Mechanisms of antioxidant action: Mechanochemical addition of thiol antioxidants to ABS

It is shown that thiol-containing antioxidants and stabilisers can be chemically reacted with ABS in high yields and in substantial concentrations under conditions of high temperature and high shear during processing. The resulting antioxidant concentrates are shown to be very effective thermal and photo-oxidative stabilisers for ABS when used as masterbatch additives for unstabilised ABS. Synergistic combinations of a bound antioxidant (BHBM (I(a))) and a bound uv stabiliser (EBHPT (II)) confer a high level of uv stability on ABS when incorporated into ABS. All the antioxidants show a high resistance to removal from the polymer by solvent extraction. The effect of the mechano-chemical process on the efficiency of adduct formation and on the effectiveness of the stabilisers so formed is discussed.     

Synthesis of New Furo[2,3‐d]pyrimidines and Pyrimido[4′,5′:4,5]furo[2,3‐d]pyrimidines

Sodium salt of 4‐hydroxy‐6‐methyl‐2‐phenylpyrimidine‐5‐carbonitrile ( 3 ) was subjected to alkylation with different a‐halo compounds, where the corresponding O‐alkylated products 4_a‐g were obtained. Ring closure of the O‐alkylated product 4_a‐c performed using sodium ethoxide in refluxing ethanol afforded furo[2,3‐d]pyrimidines 5_a‐c The latter compounds on reaction with a variety of reagents gave other new furopyrimidines as well as a number of furodipyrimidines.     

Crystallization kinetics and optical band gap studies of Se96In4 glass before and after slow neutron irradiation

Results of differential scanning calorimetry (DSC) under non-isothermal condition on Se₉₆In₄ semiconducting chalcogenide glass before and after slow neutron irradiation, for different exposure times, have been reported and discussed. Some of Sn atoms have been injected into the glass by nuclear transmutation processes and the binary glass is converted into a ternary. This is accompanied by an increase in the activation energy of crystallization, E_c, and in the glass transition temperature, T_g and a decrease in the glass transition activation energy, E_t, in the onset crystallization temperature, T_c and in the peak temperature of crystallization T_p. Optical band gap measurements have also been carried out, before and after irradiation, on identical thin pellets of Se₉₆In₄ glass. The energy band gap, E_g, is found to decrease upon irradiation. These effects have been attributed to a structural change upon doping and to irradiation induced defects.     

Three 2-(2-phenylethyl) chromones and two terpenes from agarwood

A new Chromone, 7,8-dimethoxy-2-[2-(3'-acetoxyphenyl)ethyl]chromone (1) was isolated from an acetone extract of the Cambodian agarwood along with two known chromones, 6-methoxy-2-(2-phenylethyl)chromone (2) and 6,7-dimethoxy-2-(2-phenylethyl)chromone (3). In addition, an abietane ester (4) and the sesquiterpene dehydrofukinone (5) were isolated from the agarwood oil of the same origin. Structural elucidation of all isolated compounds was made based on IR, 1H and 13C NMR spectroscopic data.     

Silver-doped silver vanadate glass composite electrolyte: structure and an investigation of electrical properties

Ionics - Structural and electrical properties of the ternary ionic–electronic conducting glass system xAgI–(1 − x)[0.67Ag2O–0.33V2O5], where x = 0.4,...     

Microemulsions of Potassium Oleate,Tween-20, Propylene Carbonate,and Ethylene Glycol as Drug Vehicles for Mefenamic Acid

Different microemulsions were prepared with and without mefenamic acid (MFA). The base microemulsion was mainly composed of distilled water; the aqueous phase, propylene carbonate; the oil phase, potassium oleate; the surfactant, and finally di-ethylene glycol; the cosurfactant. The effect of mixing ionic (potassium oleate) with nonionic (Tween-20) surfactant was investigated via constructing the phase diagrams of such systems. Changes in conductivity and viscosity of the freshly prepared microemulsion over time were monitored as an indication for the stability of the microemulsion. Measurements were carried out at room temperature, after a freeze-thaw cycle and also after storage for 3 days at 60°C, where the latter is treated as an accelerated test for the time-temperature effects on the stability of a microemulsion. It was found that a set of surfactants, instead of a single surfactant, and inclusion of cosurfactant resulted in a broader region where a stable microemulsion is predominant. At a mass ratio of 1:2 of potassium oleate to Tween-20, O/W microemulsions were found to have maximum stability among all examined systems, under the accelerated test, such that they have a minimum portion of combined surfactants and cosurfactant of 60 wt% and maximum of 80 wt%. With the aforementioned specifications, no phase separation and neither significant change in the conductivity nor in the viscosity was observed in any of the examined systems after subjecting them both to the accelerated and freeze-thaw cycle test, indicating that such systems were thermodynamically stable. Samples of micro emulsions passing previous tests were further subjected to an acidic medium by dispersing 1 g of MFA-containing microemulsion in 10 g HCl solution (pH 1) in a shaking water bath at 37°C, for a 6 hour period. The maximum solubility of MFA in a stable microemulsion was approximately 5 wt%, evaluated at room temperature.     

