Ion channel behavior of amphotericin B in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes investigated by electrochemistry and spectroscopy

Amphotericin B (AmB) is a popular drug frequently applied in the treatment of systemic fungal infections. In the presence of ruthenium (II) as the maker ion, the behavior of AmB to form ion channels in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes were studied by cyclic votammetry, AC impedance spectroscopy, and UV/visible absorbance spectroscopy. Different concentrations of AmB ranging from a molecularly dispersed to a highly aggregated state of the drug were investigated. In a fixed cholesterol or ergosterol content (5 mol %) in glassy carbon electrode-supported model membranes, our results showed that no matter what form of AmB, monomeric or aggregated, AmB could form ion channels in supported ergosterol-containing phosphatidylcholine bilayer model membranes. However, AmB could not form ion channels in its monomeric form in sterol-free and cholesterol-containing supported model membranes. On the one hand, when AmB is present as an aggregated state, it can form ion channels in cholesterol-containing supported model membranes; on the other hand, only when AmB is present as a relatively highly aggregated state can it form ion channels in sterol-free supported phosphatidylcholine bilayer model membranes. The results showed that the state of AmB played an important role in forming ion channels in sterol-free and cholesterol-containing supported phosphatidylcholine bilayer model membranes.

Electrochemical and Raman studies of the biointeraction between Escherichia coli and mannose in polydiacetylene derivative supported on the self-assembled monolayers of octadecanethiol on a gold electrode

Here, we describe a new method to study the biointeraction between Escherichia coli and mannose by using supramolecular assemblies composed of polydiacetylene supported on the self-assembled monolayer of octadecanethiol on a gold electrode. These prepared bilayer materials simply are an excellent protosystem to study a range of important sensor-related issues. The experimental results from UV-vis spectroscopy, resonance Raman spectroscopy, and electrochemistry confirm that the specific interactions between E. coli and mannose can cause conformational changes of the polydiacetylene backbone rather than simple nonspecific adsorption. Moreover, the direct electrochemical detection by polydiacetylene supramolecular assemblies not only opens a new path for the use of these membranes in the area of biosensor development but also offers new possibilities for diagnostic applications and screening for binding ligands.

Direct formation of form I poly(1-butene) single crystals from melt crystallization in ultrathin films

The morphologies and crystalline structures of melt-crystallized ultrathin isotactic poly(1-butene) films have been studied with transmission electron microscopy and electron diffraction. It is demonstrated that a bypass of form II crystallization can be achieved with an increase in its crystallization temperature. Electron microscopy observations show that melt-grown isotactic poly(1-butene) single crystals have a well-shaped hexagonal form, whereas form I crystals converted from form II display the morphologies of their tetragonal precursors. Electron diffraction results indicate that, instead of the twinned hexagonal pattern of the converted form I crystal, the directly formed form I single crystals exhibit an untwinned hexagonal pattern.

The chemical resolution of racemic cis-2-hydroxymethyl-5(cytosine-1 '-yl)-1,3-oxathiolane (BCH-189)-one direct method to obtain lamivudine as anti-HIV and anti-HBV agent

Racemic cis-BCH-189 can be resolved to (-)-enantiomer (lamivudine) and (+)-enantiomer by esterification of cis-2-hydroxymethyl-5-(N-4(')-acetylcytosine-1'-yl)-1,3-oxathiolane and (+)-menthyl chloroformate in CH3CN with pyridine as base. The two diastereomers of ester were seperated by recrystallization in methanol at 0degreesC. Lamivudine was obtained by deprotection of (-)-diastereomer with high yield.

In situ analysis of electropolymerization of aniline by combined electrochemistry and surface plasmon resonance

The combination of electrochemistry with surface plasmon resonance (SPR) has been used to characterize the growth of polyaniline (PAn) on a gold electrode surface during potential cycling. Potential-modulated SPR characteristics of the PAn film were also revealed. The potential switch between the oxidized and reduced states of PAn can lead to a large change of SPR response due to the variation in the imaginary part of the dielectric constant of PAn film resulting from the transition of the film in conductivity. The redox transition of the PAn film during potential cycling is very profitable to the SPR measurements. Two modes of SPR measurement, SPR angular scan (R-theta) and the time evolution of the reflectivity change at a fixed angle (R-t), were displayed to study the growth process of the PAn film. The angle shift of the resonance minimum recorded at each cathodic limit of cyclic potential scanning allows for the unambiguous measurement of the film growth. During cyclic potential scanning, the R-t curve was repeatedly modulated with the direction of the potential ramp as a result of the redox switch of the PAn film, and the amplitude of potential-modulated reflectivity change was well correlated with the cyclic number. The time differential of the R-t curve permits continuous monitoring of the film growth process. These results illustrate that the combined technique is suitable for studying the electropolymerization process of a conducting polymer.

