Mechanism of Charge Transport in DNA:  Internally-Linked Anthraquinone Conjugates Support Phonon-Assisted Polaron Hopping

Abstract

A series of anthraquinone-containing (AQ) DNA conjugates was prepared. In each case, the AQ is linked to the 2‘-oxygen of a uridine. Physical and spectroscopic data suggest that the AQ is intercalated in the duplex DNA on the 3‘-side of the uracil. Irradiation of the AQ-DNA conjugates with UV light results in piperidine-requiring strand cleavage at GG steps of both the AQ-containing strand and its complement. The AQ-conjugates were designed to have GG steps disposed symmetrically about the AQ intercalation site. The distance dependence of reaction efficiency at GG steps following AQ irradiation was measured by means of an AQ-containing 71 mer having 7 GG steps. The efficiency of reaction in this sequence falls off exponentially with a distance dependence of 0.071 Å-1. AQ-containing conjugates were prepared that incorporate 7,8-dihydro-8-oxoguanines (8-OxoG) at various locations. 8-OxoG has a lower oxidation potential than any of the normal DNA bases and serves as a trap for the migrating radical cation. The 8-OxoG is a very effective trap when the radical cation must migrate through it to reach the GG step, it is a less effective trap when it is on the strand complementary to the GG step. These findings support the mechanism for long-range radical cation migration described as phonon-assisted polaron hopping.

Charge Transport in Poly(dG)–Poly(dC) and Poly(dA)–Poly(dT) DNA Polymers

“…Although the debate whether DNA constitutes a conductor is still continuing, there already exist strong experimental evidence that DNA forms an effectively one-dimensional molecular wire [3]. Among several theoretical attempts to describe the charge transport mechanism in DNA the polaron approach has turned out to be a promising candidate for modeling constructive interplay between the charge-carrying system and vibrational degrees of freedom of the DNA conspiring to establish coherent ET [4][5][6][7][8]. Recent experiments support the polaron mechanism for ET in DNA polymers [9].…”

Effects of strand and directional asymmetry on base–base coupling and charge transfer in double-helical DNA

“…A wealth of experimental evidence has established, undeniably, that DNA can act as a conduit for rapid and long-range charge transfer (CT), not only in DNA assemblies designed in the laboratory (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), but also in biologically significant environments (25,26). DNA, remarkable for its role in the molecular basis of life, may also play a role as a mediator of CT in diverse areas of chemistry and biology.…”

On the Possibility of Superfast Charge Transfer in DNA

“…Шустер с соавторами [1,19,20] при объяснении этого явления использовали представление о поляроне большого радиуса, но, как было сказано выше, это представление противоречит картине полностью локализованных сольватированных поляронов для ДНК в растворе.…”

“…В экспериментах [21][22][23][24][25] и [19,20] по миграции катион-радикалов (дырок) G + в находящейся в растворителе ДНК заряд может быть обнаружен вследствие захвата G + нуклеофильными молекулами воды, который приводит к распределению заселенностей PG, PGG, PGGG в продуктах разрезанных цепочек в различных позициях радиомеченной цепи. Основное предположение, которое мы будем использовать при объяснении совокупности экспериментов [19][20][21][22][23][24][25], состоит в том, что вследствие медленности реакции между G + и водой катион-радикалы долгое время не захватываются окружающей средой и совершают множественные обратимые прыжки, что приводит к динамически равновесному распределению положительного заряда по сайтам ДНК. Совокупность рассматриваемых экспериментов получает объяснение, если считать, что рассматриваемое квазиравновесное состояние устанавливается быстрее характерного времени сольватации.…”