Solution behavior of ampholytic styrene ionomers

In this article are described the solution properties of ampholytic ionomers obtained by the radical copolymerization of styrene with the ion-pair comonomer 3-methacrylamidopropyltrimethylammonium, 2-acrylamido-2-methylpropanesulfonate. The solution properties were studied in mixed solvents, with a good solvent for the polystyrene backbone and another for the ionic moieties, and in the individual good solvent of benzyl alcohol. The data obtained strongly support extensive intermolecular ionic interactions in solution.     

On the structure-function relationship of nitrogenase M-cluster and P-cluster pairs

It A proposed that the M-cluster cage (Kim-Rees model) in active N₂-ase can exert shape-selective molecular-sieve effects in molecular recognition of exogenous substrates, by providing inside multinuclear active-sites the cavity for N₂, C₂H₂, cyclopropene, and N₂O reduction, with [Mo-3Fe]-site available only for N₂ reduction: on the other handn-RC— CH,n-RC— N,n-RN-C , C—N^– and N₃ ^–, are bound outside the cavity at the [2Fe]-site left by the labilizable ligand Y. A terminal carboxylate of the Mo-bound (R)-homocitrate is just in position to protect a H₂-evolution site on the P-cluster pair from CO inhibition, and also to take part in mediating a P-cluster-to-Mo-site H⁺-relay system (involving two hydrogen-bonded H₂O) specifically required for N. reduction. The nonreducibility of CO at the [Mo-3Fe]-site is also explained. Experimental support for molecular-sieve effects of M-cluster cage has been obtained from the observed decrease in ethene-cis-d: selectivity by competitive inhibition of HC—CH reduction in D₂O by N—N.Dedicated to Jiaxi Lu on the occasion of his 80th birthday.     

Synthesis of carbonate-containing high temperature poly(arylene-siloxanylenes)

A method for the first synthesis of high molecular weight carbonate-containing siloxanylene polymers was successfully developed. The procedure covered the preparation and polymerization of pure carbonate-containing bis-silanols which included bis(4-hydroxydimethylsilylphenyl)-carbonate, bis[4-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)-phenyl] carbonate, and their meta analogs. Because conventional siloxane polymerization methods, such as the heterocondensation of bis-silanols with diaminosilanes or homocondensation reactions catalyzed by alkali reagents, decomposed carbonate linkages, a new polymerization technique that involved the use of phosgene was used. The procedure was both facile and effective in the polymerization of other arylene bis-silanols.     

Determination of trace amounts of rare earth elements by neutron activation analysis after preconcentration using hydrated magnesium oxide

A preconcentration method of 13 rare earth elements (REES) was studied for neutron activation ananlysis (NAA). Hydrated magnesium oxide was used as the preconcentration agent to absorb the REES ions from aqueous solution onto the solid magnesium oxide, which was separated and analyzed. It was observed that the Langmuir equation for isothermal adsorption was well obeyed by the REES under the condition studied. The efficiency of the preconcentration process using hydrated magnesium oxide was critically examined for each of REE and for mixture of REES by preparing a known volume of solution containing known amount of trace REES. NAA was used to analyze REES recovered by the preconcentration process. It was found that the REES recoveries were satisfactory and the preconcentration process is reliable. There are several resort resort areas in Taiwan where local people are enjoying its hot spring water. It is generally believed that the hot spring water spa would bring about some sorts of therapeutic functions. The preconcentration method developed above, was applied to analyze the trace amounts of REES in hot spring wate in Taiwan.     

Evaluating adsorption ability of granite to radioselenium by chemical sequential extraction

A good understanding of the migration of selenite, Se(IV), through deep granitic layers depends on a good understanding of the geochemistry of these layers. Chemical sequential extraction is applied herein to evaluate the ability of granite to adsorb Se(IV) in DW, GW and SW systems. The experimental results indicate that the removal of crystalline Fe oxides reduces the adsorption of Se(IV), suggesting its importance in granite. The normalized concentrations of Se(IV) adsorbed onto crystalline Fe oxides is approximately 0.0301, 0.0330 and 0.0335 mole Se(IV) adsorbed/mole of Fe in DW, GW and SW systems. Kinetic adsorption experiments are conducted to elucidate the results of the chemical sequential extraction. Both the treated and the untreated granite take the same time to reach their equilibrium, suggesting that crystalline Fe oxides dominate the adsorption of Se(IV). Meanwhile, the one-site model suffices to simulate the kinetics of adsorption.     

