Novel tris(2,2-bipyridine)ruthenium(II) cathodic electrochemiluminescence in aqueous solution at a glassy carbon electrode

A novel approach of generating cathodic electrochemiluminescence lof Ru(bpy)(3)(2+) at -0.4 V triggered by reactive oxygen species is reported for detecting alkylamines and some organic acids.

Conformational transition of DNA induced by cationic lipid vesicle in acidic solution: spectroscopy investigation

The conformational transition of DNA induced by the interaction between DNA and a cationic lipid vesicle, didodecyidimethylammonium bromide (DDAB), had been investigated by circular dichroism (CD) and UV spectroscopy methods. We used singular value decomposition least squares method (SVDLS) to analyze the experimental CD spectra. Although pH value influenced the conformation of DNA in solution, the results showed that upon binding to double helical DNA, positively charged liposomes induced a conformational transition of DNA molecules from the native B-form to more compact conformations. At the same time, no obvious conformational changes occurred at single-strand DNA (ssDNA). While the cationic lipid vesicles and double-strand DNA (dsDNA) were mixed at a high molar ratio of DDAB vesicles to dsDNA, the conformation of dsDNA transformed from the B-form to the C-form resulting in an increase in duplex stability (DeltaT(m) = 8 +/- 0.4 degreesC). An increasing in T-m was also observed while the cationic lipid vesicles interacted with ssDNA.

Electrochemiluminescence of dichlorotris (1,10-phenanthroline) ruthenium (II) with peroxydisulfate in purely aqueous solution at carbon paste electrode

The electrochemiluminescence (ECL) of dichlorotris (1,10-phenanthroline) ruthenium (11) [Ru(phen)(3)(2+)] with peroxydisulfate (S2O82-) was first described. The use of carbon paste electrodes, organic solvent modified electrodes, allowed obtaining ECL in purely aqueous solution. The ECL produced by the reaction of electrogenerated C Ru(phen)(3)(2+) with the strongly oxidizing intermediate SO4-., was observed only when the applied potential was negative enough to reduce Ru(phen)(3)(2+). In comparison with Ru(bpy)(3)(2+)/S2O82- ECL, the Ru(phen)(3)(2+)/O-8(2-)/S2O82- ECL was more stable in aqueous solution. It was not affected by the storage of the carbon paste electrodes, and it quenched only at quite high S2O82- concentrations. The ECL intensity was a function of S2O82- concentration, increasing linearly with the S2O82- concentration from 5 X 10(-6) to 2 X 10(-3) mol l(-1), and dropping off sharply at S2O82- concentration higher than 20 mmol l(-1). The proposed ECL method with Ru(phen)(3)(2+) was sensitive and selective for the determination of S2O82-. (C) 2002 Elsevier Science B.V. All rights reserved.

Statistical thermodynamics of polydisperse polymer systems in the framework of lattice fluid model: Effect of molecular weight and its distribution on the spinodal in polymer solution

With the aid of thermodynamics of Gibbs, the expression of the spinodal was derived for the polydisperse polymer-solvent system in the framework of Sanchez-Lacombe Lattice Fluid Theory (SLLFT). For convenience, we considered that a model polydisperse polymer contains three sub-components. According to our calculation, the spinodal depends on both weight-average ((M) over bar (w)) and number-average ((M) over bar (n)) molecular weights of the polydisperse polymer, but the z-average molecular weight ((M) over bar (z)) dependence on the spinodal is invisible. The dependence of free volume on composition, temperature, molecular weight, and its distribution results in the effect of (M) over bar (n) on the spinodal. Moreover, it has been found that the effect of changing (M) over bar (w) on the spinodal is much bigger than that of changing (M) over bar (n) and the extrema of the spinodal increases with the rise of the weight-average molecular weight of the polymer in the solutions with upper critical solution temperature (UCST). However, the effect of polydispersity on the spinodal can be neglected for the polymer with a considerably high weight-average molecular weight. A more simple expression of the spinodal for the polydisperse polymer solution in the framework of SLLFT was also derived under the assumption of upsilon(*)=upsilon(1)(*)=upsilon(2)(*) and (1/r(1)(0))-(1/r(2i)(0))-->(1/r(1)(0)).

