Mechanisms of sodium and potassium ions transfer facilitated by dibenzo-15-crown-5 across the water /1,2-dichloroethane interface using micropipettes

The transfer of sodium and potassium ions facilitated by dibenzo-15-crown-5 (DB15C5) has been studied at the micro-water/1,2-dichloroethane (water/DCE) interface supported at the tip of a micropipette. Cyclic volt-ammetric measurements were performed in two limiting conditions: the bulk concentration of Na+ or K+ in the aqueous phase is much higher than that of DB15C5 in the organic phase (DB15C5 diffusion controlled process) and the reverse condition (metal ion diffusion controlled process). The mechanisms of the facilitated Na+ transfer by DB15C5 are both transfer by interfacial complexation (TIC) with 1 : 1 stoichiometry under these two conditions, and the corresponding association constants were determined at log beta(1) = 8.97 +/- 0.05 or log beta(1) = 8.63 +/- 0.03. However, the transfers of K+ facilitated by DB15C5 show different behavior. In the former case it is a TIC process and its stoichiometry is 1 : 2, whereas in the latter case two peaks during the forward scan were observed, the first of which was confirmed as the formation of K (DB15C5)(2) at the interface by a TIC mechanism, while the second one may be another TIC process with 1 : 1 stoichiometry in the more positive potential. The relevant association constants calculated for the complexed ion, K+(DB15C5)(2), in the organic phase in two cases, logbeta(2), are 13.64 +/- 0.03 and 11.34 +/- 0.24, respectively.

Interactions of thiamine monophosphate (TMP) with one- and two-dimensional polymeric halogenomercurate anions. Crystal structures of (TMP)(Hg2Br5)center dot 0.5H(2)O and (TMP)(2)(Hg3I8)

An investigation into the interactions between thiamine monophosphate (TMP) and anions has resulted in the preparation and X-ray characterization of the compounds (TMP)(Hg2Br5).0.5H(2)O (1) and (TMP)(2)(Hg3I8) (2). In each compound the TMP molecule exists as a monovalent cation in the usual F conformation. The halogenomercurate anions occur in two-dimensional (2-D) network in 1 or one-dimensional (1-D) chain in 2. In both 1 and 2, the structures consist of alternating cationic sheets of the hydrogen-bonded TMP molecules and anionic sheets of the polymeric halogenomercurate anions. The TMP molecule binds to the polymeric anions through the characteristic 'anion bridge I', C(2)-H..X...pyrimidinium (X = Br in 1 and 1 in 2), and electrostatic interactions between electropositive S(1) and halogen atoms. The 'anion bridge II' of the type N(4'1)-H...X...thiazolium (X = phosphate group) plays a role in stabilizing the molecular conformation. The biological implication of the host-guest-like complexation between TMP and polymeric anions is discussed.

Investigation of ion transfer across the micro-water/nitrobenzene interface facilitated by a fullerene derivative

A functionalized fullerene derivative containing a monoaza-18-crown-6 moiety was investigated by facilitated ion (such as Li+, Na+, K+, NH4+, Mg2+, and Ca2+) transfer across the micro-water/nitrobenzene interface supported at the tip of a micropipet. The current responses were detected by cyclic voltammetry and Osteryoung square wave voltammetry, which demonstrated that the facilitated ion transfer does occur by an interfacial complexation-dissociation process. The diffusion coefficient of this compound in nitrobenzene was approximately (5.90 +/- 0.04) x 10(-7) cm(2) s(-1), which is 1 order of magnitude less than other common ionophores due to the large size of the molecule. The selectivity of this molecule toward the metal ions followed the sequence Na+ > Li+ > K+ > NH4+ > Ca2+ similar to Mg2+. In addition, this compound was also easy to form film at the water/nitrobenzene interface to inhibit the simple ion transfer of tetramethylammonium ion. However, the adsorption of this ionophore has less influence on the facilitated metal ion transfer.

