Effect of Showerhead Configuration on Coherent Raman Spectroscopically Monitored Pulsed Radio Frequency Plasma Enhanced Chemical Vapor Deposited Silicon Nitride Thin Films

The effect of showerhead design, number of holes and geometry, in a parallel plate reactor was studied by measuring the concentration of silane reactant by coherent anti-Stokes Raman scattering (CARS) spectroscopy as a function of radio frequency (rf) pulse width and peak power during pulsed power plasma enhanced chemical vapor deposition (PECVD) of silicon nitride thin films. Film deposition rate, stress, SiH/NH ratio, and thickness and index of refraction homogeneity were correlated with the change in silane concentration for each of the three head geometries: radial, square, and asymmetrical. The asymmetrical head caused plasma quality problems which affected the films' qualities. The square pattern showed good mixing qualities, but produced a film with high compressive stress. The radial head provided the most homogenous film, with respect to index of refraction and film thickness. With a 10 ms pulse width, however, the radial head plasma acted as a continuous plasma for depletion and stress data. The showerhead geometry affects plasma qualities, like stability and intensity, and reactant gas velocities, which in turn affect the nitride film thickness, nitride composition, and stress.     

Bioluminescent detection of insect pheromones using an enzyme-based flow injection analysis system

The combination of flow injection analysis with chemiluminescent detection is shown to provide extremely selective and sensitive detection of insect pheromones which possess an aldehyde moiety. The flow injection analysis system provides reproducible control of both the reaction chemistry and the sample introduction process. Microliter volume samples can be precisely handled and analyzed with this experimental configuration. The detection system is based on the luciferase-catalyzed oxidation of reduced flavin mononucleotide which occurs in the presence of aldehydes with carbon backbones of between 14 and 16 carbons. A limit of detection of 3 fmol of tetradecyl aldehyde is demonstrated and the system is shown to be insensitive to the presence of various organic solvents up to concentrations of approximately 10%. The key experimental variables which control sensitive detection of pheromone at the femtomole level with be investigated and discussed.     

Direct determination of free methionine in soy-based infant formula

A method was developed for the direct determination of free methionine in soy-based infant formula, with analyte separation and quantitation by reversed-phase liquid chromatography (LC), and UV absorbance at 214 nm, respectively. Sample preparation required only dilution with mobile phase and syringe filtration. Using a 0.02M KH2PO4 mobile phase (pH adjusted to 2.9 with 85% o-phosphoric acid) and 0.7 mL/min flow rate, methionine eluted at approximately 8 min, and total run time was 14 min after column regeneration with acetonitrile-water. System linearity was demonstrated as peak area versus analyte concentration, ranging from 80 to 120% of the formula specification for free methionine (r > 0.999, and all residuals < 0.45%). Intermediate precision relative standard deviation values were < 1.5% for ready-to-feed and reconstituted powder samples, and recoveries ranged from 98.0 to 103.5% for inter-method comparison with an amino acid analyzer method. The limit of quantitation was 3 mg methionine/L in the "as fed" infant formula. Despite the relatively weak UV absorptivity of methionine, the 214 nm signal was sufficiently intense in the 30-65 mg/L (201-436 microM) range to afford quantitation by peak area proportionation versus a 2-point external standard calibration. This direct UV detection after reversed-phase LC separation provides a simple and accurate method for determining free methionine without derivatization.     

Practical and highly selective oxazolidinethione-based asymmetric acetate aldol reactions with aliphatic aldehydes

[reaction: see text] The utility of a valine-derived oxazolidinethione for auxiliary-based asymmetric acetate aldol reactions is reported. Titanium(IV) chloride, along with (-)-sparteine and N-methylpyrrolidinone, is employed for enolization. Subsequent aldol reaction with aliphatic aldehydes occurs with high diastereoselectivity (from 92:8 to 99:1 dr).     

Chemical analysis of ceramic materials, containing uranium and plutonium, arising from the development of nuclear fuels

A comprehensive and critical review of analytical methods used in nuclear fuel technology.     

The photo- and electroinitiated polymerization of N-vinyl phthalimide

To elucidate mechanisms in electroinitiated polymerization reactions a comparison was conducted between ultraviolet (UV) photoinitiation and electroinitiation of N-vinyl phthalimide with zinc chloride as a catalyst. Both methods give low yields of a complex polymer product. A detailed analysis, infrared (IR), gel permeation chromatography (GPC), elemental, and molecular weight, conducted on the polymeric products, indicated that phthalimide ring opening was occurring and that complex mixtures of poly(N-vinyl phthalimide) derivatives were formed. Both initiation methods gave comparable results, which further indicated mechanistic similarity between photo-and electroinitiation in these donor–acceptor charge transfer polymerizations.     

Comparison of the photophysics of an aggregating and non-aggregating aluminium phthalocyanine system incorporated into unilamellar vesicles

The hydrophobic sensitizer, aluminium phthalocyanine chloride (AIPcCI), and the amphiphilic sensitizer, cis-disulphonated aluminium phthalocyanine (cis-AIPcS₂), were incorporated into small unilamellar vesicles (SUVs) and large unilamellar vesicles (LUVs). AIPcCI exhibits aggregation, which increases with increasing sensitizer concentration, whereas cis-AlPcS₂ is monomeric at all concentrations studied. Complex fluorescence decays are observed, showing decay time distributions which broaden with increasing phthalocyanine concentration. The phthalocyanine aggregate, although non-fluorescent, influences the overall photophysical behaviour of the phthalocyanine-vesicle system. The effect of aggregation on the resulting photophysics of phthalocyanines was investigated by comparing aggregated and non-aggregated phthalocyanine systems. The implications for photodynamic therapy (PDT) are briefly discussed.     

Gas Hydrate Formation in Reversed Micelles

We describe a technique to modify protein solubility and optimize enzyme activity in reversed micellar solutions. The technique is based on the ability of hydrates of natural gas to form in the micro-aqueous phase. Clathrate hydrates are crystalline inclusions of water and gas, and their formation in bulk water has traditionally been studied with relevance to natural gas recovery. We have found that hydrates can form in the environment of the microaqueous pools of reversed micelles, and that their extent of formation can be well controlled through the thermodynamic variables of temperature and pressure. Additionally, formation of hydrates affects the size and aggregation number of the micelles, and thus influences the solubility and conformation of encapsulated proteins. We demonstrate how the concept can be used in two applications: (i) protein extraction into reversed micelles and subsequent recovery, and (ii) optimization of enzyme activity in reversed micelles.