The mild hydrothermal synthesis of complex fluorides of AZnF(3) (A = Na, K)

The complex fluorides of AZnF(3) (A = Na, K), which are isostructural with perovskite phases were obtained by the method of hydrothermal synthesis at 160-220 degrees C. Compared with traditional high-temperature solid-state method, the products were pure and contained lower amount of oxygen.

Electrochemiluminescence of the Ru(bpy)(3)(2+)/S(2)O(8)(2-)system in purely aqueous solution at carbon paste electrode

The electrochemiluminescence (ECL) of the Ru(bgy)(3)(2-)/S2O82- system in purely aqueous solution at a carbon paste electrode can be clearly seen with the naked eye for Ru(bpy)(3)(2+) concentrations higher than 1 mmol L-1. The log-log plot of the emmitted light intensity vs. Ru(bpy)(3)(2+) concentration is linear over the region 10(-3)-10(-7) mol L-1 with a correlation coefficient of 0.997. The ECL intensity increases linearly with the S2O82- concentration from 10(-6) mol L-1 up to 0.3 mmol L-1 and drops off sharply at concentrations higher than 1 mmol L-1. In addition, a weak ECL signal was obtained when the potential was biased more negative than -0.6 V even in the absence of S2O82-.

A study on the catalytic behaviors of concentrated heteropolyacid solution - I. A novel catalyst for isobutane alkylation with butene

The catalytic behaviors of a novel liquid acid catalyst (composed of heteropolyacid and acetic acid) for alkylation of isobutane with butene was investigated. As a solvent acetic acid had a synergistic effect. It enhanced the acid strength of HPA and its stability. The conditions for the formation of the catalytically active phase were studied systematically. The content of crystal water of HPA and the quantity of solvent affect the formation of active phase and the catalytic activity. Catalytically active phase consists of HPA, acetic acid and hydrocarbon produced from the reaction, as well as traces of water from the crystal water of HPA. This catalyst system is comparable to the sulfuric acid in catalytic activity.

Shear induced mixing/demixing: Blends of homopolymers, of homopolymers plus copolymers, and blends in solution

Shear may shift the phase boundary towards the homogeneous state (shear induced mixing, SIM), or in the opposite direction (shear induced demixing, SID). SIM is the typical behavior of mixtures of components of low molar mass and polymer solutions, SID can be observed with solutions of high molar mass polymers and polymer blends at higher shear rates. The typical sequence with increasing shear rate is SIM, then occurrence of an isolated additional immiscible area (SLD), melting of this island into the main miscibility gap, and finally SIM again. A three phase line originates and ends in two critical end points. Raising pressure increases the shear effects. For copolymer containing systems SID is sometimes observed at very low shear rates, preceding the just mentioned sequence of shear influences.

Electrochemiluminescent determination of peroxydisulfate with Cr(bpy)(3)(3+) in purely aqueous solution

A novel method for the sensitive and selective determination of peroxydisulfate was proposed. It was based on an electrochemiluminescent method with Cr(bpy)(3)(3+). The applied potential was set at -0.5 V in Cr(bpy)(3)(3+) system which was much more positive than those in Ru(bpz)(3)(2+) and Ru(bpy)(3)(2+) systems. A linear calibration was obtained over the range of 7-100 mu mol l(-1) with a correlation coefficient of 0.993. The relative standard deviation was 2% for 10 replicate injections of 0.01 mol l(-1) S2O82- solution. The detection limit (S/N=3) was 1 mu mol l(-1). The method was successfully applied to determination of peroxydisulfate in phase transfer catalysis. (C) 2000 Elsevier Science B.V. All rights reserved.

Studies of Gd-diethylenetriamine pentaacetic acid in boving serum albumin solution by nuclear magnetic resonance spectroscopy

In this paper, the water relaxation enhancement behavior of Gd-diethylenetriamine pentaacetic acid(DTPA) in water and in aqueous solution of bovine serum albumine(BSA) has been studied. The T-1 relaxivity of Gd-DTPA in BSA solution is higher than that in aqueous solution. The results indicate that Gd-DTPA can integrate non-covalently with BSA mainly in forms of (Gd-DTPA) . BSA, (Gd-DTPA)(2) . BSA, for which the apparent equilibrium constant is 0.026 mmol(-1).L,0.0018 mmol(-2).L-2 respectively. This method would be used to study the interactivities between protein and contrast agent.

