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Charge Transport in DNA - Insights from Simulations
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7.2Modeling the IonizationPotentials Table7.3: Statistics of the IP of adenine nucleobases in a polyA oligomer. Left: Sim- ulation without QM/MM coupling; only internal modes of vibration con- tribute to the fluctuations. Right: Simulation with QM/MM coupling to the environment; fluctuations of solvent and DNA backbone contribute to thefluctuations of IP. invacuo nucleobase mean± std. dev. [eV] A1 5.354± 0.099 A2 5.356± 0.090 A3 5.357± 0.101 A4 5.357± 0.095 A5 5.357± 0.095 A6 5.359± 0.096 QM/MM nucleobase mean± std. dev. [eV] A1 5.565± 0.304 A2 5.572± 0.303 A3 5.563± 0.301 A4 5.554± 0.302 A5 5.549± 0.304 A6 5.551± 0.305 an additional shift of IP had to be introduced to account for the environmental effect. Then theamplitudesAn of thecosine functionsof theenvironmentalfluctu- ationswerefitted in combinationwith theamplitudes for the internalfluctuations, obtainedpreviously, so that the largerfluctuations of about 0.3 eVobserved in the QM/MMenvironment are reproduced. Additionally, the amplitudes of the cosine functions that correspond to the nine lowest environmentalfluctuationswere scaleddownbya factorof0.6. These slow fluctuations correspond to movements of the whole molecular system, therefore theyhavevery longperiodsand rather lowamplitudes. TheMDsimulationsperformed toobtain the time series of IPwere conductedus- ing anon-polarizable forcefield. In such simulations, the electric field inducedby the environment is overestimated by 26-34%[80], thereforeQM/MMinteractions have to be scaled down by a factor of 1.5 for charge transfer calculations[73]. To model this scaling,MDsimulationswith andwithout this scaling factorwereper- formedand theCTparameters recorded. The time serieswere analyzed formean values and standard deviations. A new set of amplitudes for the environmental fluctuationswas introduced to reproduce these scaledfluctuations. 95
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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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