In-situ FTIR study on adsorption and oxidation of native and thermally denatured calf thymus DNA at glassy carbon electrodes

In-situ Fourier transform infra-red (FTIR) spectra of native and thermally denatured calf thymus DNA (CT DNA) adsorbed and/or oxidized at a glassy carbon (GC) electrode surface are reported. The adsorption of native DNA occurs throughout the potential range (-0.2 similar to 1.3 V) studied, and the adsorbing state of DNA at electrode surface is changed from through the C=O band of bases and pyrimidine rings to through the C=O of cytosine and imidazole rings while the potential shifts negatively from 1.3 V to -0.2 V. An in-situ FTIR spectrum of native CT DNA adsorbed at GC electrode surface is similar to that of the dissolved DNA, indicating that the structure of CT DNA is not distorted while it is adsorbed at the GC electrode surface. In the potential range of -0.2 similar to 1.30 V, the temperature-denatured CT DNA is adsorbed at the electrode surface first, then undergoes electrochemical oxidation reaction and following that, diffuses away from the electrode surface. (C) 2001 Elsevier Science B.V. All rights reserved.

Electrochemical behavior of heteropoly acid anions adsorbed in electrodes modified with mesoporous molecular sieve silica

Heteropoly acid H4SiW12O48 (denoted as SiW12) was assembled with the mesoporous materials MCM-41 modified with 3-aminopropyltriethoxysilane (APTES) (denote MCM-41((m))). The electrochemical behavior of SiW12/MCM-41((m)) complexes-based electrode indicated SiW12 anion was adsorbed by MCM-41((m)). In MCM-41((m)) electrode, large voltammetric waves, showing that the electrostatic bound ions adsorbed in MCM-41((m)) were electrochemically active. The potential application as amperometric sensors for nitrite is anticipated.

Photoreduction behaviors of microperoxidase-11 adsorbed on the roughened silver electrodes

It was found that microperoxidase-ll (MP-II) can undergo photoreduction at the bale roughened silver electrode. No photoreduction happens at the roughened silver electrode modified with mercaptoundecanoic carboxylic acid/poly-lysine. The photoreduction mechanism is discussed.

A rule to design high spin molecules with hetero-spin centers

The series of biradicals with m-phenylene coupling unit and hetero-spin centers were calculated compared with those possessing home-spin centers using AM1-CI method. A simple rule was proposed to design high spin molecules with ferromagnetic coupling unit and hetero-spin centers. Two neutral (or charged) hetero-spin centers resulted in high spin ground state, one neutral and another charged hetero-spin centers correspond to low spin ground state. The latter was ascribed to the huge splitting of two partially occupied molecular orbitals.

The intermolecular coupling through space for stacked high spin molecules

Intermolecular ferromagnetic interactions in two stacking models for the dimer of high spin molecules are investigated by means of AM1-CI approach. It is shown that the stability of high spin ground state versus low spin state can be simply traced back to the number and the extent of atoms with reversed signs of pi-spin density in neighboring molecules coupled to each other in shortest distance.

Electrochemical growth and characterization of polyoxometalate-containing monolayers and multilayers on alkanethiol monolayers self-assembled on gold electrodes

A general strategy has been developed for fabrication of ultrathin monolayer and multilayer composite films composed of nearly all kinds of polyoxometalates (POMs), including isopolyanions (IPAs), and heteropolyanions (HPAs). It involves stepwise adsorption between the anionic POMs and a cationic polymer on alkanethiol (cysteamine and 3-mercaptopropionic acid) self-assembled monolayers (SAMs) based on electrostatic interaction. Here a Keggin-type HPA SiMo11VO405- was chosen as a main representative to elucidate, in detail, the fabrication and characterization of the as-prepared composite films. A novel electrochemical growth method we developed for film formation involves cyclic potential sweeps over a suitable potential range in modifier solutions. It was comparatively studied with a commonly used method of immersion growth, i.e., alternately dipping a substrate into modifier solutions. Growth processes and structural characteristics of the composite films are characterized in detail by cyclic voltammetry, UV-vis spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), micro-Fourier transform infrared reflection-absorption spectroscopy (FTIR-RA), and electrochemical quartz crystal microbalance (EQCM). The electrochemical growth is proven to be more advantageous than the immersion growth. The composite films exhibit well-defined surface waves characteristic of the HPAs' redox reactions. In addition, the composite films by the electrochemical growth show a uniform structure and an excellent stability. Ion motions accompanying the redox processes of SiMo11VO405- in multilayer films are examined by in situ time-resolved EQCM and some results are first reported. The strategy used here has been successfully popularized to IPAs as well as other HPAs no matter what structure and composition they have.