Sequence-independent and rapid long-range charge transfer through DNA

Unexpected large charge transfer rate mediated by adenine in twisted DNA structure

DNA exhibits remarkable charge transfer ability, which is crucial for its biological functions and potential electronic applications. The charge transfer process in DNA is widely recognized as primarily mediated by guanine, while the contribution of other nucleobases is negligible. Using the tight-binding models in conjunction with first-principles calculations, we investigated the charge transfer behavior of homogeneous GC and AT pairs. We found that the charge transfer rate of adenine significantly changes. With overstretching, the charge transfer rate of adenine can even surpass that of guanine, by as much as five orders of magnitude at a twist angle of around 26°. Further analysis reveals that it is attributed to the turnover of the relative coupling strength between homogeneous GC and AT base pairs, which is caused by the symmetry exchange between the two highest occupied molecular orbitals of base pairs occurring at different twist angles. Given the high degree of flexibility of DNA in vivo and in vitro conditions, these findings prompt us to reconsider the mechanism of biological functions concerning the charge transfer in DNA molecules and further open the potential of DNA as a biomaterial for electronic applications.

Polymerization-Mediated Through-Space Charge Transfer: An Emerging Strategy for Light-Emitting Materials

Through-space charge transfer (TSCT) has attracted increasing attention owing to its great potential in designing efficient light-emitting molecules and polymers. Complementary to through-bond charge transfer and Förster resonance energy transfer, TSCT offers an alternative approach for the manipulation of molecular fluorescence. Recently, the synergy between TSCT and polymer systems through polymerization-mediated charge transfer has fostered the advancements of innovative light-emitting functional materials featuring thermally activated delayed fluorescence and/or aggregation-induced emission. This perspective highlights the significant progress in tailoring emission properties through structural engineering of donor and acceptor groups within polymeric systems, leveraging the TSCT mechanism. This strategy has transcended the limitations of traditional charge transfer systems with its tolerance to extended donor-acceptor distance, paving the way for novel applications beyond organic light-emitting diodes. The discussion concludes with a forward-looking analysis of potential future research trajectories in the field of polymerization-mediated charge transfer for developing next-generation light-emitting materials.

Development of a QM/MM(ABEEM) method for the deprotonation of neutral and cation radicals in the G-tetrad and GGX(8-oxo-G) tetrad

The rapid deprotonation of G˙+ in the DNA strand impedes positive charge (hole) transfer, whereas the slow deprotonation rate of G˙+ in the G-tetrad makes it a more suitable carrier for hole conduction. The QM/MM(ABEEM) combined method, which involves the integration of QM and the ABEEM polarizable force field (ABEEM PFF), was developed to investigate the deprotonation of neutral and cation free radicals in the G-tetrad and GGX(8-oxo-G) tetrad (xanthine and 8-oxoguanine dual substituted G-tetrad). By incorporating valence-state electronegativity piecewise functions χ*(r) and implementing charge local conservation conditions, QM/MM(ABEEM) possesses the advantage of accurately simulating charge transfer and polarization effect during deprotonation. The activation energy calculated by the QM method of X˙ is the lowest among other bases in the GGX(8-oxo-G) tetrad, which is supported by the computation of the average electronegativity calculated by ABEEM PFF. By utilizing QM/MM(ABEEM) with a two-way free energy perturbation method, the deprotonation activation energy of X˙ in the GGX(8-oxo-G) tetrad is determined to be 33.0 ± 2.1 kJ mol-1, while that of G˙+ in the G-tetrad is 20.7 ± 0.6 kJ mol-1, consistent with the experimental measurement of 20 ± 1.0 kJ mol-1. These results manifest that X˙ in the GGX(8-oxo-G) tetrad exhibits a slower deprotonation rate than G˙+ in the G-tetrad, suggesting that the GGX(8-oxo-G) tetrad may serve as a more favorable hole transport carrier. Furthermore, the unequal average electronegativities of bases in the GGX(8-oxo-G) tetrad impede the deprotonation rate. This study provides a potential foundation for investigating the microscopic mechanism of DNA electronic devices.

