Etude d'un schema de synthese peptidique intramoleculaire a l'aide de derives du phosphore tetraedrique

A new scheme of repetitive and controlled peptide synthesis offers two advantages compared to the usual methods of synthesis : two steps only are used for the prolongation of a peptide chain with an aminoacid residue and the risk of racemisation is minimized. The two postulated steps are verified particularly by the rearrangement, in an alkaline alcoholic medium, of phosphordiamides 1 incorporating one amino-acid residue, leading to the formation of the peptide derivatives 6 and 8. The severe limitations of this method are discussed.     

Photolysis of Phosphoniums and Phosphoranes Azides

Abstract

First evidence for a Curtius type rearrangement involving a pentacoordinated atom and charged species are described     

CATALYSE INTRAMOLECULAIRE DE L'AMINOLYSE DES HETEROCYCLES PHOSPHORES DERIVES DES α AMINOAMIDES. II: ETUDE DE LA CYCLISATION DES PHOSPHORDIAMIDES INCORPORANT UN RESIDU DE β AMINOACIDE,REACTIVITE VIS A VIS DE NUCLEOPHILES DES HETEROCYCLES FORMES

Abstract

Derivatives of β aminoacids in form of esters 1 or nitrile 4 (table I) undergo in an alcohol-ate/alcohol medium a rearrangement (Fig. 2), with formation of a β peptide link, resulting in the formation of esters 6 (table II). According to the experimental conditions the six membered ring heterocycles 5 are detected or isolated. They are also synthetized by cyclisation of acids 2 or hydrazide 3 (Fig. 5). While phosphorus easily reacts with alcohols and water, leading respectively to esters 6 and acids 9 (Fig. 7), it remains unaffected by amines. These results are discussed in term of mechanisms of the phosphorylation. The applications for β peptide synthesis and the participation of the p amide group in phosphorylation are limited.     

EPR Studies of Tl0.5Pb0.5Sr1.6Ba0.4CaCu2?xRuxO7?δ Superconductor

Bulk superconducting samples of type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ, (Tl, Pb)/Sr-1212, with 0.0 ≤ x ≤ 0.525 were prepared by the conventional one-step solid-state reaction technique. The prepared samples were investigated using X-ray powder diffraction, electrical resistivity and electron paramagnetic resonance (EPR) measurements. Enhancement of the phase formation, superconducting transition temperature T _c and hole carriers concentration P was observed up to x = 0.075. For x > 0.075, a reverse trend was observed. EPR spectra were measured at different temperatures (120–290 K) for all prepared samples. The number of spins N participating in the resonance and the paramagnetic susceptibility χ were calculated as a function of both Ru-content and temperature. N and χ increased as the Ru-content increased. A linear relationship between logN and 1/T was established, from which the activation energy E _a was calculated as a function of the Ru-content. The temperature dependence of χ was fitted according to Curie–Weiss type of magnetic behavior. Curie constant C, Curie temperature θ, the effective magnetic moment μ and the electronic specific heat γ were estimated as a function of the Ru-content.     

Effect of IR laser radiation on the structure and optical properties of PC-PBT/Pd polymer nanocomposite films

ABSTRACT

Bayfol (PC-PBT blend ?lm) is a class of polymeric solid-state nuclear track detector which has a lot of applications in several radiation detection ?elds. It is a bisphenol-A polycarbonate PC blended with polybutylene terephthalate PBT. Bayfol/Palladium (PC-PBT/Pd) nanocomposite films have been deposited using the molding technique. It is worth mentioning that this report is almost the first one dealing with the topic of the changes of physical properties of Bayfol/Pd nanocomposite due to laser exposure. Samples from PC-PBT/Pd (5?wt%) nanocomposite were exposed to IR-pulsed laser of 5-W power, capable of producing 2000 pulses per second with pulse duration of 200?ns at 904?nm. The laser fluences were in the range 2–25?J/cm². The resultant modi?cations in the exposed nanocomposite samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction (XRD), UV spectroscopy and color difference studies. The results indicate the proper dispersion of Pd nanoparticles in the PC-PBT matrix that causes a strong intermolecular interaction between Pd and PC-PBT, resulted in an increase in refractive index and the amorphous phase. Also, it is found that the laser exposure reduces the optical energy gap that could be attributed to the increase in structural disorder of the exposed PC-PBT/Pd nanocomposites due to crosslinking. Further, the color intensity ΔE, which is the color difference between the exposed samples and the non-exposed one, was increased with increasing the laser fluence, convoyed by a significant increase in the green and yellow color components.     

New light on methylthiolation reactions

A novel enzyme, named RimO for ribosomal modification (Anton et al., 2008) catalyzes the methylthiolation of aspartate 88 of the S12 ribosomal protein in Escherichia coli and shows a strong similarity with the iron-sulfur enzyme MiaB involved in the methylthiolation of tRNAs.     

昆虫信息素研究III: 拟蚜虫警戒素的研究

合成了一系列碳数为十五和十四的倍半萜类蚜虫警戒素,并进行了生物活性测定,从中筛选有效化合物.     

Intramolecular catalysis of aminolysis of phosphorus heterocycles incorporating an α‐aminoamide moiety. III. Synthesis of 2‐oxo or 2‐thioxo 1,3‐disulfonyl‐1,3,2‐diazaphospholidines and reactions with amines and alcohols

A series of 2‐oxo or 2‐thioxo 1,3‐disulfonyl‐1,3,2‐diazaphospholidines 4 was prepared by condensation of phosphonyl dichlorides 2 with bis‐N,N'‐sulfonylethylenediamines 1 in pyridine. Complete aminolysis or alcoholysis of heterocycles 4 took place with regeneration of sulfonyldiamines 1 . These reactions are very sensitive to steric hindrance, and hydrolysis is generally favoured over aminolysis. The results are discussed in terms of mechanisms of phosphorylation.     

羧甲基纤维素钠水凝胶的制备及其生物降解性研究

用羧甲基纤维素钠(CMC—Na)制得了含水量高达98％的水凝胶，考察了防腐剂、交联剂、无机态氮素、有机态氮素、碳水化合物的加入量以及环境中pH值等因素对生物降解性的影响。结果表明：制备条件不同，水凝胶的生物降解性不同；环境中一定量铵根离子的存在有利于水凝胶的生物降解；在pH=5．2的环境中纤维素酶活性最高，降解程度最大。