Phospholipid synthesizing enzymes of dermatophytes III. Glycerol kinase of dermatophytes

Glycerol kinase, the key enzyme for glycerol use in phospholipid synthesis, was identified in cytosolic fractions of 2 dermatophytes,Microsporum gypseum andEpidermophyton floccosum. Ammonium sulfate was observed to activate and stabilize this enzyme in both dermatophytes. Two pH optima, 8.0 and 10.5, were observed for both dermatophyte enzymes. Glycerol kinase fromM. gypseum was purified up to 33-fold with a 225% recovery by ammonium sulfate precipitation and gel filtration. The molecular weight of the enzyme was ca. 4.5×10⁵. It had 2 pH optima of 8.0 and 10.5. The enzyme had Km values of 0.35 mM and 2.3 mM for glycerol and ATP. Reactivity of the enzyme for various nucleotides was ATP>TTP>GTP>ITP=CTP=UTP. Kinetic studies showed the enzyme to catalyze the reaction by the ping-pong mechanism. Fructose 1,6-bisphosphate and glucose-6-phosphate inhibited the enzyme competitively, whereas glucose was not inhibitory.     

Fibrous support for immobilization of enzymes. II

A series of adsorption experiments was conducted with varying initial enzyme concentrations. The observed values are compared with the results calculated from the adsorption equations based on Langmuir adsorption mechanism. The values of three parameters, adsorption equilibrium constant K_a, maximum value of adsorbed enzyme per unit mass of SFF, N, and forward adsorption rate constant k_a, were determined from Langmuir adsorption equations and experimental data. In the initial enzyme concentration range below 100 (mg enz./dL), the simulated enzyme concentration vs. time curve agreed well with observed values. However, it was found that the adsorption in the higher concentration range was slow, and the corrected forward adsorption rate constant should be employed.     

Lipids of dermatophytes II. Effect of growth condition on the lipid composition and membrane transport ofMicrosporum gypseum

Supplementation of glucose-containing medium with ethanol and replacement of glucose by glycerol in the Sabouraud’s growth medium ofMicrosporum gypseum altered the levels of total phospholipids as well as their apolar and polar head groups. The levels of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) increased under these growth conditions; also, the ratio of unsaturated/saturated phospholipid fatty acids decreased on ethanol supplementation but increased in the presence of glycerol. Steady state accumulation of labelled amino acids (glycine, lysine and aspartic acid) was affected under these conditions.     

Insight into the inhibition of human choline kinase: homology modeling and molecular dynamics simulations

A homology model of human choline kinase (CK-alpha) based on the X-ray crystallographic structure of C. elegans choline kinase (CKA-2) is presented. Molecular dynamics simulations performed on CK-alpha confirm the quality of the model, and also support the putative ATP and choline binding sites. A good correlation between the MD results and reported CKA-2 mutagenesis assays has been found for the main residues involved in catalytic activity. Preliminary docking studies performed on the CK-alpha model indicate that inhibitors can bind to the binding sites of both substrates (ATP and choline). A possible reason for inhibition of choline kinase by Ca(2+) ion is also proposed.     

Orientation in amorphous polymers II. Characterization of orientation

A method based on network theory is developed for characterizing molecular orientation in amorphous polymers. The proposed procedure gives not only the orientation distribution function for the chain segments in the polymer network (and hence the average orientation) but also a quantitative measure of how this orientation is distributed among the various types of entanglement junctions. The orientation of chain segments can be characterized by two parameters, one which gives the average orientation and another which reflects how much orientation is concentrated in long time entanglement junctions. The new method of characterizing orientation is used to interpret tensile strength data for both brittle and ductile failures.     

Characterization of pressure-sensitive adhesives. II. Water vapor permeation studies

The permeability of water vapor in a composite film [a Mylar (trademark of DuPont, Inc.) film coated with a pressure sensitive adhesive on both sides] and a Mylar film (type D) have been determined at 23°C. The water vapor permeability in the pressure sensitive adhesive, Flexbond 150 (a trademark of Air Products and Chemicals), and the Mylar film have been found to be 3.23 × 10^?7 and 2.30 × 10^?8 cm³ (STP) cm · cm^?2 · s^?1 · (cm Hg)^?1, respectively, at 23°C.     