Study of the catalytic behaviors of concentrated heteropolyacid solution. I. A novel catalyst for isobutane alkylation with butenes

A novel liquid acid catalyst, composed of heteropolyacid and acetic acid for the alkylation of isobutane with butenes is reported. The conditions for the formation of catalytic active phase as well as its catalytic behaviors in alkylation of isobutane with butenes have been studied. It was found that acetic acid, as a solvent, exerts a synergistic effect on the acid strength of heteropolyacid, and the contents of crystal water in HPAs have influence over the formation of active phase and the catalytic activity. This novel catalyst is comparable to the sulfuric acid in catalytic activity.

A heterogeneous catalytic kinetics for enzymatic biodegradation of poly(epsilon-caprolactone) nanoparticles in aqueous solution

Water insoluble poly(epsilon-caprolactone) (PCL) was micronized into narrowly distributed stable nanoparticles. The biodegradation of such PCL nanoparticles in the presence of the enzyme, Lipase PS, was monitored by using laser light scattering because the scattering intensity is directly related to the particle concentration. The PCL and enzyme concentration dependence of the biodegradation rate supports a heterogeneous catalytic kinetics in which we have introduced an additional equilibrium between the inactive and active enzyme/substrate complexes. The initial rate equation derived on the basis of this mechanism was used to successfully explain the influence of surfactant, pH and temperature on the enzymatic biodegradation. Our results confirmed that both the adsorption and the enzymatic catalysis were important for the biodegradation of the PCL nanoparticles. (C) 2000 Elsevier Science Ltd. All rights reserved.

Mild hydrothermal synthesis and optical properties of the complex fluoride KMgF3 doped with Eu

KMgF3 doped with Eu was synthesized by mild hydrothermal method at 240 degreesC for the first time. The excitation and emission spectra of the KMgF3 : Eu2+ phosphor were measured. Comparing with the sample synthesized through solid state reaction, the variation in the excitation spectra at 360 nm resulted from the existences of V-K color centers; the low emission intensity was due to Eu2+ having transferred part energy to V-K color centers.

Studies on the solution structures of lanthanide(III) complexes of DTPA-BIN by NMR

The solution structures of diamagnetic lanthanide (III) complexes of DTPA-BIN (Ln = La, Y, Lu, Sc) have been investigated by H-1 NMR, C-13 NMR and 2D NMR. For each complex, two or more species of asymmetric conformations with little distinction were identified at room temperature. And their solution structures vary with the radius of the central metals. NMR spectra support the hypothesis that Sc3+ with smaller radius formed an eight-coordinated structure with DTPA-BIN, La3+ with larger radius formed nine- or ten-coordinated structures with DTPA-BIN, and Y (DTPA-BIN) and Lu (DTPA-BIN) had nine-coordinated solution structures. The solution structure of Gd (DTPA-BIN) was obtained from the similarity of radius between Gd3+ and Y3+, which is a nine-coordinated structure formed by three nitrogens, three acetate oxygens, two acetyl oxygens, one water molecule and a gadolinium(III) cation.

Catalytic behavior of concentrated heteropolyacid solution in acylation of anisole with acetic anhydride

The catalytic behavior of concentrated heteropolyacid solution in acylation. of anisole with acetic anhydride has been investigated under the reaction conditions such as molar ratio of anisole to acetic anhydride, reaction temperature and mass ratio of reactant to catalyst. When the molar ratio of anisole to acetic anhydride is changed from 2:1 to 1:1, the yield of methoxyacetophenone (MOAP) increases a little, but when it is changed from 1: 1 to 1: 2, the yield has a greater increase from 15% to 30%. The yield of MOAP at the reaction temperature of 363 K doubles that at 333 K. The highest yield is obtained when the mass ratio of reactant to catalyst is 12.8. The conclusion is therefore that the heteropolyacid in acetic acid can effectively catalyze the acylation of anisole with acetic anhydride, and its activity and selectivity are comparable to those of acid clay and molecular sieve.