Surprising acidity of hydrated lithium cations in organic solvents.

Lithium cations are shown to have a significant role in catalyzing oxygen and proton reduction along with S(N)1 reactions in biphasic systems. We propose that this catalytic effect is due to the surprising acidity of the hydrated cations; interactions between the cation and its surrounding solvation shell will make the constituent water molecules more acidic.

Towards a thermally regenerative all-copper redox flow battery.

An all-copper redox flow battery based on strong complexation of Cu(+) with acetonitrile is demonstrated, exhibiting reasonable battery performance. More interestingly, the battery can be charged by heat sources of 100 °C, by distilling off the acetonitrile. This destabilizes the Cu(+) complex, leading to recovery of the starting materials.

Ion-exchange and iontophoresis-controlled delivery of apomorphine.

The objective of this study was to test a drug delivery system that combines iontophoresis and cation-exchange fibers as drug matrices for the controlled transdermal delivery of antiparkinsonian drug apomorphine. Positively charged apomorphine was bound to the ion-exchange groups of the cation-exchange fibers until it was released by mobile counter-ions in the external solution. The release of the drug was controlled by modifying either the fiber type or the ionic composition of the external solution. Due to high affinity of apomorphine toward the ion-exchanger, a clear reduction in the in vitro transdermal fluxes from the fibers was observed compared to the respective fluxes from apomorphine solutions. Changes in the ionic composition of the donor formulations affected both the release and iontophoretic flux of the drug. Upon the application of higher co-ion concentrations or co-ions of higher valence in the donor formulation, the release from the fibers was enhanced, but the iontophoretic steady-state flux was decreased. Overall, the present study has demonstrated a promising approach using ion-exchange fibers for controlling the release and iontophoretic transdermal delivery of apomorphine.

Electrochemically controlled proton-transfer-catalyzed reactions at liquid-liquid interfaces: nucleophilic substitution on ferrocene methanol.

The generation of α-ferrocenyl carbocations from ferrocenyl alcohols for S(N)1 substitution at the water-organic solvent interface is initiated by the transfer of protons into the organic phase. The proton flux, and hence the reaction rate, can be controlled by addition of a suitable "phase-transfer catalyst" anion or by external polarization with a potentiostat, providing a new method for the synthesis of ferrocene derivatives.

Anomalous dependence of particle size on supersaturation in the preparation of iron nanoparticles from iron pentacarbonyl.

Iron nanoparticles were prepared by decomposing iron pentacarbonyl (Fe(CO)(5)) at 170-220°C in the presence of amine surfactant and alkane solvent and under 1-12 bar carbon monoxide (CO) pressure. It was found that the amine not only acted as a stabilizer for the growing particles but also had a critical role as a promotor in the decomposition reaction. Relatively small changes in the CO pressure had anomalous effects on the particle size distribution. Typically, monodisperse particles were obtained at 1 bar, while pressures in the 2-6 bar range led to wider and even bimodal size distributions due to an emergence of smaller particles. At still higher pressures, the larger particle size disappeared leaving the distribution monodisperse again. The CO pressure, at which the bimodal transition took place, increased with the reaction temperature. Polycrystalline particles were formed at lower pressures and monocrystalline particles at higher pressures. This indicates that increased CO pressure inhibits aggregation.

Hydrogen evolution across nano-Schottky junctions at carbon supported MoS2 catalysts in biphasic liquid systems.

The activities of a series of MoS(2)-based hydrogen evolution catalysts were studied by biphasic reactions monitored by UV/Vis spectroscopy. Carbon supported MoS(2) catalysts performed best due to an abundance of catalytic edge sites and strong electronic coupling of catalyst to support.

Biomimetic oxygen reduction by cofacial porphyrins at a liquid-liquid interface.

Oxygen reduction catalyzed by cofacial metalloporphyrins at the 1,2-dichlorobenzene-water interface was studied with two lipophilic electron donors of similar driving force, 1,1'-dimethylferrocene (DMFc) and tetrathiafulvalene (TTF). The reaction produces mainly water and some hydrogen peroxide, but the mediator has a significant effect on the selectivity, as DMFc and the porphyrins themselves catalyze the decomposition and the further reduction of hydrogen peroxide. Density functional theory calculations indicate that the biscobaltporphyrin, 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene, Co(2)(DPX), actually catalyzes oxygen reduction to hydrogen peroxide when oxygen is bound on the "exo" side ("dock-on") of the catalyst, while four-electron reduction takes place with oxygen bound on the "endo" side ("dock-in") of the molecule. These results can be explained by a "dock-on/dock-in" mechanism. The next step for improving bioinspired oxygen reduction catalysts would be blocking the "dock-on" path to achieve selective four-electron reduction of molecular oxygen.

