Treatment of cellulose yarns by a polysiloxane followed by a fast pyrolysis step gave carbon fibres exhibiting strong enhancement of their mechanical resistance. To account for the beneficial effect of the polysiloxane, an investigation of the pyrolysis mechanisms was performed on a model system based on cellobiose and a polysiloxane resin. A chemical interaction between cellobiose and the resin (e.g. grafting of siloxane fragments onto the cellobiose) was established by using various physicochemical analysis techniques: nuclear magnetic resonance (NMR), photoelectron spectrometry (XPS), electronic paramagnetic resonance (EPR), Flash pyrolysis–gas chromatography–mass spectrometry (FP/GC/MS) and IR.

From the perspective of the utilization of the wood waste from African timber industry in the field of wood/polymer composites, the reactivity of four tropical hardwood species from Gabon, Tesula gabonensis Pellegr (T. gabonensis), Holoptelea grandis Hutch (H. grandis), Aucoumea klaineana Pierre (A. klaineana Pierre) and Tieghemella africana Pierre (T. africana) towards succinic anhydride (SA) and 2-octen-1-yl succinic anhydride (OSA) was studied on the basis of their carbohydrate complex and lignin polymers structure and composition as well as on the basis of the capability of their wood cell walls to absorb the dimethylformamide (DMF) and pyridine (Py) solution. T. gabonensis, H. grandis and T. africana wood sawdust are more reactive with SA than A. klaineana. However, T. gabonensis is the most reactive with SA as well as with OSA. The better reactivity of T. gabonensis should be connected to the abundance of the reactive hydroxyl functions in its native lignin. Furthermore, T. gabonensis, H. grandis and T. africana are rich in long polysaccharide fibers; their cell walls displayed a strong capability for swelling after DMF/Py absorption than A. klaineana. The latter displays short polysaccharide fibers assumed to agglomerate within the cell walls, limiting like this the contribution of the polysaccharide chains located within A. klaineana cell walls on its chemical reactivity; protecting thereby its cellulose matrix from a decrystallization as pointed out by X-ray diffraction (XRD) analysis. The crystalline lattice of T. gabonensis, H. grandis and T. africana for which the cell walls are more accessible to DMF/Py exhibit the most important decrease of the crystallinity index (CrI) and the crystallite sizes (D002).

Abstract The time domain of 1H NMR spectroscopy allows straightforward editing of the T 2 relaxation profiles in maritime pine wood. A new method from the Carr-Purcell-Meiboom-Gill sequence is proposed to measure the amount and distribution of water in wood, as well as the location of major dissolved organic materials. A general calibration model giving reliable and precise identification of these parameters is described. The method presented for editing T 2 relaxation profiles (obtained by the Contin program) may be helpful in solving practical drying and gluing problems in the wood industry. It can be used for monitoring chemical modifications of wood fibers involved in the design of wood composite materials.

A new alkaloid of Aconitum karacolicum Rapcs, from the Ranunculaceae family, collected in Kirghizstan, was isolated from the roots of this plant, using a purification scheme based upon its in vitro antiproliferative properties against three human tumour cell lines in culture. Structural identification was performed using high resolution MS-MS mass spectrometry and (1)H, (13)C, 2D NOESY NMR spectroscopy analysis. This compound consists of a 14-benzoylaconine moiety substituted on C-8 by an azeloyl chain. It presents in vitro cytotoxicity with an IC(50) of about 10-20 microM, which warrants further investigation on its possible interest in cancer chemotherapy.

Abstract The chemical modification of maritime pine sapwood (Pinus pinaster) with alkoxysilanes was studied according to three different pathways: carbamoylation with 3-isocyanatopropyltriethoxysilane, etherification with 3-glycidoxypropyltrimethoxysilane and alcoholysis of n-propyltrimethoxysilane. Grafting was confirmed by weight percent gain calculations (WPG), infrared spectroscopy (FTIR) as well as 13C and 29Si NMR CP MAS analysis. Signals of the grafted groups in the different spectra were assigned and the reactivity of the trialkoxysilane moieties towards wood was discussed. Experiments with model wood blocks showed that the reactions investigated occurred within the wood cell walls. Grafted chemicals were found to be relatively stable with regard to water leaching but only slight dimensional stabilisation was noted after treatment.

SummaryThe low field1H NMR relaxometry technique has been shown to be effective in determining the qualitative and quantitative moisture content and the water state distribution in maritime pine wood (Pinus pinasterAit). Further investigations on extractive materials in resin-rich samples evinced the presence of oleoresin components, which may disturb adhesion on pine wood boards.

Novel stable organosilylboranes possessing dimesityl groups attached to boron were synthesised. They gave an addition reaction with terminal acetylenic hydrocarbons in the presence of a transition metal complex. Thus, (diphenylmethylsilyl)dimesitylborane and (diphenyl-tert-butylsilyl)dimesitylborane reacted in good yields with phenylacetylene and alk-1-ynes in the presence of Pd2(dba)3(etpo)2 as a catalyst. The structures of the products were determined by NMR spectroscopy using INEPT techniques coupled to computational simulation. Various heteronuclear coupling constants J13C−H and J29Si−H were determined for the first time in this series. The results showed that the dimesitylboryl group added to the terminal acetylenic carbon atom and the organosilyl group to the internal carbon atom, according to a regio- and stereoselective syn-addition.

