Thermodynamic Control of 2D Bicomponent Porous Networks of Melamine and Melem: Diverse Hydrogen-Bonded Networks

Different bicomponent self-assembled structures comprising melamine and melem were formed at aqueous solution–Au(111) interfaces by varying the concentrations of melamine and melem and the electrochemical potential. The structures were observed by in situ scanning tunneling microscopy. The structures of the bicomponent networks were controlled thermodynamically through the surface concentration and the molecular ratio. Interestingly, the solution concentration did not directly reflect the surface density of the self-assembled structures because of the flocculation-like behavior around the interface. Furthermore, structural phase transitions between the melem monocomponent honeycomb network, the bicomponent honeycomb network, and the melamine monocomponent honeycomb network with aggregates were directly and reversibly observed by controlling the electrochemical potential

Electrochemically Controlled 2D Assembly of Paddle-Wheel Diruthenium Complexes on the Au(111) Surface and Identification of Their Redox States

The 2D molecular assemblies of chloride-coordinated mixed-valence diruthenium complexes, each possessing phenyl, naphtyl, or anthracenyl moieties, were examined on an Au(111) at electrochemical interface. In situ scanning tunneling microscopy images revealed a clear dependence of the molecular assembly on both the nature of the aryl functional groups and on the redox state of the dinuclear ruthenium complex, either chloride-coordinated Ru^II/Ru^III or noncoordinated Ru^II/Ru^II. At potentials where the Ru^II/Ru^III and Ru^II/Ru^II redox states were in equilibrium, two distinct redox states were clearly identified at the single-molecular level. We found that manipulating both the electrochemical potential and the aryl functional group substitution was important for controlling the 2D molecular assembly of a chloride-coordinated diruthenium complex on an Au(111) surface

Direct Analysis of Lipophilic Antioxidants of Olive Oils Using Bicontinuous Microemulsions

Quantitative analyses of olive oil for lipophilic antioxidants, such as α-tocopherol and phenolics, by simple electrochemical measurements were conducted in a bicontinuous microemulsion (BME), which was bicontinuously composed of saline and toluene microphases with a surfactant system. Lipophilic antioxidants in oils were directly monitored in BME solutions using a lipophilic, fluorinated nanocarbon-film electrode (F–ECR). The combination of a well-balanced BME and extremely biased electrodes, such as strongly hydrophilic indium/tin oxide and strongly lipophilic (hydrophobic) F–ECR, allowed individual monitoring of hydrophilic and lipophilic antioxidants in the same BME solution without any required extraction. Furthermore, values for the charge <i>Q</i>, integrated from observed currents, showed good linear relationships with the results of conventional assays for antioxidant activity, namely, total phenolics and oxygen radical absorbance capacity assays, even with practical food samples. This proposed methodology provided a very simple, rapid, easily serviceable, and highly reproducible analysis that possesses great potential for applications to a wide range of chemical mixtures, in terms of analyte and media, beyond food oils

Simultaneous Electrochemical Analysis of Hydrophilic and Lipophilic Antioxidants in Bicontinuous Microemulsion

Qualitative and quantitative analyses of hydrophilic and lipophilic antioxidants, such as polyphenols, by simple electrochemical measurements were conducted in a bicontinuous microemulsion (BME), in which water and oil phases coexisted bicontinuously on a microscopic scale. Hydrophilic and lipophilic antioxidants were individually monitored in the same BME solution using a hydrophilic indium tin oxide (ITO) electrode and a lipophilic fluorinated nanocarbon film electrode (F-ECR), respectively. The combination of well-balanced BME and extremely biased electrodes, such as ITO and F-ECR, in terms of hydrophilic–lipophilic balance allowed us to achieve individual monitoring of hydrophilic and lipophilic antioxidants in the same BME solution without extraction. Furthermore, the antioxidant activities of functional liquid foods, such as coffee and olive oil, were also evaluated by means of electrochemical measurements in BME solutions containing analytes in concentrations of several percent. The technique we propose provides a very simple, rapid, easily serviceable, and highly reproducible analysis and can be extended to a wide range of analytes and media

<i>In Situ</i> STM Investigation of Aromatic Poly(azomethine) Arrays Constructed by “On-Site” Equilibrium Polymerization

Two-dimensional (2D) arrays of π-conjugated aromatic polymers produced by surface-selective Schiff base coupling reactions between an aromatic diamine and an aromatic dialdehyde were investigated in detail using <i>in situ</i> scanning tunneling microscopy. Surface-selective coupling was achieved for almost all diamine/dialdehyde combinations attempted, although several combinations did not proceed even in homogeneous aqueous alkaline solution. Most of the combinations of an aromatic diamine and a dialdehyde, except the combinations of 4,4′-azodianiline with mono/bithiophenedicarboxaldehyde, formed highly ordered π-conjugated polymer arrays on an iodine-modified Au(111) surface in aqueous solution at a suitable pH. The simplest polymer of the various combinations tested, obtained from the combination of 1,4-diaminobenzene with terephthaldicarboxaldehyde, gave a 2D array consisting of linearly connected benzene units. Poly­(azomethine) adlayers caused a positive shift in the electrochemical potential of the butterfly shaped oxidative adsorption and reductive desorption of iodine. The acceleration of the reductive desorption of iodine suggests the existence of a weak interaction between the polymer layer and iodine. Not only the first polymer adlayers but also partially adsorbed secondary adlayers with “on-top” epitaxial behavior were frequently observed for all polymer systems. The alignment of the polymer chains in the adlayers possessed a certain regularity in terms of a regular interval between polymer chains because of repulsive interpolymer interactions

Cohelical Crossover Network by Supramolecular Polymerization of a 4,6-Acetalized β‑1,3-Glucan Macromer

Natural polysaccharides represent a renewable resource whose effective utilization is of increasing importance. Chemical modification is a powerful tool to transform them into processable materials but usually sacrifices the original structures and properties of value. Here we introduce a chemical modification of Curdlan, a β-1,3-glucan, via 4,6-acetalization. This modification has successfully combined a helix-forming ability of Curdlan with new solubility in organic media. Furthermore, it has operationalized efficient cohelical crossovers (CCs) among the helices to demonstrate the formation of an extensive supramolecular network that goes well beyond the nanoscopic regime, allowing for preparation of flexible self-supporting films with macroscopic dimensions. This protocol, which is now viewed as supramolecular polymerization of a helical polysaccharide macromer, can add a new dimension to “polysaccharide nanotechnology”, opening a door for the creation of unconventional polymer materials based on the cohelical crossover network (CCN)