Surface Accumulation (surface + accumulation)

Distribution by Scientific Domains

Selected Abstracts

Mineral surfaces and soil organic matter

K. Kaiser
Summary The organic carbon content of soil is positively related to the specific surface area (SSA), but large amounts of organic matter in soil result in reduced SSA as determined by applying the Brunauer,Emmett,Teller (BET) equation to the adsorption of N2. To elucidate some of the controlling mechanisms of this relation, we determined the SSA and the enthalpy of N2 adsorption of separates with a density > 1.6 g cm,3 from 196 mineral horizons of forest soils before and after removal of organic matter with NaOCl. Likewise, we investigated these characteristics before and after sorption of increasing amounts of organic matter to four mineral soil samples, oxides (amorphous Al(OH)3, gibbsite, ferrihydrite, goethite, haematite), and phyllosilicates (kaolinite, illite). Sorption of organic matter reduced the SSA, depending on the amount sorbed and the type of mineral. The reduction in SSA decreased at larger organic matter loadings. The SSA of the mineral soils was positively related to the content of Fe oxyhydroxides and negatively related to the content of organic C. The strong reduction in SSA at small loadings was due primarily to the decrease in the micropores to which N2 was accessible. This suggests preferential sorption of organic matter at reactive sites in or at the mouths of micropores during the initial sorption and attachment to less reactive sites at increasing loadings. The exponential decrease of the heat of gas adsorption with the surface loading points also to a filling or clogging of micropores at early stages of organic matter accumulation. Desorption induced a small recovery of the total SSA but not of the micropore surface area. Destruction of organic matter increased the SSA of all soil samples. The SSA of the uncovered mineral matrix related strongly to the amounts of Fe oxyhydroxides and the clay. Normalized to C removed, the increase in SSA was small in topsoils and illuvial horizons of Podzols rich in C and large for the subsoils containing little C. This suggests that micropores preferentially associate with organic matter, especially at small loadings. The coverage of the surface of the soil mineral matrix as calculated from the SSA before and after destruction of organic matter was correlated only with depth, and the relation appeared to be linear. We conclude that mineralogy is the primary control of the relation between surface area and sorption of organic matter within same soil compartments (i.e. horizons). But at the scale of complete profiles, the surface accumulation and stabilization of organic matter is additionally determined by its input. [source]

Chlorophenol dehalogenation in a magnetically stabilized fluidized bed reactor

AICHE JOURNAL, Issue 3 2006
Lisa J. Graham
Abstract Aromatic halocarbons are often present in contaminated aquifers, surface waters, wastewater streams, soils, and hazardous wastes. The dehalogenation of p-chlorophenol as a model compound in both the aqueous phase and in slurries of contaminated solids using a magnetically stabilized fluidized bed (MSFB) reactor is discussed. Composite palladium-iron (Pd/Fe) media are employed as both catalyst and sacrificial reactant for the reductive dechlorination of p-chlorophenol. Calcium alginate beads impregnated with Pd/Fe granules are fluidized in a recirculating aqueous stream containing either dissolved p-chlorophenol or a slurry of soil contaminated with this chlorocarbon. Magnetic stabilization of the fluidized bed allows substantially higher rates of mass transfer than would otherwise be achievable, and allows circulation of contaminated solids while fluidization media are retained. Anoxic conditions are sustained under a nitrogen purge and the solution pH of 5.8 is maintained by active control to minimize surface fouling by hydroxides, and to minimize mass-transfer resistances resulting from the surface accumulation of hydrogen bubbles. A model of this process is described and the resulting predictions are compared to the experimentally derived data. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source]

Drying-induced variations in physico-chemical properties of amorphous pharmaceuticals and their impact on stability (I): Stability of a monoclonal antibody,

Ahmad M. Abdul-Fattah
Abstract The present study was conducted to investigate the impact of drying method and formulation on the storage stability of IgG1. Formulations of IgG1 with varying levels of sucrose with and without surfactant were dried by different methods, namely freeze drying, spray drying, and foam drying. Dried powders were characterized by thermal analysis, scanning electron microscopy, specific surface area (SSA) analysis, electron spectroscopy for chemical analysis (ESCA), solid state FTIR, and molecular mobility measurements by both isothermal calorimetry and incoherent elastic neutron scattering. Dried formulations were subjected to storage stability studies at 40°C and 50°C (aggregate levels were measured by size exclusion chromatography initially and at different time points). Both drying method and formulation had a significant impact on the properties of IgG1 powders, including storage stability. Among the drying methods, SSA was highest and perturbations in secondary structure were lowest with the spray-dried preparations. Sucrose-rich foams had the lowest SSA and the lowest protein surface accumulation. Also, sucrose-rich foams had the lowest molecular mobility (both fast dynamics and global motions). Stability studies showed a log-linear dependence of physical stability on composition. Preparations manufactured by "Foam Drying" were the most stable, regardless of the stabilizer level. In protein-rich formulations, freeze-dried powders showed the poorest storage stability and the stability differences were correlated to differences in secondary structure. In stabilizer-rich formulations, stability differences were best correlated to differences in molecular mobility (fast dynamics) and total protein surface accumulation. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:1983,2008, 2007 [source]

