Zhonghua Lin

Spectroelectrochemical studies of poly-o-phenylenediamine. Part 1. In situ resonance Raman spectroscopy

The redox process of poly-o-phenylenediamine (PoPD) film in strong acid solution has been studied by in situ resonance Raman spectroscopy, in situ UV-vis subtractive reflectance spectroscopy and cyclic voltammetry. A marked potential-dependent spectral change is observed in the in situ resonance Raman spectra, which reveals that at least three redox states of PoPD are formed in the redox process and the structure of PoPD is dominated by a ladder polymer with phenazine rings. The three kinds of PoPD display different resonance Raman enhancement effects, which is verified by the in situ UV-vis subtractive reflectance spectra. The ex situ resonance Raman spectra indicate that the electronic structure of the PoPD molecule is evidently influenced by protonation and that the most stable state of PoPD is its semi-oxidized state. Finally, a possible reaction scheme of the electrochromic process of PoPD film in strong acid solution is proposed.

Electrochemical assembly of nano-organized poly-o-phenylenediamine films

Abstract Potential-dependent surface-enhanced Raman scattering spectra reveal that the orientation of o -phenylenediamine (OPD) molecules adsorbed on a Au electrode depends on the electrode potential and electropolymerization of OPD can be carried out at +0.3 V. The electrochemical-assembly technique was successfully applied to the fabrication of a nano-structured o -phenylenediamine oligomer (POPD) film on a bare Au substrate and on a p -aminothiophenol (PATP) self-assembled Au substrate in phosphate buffer solution (pH=7.0). Electrochemistry and scanning tunneling microscopy measurements indicate that a POPD/Au(111) surface displays a nano-scale dot array structure. At the same time, a POPD/PATP/Au(111) surface shows a nano-scale line array structure.

Oxidation and adsorption of deoxyribonucleic acid at highly ordered pyrolytic graphite electrode

It shows that calf thymus DNA(CT DNA) can be adsorbed at a highly ordered pyrolytic graphite (HOPG) electrode and detected by differential pulse voltammetry (DPV) and electrochemical atomic force microscopy (ECAFM). It is found that controlled potential pre-polarization influences largely the adsorption of dsDNA while it has little influence on ssDNA. It is demonstrated that ECAFM is useful to exploit adsorption of DNA at HOPGE. The mode of adsorption of DNA at the HOPG electrode that fits best with the experimental data is proposed.

Spectroelectrochemical studies of poly-o-phenylenediamine - Part 2. In situ UV-vis subtractive reflectance spectroscopy

Abstract In our previous paper, the phenazine-like structure of the poly- o -phenylenediamine (P o PD) and its three steady redox states have been revealed mainly by using in situ resonance Raman spectroscopy. It has also been shown that the semi-oxidized state of P o PD is the most stable state of P o PD, while the totally-oxidized state of P o PD is chemically unstable and can exist only at certain electrode potentials. In the present work, the more detailed reaction mechanism of a P o PD film in strong acid solution has been studied by using in situ UV—vis substractive reflectance spectroscopy. The semi-oxidized state and the totally-oxidized state of P o PD have electronic absorption bands around 300 nm, 430 nm, 500 nm and 300 nm, 450 nm, 530 nm, 735 nm respectively in the in situ steady state UV—vis subtractive reflectance spectra with respect to the reduced state of P o PD, which verifies once again that three redox states of P o PD exist in the redox process of P o PD. Moreover, the relative intensity between two oxidized states of P o PD at the maximum absorption wavelength (λ max ) reveals that only about one third of the semi-oxidized state of P o PD can be oxidized to the totally-oxidized state of P o PD. The in situ resonance Raman spectra and the cyclic voltammograms of P o PD display the same quantitative relationship. New absorption bands were observed in the in situ time-resolved UV—vis subtractive reflectance spectra with appropriate time resolutions, which illustrate the dynamic structure changes of P o PD in its redox process. These intermediate states of P o PD are more unstable than its three redox states.

Electrochemical behaviors of DNA at mercury film electrode

Abstract DNA was studied by means of cyclic voltammetry (CV) in combination with a mercury film electrode (MFE) using conventional CV, differential pulse voltammetry (DPV), alternating current voltammetry (ACV). The MFE is sufficiently stable and can be used to study electrochemical behaviors of DNA in negative potential region. This means that MFE is ready to be one kind of solid electrode at which more useful electrochemical techniques can be carried out, such as spectroelectrochemical techniques. Redox characters of DNA treated by pure perchloric acid (HClO 4 ) was studied at MFE. It seems that pure HClO 4 would not only bring about the denaturation of DNA but the degradation of it. Pure HClO 4 is not suitable for performing the denaturation of DNA.

Electrochemical-Assembly Approach to Nano-Ordered Conducting Polymer Films

Abstract ECA (electrochemical-assembly), a new method for preparing nano-ordered conducting polymer films is reported A nano-ordered conducting film of polyaniline/ p-aminothiolphenol (PANI/PATP) is constructed by this new technique. The properties, structure and surface topography of the polymer film of PANI/PATP are investigated by surface enhanced Raman scattering (SERS), scanning tunneling microscopy (STM) and cyclic voltammetry. The results indicate that the close packed PANI/PATP film is flat, uniform and ordered.

Time-resolved UV-vis spectroelectrochemical studies of the electron transfer process of cytochrome c

The present work used mainly electrochemical in situ time-resolved UV-vis subtractive reflectance spectroscopy to study the electron transfer process of cytochrome c in the presence of promoter (the equal molar mixture of guanine and cytosine). Two new absorption bands 450 and 500 nm and two bipolar bands 250 and 300 nm are observed in the spectra with different time resolutions. In addition, the intensity of another band 420 nm changes with the time resolutions. All the results show that the electron transfer of cytochrome c is accompanied by significant conformational rearrangement.

Spectroscopic and photoelectrochemical properties of DNA/CdS nanoparticle composites

DNA/CdS nanoparticle composites (DNA/CdS NPC) containing single or double strands and different concentrations of DNA were constructed in aqueous solutions. The effect of DNA on the photoelectrochemical properties of DNA/CdS NPC was investigated and the spectroscopic properties of DNA/CdS NPC were characterized by TEM, UV-Vis, IR, and fluorescent spectrometry. The results showed that CdS nanoparticles (CdS NPs) were combined with DNA strands through the electrostatic interaction; DNA templates did not affect the band gap of CdS NPs; DNA-templated CdS NPs had a higher density of surface states than that stabilized by Na4P2O7, which enhanced the photoluminescence (PL) intensity whereas restrained the photocurrent response of CdS NPs. Besides, there was certain dependency of both the increase of PL intensity and the decrease of photocurrent response on DNA concentrations in DNA/CdS NPC. The composites were hopeful for applications in both fluorescent tagged detections and quantitative analysis of DNA.