In-situ circular dichroism spectroelectrochemical study on the redox process of norepinephrine

The redox process of norepinephrine in pH = 7.0 phosphate buffer solution at glassy carbon electrode was studied by circular dichroism spectroelectrochemistry with a long optical path thin layer cell. The spectroelectrochemical data were analyzed with the double logarithm method. According to the double logarithsmic plot results, the mechanism of electrochemical oxidation of norepinephrine is an irreversible process with a subsequent chemical reaction (EC) to form a norepinephrinechrome. Both of norepinephrinequinone and norepinephrinechrome are followed E mechanisms. Some kinetic parameters about the electrochemical process, i.e. the electron transfer coefficient and number of electron transfered, alpha n = 0.38, the formal potential, E-1(0)' = 0.20 V, the standard heterogenous electron transfer rate constant, k(1)(0) = 1.2 x 10(-4) cm s(-1) for the oxidation of norepinephrine, alpha n = 0.37, E-2(0)' = 0.25 V and k(2)(0) = 4.4 x 10(-5) cm . s(-1) for the reduction of norepinephrinequnone and alpha n = 0.33, E-3(0)' = -0.25V and k(3)(0) = 1.1 x 10(-4) cm . s(-1) for the reduction of norpinephrinechrome, were also estimated.

Study of electrochemical behavior of ergosterol by in situ thin layer circular dichroic spectroelectrochemistry

The electroxidation of ergosterol was studied by in situ circular dichroic (CD) spectroelectrochemistry with a long optical path length thin layer cell. It was confirmed that the oxidation of ergosterol in ethanol solution is a two-electron irreversible electrochemical process with strong adsorption of an electroinactive product at the glassy carbon electrode, which blocks the electrochemical reaction. The CD spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential, E-0 = 1.00 V, alpha n(alpha) = 0.302, the standard electrochemical rate constant, k(0) = 6.1(+/-0.4) x 10(-4) cm s(-1) and the adsorption constant, beta = 19 +/- 1, were obtained. The number of electrons transferred (n = 1.86) was estimated by cyclic voltammetry.

Investigation of the self-accelerating process of ascorbic acid by in-situ circular dichroism spectroelectrochemistry

The electrode reaction process of ascorbic (Vc) was studied by in-situ circular dichroic(CD) spectroelectrochemistry with a long optical path thin layer cell on glassy carbon(GC) electrode. The spectroelectrochemical data were analyzed by the double logarithmic method together with nonlinear regression. The results suggested that the mechanism of Ve in pH 7.0 phosphate buffer solution at GC electrode was a two-electron irreversible electrooxidation followed by adsorption of the oxidation product. That is a self-accelerated process. Some kinetic parameters at free and at adsorbed electrode surface, i.e, the formal potentials, E-0' = 0.09 V, E-a(0') = 0.26 +/- 0.02 V; the electron transfer coefficient and number of transfered electron, alpha n = 0.41, alpha(a)n = 0.07;the standard heterogeneous electron transfer rate constant, k(0) = 8.0 x 10(-5) cm.s(-1), k(a)(0) = 1.9 x 10(-4) cm.s(-1) and adsorption constant, beta = 102.6 were also estimated.

In situ UV-vis and CD thin-layer spectroelectrochemistry study of the electrochemical behavior of L-noradrenaline in alkaline solution

Electrochemical redox behavior of noradrenaline in alkaline solution on a glassy carbon electrode has been investigated by in situ UV-vis and CD spectroelectrochemistry by using a long optical path thin-layer cell. The experimental data were processed by using a double logarithmic method of analysis together with nonlinear regression which confirmed that the first step in both the oxidation of noradrenaline and reduction of noradrenochrome is a two-electron irreversible process governed by an EE mechanism. The kinetic parameters of the electrode reactions, i.e., charge transfer coefficient and the number of electrons transferred, alpha(1)n(1) = 0.11 and alpha(2)n(2) = 0.23, formal potentials modified with kinetics, E-1(0') = 0.65 (+/- 0.01) V and E-2(0') = 0.72V and standard rate cnstants, k(1)(0) = 7.0(+/-0.5)x10(-5) cm s(-1), for the first and second steps in the oxidation process of noradrenaline, and similarly, alpha(1)n(1) = 0.33, alpha(2)n(2) = 0.58, E-1(0') = 0.37(+/-0.01) V, E-0' = -0.25 (+/-0.01) V and k(1)(0) approximate to k(2)(0) = 1.06 (+/-0.05)x10(-4) cm s(-1) for the first and second steps in the reduction process of noradrenochrome were also determined.

