Spectroelectrochemical Analysis of Ion Transfer Mechanisms of Mitoxantrone at Liquid|Liquid Interfaces: Effects of Zwitterionic Dendrimer and Phospholipid Layer.

The ionic partition property and transfer mechanism of the anthraquinone antitumor agent mitoxantrone (MTX) were studied in detail at the water|1,2-dichloroethane (DCE) interface by means of surface-sensitive spectroelectrochemical techniques. The interfacial mechanism of the cationic MTX species was composed of potential-driven ion transfer and adsorption processes. The ion association between MTX and zwitterionic polyamidoamine (PAMAM) dendrimers with peripheral carboxy groups was also investigated in terms of the effects of pH and dendritic generation. The monovalent HMTX+ interacted effectively with the negatively charged dendrimers at neutral pH, while the divalent H2MTX2+ exhibited a weak association under acidic conditions. The higher stability of the dendrimer-MTX associates in the interfacial region was found for higher dendritic generations: G3.5 ≥ G2.5 > G1.5. The interfacial behavior of MTX and its dendrimer associates was further analyzed at the phospholipid-modified interface as a model biomembrane surface. The adsorption process of HMTX+ occurred mainly on the hydrophilic side of the phospholipid layer. The spectroelectrochemical results indicated that the dendrimers penetrate into the phospholipid layer and alter the transfer mechanism of HMTX+ across the interface.

Selective determination of formaldehyde by high-performance liquid chromatography with porous graphitic carbon column using N,N'-bis(9-anthrylmethyl)propane-1,3-diamine as derivatizing reagent.

Aromatic compounds containing two secondary amino groups were designed and prepared as new derivatizing reagents for aldehydes. One of them, N,N'-bis(9-anthrylmethyl)propane-1,3-diamine (APD), could achieve selective determination of formaldehyde (FA) on a porous graphitic carbon (PGC) column using xylenes, chlorobenzene, and 1-chloronaphthalene as mobile phases by high-performance liquid chromatography (HPLC). The APD-FA derivative was eluted from the PGC column, while the other APD-aldehyde derivatives remained on the column during the HPLC measurements. This specific elution was not observed using mobile phases such as acetonitrile, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, chloroform, benzene, toluene, benzyl alcohol, 2-ethyl-1-hexanol, and pyridine. The APD-FA derivative had a six-membered ring of two tertiary amines identified using 1H NMR spectroscopy. When the π-π interaction of the solvent molecule of the mobile phase with PGC overcame that between the APD-FA derivative and PGC, the APD-FA derivative could be eluted from the column. The best resolution between the peak of the APD-FA derivative and that of free APD was observed when using o-xylene. The optimum derivatization and the HPLC conditions for selective HPLC determination of FA were to conduct the derivatization of FA by heating in an aqueous phase with APD in o-xylene at 100 °C. In this method, FA could be derivatized with APD at a mildly neutral pH of 6.7, unlike the low pH required for the derivatization of aldehydes with 2,4-dinitrophenylhydrazine (DNPH), which is commonly used for the derivatization of aldehydes. The detection and quantification limits of FA were 0.8 and 3.5 ng mL-1 in this HPLC method with fluorescent detection, respectively. This selective HPLC method could be applied to the determination of FA in various water samples. It was found that only APD among the derivatizing reagents containing two secondary diamines was useful for the selective determination of FA.

Tetraphenylantimony(V)-assisted transfer of hydroxide and fluoride anions across the 1,6-dichlorohexane | water interface.

The ion-transfer reaction at the 1,6-dichlorohexane (DCH) | water (W) interface in the presence of an organometallic cation, tetraphenylantimony (TPhSb+), in DCH was studied voltammetrically. When TPhSb+ salt with [(C4F9SO2)2N]- ion was added to the DCH-phase and the W-phase was buffered at pH < 6, a reversible cyclic voltammogram due to the simple transfer of TPhSb+ ion across the DCH | W interface was observed within the polarizable potential window. When the W-phase was buffered at pH > 7, the midpoint potential shifted to more positive potentials with increasing pH. The voltammogram could be attributed to the transfer of the OH- ion assisted by the formation of TPhSbOH, which is stable in DCH. Also, a 7reversible voltammogram due to the TPhSb+-assisted transfer of F- ion was observed at the TPhSb+ (DCH) | F- (W, unbuffered) interfacial system. The same results were achieved when TPhSb[(C4F9SO2)2N] in DCH was replaced by TPhSbOH or TPhSbF, indicating the applicability of the TPhSb+ and TPhSbOH (DCH) | OH- (W) interfacial system to a pH sensor for alkaline solution and that of the TPhSb+ and TPhSbF (DCH) | F- (W) interface to a F- ion sensor.

Fluorination Effect on the Gibbs Transfer Energy for Methylene Group from 1,2-Dichloroethane or 1,1,1,2,3,4,4,5,5,5-​Decafluoropentane to Water.

The ion-transfer reactions of alkyl and perfluoroalkyl carboxylate ions (CH3(CH2)n-2COO- and CF3(CF2)n-2COO-) at 1,2-dichloroethane (DCE) | water (W) and 1,1,1,2,3,4,4,5,5,5-decafluoropentane (DFP) | W interfaces were investigated. These ions gave reversible or quasi-reversible voltammetric waves due to their ion transfer across the interfaces, and the formal potentials and the formal Gibbs transfer energies from a non-aqueous solvent to water, ΔG°'tr,α→W (α = DCE and DFP), were determined. The ΔG°'tr,α→W for CH3(CH2)n-2COO- and CF3(CF2)n-2COO- linearly increased with n, allowing for estimating ΔG°'tr,α→W for methylene groups. The estimated value of ΔG°'tr,DCE→W for the -CH2- group was higher than that of ΔG°'tr,DCE→W for the -CH2- group, whereas the ΔG°'tr,DCE→W for the -CF2- group was lower than that of ΔG°'tr,DCE→W for the -CF2- group, indicating that the -CH2- (or -CF2-) group is more favorably (or unfavorably) solvated in the DCE phase compared to the DFP phase. From the estimated values, the fluorination effect of alkyl chains on partitioning the alkyl group between the biphase media has also been discussed.

