Modified Indigo Method For Gaseous And Aqueous Ozone Analyses

The indigo method developed by Bader and Hoigné for aqueous ozone analysis was modified to allow for both gaseous and aqueous ozone determination. Gas or water samples were extracted with a gas-tight syringe containing a known volume of indigo reagent. The modified procedure provided a more consistent basis for gaseous and aqueous ozone determination allowing for more accurate ozone mass balance calculations. Direct gaseous ozone UV absorbance with molar absorptivity of 3,000 M^?1cm^?1 at 258 nm was used as primary standard to determine the molar absorptivity of the indigo reagent. The molar absorptivity of indigo reagent, assuming a 1:1 stoichiometric ratio for the reaction between indigo and ozone, was determined to be 23,150 ± 80 M^?1cm^?1, or approximately 16 percent higher than that of 20,000 M^?1cm^?1 suggested by Bader and Hoigné. An independently calibrated membrane-electrode ozone monitor showed good correlation with indigo method results using the molar absorptivity value determined in this study. The apparent molar absorptivity of aqueous ozone at the wavelength of 258 nm measured by the modified indigo method increased from 2,400 to 3,600 M^?1cm^?1 in the investigated ozone concentration range of 0.4 to 11.0 mg/L. This variation might have been caused by the inherent interference of unidentified ozone byproducts, which presence was supported with scanning spectra in the wavelength range of 200 to 300 nm.     

Cholesterol transport and uptake in miniature swine fed vegetable and animal fats and proteis. 1. Plasma lipoproteins and LDL clearance

In a 2×2 factorial arrangement, miniature pigs were fed four diets containing vegetable protein/fat (soybean) and animal protein (egg white)/fat (beef tallow) to demonstrate the effects of protein and fat source on total plasma cholesterol, lipoprotein distribution, low density lipoprotein (LDL) composition, and plasma clearance of LDL-cholesterol and protein. Beef tallow consumption resulted in greater plasma cholesterol concentration, decreased LDL-cholesterol concentration, and a lower LDL-cholesterol to LDL-protein ratio than did consumption of soybean oil. High density lipoprotein (HDL)-cholesterol concentration was increased by beef tallow consumption. Cholesterol percentage by weight in LDL was significantly greater in pigs consuming soybean oil than those consuming beef tallow. Percentages by weight of protein, triglyceride and phospholipid in LDL were not significantly different in any group. Dietary protein source had no significant effect on total plasma cholesterol concentration, lipoprotein concentration or LDL composition. Egg white consumption decreased fractional catabolic rate and irreversible loss of LDL-cholesterol and LDL-protein when compared with consumption of soy protein. Dietary fat source had no consistent effect on LDL clearance from plasma. Dietary fat and protein seemed to influence lipoprotein metabolism by different mechanisms. Fat source altered lipoprotein concentration and LDL composition, whereas protein source affected the removal rate of LDL from plasma. Data taken from a dissertation submitted to Iowa State University by L. S. Walsh Hentges as partial fulfillment of the requirements for the Ph.D. degree. A preliminary paper, was presented at the meeting of the American Oil Chemists' Society in Dallas, Texas, May, 1984.     

Molecular sieve properties obtained by cracking of methane on activated carbon fibers

Molecular sieve properties of activated carbon fibers modified by cracking treatment with methane are studied herein. The effect of methane treatment on the porous texture of the samples has been studied while varying temperature and time. These materials have been evaluated for their selectivity during CO₂ and CH₄ separation; their uptakes have been compared with non-treated activated carbon fibers (studied previously), which were considered suitable to be used as molecular sieves. Kinetics of CO₂ and CH₄ uptake have also been investigated in this research. The treatment produced materials exhibiting fast kinetics and high selectivity during CO₂ and CH₄ separation; at the same time however, the CO₂ uptake capacity was diminished.     