A facile template-free approach to magnetodriven, multifunctional artificial cilia.

Flexible and magnetic artificial cilia were grown on various substrates by a facile bottom-up approach based on template-free magnetic assembly. The magnetic cilia formed spontaneously from a suspension of micrometer-sized ferromagnetic particles and elastomeric polymer in a liquid solvent when dried in an external magnetic field. The cilia mimics were mechanically stable even in the absence of an external magnetic field and a solvent due to the polymer, which acted as "glue" holding the particles together and connecting the cilia to the substrate. The length of the magnetic cilia was in the millimeter range, that is, two to three orders of magnitude times the length of typical biological cilia. The aspect ratio reached values over 100 and was tunable with the magnetic field gradient and the size of the ferromagnetic particles. The cilia mimics responded to an external magnetic field by reversibly bending along the field. The bending actuation was sufficiently powerful to allow two functions: to translate macroscopic nonmagnetic objects placed over the cilia mimics and to mix liquids of even high viscosity. The mechanical properties of the magnetic cilia could be easily tuned by changing the impregnating polymer. The particularly simple template-free construction and fixation on various surfaces suggest applications as an externally controllable surface.

Cobalt nanoparticle Langmuir-Schaefer films on ethylene glycol subphase.

The Langmuir-Schaefer (LS) technique was applied to prepare two-dimensional films of tridodecylamine (TDA)-stabilized Co nanoparticles. Ethylene glycol was used as the subphase because the Co nanoparticles spread better on it than on water. Surface pressure-area isotherms provided very little information on the floating films, and Brewster angle microscopy (BAM) was needed to characterize the film formation in situ. In addition to the subphase, various other experimental factors were tested in the LS film preparation, including solvent and presence of free TDA ligands and poly(styrene-b-ethylene oxide) (PS-b-PEO) in the nanoparticle dispersion. LS films deposited from dispersions from which the excess TDA ligands had been removed by washing the Co nanoparticles with 2-propanol consisted of hexagonally organized particles in rafts that were organized in necklace structures. The addition of PS-b-PEO to the deposition dispersion resulted in small nanoparticle rafts evenly distributed over the substrate surface. The best Co-nanoparticle-PS-b-PEO films were obtained with a mass ratio of 20:1 between Co (9 nm) and block copolymer (38 200 g/mol, PEO content 22 mass %). These films were successfully transferred onto Formvar-coated TEM grids and characterized by transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer. At room temperature the films showed superparamagnetic behavior with a saturation magnetization M(s) of 100 emu/g (Co). Our work indicates that it is possible to obtain thin superparamagnetic LS films of TDA-stabilized Co nanoparticles. This is an important result as the TDA-stabilized Co nanoparticles show a very good resistance to corrosion.

Directing oxidation of cobalt nanoparticles with the capping ligand.

The oxidation of Co nanoparticles stabilized with various ligands has been studied in an autoclave. Tridodecylamine stabilized Co nanoparticles with different sizes (8 nm, 22 nm and 36 nm) were prepared by thermal decomposition of Co(2)(CO)(8) in dodecane. The oxidation of the particles was studied by introducing oxygen into the autoclave and following the oxygen consumption with a pressure meter. Tridodecylamine capped particles were initially oxidized at a high rate, however, the oxidation layer quickly inhibited further oxidation. The thickness of the oxide layer estimated from the oxygen consumption was 0.8 nm for all three particle sizes showing that the oxidation is size independent in the studied particle size range. The tridodecylamine ligand was exchanged for various long chain carboxylic acids and the oxidation was studied. While the carboxylic acids give a slower initial oxidation rate, the formed oxide layer does not inhibit further oxidation as effectively as in the case of tridodecylamine. TEM studies show that tridodecylamine capping leads to particles with a metal core surrounded by an oxide layer, while particles capped with long chain carboxylic acids form hollow cobalt oxide shells.

