Mechanically driven syntheses of carbides and silcides

Most metal carbides or slicides may be synthesized at room temperature, by ball milling mixtures of elemental powders for some tens of hours with a vibratory mill. Both stable and metastable compounds containing a high density of defects can be obtained. In general, phases stable at low temperatures are synthesized. This observation allows us to confirm recent estimations for the maximum temperature (600 K) attained in these powders during mechanical alloying. Exceptions are found for some MSi₂ suicides with M = titanium, iron or molybdenum for which both low- and high-temperature phases are formed.     

Link between Lipid Second Messengers and Osmotic Stress in Plants

Plants are subject to different types of stress, which consequently affect their growth and development. They have developed mechanisms for recognizing and processing an extracellular signal. Second messengers are transient molecules that modulate the physiological responses in plant cells under stress conditions. In this sense, it has been shown in various plant models that membrane lipids are substrates for the generation of second lipid messengers such as phosphoinositide, phosphatidic acid, sphingolipids, and lysophospholipids. In recent years, research on lipid second messengers has been moving toward using genetic and molecular approaches to reveal the molecular setting in which these molecules act in response to osmotic stress. In this sense, these studies have established that second messengers can transiently recruit target proteins to the membrane and, therefore, affect protein conformation, activity, and gene expression. This review summarizes recent advances in responses related to the link between lipid second messengers and osmotic stress in plant cells.     

Stereoselective Synthesis and Antiallodynic Activity of 3-Hydroxylated Paroxetines

The design, stereoselective synthesis and in vivo antiallodynic activity of four novel paroxetine analogs, named 3-hydroxy paroxetines (3HPXs), is reported herein. Among the novel synthesized compounds, three showed an antiallodynic effect, while (R,R)-3HPX was found to be 2.5 times more bioactive than (-)-paroxetine itself in neuropathic rats. Consequently, the current investigation not only discloses a novel promising analgesic drug, but also reveals that functionalization at the C3 position of paroxetine could be as effective as the common functionalization at either C4 or within the sesamol group.     

Volatile Emissions Triggered by Multiple Herbivore Damage: Beet Armyworm and Whitefly Feeding on Cotton Plants

Plants are commonly attacked by more than one species of herbivore, potentially causing the induction of multiple, and possibly competing, plant defense systems. In the present paper, we determined the interaction between feeding by the phloem feeder silverleaf whitefly (SWF), Bemisia tabaci Gennadius (B-biotype = B. argentifolii Bellows and Perring), and the leaf-chewing beet armyworm (BAW), Spodoptera exigua Hübner, with regard to the induction of volatile compounds from cotton plants. Compared to undamaged control plants, infestation with SWF did not induce volatile emissions or affect the number and density of pigment glands that store volatile and nonvolatile terpenoid compounds, whereas infestation by BAW strongly induced plant volatile emission. When challenged by the two insect herbivores simultaneously, volatile emission was significantly less than for plants infested with only BAW. Our results suggest that tritrophic level interactions between cotton, BAW, and natural enemies of BAW, that are known to be mediated by plant volatile emissions, may be perturbed by simultaneous infestation by SWF. Possible mechanisms by which the presence of whiteflies may attenuate volatile emissions from caterpillar-damaged cotton plants are discussed.     

A new combined computational and NMR-spectroscopical strategy for the identification of additional conformational constraints of the bound ligand in an aprotic solvent

This study documents the feasibility of switching to an aprotic medium in sugar receptor research. The solvent change offers additional insights into mechanistic details of receptor--carbohydrate ligand interactions. If a receptor retained binding capacity in an aprotic medium, solvent-exchangeable protons of the ligand would not undergo transfer and could act as additional sensors, thus improving the level of reliability in conformational analysis. To probe this possibility, we first focused on hevein, the smallest lectin found in nature. The NMR-spectroscopic measurements verified complexation, albeit with progressively reduced affinity by more than 1.5 orders of magnitude, in mixtures of up to 50% dimethyl sulfoxide (DMSO). Since hevein lacks the compact beta-strand arrangement of other sugar receptors, such a structural motif may confer enhanced resistance to solvent exchange. Two settings of solid-phase activity assays proved this assumption for three types of alpha- and/or beta-galactoside-binding proteins, that is, a human immunoglobulin G (IgG) subfraction, the mistletoe lectin, and a member of the galectin family of animal lectins. Computer-assisted calculations and NMR experiments also revealed no conspicuous impact of the solvent on the conformational properties of the tested ligands. To define all possible nuclear Overhauser effect (NOE) contacts in a certain conformation and to predict involvement of exchangeable protons, we established a new screening protocol applicable during a given molecular dynamics (MD) trajectory and calculated population densities of distinct contacts. Experimentally, transferred NOE (tr-NOE) experiments with IgG molecules and the disaccharide Gal'alpha1-3Galbeta1-R in DMSO as solvent disclosed that such an additional crosspeak, that is, Gal'OH2--GalOH4, was even detectable for the bound ligand under conditions in which spin diffusion effects are suppressed. Further measurements with the plant lectin and galectins confirmed line broadening of ligand signals and gave access to characteristic crosspeaks in the aprotic solvent and its mixtures with water. Our combined biochemical, computational, and NMR-spectroscopical strategy is expected to contribute notably to the precise elucidation of the geometry of ligands bound to compactly folded sugar receptors and of the role of water molecules in protein--ligand (carbohydrate) recognition, with relevance to areas beyond the glycosciences.     

Preparation and metal ion adsorption properties of the resin containing sulfonic acid groups

In this study, we explored a new ion exchange material synthesized by radical polymerization of styrene and 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid by using 2,2′‐azo‐isobutyronitrile (1 mol %) and divinylbenzene (0.5 mol %) as initiator and crosslinking reagents, respectively. The resin was obtained from a large excess (90%) of styrene in the feed. The yield was 72.3%. The resin was completely insoluble in water and characterized by elemental analysis, FTIR spectroscopy, scanning electron microscopy, and thermal analysis. The metal ion retention capability was investigated for Ag(I), Hg(II), Cd(II), Zn(II), Pb(II), and Cr(III). The effect of pH, time, and resin/metal ion mol ratio on the metal ion retention was studied. Selectivity of the resins from a mixture of metal ions and the maximum retention capacity at optimum pH were also determined. The recovery of the resin by using 1 and 4 M HClO₄ and HNO₃ demonstrated that it is possible to recover the resin above 80%. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1230–1235, 2003     

Catalytic combustion of trichloroethene over Ru/Al2O3: Reaction mechanism and kinetic study

The performance of 0.5% Ru/Al₂O₃ for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h⁻¹) in air was studied in this work. Experiments were carried out both at dry and wet (20,000 ppmV of H₂O) conditions. Catalytic performance was studied in terms of activity and selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃). Both the activity and the selectivity for total combustion are higher than other catalysts suggested in the literature for this process (especially Pd and Pt).The main organic by-products are CCl₄ and CHCl₃, whereas in all the other catalysts tested in the literature, tetrachloroethene is the main organic by-product. This fact suggests that the mechanism of the combustion reaction, involving a double-bond scission, is essentially specific for this catalyst.Kinetic data was fit to a pseudo-first order kinetic expression, providing fairly good fit.