DNA-based electronics

Razskazovskiy et al. employ ESR spectroscopy at low temperatures to investigate electron transfer within brominated DNA [8]. The brominated DNA base electron traps were introduced by bromination of DNA in ice-cooled aqueous solution. The procedure is shown by NMR and GC/MS techniques to modify thymine, cytosine, and guanine, transforming them into 5-bro-mo-6-hydroxy-5,6-dihydrothymine, T(OH)Br, 5-bromocytosine, CBr, and 8-bromoguanine, GBr, derivatives. The bromination products formed in molar ratio close to T(OH)Br/CBr/GBr 0.2 1 0.23 and serve as internal electron scavengers on y-irradiation. Structurally the CBr and GBr are planar, but T(OH)Br is quite nonplanar with the bromine directly above the molecular plane. This disrupts the DNA base stack. Paramagnetic products that result... 

Colson A-O, Sevilla MD (1995) Ab initio molecular orbital calculations of radicals formed by H and OH addition to DNA bases electron affinities and ionization potentials. J Phys Chem 99 13033-13037... 

High-resolution in situ STM as well as phase transition dynamics of nucleobases on Au(lll) and other low-index electrode surfaces supported by infrared spectroscopy have been reviewed recently by Nichols and coworkers [142] and Wandlowski and coworkers [143]. We refer to these reviews for details and note instead another aspect of single-molecule dynamics of DNA-based molecules. The observed electronic conductivity of oligonucleotides of variable length and variable base composition has opened almost a Pandora s box of novel DNA-based electronic properties. These include particularly photochemical and interfacial electrochemical ET. We refer to other recent reviews [144, 145] for this, still far from settled, issue but note the following STM-based studies that illuminate the conductivity issue at the single-molecule level (Figure 2.4). 

In comparison, DNA-based molecules functionalized by suitable redox groups display efficient long-range interfacial electrochemical electron (or hole) transmission between the electrode and oligonucleotide-tethered redox groups under mild conditions, i.e. close to reversible electrochemical conditions in aqueous buffers, cf Chapter 5 and below. This remains as one of the puzzles of DNA-based electronic transmission behaviour. 

Investigations such as these are important in interfaeial DNA-based electronic conductivity, because they have mapped the loeal environments for the electronie conductivity of the DNA-based moleeules directly in the... 

In 2002, Keren et al. [9] demonstrated a detailed masking process for creating DNA-based electronic components. A region of DNA was coated with RecA protein. The DNA was then exposed to silver nitrate and then gold was deposited onto the regions of DNA unprotected by RecA. The RecA protein was then... 

Sharma, P., Singh, H Sharma, S. and Singh, H. (2007) Binding of Gold Nanoclusters with Size-Expanded DNA Bases A Computational Study of Structural and Electronic Properties. Journal of Chemical Theory and Computation, 3, 2301-2311. 

Substitution-inert complexes have also recently been introduced into DNA as modified-base phosphoramidites. Interest here is generally focused on photo- and redox-active metal species for use as probes for sensing applications (165) and in studies on DNA-mediated electron... 

Broo A, Holmen A (1997) Calculations and characterization of the electronic spectra of DNA bases based on ab initio MP2 geometries of different tautomeric forms. J Phys Chem A 101 3589... 

Bouvier B, Gustavsson T, Markovitsi D, Millie P (2002) Dipolar coupling between electronic transitions of the DNA bases and its relevance to exciton states in double helices. Chem Phys 275 75—92... 

One-Electron Oxidation Reactions of the Pyrimidine and Purine DNA Bases... 

One-Electron Oxidation Reactions of Cytosine and 5-methylcytosine DNA Base... 

Extended solid state n systems facilitate CT, particularly when doped [4-6]. The analogy between DNA and conductive solid state -stacks therefore establishes that a requisite condition for CT may exist in DNA. DNA contains an array of heterocyclic aromatic base pairs, stacked at a distance of 3.4 A, wrapped within a negatively charged sugar phosphate backbone [7] (Fig. 1). The interactions between the n electrons of the DNA base pairs provide the electronic coupling necessary for CT to occur. 

Anthraquinones are nearly perfect sensitizers for the one-electron oxidation of DNA. They absorb light in the near-UV spectral region (350 nm) where DNA is essentially transparent. This permits excitation of the quinone without the simultaneous absorption of light by DNA, which would confuse chemical and mechanistic analyses. Absorption of a photon by an anthraquinone molecule initially generates a singlet excited state however, intersystem crossing is rapid and a triplet state of the anthraquinone is normally formed within a few picoseconds of excitation, see Fig. 1 [11]. Application of the Weller equation indicates that both the singlet and the triplet excited states of anthraquinones are capable of the exothermic one-electron oxidation of any of the four DNA bases to form the anthraquinone radical anion (AQ ) and a base radical cation (B+ ). 

Fig. 1 Schematic mechanism for the long-distance oxidation of DNA. Irradiation of the anthraquinone (AQ) and intersystem crossing (ISC) forms the triplet excited state (AQ 3), which is the species that accepts an electron from a DNA base (B) and leads to products. Electron transfer to the singlet excited state of the anthraquinone (AQ 1) leads only to back electron transfer. The anthraquinone radical anion (AQ ) formed in the electron transfer reaction is consumed by reaction with oxygen, which is reduced to superoxide. This process leaves a base radical cation (B+-, a hole ) in the DNA with no partner for annihilation, which provides time for it to hop through the DNA until it is trapped by water (usually at a GG step) to form a product, 7,8-dihydro-8-oxoguanine (8-OxoG)...

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