Page - 87 - in Charge Transport in DNA - Insights from Simulations

6.5Conclusion Table6.3: Number of CT events per ns observed in non-adiabatic simulations of hole transfer in theAGoligo. system mean-field surfacehopping Full 33±5 45±11 Dry1 20±8 24±8 twice, usingdifferent non-adiabatic propagators – themean-fieldmethod and the surfacehopping. The events of holehopping fromoneG toanotherwere counted andaveragedovereachgroupof tensimulations; theresultsareshownin table6.3. Very similar rates of CT are obtainedwith the twomethods used. Although, the rate is decreased by ca. 45% in themicrohydrated systemDry1. In contrast, the electric transmission obtained with the Landauer model was larger in the Dry1 systems than in the fullyhydratedones, formostof theDNAoligos includingAG. While thisdifferencemaysurelybeaccounted to theentirelydifferent character of themethods, another point should be emphasized here: The difference observed between the fullyhydrated systemsand themicrohydratedDry1 (andDry2where applicable) is actually smaller thanwhatmayhavebeenexpected, considering the verydifferent structureof thesystems–DNAinbulksolutionvs.DNAincomplex withwatermolecules, however in thegasphase. 6.5 Conclusion In this chapter, the charge transport and charge transfer in microhydrated DNA strands was investigated. The idea of microhydrated DNA was induced by the experiments,where theDNAstrand is dried before themeasurements. However, theexactamountofwaterpreservedat theDNAstrand isunknownandcannotbe determinedby the experiments alone. The simulationunder these conditionswas able to resolve thequestionhowthese conditions affect theCT. Inconclusion, theefficiencyofelectron transfer/ transport inmicrohydratedDNA that has retained regular double-stranded structure is similar to that in DNA in bulksolution. Themagnitudeaswellasfluctuationsof theelectricfield inducedby theaqueousenvironmentaredue to theclosesthydrationshell(s) fromthedecisive 87