Excess electron transfer

Excess Electron Transfer in Defined Donor-Nudeobase and Donor-DNA-Acceptor Systems... 

Excess Electron Transfer in DNA PNA Hybrid Double Strands. . 200... 

Excess Electron Transfer in Flavin-Capped DNA Hairpins. 201... 

Oxidative Hole Transfer Reductive Excess Electron Transfer... 

The cycloreversion experiments showed a clean Tf=T-DNA to T/T-DNA transformation. No by-products were detected, which supports the idea that DNA may be more stable towards reduction compared to oxidation. Even heating the irradiated DNA with piperidine furnished no other DNA strands other then the repaired strands, showing that base labile sites - indicative for DNA damage - are not formed in the reductive regime. The quantum yield of the intra-DNA repair reaction was therefore calculated based on the assumption that the irradiation of the flavin-Tf=T-DNA strands induces a clean intramolecular excess electron transfer driven cycloreversion. The quantum yield was found to be around 0=0.005, which is high for a photoreaction in DNA. A first insight into how DNA is able to mediate the excess electron transfer was gained with the double strands 11 and 12 in which an additional A T base pair compared to 7 and 8 separates the dimer and the flavin unit. 

Scheme 6 a Incorporation of a silyl-spaced dimer into DNA, and treatment of the DNA strand with fluoride furnished DNA strand containing a dimer-unit with an open backbone. b Schematic representation of the light (ho) induced excess electron transfer (ET) from the reduced flavin to the dimer, followed by cycloreversion (CR). c The five DNA duplexes 13-17 containing the flavin donor and the dimer acceptor at increasing distances, together with the measured repair yields after irradiation for 1 min... 

The fact that the stacking situation also influences the excess electron transfer was finally established with the double strands P3 and P7. P3 exhibits increased fraying of the T=T containing double strand ends due to a lack of proper base pairing. Strand P7 contains, instead of FI, the flavin donor F2, which is located more deeply inside the duplex. The transfer efficiency responds to both changes. The excess electron transfer is decreased in P3 compared to PI and increased in P7 relative to P5. 

In order to gain a more detailed insight into how the flavin and thymine dimer orientation may influence the excess electron transfer process, rigid... 

Fig. 5 Flavin-capped and dimer containing DNA hairpin for excess electron transfer studies through DNA...

Incorporation of an artificial flavin nucleobase and of a cyclobutane pyrimidine dimer building block into DNA DNA double strands, DNArPNA hybrid duplexes, and DNA-hairpins, provided compelling evidence that an excess electron can hop through DNA to initiate dimer repair even at a remote site. The maximum excess electron transfer distance realised so far in these defined Donor-DNA-Acceptor systems is 24 A. New experiments are now in progress to clarify whether even larger transfer distances can be achieved. 

Because DNA is much more stable under reductive conditions, excess electron transfer may in the future, open the door to side reaction free chemistry at a distance, and may pave the way for DNA-based nanoelectronics devices. 

Behrens C, Cichon MK, Grolle F, Hennecke U, Carell T (2004) Excess Electron Transfer in Defined Donor-Nucleobase and Donor-DNA-Acceptor Systems. 236 187-204 Bertrand G, Bourissou D (2002) Diphosphorus-Containing Unsaturated Three-Menbered Rings Comparison of Carbon, Nitrogen, and Phosphorus Chemistry. 220 1-25 Betzemeier B, Knochel P (1999) Perfluorinated Solvents - a Novel Reaction Medium in Organic Chemistry. 206 61-78 Bibette J, see Schmitt V (2003) 227 195-215 Blais J-C, see Astruc D (2000) 210 229-259 Bogar F, see Pipek J (1999) 203 43-61 Bohme DK, see Petrie S (2003) 225 35-73 Bourissou D, see Bertrand G (2002) 220 1-25 Bowers MT, see Wyttenbach T (2003) 225 201-226 Brand SC, see Haley MM (1999) 201 81-129... 