INVESTIGATION OF THE ELECTROCHEMICAL-BEHAVIOR OF TRYPTOPHAN BY IN-SITU CIRCULAR DICHROIC SPECTROELECTROCHEMISTRY

The electrochemical redox processes of tryptophan were studied by in situ circular dichroic (CD) spectroelectrochemistry with a long optical path length thin-layer cell. The oxidation of tryptophan at low concentrations in basic aqueous solution is a two-electron irreversible electrochemical process which results from an irreversible subsequent chemical reaction. A method of treatment of CD spectral data for the irreversible electrochemical reaction is suggested, from which the values E(p/2) = 0.46 V, alphan(alpha) = 0.313 and k0 = 2.4 x 10(-4) cm s-1 (the standard heterogeneous reaction rate constant for tryptophan oxidation) were obtained.

DETERMINATION OF PARAMETERS OF FAST CHEMICAL REACTION OF ALIZARIN RED S BY SPECTROELECTROCHEMICAL METHOD WITH LOPTLC

The rate constant of very fast chemical reaction generally can be measured by electrochemical methods, but can not by the thin layer electrochemical methods because of the influence of diffusion effect. Long optical path length thin layer cell (LOPTLC) with large ratio of electrode area to solution volume can be used to monitor the fist chemical reaction in situ with high sensitivity and accuracy. It enable the adsorption spectra to be measured without the influence of diffusion effect. In the present paper, a fast chemical reaction of Alizarin Red S (ARS) with its oxidative state has been studied. The reaction equilibrium constant (K) under different potentials can be determined by single step potential-absorption spectra in LOPTLC. An equilibrium constant of 7.94 x 10(5) l.mol(-1) for the chemical reaction has been obtained from the plot of lgK vs. (E - E-1(0)'). Rate constant (k) under different potentials can be measured by single step potential-chronoabsorptiometry. A rate constant of 426.6 l.mol(-1).s(-1) for the chemical reaction has been obtained from the plot of lgK vs. (E - E-1(0)') with (E - E-1(0)') = 0.

Quantum path control in few-optical-cycle regime

We theoretically show that selection of a single quantum path in high-order harmonics generation can be realized in a few-optical-cycle regime with two-color schemes. We also demonstrate, in theory as well, the generation of spectrally smooth and ultrabroad extreme ultraviolet supercontinuum in argon gas which can produce single similar to 79 as pulses with currently available ultrafast laser sources. Our finding can be beneficial for generating isolated sub-100 as extreme ultraviolet pulses.

Interface-related in-plane optical anisotropy of quantum wells studied by reflectance-difference spectroscopy

The in-plane optical anisotropy of three groups of GaAs/AlGaAs quantum well structures has been studied by reflectance-difference spectroscopy (RDS). For GaAs/Al0.36Ga0.64As single QW structures, it is found that the optical anisotropy increases quickly as the well width is decreased. For an Al0.02Ga0.98As/AlAs multiple QW with a well width of 20nm, the optical anisotropy is observed not only for the transitions between ground states but also for those between the excited states with transition index n up to 5. An increase of the anisotropy with the transition energy, or equivalently the transition index n, is clearly observed. The detailed analysis shows that the observed anisotropy arises from the interface asymmetry of QWs, which is introduced by atomic segregation or anisotropic interface roughness formed during the growth of the structures. More, when the 1 ML InAs is inserted at one interface of GaAs/AlGaAs QW, the optical anisotropy of the QW can be increased by a factor of 8 due to the enhanced asymmetry of the QW. These results demonstrate clearly that the RDS is a sensitive and powerful tool for the characterization of semiconductor interfaces.