Nanocoating individual cohesive boron nitride particles in a fluidized bed by ALD

Experiments are conducted with alumina (Al₂O₃) deposition on a wide size range of hexagonal boron nitride (BN) platelet-like particles. Successful deposition of alumina films on these particles, with film thickness controllable at the Angstrom level, is observed based upon TEM imaging, ICP-AES, particle size distributions, and surface area analysis. While fluidizing, fine BN particles aggregate in the bed. The aggregates are the entities fluidizing, not the primary particles. However, individual particles are coated using Atomic Layer Deposition (ALD), not aggregates. Since ALD is a surface chemistry phenomenon, the films grow uniformly on every primary particle. BN particles are small platelets with different functional groups on the basal planes and edge planes. A small exposure to reagents [2.5×10⁶ Langmuir (L) per reagent per cycle], will only coat the edge planes of uncoated BN particles. A larger dose of 1×10⁸ L will coat the entire uncoated BN particle (edge and basal planes). After 10 ALD cycles of the 1×10⁸ L dose, the exposures can be reduced to 1×10⁶ L as the film is then growing on alumina and not BN. Peel strength data indicate that adhesion between the coated particles and a cured epoxy in a filled composite is ∼25% stronger than that of uncoated particles and the epoxy. The overall thermal conductivity drops ∼17% for an identical filler loading as expected due to the additional thermal resistance added by the film. However, the viscosity of an epoxy resin loaded with coated BN is as much as five times lower than that of the resin loaded with the same amount of uncoated BN. These results indicate that the loading of Al₂O₃ nanocoated BN particles in an epoxy matrix can be substantially increased relative to that of uncoated particles. The thermal conductivity of the more highly filled composite will be increased without adversely impacting filled resin viscosity or the peel strength of the cured material. This is the first reported study indicating that cohesive primary particles that fluidize as aggregates in a fluidized bed can be individually coated with a nano-thick ceramic film using ALD.     

Effect of sample size on solvent extraction for detecting cocontinuity in polymer blends

The effect of sample size on the results of solvent extraction measurements for detecting cocontinuity in polymer blends was investigated. Poly(ethylene oxide)/polystyrene (PEO/PS) blend samples of several thicknesses were analyzed by removing the PEO phase using water extraction. The experimental degree of continuity was shown to have a linear dependence on the reciprocal of sample thickness. A model is proposed to explain this dependence and to allow the bulk or true degree of continuity to be determined. Measurement of the bulk degree of continuity is useful for understanding properties of cocontinuous polymer blends such as electrical conductivity, impact strength, or tensile strength.     

Cellulose-binding domains: potential for purification of complex proteins

The endoglucanase CenA and the exoglucanase Cex from Cellulomonasfimi each contain a discrete cellulose-binding domain (CBD),at the amino-terminus or carboxyl-terminus respectively. Thegene fragment encoding the CBD can be fused to the gene of aprotein of interest. Using this approach hybrid proteins canbe engineered which bind reversibly to cellulose and exhibitthe biological activity of the protein partner. Alkaline phosphatase(PhoA) from Escherichia coli, and a ß-glucosidase(Abg) from an Agrobacterium sp. are dimeric proteins. The fusionpolypeptides CenA-PhoA and Abg-CBC_cex are sensitive to proteolysisat the junctions between the fusion partners. Proteolysis resultsin a mixture of homo- and heterodimers; these bind to celluloseif one or both of the monomers carry a CBD, e.g. CenA-PhoA/CenA-PhoAand CenA-PhoA/PhoA. CBD fusion polypeptides could be used inthis way to purify polypeptides which associate with the fusionpartner.     

Characterization of polymer‐layered silicate (clay) nanocomposites by transmission electron microscopy and X‐ray diffraction: A comparative study

Several polymer‐layered silicate (clay) nanocomposites (PLSNs) were analyzed by transmission electron microscopy (TEM) and wide‐angle X‐ray diffraction (XRD) in an effort to characterize the nanoscale dispersion of the layered silicate. The PLSNs investigated included thermoset (cyanate esters) and thermoplastic polymers (polystyrene, nylon 6, and polypropylene‐g‐maleic anhydride). The results of this study reveal that the overall nanoscale dispersion of the clay in the polymer is best described by TEM, especially when mixed morphologies are present. XRD is useful for the measurement of d‐spacings in intercalated systems but cannot always observe low clay loadings (<5%) or be used as a method to identify an exfoliated nanocomposite where no XRD peaks are present (constituting a negative result). Most importantly, the study showed that XRD is not a stand‐alone technique, and it should be used in conjunction with TEM. Our studies suggest that new definitions, or a clarification of existing definitions, are needed to properly describe the diversity of PLSN nanostructures seen in various materials. Published 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1329–1338, 2003     

