Disorder driven optical processes in nanocrystalline ZnO

A systematic study on the modification of optical properties in mechanically milled ZnO powder has been reported here. The average grain size of the powder becomes ～20 nm within 4 h of milling. Fluctuations of average grain size have been noticed at the initial stage of milling (within 15 min). Changes in grain morphology with milling have also been noticed in scanning electron micrographs of the samples. Room temperature optical absorption data shows a systematic red shift of absorption band edge (～3.25 eV). The band tail parameter (extracted from the optical absorption just below the band edge) follows a simple exponential relation with the inverse of the average grain size. Significant increase of the band tail parameter has been noticed at low grain size regime. It has been analyzed that high values of band tail parameter is a representative of V_Zn–V_O type divacancy clusters. Room temperature photoluminescence spectra show decrease (except for 120 min milling) of band edge emission intensity with increase of milling time. Subsequent decrease of sub-band edge emission is, however, less prominent. The variation of PL intensity ratio (intensity at band edge peak with that at 2.3 eV) follows simple exponential decrease with the increase of band tail parameter. This indeed shows that band edge emission in ZnO is related with the overall disorder in the system, not grain size induced only.     

In situ derivatization-liquid liquid extraction as a sample preparation strategy for the determination of urinary biomarker prolyl-4-hydroxyproline by liquid chromatography-tandem mass spectrometry

Polar analytes that possess protic functional groups have often been treated with alkyl chloroformates to decrease their polarity and increase their volatility prior to gas chromatography-mass spectrometry analysis. This derivatization reaction has two distinct advantages. It proceeds smoothly in aqueous media, and the desired reaction products are efficiently separated from interfering ionic components by their extraction into a water-immiscible organic phase. In the present work, the derivatization-liquid liquid sample preparation was examined in detail for analysis of a potential urinary dipeptide biomarker L-prolyl-4-L-hydroxyproline (PHP) by downstream liquid chromatography coupled to electrospray mass spectrometry. PHP was treated with a series of alkyl and fluoroalkyl chloroformates in aqueous media, and the detected reaction products were investigated. Smooth conversion of PHP into the N-isobutyloxycarbonyl isobutyl ester was accomplished by the coupled action of isobutanol, isobutyl chloroformate and the pyridine catalyst. This derivative afforded a highest detector response from all the derivatized forms examined, including the nonderivatized PHP. A simple isocratic elution on a common RP-C18 HPLC column coupled with tandem mass spectrometry, and use of the synthesized heptadeuterated analog (D7-PHP) as an internal standard, enabled validation of the method and determination of PHP in human urine in less than 5?min. The in situ derivatization-liquid liquid extraction has thus been demonstrated to be a useful sample preparation strategy for the analysis of polar metabolites by liquid chromatography-tandem mass spectrometry in the complex urine matrix.     

Classroom video in teacher professional development program: community documentational genesis perspective

We examine classroom video recordings as a means of supporting the learning of teacher communities. Drawing on a longitudinal professional development program for middle years mathematics teachers in the USA, we first outline two contrasting episodes in which the teachers analyzed same segments of classroom video in two different points in the program, 2 years apart. We document that the teachers considered dramatically different aspects of video-recorded instruction as relevant to their professional interests and learning in the two episodes. We then analyze the episodes, and the intervening developments, from point of view of the community documentational genesis. In doing so, we highlight the teacher community’s creation of shared repertoire of ways of reasoning.     

Study of properties of the glass batch melting filter dust

The filter dust from the container glass production was studied by the X-Ray powder diffraction, differential thermal analysis (DTA), X-Ray fluorescent spectroscopy, and Raman spectroscopy. The analysis of the elemental composition indicated that the major portion (≈96 wt%) of filter dust is comprised of sulfates. Predominant abundance of sodium sulfate was confirmed by comparative DTA of investigated filter dust. The characteristic redox property (COD—Chemical Oxygen Demand) was determined. The raw materials used in manufacturing of container glass in Vetropack Nem?ová with 0, 25, 50, 75 or 100 wt% of filter dust as a substitution of sulfate raw material were used for the preparation of samples of glass batch. Thermal properties of prepared samples were characterized by means of DTA. The substitution of sulfate raw material by filter dust does not significantly affect the thermal properties of the examined glass batches and consequently the course of the glass melting.     