Programmed Control of Fluorescence Blinking Patterns based on Electron Transfer in DNA

Fluorescence imaging uses changes in the fluorescence intensity and emission wavelength to analyze multiple targets simultaneously. To increase the number of targets that can be identified simultaneously, fluorescence blinking can be used as an additional parameter. To understand and eventually control blinking, we used DNA as a platform to elucidate the processes of electron transfer (ET) leading to blinking, down to the rate constants. With a fixed ET distance, various blinking patterns were observed depending on the DNA sequence between the donor and acceptor units of the DNA platform. The blinking pattern was successfully described with a combination of ET rate constants. Therefore, molecules with various blinking patterns can be developed by tuning ET. It is expected that the number of targets that can be analyzed simultaneously will increase by the power of the number of blinking patterns.

The effect of spermidine on guanine decomposition via photoinduced electron transfer in DNA

The addition of spermidine caused the attenuation of guanine decomposition via photoinduced electron transfer in pyrene-modified DNA, and higher added concentrations of spermidine resulted in the promotion of decomposition in condensed DNA.

Electron Transfer in DNA at Electrified Interfaces

The ability of the DNA double helix to transport electrons underlies many life-centered biological processes and bio-electronic applications. However, there is little consensus on how efficiently the base pair π-stacks of DNA mediate electron transport. This minireview scrutinizes the current state-of-the-art knowledge on electron transfer (ET) properties of DNA and its long-range ability to transfer (mediate) electrical signals at electrified interfaces, without being oxidized or reduced. Complex changes an electric field induces in the DNA structure and its electronic properties govern the efficiency of DNA-mediated ET at electrodes and allow addressing the existing phenomenological riddles, while recently discovered rectifying properties of DNA contribute both to our understanding of DNA's ET in living systems and to advances in molecular bioelectronics.

Scanning Tunneling Microscopy and Spectroscopy of Novel Silver-Containing DNA Molecules

The quest for a suitable molecule to pave the way to molecular nanoelectronics has been met with obstacles for over a decade. Candidate molecules such as carbon nanotubes lack the appealing trait of self-assembly, while DNA seems to lack the desirable feature of conductivity. Silver-containing poly(dG)-poly(dC) DNA (E-DNA) molecules have recently been reported as promising candidates for molecular electronics, owing to the selectivity of their metallization, their thin and uniform structure, their resistance to deformation, and their maximum possible high conductivity. Ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) of E-DNA presents an elaborate high-resolution morphology characterization of these unique molecules, along with a detailed depiction of their electronic level structure. The energy levels found for E-DNA indicate a novel truly hybrid metal-molecule structure, potentially more conductive than other DNA-based alternatives.

Generation of the Thymine Triplet State by Through-Bond Energy Transfer

Benzophenone (BP) and drugs containing the BP chromophore, such as the non-steroidal anti-inflammatory drug ketoprofen, have been widely reported as DNA photosensitizers through triplet-triplet energy transfer (TTET). In the present work, a direct spectroscopic fingerprint for the formation of the thymine triplet (³ Thy*) by through-bond (TB) TTET from ³ BP* has been uncovered. This has been achieved in two new systems that have been designed and synthesized with one BP and one thymine (Thy) covalently linked to the two ends of the rigid skeleton of the natural bile acids cholic and lithocholic acid. The results shown here prove that it is possible to achieve triplet energy transfer to a Thy unit even when the photosensitizer is at a long (nonbonding) distance.

