Kooperativer Bibliotheksverbund

Berlin Brandenburg


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  • 1
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007, Vol.303(3), pp.249-252
    Description: Colloids play a crucial role in the translocation of trace elements in soils. Recent studies provided hints that colloid hydrophobicity may be an important factor controlling colloid (im)mobilization in soils. However, existing methods for the determination of hydrophobicity are limited to the bulk soil. Therefore, we developed a method to determine the hydrophobicity of suspended colloids in aqueous soil suspensions, which was based on a distribution between a polar and a non-polar phase. The proposed method uses 30 mg of an unpolar solid phase (C18-column material) which are mixed with 10 mL of suspension for 2 h. The turbidity of the suspensions is measured before and after mixing. The ratio of the colloids in the hydrophilic aqueous and the hydrophobic solid phase is calculated as a measure of colloid hydrophobicity. This method was successfully tested on differently hydrophobized goethite particles. At DOC concentrations exceeding 20 mg L , organic molecules sorbed to C18-material limit the applicability of the method.
    Keywords: Water Repellence ; Zeta Potential ; Colloid ; Soil Drying ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
    Source: ScienceDirect Journals (Elsevier)
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  • 2
    Language: English
    In: Journal of environmental quality, 2007, Vol.36(4), pp.1187-93
    Description: Drying of soil may increase the hydrophobicity of soil and affect the mobilization of colloids after re-wetting. Results of previous research suggest that colloid hydrophobicity is an important parameter in controlling the retention of colloids and colloid-associated substances in soils. We tested the hypothesis that air-drying of soil samples increases the hydrophobicity of water-dispersible colloids and whether air-drying affects the mobilization of colloid-associated heavy metals. We performed batch experiments with field-moist and air-dried (25 degrees C) soils from a former sewage farm (sandy loam), a municipal park (loamy sand), and a shooting range site (loamy sand with 25% C(org)). The filtered suspensions (〈1.2 microm) were analyzed for concentrations of dissolved and colloidal organic C and heavy metals (Cu, Cd, Pb, Zn), average colloid size, zeta potential, and turbidity. The hydrophobicity of colloids was determined by their partitioning between a hydrophobic solid and a hydrophilic aqueous phase. Drying increased hydrophobicity of the solid phase but did not affect the hydrophobicity of the dispersed colloids. Drying decreased the amount of mobilized mineral and (organo-)mineral colloids in the sewage farm soils but increased the mobilization of organic colloids in the C-rich shooting range soil. Dried samples released less colloid-bound Cd and Zn than field-moist samples. Drying-induced mobilization of dissolved organic C caused a redistribution of Cu from the colloidal to the dissolved phase. We conclude that drying-induced colloid mobilization is not caused by a change in the physicochemical properties of the colloids. Therefore, it is likely that the mobilization of colloids in the field is caused by increasing shear forces or the disintegration of aggregates.
    Keywords: Desiccation ; Hydrophobic and Hydrophilic Interactions ; Colloids -- Chemistry ; Metals, Heavy -- Analysis ; Soil -- Analysis
    ISSN: 0047-2425
    E-ISSN: 15372537
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  • 3
    In: Antimicrobial Agents and Chemotherapy, 2007, Vol. 51(1), p.275
    Description: Squalene epoxidase (SE) is the target of terbinafine, which specifically inhibits the fungal enzyme in a noncompetitive manner. On the basis of functional homologies to p-hydroxybenzoate hydroxylase (PHBH) from Pseudomonas fluorescens, the Erg1 protein contains two flavin adenine dinucleotide (FAD) domains and one nucleotide binding (NB) site. By in vitro mutagenesis of the ERG1 gene, which codes for the Saccharomyces cerevisiae SE, we isolated erg1 alleles that conferred increased terbinafine sensitivity or that showed a lethal phenotype when they were expressed in erg1-knockout strain KLN1. All but one of the amino acid substitutions affected conserved FAD/nucleotide binding sites. The G sub(25)S, D sub(335)X (W, F, P), and G sub(210)A substitutions in the FADI, FADII, and NB sites, respectively, rendered the SE variants nonfunctional. The G sub(30)S and L sub(37)P variants exhibited decreased enzymatic activity, accompanied by a sevenfold increase in erg1 mRNA levels and an altered sterol composition, and rendered KLN1 more sensitive not only to allylamines (10 to 25 times) but also to other ergosterol biosynthesis inhibitors. The R sub(269)G variant exhibited moderately reduced SE activity and a 5- to 10-fold increase in allylamine sensitivity but no cross-sensitivity to the other ergosterol biosynthesis inhibitors. To further elucidate the roles of specific amino acids in SE function and inhibitor interaction, a homology model of Erg1p was built on the basis of the crystal structure of PHBH. All experimental data obtained with the sensitive Erg1 variants support this model. In addition, the amino acids responsible for terbinafine resistance, although they are distributed along the sequence of Erg1p, cluster on the surface of the Erg1p model, giving rise to a putative binding site for allylamines.
    Keywords: Data Processing ; Amino Acid Substitution ; Flavin-Adenine Dinucleotide ; Flavin ; Enzymes ; P-Hydroxybenzoate Hydroxylase ; Erg1 Gene ; Nucleotides ; Antimicrobial Agents ; Mrna ; Mutagenesis ; Models ; Squalene Epoxidase ; Flavin-Adenine Dinucleotide ; Homology ; Crystal Structure ; Adenine ; Enzymatic Activity ; Ergosterol ; Sterol Composition ; Squalene Monooxygenase ; Terbinafine ; Amino Acid Sequence ; Pseudomonas Fluorescens ; Saccharomyces Cerevisiae ; Genetics & Taxonomy ; Genetics & Taxonomy ; Antibiotics & Antimicrobials;
    ISSN: 0066-4804
    ISSN: 00664804
    E-ISSN: 10986596
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