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Solution Interface (solution + interface)
Selected AbstractsA Colloidal Au Monolayer Modulates the Conformation and Orientation of a Protein at the Electrode/Solution InterfaceCHEMPHYSCHEM, Issue 8 2005Xiue Jiang Abstract The orientation and conformation of adsorbed cytochrome c (cyt c) at the interface between an electrode modified with colloidal Au and a solution were studied by electrochemical, spectroscopic, and spectroelectrochemical techniques. The results indicate that the colloidal Au monolayer formed via preformation of an organic self-assembled monolayer (SAM) can increase the electronic coupling between the SAM and cyt c in the same manner as bifunctional molecular bridges, one functional group of which is bound to the electrode surface while the other interacts with the protein surface. The approach of cyt c to the modified electrode/solution interface can be assisted by strong interactions of the intrinsic charge of colloidal particles with cyt c, while the heme pocket remains almost unchanged due to the screening effect of the negatively charged field created by the intrinsic charge. The conformational changes of cyt c induced by its adsorption at a bare glassy carbon electrode/solution interface and the effect of the electric field on the ligation state of the heme can be avoided at the colloidal-Au-modified electrode/solution interface. Finally, a possible model for the adsorption orientation of cyt c at the colloidal-Au-modified electrode/solution interface is proposed. [source] Charge and Mass Transfer Across the Metal/Solution InterfaceISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Eliezer Gileadi Electrode reactions are characterized by charge transfer across the interface. The charge can be carried by electrons or by ions. It is shown here that when both mass and charge cross the interface, the charge must be carried by the ionic species, not by the electrons, as a result of the very large difference in the time scale for electron and ion transfer. A prime example of charge transfer by ions is metal deposition. It is proposed that ion transfer occurs by migration of the ions across the interface, under the influence of the high electrostatic field in the double layer. The rate constants observed for metal deposition are comparable to those for outer-sphere charge transfer. These unexpectedly high rate constants for metal deposition are explained by a model in which removal of the solvation shell and reduction of the effective charge on the metal ion occur in many small steps, and a make-before-break mechanism exists, which lowers the total Gibbs energy of the system as it moves along the reaction coordinate from the initial to the final state. [source] Thermodynamic Modeling of Polymer Solution InterfaceMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2009Majid Ghiass Abstract A new method is presented to characterize the interfacial concentration field and interfacial tension between equilibrium polymer solution phases, using readily accessible equilibrium concentration data. The new method is tested and validated using experimental data from different polystyrene solutions and it consists of i) calculation of a universal expression for the concentration gradient coefficient based on the Cahn-Hilliard model and the Wolf interfacial tension master equation, and ii) development of a highly accurate algebraic function (Kappa distribution) that, for a given equilibrium polymer concentration set, yields the essentially exact interfacial profile predicted by the classical gradient theory for polymer solutions. [source] Polymer-Controlled Crystallization of Unique Mineral SuperstructuresADVANCED MATERIALS, Issue 4 2010Shao-Feng Chen Abstract The origin of complex superstructures of biomaterials in biological systems and the amazing self-assembly mechanisms of their emergence have attracted a great deal of attention recently. Mimicking nature, diverse kinds of hydrophilic polymers with different functionalities and organic insoluble matrices have been designed for the morphogenesis of inorganic crystals. In this Research News, emerging new strategies for morphogenesis and controlled crystal growth of minerals, that is, selective adsorption and mesoscale transformation for highly ordered superstructures, the combination of a synthetic hydrophilic polymer with an insoluble matrix, a substrate, or the air/solution interface, and controlled crystallization in a mixed solvent are highlighted. It is shown that these new strategies can be even further extended to morphogenesis and controlled crystallization of diverse