High-Precision Electrochemical Measurements of the Guanine-, Mismatch-, and Length-Dependence of Electron Transfer from Electrode-Bound DNA Are Consistent with a Contact-Mediated Mechanism

Despite 25 years' effort, serious questions remain regarding the mechanism(s) underlying electron transfer through (or from) electrode-bound double-stranded DNA. In part this is because a control experiment regarding the putatively critical role of guanine bases in the most widely proposed transport mechanism (hopping from guanine to guanine through the π-stack) appears to be lacking from the prior literature. In response, we have employed chronoamperometry, which allows for high-precision determination of electron transfer rates, to characterize transfer to a redox reporter appended onto electrode-bound DNA duplexes. Specifically, we have measured the effects of guanines and base mismatches on the electron transfer rate associated with such constructs. Upon doing so, we find that, counter to prior reports, the transfer rate is, to within relatively tight experimental confidence intervals, unaffected by either. Parallel studies of the dependence of the electron transfer rate on the length of the DNA suggest that transfer from this system obeys a "collision" mechanism in which the redox reporter physically contacts the electrode surface prior to the exchange of electrons.

Mitochondria-Targeted DNA Nanoprobe for Real-Time Imaging and Simultaneous Quantification of Ca2+ and pH in Neurons

Herein, a single highly selective DNA nanoprobe was designed and created for the real-time imaging and simultaneous quantification of two kinds of biological species using Ca²⁺ and pH; the molecules were selected as models because of their close relationship with cellular functions and diseases. A Ca²⁺ fluorescent probe was synthesized and assembled onto a DNA nanostructure together with pH-responsive, inner-reference, and mitochondria-targeted molecules. This nanoprobe with high spatial resolution, together with long-term fluorescent and structural stability, powerfully tracked pH and Ca²⁺ dynamics at the same localization in mitochondria in response to O₂^•--induced oxidative stress and aggregated amyloid β (Aβ) stimulation with a temporal resolution of milliseconds. Using this tool, we discovered that O₂^•- and Aβ triggered transitory cytoplasmic acidosis and then activated acid-sensing ion channel 1a (ASIC1a) in the mitochondrial membrane, leading to mitochondrial Ca²⁺ overload and pH abnormalities, which contribute to neuron death. Moreover, psalmotoxin 1 effectively protected against O₂^•-- and Aβ-induced neuron injury.

DNA Generated Electric Current Biosensor

In addition to its primary function as a genetic material, deoxyribonucleic acid (DNA) is also a potential biologic energy source for molecular electronics. For the first time, we demonstrate that DNA can generate a redox electric current. As an example of this new functionality, DNA generated redox current was used for electrochemical detection of human epidermal growth factor receptor 2 (HER2), a clinically important breast cancer biomarker. To induce redox current, the phosphate of the single stranded DNA aptamer backbone was reacted with molybdate to form redox molybdophosphate precipitate and generate an electrochemical current of ∼16.8 μA/μM cm². This detection of HER2 was performed using a sandwich detection assay. A HER2 specific peptide was immobilized onto a gold electrode surface for capturing HER2 in buffer and serum. The HER2 specific aptamer was used as both ligand to bind the captured HER2 and to generate a redox current signal. When tested for HER2 detection, the electrochemical current generated by the aptasensor was proportional to HER2 concentration in the range of 0.01 to 5 ng/mL, with a current generated in the range of ∼6.37 to 31.8 μA/cm² in both buffer and serum. This detection level is within the clinically relevant range of HER2 concentrations. This method of electrochemical signal amplification greatly simplifies the signal transduction of aptasensors, broadening their use for HER2 analysis. This novel approach of using the same aptamer as biosensor ligand and as transducer can be universally extended to other aptasensors for a wide array of biodetection applications. Moreover, electric currents generated by DNA or other nucleic acids can be used in molecular electronics or implanted devices for both power generation and measurement of output.

Conformational gating of DNA conductance

DNA is a promising molecule for applications in molecular electronics because of its unique electronic and self-assembly properties. Here we report that the conductance of DNA duplexes increases by approximately one order of magnitude when its conformation is changed from the B-form to the A-form. This large conductance increase is fully reversible, and by controlling the chemical environment, the conductance can be repeatedly switched between the two values. The conductance of the two conformations displays weak length dependencies, as is expected for guanine-rich sequences, and can be fit with a coherence-corrected hopping model. These results are supported by ab initio electronic structure calculations that indicate that the highest occupied molecular orbital is more disperse in the A-form DNA case. These results demonstrate that DNA can behave as a promising molecular switch for molecular electronics applications and also provide additional insights into the huge dispersion of DNA conductance values found in the literature.