Bifurcation and chaotic behaviour of a coupled acetylcholinesterase/choline acetyltransferase diffusion-reaction enzymes system

A novel model is developed for the investigation of the dynamic and static characteristics of the cholinergic neurocycle. In its simplest form it involves a two-enzymes/two-compartments diffusion-reaction system. The bifurcation, instability and chaotic behaviour of this system are investigated with special emphasis on the neural transmission in human brain. Complex dynamic bifurcations, hysteresis, multiplicity, period doubling and period halving, as well as period adding and period subtracting dominate the dynamics of the system. The behaviour of the system using the acetylcholinestrase enzyme activity as the bifurcation parameter is strongly dominated by hysteresis and multiplicity phenomena, in which the neurotransmitter concentration in the postsynaptic cell changes dramatically for different parameter values. A detailed analysis of this behaviour may give an explanation for the phenomenology associated to Alzheimer disease. This type of work may help to stimulate new research directions on cholinergic brain diseases, such as Alzheimer and Parkinson.     

Characterization of fluoroelastomer networks: II. SEC,FTIR, and ODR analysis

The role of an accelerator in the nucleophilic cure of fluorocarbon compounds was further examined by preparing materials without a crosslinker. Under the previously used curing conditions, ODR reveals the formation of a secondary, accelerator-induced network that is unstable at slightly higher temperature, i.e., ≥190°C. Increased crosslink density and color are observed with the cure time, indicating slow curing reactions and likely formation of conjugated unsaturation. SEC of selective solvent-soluble fractions derived from specimens obtained from the key cure stages shows initially a falling refractive-index response. However, this change is followed by a shift in MWDs toward lower average molecular weights. On the other hand, infrared examination shows a continuous increase in the 1718 cm⁻¹ absorption, but no major presence for the 1680 cm⁻¹ absorption seen in the previous study in the presence of a crosslinker. The concurrent increase in the 3114 cm⁻¹ peak confirms the presence of a  CFCH double bond. The solvent-soluble portions and bulk specimens have very similar infrared features. © 1996 John Wiley & Sons, Inc.     

Characterization of carbon-carbon composites—II: Oxidation behaviour

Carbon-carbon composites made from ex-acrylic fibres and pyrocarbon matrices have been gasified in air in order to investigate their resistance to oxidation. The carbon fibres and the surrounding pyrocarbon layers are preferentially oxidized due to a catalytic process. The importance of the catalytic phenomenon depends primarly on the heat treatment of the composites. Lowest oxidation rates are obtained after heat treatment at 2900 K. Oxidation tests allow a simple evaluation of the carbon-carbon composites performance at the laboratory scale.     

Characterization of the efficiency of antiscale treatments of water. Part II: Physical processes

The efficiency of physical antiscale treatments of water was evaluated by various techniques, such as chronoamperometry, electrochemical impedance and chronoelectrogravimetry. It was found that the antiscale electrolytic treatment is more efficient than magnetic treatment, at least for the commercial devices used here, and that it also has a longer lasting effect. The electrolytic process generates CaCO3 nuclei in suspension in the bulk water, which provokes homogeneous scaling rather than heterogeneous scaling on the walls which is to be avoided. If the small crystals generated in the bulk are eliminated by filtration, surface scaling is again observed.     

Copper (II) Acylhydrazinates. Their Synthesis and Characterization

Acylhydrazine derived furanyl and thienyl Schiff bases and their Cu(II) complexes have been prepared and characterized on the basis of their physical, spectral and analytical data. The preferred enolic form of the Schiff base function as a tetradentate ligand during coordination to the metal ion yielding a square planar complex. The Schiff bases and their complexes with different anions were tested for their antibacterial activity against bacterial species such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa andKlebsiella pneumonae.     

Particle coagulation at semicontinuous emulsion polymerization. II. Characterization of surface groups

Semicontinuous emulsion polymerization of acrylic monomers with a monomer emulsion feed has been investigated. The amount of coagulum appearing during the polymerization under conditions of insufficient covering of particle surface by emulsifier was studied from the point of view of particle surface charge. Increasing the surface group concentration via copolymerization of butyl acrylate with acrylic acid or sulfoethyl methacrylate caused increased colloid stability of the system and a rapid decrease in coagulum formation. It was established that during the polymerization acid hydrolysis of ester groups took place, which caused an increase in the carboxyl groups concentration at the particle surface. These carboxyl groups contribute to the colloid stability of the polymerizing system.     