Microcalorimetric and zeta potential study on binding of drugs on liposomes.

In this work, isothermal titration calorimetry (ITC) combined with zeta potential measurements was used to study the binding and partitioning of three beta-blockers, alprenolol, labetalol and propranolol, and the local anaesthetic tetracaine into liposomes. The thermodynamic parameters of enthalpy, entropy, the Gibbs energy and the binding constant were determined using the one site model. Furthermore, the binding constants corrected for the electrostatic contribution were used to assess the partition coefficients for the drugs. Also, the effect of the concentration, ionic strength, temperature and membrane curvature on the interaction was included in the evaluation.

Evolution of size distribution in pressure drop induced decomposition synthesis of cobalt nanoparticles.

Cobalt nanoparticles with average diameters of 8.8 nm and a standard deviation of 8% were obtained in a pressure drop induced decomposition synthesis in an autoclave. Samples were taken during the experiment and characterized with TEM. A significant narrowing of the size distribution coincident with particle growth was observed. The standard deviation decreased from 31% to 8% while the average size increased from 5.5 nm to 8.8 nm. In order to explain the experimentally observed narrowing of the size distribution, a model that accounts for the influence of the capping layer on the growth rate was developed. The transfer of the reacting monomer into the capping layer was considered to be similar to an adsorption process. A rate constant of 4x10(-5) cm(4) mol(-1) s(-1) was obtained for the growth reaction, and it was thus concluded that the growth reaction proceeds under kinetic control rather than under diffusion control.

Selective nanopatterning using citrate-stabilized Au nanoparticles and cystein-modified amphiphilic protein.

We present an approach where biomolecular self-assembly is used in combination with lithography to produce patterns of metallic nanoparticles on a silicon substrate. This is achieved through a two-step method, resulting in attachment of nanoparticles on desired sites on the sample surfaces, which allowed a detailed characterization. First, a genetically modified hydrophobin protein, NCysHFBI, was attached by self-assembly on a hydrophobic surface or a surface patterned with hydrophobic and hydrophilic domains. The next step was to label the protein layers with 17.8 nm gold nanoparticles, to allow microscopic characterization of the films. Kinetics and extent of attachment of nanoparticles were characterized by UV-vis spectroscopy and transmission electron microscopy. It was shown that the attachment of citrate-stabilized gold nanoparticles was strongly dependent on the electrostatic properties of the capping ligand layer and the density of nanoparticles in the monolayer could be controlled via pH. The resulting nanoparticle assemblies followed the original pattern created by optical lithography in high accuracy. We demonstrate that combining bottom-up and top-down nanotechnological approaches in a good balance can provide very effective ways to produce nanoscale components providing a functional interface between electronics and the biological world.

Studying the interactions of drugs and hydrophobic model membranes using contact angle goniometry.

This study demonstrates a method where contact angle goniometry combined with surface tension measurements is used to assess the interactions of drugs with the hydrophobic core of a biological membrane. To this end, self-assembled monolayers (SAMs) of two alkanethiol and one thiolipid on Au(111) surfaces are used as model membranes and their interaction with six beta-blockers is studied. The Gibbs equation and the Langmuir adsorption isotherm are used to determine the partition coefficients for the adsorption of the drugs, which are compared to the octanol-water partition coefficients as well as the liposome-water partition coefficients. The ability of the different SAMs to serve as model membranes in partitioning of drugs is discussed.

Controlled complexation of plasmid DNA with cationic polymers: effect of surfactant on the complexation and stability of the complexes.

The aggregation of the cationic polymer-plasmid DNA complexes of two commonly used polymers, polyethyleneimine (PEI) and poly-l-lysine (PLL) were systematically compared. The complexation was studied in 5% glucose solution at 25 degrees C using dynamic light scattering and isothermal titration calorimetry. The aggregation of the complexes was controlled by addition of the surfactant polyoxyethylene stearate (POES). The stability of the complexes was evaluated using dextran sulphate (DS) as relaxing agent. The relaxation of the complexes in the presence of DS was studied using agarose gel electrophoresis. This study elucidates the role of surfactant in controlling the size of the PEI/pDNA complex and reveals the differences of the two polymers as complexing agents.

Influence of ligand structure on the stability and oxidation of copper nanoparticles.