inorganic or inorganic,organic hybrid materials with structural complexity, structural specialties, and improved functionalities. [source] Polymerization at the gas/solution interface: Preparation of polymer microstructures with gas bubbles as templatesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Maciej Mazur Abstract We report on the chemical polymerization of 2-methoxyaniline at the interface between an aqueous solution and air. The polymer is formed in the interfacial region, whereas the soluble trimer is yielded in the bulk of the polymerization solution. The preferential polymerization of 2-methoxyaniline is discussed in terms of monomer and oligomer accumulation at the interface, which influences the reactivity of these species and allows further polymerization. The phenomenon of polymer growth is employed to selectively deposit polymeric material onto glass slides decorated with gas microbubbles. Because of preferential polymerization at the bubble/solution interface, hemispherical features are produced on the surface of glass. When some polymeric material is mechanically removed, microrings or microholes are obtained. The anomalous polymerization of 2-methoxyaniline is compared to that of 2-methylaniline. This monomer polymerizes uniformly within the entire volume of the reaction mixture; thus, no preferential polymer formation at the gas/solution interface is observed. As a result, deposition on microbubble-decorated glass slides produces polymeric films containing a number of microholes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Autocatalytic Enantiomerisation at the Crystal Surface in Deracemisation of Scalemic ConglomeratesCHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009Shengwei Wei Dr. Abstract Deracemisation of racemic or scalemic conglomerates of intrinsically chiral compounds appears to be a promising method of chiral resolution. By combining the established methods of asymmetric synthesis and the physical process of crystal growth, we were able to achieve a complete deracemisation (with 100,%,ee) of an asymmetric Mannich product conglomerate,vigorously stirred in its saturated solution,from a starting enantiomeric excess value of 15.8,% in the presence of pyrrolidine (8,mol,%) as an achiral catalyst for the CC bond-forming reaction. Strong activation of this deracemisation process was observed on mild isothermal heating to only 40,°C, resulting in dramatic acceleration by a factor of about 20 with respect to the results obtained at room temperature. Despite the fact that the racemisation half-life time of the nearly enantiopure Mannich product (with 99,%,ee) in the homogenous solution at the reaction temperature is eight days, the deracemisation process took only hours in a small-scale experiment. This apparent paradox is explained by a proposed rapid enantiomerisation at the crystal/solution interface, which was corroborated by a 13C labelling experiment that confirmed the involvement of rapid enantiomerisation. Frequent monitoring of the solution-phase ee of the slowly racemising compound further revealed that the minor enantiomer dominated in solution, supporting an explanation based on a kinetic model. A generalisation of the process of "aymmetric autocatalysis" (resulting in automultiplication of chiral products in homogenous media) to encompass heterogeneous systems is also suggested. [source] Electrochemically-Induced Deposition of Amine-Functionalized Silica Films on Gold Electrodes and Application to Cu(II) Detection in (Hydro)Alcoholic MediumELECTROANALYSIS, Issue 19 2005Alain Walcarius Abstract Well-adherent amine-functionalized porous silica films have been deposited on gold electrodes by combining the self-assembly technology, the sol,gel process, and the electrochemical modulation of pH at the electrode/solution interface. A partial self-assembled monolayer of mercaptopropyl-trimethoxysilane (MPTMS) was first formed on disposable gold electrodes from recordable CDs (Au-CDtrodes). The so pretreated MPTMS-Au-CDtrodes were immersed in a stable sol solution (pH,3) containing (3-aminopropyl)-triethoxysilane (APTES) and tetraethoxysilane (TEOS). Polycondensation of the APTES and TEOS precursors was then achieved by applying a negative potential for a given period of time to generate a local pH increase at the electrode/solution interface and promote the deposition of the amine functionalized silica film adhering well to the electrode surface owing to the MPTMS monolayer acting somewhat as a "molecular glue". Various parameters affecting the electrodeposition process have been studied and the film permeability to redox probes in solution was