Synthesis of 1,4-polyisoprene support of 2-chloroethylphosphonic acid (ethephon), a stimulating compound for the latex production by the Hevea brasiliensis

2-Chloroethylphosphonic acid (ethephon) is a well known stimulating product used to improve the latex production by the rubber tree (Hevea brasiliensis). Its chemical fixation in side position of 1,4-polyisoprene chains by weak chemical bond was considered in order to prepare new derivatives having prolonged stimulating activity. The synthesis was considered by using a chemical modification procedure according to a two-step process. Firstly, an epoxidized 1,4-polyisoprene intermediate was prepared by partial epoxidation of 1,4-polyisoprene. Secondly, the grafting of 2-chloroethylphosphonic acid was achieved by using the reactivity of the P-OH acidic function (or a P-OSiMe₃ derived from P-OH) of the reagent toward oxirane rings of epoxidized 1,4-polyisoprene. It was noted that grafting yields are improved when the reaction is carried out in bulk or in a non-polar solvent, and more especially in neutral conditions, that is by replacing ethephon with its trimethylsilylated derivatives [monotrimethylsilyl 2-chloroethylphosphonic acid or, more especially, di(trimethysilyl) 2-chloroethylphosphonate]. With this latter, the addition occurs by the intermediate of the P-OSiMe₃ bond, and the formation of 2-oxo-l,3,2-dioxaphospholane structures is highly favored.     

New strategies for the screening of a large number of immobilized dyes for the purification of enzymes. Application to the purification of enzymes from human haemolysate

A method is presented for screening immobilized dyes applicable to the purification of enzymes from haemolysate (haemolysate can be considered as a nearly pure solution of haemoglobin containing only marginal amounts of enzymes). Haemolysate is loaded on immobilized dye mini-columns until haemoglobin and the studied enzymes are found in the column eluate at the same concentrations as those present in the haemolysate. Such a frontal mode of screening allows those dyes to be selected which, displaying a higher affinity for the enzyme of interest than for haemoglobin, can be used to displace the unwanted protein (haemoglobin) from the column by the enzyme of interest (present at a much lower concentration).     

Taking advantage of luminescent lanthanide ions

Lanthanide ions possess fascinating optical properties and their discovery, first industrial uses and present high technological applications are largely governed by their interaction with light. Lighting devices (economical luminescent lamps, light emitting diodes), television and computer displays, optical fibres, optical amplifiers, lasers, as well as responsive luminescent stains for biomedical analysis, medical diagnosis, and cell imaging rely heavily on lanthanide ions. This critical review has been tailored for a broad audience of chemists, biochemists and materials scientists; the basics of lanthanide photophysics are highlighted together with the synthetic strategies used to insert these ions into mono- and polymetallic molecular edifices. Recent advances in NIR-emitting materials, including liquid crystals, and in the control of luminescent properties in polymetallic assemblies are also presented. (210 references.).     

Substitution effects enhancing the lasing ability of organic compounds

Simple calculations can help to predict which derivatives in a series of organic compounds are potential lasing material. In conjugated systems, a necessary condition for lasing is that there is not less than a specific minimum energy difference between a first excited allowed and a second excited forbidden transition. This order of transition and energy spacing can be obtained by judicious substitutions even in molecules that do not meet these conditions. Lasing action in the near UV has been observed in five new compounds.     

Regioselective electrophilic trifluoromethylation of indolines, oxindoles and indoles in superacid

Treatment of indolines and N-acylindoles with HF/SbF₅/CCl₄ yields 6-trifluoro derivatives (indole numbering) whereas indoles and oxindoles give the 5-trifluoro derivatives in good yield.     

A universal constant for the convergence of Newton's method and an application to the classical homotopy method

We give a new theorem concerning the convergence of Newton's method to compute an approximate zero of a system of equations. In this result, the constanth ₀=0.162434... appears, which plays a fundamental role in the localization of good initial points for the Newton iteration. We apply it to the determination of an appropriate discretization of the time interval in the classical homotopy method.     

Approximating the zeros of analytic functions by the exclusion algorithm

We give a practical version of the exclusion algorithm for localizing the zeros of an analytic function and in particular of a polynomial in a compact of . We extend the real exclusion algorithm to a Jordan curve and give a method which excludes discs without any zero. The result of this algorithm is a set of discs arbitrarily small which contains the zeros of the analytic function.     

Level crossing resonance due to chlorine nuclei in a free radical

Muonium adds to allyl chloride, CH₂=CHCH₂Cl, to form two radicals: MuCH₂CHCH₂Cl (main product) and CH₂CHMuCH₂Cl (minor product). Both radicals were fully characterized bySR andLCR. In the main product, the LCR lines due to the³⁵Cl and³⁷Cl nuclei were observed. Also, the temperature dependence of various hyperfine coupling constants (hfc) indicates that both Mu and Cl eclipse the unpaired electronp ₂-orbital in the minimum energy conformation. For the fragment-CH₂Cl, the presence of Mu in the-position is found to affect significantly the hfc of Cl in the-position; an internal rotational barrier of 12 kJ mol^–1 was estimated using a simpleV ₂ torsional potential.     

μSR Investigation of ethyl radicals adsorbed on silica

SR spectra of the ethyl radical adsorbed on porous silica were observed in transverse and in longitudinal magnetic fields in the temperature range 190–298 K. The line widths reflect the dynamic partial averaging of the hyperfine anisotropy due to reorientation and surface diffusion.     

Arsenite oxidation and arsenate determination by the molybdene blue method

Based on the similarity in properties of arsenate and phosphate, the colorimetric method using the molybdene blue complex was tested in order to determine low As(V) concentration in waters. The influence of complex formation time, daylight, temperature and competitive anions (silicate and sulphate) upon complex formation was determined. Optimal complex formation was reached in 1 h at 20±1 °C and was slightly favoured when developed in daylight. The formation rate declined with decreasing reaction temperature and no influence of any of the competitive anions tested (at concentrations usually found in natural waters of granitic areas) was noted. The detection limit of this method was 20 μg As(V) l⁻¹. This simple, fast and sensitive arsenic determination method is suitable for field analysis, especially for waters containing low levels of phosphate and organic matter. Through arsenate determination, this colorimetric method allowed the arsenite oxidation efficiency of five common industrial oxidants to be compared. H₂O₂ and MnO_2(s) were not considered as effective oxidants as a high excess was necessary to ensure As(III) oxidation. NaOCl and KMnO₄ were promising oxidants as they allowed complete arsenite oxidation with a small excess for NaOCl or even less than the electron stoichiometric ratio in the case of KMnO₄. FeCl₃ was the most effective oxidant among the reagents tested here.