Scanning electrochemical mapping of spatially localized electrochemical reactions induced by surface potential gradients

The influence of a surface potential gradient on the location and extent of electrochemical reactions was examined using a scanning electrochemical microscope. A linear potential gradient was imposed on the surface of a platinum-coated indium tin oxide electrode by applying two different potential values at the edges of the electrode. The applied potentials were used to control the location and extent of several electrochemical reactions, including the oxidation of Ru(NH3)6(2+), the oxidation of H2, and the oxidation of H2 in the presence of adsorbed CO. Scanning electrochemical mapping of these reactions was achieved by probing the feedback current associated with the oxidation products. The oxidation of Ru(NH3)6(2+) occurred at locations where the applied potential was positive of the formal potential of the Ru(NH3)6(2+/3+) redox couple. The position of this reaction on the surface could be spatially translated by manipulating the terminal potentials. The rate of hydrogen oxidation on the platinum-coated electrode varied spatially in the presence of a potential gradient and correlated with the nature of the electrode surface. High oxidation rates occurred at low potentials, with decreasing rates observed as the potential increased to values where platinum oxides formed. The extent of oxide formation versus position was confirmed with in-situ ellipsometry mapping. In the presence of adsorbed carbon monoxide, a potential gradient created a localized region of high activity for hydrogen oxidation at potentials between where carbon monoxide was adsorbed and platinum oxides formed. The position of this localized region of activity could be readily translated along the surface by changing the terminal potential values. The ability to manipulate electrochemical reactions spatially on a surface has potential application in microscale analytical devices as well as in the discovery and analysis of electrocatalytic systems.     

Reaction of 2‐diazo‐1,2‐diarylethanones with benzophenone n‐(diaryl)acyl hydrazones: Formation of 1,3,4‐oxadiazolines

The reaction of 2‐diazo‐1,2‐diarylethanones with benzophenone N‐(diaryl)acyl hydrazones leads to the formation of 1,3,4‐oxadiazolines. The products have been characterized on the basis of satisfactory analytical and spectral (IR, ¹H and ¹³C NMR, and Mass) data. The mechanism for the formation of products through the reaction of diarylketenes, generated in situ from thermal decomposition of the 2‐diazo‐1,2‐diarylethanones, with imino nitrogen and intramolecular [2 + 3] dipolar cycloaddition is suggested.     

Combined Extraction and Electrochemical Detection of Amines and Phenols Using Microelectrodes in Organic Solvents

A straightforward approach for liquid‐liquid extractive detection of aromatic amines and phenols is described based on the spontaneous transfer of the molecule from the aqueous to an organic phase and subsequent electrochemical detection in the latter phase using a microelectrode. It is demonstrated that the extent of the transfer can be modified by altering the pH of the aqueous solution and the organic solvent. It is also concluded that the presence of an ion‐pair formation agent does not increase the transfer yield for 4‐chloroaniline and phenol. The present approach combines liquid‐liquid sample clean‐up and quantification into a single step which significantly facilitates determinations of aromatic amines and phenols present in complex samples.     

Hydro­gen‐bonding and C—H⋯π interactions in 1,7‐bis(4‐hydroxy‐3‐methoxy­phenyl)­heptane‐3,5‐dione (tetra­hydro­curcumin)

The title compound, C₂₁H₂₄O₆, is the reduced form of curcumin, and exhibits important cosmoceutical properties. The mol­ecule is non‐planar and the benzene rings positioned at the ends of the heptane chain are orthogonally placed, with a dihedral angle of 84.09 (7)° between them. The molecular geometry and H‐atom locations reveal that the `heptane‐3,5‐dione' moiety exists in the keto–enol form, with the hydroxy H atom disordered over two adjacent sites. The packing of the mol­ecules in the lattice is directed by strong O—H⋯O intermolecular hydrogen bonds, which generate two‐dimensional sheets. These sheets are linked by C—H⋯O hydrogen bonds and weak C—H⋯π interactions to develop a three‐dimensional network.     

A variable boundary method for modelling two dimensional free surface flows with moving boundaries

A coordinate transformation method is proposed for modelling unsteady, depth-averaged shallow water equations for a open channel flow with moving lateral boundaries. The transformation technique which maps the changing domain onto a fixed domain and solves the governing equations in the mapped domain, facilitates the numerical treatment of an irregular boundary configuration. The transformed equations are solved on a staggered grid with a conditionally stable, explicit finite difference scheme. Several numerical experiments are carried out corresponding to different situations, viz., flow with constant discharge, flow with constant discharge and a closed boundary at the downstream, flow in a converging channel with constant discharge and finally flow with varying discharge. The experiments are used to verify the model ability to predict free surface elevation, circulatory pattern and displacement of the boundaries. The simulated results such as displaced area, depth, displacement–time and flow-field are used to evaluate the effects of excess discharge at the upstream on the movement of lateral boundaries.     

Determination of the water content in organic compounds by gas chromatography using back flush technique

Summary A technique has been developed for the determination of water in various organic compounds by gas chromatography using back-flush. Relative standard deviations were in the range of 0.2 to 3%. Comparison with Karl Fischer titration showed consistently better precision of the new technique, in particular for water contents of more than 50%.     

Effect of couple stresses on transient MHD poiseuille flow

The unsteady laminar flow of an electrically conducting viscous fluid between parallel insulating plates subject to a transverse magnetic field is considered. The plates are fixed and flow is due to a constant pressure gradient. The induced field is taken into account. The fluid is incompressible and of couple stress type. The defining equations are coupled and numerical solutions for different values of couple stress parameter are obtained. The velocity and induced magnetic field profiles are sketched as functions of time, Hartmann number, and magnetic Prandtl number. The velocity decreases with increase in couple stress parameter.