Voltammetric study of the sodium ion transfer across micro-water/1,2-dichloroethane interface facilitated by terminal-vinyl liquid crystal crown ether

Sodium ion transfer across micro-water/1,2-dichloroethane (DCE) interface facilitated by a novel ionophore, terminal-vinyl liquid crystal crown ether (LCCE) was studied by cyclic voltammetry. LCCEs have potential applications because of their physicochemical properties and the utilization of crown ethers as selective ionophoric units in other functionalized compounds are interesting. Host-guest-type behavior for such compounds in the liquid-crystalline state is studied. The experimental results suggest that the transfer of the sodium ion facilitated by LCCE was controlled by diffusion of LCCE from bulk solution of DCE to the interface. The diffusion coefficient of LCCE in DCE was calculated to be equal to (3.62 +/- 0.20) x 10(-6) cm(2)/s. Steady-state voltammograms are due to sodium ion transfer facilitated by the formation of 1: 1 metal (M)-LCCE complex at the interface and the mechanism tends to be transfer by interfacial complexation or dissociation (TIC or TID). The stability constant of the complex formed was determined to be log beta(o) = 5.5 in DCE phase. The influence of parameters such as concentration of sodium ion and concentration of LCCE on the sodium ion transfer was investigated.

Effect and mechanism in compatibilization of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide) poly(ethylene-ran-acrylic acid) blends

The compatibilization effect of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer, P(S-b-EOx), on immiscible blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(ethylene-co-acrylic acid) (EAA) is examined in terms of phase structure and thermal, rheological and mechanical properties, and its compatibilizing mechanism is investigated by Fourier-transform infrared spectroscopy. The block copolymer, synthesized by a mechanism transformation copolymerization, is used in solution blending of PPO/EAA. Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion on addition of a small amount of P(S-b-EOx). Thermal analysis indicates that the grass transition of PPO and the lower endothermic peal; of EAA components become closer on adding P(S-b-EOx), and the added diblock copolymer is mainly located at the interface between the PPO and EAA phases. The interfacial tension estimated by theological measurement is significantly reduced on addition of a small amount of P(S-b-EOx). The tensile strength and elongation at break increase with the addition of the diblock copolymer for PPO-rich blends, whereas the tensile strength increases but the elongation at break decreases for EAA-rich blends. This effect is interpreted in terms of interfacial activity and the reinforcing effect of the diblock copolymer, and it is concluded that the diblock copolymer plays a role as an effective compatibilizer for PPO/EAA blends. The specific interaction between EAA and polar parts of P(S-b-EOx) is mainly hydrogen bonding. (C) 1998 Elsevier Science Ltd. All rights reserved.

C-13 NMR study on the aqueous structure of lanthanide citrate complexes

The aqueous complexation of lanthanide complexes of citrate in pH 7.4 solutions has been studied by using lanthanide-induced shift and relaxation times measurement methods. These results indicate that citrate coordinate via 3-hydroxyl and 3-carboxylate groups with lanthanide ions and form 1:2 (Ln/cit) isostructural complexes through lanthanide series. We suggest a new coordination geometry which is different from that described in literature.

STUDY ON ELECTROCATALYTIC OXIDATION OF NADH BY FERROCENE DERIVATIVES AND DETERMINATION OF CATALYTIC RATE-CONSTANT AT MICRODISK ELECTRODE

The electrocatalytic oxidation of NADH by ferrocene derivatives and the influence of complexation with beta-cyclodextrin (beta-CD) were investigated at a microdisk electrode in a buffer solution. The cyclic voltammetric behavior of the ferrocene derivatives on the microdisk electrode was used to determine the electron-transfer rate constant from NADH to the ferricinium species. The heterogeneous rate constants and the diffusion coefficient of ferrocene derivatives were determined with the microdisk electrode. The effect of temperature and pH on the electrocatalytic oxidation of NADH were assessed.

STUDY ON THE KINETIC PROCESS OF THE COMPLEX-REACTION BETWEEN BILIRUBIN AND CYCLODEXTRINS

The complex behavior of bilirubin (BR) with beta-CD (cyclodextrin) and gamma-CD in aqueous and dimethylformamide (DMF) solution was investigated by absorption spectroscopy and cyclic voltammetry, respectively. The data shows that the complexation mechanis

XPS Study of the Oxygen State in LaMnyCo1-yO3 Catalysts

A series of LaMnyCo1-yO3 compounds were prepared by the complexation method with citric acid. XPS was used to investigate the oxygen state in perovskite-type (ABO(3)) Complex oxide LaMnyCo1-yO3 catalysts. The result showed that three oxygen species (alpha