characterized by cyclic voltammetry. The amine-functionalized silica film electrodes were then applied to the preconcentration of copper(II) species prior to their electrochemical detection by anodic stripping differential pulse voltammetry. Getting high sensitivity has however required the application of an electrochemical pre-activation step as the majority of the organo-functional groups were in the form of ammonium moieties (because the film was prepared from an acidic sol). This was achieved by applying a sufficiently negative potential to the electrode surface to reduce protons and increase consequently the amine-to-ammonium ratio within the film and, thus, the efficiency of the precocentration process. The resulting device was then optimized for copper(II) determination in hydroalcoholic medium, giving rise to a linear response in the 0.1,10,,M concentration range. [source] Electroactive Films of Multicomponent Building Blocks,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2007I. Yildiz Abstract A ligand consisting of a 2,2,-bipyridine core and two 4,4,-bipyridinium arms terminated by a thiol group is prepared following a multistep synthetic procedure. Two of these ligands assemble around a single CuI center as a result of the tetrahedral coordination of their 2,2,-bipyridine cores by the metal. Both the ligand and the complex adsorb spontaneously on the surface of polycrystalline-gold electrodes. The surface coverage of the films prepared by immersing a gold substrate into a solution of the ligand increases from monolayer to multilayer values with immersion time. Instead, the complex can only form monolayers. The cyclic voltammograms of the resulting films show the characteristic response for the reversible reduction of the 4,4,-bipyridinium dications to their radical cations. In the case of the complex, a wave for the monoelectronic oxidation of the metal center can also be observed. The back reduction wave, however, is markedly broader and appears at significantly lower potentials. Model studies in solution indicate that this response is a result of the presence of free thiol groups and is consistent with a change in the coordination geometry of the metal. Specifically, the oxidation of the CuI center to a CuII ion is, presumably, accompanied by the folding of one of the thiol groups back to interact with the metal. Thus, oxidation/reduction cycles of the metal center can, in principle, be exploited to control reversibly large amplitude molecular motions at the electrode/solution interface in the shape of the folding/unfolding of oligomethylene chains. [source] A Colloidal Au Monolayer Modulates the Conformation and Orientation of a Protein at the Electrode/Solution InterfaceCHEMPHYSCHEM, Issue 8 2005Xiue Jiang Abstract The orientation and conformation of adsorbed cytochrome c (cyt c) at the interface between an electrode modified with colloidal Au and a solution were studied by electrochemical, spectroscopic, and spectroelectrochemical techniques. The results indicate that the colloidal Au monolayer formed via preformation of an organic self-assembled monolayer (SAM) can increase the electronic coupling between the SAM and cyt c in the same manner as bifunctional molecular bridges, one functional group of which is bound to the electrode surface while the other interacts with the protein surface. The approach of cyt c to the modified electrode/solution interface can be assisted by strong interactions of the intrinsic charge of colloidal particles with cyt c, while the heme pocket remains almost unchanged due to the screening effect of the negatively charged field created by the intrinsic charge. The conformational changes of cyt c induced by its adsorption at a bare glassy carbon electrode/solution interface and the effect of the electric field on the ligation state of the heme can be avoided at the colloidal-Au-modified electrode/solution interface. Finally, a possible model for the adsorption orientation of cyt c at the colloidal-Au-modified electrode/solution interface is proposed. [source] Polymerization at the gas/solution interface: Preparation of polymer microstructures with gas bubbles as templatesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Maciej Mazur Abstract We report on the chemical polymerization of 2-methoxyaniline at the interface between an aqueous solution and air. The polymer is formed in the interfacial region, whereas the soluble trimer is yielded in the bulk of the polymerization solution. The preferential polymerization of 2-methoxyaniline is discussed in terms of monomer and oligomer accumulation at the interface, which influences the reactivity of