Synthesis, 2D NMR, electrochemistry and luminescence of ruthenium(II) complexes with 2,2 '-bipyridine and 5-(omega-bromoalkylamido)-1,10-phenanthroline

The efficient synthesis of 5-(5-bromovaleramido)-1,10-phenanthroline, 5-(6-bromohexanamido)-1,10-phenanthroline, and 5-(11-bromoundecanamido)-1,10-phenanthroline are described, which reacted with cis-Ru(bpy)(2)Cl-2. 2H(2)O and sodium hexafluorophosphate to form Ru(bpy)(2)[phen-NHCO(CH2)(n)Br](PF6)(2) (n = 4, 5 or 10; phen = 1,10-phenanthroline). The intricate H-1 NMR spectra at low field of these complexes were completely assigned in virtue of H-1-H-1 COSY technique. Cyclic voltammetry was used to study electrochemical behaviours of these complexes, and their luminescent properties were investigated with fluorescent spectra.

Preparation, structures, and electrochemistry of a new polyoxometalate-based organic/inorganic film on carbon surfaces

The preparation, structure, and electrochemical and electrocatalytical properties of a new polyoxometalate-based organic/inorganic film, composed of cetyl pyridinum 11-molybdovanadoarsenate (CPMVA) molecules, have been studied. Cyclic potential scanning in acetone solution led to a stable CPMVA film formed on a highly oriented pyrolytic graphite (HOPG) surface. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used for characterizing the structure and properties of the CPMVA film. These studies indicated that self-aggregated clusters were formed on a freshly cleaved HOPG surface, while a self-organized monolayer was formed on the precathodized HOPG electrode. The CPMVA film exhibited reversible redox kinetics both in acidic aqueous and in acetone solution, which showed that it could be used as a catalyst even in organic phase. The CPMVA film remained stable even at pH > 7.0, and the pH dependence of the film was much smaller than that of its inorganic film (H4AsMo11VO40) in aqueous solution. The CPMVA film showed strong electrocatalysis on the reduction of bromate, and the catalytic currents were proportional to the square of the concentration of bromate. The new kind of polyoxometalate with good stability may have extensive promise in catalysis.

Synthesis, electrochemistry, and photophysics of a novel binuclear polypyridyl Ru ( II ) complex with an 1,8-adipoylamido-bis(1, 10-phenanthroline-5-yl) ligand

The present paper covers the syntheses of 1,8-adipoylamido-bis(1,10-phenanthroline-5-yl)(bphaa) and its binuclear complex {[(bpy)(2)Ru](2)(bphaa)} (PF6)(4), where bpy is 2,2'-bipyridine. The two novel compounds were confirmed by means of elemental analysis, IR, and LD-MS and H-1 NMR, and H-1 NMR spectra were completely assigned in virtue of H-1-H-1 COSY. chemical behavior of the binuclear Ru (I) complex was obtained using cyclic and voltammetry. Its photophysical property was investigated by electronic absorption, excitation and emission spectra.

Self-assembled monolayer of polyoxometalate on gold surfaces: Quartz crystal microbalance, electrochemistry, and in-situ scanning tunneling microscopy study

A new kind of inorganic self-assembled monolayer (SAM) was prepared by spontaneous adsorption of polyoxometalate anion, AsMo11VO404-, onto a gold surface from acidic aqueous solution. The adsorption process, structure, and electrochemical properties of the AsMo11VO404- SAM were investigated by quartz crystal microbalance (QCM), electrochemistry, and scanning tunneling microscopy (STM). The QCM data suggested that the self-assembling process could be described in terms of the Langmuir adsorption model, providing the value of the free energy of adsorption at -20 KJ mol(-1). The maximum surface coverage of the AsMo11VO404- SAM on gold surface was determined from the QCM data to be 1.7 x 10(-10) mol cm(-2), corresponding to a close-packed monolayer of AsMo11VO404- anion. The analysis of the voltammograms of the AsMo11VO404- SAM on gold electrode showed three pairs of reversible peaks with an equal surface coverage of 1.78 x 10(-10) mol cm(-2) for each of the peaks, and the value was agreed well with the QCM data. In-situ STM image demonstrated that the AsMo11VO404- SAM was very uniform and no aggregates or multilayer could be observed. Furthermore, the high-resolution STM images revealed that the AsMo11VO404- SAM on Au(lll) surface was composed of square unit cells with a lattice space of 10-11 Angstrom at +0.7 V (vs Ag\AgCl). The value was quite close to the diameter of AsMo11VO404- anion obtained from X-ray crystallographic study. The surface coverage of the AsMo11VO404- SAM on gold electrode estimated from the STM image was around 1.8 x 10(-10) mol cm(-2), which was consistent with the QCM and electrochemical results.