Behrens C, Cichon MK, Grolle F, Hennecke U, Carell T (2004) Excess Electron Transfer in Defined Donor-Nucleobase and Donor-DNA-Acceptor Systems. 236 187-204 Belisle H, see Bussiere G (2004) 241 97-118 Beratan D, see BerUn YA (2004) 237 1-36... 

Also for other systems, V a values for hole transfer depend only weakly on the basis set [14, 41, 46]. This is at variance with results for the coupling of excess electron transfer where energies of more diffuse states are involved in the ground strategy this would correspond to employing energies of unoccupied molecular orbitals. 

When estimating the energetics of excess electron transfer in DNA via differences of electron affinities (EA) of nucleobases B in WCP trimers 5 -XBY-3 [92], we found the EA values of bases to decrease in the order C T A>G. The destabihzing effect of the subsequent base Y is more pronounced than that of the preceding base X. As strongest electron traps, we predicted the sequences 5 -XCY-3 and 5 -XTY-3, where X and Y are pyrimidines C and T. These triads exhibit very similar EA values, and therefore, the corresponding anion radical states should be approximately in resonance, favoring efficient transport of excess electrons in DNA [92]. 

Cai et al. [7e] investigated electron and hole transfer in various polynucleotide duplexes and compared them with previous results found for salmon sperm DNA, to examine the effect of base sequence on excess electron and hole transfer along the DNA 71-way at low temperature. Electron and hole transfer in DNA was found to be clearly base sequence dependent. In glassy aqueous systems (7M LiBr glasses at 77 K), excess electron-transfer rates increase in the order polydIdC-polydIdC<salmon testes DNAexcess electron and hole transfer rates increase in the order polyC-polyG<salmon testes DNATransfer distances at 1 min and distance decay constants for electron and hole transfer from base radicals to MX in polynucleotides-MX and DNA-MX at 77 K are derived and compiled in Table 3. This table clearly shows that the electron-transfer rate from donor sites decreases in... 

Base Sequence Effects on Excess Electron Transfer. Cai et al.69 investigated low temperature electron and hole transfer to intercalator trapping sites in various polynucleotide duplexes and compared them with previous results found for salmon sperm DNA. Electron and hole transfer in DNA was found to be base sequence dependent. In glassy aqueous systems (7 M LiBr, D20 glasses at 77 K), excess electron-transfer rates increase in the order polydldC-polydldC < DNA... 

Cai Z, Gu Z, Sevilla MD (2001) Electron spin resonance study of electron and hole transfer in DNA effects of hydration, aliphatic amine cations and histone proteins. J Phys Chem B 105 6031-6041 Cai Z, Li X, Sevilla MD (2002) Excess electron transfer in DNA effect of base sequence and proton transfer. J Phys Chem B 106 2755-2762... 

Messer A, Carpenter K, Forzley K, Buchanan J, Yang S, Razskazovskii Y, Cai Z, Sevilla MD (2000) Electron spin resonance study of electron transfer rates in DNA determination of the tunneling constant (1 for single-step excess electron transfer. J Phys Chem B 104 1128-1136 Meunier B (1992) Metalloporphyrins as versatile catalysts for oxidation reactions and oxidative DNA cleavage. Chem Rev 92 1411-1456... 

Voityuk AA, Michel-Beyerle M-E, Rosch N (2001) Energetics of excess electron transfer in DNA. Chem Phys Lett 342 231-238... 

In a series of papers, Cai and co-workers presented an explication of electron and hole transfer in /-irradiated DNA that clarified some confusion and some inconsistencies that existed in the literature at the time7 ° Using ESR at 77 K, Cai co-workers analyzed hole and excess electron transfer by observing, simultaneously, the concentration of both the electron/hole donor and the electron/hole acceptor as a function of time, thereby verifying that the underlying transfer occurs in the specific manner assumed for the mathematical analysis used. Because the analysis for excess electrons is identical to that for holes, we present both analyses here. 

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