Justification de la méthode fonctionnelle pour les courbes gauches

Sans résumé (1) Le contenu de cet article représente le thèse de Doctorat de l'auteur. Pendant sa préparation l'auteur a été boursier du Consiglio Nazionale delle Ricerche (I) et ensuite du Ministero della Pubblica Istruzione (I). Je remercie mes parents pour leur soutien constant.     

Reductive decyanation of pyridinecarbonitriles by titanium trichloride

Titanium(III) chloride promotes reductive decyanation of 4-CN- and 2-CN-pyridine. The role of complex forming agents is discussed.     

A rapid method to determine plasma homocysteine concentration and enrichment by gas chromatography/mass spectrometry

Homocysteine is an independent risk factor for cardio- and/or cerebrovascular diseases. Many methods are used to measure plasma homocysteine levels in physiological fluids. Current gas chromatographic/mass spectrometric (GC/MS) methods allow determination not only of plasma homocysteine concentration, but also of its turnover. However, they have some methodological limitations due to the reduction of disulfide bonds between homocysteine and other thiols or proteins often requiring the use of several very toxic compounds or multi-step procedures that are particularly time-consuming, and/or utilize expensive instruments. Herein is described a rapid and precise GS/MS method to determine homocysteine turnover from a relatively low volume of plasma (200 microL). First disulfide bonds were reduced by 2-mercaptoethanol, which allows the maintenance of the reduced status preventing the rebuilding of the disulfide bond. Then the sample was derivatized to form the bis-tert-butyldimethylsilyl derivative. A deuterated internal standard, DL-[3,3,3',3',4,4,4',4'-2H8]-homocystine, was employed to account for losses associated with each analytical step. To evaluate the 'in vivo' homocysteine metabolic turnover, [1-13C]-methionine was infused and the derived [1-13C]-homocysteine quantitated. So a standard curve of [1-13C]-homocysteine was prepared by the decomposition of the [1-13C] methionine. The ions at m/z 325 and 326 were monitored, corresponding to the unlabeled [12C]-homocysteine and to labeled [13C]-homocysteine, respectively. The ion at m/z 325 ([M-114)]+) probably resulted from the loss of one derivatizing group to regenerate a free amino group. The intra-assay coefficient of variation (CV-intra%) was consistently less than 1.06%, the inter-assay (CV-inter%) less than 1.05%. The method described here seems to be simpler, more rapid, and less toxic than those published so far. In particular, its main strength appears to be the degree of precision obtained. We suggest applying this method to the measurement of the 'in vivo' rate of production of homocysteine (by the plasma 13C-homocysteine enrichment) from its precursor (13C-methionine).     

Second-order MS-MA calculations for the triplet state of H2 in the van der Waals region

Second-order MS-MA calculations by the variation-perturbation method for the triplet state of H₂ show that in the van der Waals region induction including exchange is practically negligible and the depth and position of the potential minimum are determined by the competition between repulsive first-order exchange and attractive Coulomb dispersion. Accurate interaction energies are obtained in second order only if all non-expanded multipoles up to the dipole-octupole term are properly accounted for.     

GC-FID/MS method for the impurity profiling of synthetic d-allethrin

A GC/FID/MS method was developed for the identification and quantification of d-allethrin (DA) and its major impurities in commercial samples. Optimisation of the experimental conditions was carried out considering such important requirements as resolution, reproducibility, detection limits of 0.1% (m/m) for the impurities, and short analysis time. Under the optimised final conditions the method was validated for specificity, precision (CV% = 0.133 at 2.10 mg/mL and CV% = 0.035 at 3.00 mg/mL), linearity (0-3.00 microg injected), limits of detection (0.09 ng injected) and quantitation (0.28 ng injected), and robustness. The DA related impurities were identified by using a GC/MS method with ion trap mass detection and also by comparison with synthesised standards. The most abundant impurities were crysolactone, allethrolone, chrysanthemic acid, and chloro-derivatives of DA.     

Synthesis,NMR spectra and X‐ray data of chloro and dichloro derivatives of 3‐hydroxy‐2‐phenylquinolin‐4(1H)‐ones and their cytostatic activity

As known, some derivatives of quinolin‐4(1H)‐one possess interesting biological properties. The biological and cytostactic activity of 2‐substituted 3‐hydroxyquinolin‐4(1H)‐ones has not been reported yet. In this paper the synthesis of a series of chloro and dichloro 2‐phenyl‐3‐hydroxyquinolin‐4(1H)‐ones and their characterization by NMR spectra and X‐ray data is described. Their cytostatic properties have been evaluated and the results are reported.     

Assessment of systematic errors in measurement of vapor pressures by thermogravimetric analysis

The present study explores the application of the diffusion limited evaporation theory to the estimation of vapor pressure from TG experimental data. A simplified method was developed to calculate the apparent values of the vapor pressure of pure substances from TG data, based on isothermal TG runs with crucibles having different surface areas available for evaporation. Antoine parameters are estimated through a numerical procedure based on a non-linear least square algorithm. The procedure also evaluates the substance diffusivity in nitrogen. The methodology developed might be used for a preliminary screening of the vapor pressure of pure compounds, due to the limited amounts of sample that are necessary and to the limited time frame required for the experimental runs. However, the estimation of diffusivity and vapor pressures values by the TG technique is possible with limited accuracy. Possible sources of error were thoroughly investigated and discussed.     

The preparation and properties of some allyltin carboxylates:R3SnOOCR′ (R′ = CH3, CH2Cl), R2Sn(OOCR′)2 (R′ = CH2Cl,CHCl2) and [R2Sn(OOCR′)]2O (R′ = CH2Cl,CHCl2, CCl3)

Triallyl- and diallyltin carboxylates [(CH₂CHCH₂)₃SnOOCR′ with R′ = CH₃ and CH₂Cl, (CH₂CHCH₂)₂Sn(OOCR′)₂ with R′ = CH₂Cl and CHCl₂)] and tetraallyl-1,3-diacyloxydistannoxanes {[(CH₂CHCH₂)₂SnOOCR′]₂ with R′ = CH₂Cl,CHCl₂ and CCl₃}, have been prepared from the reaction of tetraallytin with carboxylic acids in methanol.