Effect of arabinose substitution on the material properties of arabinoxylan films

This study was undertaken to investigate the effect of arabinose content on film properties. The substrate used was a rye arabinoxylan that had an Ara/Xyl ratio of 0.52 and an average number molecular weight of 305 kDa. Oxalic acid was used to attempt selective removal of the arabinose substituents on the xylan main chain. The debranching of the polymer was coupled with a decrease in molecular weight. The effect of reaction conditions on the decrease in arabinose content and loss of molecular weight was investigated. Optimal conditions were selected using an experimental design. Treatment at lower temperature for longer period of times resulted in debranching with less degradation of the main chain. As the Ara/Xyl ratio was lowered, aggregates began to form in an interval of the Ara/Xyl ratio between 0.31 and 0.23 in a water solution. Precipitation occurred below an Ara/Xyl ratio of 0.1. Thus, removal of arabinose substituents results in a gradual association of unsubstituted chains. There is a linear correlation between arabinose substitution and the moisture content of arabinoxylan at 98% RH. A decrease in arabinose content resulted in the loss of a plasticizing effect, as determined by dynamic mechanical analysis, which is correlated to water binding capacity.     

Bacterial adsorption to smooth surfaces: Rate, extent, and spatial pattern

The influence of bulk-water bacterial cell concentration and specific growth rate history on bacterial adsorption rates to surfaces was investigated using response surface analysis. A pure culture of Pseudomonas sp. 224S was grown in a chemostat and pumped into a continuous flow reactor where the bacteria were exposed to clean, glass surfaces under turbulent flow conditions for a period of six hours. Adsorption rate decreased approximately linearly with increasing specific growth rate history. Glass surfaces became saturated with 224S at ca. 0.1% coverage and the resulting spatial pattern of the adsorbed cells deviated from random in the direction of uniformity.     

The influence of insecticide-pheromone substitution on the abundance and distributional pattern of soil oribatid mites

A comparative study has been made on the abundance and distributional pattern of soil oribatid mites in an Egyptian cotton field. Samples were collected from two pesticide-treated fields (profenofos, chlorofluazuron, fenvalerate) and a control plot where cotton bollflies and leaf-flies were caught using pheromone traps. Sampling was done monthly, from the period of early cultivation of the cotton until the crop was full grown. The scheme concerning the dominance classification was adopted. Aggregation of the dominant species was estimated in relation to insecticide effect. Rhysotritia ardua ardua appeared to be insecticide-loving species (insecticide-resistant species) and was not influenced either by the sort of insecticide or by its quantity. Multiple application of two insecticides has a significant negative effect on the abundance of Scheloribates laevigatus. Zygoribatula exarata and Xylobates capucinus were considered good bioindicators for pesticide-untreated field. It can be suggested that the substitution of insecticide with pheromone trap can produce a greater, more stabilized community and a high productive agroecosystem. Accordingly, our findings support the current tendency to replace chemical control of pests with pheromone traps which seem to be a good tool compared with pesticide application in all cotton fields and oribatid mites may be useful test species for risk evaluation of soil contamination by pesticides.     

The influence of the degree of cross-linking on the adsorption properties of chitosan beads

The influence of the degree of cross-linking (DCL) on chitosan beads was studied. Chitosan was prepared from the exoskeleton of Cape rock-lobsters, collected from the surroundings of Cape Town, South Africa. The chitosan beads were characterized; the beads water contents and pKa varied in the range of 90-96% and 4.3-6.0, respectively, and were found to decrease with increasing DCL (0.0-34.0%). A pH-model, which described the reversibility of the metal adsorbed onto the beads, was used to predict the equilibrium properties of copper adsorption onto the cross-linked beads. The model accounts for the effect of pH and the important model parameters, the equilibrium adsorption constant (Kads) and to a lesser extent the adsorbent adsorption capacity (qmax) showed to decrease with the DCL. The adsorbent capacity and the adsorption constant were determined as 3.8-5.0mmol/g chitosan and (9-90)x10(-4), respectively. The adsorption kinetics could be described using a shrinking core model and the effective diffusion coefficient (Deff) was determined as (8.0-25.8)x10(-11)m2/s. It was found that Deff decreases with the DCL mainly due to the decreased in water content of the beads at high DCL.     

