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PubMed1997

Vacuolar reticulum in oomycete hyphal tips: An additional component of the Ca2+Regulatory system?

Cultures of Achlya sp., Phytophthora cinnamomi, Saprolegnia diclina, S. ferax, and S. parasitica, treated with 6-carboxyfluorescein diacetate solution, accumulate 6-carboxyfluorescein in a reticulate system of fine tubules. The network shows longitudinal polarity within the hyphae, tubules being finest toward the hyphal tips. In more mature subapical regions the network is connected with large vacuoles that also accumulate 6-carboxyfluorescein. A morphologically similar system has also been identified in freeze-substituted hyphae of S. ferax. The network is considered to be vacuolar, but differs from the tubular vacuole system of true fungi in that tubules are less motile, more frequently branched, and do not alternate with clusters of spherical vacuoles. The appearance of the network resembles patterns of calcium-sensitive dye staining and it is suggested that the vacuolar reticulum in the tip region of oomycete hyphae may act as a Ca2+ sink. The tubular reticulum in oomycetes is very fragile and can be shown with 6-carboxyfluorescein in only those hyphal tips with a motility and organelle distribution characteristic of growing hyphae with normal morphology. Diverse abnormal hyphae show a range of other fluorochrome localizations. These include large irregular compartments filled with fluorochrome, and fluorescent cytoplasm with organelles and vacuoles standing out in negative contrast. These localizations in abnormal hyphae are correlated with other structural changes indicative of damage. Special care is required in experiments with oomycetes to avoid such artefacts of localization. Copyright 1997 Academic Press. Copyright 1997 Academic Press

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PubMed1997

Mutants of the phytopathogenic fungus magnaporthe grisea deficient in alternative, cyanide-resistant, respiration

The phytopathogenic fungus Magnaporthe grisea has a cyanide-resistant respiratory pathway. The fungicide SSF-126 ((E)-2-methoxyimino-N-methyl-2-(2-phenoxyphenyl) acetamide) blocks the cytochrome electron transport of M. grisea and induces the alternative respiratory pathway. Twelve mutants of M. grisea more susceptible to SSF-126 than wild type were identified after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. Five mutants retained a reduced alternative respiration activity, and seven mutants lacked alternative pathway activity. A monoclonal antibody against the maize alternative oxidase cross-reacted against a 40-kDa mitochondrial protein of M. grisea, indicating that the 40-kDa protein is an alternative oxidase. Immunoblot analysis indicated that the seven completely deficient mutants grouped into two classes: four mutants produced the 40-kDa proteins while the other three mutants failed to produce the functional protein. Copyright 1997 Academic Press. Copyright 1997 Academic Press

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PubMed1997

Compact Fiber Optic Dynamic Light Scattering System

Fiber optic dynamic light scattering (FODLS) is fast developing as a technique for sizing particles in concentrated dispersions. Fiber optic systems have the potential to be made into online particle size measuring equipment in process industries. Two different laser light sources were used to study monodisperse polystyrene latex dispersion with different particle sizes and volume fractions. The apparent diffusion coefficients were a function of particle size, volume fraction, and signal to noise ratios. The apparent diffusion coefficient data showed that FODLS probes collective diffusion for smaller particles and self diffusion for larger particles. It was observed that for a polydisperse concentrated dispersion, both self and collective diffusion were probed by FODLS. This means that the apparent diffusion coefficient can be used only as a relative quantity. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

LETTER TO THE EDITOR

An isocyanurate silane coupling agent effectively attaches to E-glass fibers both from aqueous or CCl4 solution. SEM revealed remarkably different glass surface topographies that were solvent dependent. Application of the coupling agent from CCl4 solution gave rise to unprecendented polymeric bridges between adjacent parallel fibers. The existence of such large bridging structures has only recently been postulated, and it was not thought that such theoretical projections would ever be observed, as polymeric bridging structures typically should collapse in the absence of solvent. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Adsorption of Dextrin at Mineral/Water Interface

The adsorption mechanism of dextrin on aqueous minerals such as fluorite, apatite, galena, magnetite, gamma-alumina, and graphite was studied by adsorption experiments, zeta potential measurements, and FT-IR studies. Depending on the nature of the mineral surface, dextrin was found to interact in three different ways viz. by chemisorption, physisorption, or hydrophobic-hydrophobic interaction. The adsorption density of dextrin was found to be pH dependent. Maximum adsorption of dextrin was obtained around the pH at which the mineral surface is highly hydroxylated. The mechanism of dextrin interaction with the surface metal hydroxy sites, ( identical withMeOH), was found to proceed via chemical complexation. A linear relationship was observed between the adsorption density of dextrin and the pH of maximum surface hydroxylation. Zeta potential measurements have indicated the possibility of dextrin adsorption by electrostatic interaction under the conditions where mineral surface and dextrin are oppositely charged. Furthermore dextrin was found to adsorb on hydrophobic minerals such as graphite by hydrophobic-hydrophobic interaction. However, the magnitude of adsorption by electrostatic and hydrophobic interaction was found to be very marginal compared to that of chemical complexation. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Estimation of Gelatin Layer Thickness on Polystyrene Particles by a Viscometric Study

