CONFORMATIONAL ANALYSIS OF 2-(DIPHENYLPHOSPHANYL)-N,N-DIMETHYL-1-BENZ AMIDE AND 2-(DIPHENYLPHOSPHANYL)-PHENYL-PYRROLIDIN-1-YL-METHANONE BY NMR SPECTROSCOPY

We have synthesized 2-(Diphenylphosphanyl)-N, N-dimethyl-1-benzamide (1) and 2-(Diphenylphosphanyl)- phenyl-pyrrolidin-1-yl-methanone (2), and examined their conformations on the basis of NMR spectral data. Conformational analysis of the compounds is useful in deducing the structure in which they are active as a catalyst. In the present NMR measurements, ¹H-X fg-JHMBC (field gradient J-Resolved Hetero-nuclear Multiple-Bond Correlation) spectroscopy was implemented as a tool for the determination of hetero-nuclear three bond, phosphorus and protons and carbon-protons coupling constants. By fitting a sine curve to the experimental data by the method of 3D J-resolved HMBC NMR measurements, accurate ⁿ J _HX coupling constants were obtained. From the coupling constants, the corresponding dihedral angles, H3-C2-C3-P, H12-C12-C11-P, H16-C16-C11-P, H18-C18-C17-P, and H22-C22-C17-P, of compounds (1) and (2) were determined. The optimized structures of the compounds were obtained by molecular orbital calculations in which the dihedral angles experimentally determined were used.     

Reactive Extrusion of Stereocomplexed Poly‐L,D‐lactides: Processing,Characterization, and Properties

This work reports a facile route to synthesize homochiral and stereocomplexed polylactide by reactive extrusion. The effect of the polymerization catalyst (combination of tin(II)octanoate and triphenylphosphine) before and after its deactivation is discussed. Poly‐L ‐lactide (PLLA) exhibits homochiral crystallinity and diblock poly‐L ,D ‐lactide (PDLLA) exhibits stereocomplex crystallinity. The presence of residual monomer leads to a plasticizing effect, reducing glass transition temperature (T_g). Changes of the tacticity (L ,D ‐tacticity) of the stereocomplex are due to the transesterification reactions between L and D units. Deactivation of the catalyst reduces transesterification reactions and preserves the polylactide stereocomplex upon heating.

     

Heparin Modulates the Mitogenic Activity of Fibroblast Growth Factor by Inducing Dimerization of its Receptor. A 3D View by Using NMR

In vitro mitogenesis assays have shown that sulfated glycosaminoglycans (GAGs; heparin and heparan sulfate) cause an enhancement of the mitogenic activity of fibroblast growth factors (FGFs). Herein, we report that the simultaneous presence of FGF and the GAG is not an essential requisite for this event to take place. Indeed, preincubation with heparin (just before FGF addition) of cells lacking heparan sulfate produced an enhancing effect equivalent to that observed when the GAG and the protein are simultaneously added. A first structural characterization of this effect by analytical ultracentrifugation of a soluble preparation of the heparin‐binding domain of fibroblast growth factor receptor 2 (FGFR2) and a low molecular weight (3 kDa) heparin showed that the GAG induces dimerization of FGFR2. To derive a high resolution structural picture of this molecular recognition process, the interactions of a soluble heparin‐binding domain of FGFR2 with two different homogeneous, synthetic, and mitogenically active sulfated GAGs were analyzed by NMR spectroscopy. These studies, assisted by docking protocols and molecular dynamics simulations, have demonstrated that the interactions of these GAGs with the soluble heparin‐binding domain of FGFR induces formation of an FGFR dimer; its architecture is equivalent to that in one of the two distinct crystallographic structures of FGFR in complex with both heparin and FGF1. This preformation of the FGFR dimer (with similar topology to that of the signaling complex) should favor incorporation of the FGF component to form the final assemblage of the signaling complex, without major entropy penalty. This cascade of events is probably at the heart of the observed activating effect of heparin in FGF‐driven mitogenesis.     

