Kinetics and thermoluminescence glow curve study of Ba2MgSi2O7:Eu3+, Dy3+

This paper reports thermoluminescence glow curves of Eu³⁺, Dy³⁺-doped Ba₂MgSi₂O₇ phosphor for different UV exposure times. Kinetic data were evaluated by the peak-shape method. The glow curves shift toward higher intensity with increasing exposure time to UV at 365 nm. When the heating rate was 5 °C s^?1, peaks were observed at 101.76, 109.69, 102.67, and 104.05 °C, respectively, after UV exposure for 5, 10, 15, and 20 min. The glow peaks are indicative of second-order kinetics. Different kinetic data, i.e. trap depth, order of kinetics, activation energy, and frequency factor were also calculated. To evaluate the persistence characteristics of the luminescence of the phosphor, the lifetime of the charge in the trap was calculated; it was 348, 660, 368, and 428 s for UV exposure of 5, 10, 15, and 20 min, which indicates the luminescence of the phosphor is persistent.     

Stretching and collapse of neutral polymer layers under association with ionic surfactants

We provide experimental evidence for stretching and collapse of neutral polymer layers, already adsorbed at an oil-in-water interface, due to its interaction with surfactants. Upon stretching, the first interaction length (2L(0)) follows a power law dependence on surfactant concentration ( proportional, variant C(x)(s), where x approximately 0.5 for cationic surfactants) and collapses in the presence of salt, as a relatively weak power law (C(-y)(s), where y=0.17), in good agreement with brush length decay for polyelectrolyte brushes.     

Diffusion Kinetics of Vitamin B12 from Alginate and Poly(vinyl acetate) Based Gel Scaffolds for Targeted Drug Delivery

Abstract

The research described here probed the thermodynamics and kinetics of Vitamin B₁₂ release from two types of polymeric gel scaffolds for targeted drug delivery applications. The polymeric gel scaffolds were successfully prepared from sodium alginate and polyvinyl acetate (PVA) using crosslinking and casting mechanisms, respectively. Vitamin B₁₂ was effectively blended into the polymeric gel scaffolds during their synthesis processes. The release of Vitamin B₁₂ from the polymeric gel scaffolds was characterized by immersing the scaffolds in a brine solution at various temperatures (25?°C, 32?°C and 37?°C) and, simultaneously, the transient concentrations were measured using a UV visible spectrophotometer. The sodium alginate gel scaffolds exhibited a more rapid release of Vitamin B₁₂ as compared to the PVA gel scaffolds. The Vitamin B₁₂ release kinetics from the alginate and PVA scaffolds were characterized by fitting the experimental data with various diffusion kinetic models. The Vitamin B₁₂ release from the alginate gel scaffolds followed the Peppas-Sahlin model, whereas releases from the PVA gel scaffolds were fitted to the Hopfenberg model. The diffusion coefficients for the alginate scaffolds with respect to the three temperatures were found to be 15.72?m²/s, 17.17?m²/s and 18.58?m²/s respectively whereas the diffusion coefficients for the PVA scaffolds with respect to the three temperatures were found to be 0.23?m²/s, 0.29?m²/s and 0.32?m²/s respectively. The activation energies (E_a) for the two types of polymeric scaffolds were calculated using the Stannett equation and found to be 10.38?kJ.mol^?1 and 20.47?kJ.mol^?1 for the alginate and PVA scaffolds, respectively, for all three temperatures.     

Luminescence studies on europium- and dysprosium-doped di-strontium magnesium silicate phosphor

Research on Chemical Intermediates - Europium- and dysprosium-doped strontium magnesium silicate powder with different concentration ratios of dysprosium were synthesized using solid-state...     

