The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured
alkali halide crystals. When the F-centre electrons captured by moving dislocations are picked up by holes, deep traps and other compatible traps, then deformation
bleaching occurs. At the same time, radiative recombination of dislocation captured electrons with the holes gives rise to
the mechanoluminescence. Expressions are derived for the strain dependence of the density of colour centres in deformed crystals
and also for the number of colour centres bleached. So far as strain, temperature, density of colour centres, Ea and volume dependence are concerned, there exists a correlation between the deformation bleaching and ML in coloured alkali
halide crystals. From the strain dependence of the density of colour centres in deformed crystals, the value of coefficient
of deformation bleaching D is determined and it is found to be 1.93 and 2.00 for KCl and KBr crystals, respectively. The value of (D+χ) is determined from the strain dependence of the ML intensity and it is found to be 2.6 and 3.7 for KCl and KBr crystals,
respectively. This gives the value of coefficient of deformation generated compatible traps χ to be 0.67 and 1.7 for KCl and KBr crystals, respectively. 相似文献
Among the synthetic polymers of commercial potential, poly-butadiene is an important rubbery material and it encompasses the bulk elastomers in use. To the best of our knowledge, a complete normal coordinate analysis with full phonon dispersion curves for cis 1,4 polybutadiene (CPBD) have not been reported so far. In the present communication, we report a complete normal coordinate analysis with full dispersion curves, density-of-states and calculation of heat capacity. The normal coordinate analysis has been carried out using the Urey-Bradley force field and the Wilson's GF matrix method as modified by Higgs. A comparison has been made with trans 1,4 polybutadiene (TPBD). The prominent features of the dispersion curves like crossing over and regions of zero-slope away from the zone centre are discussed. To check the validity of the force field used and the assignments, normal mode calculations are also performed for unsaturated C-deuterated and fully deuterated CPBD. 相似文献
A metal‐free, regioselective synthesis of trisubstituted pyrroles has been developed through a formal [3+2] cycloaddition reaction between 2H‐azirines and nitroalkenes under visible light/photoredox‐catalyzed conditions. The reaction proceeds through 2H‐azaallenyl radical addition on β‐nitrostyrenes in a Michael fashion followed by a base‐mediated denitration reaction. The directive group influence of the nitro group controls the regiochemistry of the reaction. 相似文献
Bimodal polyethylenes comprising varying proportions of high‐ and low‐molecular‐weight fractions are synthesized in a single polymerization stage, via the co‐immobilization of a chromium and an iron catalyst on an MgCl2/AlEtn(OEt)3?n support. Changes observed in the viscoelastic response of the polymer melt with increasing content of the high‐molecular‐weight fraction indicate effective mixing in the bimodal blend. In flow, chains in the high‐molecular weight fraction tend to orient and stretch under shear. Due to the longer relaxation time of the high‐molecular‐weight component, X‐ray diffraction and scattering reveal that shear‐induced crystallization takes place at temperatures close to the equilibrium melting point of linear polyethylene. The so‐crystallized high‐molecular‐weight component suppresses the nucleation barrier for further crystallization, leading to the formation of a “shish‐kebab” polymer morphology.
Prodigiosin, a metabolite isolated from Serratia bacteria, is a potent anti-cancer agent. The goal of this research was to determine if prodigiosin could bind to G-quadruplex DNA. We found by using UV–vis spectroscopy that the G-quadruplex K+√d[TG4T]4, but not the single-stranded Li+√d[TG4T], increased the water solubility of prodigiosin. In addition, we found that prodigiosin's fluorescence was strongly enhanced in the presence of K+√d[TG4T]4, further evidence for quadruplex-ligand binding. Using 1H and 31P NMR experiments, we confirmed that prodigiosin binds at the 3′-end of K+√d[TG4T]4. Saturation transfer difference NMR experiments, done by irradiating the G5 H8 signal in K+√d[TG4T]4, indicated specific interactions between the G-quadruplex and prodigiosin's A and B rings. This study raises the possibility that G-quadruplex DNA may well be a target for the anti-cancer agent prodigiosin. 相似文献
Raman spectrum of 2,4-dichlorobenzonitrile (2,4-DCBN) in powder form has been recorded in the region 50-4000 cm(-1) on a Jasco K-500 Raman spectrophotometer using the 488.0 nm radiation from an argon laser. FTIR spectra in the region 200-4000 cm(-1) have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer. Using the observed Raman and IR frequencies, normal co-ordinate analysis has been carried out to support the vibrational analysis and to determine the planar and non-planar force fields. 相似文献
The kinetics of metal exchange between copper(II) and tetramethylenediaminetetraacetatonickel(II), [Ni(TMDTA)] has been studied
between pH 3.4 and 4.8 at an ionic strength of 1.25 M (NaClO4) and a temperature of 25.0 ± 0.1 °C. The reaction is first order in [Ni(TMDTA)]. The reaction order in [Cu2+] varies from first to zero and then back to first as [Cu2+] is increased. At low copper concentration, the first-order rate constant is pH independent and represents the attack of
copper on the nickel complex through a pathway in which TMDTA is partially uncoordinated before reaction with copper. Evidence
is presented for a stepwise dechelation mechanism followed by attack of copper to give a dinuclear intermediate. The zero-order
rate is pH dependent. At higher [Cu2+], the swing back to first order is due to the formation of a weak copper-tetramethylenediaminetetraacetatonickelate complex
which then converts to products through a dinuclear intermediate. A plausible mechanism, consistent with all the kinetic data,
is presented. 相似文献
A co-axial dual core resonant leaky optical fiber (DCRLF) is designed for inherent gain equalization of S-band erbium doped fiber amplifier (EDFA). Resonance tail of leakage loss of the fiber into the S-band region is utilized to flatten the gain. We have numerically studied the effect of various design parameters and their fabrication tolerances on gain flattening. We show 23.5 dB flat gain with ± 0.9 dB ripple over 30 nm bandwidth (1490–1520 nm) using 120 mW pump. The study should be useful in designing optical fiber amplifiers for optical communication system employing wavelength division multiplexing. 相似文献
The effects of multivalent metal ions (Cu(2+)/Zn(2+)/Al(3+)) on the aggregation of salmon calcitonin (sCT)--a therapeutic peptide used worldwide in the treatment of osteoporosis and Paget's disease--have been studied in vitro using NMR (both solution state and solid state), TEM, ThT-fluorescence, and FT-IR spectroscopy. Overall, the various results indicated that the metal-ions-induced conformational transitions in the peptide--mostly toward the β-sheet--facilitate the aggregation of sCT in solution. First, the solution NMR has been used to check the interaction between the peptide and the metal ions. Following this, the formation and characterization of calcitonin aggregates has been performed using TEM, solid state NMR, and FT-IR spectroscopy. The TEM and ThT-fluorescence results revealed that the sCT peptide incubated with Cu(2+) and Zn(2+) metal ions (in aqueous environment) forms globular aggregates, while that with Al(3+) ions forms fibrils. The solid state NMR and FT-IR studies revealed the presence of a substantial amount of β-sheet content in sCT aggregates (formed in the presence of these metal ions) compared to the monomeric sCT, indicating that the metal binding is concomitant with conformational changes. The present study becomes crucial while prescribing this drug peptide under physio-pathological conditions associated with an abnormal accumulation of metal ions (Cu(2+)/Zn(2+)/Al(3+)) in the body (i.e., abnormal metal ion homeostasis). 相似文献