The application of the refocused-decoupled INEPT pulse sequence in 13C-NMR spectroscopy allows, in conjonction with computer simulations, a straightforward editing of the spectra of a raw mixture of glycosidic compounds.

This paper reports application of the one-dimensional 13C NMR “extended” distortionless enhancement by polarization transfer (DEPT) editing method to the determination of hexopyranose ring 13C nuclei. Relative spatial arrangements of the vicinal protons in the local environment of a skeletal carbon atom are determined from the signs of intensity modulation profiles and connected with their specific positions in the ring. In combination with a computer simulation program, the “extended” DEPT sequence allows the straightforward and unambiguous assignment of the hexopyranose ring carbon atoms.

Rayon fibres were pyrolysed under inert gas flows up to 1200 degreesC. Changes in the mechanical properties of the fibres at various stages of the thermal treatment were studied and correlated with structural analyses of the char by CP/MAS C-13 NMR and DRIFT spectroscopies. The force/displacement curve of fibres pyrolysed at 500 degreesC is non-linear but reversible within the deformation, which is approximately 10% at ultimate failure. (C) 2001 Elsevier Science Ltd. All rights reserved.

The application of the refocused-decoupled INEPT pulse sequence in 31P NMR spectroscopy allows, in conjunction with computer simulations, a straightforward editing of the spectra. Experiments were performed on phosphite derivatives of selected mono- and disaccharide model compounds. Structural investigations point towards the existence of homonuclear 31P– 31P couplings through O— P coordination versus coupling through the ring chains, the origin of which is being attributed to donor– acceptor chelating interactions between phosphorus and oxygen atoms in spatially closely related dioxaphospholane rings. Copyright © 2000 John Wiley & Sons, Ltd.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The conformational dependence on temperature and concentration of methyl 3,3-bis(tributylstannyl)propionate compounds of the type (Bu3Sn)2CH−CHR−CO2Me (R = H, 1; R = CH2CHCH2, 2; R = CH2Ph, 3; R = CH2NMe2, 5) was studied by means of Karplus-type dihedral angle relations for 3J(119Sn−13C) couplings from 13C NMR spectra and 3J(119Sn−1H) couplings from 1H−119Sn correlation NMR experiments, assisted by 17O and 119Sn NMR spectroscopy. The results from these structural investigations point toward a dominant conformation in which a very weak tin−carbonyl oxygen Sn←OC−O interaction is possible.

The use of routine refocused-decoupled INEPT 29Si NMR spectroscopy, in the presence of the chiral lanthanide shift reagent Eu(tfc)3, allows convenient enantiomeric excess determination of chiral α-C-silylated amines and alcohols for the first time.

A new one-dimensional 13C NMR approach for the determination of methoxyl substituents configuration in O-methylated glycosides is presented. Assignments are based on structural investigations by non-refocused INEPT experiments associated with numerical methods.

The mechanism of competing double stannylation and double hydrostannation reactions of terminal alkynes in the presence of arylthiol has been investigated. The data reveal the radical character of the reactions, the importance of the [tributylstannane/arylthiol] system as radical initiator at ambient temperature and the occurrence of a polarity reversal catalysis process in the double hydrostannation pathway.

Two macrocyclic polyether isomers were obtained by radical cyclization of (E)-8-iodo-3,6-dioxaoctyl-3-ethoxycarbonylpropenoate and separated by liquid-solid chromatography over silica gel. They were characterized, for the first time, by two-dimensional NMR; notably, the HMBC experiment gave access to the assignment of the two isomers through coupling via the carbonyl oxygen belonging to the macroheterocycle. The determination of the (3)J(HH) coupling, associated with Monte Carlo simulation, gave information on the conformational space of these two isomers and showed that 85 conformers for one isomer and 29 conformers for the other were in equilibrium in the solution mixture. These results are discussed with regard to the complexing properties of these macrocyclic polyethers. (C) 1997 John Wiley & Sons, Ltd.

The influence of homonuclear coupling contributions in C-13 and Si-29 NMR refocused-decoupled 1D/2D INEPT experiments was graphically visualized by monitoring the computed variations of the theoretical signal intensities as a function of the refocused delay time Delta. The appearance and exploitation of a hitherto unknown characteristic 'geometrical imprint domain' closely Linked to the spatial environment around the heteroatom under investigation allow a straightforward editing of the spectra. (C) 1997 John Wiley & Sons, Ltd.

A rapid, convenient and portable computer simulation program based on the general INEPT equations is described. It allows an easy calculation of the spectra for any weakly coupled structure up to nine systems of spins-12 [ca 25 spins] and an optimization of the experimental polarization and refocusing time parameters.

Sn-115 and Sn-119 NMR parameters of diastereotopic tins in model gem-distannyl compounds of the type Sn(2)CHR are presented. The use of Sn-115 NMR INEPT experiments provides a useful simplification of spectral analysis, resulting in a complete elimination of higher-order homonuclear satellite patterns.