Strain-induced in-plane optical anisotropy in (001) GaAs/AlGaAs superlattice studied by reflectance difference spectroscopy

In-plane optical anisotropy (IPOA) in (001) GaAs/AlGaAs superlattice induced by uniaxial strain has been investigated by reflectance difference spectroscopy (RDS). Uniaxial strain on the order of 10(-4) was introduced by bending a strip sample with a stress apparatus. The IPOA of all interband transitions shows a linear dependence on strain. The birefringence and dichroism spectra induced by strain are obtained by RDS on the basis of a three-phase model, which is in good agreement with the reported results. (c) 2006 American Institute of Physics.

Study on in-plane optical anisotropy of semiconductor materials by reflectance difference spectroscopy

In the present review, the measuring principle of reflectance difference spectroscopy (RDS) is given. As a powerful tool in the surface and interface analysis technologies, the application of RDS to the research on semiconductor materials is summarized. along with the origins of the in-plane optical anisotropy of semiconductors. And it is believed that RDS will play an important role in the electrooptic modification of Si-based semiconductor materials.

Study on in-plane optical anisotropy of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice by reflectance difference spectroscopy - art. no. 071908

Si0.75Ge0.25/Si/Si0.5Ge0.5 trilayer asymmetric superlattices were prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The nonlinear optical response caused by inherent asymmetric interfaces in this structure predicted by theories was verified by in-plane optical anisotropy in (001) plane measured via reflectance difference spectroscopy. The results show Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice is optically biaxial and the two optical eigen axes in (001) plane are along the directions [110] and [-110], respectively. Reflectance difference response between the above two eigen axes can be influenced by the width of the trilayers and reaches as large as similar to 10(-4)-10(-3) in 15-period 2.7 nm-Si0.75Ge0.25/8 nm-Si/1.3 nm-Si0.5Ge0.5 superlattice when the normal incident light wavelength is in the range of 500-1100 nm, which is quite remarkable because the optical anisotropy does not exist in bulk Si.

Interface-related in-plane optical anisotropy in GaAs/AlxGa1-xAs single-quantum-well structures studied by reflectance difference spectroscopy

The in-plane optical anisotropies of a series of GaAs/AlxGa1-xAs single-quantum-well structures have been observed at room temperature by reflectance difference spectroscopy. The measured degree of polarization of the excitonic transitions is inversely proportional to the well width. Numerical calculations based on the envelope function approximation incorporating the effect of C-2v-interface symmetry have been performed to analyze the origin of the optical anisotropy. Good agreement with the experimental data is obtained when the optical anisotropy is attributed to anisotropic-interface structures. The fitted interface potential parameters are consistent with predicted values.

Polishing-related optical anisotropy of semi-insulating GaAs studied by reflectance difference spectroscopy

The strong in-plane optical anisotropy of (001) semi-insulating GaAs, which comes from the submicron region under the surface, has been observed by reflectance difference spectroscopy. The optical anisotropy can be explained by the anisotropic strain that is introduced by the asymmetric distribution of 60 degrees dislocations during surface polishing. The simulated spectra reproduce the line shape of the experimental ones. The simulations show that the anisotropic strain is typically about 2.3x10(-4). (C) 2000 American Institute of Physics. [S0021-8979(00)01315-3].

In-plane optical anisotropy in GaAsN/GaAs single-quantum well investigated by reflectance-difference spectroscopy

The interface properties of GaNxAs1-x/GaAs single-quantum well is investigated at 80 K by reflectance difference spectroscopy. Strong in-plane optical anisotropies (IPOA) are observed. Numerical calculations based on a 4 band K . P Hamiltonian are performed to analyze the origin of the optical anisotropy. It is found that the IPOA can be mainly attributed to anisotropic strain effect, which increases with the concentration of nitrogen. The origin of the strain component epsilon(xy) is also discussed.