these species and allows further polymerization. The phenomenon of polymer growth is employed to selectively deposit polymeric material onto glass slides decorated with gas microbubbles. Because of preferential polymerization at the bubble/solution interface, hemispherical features are produced on the surface of glass. When some polymeric material is mechanically removed, microrings or microholes are obtained. The anomalous polymerization of 2-methoxyaniline is compared to that of 2-methylaniline. This monomer polymerizes uniformly within the entire volume of the reaction mixture; thus, no preferential polymer formation at the gas/solution interface is observed. As a result, deposition on microbubble-decorated glass slides produces polymeric films containing a number of microholes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Radical clocks and electron transfer.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2005Comparison of crown ether effects on the reactivity of potassium, magnesium towards 1-bromo-2-(3-butenyl)benzene. Abstract The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis -dicyclohexano-18-crown-6 or tert -butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia,33% tert -butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal,solution interface. More specifically, the non-observation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright © 2005 John Wiley & Sons, Ltd. [source] Bioadhesive Properties of a Polyaminoacidic Hydrogel: Evaluation by ATR FT-IR SpectroscopyMACROMOLECULAR BIOSCIENCE, Issue 7 2005Filippo Saiano Abstract Summary: The bioadhesive properties of a novel chemical hydrogel based on a polymer of protein-like structure, have been investigated by using ATR FT-IR spectroscopy. In particular, the copolymer PHG obtained by partial derivatization of PHEA with GMA was chemically crosslinked by UV irradiation at 313 nm. Crosslinked PHG was treated with water to obtain a swelled sample, named PHG-UV gel, that was brought into contact with a phosphate buffer/citric acid solution at pH 7.0 in the absence or in the presence of mucin at various concentrations (0.01, 0.1 and 1 wt.-%). Preliminary dynamic swelling studies have evidenced the occurrence of an interaction between the PHG-UV gel and the glycoprotein. This result was confirmed by ATR FT-IR measurements. A diffusion model using a solution of Ficks' second law was employed to determine the diffusion coefficient of water into PHG-UV gel as a consequence of adsorption and/or interdiffusion which occur at the PHG-UV gel/mucin solution interface. Experimental results suggest a potential use of PHG-UV gel to prepare bioadhesive devices. [source] Self-Assembly of an Alkylated Guanosine Derivative into Ordered Supramolecular Nanoribbons in Solution and on Solid SurfacesCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2007Stefano Lena Dr. Abstract We report on the synthesis and self-assembly of a guanosine derivative bearing an alkyloxy side group under different environmental conditions. This derivative was found to spontaneously form ordered supramolecular nanoribbons in which the individual nucleobases are interacting through H-bonds. In toluene and chloroform solutions the formation of gel-like liquid-crystalline phases was observed. Sub-molecularly resolved scanning tunneling microscopic imaging of monolayers physisorbed at the graphite,solution interface revealed highly ordered two-dimensional networks. The recorded intramolecular contrast can be ascribed to the electronic properties of the different moieties composing the molecule, as proven by quantum-chemical calculations. This self-assembly behavior is in excellent agreement with that of 5,- O -acylated guanosines, which are also characterized by a self-assembled motif of guanosines that resembles parallel ribbons. Therefore, for guanosine derivatives (without sterically demanding groups on the guanine base) the formation of supramolecular nanoribbons in solution, in the solid state, and on flat surfaces is universal. This result is truly important in view of the electronic properties of these supramolecular anisotropic architectures and thus for potential applications in the fields of nano- and opto-electronics. [source] Interaction of Cytidine 5,-Monophosphate with Au(111): An In Situ Infrared Spectroscopic StudyCHEMPHYSCHEM, Issue 9-10 2009Thomas Doneux Dr. Abstract Attracted to gold: The interaction of cytidine 5,-monophosphate (CMP) with gold surfaces is studied at the Au(111) | aqueous solution interface. In situ infrared spectroscopy studies show that cytidine 5,-monophosphate is chemisorbed on Au(111) through the N3 atom of the