Polymeric absorbent for water sorption based on chemically crosslinked poly (acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt) hydrogels

Summary Swelling equilibrium of polyelectrolyte copolymer gels containing of acrylamide (AAm) and 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS) have been studied as a function of copolymer composition. AAm/AMPS hydrogels were prepared by free radical solution polymerization in aqueous solution of AAm with AMPS as anionic comonomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and trimethylolpropane triacrylate (TMPTA). Swelling experiments were performed in water at 25 °C, gravimetrically. The influence of AMPS content in hydrogels was examined. Swelling of AAm/AMPS hydrogels was increased up to 1018% (for containing 2% AMPS and crosslinked by EGDMA) 15246% (for containing 8% AMPS and crosslinked by TMPTA), while AAm hydrogels swelled up to 804% (crosslinked by TMPTA)–770% (crosslinked by EGDMA). The values of equilibrium water content of the hydrogels are 0.8851–0.9935. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non-Fickian in character.     

Single amino acid substitutions can further increase the stability of a thermophilic L-lactate dehydrogenase

Lactate dehydrogenases are of considerable interest as stereospecificcatalysts in the chemical preparation of enantiomerically pure-hydroxyacid synthons. For such applications in synthetic organicchemistry it would be desirable to have enzymes which tolerateelevated temperatures for prolonged reaction times, to increaseproductivity and to extend then applicability to poor substrates.Here, two examples are reported of significant thermostabilizations,induced by sitedirected mutagenesis, of an already thermostableprotein, the L-lactate dehydrogenase (EC 1.1.1.27 [EC] , 35 kDa permonomer subunit) from Bacillus stearothermophilus. Thermal inactivationof this enzyme is accompanied by irreversible unfolding of thenative protein structure. The replacement of Argl71 by Tyr stabilizesthe enzyme against thermal inactivation and unfolding. Thisstabilizing effect appears to be based on improved interactionsbetween the subunits in the core of the active dimeric or tetramericforms of the enzyme. The thermal stability of L-lactate dehydrogenasevariants with an active site Arg residue, either in the 171(wild-type) or in the 102 position, is further increased bysulfate ions. The two stabilizing effects are additive, as foundfor the Argl71Tyr/ Gln1O2Arg double mutant, for which the stabilityof the protein in 100 mM sulfate solution reaches that of L-lactatedehydrogenases from extreme thermophiles. All mutant proteinsretain significant catalytic activity, both in the presenceand absence of stnhilfoing salts, and are viable catalysts inpreparative scale reactions.     

Transport of Dissolved Si from Soil to River: A Conceptual Mechanistic Model

This paper reviews the processes which determine the concentrations of dissolved silicon (DSi) in soil water and proposes a conceptual mechanistic model for understanding the transport of Si through soils to rivers. The net DSi present in natural waters originates from the dissolution of mineral and amorphous Si sources in the soil, as well as precipitation processes. Important controlling factors are soil composition (mineralogy and saturated porosity) and soil water chemistry (pH, concentrations of organic acids, CO₂ and electrolytes). Together with production, polymerization and adsorption equations they constitute a mechanistic framework determining DSi concentrations. We discuss how key controls differ across soil horizons and how this can influence the DSi transport. A typical podzol soil profile in a temperate climate is used as an example, but the proposed model is transferrable to other soil types. Additionally, the impact of external forcing factors such as seasonal climatic variations and land use is evaluated. This blueprint for an integrated model is a first step to mechanistic modelling of Si transport processes in soils. Future implementation with numerical methods should validate the model with field measurements.     

Mechanisms of Solution Reactions of Cyclo-Penta[cd]Pyrene Oxide and Acenaphthylene Oxide

Rates and products of the acid-catalyzed and spontaneous reactions of cyclopenta[cd]pyrene oxide (2) and acenaphthalene oxide (3) in 1:3 dioxane-water and water, respectively, have been determined. Both 2 and 3 undergo acid-catalyzed hydrolyses to yield cis diol as the major product, and undergo spontaneous reactions to yield predominantly ketone products. The mechanisms of these reactions are discussed.     

The influence of structure order on the kinetics of dehydroxylation of kaolinite

The structural order of kaolinite is an important factor that shows a substantial effect on the processes which take place during the thermal treatment of kaolin. The influence of structural order on the dehydroxylation process was investigated by simultaneous thermogravimetry and differential thermal analysis (TG-DTA). The thermal analysis was performed on the samples with gradually decreasing structural order prepared by milling procedure. The apparent activation energy of dehydroxylation process decreases with decreasing structural order according to the exponential function. The extrapolation of experimental data leads to the estimation of apparent activation energy of 76.6 kJ mol^?1 and of frequency factor of 0.12 × 10⁴ s^?1 related to completely disordered form of kaolinite, while the ordered form shows the apparent activation energy of 216.17 kJ mol^?1 and the frequency factor of 9.26 × 10⁴ s^?1. The relationships between features such as the infrared pattern of treated material, the degree of structural order and the apparent activation energy were established.     