A model for studying LCAT reaction: In vitro cholesterol esterification in pig ovarian follicular fluid

Phosphatidylcholine acyltransferase (lecithin:cholesterol acyltransferase or LCAT; EC 2.3.1.43) activity was found to be present in pig ovarian follicular fluid (POFF), in addition to pig serum (PS). The cholesterol esterification rate in both POFF and PS is linear with incubation time up to 2 hr. The mean absolute rate of POFF-cholesterol esterification was 8.1±0.4 nmoles per ml per hr approximately one-fourth of that in PS. However, the fractional rate (percent of labeled cholesterol esterified per hr) of POFF-cholesterol esterification was similar to that observed in PS. There was little variation of absolute rate of cholesterol esterification in the fluid obtained from different sizes of follicles. Fatty acid or triacylglycerol did not participate in the reaction of cholesterol esterification in POFF. No appreciable change in enzymatic activity was found from storing POFF at 4 C for periods of time up to 24 hr or at −70 C up to 2 months, but activity was lost thereafter. On the other hand, PS showed a much longer period of stability (5 days at 4 C and 9 months at −70 C). A discrepancy between the fatty acid composition of cholesteryl esters formed by the LCAT reaction and the fatty acid composition at the C-2 position of phosphatidylcholine led us to propose a two-step mechanism for the LCAT reaction. It is concluded that the LCAT of POFF, as well as that of plasma, is specific for individual fatty acids rather than for the fatty acid composition of phosphatidylcholine. The fatty acid concentration of lysophosphatidylcholine decreased during prolonged incubation times (6 to 21 hr) suggesting that the increased lysophosphatidylcholine formed as a product of the LCAT reaction may be reused as substrate for the LCAT reaction or for hydrolysis by lysophosphatidylcholine hydrolase. Presented at the AOCS Meeting, New York, May 1977.     

Functionally substituted tetramethylcyclopentadienes: Synthesis of 1-(p-hydroxyphenyl)-2,3,4,5-tetramethylcyclopentadiene and its use in the synthesis of an organometallic polymer

Reaction of 2,3,4,5-tetramethylcyclopent-2-enone (1) withp-LiC₆H₄OC-Me₂OMe, followed by treatment with aqueous acid afforded 1-(p-hydroxyphenyl)-2,3,4,5-tetramethylcyclopentadiene (2). This new ligand was then used in the synthesis of the functionally substituted organomolybdenum reagent (⁵-C₅Me₄-p-C₆H₅OH)Mo(CO)₂(NO) (3). Treatment of a preformed 1/1 styrene/maleic anhydride copolymer ( ) with 5 mol% 3 led to chemical incorporation of the organometallic species into the polymer. The final product contained 3 mol% of the organometallic moiety.     

Microstructure, mechanical and tribological properties of Cr1−xAlxN films deposited by pulsed-closed field unbalanced magnetron sputtering (P-CFUBMS)

Nanocrystallized Cr_1−xAl_xN films with various Al contents (0 to 68 at.%) were deposited by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The effects of aluminum content on the microstructure, mechanical and tribological properties of the Cr_1−xAl_xN films have been investigated. It was found that the hardness and elastic modulus of Cr_1−xAl_xN films increased with increasing Al contents in the films and reached the highest value of 36 GPa and 370 GPa, respectively, at an Al content of 58.5 at.%. Addition of Al beyond 64.0 at.% resulted in a change in crystal structure from B1 cubic to B4 hexagonal phase. The wear resistance improved gradually with the increase of Al in the Cr_1−xAl_xN films. A combination of the abrasive and adhesive wear mechanism was proposed based on the SEM and EDS analysis of the wear track. The steady state dry coefficient of friction measured against a WC ball for the Cr_1−xAl_xN films were in the range of 0.36-0.55, and the wear rate was in the 10^− 6 mm³ N^− 1 m^− 1 range.