot of PbSrWO₄ and PbBaWO₄ shows rapid increase of dielectric constant above 590 K and 640 K, respectively.     

Relativistic dynamics for spin-zero and spin-half particles

The classical and quantum mechanics of a system of directly interacting relativistic particles is discussed. We first discuss the spin-zero case, where we basically follow Rohrlich in introducing a set of covariant centre of mass (CM) and relative variables. The relation of these to the classic formulation of Bakamjian and Thomas is also discussed. We also discuss the important case of relativistic potentials which may depend on total four-momentum squared. We then consider the quantum mechanical case of spin-half particles. The negative energy difficulty is solved by introducing a number of first class constraints which fix the spinor structure of physical solutions and ensure the existence of proper CM and relative variables. We derive the form of interactions consistent with Lorentz invariance, space inversion, time reversal and charge conjugation and with the above mentioned first class constraints and find that it is analogous to that for the non-relativistic case. Finally the relationship of the present work with some previous work is briefly discussed.     

Semiclassical approximation for relativistic potentials

We consider the application of semiclassical approximation to relativistic potentials for massless particles where the kinetic energy is a nontrivial, nonlocal operator. Quantization rules are derived for an arbitrary confining potential and compared to some exact results forS-waves. These results admit of a partial generalization to smalll values.     

Phytosynthesis of Silver Nanoparticles Using Walnut (Juglans regia) Bark with Characterization of the Antibacterial Activity against Streptococcus mutans

A green method using Juglans regia bark extract was used to synthesize silver nanoparticles at room temperature with monitoring by absorption spectroscopy. The size and shape of the synthesized nanoparticles were characterized by infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and small-angle X-ray scattering. The average particle size was from 10 to 30?nm. Gas chromatography–mass spectrometry (GC–MS) was used for the separation, identification, and quantification of components of the plant extracts. A possible mechanism for the synthesis of nanoparticles was elucidated based on the GC–MS results. The synthesized silver nanoparticles showed effective inhibition against Streptococcus mutans, which is the main causative agent for dental caries. The nanoparticles also showed promising antibiofilm activity by inhibiting the glucosyltransferase enzyme.     

Two new eudesmane derivatives from Verbesina virginica

<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods.     

Focus on quantum dots as potential fluorescent probes for monitoring food toxicants and foodborne pathogens

Water-soluble quantum dots (QDs) are fluorescent semiconductor nanoparticles with narrow, very specific, stable emission spectra. Therefore, the bioconjugation of these QDs for biological fluorescent labeling may be of interest due to their unique physical and optical properties as compared to organic fluorescent dyes. These intrinsic properties of QDs have been used for the sensitive detection of target analytes. From the viewpoint of ensuring food safety, there is a need to develop rapid, sensitive and specific detection techniques to monitor food toxicants in food and environmental samples. Even trace levels of these toxicants can inadvertently enter the food chain, creating severe health hazards. The present review emphasizes the application of water-soluble bioconjugated QDs for the detection of food contaminants such as pesticides, pathogenic bacterial toxins such as botulinum toxin, enterotoxins produced by Staphylococcus aureus, Escherichia coli, and for the development of oligonucleotide-based microarrays. This review also emphasizes the application of a possible resonance energy transfer phenomenon resulting from nanobiomolecular interactions obtained through the bioconjugation of QDs with biomolecules. Furthermore, the utilization of significant changes in the spectral behavior of QDs (attributed to resonance energy transfer in the bioconjugate) in future nanobiosensor development is also emphasized.     

Magnetoelectric behavior of ferrimagnetic BixCo2−xMnO4 (x=0, 0.1 and 0.3) thin films

Thin films of Bi_xCo_2−xMnO₄ (x=0, 0.1 and 0.3) were grown on quartz, LaAlO₃ (LAO) and YBa₂Cu₃O₇ (YBCO) buffer layer coated LAO substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) and Raman scattering measurements showed that the thin films exhibit single phase polycrystalline cubic spinel structure on all the substrates. Near edge X-ray absorption fine structure (NEXAFS) studies confirmed the octahedral occupancy of the substituted Bi³⁺ ions. Temperature dependent zero-field cooled (ZFC) magnetization measurements show the ferrimagnetic (FM) behavior (T_C∼186 K) and magnetization undergoes a crossover from positive to negative, owing to the opposite contributions of magnetic moments from Co and Mn ions. A weak ferroelectric property exhibited by the films above room temperature was evidenced through the capacitance-voltage (C-V) and dielectric measurements. Magnetoelectric coupling was found to be maximum just below FM-T_C.