DNA could find a role in molecular electronics. Here, the authors show that the conductance of DNA can be reversibly changed by an order of magnitude when its conformation is changed from one form to another by controlling its chemical environment.

Triple helix conformation-specific blinking of Cy3 in DNA

We report that Cy3 undergoes triple helix conformation-specific blinking in DNA. Blinking patterns were affected by the stabilization of the Hoogsteen base-pair, suggesting that not only the presence but also the fluctuating behaviour of the triple helix can be monitored by the changes in the Cy3 blinking patterns.

Vibronic couplings and coherent electron transfer in bridged systems

A computational strategy to analyze the dynamics of coherent electron transfer processes in bridged systems, involving three or more electronic states, is presented.

Applicability of optimal functional tuning in density functional calculations of ionization potentials and electron affinities of adenine–thymine nucleobase pairs and clusters

Successful application of optimally tuned long-range corrected functionals for calculation of vertical ionization potentials and electron affinities of various adenine–thymine nucleobase pairs and clusters is demonstrated.

Electron-soliton dynamics in chains with cubic nonlinearity

In our work, we consider the problem of electronic transport mediated by coupling with solitonic elastic waves. We study the electronic transport in a 1D unharmonic lattice with a cubic interaction between nearest neighboring sites. The electron-lattice interaction was considered as a linear function of the distance between neighboring atoms in our study. We numerically solve the dynamics equations for the electron and lattice and compute the dynamics of an initially localized electronic wave-packet. Our results suggest that the solitonic waves that exist within this nonlinear lattice can control the electron dynamics along the chain. Moreover, we demonstrate that the existence of a mobile electron-soliton pair exhibits a counter-intuitive dependence with the value of the electron-lattice coupling.

A three-step kinetic model for electrochemical charge transfer in the hopping regime

Single-step nonadiabatic electron tunneling models are widely used to analyze electrochemical rates through self-assembled monolayer films (SAMs). For some systems, such as nucleic acids, long-range charge transfer can occur in a "hopping" regime that involves multiple charge transfer events and intermediate states. This report describes a three-step kinetic scheme to model charge transfer in this regime. Some of the features of the three-step model are probed experimentally by changing the chemical composition of the SAM. This work uses the three-step model and a temperature dependence of the charge transfer rate to extract the charge injection barrier for a SAM composed of a 10-mer peptide nucleic acid that operates in the hopping regime.

Ultrafast dynamics of solvation and charge transfer in a DNA-based biomaterial

Charge migration along DNA molecules is a key factor for DNA-based devices in optoelectronics and biotechnology. The association of a significant amount of water molecules in DNA-based materials for the intactness of the DNA structure and their dynamic role in the charge-transfer (CT) dynamics is less documented in contemporary literature. In the present study, we have used a genomic DNA-cetyltrimethyl ammonium chloride (CTMA) complex, a technological important biomaterial, and Hoechest 33258 (H258), a well-known DNA minor groove binder, as fluorogenic probe for the dynamic solvation studies. The CT dynamics of CdSe/ZnS quantum dots (QDs; 5.2 nm) embedded in the as-prepared and swollen biomaterial have also been studied and correlated with that of the timescale of solvation. We have extended our studies on the temperature-dependent CT dynamics of QDs in a nanoenvironment of an anionic, sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle (AOT RMs), whereby the number of water molecules and their dynamics can be tuned in a controlled manner. A direct correlation of the dynamics of solvation and that of the CT in the nanoenvironments clearly suggests that the hydration barrier within the Arrhenius framework essentially dictates the charge-transfer dynamics.