A viscometric method has been used to determine the layer thickness of gelatin adsorbed on polystyrene (PS) particles. The layer thickness was found to be 28 nm regardless of the diameter of PS particles. The value of Einstein's coefficient, alpha0 for the relative viscosity-volume fraction relation was estimated to be 2.63. Since the PS latex particles were spherical, the value of alpha0 indicates that even at high shear rates, some aggregation still occurred in the dispersion. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Formation of Surface Active Gelatin by Covalent Attachment of Hydrophobic Chains

Surface active gelatin was formed by covalent attachment of hydrophobic groups to gelatin molecules. The modification was carried out at various degrees of attachment and with various chain lengths. These modified gelatins (MGs) were synthesized in dry DMSO by a simple and rapid method. The new method leads to high yields and allows high degrees of modification. The MGs, which have various hydrophobicities, have better surface activity than the native gelatin, as determined by surface tension reduction. The surface tension reduction is correlated to the hydrophobicity of the modified molecule, which was determined by a fluorescent probe. It appears that both the increase in the number of the hydrophobic groups and the increase in the chain lengths lead to decreased surface tension. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Calculation of the Static Permittivity of Suspensions from the Stored Energy

It is shown that the static permittivity of suspensions of charged particles in electrolyte solution can be deduced from the field-induced change of the Gibbs free energy stored outside the double layer. This energy is related to the changes of the electrolyte concentration around the particle and is obtained solving a purely static problem. The method is first verified deducing well-known results corresponding to suspensions of spherical particles. It is then used to calculate the static permittivity of suspensions of spheroidal particles, leading to a new result that cannot be analytically obtained using the classical approach. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Surface Chemical Analysis and Electrokinetic Properties of Synthetic Spherical Mixed Zinc-Cadmium Sulfides

In this work, we analyze the surface and bulk chemical composition, as well as the crystal structure, of colloidal spherical particles of Zn-Cd mixed sulfides of different Zn/Cd ratios. The particles were obtained by precipitation from solution according to the method described by Wilhelmy and Matijevic [Colloids Surfaces 16, 1 (1985)]. Transmision electron microscopy of the particles show that their average diameter ranges from 50-60 nm (when the synthesis is carried out at 50degreesC) up to 150-200 nm (for a temperature of 70degreesC). Atomic absorption analysis of the twelve samples obtained indicated that the bulk Zn/Cd ratio increases with aging temperature; the same behavior is found when the concentration of Cd(NO3)2 used in the synthesis is decreased. Similarly, the bulk proportion of Zn in the particles is higher the longer the growth time. EDX microanalysis was also performed on all the samples; although this technique is not a bulk (but rather surface) analytical tool, the fact that it gives information down to a depth of approximately 500 A from the surface makes the type of information obtained with EDX comparable to atomic absorption. Although the overall Zn/Cd trends are reproduced by EDX data, these are not as sensitive as atomic absorption. The surface composition of three selected samples (M3, 50 min growth time, 50degreesC, 0.52 mM Cd2+ in the growing solution; M8, 100 min, 60degreesC, 0.52 mM; M12, 100 min, 70degreesC, 0.52 mM) was determined by XPS spectra od Cd 3d5/2, Zn 2p3/2, and O 1s electrons, for the three samples. The sequence of variation of the Zn/Cd ratio of M3, M8, and M12 particles agrees qualitatively with that found by atomic absorption or EDX; the fact that no detectable Cd is found in sample M12 suggests that the particles have a nonhomogeneous composition that changes from the core to the surface layer. The analysis of O 1s electrons allows to reach the conclusion that the surface oxidation changes in the order M3 > M8 > M12, i.e., the particles are more oxidized the larger the amount of cadmium on their surface. This is confirmed by electric conductivity determinations in aqueous suspensions of the samples, both in the presence of natural light and in the dark, as a function of time. These data, together with crystal structure determinations by XRD, suggest that, when the growth temperature is 50-60degreesC, the particles contain a ZnS (sphalerite) nucleus covered by a layer of mixed, hexagonal Zn-CdS and a surface layer of cubic ZnS. When the aging temperature is 70degreesC, the ZnS core is surrounded by a shell containing cubic ZnS and amorphous CdS. The surface electrical properties of the particles in aqueous suspensions were analyzed by electrophoresis: the effect of pH on the electrophoretic mobility, and in particular the pH value at which the mobility is zero (isoelectric point or pHiep) confirms the conclusions obtained from our previous surface chemical analysis concerning the surface oxidation of the particles. The effect of lattice ions (Zn2+, Cd2+, S2-) in solution on the mobility (and hence on the surface charge) of the particles is very significant: the latter ions are able to find easily their way to the surface of the sulfides and change to a large extent the overall pH-dependence of the mobility and specifically the values of the pHiep. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Adsorption of Benzoic Compounds onto Stainless Steel Particles

