2′,5,6,7-tetramethoxyflavone and the structure of zapotin

2′,5,6,7-Tetramethoxyflavone, synthesized by two methods has been found to be different from zapotin.     

N-Silylation of amines and amino acid esters under neutral conditions employing TMS-Cl in the presence of zinc dust

An expedient synthetic approach to N-silylamines has been developed. The protocol, using TMS-Cl/zinc dust instead of BSA, is useful for the conversion of amines or amino acid esters to the corresponding silyl derivatives, followed by acylation with an acyl chloride or Fmoc-amino acid chloride to give the corresponding amide or peptide. This procedure, affording products in good to excellent yields, is also efficient for the coupling of sterically hindered amino acids like α,α-dialkylamino acids and NMe-amino acids. Further, the use of an equimolar quantity of organic base, such as Et₃N/pyridine, is circumvented.     

Thermal expansion of irradiated polyethylene from 10 to 340 K

The coefficient of thermal expansion of γ-irradiated polyethylene has been measured from 10 to 340 K by using the three-terminal capacitance technique. The samples are irradiated to 500 Mrad in steps of 100 Mrad in air at room temperature with γ-rays from a Co⁶⁰ source at a dose rate of 0.3 Mrad/h. The crystallinity of the sample is measured by x-ray diffraction. The crystallinity is found to decrease with radiation dose. The thermal expansion coefficient is found to be constant with radiation doses from 10 to 110 K and decreases with doses from 110 to 340 K. © Wiley & Sons, Inc.     

Thermal expansion of irradiated polytetrafluoroethylene

The thermal expansion coefficient of gamma-irradiated Polytetrafluoroethylene (PTFE) has been measured in the temperature range 80–340 K by using a three-terminal capacitance technique. The samples are irradiated in air at room temperature with gamma rays from a Co⁶⁰ source at a dose rate of 0.26 Mrad/h. The change in crystallinity is measured by an x-ray technique. The expansion coefficient is found to increase with radiation dose below 140 K owing to the predominant effect of degradation. Above 140 K, the expansion coefficient is found to decrease with radiation dose because of the enhanced crystallinity. The temperatures of the two first-order phase transitions are also found to shift to lower temperatures owing to degradation of PTFE.     

Diastereoselective alkylation reactions of 1-methylcyclohexa-2,5-diene-1-carboxylic acid

The deprotonation and alkylation of 1-methylcyclohexa-2,5-diene-1-carboxylic acid has been investigated under a range of conditions. In all cases, the formation of compounds 14 was found to be completely stereoselective, although compound 14c was formed as an impurity when alkyl iodides were used as electrophiles, and doubly-alkylated compounds 17 were formed in some cases when alkyl bromides were used.     

Second order elastic anomalies in barium titanate from orthorhombic to rhombohedral phase transition

The anomalies in second order elastic constants have been derived for barium titanate for the phase transition from orthorhombic to rhombohedral state. The equilibrium values of order parameter, strain variables and fluctuations in order parameter have been derived using stability conditions and Landau-Khalatnikov equations respectively. Expression for shift in specific heat is obtained. All the anomalies in second order elastic constants have been derived and relations among them reported. The numerical values of anomalies in the individual constants are calculated and their variation is represented graphically. Changes in elastic constants occur over a range of temperature of the order 10⁻²K.     

Solvent-free sonochemical kabachnic-fields reaction to synthesize some new α-aminophosphonates catalyzed by nano-BF3•SiO2

To obtain a rapid, efficient synthesis of some new α-aminophosphonates, ultrasonic irradiation has been applied to the reaction mixtures containing amine, aromatic or heteroaromatic aldehydes and triethyl phosphite. The Kabachnik-Fields reaction was performed by using nano-BF₃?SiO₂ as a recyclable catalyst under solvent free conditions. Key advantages of this procedure consist in the eco-friendly and highly efficient reaction conditions, high yields, an easy work-up procedure, short reaction times and solvent free conditions. All title compounds were characterized by spectral and elemental analysis. They were further screened for their in vitro antioxidant activity by the DPPH, O^2? and NO methods. The majority of the title compounds showed good antioxidant activity when compared with the standard antioxidants.