Spectroscopic Analysis of Apoferritin Associates with the Water-Soluble Porphyrins.

The association behavior of apoferritin species with the anionic porphyrins, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2 TPPS4- ) and its zinc(II) complex (ZnTPPS4- ), which are water-soluble even in acidic solutions, was investigated for the first time through UV-Vis absorption and fluorescence spectroscopy in order to evaluate a potential ability of apoferritin as a stimuli-responsive molecular capsule. The absorption maximum wavelengths of both porphyrins were redshifted and the fluorescence intensity decreased, indicating the effective association between apoferritin species and the porphyrins, although it depended on the pH adjustment procedure. At pH 2, the ZnTPPS4- associated with apoferritin subunits without demetallating and protonating, while the free base porphyrin formed the J-aggregate of the diprotonated species (H4 TPPS2- )n , with extremely low fluorescence. As the concentration of apoferritin subunits increased, the H2 TPPS4- -subunits associates were formed accompanied by recovering the fluorescence. The association stoichiometries of 1 or 2 subunits/porphyrin obtained under neutral and acidic conditions. The significantly large association constant of ZnTPPS4- as compared with that of H2 TPPS4- indicated that the coordination to the zinc(II) center strongly contributes to the association in addition to the electrostatic interaction between apoferritin subunits and the porphyrin under acidic conditions.

Photoinduced Electron Transfer of PAMAM Dendrimer-Zinc(II) Porphyrin Associates at Polarized Liquid|Liquid Interfaces.

The heterogeneous photoinduced electron-transfer reaction of the ion associates between NH2-terminated polyamidoamine (PAMAM) dendrimers and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato zinc(II) (ZnTPPS(4-)) was studied at the polarized water|1,2-dichloroethane (DCE) interface. The positive photocurrent arising from the photoreduction of ZnTPPS(4-) by a lipophilic quencher, decamethylferrocene, in the interfacial region was significantly enhanced by the ion association with the PAMAM dendrimers. The photocurrent response of the dendrimer-ZnTPPS(4-) associates was dependent on the pH condition and on the generation of dendrimer. A few cationic additives such as polyallylamine and n-octyltrimethyammonium were also examined as alternatives to the PAMAM dendrimer, but the magnitude of the photocurrent enhancement was rather small. The high photoreactivity of the dendrimer-ZnTPPS(4-) associates was interpreted mainly as a result of the high interfacial concentration of photoreactive porphyrin units associated stably with the dendrimer which was preferably adsorbed at the polarized water|DCE interface. The photochemical data observed in the second and fourth generation PAMAM dendrimer systems demonstrated that the higher generation dendrimer which can incorporate a porphyrin molecule more completely in the interior is less efficient for the photocurrent enhancement at the interface. These results indicated that the photoreactivity of ionic reactant at a polarized liquid|liquid interface can readily be modified via ion association with the charged dendrimer.

Communication: Coordination structure of bromide ions associated with hexyltrimethylammonium cations at liquid/liquid interfaces under potentiostatic control as studied by total-reflection X-ray absorption fine structure.

Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference (Δ(o)(w)φ). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br(-)-exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA(+) at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA(+), where the interfacial concentration of C6TA(+) is increased as a function of Δ(o)(w)φ.

Spectroelectrochemical characterization of dendrimer-porphyrin associates at polarized liquid|liquid interfaces.

Molecular encapsulation of anionic porphyrins in NH2-terminated polyamidoamine (PAMAM) dendrimers and the interfacial behavior of the dendrimer-porphyrin associates were studied at the polarized water|1,2-dichloroethane (DCE) interface. Formation of the ion associates was significantly dependent on the pH condition and on generation of dendrimers. 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS(4-)) associated with the positively charged fourth-generation (G4) PAMAM dendrimer was highly stabilized in acidic aqueous solution without protolytic demetalation in a wide range of pH values (pH > 2). In contrast to the zinc(II) complex, the free base porphyrin (H2TPPS(4-)) was readily protonated under acidic conditions even in the presence of the dendrimers. In addition, the J-aggregates of diprotonated species, (H4TPPS(2-))n, were preferably formed on the dendrimer. The interfacial mechanism of the dendrimer-porphyrin associates was analyzed in detail by potential-modulated fluorescence (PMF) spectroscopy. PMF results indicated that the dendrimers incorporating porphyrin molecules were transferred across the positively polarized water|DCE interface via adsorption step, whereas the transfer responses of the porphyrin ions released from the dendrimers were observed at negatively polarized conditions. A negative shift of the transfer potential of porphyrin ions compared to the intrinsic transfer potential was apparently observed for each ion association system. The ion association stability between the dendrimer and the porphyrin molecules could be estimated from a negative shift of the transfer potential. ZnTPPS(4-) exhibited relatively strong interaction with the higher generation dendrimer, whereas H2TPPS(4-) was less effectively associated with the dendrimers.

Development of a GC-MS system with an array detector system for endocrine disruptor analysis.

A mass spectrograph using a position sensitive detector was designed and constructed. It has an image contractor lens system and a zoom lens system. The position sensitive detector consists of a micro channel plate (MCP) and a charge-coupled device (CCD). The performance of this new instrument was tested with methylstearate as a sample.