The Crystal Structure of 1, 4, 7, 10- Tetraazacyclododecane Hydrate Triperchlorate

1=mTRODUCTIONMacroazacyclicligandisofwideinterestbecauseofitsstructuralsimilaritywiththeskeletonofPOrphyrinringinsomebibectivesubstancessuchaschlorophyllandhemeetc.tl1.Asametalsimulationenzyme,macroazacyclicligandcoordinatedwithtransitionmetalhasbeeninvestigatedthoroghlyinkinetic,dynamicandstructuralcharactert2.3).Butthere'isnorePOrtaboutthecrystalstructureof1,4,7,1o-tetraaza-cyclododecanehydratetriperchlorate.2EXPERIMENTAL2-lSynthesisoftheTitleComplexTetraazacycldodecanewassynthes…     

Electrochemical Detection of 2‐Naphthol at a Glassy Carbon Electrode Modified with Tosflex Film

In this study, a Tosflex (a perfluoro‐anion‐exchange membrane) modified glassy carbon electrode has been used to detect 2‐naphthalenol (2‐naphthol) in aqueous solutions in order to demonstrate the electroanalytical application of Tosflex. 2‐naphthol polymerizes upon electrochemical oxidation at a glassy carbon electrode; however, the current related to this oxidation is too small for analytical purpose at low concentration level. A Tosflex polymer modified glassy carbon electrode (TFGCE) was found of having capability to improve the detection limit because 2‐naphthol molecules deprotonated in basic solutions to form 2‐naphtholate anions that were accumulated to TFGCE by the anion‐exchange characteristic of Tosflex. The accumulated 2‐naphtholate anions were determined with the following differential pulse voltammetry. With 3 minutes accumulation at +0.05 V, the dependence of oxidation current versus concentration was linear from 8×10^?7 M to 1×10^?5 M with a regression coefficient of 0.999 and a detection limit of 2×10^?7 M. Unlike many other anion‐exchange polymer modified electrodes, the TFGCE is stable at highly basic condition.     

Determination of Thorium and Total Rare Earths in Monazite Sand with Fluoride Electrode

A new method has been proposed to determine the total rare earths and thorium in monazite sand with fluoride electrode. The total amount of thorium and rare earths could be determined by back-titration with standard lanthanum solution in excess fluoride, and the rare earths were titrated directly with fluoride from separate sample. Fluoride electrode was used as indicator electrode. Precision and accuracy were improved by Gran's plot technique.     

Ultraviolet difference spectroscopic study on the interactions of cellulase fromTrichoderma reesei with cellodextrins

The formation of cellodextrin-cellobiohydrolase complex was studied by ultraviolet difference spectroscopy. Upon the binding of cellodextrins (G₇‐G₃), cellobiohydrolase (EC 3.2.1.91) purified fromTrichoderma reesei produced difference spectra having maxima at 289‐293 nm and 283‐286 nm. These spectra are consistent with prior observations reported for lysozyme and amylase. In this case, water soluble cellulose oligomers (i.e., cellodextrins) are shown to interact with tryptophan residue(s) on cellobiohydrolase. The difference spectral maxima observed at acidic or alkaline pH were shifted. This was accompanied by a marked decrease of binding ability of cellobiohydrolase for cellodextrins. The standard free energy change for the association of cellodextrins to the cellobiohydrolase was an order of 4 kcal/gmol. The association constant of enzyme for substrate decreases by 15‐20% as temperature increases from 20 to 48°C. At 25°C, the dissociation constants for the enzyme with respect to cellohexose and cellotriose were estimated to be 1.19 and 1.37 mM, respectively. A decrease in dissociation constants was observed with an increase in the number of glucosyl units from 3 to 6. This suggests that there may be six or more subsites in the active center of cellobiohydrolase.     

Natural Product Chemistry: From Plants to Human

Conventionally, natural product chemistry deals with the isolation, characterization, and synthesis of compounds from plants. It a broad sense, natural product chemistry may include all fields of biochemistry. Two projects are presented to illustrate the expanded definition of natural product chemistry. One deals with phosphatidylinositol (PI) and the key enzyme involved in its metabolism, PI-specific phospholipase C. The other project is on the structure-function relationship of human tumor suppressor p16.