Electrochemical determination of guanine and adenine by CdS microspheres modified electrode and evaluation of damage to DNA purine bases by UV radiation.

Sensitive electrochemical sensor based on a composite of novel pearl-like CdS microspheres and chitosan (CdS-CHIT/GCE) was constructed and characterized using cyclic voltammetry. Single-stranded (ssDNA) and double-stranded (dsDNA) deoxyribonuleic acid were electrochemically adsorbed onto CdS-CHIT/GCE and a significant difference in electrochemical impedance spectra of the ssDNA/CdS-CHIT/GCE and dsDNA/CdS-CHIT/GCE electrodes was found. Electrocatalytic properties of CdS allowed to use the CdS-CHIT/GCE successfully for the trace determination of simple guanine and adenine with nanomolar detection limits by differential pulse voltammetry (DPV). Moreover, damage to the DNA purine bases, guanine and adenine, liberated in previously hydrolyzed calf thymus dsDNA, caused by UV-B, UV-C, and visible light was evaluated. While only minor changes in anodic DPV response of guanine and adenine could be seen after 60 min exposition to UV-B and visible light, total degradation of DNA bases was observed after 20 min exposure to UV-C. A great potential of the CdS microspheres used as the interface at the nucleic acid based biosensors was demonstrated.

Association interaction and voltammetric determination of 1-aminopyrene and 1-hydroxypyrene at cyclodextrin and DNA based electrochemical sensors.

The aim of this work was voltammetric determination of 1-aminopyrene and 1-hydroxypyrene using carbon paste electrodes modified with cyclodextrin derivatives and double stranded deoxyribonucleic acid (dsDNA). The detection schemes based on a preconcentration and differential pulse voltammetric (DPV) determination at beta-cyclodextrin and gamma-cyclodextrin modified carbon paste electrode (beta-CD/CPE, gamma-CD/CPE), neutral beta-cyclodextrin polymer and carboxymethyl-beta-cyclodextrin polymer modified screen-printed electrode (beta-CDP/SPE, beta-CDPA/SPE) and dsDNA modified screen-printed electrode (DNA/SPE) are proposed for the trace determination of studied analytes within the concentration range from 2 x 10(-8) to 4 x 10(-7) mol dm(-3) and from 2 x 10(-7) to 4 x 10(-6) mol dm(-3) with the limits of quantification down to 10(-8) mol dm(-3). Depending on pH, 1-aminopyrene interacts with both surface attached CD and DNA by electrostatic bonds and supramolecular complexation while 1-hydroxypyrene associates with the CD hosts via complexation. The 1-aminopyrene interaction with dsDNA was confirmed by fluorimetric measurements in the solution phase using a competing DNA-TO-PRO-3 dye complex. In addition, the effect of temperature on this association was investigated using an electrically heated DNA-modified carbon paste electrode (DNA/CPE).

Cyclodextrins as electrode modifiers.

Complexation abilities and analytical applications of working electrodes with attached cyclodextrins (CDs) are reviewed. For the immobilization of CDs, their adsorption and formation of self-assembled monolayers, preparation of polymer films, as well as incorporation within plasticized membranes and composites such as carbon paste and gels are considered. Some electrochemical investigations of the CD interactions in solution are also reported with respect to their use at CD modified electrodes.

Separations of enantiomers by preparative capillary isotachophoresis.

The use of capillary isotachophoresis (ITP), operating in a discontinuous fractionation mode, for preparative separations of enantiomers of chiral compounds was studied. The ITP separations were carried out in the column-coupling configuration of the separation unit provided with the preseparation column of a 1.0 mm ID and the trapping column of a 0.8 mm ID. Such a configuration of the CE separation unit offers several working regimes suitable to preparative separations of enantiomers. 2,4-Dinitrophenyl-DL-norleucine (DNP-Norleu) was employed as a model analyte in our experiments with beta-cyclodextrin serving in the electrolyte solutions as a chiral selector. The preparative separations lasting about 20 min were evaluated by ITP and (more often) by capillary zone electrophoresis (CZE). It was found that one preparative run provided up to 14 microg of pure DNP-Norleu enantiomers. This corresponded to a 75 times higher production rate of ITP relative to a maximum value of this parameter as estimated for preparative CZE runs in cylindrical capillaries (0.5 pmol/s). About 75% of the DNP-Norleu enantiomers loaded into the preparative equipment could be recovered in pure enantiomer fractions. Contiguous natures of the zones in the ITP stack and adsorption losses of the enantiomers in the isolation step were found to set practical limits for a further enhancement of the recovery rates in the isolation of pure enantiomers.