Defect related luminescence in Hg0.2Cd0.8Te nano- and micro-crystals grown by the solvothermal method

The photoluminescence (PL) properties of nano- and micro-crystalline Hg1-xCdxTe (x approximate to 0.8) grown by the solvothermal method have been studied over the temperature range 10-300 K. The emission spectra of the samples excited with 514.5 nm Ar+ laser consist of five prominent bands around 0.56, 0.60, 0.69, 0.78 and 0.92 eV. The entire PL band in this NIR region is attributed to the luminescence from defect centers. The features like temperature independent peak energy and quite sensitive PL intensity, which has a maximum around 50 K is illustrated by the configuration coordinate model. After 50 K, the luminescence shows a thermal quenching behavior that is usually exhibited by amorphous semiconductors, indicating that the defects are related to the compositional disorder. (C) 2010 Elsevier B.V. All rights reserved.

Mechanism of gel-to-crystallite conversion process in the synthesis of nanocrystalline multinary oxides

Description of gel-to-crystallite conversion process is made towards the synthesis of nanocrystalline titanates and aluminates. Thermodynamic and kinetic factors governing the conversion of a gel to meta-stable and stable nanocrystalline products(s) are discussed. Correlations between these factors and the preparative conditions employed for the syntheses of titanates and aluminates are arrived at.

Mechanism-based inhibition of CYP2C8 by gemfibrozil in humans : characterisation of time and dose relationships

Drug-drug interactions may cause serious, even fatal clinical consequences. Therefore, it is important to examine the interaction potential of new chemical entities early in drug development. Mechanism-based inhibition is a pharmacokinetic interaction type, which causes irreversible loss of enzyme activity and can therefore lead to unusually profound and long-lasting consequences. The in vitro in vivo extrapolation (IVIVE) of drug-drug interactions caused by mechanism-based inhibition is challenging. Consequently, many of these interactions have remained unrecognised for many years. The concomitant use of the fibrate-class lipid-lowering agent gemfibrozil increases the concentrations of some drugs and their effects markedly. Even fatal cases of rhabdomyolysis occurred in patients administering gemfibrozil and cerivastatin concomitantly. One of the main mechanisms behind this effect is the mechanism-based inhibition of the cytochrome P450 (CYP) 2C8 enzyme by a glucuronide metabolite of gemfibrozil leading to increased cerivastatin concentrations. Although the clinical use of gemfibrozil has clearly decreased during recent years, gemfibrozil is still needed in some special cases. To enable safe use of gemfibrozil concomitantly with other drugs, information concerning the time and dose relationships of CYP2C8 inhibition by gemfibrozil should be known. This work was carried out as four in vivo clinical drug-drug interaction studies to examine the time and dose relationships of the mechanism-based inhibitory effect of gemfibrozil on CYP2C8. The oral antidiabetic drug repaglinide was used as a probe drug for measuring CYP2C8 activity in healthy volunteers. In this work, mechanism-based inhibition of the CYP2C8 enzyme by gemfibrozil was found to occur rapidly in humans. The inhibitory effect developed to its maximum already when repaglinide was given 1-3 h after gemfibrozil intake. In addition, the inhibition was shown to abate slowly. A full recovery of CYP2C8 activity, as measured by repaglinide metabolism, was achieved 96 h after cessation of gemfibrozil treatment. The dose-dependency of the mechanism-based inhibition of CYP2C8 by gemfibrozil was shown for the first time in this work. CYP2C8 activity was halved by a single 30 mg dose of gemfibrozil or by twice daily administration of less than 30 mg of gemfibrozil. Furthermore, CYP2C8 activity was decreased over 90% by a single dose of 900 mg gemfibrozil or twice daily dosing of approximately 100 mg gemfibrozil. In addition, with the application of physiological models to the data obtained in the dose-dependency studies, the major role of mechanism-based inhibition of CYP2C8 in the interaction between gemfibrozil and repaglinide was confirmed. The results of this work enhance the proper use of gemfibrozil and the safety of patients. The information related to time-dependency of CYP2C8 inhibition by gemfibrozil may also give new insights in order to improve the IVIVE of the drug-drug interactions of new chemical entities. The information obtained by this work may be utilised also in the design of clinical drug-drug interaction studies in the future.

Eu2+ luminescence in MAl3BO7 aluminoborates (M=Ca, Sr, Ba)

Three new aluminoborates having the composition MAl3BO7, where M = Ca,Sr or Ba, have been prepared. X-ray diffraction data indicate that all the phases are monoclinic, with close structural similarity to the meta stable aluminate, SrAl4O7. These aluminoborates are good host lattices for Eu2+ luminescence. The emission spectra show multiple bands in the blue region, corresponding to two inequivalent sites in each case, with one of them having quantum efficiency greater-than or equivalent to 75%. In the case of SrAl3BO7:Eu2+, the d–f band emission dominates at 300 K whereas at 77 K both d–f band and f–f line emissions are observed. Efficient Eu2+→Mn2+ energy transfer is observed in MAl3BO7 leading to strong green emission of Mn2+in the tetrahedral sites.aluminoborates; europium

A Study on Effect of Wetting on Mechanism of Coalescence in a Model Coalescer

In order to depict the mechanism of coalescence in fibrous bed coalescers, a model coalescer was fabricated. Both water/oil and oil/water dispersions were run through this model coalescer to check for coalescence on PTFE and glass surfaces. The equilibrium contact angle and the dynamic contact angle of the dispersed drops were measured on these surfaces in the presence of the continuous phase. Coalescence was monitored using a microscope. Based on these observations a mechanism of coalescence in the model coalescer is proposed. Different modes of coalescence are correlated to the equilibrium contact angle and the dynamic contact angle. Deposition of dirt on the coalescing surface is observed to result in change of wettability, leading to redispersion of the already coalesced dispersed phase into larger droplets.