On the dissociation of DNA enhanced by radical cations

This concerns the heat of reaction, Delta H-react degrees = Delta H-f degrees(K.) + Delta H-f degrees(L.) - Delta H-f degrees(KL), accompanying the cleavage of deoxyribonucleosides (KL) to give sugar radicals (K.) and (adenine or guanine) base radicals (L) under the influence of radical cations R+ = H+ . CH3+ and C2H5+. (The cited Delta H-f degrees's are the appropriate standard enthalpies of formation at 298.15 K.) Addition of R+ onto one or another nitrogen of the bases does indeed perturb the zero-point + heat-content energies Z, namely, Z(KL) -> Z(KL'), Z(L.) -> Z(L.'), as well as the "reorganizational energies" Re, i.e., Re(L) Re(L.'). (Re describes how a free radical differs from its hypothetical electroneutral counterpart found in a symmetrical molecule L-L) Finally, the "Charge Neutralization Energy" CNE describes the energetics accompanying charge transfers between the fragments K and L in the original molecule, linked to one another by the bond with energy epsilon(kl) (k is an element of K. I is an element of L). It turns out that CNE and Z have little (or no) saying in the decomposition KL -> K . +L.. The driving force is clearly in the weakening of epsilon(kl) under the influence of added R+ cations. The gas-phase Re energies, whose evaluation is reported in detail, would magnify this effect but are unlikely to be of any relevance in in vivo depurinations of DNA molecules. (C) 2010 Elsevier B.V.. All rights reserved.