Synthesis,Characterization and Anti-inflammatory Activity of 5-{[((5-Substituted-aryl)-1,3,4-thiadiazol-2-yl)thio]-n-alkyl}-1,3,4-oxadiazole-2-thiol

A series of potent and less toxic, 5‐{[((5‐substituted aryl)‐1,3,4‐thiadiazol‐2‐yl) thio]‐n‐alkyl}‐1,3,4‐oxadiazole‐2‐thiol was synthesized. Each compound was evaluated for anti‐inflammatory activity by carrageenan‐induced rat paw oedema method. Compounds PS1 , PS4 , PS9 , and PS12 showed comparatively potent anti‐inflammatory activity as compared to control as well as other test compounds. These potent compounds were also tested for acute ulcerogenic activity. Results of both studies were found statistically significant.     

Synthesis and determination of the absolute configuration of fugomycin and desoxyfugomycin: CD spectroscopy and fungicidal activity of butenolides

The dibromoalkenes (S)-3 and (R)- and (S)-4 are intermediates in the syntheses of the naturally occurring fungicidal butenolides fugomycin (1) and desoxyfugomycin (2), respectively. The stereoselective bromine-lithium exchange that leads to the carbenoid 12 and the vinyllithium reagent 17 a on the one hand, and palladium-catalyzed coupling reactions of the dibromoalkene 3 and the bromolactone 22 on the other are key steps en route to the butenolides 1 and 2. The chiral building blocks (S)-3, (R)-4, and (S)-4 are readily available from (R)-isopropylideneglyceraldehyde 5, isobutyl (R)-lactate 6 a, and ethyl (S)-lactate 6 b, respectively. The synthetic procedure adopted here permits the absolute configuration of the natural products fugomycin (1) and desoxyfugomycin (2) to be assigned by comparison of their chiroptical properties with those of the synthetic products. The CD spectra of the bromolactone 22, calculated by two different density functional methods (TDDFT, DFT/MRCI), are found to be in good agreement with the measured spectra. On the basis of these calculations, the two CD bands observed could be assigned to n-pi* and pi-pi* transitions, respectively. Fugomycin (1) and the synthetic butenolide 20 displayed high fungicidal activity against botrytis in greenhouse experiments, whereas the saturated lactone 21 was practically inactive.     

Phytochemical composition,antioxidant activity and HPLC profiles of Swertia species from Western Ghats

Swertia chirayita is one of the potential medicinal plants of the family Gentianaceae in traditional medicine. Due to its high demand and scarcity, trade of chirayita is affected by adulterants. Swertia species from Western Ghats were compared with S. chirayita for phytochemical characterisation and antioxidant activities by using different extracts. This study revealed that acetone is the best extraction solvent of phenolic and flavonoid compounds with antioxidant properties as compared with other extracts. S. chirayita showed better antioxidant activity than other species with highest content of phenolics and flavonoids. Among the species from Western Ghats, Swertia minor has better antioxidant properties with higher content of phenolics and flavonoids when compared with S. chirayita. Gallic acid was detected in all species under study by using HPLC analysis. The Swertia species under study showed similar phytochemical properties and antioxidant potential and hence their use as substitute to S. chirayita needs to be further investigated.     

Studies on the persistent luminescence of Eu2+ and Dy3+-doped SrAl2O4 phosphors: a review

This review includes research papers on different methods of preparation of Eu²⁺ and Dy³⁺-doped SrAl₂O₄ phosphors and papers reporting luminescence studies of the materials. The methods of preparation were compared and it was concluded that solid state reaction is the best method. Papers on characterization of these phosphors by X-ray diffraction and scanning electron microscopy are also discussed. The review ends with a few important conclusions.     

Synthesis and the magnetic characterization of iridium–cobalt substituted calcium hexaferrites

M-type hexagonal ferrite powder with partial substitution lr⁴⁺+Co²⁺ has been synthesized by chemical-coprecipitation technique. The saturation magnetization M_s decreases linearly from 69.8 to 40.3 emu/g with increasing doping content from 0.5 to 1. The Coerecivity sharply drops for x=0.5, which can be explained by the decrease of the anisotropy constant K₁ Curie temperature T_c decreases linearly with increasing ‘x’. Crystallographic studies were explained on the cation distribution consistent with Gorter spin model of parallel alignment.