Equilibrium experiment was conducted to investigate the factors determining the adsorption of benzoic acid (BA) and its derivatives, m- and p-hydroxy BA, onto SUS316L stainless steel particles of 8-10 &mgr;m diameter and under 100 mesh. Adsorption isotherms of these benzoic compounds were determined in the presence of 0.05 M NaCl at pH 4 and 30°C. The adsorptions of the these compounds were described well by a Langmuirian model for both adsorbents. When the maximum number of the benzoic compound adsorption sites was expressed on the basis of unit surface area (N, mol/m2), the N values were relatively constant, while the greatest value of the affinity (K, ml/&mgr;mol) was obtained for p-hydroxy BA, although its value was in the same range as that of the other two adsorbates. Diffuse-reflectance Fourier transform infrared spectra of the fine adsorbent (8-10 &mgr;m diameter) after equilibration suggest that the adsorption mainly takes place through the carboxyl group of the adsorbate-stainless steel surface interaction for all adsorbates, whereas concomitant interaction occurs in part with participation of the phenolic hydroxyl group for p-OH BA adsorbate, accounting for the difference in adsorption properties. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Surface-Enhanced Raman Spectroscopic Study of Isomeric Formylthiophenes in Silver Colloid

Surface enhanced Raman (SER) spectra of 2- and 3-formylthiophenes (2FT and 3FT) in silver colloids are compared with their normal Raman spectra in bulk and in acetonitrile solution. Experimental results indicate adsorption of 2FT on metal surface through the sulfur and the oxygen atoms with the ring plane vertical to the metal surface, whereas the ring plane of the 3FT molecule is inclined to the surface. Moreover, the SER spectrum of 2FT molecule predicts the existence of syn-form of this molecule in the adsorbed state because of large enhancement of the carbonyl stretching mode. Concentration dependence of relative enhancement infers the monolayer formation on metal surface at a specific concentration, implying strong evidence of chemisorption of the adsorbates. The excitation profile of C identical withC symmetric stretching mode of 2FT suggests classical plasmon resonance as the main contributor to surface enhancement. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Equilibrium Adsorption Studies of Some Aromatic Pollutants from Dilute Aqueous Solutions on Activated Carbon at Different Temperatures

Aqueous solutions of phenol, p-chlorophenol, and p-nitrophenol have been used to determine the adsorption isotherm for single solute systems on activated carbon at different temperatures. The experimental program has been conducted to investigate the influence of concentration and temperature. All the reported equilibrium isotherm equations have been tried on present and published experimental data. A generalized isotherm equation which was proposed by Khan et al. (6, 10) and tested for bi-solute adsorption data has been modified for single-solute system. The temperature dependency has also been incorporated into a generalized equation. It has been noticed that the Radke and Prausnitz (7) and generalized isotherm equations could represent the entire data with a minimum average percentage error. The influence of different adsorbents, sorbate concentrations, and pH of aqueous solutions has also been discussed in detail. The temperature dependency has been investigated using both the Dubinin-Astakov (13) and the modified generalized equation. The generalized equation describes the experimental and published data adequately and provides a single value of differential molar heat of adsorption, DeltaHads, for a single solute adsorption system. The Dubinin-Astakov isotherm equation has shown an increasing trend of DeltaHads as the loading of adsorbent has increased. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

A Comparison between Hydrophobically End-Capped Poly(ethylene oxide) with Ether and Urethane Bonds

Two models of HEUR (hydrophobically modified ethylene oxide urethane) associative polymers (AP) are compared. The two polymers are polyethyleneoxides simply end-capped with dodecyl groups, one through an ether bond H25C12-O-(CH2CH2O)304-C12H25 (AP14, Mw = 13,700) and the other through an urethane bond H25C12-NHCOO-(CH2CH2O)304-CONH-C12H25 (AP14NCO, Mw is about the same as for AP14). The results indicate that this subtle difference in polymer architecture dramatically influences the initial association and the clouding of the polymer in water, so that AP14NCO starts to aggregate earlier but has a higher clouding temperature. However, at more elevated polymer contents (above 2-3 wt%) the differences in solution behavior and transport dynamics between the two polymers seems less significant. These conclusions are drawn through fluorescence, dynamic light scattering, NMR self-diffusion, turbidimetry, and viscosity measurements. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