ELECTROCHEMICAL AND INSITU SPECTROELECTROCHEMICAL STUDY OF (TETRAPHENYLPORPHINATO)MANGANESE (III) PERCHLORATE IN THE PRESENCE OF CHLORIDE ANIONS .1. REDUCTION PROCESSES

The mechanism of electrochemical redox reactions of (tetra-phenylporphinato) managanese(III) perchlorate, (TPP)Mn(III)ClO4, was studied In the presence of chloride anions in dichloroethane solution. It was demonstrated that Mn(II) or Mn (III) centre can be coordinated with only one chloride anion, this result makes an about 100 mV negative shift of half-wave potential of Mn (III)/Mn (II) reduction. An equilibrium constant of 2.2 x 10(4) was determined for the complexation reaction of Cl- and Mn(III) centre.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CARBOXYLIC-ACIDS AND PHENOLIC-ACIDS WITH A COPPER-BASED CHEMICALLY-MODIFIED ELECTRODE

A copper-based chemically-modified electrode has been constructed and characterized by various experimental parameters in flow-through amperometric detection of carboxylic acids and phenolic acids. Novel hydrodynamic voltamperograms were first obtained in flow-through amperometric detection with the Cu-based CME and subsequently negative and positive peaks were observed in a single chromatogram. This unique and flexible potential dependence could be of great benefit in chromatographic speciation and quantification. These observations suggest that the detector response was governed by the complexation reaction of copper ions with the solutes.

Experimental study on the fractionation of yttrium from holmium during the coprecipitation with calcium carbonates in seawater solutions

The partitioning of Y and Ho between CaCO3 (calcite and aragonite respectively) and seawater was experimentally investigated at 25 degrees C and I atm. Both Y and Ho were observed to be strongly partitioned into the overgrowths of calcite or aragonite. Their partition coefficients, D-Y and D-Ho, were determined to be similar to 520-1400 and similar to 700-1900 in calcite, similar to 1200-2400 and similar to 2400-4300 in aragonite, respectively. Y fractionates from Ho during the coprecipitation with either calcite or aragonite. Within our experimental conditions, the fractionation factor, k = D-Y/D-Ho, was determined to be similar to 0.62-0.77 in calcite and similar to 0.50-0.57 in aragonite, respectively. The aqueous complexation of Y and Ho, which is a function of solution chemistry, probably plays an important role in both the partitioning and the fractionation. Further analyses suggest that the difference in covalency between Y and Ho associated with changes in their coordination environments is the determinant factor to the Y-Ho fractionation in the H2CO3-CaCO3 System.

Behavior of uranium in the Yellow River plume (Yellow river estuary)

The Yellow River (Huanghe) is the second largest river in China and is known for its high turbidity. It also has remarkably high levels of dissolved uranium (U) concentrations (up to 38 nmol l(-1)). To examine the mixing behavior of dissolved U between river water and seawater, surface water samples were collected along a salinity gradient from the Yellow River plume during September 2004 and were measured for dissolved U concentration, U-234:U-238 activity ratio, phosphate (PO43-), and suspended particulate matter. Laboratory experiments were also conducted to simulate the mixing process in the Yellow River plume using unfiltered Yellow River water and filtered seawater. The results showed a nonconservative behavior for dissolved U at salinities < 20 with an addition of U to the plume waters estimated at about 1.4 X 10(5) mol yr(-1). A similarity between variations in dissolved U and PO43- with salinity was also found. There are two major mechanisms, desorption from suspended sediments and diffusion from interstitial waters of bottom sediments, that may cause the elevated concentrations of dissolved U and PO43- in mid-salinity waters. Mixing experiments indicate that desorption seems more responsible for the elevated dissolved U concentrations, whereas diffusion influences more the enrichment of PO43-.

水环境中的溶解有机质及其与金属离子的相互作用——荧光光谱学研究

本论文通过选择这一国际前沿科学领域,主要运用三维荧光光谱仪、紫外-可见分光光度仪、溶解有机碳/氮分析仪、高效体积排阻色谱、荧光猝灭滴定等分析化学方法和手段,对云贵高原湖泊红枫湖、百花湖、洱海沉积物孔隙水以及一些河流等当中的DOM及其水化学特征进行了深入细致的研究,并且运用三维激发发射荧光光谱研究DOM中不同组分与Hg的相互作用,在溶解有机质的化学结构及其与金属汞的相互作用机理等方面取得了一些进展.