Cytosporins F–K,new epoxyquinols from the endophytic fungus Pestalotiopsis theae

Chemical investigation of an endophytic fungus, Pestalotiopsis theae, isolated from the leaves of Turraeanthus longipes (Meliaceae) collected in Cameroon, resulted in the isolation of six new epoxyquinols, cytosporins F–K (2–7), together with the known cytosporin D (1). The structures of the new compounds were unambiguously determined by analysis of the 1D, 2D NMR, and HRMS spectra. Cytosporins G–K (3–7) are the first cytosporins with a hydroxyl substituted C₇ side chain, while cytosporins F–I (2–5) contain a 13-acetoxyl group that was not reported previously. A plausible biosynthetic pathway for the cytosporin derivatives is proposed.     

1,3‐Dipolar Cycloadditions of Aldehydes or Imines with Carbonyl Ylides Generated from Epoxides: Classical Heating and Microwave Irradiation

Abstract

Cycloadditions of aldehydes with carbonyl ylides to give dioxolanes have been carried out without solvent under microwave irradiation. The reactions proceeded in similar yields and stereoselectivities, but in shorter reaction times, than those obtained in toluene at reflux using an oil bath. Cycloadditions conducted between imines and carbonyl ylides using the same protocol were less efficient because the oxazolidines formed proved unstable under the reaction conditions.     

Sugar recovery of enzymatic hydrolysed oil palm empty fruit bunch fiber by chemical pretreatment

An investigation was conducted to study the effect of solvent composition and temperature on the efficiency of pretreatment prior to enzymatic hydrolysis. The aim was to improve the sugar recovery of oil palm empty fruit bunch fiber (EFBF) through enzymatic hydrolysis. Two types of pretreatments, namely, acidified-glycerol (AC-g) pretreatment and alkaline-glycerol (AL-g) pretreatment were conducted. The study proved that AL-g pretreatment promoted higher delignification and enzymatic hydrolyzed sugar yield compared to AC-g pretreatment. Total sugar recovery of 81.44 and 96.55 % was achieved from AL-g pretreatment at 80 and 120 °C respectively, following the enzymatic hydrolysis. However, downstream industrial processes, involving enzyme treatment along the processing line have the preference of acidic condition. Thus, AC-g pretreatment was favorable. Approximately 51.74 % total sugar had been recovered successfully from enzymatic hydrolysis of EFBF after 3 h of pretreatment by using solvent comprising of 50 % acetic acid and 80 % aqueous glycerol at a ratio of 97:3 at 120 °C.     

Biphenyl esters and biflavonoids from the fruits of <Emphasis Type="Italic">Schinus terebenthefolus</Emphasis>

Two new biphenyl esters and three biflavonoids were isolated from the aqueous methanol extract of the fruits of Schinus terebenthefolus. The spectral data of tetrahydrorobustaflavone have been recorded and assigned for the first time. Characterization of the structures was achieved by various spectroscopic methods.Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 369–371, September–October, 2004.     

Convergence Rates to Equilibrium for Neutron Chain Fissions

We study a class of nonlinear equations arising in the stochastic theory of neutron transport. After proving existence and uniqueness of the solution, we consider the large-time behaviour of the solution and give explicit rates of convergence of the solution towards the asymptotic state.     

Simplification d’idéaux fractionnaires

Riassunto SianoI, J, N eL degli ideali frazionari di un dominioA. Mostriamo che se dueA-moduli moltiplicativi (I ⊕J, 〈,〉) e (L ⊕N, 〈,〉) sono isometrici suA alloraI è isomorfo aL (rispettivamenteJ≈N) o aN (rispettivamenteJ≈L); se ne deduce un criterio che permette di sapere se dueA-moduli quadratici, isotropici di rango 2, sono isometrici o no su un anello di Prüfer.

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Summary LetI, J, L andN be fractional ideals of a domainA. We prove that if two ?Multiplicative modules? (I⊕J, 〈,〉) and (L⊕N, 〈,〉) are isometric, thenI is isomorphic toL (respectivelyJ is isomorphic toN) or toN (respectively toL). As a consequence, we can know if two isotropic quadratic spaces of rank 2 are isometric on a Prüfer domain.

     

Electro‐Optical Properties of Polymer‐Dispersed Liquid Crystals

This paper deals with the electro‐optic (EO) properties of polymer‐dispersed liquid crystals (PDLCs). Several systems are considered to analyze the effects of preparation conditions and film characteristics on the EO response functions. Particular emphasis is put on systems based on mixtures of the commercial compound ASX‐95, the difunctional acrylate tripropylene diacrylate and the eutectic mixture of low‐molecular‐weight liquid crystals E7. Other systems are considered to assess the influence of monomer functionality on EO properties using for example the trifunctional glycerylpropoxytriacrylate. Various modes of preparing PDLCs are considered based on the mechanism of polymerization‐induced phase separation using either electron‐beam (EB) or UV radiation curing processes. The dose is changed in both techniques to improve film strength and determine which method leads to the best samples in terms of EO response functions. Other important parameters, such as film thickness, composition and applied voltage, are also considered to evaluate the impact on these functions. The article focuses on a comparison of EO performances of films elaborated by exposure to EB and UV radiations. Under similar conditions, one definitively finds a net superiority of the former technique. In addition this technique does not require any photoinitiator and leads to a higher conversion of the monomeric compounds, i.e. higher mechanical strength and less severe aging conditions.