The Role of Lipid Domains in Bacterial Cell Processes

Membranes are vital structures for cellular life forms. As thin, hydrophobic films, they provide a physical barrier separating the aqueous cytoplasm from the outside world or from the interiors of other cellular compartments. They maintain a selective permeability for the import and export of water-soluble compounds, enabling the living cell to maintain a stable chemical environment for biological processes. Cell membranes are primarily composed of two crucial substances, lipids and proteins. Bacterial membranes can sense environmental changes or communication signals from other cells and they support different cell processes, including cell division, differentiation, protein secretion and supplementary protein functions. The original fluid mosaic model of membrane structure has been recently revised because it has become apparent that domains of different lipid composition are present in both eukaryotic and prokaryotic cell membranes. In this review, we summarize different aspects of phospholipid domain formation in bacterial membranes, mainly in Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. We describe the role of these lipid domains in membrane dynamics and the localization of specific proteins and protein complexes in relation to the regulation of cellular function.     

The Effect of Ambient Conditions on the Burning Rate of Gel Fuel Droplets

An experimental study was conducted to determine the dependence of the burning rate coefficient of gel fuel droplets on the pressure at different ambient oxygen nitrogen mixtures. Experiments were conducted using a pressure chamber, in which the droplet was suspended and the combustion process was video‐photographed by a high‐speed digital video camera. The tests were conducted at pressures between 0.1–4 MPa at different ambient oxygen nitrogen compositions (air, 40 % O₂ – 60 % N₂, and 60 % O₂ – 40 % N₂). The fuel was a compound of 95 % kerosene and 5 % gellant. At sub‐critical pressure conditions, the burning rate coefficient was found to increase with increasing ambient oxygen mass fraction. At supercritical conditions, no dependence of the burning rate coefficient on the ambient mixture was found. The results indicate that the burning rate coefficient depends on the oxygen partial pressure, at least at low pressures.     

Substitution of Reduction Clearing Step by Ozone Treatment at Disperse Dyeing of Polyester

The effectiveness of ozone treatment for the afterclearing of disperse dyed poly (ethylene terephthalate) (PET) fibers has been examined. Two types of disperse dyed PET samples were selected among commercial mass production range of Akbaslar textile mill. The reduction clearing procedure applied during mass production was taken as the reference reduction clearing treatment; these reference samples were taken after dyeing and reduction clearing processes at the mill. Samples of disperse dyed PET were also taken before reduction clearing in order apply ozone treatment in the laboratory as the tested afterclearing method. Color and wash-fastness properties of the reduction cleared and ozone treated fabric samples were compared and reported. Results indicated acceptable color and wash-fastness results comparable to those of reduction cleared samples for ozone treated samples. The success of ozone treatment for the black dyed PET sample at 7.0% depth of shade was especially outstanding. Ozone treatment was applied in cold water without addition of any chemicals for very short treatment times when compared to conventional reduction clearing. Ozone treatment created substantial energy and chemical savings as well as lower environmental impact.     

Olfactory Responses of Banana Weevil Predators to Volatiles from Banana Pseudostem Tissue and Synthetic Pheromone

As a response to attack by herbivores, plants can emit a variety of volatile substances that attract natural enemies of these insect pests. Predators of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) such as Dactylosternum abdominale (Coleoptera: Hydrophilidae) and Pheidole megacephala (Hymenoptera: Formicidae), are normally found in association with weevil-infested rotten pseudostems and harvested stumps. We investigated whether these predators are attracted to such environments in response to volatiles produced by the host plant, by the weevil, or by the weevil–plant complex. We evaluated predator responses towards volatiles from banana pseudostem tissue (synomones) and the synthetic banana weevil aggregation pheromone Cosmolure+ in a two-choice olfactometer. The beetle D. abdominale was attracted to fermenting banana pseudostem tissue and Cosmolure+, whereas the ant P. megacephala was attracted only to fermented pseudostem tissue. Both predators were attracted to banana pseudostem tissue that had been damaged by weevil larvae irrespective of weevil presence. Adding pheromone did not enhance predator response to volatiles from pseudostem tissue fed on by weevils. The numbers of both predators recovered with pseudostem traps in the field from banana mats with a pheromone trap were similar to those in pseudostem traps at different distance ranges from the pheromone. Our study shows that the generalist predators D. abdominale and P. megacephala use volatiles from fermented banana pseudostem tissue as the major chemical cue when searching for prey.     

Characteristics of Eutectic Compositions of Restructured Palm Oil Olein,Palm Kernel Oil and Their Mixtures

The physico-chemical characteristics of blends of palm olein and palm kernel oil which were further modified by chemical interesterification were studied. The slip melting points of non-interesterified blends were 19.7, 16.2, 14.5, 14.5 and 14.4 °C while those of the chemically interesterified blends were 17.7, 16.2, 19.8, 18.7 and 18.7 °C at 40, 30, 20, 10 and 0% palm kernel oil, respectively. Chemical interesterification lowered the solid fat content of the pure samples and blends across different temperatures except 90% palm olein at 15 °C where the solid fat content was higher than for non-interesterified samples. Palm kernel oil, palm olein and their blends before and after chemical interesterification, crystallized mainly in the β′ form. However, chemical interesterification modified the microstructure from a combination of fat particles with void regions of crystalline materials to fat particles without regions of void crystalline materials. Palm olein and palm kernel oil blends are mainly used for food preparation in Nigeria. This study has shown that there are no significant differences in the physical and chemical properties of non-chemically interesterified and chemically interesterified blends of palm olein and palm kernel oil. This implies that blending of palm olein and palm kernel oil without chemical interesterification can provide the fluidity desirable at ambient temperatures for food applications in the tropics.