Self electro-catalysis of hydroquinone on gold electrode in aqueous un-buffered media

Redox behavior of hydroquinone (H₂Q) in an un-buffered aqueous medium at gold electrode is reported. In multiple scanned cyclic voltammograms, appearance of a new redox couple, splitting of H₂Q oxidation peak and anodic shift of original H₂Q redox peak were observed. Comparative studies of quinone (Q) under similar conditions establish the formation of surface confined Q as an intermediate. Electro-catalysis by the electro-generated Q monolayer is proposed to be responsible for the splitting of H₂Q oxidative wave in the cyclic voltammetry.     

Measurement of237Np in the marine environment of coastal nuclear sites in India

Nepturium-237 levels in sea water and sediments from Indian coastal waters receiving radwaste discharges have been investigated. The method used for the estimation is neutron activation and using this method,²³⁷Np activity as low as 10^–7 Bq/l in sea water could be measured. Neptunium-237 levels found are compared with the values reported for other areas.     

Conformational Analyses of Glycinal and Alaninal: A Computational Study

We present computational results from detailed gas-phase conformational analyses of the -substituted aldehydes, glycinal and alaninal. A synplanar conformer of glycinal and a synperiplanar conformer of alaninal in which the C=O and C–N bonds are in an eclipsing orientation are found to be lowest in energy; the two amino hydrogen atoms in these conformers are both directed over the C–C bond, i.e., in a compact arrangement. For the Group VA analogs, H₂P–CH₂–CHO and H₂P–CH(CH₃)–CHO, skew conformers in which the C–H and C–Me groups, respectively, are in an eclipsing orientation with the C=O bond are found to be lower in energy than the syn(peri)planar conformers. The results of various self-consistent reaction-field calculations suggest that the lowest-energy conformer of glycinal in 1, 2-dichloroethane is still synperiplanar, although the orientation of the amino hydrogen atoms may be different from that in the gas phase. Similar reaction-field calculations for alaninal raise the possibility that in this solvent a skew conformer, in which the C–H bond is nearly eclipsing the C=O bond, is energetically competitive with synperiplanar conformers.     

Cadmium(II) binding by soil-derived fulvic acid measured by anodic stripping voltammetry

Titrations of aqueous solutions of soil fulvic acid (30, 45, and 60 mg l^-1) with cadmium ion solutions at pH 6 and 7 reveal unusual shapes in the stripping current (i_s) vs. total cadmium ion (C_cd²⁺) curves. The expected inflections occur in the titration curves at 8–16 μM. at pH 6 and 12–26 μM at pH 7. In addition, there is an initial rapid increase in i_s at very low C_cd²⁺. The initial rapid increase in current is attributed to labile cadmium—fulvic acid complexes that contribute to i_s by rapid dissociation. Subsequent addition of cadmium ion results in moderately labile complexes and i_s becomes partially kinetically controlled. The stripping current was corrected for kinetic current contributions from dissociation of complexes, and total ligand concentrations, conditional stability constants, and upper slopes were calculated from data well past the titration end-point. The use of upper slopes after kinetic current corrections as in situ calibration curves, allowed calculations of equilibrium cadmium concentrations. The data show that both kinetic current corrections and in situ calibration curves are necessary to avoid substantial errors in calculations of equilibrium cadmium concentrations from anodic stripping voltammetric experiments.     

Mechanistic investigations with Bromamine-T: Kinetics of oxidation of thiocyanate ion

The kinetics of oxidation of thiocyanate ion by Bromamine-T (BAT) has been investigated in alkaline medium. The rate of reaction is first order in [OH^–] and zero order in [NCS^–]. The pseudo-first order rate constants decrease with increase in [BAT]. Addition of the reaction products p-toluenesulfonamide, Br^– and neutral salts has no significant effect on the rate. The rate increases with either increase in ionic strength or decrease in dielectric constant of the medium. The activation parameters have been computed. A mechanism consistent with the experimental results has been proposed and the rate law derived. The rate constants predicted from the rate law for the variation of [BAT] are in excellent agreement with the observed rate constants.

---

- (BAT) . [OH^–] [NCS^–]. [BAT]. -, Br^– . . . , , . , , [BAT]_o, .

     

Current status of selective area epitaxy by OMCVD

In this paper we review the current status of the achievements and understanding of selective area epitaxy using organometallic chemical vapor deposition (OMCVD) in the conventional mode, atomic layer epitaxy mode, and photon assisted growth mode. The selective epitaxy of GaAs, AlGaAs, and InP can be readily achieved. However, the selective epitaxy of compounds such as GaInAs has proven to be difficult due to a large compositional deviation. In addition, the control of the lateral thickness profile and facets at the edges has proven to be difficult for both binaries and their alloys. Selective epitaxy has been used to fabricate a variety of electronic and optoelectronic devices and low-dimensional structures. While considerable progress has been made, a better understanding of the processes is necessary before they can be applied to large scale optoelectronic integration.     

FeCl3·6H2O-catalyzed selective conjugate reduction of alkylidene-β-keto esters and alkylidene-1,3-diketones

FeCl₃·6H₂O/triethylsilane composite catalyst system is successfully developed for the selective conjugate reduction of carbon-carbon double bond of Michael acceptor-alkylidene-β-keto esters and alkylidene-1,3-diketones under mild reaction conditions to afford the corresponding saturated β-keto esters and 1,3-diketones. The process involves the iron-catalyzed hydrosilylation, followed by in situ hydrolysis of silyl enol ether. The optimal reaction conditions include 20?mol% of FeCl₃·6H₂O and triethylsilane in dichloromethane at room temperature. A broad range of substrates undergoes the reduction in 1, 4-selective manner to afford the corresponding saturated compounds in excellent yields.