Machine scheme of additive calculation of physicochemical properties of paraffin hydrocarbons

Summary A machine scheme has been developed for the additive calculation of the physicochemical properties of alkanes necessary for mass calculation of the constants and as a supplementation to the automatic chemical information retrieval system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya No. 11, pp. 1985–1988, November, 1964     

Synthesis of a versatile (S)-3-(hydroxymethyl)butane-1,2,4-triol building block and its application for the stereoselective synthesis of N-homoceramides

[structures: see text] A versatile (S)-3-(hydroxymethyl)butane-1,2,4-triol building block has been synthesized starting from D-isoascorbic acid, a common food preservative. The key transformation in this approach was the introduction of branching through a high yield and fully regioselective epoxide opening. This flexible synthon has been elaborated to a new class of (dihydro-)N-homo(phyto)ceramides.     

Optical spectra and localization of excitons in inhomogeneous helical cylindrical aggregates

We study the linear optical properties of helical cylindrical molecular aggregates accounting for the effects of static diagonal disorder. Absorption, linear dichroism, and circular dichroism spectra are presented, calculated using brute force numerical simulations and a modified version of the coherent potential approximation that accounts for finite size effects by using the appropriate open boundary conditions. Excellent agreement between both approaches is found. It is also shown that the inclusion of disorder results in a better agreement between calculated and measured spectra for the chlorosomes of green bacteria as compared to our previous report, where we restricted ourselves to homogeneous cylinders [Didraga, Klugkist, and Knoester, J. Phys. Chem. B 106, 11474 (2002)]. For the excitons that govern the optical response, we also investigate the disorder-induced localization properties. By analyzing an autocorrelation function of the exciton wave function, we find a strongly anisotropic localization behavior, closely following the properties of chiral wave functions which previously have been found for homogenoeus helical cylinders [Didraga and Knoester, J. Chem. Phys. 121, 946 (2004)]. It is shown that the circular dichroism spectrum may still show a strong dependence on the cylinder length, even when the exciton wave function is localized in a region small compared to the cylinder's size.     

An efficient reagent for the phosphorylation of deoxyribonucleosides, DNA oligonucleotides, and their thermolytic analogues

[reaction: see text] The phosphoramidite 11 was prepared in three steps from methyl 2-mercaptoacetate and demonstrated efficiency in the synthesis of conventional 5'-/3'-phosphate/thiophosphate monoester derivatives of 2'-deoxyribonucleosides and DNA oligonucleotides. Moreover, the use of 11 has enabled the preparation of the dinucleoside phosphorothioate analogue 26 in high yields (>95%) with minimal cleavage (<2%) of the thermolytic thiophosphate protecting group.     

Study of support effects on the reduction of Ni2+ ions in aqueous hydrazine

We have studied the effect of silica of quartz-type on the reducibility of nickel acetate in aqueous hydrazine (80 degrees C, pH = 10-12) and metal particle formation. The obtained materials were characterized by X-ray diffraction, transmission electron microscopy, and thermodesorption experiments. With nickel acetate alone, the reduction was partial (45%) and a metal film at the liquid-gas interface or a powdered metal precipitate with an average particle size of 120 nm was obtained. In the presence of silica as the surfactant, the reduction of nickel acetate was total and the nickel phase deposited as a film on the support with an average particle size of 25 nm. Supported nickel acetate was also totally reduced. Crystallites of a mean particle size of about 3 nm were obtained. Decreasing the nickel content or increasing the hydrazine/nickel ratio decreased the metal particle size. Whiskers were formed for low nickel loadings. Hydrogen thermal treatment of the reduced phase showed that the organic acetate fragment, belonging to the precursor salt, still remained strongly attached to the nickel phase. The amount of the retained organic matrix depended on the metal particle size. Surface defects are suggested as active sites, which enhanced nickel ion reduction in the presence of silica as the surfactant or support. Metal-support interactions and the nucleation/ growth rate were the main factors determining the size and morphology of the supported metal particles formed. The organic matrix covered the reduced nickel phase.     

Janus-type isopropyl groups revealed by 1H-NMR spectra of alkylpyridines with lanthanide shift reagents (LSR)

Two Isomeric pyridines were designed and prepared : 2-isopropyl-4,5,6-trimethyl-(3) and 2-isopropyl-3,4,6-trimethyl-pyridine (7); the latter, with a buttressed isopropyl, leads to much lower induced shifts by Eu(dpm)₃ and Pr(dpm)₃ than the former, owing to the conformation in which the Janus-type iPr group how to the LSR a t-butyl-like face.     

Gas chromatographic conditions for the linearity of the relationship between σT,t and tR in open tubes

The linearity of the relationship between σ_T,t² and (1 + k)² is studied with the view of using it for the evaluation of GC equipment. Based on appropriate analytical expressions it is concluded that in general this relationship is not linear and that practical procedures for column evaluation should be developed that take this non-linearity into account.     

Sur les fibrés instables de rang 2 sur ℙ3 (ℂ)

Sans résumé     

A refined study of the [111] magnetoelastic properties of terbium iron garnet: Relation to the cotton mouton birefringence

Accurate measurement of the ^{, 2} magnetostriction constant of a single crystal of TbIG has been performed from 90 K up to the Neel temperature. Both spontaneous and forced magnetostriction differ markedly from the one ion model predictions. Moreover, the forced magnetostriction modulus is much stronger below the compensation temperature than expected from extrapolating the high temperature variations. The spontaneous [111] linear magnetic birefringence and its field derivative exhibit thermal variations proportional respectively to those of the spontaneous and forced magnetostriction from 80 to 200 K.Loboratoire associé à l'Université Scientifique et Médicale de Grenoble.