Nucleic acids, electrochemical properties

The unique practical properties of adsorption have promoted its extensive use in genetic analysis. The disadvantages of adsorption with respect to covalent immobihzation are mainly that (1) nucleic acids may be readily desorbed from the substrate, and (2) base moieties may be unavailable for hybridization if they are bonded to the substrate in multiple sites [34]. However, the electrochemical detection strategy based on the intrinsic oxidation of DNA requires the DNA to be adsorbed in close contact with the electrochemical substrate by multi-point attachment. This multi-site attachment of DNA can be thus detrimental for its hybridization but is crucial for the detection based on its oxidation signals. 

A novel application of ionic liquids in biochemistry involved duplex DNA as the anion and polyether-decorated transition metal complexes. When the undiluted liquid DNA-or molten salt-is interrogated electrochemically by a microelectrode, the molten salts exhibit cyclic voltammograms due to the physical diffusion (D-PHYS) of the polyether-transition metal complex. These DNA molten salts constitute a new class of materials whose properties can be controlled by nucleic acid sequence and that can be interrogated in undiluted form on microelectrode arrays (Leone et al., 2001). 

The electrochemical approach discussed here relies on a number of special properties of indium tin-oxide (ITO) electrodes, which had been used in particular for spectroelectrochemistry since ITO is optically transparent and can be fabricated on glass [28, 29]. The first important attribute of ITO is the ability to access potentials up to about 1.4 V (all potentials versus SSCE) in neutral solution [29]. Second, ITO electrodes do not adsorb DNA appreciably [30], which could be anticipated from the ability of metal oxides to adsorb cationic proteins [31] polyanionic nucleic acids were therefore not expected to adsorb. This property makes ITO quite different from carbon, which allows access to relatively high potentials but strongly adsorbs DNA [32]. Third, the direct oxidation of guanine at ITO is extremely slow, even... 

Because of the complex behaviour to be expected for natural nucleic acids, it is only natural that considerable effort has been devoted to studies of the electrochemical properties of their monomeric units, and defined analogues of these, as well as of synthetic oligo- and polynucleotides. A variety of techniques has been applied for this purpose, and some of the details and findings are covered in several reviews 19 24). Most investigations have dealt with electroreduction processes 15 20,24,25). Only relatively recently has attention been directed to possible electrooxidation of nucleic acids and their constituents with the aid of the graphite electrode which, in comparison with the mercury electrode, possesses a much greater accessible range of positive potentials 26 29). 

In a similar way, the emergence of nanoparticles having optical and/or electrochemical properties has led to the achievement of new labels for DNA chips. These labels, which have nanometer size, require nucleic acid grafting procedures similar to those performed on a flat surface or on micrometer size beads. 

For understanding the complicated function of nucleic acids, it is desirable to gain information about the electrochemical properties of these polymers or their components. The first study about the polarography of purine derivatives was published by Heath [77] in 1946. Most new ideas for the electrochemical study of this attractive problem [78-83] were presented by Elving, (University of Michigan, Ann Arbor) and Palecek (Institute of Biophysics, Czechoslovak Academy of Sciences, Brno). 

The synthesis and electrochemical properties of nucleic acids containing a ferrocene moiety 03UK602. 

Beyond these obvious roles, the spectroscopic and electrochemical signatures of metal complexes can be used to understand DNA reactivity and to detect DNA structures. In this review, efforts to exploit the redox and photophysical properties of metal complexes to understand DNA reactivity will be discussed (23, 39). Metal complexes provide a special opportunity for these studies, because they exhibit well-defined redox states that can be correlated with redox changes in nucleic acids and nucleotides. In metal complexes, changes in these redox states are coupled to changes in the optical spectroscopy of the metal center. 

The history of the use of electrochemical methods to study the properties of proteins, enzymes, and their component structural units is several decades old. Until quite recently, these studies were primarily associated with the use of polarography to solve analytical problems. The polarographic method of analysis has become very popular for determination of proteins, enzymes, and nucleic acids.It has been found that proteins irreversibly adsorb on mercury and in the presence of cobalt salts promote the evolution of hydrogen. In this case wave height is proportional to the amount of adsorbed protein. These studies have been summarized in some reviews and monographs. " "" ... 

Aptamers are nucleic acid sequences that specifically bind proteins or low molecular-weight substrates. Aptamers are selected from a combinatorial library of lO -lO DNAs, using the Systematic Evolution of Ligands by Exponential Enrichment Process (SELEX). Numerous aptamers that specifically bind proteins or low molecular-weight substrates have been elicited in recent years. Also, their recognition properties have been used extensively to develop electrochemical [162,163] or optical... 

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