Surface properties of poly(lactic/glycolic acid),pluronic® blend films

É. Kiss
Abstract Poly(dl -lactide) (PLA) and two of its random copolymers with glycolic acid, poly(dl -lactide- co -glycolide) (PLGA) with 75/25 and 50/50 component ratios of lactide/glycolide were blended with poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO,PPO,PEO) triblock non-ionic surfactants, known by the Pluronic® trade names of PE6100, PE6400 and PE6800. The surface chemical compositions of the blended films were identified by X-ray photoelectron spectroscopy (XPS). Based on the component of the carbon signal assigned to the ether carbon of the Pluronic® molecule, quantification of the surface accumulation of the Pluronic® additive, compared to its bulk concentration, was performed. The data demonstrated that PEO-containing surfaces were prepared by the blending process. A significant surface hydrophilization, characterized by wettability measurements, was obtained by applying the Pluronics® at a concentration of 1.0,9.1,wt% in the blends. The composition of the surface layer and, in accordance with this, the wettability of the film were found to be dependent on the type of Pluronic® and on the composition of the unmodified polymer. Protein adsorption on the polymer films was measured by the FT-IR ATR spectroscopic technique. The adsorbed amount of bovine serum albumin onto PLA was highly reduced when the polymer was blended with a Pluronic®. The increased hydrophilicity and the reduced protein adsorption properties of the PLA and PLGA obtained by blending with PEO compounds might contribute to their applications as drug carrier systems with great potential. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Alteration of articular cartilage frictional properties by transforming growth factor ,, interleukin-1,, and oncostatin M

Jason P. Gleghorn
Objective To evaluate the functional effects of transforming growth factor ,1 (TGF,1), interleukin-1, (IL-1,), and oncostatin M (OSM) on the frictional properties of articular cartilage and to determine the role of cytokine-mediated changes in cartilage frictional properties by extracting and redepositing lubricin on the surface of cartilage explants. Methods Neonatal bovine cartilage explants were cultured in the presence or absence of 10 ng/ml of TGF,1, IL-1,, or OSM over 48 hours. Boundary lubrication tests were conducted to determine the effects of endogenously produced surface localized lubricin and of exogenous lubricin at the tissue surface and in the lubricant solution. The initial friction coefficient (,0), equilibrium friction coefficient (,eq), and Young's modulus (EY) were determined from the temporal load data. Results IL-1, and OSM decreased tissue glycosaminoglycan (GAG) content by ,20% over 48 hours and decreased EY to a similar extent (11,17%), but TGF, did not alter GAG content or EY. Alterations in proteoglycan content corresponded to changes in ,0, but endogenous lubricin decreased boundary mode ,eq. The addition of exogenous lubricin, either localized at the tissue surface or in the lubricating solution, did not modulate ,0, but it did lower ,eq in cytokine-treated cartilage. Conclusion This study provides new insight into the functional consequences of cytokine-mediated changes in friction coefficient. In combination with established pathways of cytokine-mediated lubricin metabolism, these data provide evidence of distinct biochemical origins of boundary and biphasic pressure-mediated lubrication mechanisms in cartilage, with boundary lubrication regulated by surface accumulation of lubricants and biphasic lubrication controlled by factors such as GAG content that affect water movement through the tissue. [source]

Measles virus nucleocapsid transport to the plasma membrane requires stable expression and surface accumulation of the viral matrix protein

Nicole Runkler
Summary In measles virus (MV)-infected cells the matrix (M) protein plays a key role in virus assembly and budding processes at the plasma membrane because it mediates the contact between the viral surface glycoproteins and the nucleocapsids. By exchanging valine 101, a highly conserved residue among all paramyxoviral M proteins, we generated a recombinant MV (rMV) from cloned cDNA encoding for a M protein with an increased intracellular turnover. The mutant rMV was barely released from the infected cells. This assembly defect was not due to a defective M binding to other matrix- or nucleoproteins, but could rather be assigned to a reduced ability to associate with cellular membranes, and more importantly, to a defective accumulation at the plasma membrane which was accompanied by the deficient transport of nucleocapsids to the cell surface. Thus, we show for the first time that M stability and accumulation at intracellular membranes is a prerequisite for M and nucleocapsid co-transport to the plasma membrane and for subsequent virus assembly and budding processes. [source]