pyrimidine ring (see picture). The interaction of cytidine 5,-monophosphate (CMP) with gold surfaces is studied by means of in situ infrared spectroscopy and cyclic voltammetry at the Au(111) | aqueous solution interface. Similar to other nucleic acid components, cytidine 5,-monophosphate is chemisorbed on the surface at positive potentials, and the amount of adsorbed CMP increases with the potential. Subtractively normalized interfacial Fourier-transform infrared spectroscopy (SNIFTIRS) is used to identify the adsorbed and desorbed species. Upon electrochemical desorption, the molecules released in solution are unprotonated on the N3 atom. Striking similarities are found between the spectrum of adsorbed CMP and the solution spectrum of protonated CMP. The origin of such similarities is discussed. The results strongly suggest that chemisorption occurs through the N3 atom of the pyrimidine ring. A comparison is drawn with cytidine, whose electrochemical and spectroscopic behaviors are also investigated. [source] A New Method for the Study of Processes at the Liquid,Liquid Interface Using an Array of Microdroplets on a Au ElectrodeCHEMPHYSCHEM, Issue 12 2006Andrew O. Simm Dr. Abstract We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally spaced inert hydrophobic blocks on their surface. The hydrophobic blocks, with diameters of 5 ,m, are used to support liquid 5-nonyl-salicylaldoxime (Acorga-P50) droplets on the surface. By voltametrically monitoring the transport-controlled reduction rate of CuII (in pH 5 solution) at the unblocked part of the gold surface it is possible to deduce, via simulation, the parameters controlling the rate of uptake of CuII at the droplet,aqueous solution interface as the droplet "fills up" with CuII. Experimentally, it is recorded that the reduction current increases until the droplet is filled completely; after this, there is no further noticeable effect of the droplet coating. A rigorous theoretical analysis of the transients permits the deduction of partition coefficients between the aqueous solution and the organic-droplet phase and of diffusion coefficients within the droplet. The partition coefficient for CuII between water and 5-nonyl-salicylaldoxime was found to be 200 at 25,°C and the diffusion coefficient of CuII inside the organic phase was determined to be 5×10,11 cm2,s,1. [source] Supramolecular Crystal Engineering at the Solid,Liquid Interface from First Principles: Toward Unraveling the Thermodynamics of 2D Self-AssemblyADVANCED MATERIALS, Issue 13 2009Carlos-Andres Palma Abstract The formation of highly ordered 2D supramolecular architectures self-assembled at the solid,solution interfaces is subject to complex interactions between the analytes, the solvent, and the substrate. These forces have to be mastered in order to regard self-assembly as an effective bottom-up approach for functional-device engineering. At such interfaces, prediction of the thermodynamics governing the formation of spatially ordered 2D arrangements is far from being fully understood, even for the physisorption of a single molecular component on the basal plane of a flat surface. Two recent contributions on controlled polymorphism and nanopattern formation render it possible to gain semi-quantitative insight into the thermodynamics of physisorption at interfaces, paving the way towards 2D supramolecular crystal engineering. Although in these two works different systems have been chosen to tackle such a complex task, authors showed that the chemical design of molecular building blocks is not the only requirement to fulfill when trying to preprogram self-assembled patterns at the solid,liquid interface. [source] Scaling characteristics and growth of corrosion product films in turbulent flow solution containing saturated CO2MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2009Z. F. Yin Abstract In the present study, the surface and cross-section microstructures of the corrosion films were investigated by SEM and the corrosion rate was measured by mass loss at the various conditions associated with the main influencing factors such as temperature, CO2 partial pressure, and flow velocity. The results indicated that the three factors have obvious characteristics and the enhanced interactions among the main influencing factors intensively influence the formation and growth of corrosion film. In addition, there were two corrosion mechanisms connected with the forming film and damaging film. A new lattice model was proposed to describe the general aspects concerning the formation of the corrosion film at the metal surface/solution interfaces. [source] | |||||||||||||||||||||||||