M-DNA: A novel metal ion complex of DNA studied by fluorescence techniques

M-DNA, a complex formed in solution between divalent metal ions (M) and duplex DNA, has been studied extensively using fluorescence quenching. This review examines the methods used to examine the formation of M-DNA, and its ability to serve as a pathway for electron transfer between donor and acceptor chromaphores. A mass action model for M-DNA formation is presented based upon the results of fluorescence quenching studies using fluorescein/QSY-7 labeled duplexes. From the mass action analysis, it was determined that ∼1.4 protons are released per base pair, with keq on the order of 10−8, indicative of a strong interaction. As resonance energy transfer is shown to be unlikely over the distances involved in this work, the observed quenching in M-DNA is discussed in terms of an electron hopping mechanism for electron transfer, with khop = 2.5 × 1011 s−1.