Charge transport in DNA molecules: Structural and dynamical disorder

200710

Outline:2. Structure disorder and correlation3. Dynamical disorder Effects of disorder and correlation of DNA base sequencesEffects of twist modes, rotational polarons4. Conclusions1. Introduction

Charge transport in DNA is not only of fundamental importance, but also has important applications in biological process (such as in repair mechanism after radiation damage), and in possible novel device designs.Motivation:Introduction(a) DNA-Based devices1-D Nanowire2-D networkSelf-assemblyRecognition

ExperimentsDNA molecules are found to be insulator, (semi-)conductor, etc.Theories(b) Applications in biological processes

www.accessexcellence.orgDNADifferent sequences /structure propertiesFlexible structure Twisting modes

Anderson localization, scaling theoryOne puzzle: Why there is conductive behavior for 1D-DNA chain with random sequences ?Structure disorder and correlationsRandom variable

D-dimensional system with volumeconductanceStrong disorderWeak disorderd=3d=2d=1d=1All eigenstates in 1-D disordered systems are localized states. the zero temperature conductance vanishes. Localized stateExtended stateCharge transport

One-parameter scaling theoryAll eigenstates in 1-D disordered systems are localized states.Anderson localizationFor 1-D system with correlated disorderExistence of extended statesShort-range correlationrandom dimer model,Extended statesLong-range correlationexistence of mobility edge BUT

TGGTCCTheoretical modelone-dimensional DNA chain with base pairs AT and CG:Main point : Disorder with local correlation

Diagonal disorder is correlated to off-diagonal disorder.

1. Zhang et al, Phys. Rev. B 20042. Zhang et al, Microelectro. J.Random variableRandom variable

Limiting cases1.Anderson model, localized eigenstates2.Low concentration limitRepulsive impurity model, existence of extended states

Correlation enhances transportLocal correlation leads to Enhancement of transport

Additional correlation in sequences improves transport furtherA: random sequences with local correlationB: random sequences without local correlationC: random dimer sequences with local correlationCalculation method: Transfer matrix methodTransmission coefficientPhysics origin: competition between disorder and correlation

High T even for high concentration of impuritiesLocal correlation leads to resonant scatteringGolden Correlation Dependence of concentration of impuritiesWith increasing concentration,transmission coefficient decreases the peak positions shift.

one-dimensional DNA chain with base pairs AT and CG:Structural disorder and charge transport in DNAWatanabe et al, APL 2001

DNALeadLeadMobile states Mobile states Mobility gap I-V curvesLandauer-Bttiker formalismFermi function: a possible non-symmetric voltage drop at each contact

(a) Correlation enhance transportA: random sequences with local correlationB: random sequences without local correlationC: random dimer sequences with local correlation(b) Sequence dependenceDifferent DNAmoleculesE: random sequences w/local correlationsF: sequence D1S80G: PolyG-PolyCDNA L=562 base pairsT=330K300 average over disorder configurations

(d) Effects of temperatureI-V curve is nearly insensitive to Fermi level broadening.At low temperature, I-V curve is sharper.(c) Dependence of concentration of impuritiesWith increasing of impurity concentration

current amplitude decreasescurrent gap increases

Leads: end group DNA bases linkingmolecule to current electrodes

For D1S80: DNA 414 bases & leads 148 basesIn DNA D1S80, leads increase current gap

suppressing currentamplitudes but within one order of magnitude (e) Effects of leadsnearlyperiodicsequenceleadlead

Solids or molecular systems with flexible structure so that twist or rotational degrees of freedom are important. Swaminathan, et al J. Am. Chem. Soc. 1991Dynamical disorderRotational Holstein polaronsZhang et al, PRB; Bruinsma PRL;

Vibrational polaronA quasiparticle formed by a conduction electron (or hole) together with its self-induced polarization in solid or molecular systems.

Polarons: electronic phonon-hairy balls

If coupling is weak: heavier electrons, nearly extended, fermions still, e0

If strong coupling (alkali halides, organic crystals): localized/trapped electrons, fermions, e0

Rotational Holstein modelLocal EP Interaction

Anharmonic oscillation

Nonlinear interactionelectron-phonon (EP) coupling constant

Weak coupling regime Polaronic energy shiftEffective massEnergy of phonon cloundsUnlike the usual polaron (associated with translation modes), andcome from different orders of EP interaction

In Non-adiabatic and strong coupling regime:polaron energy shift:Bandwidth:vs usual vibrational Holstein polaron bandwidth:In adiabatic regime:weaker power-law suppression of bandwidthfor rotational Holstein polaronEffective mass

Non-adiabatic regimeAdiabatic regimeWeak coupling regimestrong coupling regime

Conclusions:Other issues The interference effects between twist- and vibrational-polarons The effects of water molecules and ions

Other complex molecule systems We have shown that correlations introduced by chemical structure in DNA greatly affect charge transport in the molecule and torsional motion along the DNA chain results in electron-twiston coupling effects which reduce the electronic transport. Local correlation generates new conduction channels and enhance transport.Additional correlation in sequences improves transport furtherBackbone changes the local correlationLocal twist-coupling yields power-law vs exponential bandwidth renormalization.

Experimental realization of the system in superlattice For fixed Uis smaller, BUT transport is poorer