Protein structural characterization by scanning tunneling microscopy with electrochemistry

The structure characterization of proteins or enzymes by STM on electrochemically prepared HOPG surface studied in this laboratory is reviewed. The serial structures of Hb were observed. The differences between the denaturation and inactivation of HRP were investigated by in situ and ex situ STM. The structural variation of Hb in an organic solvent was imaged while protein denaturation was easily observed in a polar solvent.

Electrochemistry and spectroscopy study on the interaction of microperoxidase-11 with lipid membrane

The interaction of microperoxidase-11 (MP11) with cationic lipid vesicles of didodecyldimethylammonium bromide (DDAB) induces an alpha -helical conformation from random coil conformations in solution and this change then makes heme macrocycle more distorted. DDAB-induced MP11 conformations were investigated by cyclic votammetry (CV), circular dichroism (CD) and UV-vis spectrometry. All results indicate that the binding of MP11 in solution to DDAB vesicles and the ordered structure formation are driven by mostly electrostatic interaction between negatively charged residues in the undecapeptide and positively charged lipid headgroups on the membrane surface. Upon binding to DDAB, its half-peak potential was also changed. The mechanism of the interaction between MP11 and DDAB was also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

A novel electrochemical SPR biosensor

In this paper, we demonstrate for the first time that upon electrochemical oxidation/reduction, the transition in the conductivity of polyaniline (PAn) film on gold electrode surface leads to a large change of surface plasmon resonance (SPR) response due to a change in the imaginary part of dielectric constant of PAn film. Based on the amplifying response of SPR to the redox transformation of PAn film as a direct result of the enzymatic reaction between horseradish peroxidase (HRP) and PAn in the presence of H2O2, a novel PAn-mediated HRP sensor has been fabricated. The electrochemical SPR biosensor, unlike a usual binding assay with SPR, can afford a larger SPR response, and can also be reused by reducing the PAn film electrochemically to its reduced state. This method opens up a new route to the fabrication of SPR biosensor. (C) 2001 Elsevier Science BN. All rights reserved.

Electrochemistry and electrochemiluminescence of stable tris(2,2 '-bipyridyl)ruthenium(II) monolayer assembled on benzene sulfonic acid modified glassy carbon electrode

An electrochemically stable monolayer of tris(2,2'-bipyridyl)ruthenium(II) was obtained for the first time. It was based on the electrostatic attachment of Ru(bpy)(3)(2+) to the benzene sulfonic acid monolayer film, which was covalently bound onto glassy carbon electrode by the electrochemical reduction of diazobenzene sulfonic acid. The surface-confined Ru(bpy)(3)(2+) underwent reversible surface process, and reacted with the coreactant, tripropylamine, to produce electrochemiluminescence. In view of the stability of the electrode, the results strongly suggested that light was emitted from the surface-confined Ru(bpy)(3)(2+), not from the detached Ru(bpy)(3)(2+). The Ru(bpy)(3)(2+) modified electrode was used to the determination of tripropylamine. It showed good linearity in the concentration range from 5 muM to 1 muM with a detection limit of 1 muM (S/N = 4). The good stability of the Ru(bpy)(3)(2+) modified electrode also showed that the benzene sulfonic acid monolayer film prepared can be served as an excellent support to construct multilayers. (C) 2001 Elsevier Science B.V. All rights reserved.

Direct measurement of plowing friction and wear of a polymer thin film using the atomic force microscope

Nanometer-scale plowing friction and wear of a polycarbonate thin film were directly measured using an atomic force microscope (AFM) with nanoscratching capabilities. During the nanoscratch tests, lateral forces caused discrepancies between the maximum forces for the initial loadings prior to the scratch and the unloading after the scratch. In the case of a nanoscratch test performed parallel to the cantilever probe axis, the plowing friction added another component to the moment acting at the cantilevered end compared to the case of nanoindentation, resulting in an increased deflection of the cantilever. Using free-body diagrams for the cases of nanoindentation and nanoscratch testing, the AFM force curves were analyzed to determine the plowing friction during nanoscratch testing. From the results of this analysis, the plowing friction was found to be proportional to the applied contact force, and the coefficient of plowing friction was measured to be 0.56 +/- 0.02. Also, by the combination of nanoscratch and nanoindentation testing, the energetic wear rate of the polycarbonate thin film was measured to be 0.94 +/- 0.05 mm(3)/(N m).

Synthesis, electrochemistry, and fluorescence of two Ru(phen)(3)(2+)-based surfactants

Two new Ru(phen)(3)(2+)-based surfactants, Ru(phen)(2)(phenNHCO-C-11)(PF6)(2) and Ru(phen)(2)(phenNHCO-C-17)(PF6)(2), have been designed and synthesized, whose chemical structures were characterized by means of IR, H-1 NMR and MS. Also, electrochemistry and fluorescence of them are reported.