Bombesin-modified 6-14 C-terminal fragments adsorption on silver surfaces: influence of a surface substrate

Surface-enhanced Raman scattering (SERS) spectroscopy has been applied to investigate the interaction with a silver colloidal surface of following seven 6-14 fragments of bombesin (BN) C-terminus: cyclo[D-Phe(6),His(7),Leu(14)]BN(6-14), [D-Phe(6),Leu-NHEt(13),des-Met(14)]BN(6-14), [D-Phe(6),Leu(13)-(R)-p-chloro-Phe(14)]BN(6-14), [D-Phe(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14), [D-Tyr(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14), [D-Tyr(6),beta-Phe(11),Phe(13),Nle(14)OH]BN(6-14), and [D-Cys(6),Asn(7),D-Ala(11),Cys(14)]BN(6-14), potent r-GRP-R receptor antagonists used in chemotherapy and potential effective drugs in cancer treatment. The adsorption active sites and molecular orientations on the colloidal silver surface have been determined on the basis of SERS "surface selection rules" subsequent to a detailed SERS analysis. In addition, the similarities and differences of these spectra with the SERS spectra of the peptides immobilized on a roughened silver electrode surface have been examined. From the data, suggestion has been made about structural properties of these peptides on the colloidal surface. (c) 2008 Wiley Periodicals, Inc. Biopolymers 89: 941-950, 2008.This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com.     

The effect of chlorination degree and substitution pattern on the interactions of polychlorinated biphenyls with model bacterial membranes

Polychlorinated biphenyls (PCB) are persistent organic pollutants that due to their chemical resistivity and inflammability found multiple applications. In spite of the global ban for PCB production, due to their long half-lives periods, PCB accumulate in the soils, so effective bioremediation of the polluted lands is of crucial importance. Some of the 209 PCB congeners exhibit increased toxicity to soil bacteria and their presence impoverish the soil decomposer community and slows down the degradation of environmental pollutants in the soils. The exact mechanism of PCB antimicrobial activity is unknown, but it is strictly related with the membrane activity of PCB. Therefore, to shed light on these interactions we applied Langmuir monolayers formed by selected phospholipids as model bacterial membranes. In our studies we tested 5 PCB congeners differing in the degree of chlorination and the distribution of the chlorine substituents around the biphenyl frame. Special attention was paid to tetra-substituted PCB because of their increased presence in the environment and disubstituted PCB being their degradation products. To characterize the model membranes as Langmuir monolayers, we used surface pressure measurements, Brewster angle microscopy and Grazing Incidence X-ray Diffraction. It turned out that among the tetra-substituted PCB the ortho-substituted non-dioxin like compound was much more membrane destructive than the flat dioxin-like congener. On the contrary, among the di-substituted PCB the flat para-substituted 2,2′-dichlorobiphenyl turned out to exhibit high membrane activity.     

The influence of adjacent nucleotides on the pattern of nucleotide substitution in mitochondrial introns of angiosperms

It has been known that in noncoding regions of the chloroplast genome, the pattern of nucleotide substitution is influenced by the two nucleotides flanking the substitution site. In a GC-rich environment, a bias toward transition was observed, whereas in an AT-rich environment, a bias toward transversion was observed. In this study, the influence of the two adjacent neighbors on the substitution pattern was observed in the first intron of the mitochondrial nad4 gene, although the AT content of this intron is only 48%. The proportion of transversions increases from 0.32 to 0.75 as the A + T content (number of A's + T's) of the two nearest neighbors increases from 0 to 2. This trend was also observed in another mitochondrial group I intron with an AT content of 64%. In addition, a similar, though weaker, effect was observed in vertebrate pseudogenes. So this effect is present in all three types of genomes. Furthermore, in contrast to the situation in the noncoding regions of chloroplast DNA, where most nucleotide substitutions occurred in the categories with an A + T content of either 1 or 2, nucleotide substitutions in the mitochondrial first nad4 intron occurred more evenly in three categories of different A + T contents. This might be due largely to the difference in the AT content (0.48 vs. 0.72) between the mitochondrial first nad4 intron and the chloroplast DNA regions studied.     

Adsorption of globular proteins on locally planar surfaces: models for the effect of excluded surface area and aggregation of adsorbed protein on adsorption equilibria.

Equilibrium statistical-thermodynamic models are presented for the surface adsorption of proteins modeled as regular convex hard particles. The adsorbed phase is treated as a two-dimensional fluid, and the chemical potential of adsorbed protein is obtained from scaled particle theory. Adsorption isotherms are calculated for nonassociating and self-associating adsorbing proteins. Area exclusion broadens adsorption isotherms relative to the Langmuir isotherm (negative cooperativity), whereas self-association steepens them (positive cooperativity). The calculated isotherm for adsorption of hard spheres using scaled particle theory for hard discs agrees well with that calculated from the hard disc virial expansion. As the cross section of the adsorbing protein in the plane of the surface becomes less discoidal, the apparent negative cooperativity manifested in the isotherm becomes more pronounced. The model is extended to the case of simultaneous adsorption of a tracer protein at low saturation and a competitor protein with a different size and/or shape at arbitrary fractional saturation. Area exclusion by competitor for tracer (and vice versa) is shown to substantially enhance the displacement of tracer by competitor and to qualitatively invalidate the standard interpretation of ligand competition experiments, according to which the fractional displacement of tracer by competitor is equal to the fractional saturation by competitor.     