Confectionery fats. II. Characterization of products prepared by interesterification and fractionation

Several cocoa butter-like fats, which had been prepared by fractional crystallization of the reaction product obtained on interesterifying highly-hydrogenated cottonseed oil and a triolein product or olive oil, were characterized and compared with cocoa butter. The fats, as obtained by fractional crystallization from acetone solutions, contained varying amounts of glycerides melting above 37°C., an undesirable feature which caused the fats to thicken too much when used in chocolate type compositions under the same conditions employed with cocoa butter. The higher-melting glycerides could be removed by filtration, or their proportions could be decreased by changing the fractionation temperatures. The fats melted mostly over the same temperature range associated with cocoa butter, and the best of the fats resembled cocoa butter closely over the temperature range 0° to 30°C. The cocoa butter-like fats resembled cocoa butter in hardness at all test temperatures. The fats were reasonably compatible with cocoa butter, that is, in mixtures of the two, one did not cause extensive premelting of the other. According to their cooling curves, the cocoa butter-like fats did not supercool as cocoa butter does. The former contain not only the 2-oleodisaturated glycerides of cocoa butter but also positional isomers of these glycerides. When the fats were molded under the same conditions employed with cocoa butter, linear shrinkage was only about one-third that of cocoa butter.     

Engineering plastics from lignin II. Characterization of hydroxyalkyl lignin derivatives

Several types of hydroxyalkyl lignin derivatives were synthesized from milled wood, organosolv, steam explosion, acid (H₂SO₄) hydrolysis, and kraft lignin with ethylene oxide, propylene oxide, and butylene oxide by either batch reaction in toluene at 180°C using KOH as catalyst, or in aqueous alkali at room temperature. The isolated derivatives were characterized in terms of their chemical structures by H-NMR and FT-IR spectroscopy. Thermal properties were determined by differential scanning calorimetry. Molecular weights were measured by gel permeation chromatography on polystyrene/lignin model compound calibrated high pressure μ-spherogel columns. Solubilities in various organic solvents spanning a solubility parameter (δ) range from 9.3 to 14.5 and a hydrogen bonding index (γ) range from 1.5 to 18.7 were tested using UV₂₈₀ absorption of solutions of up to with degrees of substitution of between 1 and 2.6 (except for ethylene oxide derivatives which were higher) and with lignin contents of around 60%. The drastic reduction of glass transition temperature of between 50° and 100° is explained with increased free volume of the copolymer and with disruption of hydrogen bonds involving especially phenolic hydroxy groups. The greatly enhanced solubility in organic solvents indicates absence of the gel structure typical of network polymers. No molecular breakdown was observed as a consequence of oxyalkylation. The derivatives had molecular weights (M_w) of between 2000 and 50,000 at dispersity factors of between 2.5 and 25. The derivatives seem to constitute useful prepolymers for thermosetting engineering plastics.     

Polyvinyl alcohol-copper II complex: Characterization and practical applications

A method to obtain microscopic and macroscopic coatings with improved resistance to debonding is described. The procedure, based on polymer-metal complexes, involved the adsorption on inorganic substrates of a poly(vinyl alcohol)-copper II chelate that is also able to catalyze the polymerization of monomers or prepolymers with grafting. The molecular structure of the complex, its adsorption on inorganic surfaces, and the mechanism of the polymerization induced by the supported catalyst are summarized. Much emphasis is placed on application of this technology to the realization of encapsulated filler and pigment and of coatings with improved adherence and solvent resistance. In the field of composite materials, it is demonstrated from several examples that the encapsulation of the filler can be a way to block chemical interactions between filler and matrix, to promote filler dispersion, and to improve mechanical properties.     

Metal Chelates with Some Cellulose Derivatives. II. Preparation and Characterization of Co(II)-CMC Complexes

Complexes of three grades of sodium carboxymethyl cellulose (CMC) with cobalt(II) chloride have been prepared and characterized by elemental analysis, magnetic measurements, and infrared (IR) and electronic spectroscopy. The studies revealed that CMCs react with cobalt(II) in the stoichiometric ratio 1:1 (metal ion:ligand). The ligand field parameters of the octahedral Co(II) complexes were calculated. The stability of these complexes was studied in DMF medium using spectrophotometric methods. The optimum conditions favoring complex formation are critically evaluated.     