A Study on the Chemical Heterogeneity of Active Surface of Solid Catalysts

A method that can be used to characterize the chemical heterogeneity of active surface of solid catalyst is given. The chemical adsorption behavior of three adsorbates on Ni-W/F-Al2O3-SiO2 catalyst and supported Ni catalyst has been investigated. On the basis of fractal geometry, the roughness fractal dimension (Dr) and the chemisorption fractal dimension (Dc) of two kinds of catalyst are estimated. We use the difference between Dc and Dr to characterize the chemical heterogeneity of active sites on the catalytic surface. As a result, the chemical heterogeneity of the acid sites of Ni-W/F-Al2O3-SiO2 catalyst is very great. As for supported Ni catalyst, the chemical heterogeneity of active sites decreased when impregnating operation times in preparation of the catalyst increased. After impregnated four times, the chemical heterogeneity of its active surface of supported Ni catalyst is eliminated. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

A Physicochemical Study of Polypyrrole-Silica Nanocomposites by Inverse Gas Chromatography

Three polypyrrole-silica nanocomposites were characterized by inverse gas chromatography (IGC) at 60 and 80degreesC using both linear and branched alkane probes. The IGC data for these materials were compared with those obtained for the ultrafine silica sol and polypyrrole (PPy) bulk powder reference materials. The London components of the surface energies (gammasd) of the nanocomposites were in the range 115-225 mJ m-2 at 60degreesC. These values are much higher than those obtained for either the polypyrrole powders or the colloidal silica sol, which suggests that the nanocomposites have significant microporosity. The gammasd values for the nanocomposites decrease in the order chloride-doped PPy > sulfate-doped PPy > tosylate-doped PPy, which is the same trend as that found for the heat of adsorption (DeltaHa) of a given n-alkane. DeltaHa values of the linear and branched alkanes are up to three times higher than the heats of vaporization, which confirms that the nanocomposites (and, to a lesser extent, the polypyrrole powders) have high adsorption capacities for these solutes. For a series of alkane isomers (e.g., C7H16 or C8H18), the difference between the DeltaHa values for the nanocomposites and the corresponding polypyrrole powders decreased as the degree of branching for these probes was increased. These observations suggest that the more sterically hindered probes are excluded from the microporous interior of the nanocomposites. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

The Effect of Head-Group on Selective Counterion Binding to Cationic Surfactants

Selectivity coefficients for the competitive adsorption of chloride, bromide, and iodide at the air/solution interface have been measured by a high accuracy ion flotation technique using the surfactant cations dodecylammonium, dodecylmethylammonium, dodecyldimethylammonium, and dodecyltrimethylammonium. Selective binding was found to depend on the nature of the head group, with selectivity increasing from primary to quaternary ammonium ions. Results are consistent with counterion binding arising from contact adsorption by mutual dehydration of head groups and counterions. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Interaction of o-Aminophenol and o-Nitrophenol with Copper, Zinc, Molybdenum, and Chromium Ferrocyanides

Removal of o-aminophenol and o-nitrophenol from aqueous solution through adsorption on copper zinc, molybdenum, and chromium ferrocyanides were studied in pH range 2-10 at 27°C. At pH 7.0 o-nitrophenol adsorbed more than o-aminophenol on all the metal ferrocyanides studied. The Langmuir type of adsorption is followed in the concentration range of 10(-3) to 10(-4) M of o-aminophenol and o-nitrophenol solutions. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Mercury Penetration and Snap-off in Lenticular Pores

During mercury porosimetry experiments two of the most basic mechanisms responsible for mercury intrusion (drainage) into and retraction (imbibition) from porous media are meniscus intrusion into constrictions and thread snap-off in narrow pores, respectively. The present work consists of an experimental and theoretical study of these phenomena in model lenticular capillaries, that is, capillaries with lens-shaped cross section. The reason for this apparently strange choice is that several porous media of interest, such as sandstone reservoir rocks (and also model pore networks etched in glass plates and used in numerous experimental studies of multiphase flow in porous media) have pores of such type. The critical pressures for mercury intrusion and snap-off in lenticular pores are measured experimentally and expressed in dimensionless form as functions of the pore aspect ratio (ratio of pore width to pore depth) and the contact angle. Analytical mathematical relationships are also developed for the calculation of these critical pressures. In the case of mercury penetration, very good agreement between experiment and theory is observed over the whole region of pore width to pore depth aspect ratio. In the case of mercury snap-off, very good agreement is observed for small and medium values of pore aspect ratio. A sizable discrepancy in the case of snap-off is observed in pores of large aspect ratio, and this is caused by the considerable deviation (in this case) of the pore shape of the experimental models from the lenticular one used in the theoretical calculations, as well as by the strong effect of the pressure of residual air on the values of measured pressures. Copyright 1997 Academic Press. Copyright 1997Academic Press

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