The stability and oxidation of copper nanoparticles stabilized with various ligands have been studied. Lauric acid-capped copper nanoparticles were prepared by a modified Brust-Schiffrin method. Then, ligand exchange with an excess of different capping agents was performed. Oxidation and stability were studied by UV-vis, XRD, and TEM. Alkanethiols and oleic acid were found to improve air stability. The oxidation resistance of thiol-capped copper nanoparticles was found to increase with the chain length of the thiol. However, excess thiol caused etching of the particles under nitrogen. With oleic acid no etching was observed under nitrogen. After oxidation, no traces of the ligand-exchanged particles were found, suggesting their dissolution due to excess ligand. Oleic acid protected the particles against oxidation better than the tested thiols at large excess (ligand-copper ratio 20:1).

Photoswitching electron transport properties of an azobenzene containing thiol-SAM.

The influence of conformational and electrical properties of azobenzene molecules on the electron transfer barrier properties of their SAMs was studied by SECM and ellipsometry.

Thermodynamic analysis of binding between drugs and glycosaminoglycans by isothermal titration calorimetry and fluorescence spectroscopy.

The thermodynamics of the interaction of positively charged drug molecules with negatively charged glycosaminoglycans (GAGs) is investigated by isothermal titration calorimetry (ITC) and fluorescence spectroscopy. The drugs considered are propranolol hydrochloride, tacrine, and aminacrine, and the polymers used as model GAGs are dextran sulfate, chondroitin sulfate, and hyaluronic acid. The ITC results show that the interaction between drugs and GAGs is via direct binding and that GAGs bind to drugs at one set of sites. Large negative values of heat capacity change (DeltaC(p)) are observed upon binding of GAGs to drugs. Such negative DeltaC(p) is not expected for purely electrostatic interactions and suggests that hydrophobic and other interactions may be also involved in the binding process. These results are corroborated by fluorescence spectroscopy measurements, which show that specific drug/GAG complex formation is accompanied by a clear enhancement of the fluorescence intensity. The results highlight the importance of the formation of drug/GAG complexes as a primary step for the drug delivery process into cell membranes. It is concluded that the interactions are dependent on the nature of both GAG and drug and this is a fact to be taken into account when new drugs are designed.

Gold nanoparticles enable selective light-induced contents release from liposomes.

A novel proof of principle demonstration for contents release from liposomes that can be selectively activated by light irradiation is presented. The content release temperature was adjusted to slightly above body temperature, and hydrophobic or hydrophilic gold nanoparticles were incorporated into the lipid bilayer or the core of the liposomes, respectively. The release of a fluorescent marker was monitored upon exposure of the liposomes to UV light. Gold nanoparticle-containing liposomes remained intact at 37 degrees C but contents release was triggered by UV light-induced heating of the gold nanoparticles. This light-induced release is mediated by heat transfer from the gold nanoparticles to the lipids and subsequent phase transition. Heating is highly localized in the liposomes and the gold nanoparticles act as energy collectors that sensitize the liposomes to the light signal. This kind of selectivity is very advantageous as it can potentially make the drug delivery mechanism biologically more compatible. The triggered contents release could also be extended to other applications where local contents release is needed.

Adsorption-penetration studies of glucose oxidase into phospholipid monolayers at the 1,2-dichloroethane/water interface.

The interaction between glucose oxidase (GOx) and phospholipid monolayers is studied at the 1,2-dichloroethane/water interface by electrochemical impedance spectroscopy. Electrochemical experiments show that the presence of GOx induces changes in the capacitance curves at both negative and positive potentials, which are successfully explained by a theoretical model based on the solution of the Poisson-Boltzmann equation. These changes are ascribed to a reduced partition coefficient of GOx and an increase of the permittivity of the lipid hydrocarbon domain. Our results show that the presence of lipid molecules enhances the adsorption of GOx molecules at the liquid/liquid interface. At low lipid concentrations, the adsorption of GOx is probably the first step preceding its penetration into the lipid monolayer. The experimental results indicate that GOx penetrates better and forms more stable monolayers for lipids with longer hydrophobic tails. At high GOx concentrations, the formation of multilayers is observed. The phenomenon described here is strongly dependent on 1) the GOx and lipid concentrations, 2) the nature of the lipid, and 3) the potential drop across the interface.