A Review of Thermo‐Oxidative Degradation of Food Lipids Studied by 1H NMR Spectroscopy: Influence of Degradative Conditions and Food Lipid Nature

This review summarizes present‐day knowledge provided by proton nuclear magnetic resonance (¹H NMR) concerning food lipid thermo‐oxidative degradation. The food lipids considered include edible oils and fats of animal and vegetable origin. The thermo‐oxidation processes of food lipids of very different composition, occurring at low, intermediate, or high temperatures, with different food lipid surfaces exposed to oxygen, are reviewed. Mention is made of the influence of both food lipid nature and degradative conditions on the thermo‐oxidation process. Interest is focused not only on the evolution of the compounds that degrade, but also on the intermediate or primary oxidation compounds formed, as well as on the secondary ones, from both qualitative and quantitative points of view. Very valuable qualitative and quantitative information is provided by ¹H NMR, which can be useful for metabolomic and lipidomic studies. The chemical shift assignments of spectral signals of protons of primary (hydroperoxides and hydroxides associated with conjugated dienes) and secondary, or further (aldehydes, epoxides, among which 9,10‐epoxy‐12‐octadecenoate [leukotoxin] can be cited, alcohols, ketones) oxidation compounds is summarized. It is worth noting the ability of ¹H NMR to detect toxic oxygenated α,β‐unsaturated aldehydes, like 4‐hydroperoxy‐, 4,5‐epoxy‐, and 4‐hydroxy‐2‐alkenals, which can be generated in the degradation of food lipids having omega‐3 and omega‐6 polyunsaturated groups in both biological systems and foodstuffs. They are considered as genotoxic and cytotoxic, and are potential causative agents of cancer, atherosclerosis, and Parkinson's and Alzheimer's diseases.     

Synthesis and Characterization of Hybrid Materials Consisting of n-octadecyltriethoxysilane by Using n-Hexadecylamine as Surfactant and Q(0) and T(0) Cross-Linkers

Novel hybrid xerogel materials were synthesized by a sol-gel procedure. n-octadecyltriethoxysilane was co-condensed with and without different cross-linkers using Q(0) and T(0) mono-functionalized organosilanes in the presence of n-hexadecylamine with different hydroxyl silica functional groups at the surface. These polymer networks have shown new properties, for example, a high degree of cross-linking and hydrolysis. Two different synthesis steps were carried out: simple self-assembly followed by sol-gel transition and precipitation of homogenous sols. Due to the lack of solubility of these materials, the compositions of the new materials were determined by infrared spectroscopy, (13)C and (29)Si CP/MAS NMR spectroscopy and scanning electron microscopy.     

Localization of Phenolics in Phloem Parenchyma Cells of Norway Spruce (Picea abies)

Norway spruce (Picea abies) bark contains specialized phloem parenchyma cells that swell and change their contents upon attack by the bark beetle Ips typographus and its microbial associate, the blue stain fungus Ceratocystis polonica. These cells exhibit bright autofluorescence after treatment with standard aldehyde fixatives, and so have been postulated to contain phenolic compounds. Laser microdissection of spruce bark sections combined with cryogenic NMR spectroscopy demonstrated significantly higher concentrations of the stilbene glucoside astringin in phloem parenchyma cells than in adjacent sieve cells. After infection by C. polonica, the flavonoid (+)‐catechin also appeared in phloem parenchyma cells and there was a decrease in astringin content compared to cells from uninfected trees. Analysis of whole‐bark extracts confirmed the results obtained from the cell extracts and revealed a significant increase in dimeric stilbene glucosides, both astringin and isorhapontin derivatives (piceasides A to H), in fungus‐infected versus uninfected bark that might explain the reduction in stilbene monomers. Phloem parenchyma cells thus appear to be a principal site of phenolic accumulation in spruce bark.     

Investigations of mechanical properties and chemical changes occurring during welding of thermally modified ash wood

Abstract

Heat treatment of wood appears as an ecological and environmentally friendly alternative in the field of wood treatment. Generally, thermal modification increase dimensional stability by reduces of hygroscopicity and water absorption but it makes it difficult to bonding in some application. During welding, changes in the morphological, chemical, and physical properties of the wood cell wall are observed due to the compression and high temperatures produced by welding. Also, the degradation of cell wall in the wood causes some mechanical properties are reduced. This modification appears without any effect on the linear welding of thermal-ash wood. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) were used for evaluation of properties of wood–welding systems and their interactions. The mass spectrometry (MS) analysis was used to identifying the organic degradation products emitted during welding of thermo-ash. The results of experiments show that the use of friction welding for the bonding of thermal ash wood in dry conditions was possible, and we had good results. The best combination was with a welding time of 3.5?s devised to 0.5?s and 3?s and welding pressure 2.5 and 4?MPa, respectively. The result obtained is comparable to the result obtained with EPI adhesives. Welding time greater than 3.5?MPa negatively affects the welding quality and gives low the mechanical strength.