Characterization of Aluminum Powders: II. Aluminum Nanopowders Passivated by Non‐Inert Coatings

Results of DTA‐TG investigation and chemical analysis of electro‐exploded aluminum nanopowders, passivated and/or coated with the non‐inert reagents: nitrocellulose (NC), oleic acid (C₁₇H₃₃COOH) and stearic acid (C₁₇H₃₅COOH), which were suspended in kerosene and ethanol, amorphous boron, nickel, fluoropolymer, ethanol and air (for comparison), are discussed. Surface protection of aluminum nanopowders by coatings of different origin results in significant advantages in the energetic properties of the powders. Aluminum nanopowders with a protecting surface show increased stability to oxidation in nitrogen, air and in water during storage period. On the basis of the experimental results, a diagram of the formation and stabilization of the coatings is proposed. The kinetics of the interaction of aluminum nanopowders with nitrogen, air and water is discussed. Recommendations concerning the efficiency of non‐inert reagent passivation are proposed on the basis of comprehensive analysis of the experimental data.     

Characterization Of Water Quality Criteria for Ozonation Processes. Part II: Lifetime of Added Ozone

The lifetime value of ozone in a water is one of the key parameters for describing the characteristics of a water considering an ozonation process and for planning, optimizing, and steadily adapting the ozonation process. This lifetime is highly sensitive with respect to the chemical composition of the water. Interferences of different radical-type chain reactions make it difficultto predict it solely from analytical characterizations. The waters with respect to the lifetime of ozone, therefore, have to be characterized by direct laboratory experiments. However, because the half-life times depend on the type of operation used for the measurement, it is appropriate to formulate corresponding standardized guidelines that allow comparison whenever the responses of different waters have to be compared, and whenever characterizations have to be followed during the decades during which a water utility applies a process.     

PtSiO2: II. Characterization of the gel and the platinum particles by X-Ray diffraction

Modern techniques for analysis of X-ray diffraction profiles have been applied to several of the platinum-silica gel catalysts described in Part I to determine average platinum crystallite size, percentage exposed, crystallite shape, size distribution, lattice parameter, residual stresses and strains, presence or absence of faulting, and mean-square amplitude of vibration. In addition the surface area of the gel was determined with small-angle scattering (SAS). There is good agreement between the percentage exposed of platinum measured by gas adsorption in Part I and the results reported here, calculated from crystallite sizes, indicating the crystallite size is the true platinum particle size. Crystallites to sizes as small as ≈25 Å have been examined. Furthermore, the crystallites are equiaxed in shape (and definitely not cuboidal) and are strain and defect free, except in the case where the average size is near the pore size of the gel. Size distributions are sharper when the catalyst preparation is by impregnation rather than by ion exchange. The size distributions indicate that there is coalescence of some surface species during preparation rather than coarsening (Ostwald ripening). The meansquare amplitude of vibration of platinum increases by ≈30% as the particles decrease in size from ≈100 to ≈25 Å. There is no change in the lattice parameter greater than ≈0.1%. The gel surface areas determined by SAS are in agreement with those determined in Part I by physisorbtion of nitrogen.     

Phospholipid studies of marine organisms: 14. Ether lipids of the spongeTethya aurantia

The novel unesterified alkyl glycerol monoethers, (2S)-1-(hexadecyloxy)-2,3-propanediol (1), (2S)-1-(16-methylheptadecyloxy)-2,3-propanediol (2) and (2S)-1-(15-methylheptadecyloxy)-2,3-propanediol (3) were isolated from the marine spongeTethya aurantia and were characterized by spectroscopic methods. These three saturated ethers as well as a series of alk-1′-enyl glycerol monoethers were also encountered in the phospholipids of the same sponge after reduction with LiAlH₄. Incorporation experiments with dissociated cells ofT. aurantia indicated that [1-¹⁴C]-hexadecanol was incorporated into the unesterified alkyl glycerol monoethers. For preceding paper, see Ayanoglu, E., Düzgünes, N., Wijekoon, W.M.D., and Djerassi, C. (1986)Biochim. Biophys. Acta 863, 110–114.