Study Kinetics of Thermal Decomposition and Electrochemical Oxidation by Using Nanocomposite Paste of Novel Poly(amide-ether)s Derived from Asymmetric Diamine

A new asymmetric diamine containing diarylimodazole pendant was synthesized from the nucleophilic substitution reaction of 1-fluoro-4-nitrobenzene and 2,4-dihydroxy benzaldehyde in the presence of K₂CO₃, followed by reaction with benzil and ammonium acetate for the preparation of imidazole ring. This novel diamine was used to prepare poly(amide-ether) (PAE) in reaction with different commercially available dicarboxylic acids via direct polycondensation using triphenyl phosphite and pyridine (Py) as catalyst. The PAEs were fully characterized and their properties such as inherent viscosity, solubility, optical, thermal and kinetics of thermal decomposition, and electrochemical oxidation were investigated. The polymers had inherent viscosity in the range of 0.47–0.65 dL/g and were noncrystalline with excellent solubility in various polar aprotic organic solvents. Their T_g values ranged from 200 to 355°C and 10% weight loss temperature above 450°C in nitrogen and left more than 70% residue at 650°C. The kinetic parameters of thermal degradation such as activation energy, entropy, enthalpy and Gibbs free energy of thermal decomposition have been evaluated using different equations. We also report electrochemical oxidation of the resulting polymers in aqueous solution by using cyclic voltammetry technique on the multi-walled carbon nanotube-modified glassy carbon electrode.     

Ultrasound assisted dehydrogenation of 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides

Dehydrogenation of various 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides (THPMs) to 2-oxo-1,2-dihydropyrimidine-5-carboxamides (DHPMs) using tetrabutylammonium peroxydisulfate (TBAPS) as an efficient oxidizing agent under thermal and sono-thermal conditions has been investigated. In contrast to the thermal reaction, a decrease of the amount of oxidant and an increase of the rate of reaction are observed by simultaneously applying heat and ultrasound. The nature of both C-4 and C-5 substituents on the heterocyclic ring influences the rate of reaction under both conditions. The proposed electron-transfer-induced dehydrogenation in this study is supported by conductometric studies.     

Improved efficacy of bio‐mineralization of human mesenchymal stem cells on modified PLLA nanofibers coated with bioactive materials via enhanced expression of integrin α2β1

Current therapeutic interventions in bone defects are mainly focused on finding the best bioactive materials for inducing bone regeneration via activating the related intracellular signaling pathways. Integrins are trans‐membrane receptors that facilitate cell‐extracellular matrix (ECM) interactions and activate signal transduction. To develop a suitable platform for supporting human bone marrow mesenchymal stem cells (hBM‐MSCs) differentiation into bone tissue, electrospun poly L‐lactide (PLLA) nanofiber scaffolds were coated with nano‐hydroxyapatite (PLLA/nHa group), gelatin nanoparticles (PLLA/Gel group), and nHa/Gel nanoparticles (PLLA/nHa/Gel group) and their impacts on cell proliferation, expression of osteoblastic biomarkers, and bone differentiation were examined and compared. MTT data showed that proliferation of hBM‐MSCs on PLLA/nHa/Gel scaffolds was significantly higher than other groups (P < .05). Alkaline phosphatase activity was also more increased in hBM‐MSCs cultured under osteogenic media on PLLA/nHa/Gel scaffolds compared to others. Gene expression evaluation confirmed up‐regulation of integrin α2β1 as well as the osteogenic genes BGLAP, COL1A1, and RUNX2. Following use of integrin α2β1 blocker antibody, the protein level of integrin α2β1 in cells seeded on PLLA/nHa/Gel scaffolds was decreased compared to control, which confirmed that most of the integrin receptors were bound to gelatin molecules on scaffolds and could activate the integrin α2β1/ERK axis. Collectively, PLLA/nHa/Gel scaffold is a suitable platform for hBM‐MSCs adhesion, proliferation, and osteogenic differentiation in less time via activating integrin α2β1/ERK axis, and thus it might be applicable in bone tissue engineering.     

Photo- and thermal oxidation of ABS: Correlation of loss of impact strength with degradation of the rubber component

The decay of the 1,4-polybutadiene absorbance (infra-red) was found to correlate with the decrease in tan δ at ?80°C during the photo- and thermal oxidation of ABS. Both parameters correlate with loss of impact resistance.