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Charge Transport in DNA - Insights from Simulations
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ThestateofknowledgeofDNAstretching in2000wassummarizedintworeviews. [24, 25]At that time, a dispute on the nature of the overstretched state of dsDNA started, and it is in fact still going on. In contrast to the proposal of S-DNA, theoverstretchingprofileofDNAwasattributed to force-induceddehybridization basedonthermodynamicobservations.[26]Sincethen,reportshavebeenconstantly appearing against,[27] as well as in favor of the thermally induced melting.[28] Importantly, the nature of the overstretched state of DNA probably depends on the rate of stretching. A dsDNA oligomer was reported to dehybridize under a certain critical stretching rate,whereas a transition to S-DNAwasobserved above this threshold.[29] Further, DNA is observedmore stablewith 3’–3’ pulling than with5’–5’, and itwaspointedout that the relevant structuresaredifferent.[30]Two distinctoverstretchedDNAstateswereshownyetagain tooccur,[31]dependingon conditions likeDNA sequence, salt concentration and temperature. An excellent discussion of the state of the art on the DNA overstretching and of the current knowledge is given inRef. [32]. As for themolecularmodeling,quitea fewstudieson theoverstretching transition ofdsDNAappeared.[33–37] Theyall dealwithdsDNAoligomers ofup to 30base pairs being stretched in different ways, pulling either the 5’ ends, the 3’ ends or eventually all ends of the double strand. Inevitably, the still substantial computa- tional costofatomisticmoleculardynamics (MD)simulationmakes the timescales probedintheexperiments inaccessible. Thepreviouslyreporteddependenceof the conformationofoverstretchedDNAonthe loadingrate is thusan issue thathas to be taken intoaccountwhen interpreting theoutcomeofMDsimulations. At this point, thedependence ofCT inDNAon the conformationof themolecule canbe investigatedwithcomputationalmethodsconveniently. Electronic structure of overstretched DNA’ was the topic of an early study[38] dealing with a single sequence and static structures. Surprising response of CT efficiency on theDNA conformationwas found,[39] however,with a simplified stretching/twisting reac- tion coordinate. Indeed, it has long been known that the dynamic character of molecular structure has to be taken into account instead of static structures.[40] Especially formore complexmolecules likeDNA, the structuraldynamics and the molecular environmentplaydecisive roles,[41] bringing theseeffects into the focus of thoroughtheoretical investigation.[42–46]Thus, thecomputationalapproachhas to involve a plausible description ofDNAconformation and its fluctuationunder 7 Introduction
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Charge Transport in DNA Insights from Simulations
Title
Charge Transport in DNA
Subtitle
Insights from Simulations
Author
Mario Wolter
Publisher
KIT Scientific Publishing
Date
2013
Language
English
License
CC BY-SA 3.0
ISBN
978-3-7315-0082-7
Size
17.0 x 24.0 cm
Pages
156
Keywords
Charge Transport, Charge Transfer, DNA, Molecular Dynamics, Quantum Mechanics
Categories
Naturwissenschaften Chemie

Table of contents

  1. Zusammenfassung 1
  2. Summary 3
  3. 1 Introduction 5
  4. 2 TheoreticalBackground 11
    1. 2.1 MolecularMechanics 11
    2. 2.2 MolecularDynamicsSimulation 13
      1. 2.2.1 Solving theEquationsofMotion 14
      2. 2.2.2 ThermodynamicEnsembles 15
    3. 2.3 QuantumChemistry 18
      1. 2.3.1 DensityFunctionalTheory 18
      2. 2.3.2 ApproximativeDFT–Density-FunctionalTight-Binding 21
    4. 2.4 DynamicsofExcessCharge inDNA 24
      1. 2.4.1 TheMulti-ScaleFramework 25
      2. 2.4.2 TheFragmentOrbitalApproach 26
    5. 2.5 ChargeTransport inDNA 29
      1. 2.5.1 Landauer–BüttikerFramework 29
    6. 2.6 ChargeTransfer inDNA 32
      1. 2.6.1 Basics ofChargeTransfer 32
      2. 2.6.2 Non-adiabaticPropagationSchemes 34
  5. 3 SimulationSetup 39
    1. 3.1 TheDNAMolecule 39
      1. 3.1.1 InvestigatedDNASequences 42
    2. 3.2 MDSimulationofDNA 44
    3. 3.3 DNAunderMechanical Stress 45
    4. 3.4 MicrohydratedDNA 46
  6. 4 DNAUnderExperimentalConditions 49
    1. 4.1 FreeMDSimulations 50
    2. 4.2 TheStructuralChangesofDNAuponStretching 51
    3. 4.3 IrreversibilityofDNAStretching inSimulations 56
    4. 4.4 Effects ofLowHydration 58
    5. 4.5 Effects ofDecreased IonContent 62
    6. 4.6 Effect ofWater and Ionson theStretchingProfileofDNA 64
    7. 4.7 Conclusion 67
  7. 5 ChargeTransport inStretchedDNA 69
    1. 5.1 InvestigatedSequences andStructures 69
    2. 5.2 ChargeTransportCalculations 71
    3. 5.3 SequenceDependentChargeTransport 73
    4. 5.4 DetailedStructuralDifferences 74
    5. 5.5 Conclusion 76
  8. 6 ChargeTransport inMicrohydratedDNA 79
    1. 6.1 InvestigatedSequences andStructures 79
    2. 6.2 ChargeTransferParameters 80
    3. 6.3 ChargeTransportCalculations 84
    4. 6.4 DirectDynamicsofChargeTransfer 86
    5. 6.5 Conclusion 87
  9. 7 AParametrizedModel toSimulateCT inDNA 89
    1. 7.1 Creating theElectronicCouplings 90
    2. 7.2 Modeling the IonizationPotentials 93
    3. 7.3 TestingwithChargeTransportCalculations 97
    4. 7.4 ChargeTransferExtensions 98
    5. 7.5 TestingwithChargeTransferMethods 102
    6. 7.6 Conclusion 103
  10. 8 Conclusion 105
  11. Appendix 111
  12. A DNAUnderExperimentalConditions 111
    1. A.1 TheStructuralChangesofDNAuponStretching 111
    2. A.2 Effect ofLowHydrationandDecreased IonContent 112
    3. A.3 StretchingofMicrohydratedDNA 116
  13. B CTinMicrohydratedDNA 117
    1. B.1 HelicalParameters -CompleteOverview 117
    2. B.2 ElectronicCouplings 118
    3. B.3 IonizationPotentials 119
    4. B.4 ESP InducedbyDifferentGroupsofAtoms 122
    5. B.5 DistanceofChargedAtomGroups fromtheHelicalAxis 123
  14. List ofPublications 137
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