Surface-engineered polyelectrolyte multilayer capsules: synthetic vaccines mimicking microbial structure and function

Immunizing: to evoke highly potent immune responses against recombinant antigens, hollow capsules consisting of layers of dextran sulphate and poly-L-arginine that encapsulate the antigen ovalbumin (orange circles) were coated with immune-activating CpG-containing oligonucleotides (green). These capsules were readily internalized by dendritic cells and showed activity in further immunization experiments.     

Gold-gold cooperation in the addition of methanol to alkynes

The gold(I)-mediated reaction between an internal alkyne and methanol proceeds by a dual activation mechanism, which directly results in formation of gem-diaurated intermediates. Reaction intermediates were investigated by IR multiphoton dissociation spectroscopy, kinetics by NMR spectroscopy, and the mechanism by DFT calculations.     

First mixed hydrazide/hydroxylamide metal aggregates

The first organometallic clusters of mixed hydrazide/hydroxylamide clusters of zinc, [Zn(MeZn)(4)(HNNMe(2))(2)(ONEt(2))(4)] and {Zn(EtZn)(4)[HNN(CH(2))(5)](2)(ONEt(2))(4)} were synthesized in one-pot synthesis protocols from dialkylzinc solutions, substituted hydrazines and N,N-diethylhydroxylamine; competing for the Zn atoms, the different binding properties of hydrazide and hydroxylamide ligands in these heteroleptic clusters are discussed.     

Crystallization of polypropylenewith a minute amount of β-nucleator

Triammonium-N-dithiocarboxyiminodiacetate, (NH₄)₃L, a new dithiocarbamato derivative of iminodiacetate, has been synthesized. The coordination properties of the ligand were tested in reactions with copper(II), nickel(II) and palladium(II) salts in acidic solutions. Complexes with a general formula M(H₂L)₂ were obtained, with the coordination taking place through the sulfur atoms of the dithiocarbamate moiety. The new compounds were characterized by elemental analysis, UV/VIS and IR spectroscopy, thermal analysis and magnetic measurements. In addition, the ligand was characterized by ¹H- and ¹³C-NMR spectroscopy and molar conductivity measurements. The copper(II) complex is paramagnetic, while the nickel(II) and palladium(II) compounds are diamagnetic. The thermal decomposition of all compounds is continuous and the thermal stability of the complexes is higher than that of the ligand, as expected.     

Self-assembly of silver nanoparticles: synthesis, stabilization, optical properties, and application in surface-enhanced Raman scattering

Silver nanoparticle aggregates were synthesized in large scale using resorcinol under alkaline condition to obtain an assembly of silver clusters. Stable dispersion of the cluster in aqueous medium has been examined out of resorcinol-capped silver nanoparticle assemblies. The UV-vis spectroscopy during the particle evolution has been studied in detail. From the high-resolution TEM (HRTEM) image and XRD pattern it was confirmed that the particles are made of pure silver only. The capping action of resorcinol has been authenticated from the FTIR spectra. UV-vis spectroscopy and TEM images reveal that the temperature, effect of vibrational energy, heat shock, and time-dependent particle evolution have unique bearing on the stability and surface properties of the clusters. The concentrations of silver nitrate, resorcinol, and NaOH have important influence on the particle evolution and its size. TEM images incite us to examine the aggregates to capitulate surface-enhanced Raman scattering (SERS) to the single molecular level using crystal violet (CV) and cresyl fast violet (CFV) as molecular probes. The SERS intensity of CV increases with increasing the size of the silver aggregate.