Page - 81 - in Charge Transport in DNA - Insights from Simulations

6.2ChargeTransferParameters Figure6.1: Electronic coupling in the oligosAt andGT, for fully hydrated system as well as the various levels ofmicrohydration. Table6.1: Helical parameter rise (distance of stacked base pairs,Åunits) inMDsim- ulations of fully solvated andmicrosolvatedDNAoligonucleotides. Oligo AA AG AT GG GC GT Full 3.36 3.38 3.29 3.39 3.35 3.34 Dry1 3.28 3.34 3.23 3.36 3.34 3.27 Dry2 2.93 3.42 2.81 3.39 3.43 3.34 and AT-GC, discussed in a previous work,[124] is even emphasized in the low- humidity environment. Note, that the absolutevaluesof theEC for fullyhydrated systems in thisworkareca.30%smaller than in thecitedpreviousworkdue to the orthogonalizationof thebasis set. The EC are linked to the structure of DNA, and are particularly sensitive to the distancebetweennucleobases,which is roughlydescribedby thehelicalparameter rise. Indeed, the rise decreases slightly for all of theDry1 systems, and increases again for Dry2 inmost of the cases, see Tab. 6.1. Thismay explain the observed differences of the ECbetween the various hydration levels. Clearly, the structural changedue todehydration impacts the electronicproperties of themolecules. The behaviorof theotherparametersupondrying is inconclusive. SeeappendixB.1 for an complete overviewof some representative helical parameters for all sequences undermicrohydratedconditions. 81