Physiological adsorption of Sulfolobus acidocaldarius on coal surfaces

Summary The adsorption of Sulfolobus acidocaldarius on bituminous coal surfaces and the respiration rate during adsorption at 70° C were enhanced at pH 1.0–2.0, in comparison with those at pH 3.0–5.0. The maximum number of bacterial cells adsorbed per unit area of coal attained a maximum (1.4 × 10¹¹ cells/m²) at pH 2.0. The rate of desulphurization at pH 2.2–2.5 was higher than at other pHs tested. Micrographs of S. acidocaldarius obtained by TEM and SEM indicated that the cells were adsorbed to the coal surfaces by extracellular slime. Specific inhibitors of membrane-bound ATPase (NaF, 20 mm) and respiration (NaN₃, 1 mm; KCN, 1 mm) had pronounced effects on suppressing adsorption. The amount of S. acidocaldarius adsorbed decreased when the coal particles were leached in advance with 2.0 m HNO₃. These facts lead to the conclusion that the adsorption of S. acidocaldarius on coal surfaces requires physiological activity relatd to respiration or energy conversion. Offprint requests to: V. B. Vitaya     

The selective adsorption of polysaccharides on polyaromatic surfaces

A new matrix, polymeric 1,3-diaminobenzene-coated Celite, which selectively adsorbs monomeric and polymeric carbohydrates, has been prepared. This matrix adsorbs glycogen and other branched polysaccharides, as opposed to neutral or charged monosaccharides. Other solid supports were coated with polymeric 1,3-diaminobenzene; some of these (coated Sephadex G10 and coated Bioglas 1,000) had better physical form for column packing. Coated Celite was considered to be the best support in view of its greater stability. The effects of ionic concentration, pH, temperature, and the concentration of carbohydrate solution on the adsorption of glycogen on to coated Celite were studied, and methods to prevent adsorption and remove adsorbed carbohydrate were investigated. A comparison is made with the adsorption of heterocyclic compounds by cross-linked dextran gels.     

Degradation of poliovirus by adsorption on inorganic surfaces

Alteration of the specific infectivity of 3H-labeled ribonucleic acid and 14C-protein labeled poliovirus type 1 by adsorption on inorganic surfaces is investigated by application of kinetic theory to data obtained from sequential extractions of adsorbed virus. Some surfaces, e.g., SiO2, appear to have no significant effect. On the other hand, CuO substantially decreases the specific infectivity of adsorbed preparations. Differences in kinetic plots between 3H-labeled ribonucleic acid and 14C-labeled protein suggest that the inactivation observed involves physical disruption of virions. Van der Waals interactions between solid surfaces and virus are suspected to induce spontaneous virion disassembly. Surface catalyzed disassembly in aquatic and soil environments is implicated as an important mechanism controlling enterovirus dissemination. Methods developed here to evaluate complete recovery of adsorbed virus have potenital application to other degradation studied and problems concerning virus recovery from adsorbents used in virus concentrators.     

The adsorption of Thiobacillus ferrooxidans on coal surfaces

The adsorption of Thiobacillus ferrooxidans to coal surfaces has been studied. Adsorption experiments were conducted on coal samples from eight different Eastern coal fields. In all cases the adsorption process was at least 90% complete within the first two minutes following inoculation. The results of these experiments were used to test the validity of two proposed adsorption models. The first model assumes that bacterial adsorption follows second-order irreversible kinetics of the second kind with respect to the concentration of bacteria and substratum surface area in the system. The second model allows for the contribution of reversible adsorption detected in desorption experiments. It was found that the combined reversible-irreversible model more accurately describes the initial stages of adsorption. Rate constants in both models were calculated for each coal sample. The relation of each of these constants to the pyrite concentration in coal is presented and the significance of these relations is discussed.Scanning electron micrographs of inoculated coal samples sho that Thiobacillus ferrooxidans selectively adsorb to exposed pyrite phases dispersed throughout the organic coal matrix. Preferential attachment was also observed along topographical faults in the caol surface. Mercury contact angle measurements on coal indicate that the selective adsorption of Thiobacillus ferrooxidans may be attributable to the lower surface free energy of pyrite relative to the organic coal matrix.     

CO2 adsorption on polar surfaces of ZnO

Physical and chemical adsorption of CO₂ on ZnO surfaces were studied by means of two different implementations of periodic density functional theory. Adsorption energies were computed and compared to values in the literature. In particular, it was found that the calculated equilibrium structure and internuclear distances are in agreement with previous work. CO₂ adsorption was analyzed by inspection of the density of states and electron localization function. Valence bands, band gap and final states of adsorbed CO₂ were investigated and the effect of atomic displacements analyzed. The partial density of states (PDOS) of chemical adsorption of CO₂ on the ZnO(0001) surface show that the p orbitals of CO₂ were mixed with the ZnO valence band state appearing at the top of the valence band and in regions of low-energy conduction band.

