Principles and Mechanisms of Photoinduced Charge Injection, Transport, and Trapping in DNA

Abstract

The first observation that the -stacked array of base pairs in B-form DNA might serve as a pathway for charge migration was published over 40 years ago [1]. Since then, the basic question of whether DNA serves as a wire or conducting biopolymer for long-range charge migration has been discussed in an intense and highly controversial scientific dispute. DNA was considered to be a molecular wire, a semiconductor, or an insulator [2]. Barton and coworkers pioneered this research through remarkable contributions about photoactivated charge transfer chemistry in DNA [3]. Motivated by the biological relevance of DNA damage and also by the controversy about charge transfer in DNA, interest in DNA-mediated charge migration grew enormously in the scientific community in the 1990s [4]. Research groups from different chemistry subdisciplines, such as organic chemistry, inorganic chemistry, physical chemistry, and biochemistry, as well as biologists, physicists, and material scientists have contributed significantly to this research topic. This interdisciplinary nature represents an important and exciting aspect of this subject. Based on these experiments and results, a clear picture about charge transfer processes in DNA has emerged by now. The extreme controversy has been solved by the description of different mechanistic aspects, mainly the superexchange and the hopping mechanisms, which have been verified experimentally [5]. It has become clear that DNA-mediated charge transfer can occur on an ultrafast time scale and can result in reactions over long distances [4]. Hence, DNA-mediated charge transfer has been the subject of considerable interest, having biological relevance in the formation of oxidative damage to DNA that can result in severe consequences such as mutagenesis, apoptosis, or cancer [6]. Additionally, charge transfer plays a growing role in the recent development of DNA chips or microarrays detecting single-base mismatches or various DNA lesions by electrochemical readout methods [7]. Moreover, knowledge about charge transfer processes in DNA can be used for nanochemical applications, such as DNA-based devices [8]. 1