Competitive protein adsorption on polysaccharide and hyaluronate modified surfaces

Adsorption of bovine serum albumin (BSA) and fibrinogen (Fg) was measured on six distinct bare and dextran- and hyaluronate-modified silicon surfaces created using two dextran grafting densities and three hyaluronic acid (HA) sodium salts derived from human umbilical cord, rooster comb and Streptococcus zooepidemicus. Film thickness and surface morphology depended on the HA molecular weight and concentration. BSA coverage was enhanced on surfaces in competitive adsorption of BSA:Fg mixtures. Dextranization differentially reduced protein adsorption onto surfaces based on oxidation state. Hyaluronization was demonstrated to provide the greatest resistance to protein coverage, equivalent to that of the most resistant dextranized surface. Resistance to protein adsorption was independent of the type of HA utilized. With changing bulk protein concentration from 20 to 40 μg ml(-1) for each species, Fg coverage on silicon increased by 4x, whereas both BSA and Fg adsorption on dextran and HA were far less dependent on protein bulk concentration.     

Competitive protein adsorption on polysaccharide and hyaluronate modified surfaces

Adsorption of bovine serum albumin (BSA) and fibrinogen (Fg) was measured on six distinct bare and dextran- and hyaluronate-modified silicon surfaces created using two dextran grafting densities and three hyaluronic acid (HA) sodium salts derived from human umbilical cord, rooster comb and Streptococcus zooepidemicus. Film thickness and surface morphology depended on the HA molecular weight and concentration. BSA coverage was enhanced on surfaces in competitive adsorption of BSA:Fg mixtures. Dextranization differentially reduced protein adsorption onto surfaces based on oxidation state. Hyaluronization was demonstrated to provide the greatest resistance to protein coverage, equivalent to that of the most resistant dextranized surface. Resistance to protein adsorption was independent of the type of HA utilized. With changing bulk protein concentration from 20 to 40 μg ml^?1 for each species, Fg coverage on silicon increased by 4x, whereas both BSA and Fg adsorption on dextran and HA were far less dependent on protein bulk concentration.     

Adsorption of chromium and zinc ions from aqueous solutions by cellulosic graft copolymers

Cellulosic graft copolymers were prepared by the reaction of bast fibers of the kenaf plant (Hibiscus cannabinus) with acrylonitrile and methacrylonitrile monomers in aqueous media initiated by the ceric ion-toluene redox pair. The cellulose-polyacrylonitrile (Cell-PAN) and cellulose-polymethacrylonitrile (Cell-PMAN) graft copolymers were used for the removal of Zn(II) and Cr(III) ions from aqueous solutions at 30°C. Zn(II) ion was more sorbed than Cr(III) ion by both copolymers by an average factor of 1.80 ± 0.40. For each metal ion, the Cell-PAN graft copolymer was a more effective sorbent than the Cell-PMAN derivative. The amount of ion sorbed decreased with an increase in percentage graft and over the range 38–149% of the graft the amounts of Zn(II) and Cr(III) ions sorbed by Cell-PAN decreased by 44% and 56%, respectively.     

Adsorption and elution characteristics of nucleic acids on silica surfaces and their use in designing a miniaturized purification unit

We report nucleic acid (NA) adsorption isotherms and elution profiles for silica surfaces and use these to design a miniaturized NA purification unit based on solid-phase extraction with silica beads. The procedure is based on a pressure drop equation for flow through a packed bed and allows estimation of key design parameters such as channel dimensions, liquid flow rates, sample volume, and amount of silica needed. The usefulness of this design procedure is demonstrated by applying it to a column-based NA purification device for influenza detection for a case study of Madin-Darby canine kidney cells infected with influenza A virus.     

Degradation of poliovirus by adsorption on inorganic surfaces.

Alteration of the specific infectivity of 3H-labeled ribonucleic acid and 14C-protein labeled poliovirus type 1 by adsorption on inorganic surfaces is investigated by application of kinetic theory to data obtained from sequential extractions of adsorbed virus. Some surfaces, e.g., SiO2, appear to have no significant effect. On the other hand, CuO substantially decreases the specific infectivity of adsorbed preparations. Differences in kinetic plots between 3H-labeled ribonucleic acid and 14C-labeled protein suggest that the inactivation observed involves physical disruption of virions. Van der Waals interactions between solid surfaces and virus are suspected to induce spontaneous virion disassembly. Surface catalyzed disassembly in aquatic and soil environments is implicated as an important mechanism controlling enterovirus dissemination. Methods developed here to evaluate complete recovery of adsorbed virus have potenital application to other degradation studied and problems concerning virus recovery from adsorbents used in virus concentrators.