Comparison of the π-stacking properties of purine versus pyrimidine residues. Some generalizations regarding selectivity

Aromatic-ring stacking is pronounced among the noncovalent interactions occurring in biosystems and therefore some pertinent features regarding nucleobase residues are summarized. Self-stacking decreases in the series adenine > guanine > hypoxanthine > cytosine ~ uracil. This contrasts with the stability of binary (phen)(N) adducts formed by 1,10-phenanthroline (phen) and a nucleobase residue (N), which is largely independent of the type of purine residue involved, including (N1)H-deprotonated guanine. Furthermore, the association constant for (phen)(A)(0/4-) is rather independent of the type and charge of the adenine derivative (A) considered, be it adenosine or one of its nucleotides, including adenosine 5'-triphosphate (ATP(4-)). The same holds for the corresponding adducts of 2,2'-bipyridine (bpy), although owing to the smaller size of the aromatic-ring system of bpy, the (bpy)(A)(0/4-) adducts are less stable; the same applies correspondingly to the adducts formed with pyrimidines. In accord herewith, [M(bpy)](adenosine)(2+) adducts (M(2+) is Co(2+), Ni(2+), or Cu(2+)) show the same stability as the (bpy)(A)(0/4-) ones. The formation of an ionic bridge between -NH3 (+) and -PO3 (2-), as provided by tryptophan [H(Trp)(±)] and adenosine 5'-monophosphate (AMP(2-)), facilitates recognition and stabilizes the indole-purine stack in [H(Trp)](AMP)(2-). Such indole-purine stacks also occur in nature. Similarly, the formation of a metal ion bridge as occurs, e.g., between Cu(2+) coordinated to phen and the phosphonate group of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA(2-)) dramatically favors the intramolecular stack in Cu(phen)(PMEA). The consequences of such interactions for biosystems are discussed, especially emphasizing that the energies involved in such isomeric equilibria are small, allowing Nature to shift such equilibria easily.

Structure and electronic spectra of purine-methyl viologen charge transfer complexes

The structure and properties of the electron donor-acceptor complexes formed between methyl viologen and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and (1)H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well-described by time-dependent DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2'-deoxyguanosine 3'-monophosphate (DAD'DAD' type) and 7-deazaguanosine (DAD'ADAD' type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors.

Hole transfer kinetics of DNA

Not long after the discovery of the double-helical structure of DNA in 1952, researchers proposed that charge transfer along a one-dimensional π-array of nucleobases might be possible. At the end of the 1990s researchers discovered that a positive charge (a hole) generated in DNA migrates more than 200 Å along the structure, a discovery that ignited interest in the charge-transfer process in DNA. As a result, DNA became an interesting potential bottom-up material for constructing nanoelectronic sensors and devices because DNA can form various complex two-dimensional and three-dimensional structures, such as smiley faces and cubes. From the fundamental aspects of the hole transfer process, DNA is one of the most well-studied organic molecules with many reports on the synthesis of artificial nucleobase analogues. Thus, DNA offers a unique system to study how factors such as the HOMO energy and molecular flexibility affect hole transfer kinetics. Understanding the hole transfer mechanism requires a discussion of the hole transfer rate constants (kHT). This Account reviews the kHT values determined by our group and by Lewis and Wasielewski's group, obtained by a combination of the synthesis of modified DNA and time-resolved spectroscopy. DNA consists of G/C and A/T base pairs; the HOMO localizes on the purine bases G and A, and G has a lower oxidation potential and a higher energy HOMO. Typically, long-range hole transfer proceeded via sequential hole transfer between G/C's. The kinetics of this process in DNA sequences, including those with mismatches, is reproducible via kinetic modeling using the determined kHT for each hole transfer step between G/C's. We also determined the distance dependence parameter (β), which describes the steepness of the exponential decrease of kHT. Because of this value, >0.6 Å(-1) for hole transfer in DNA, DNA itself does not serve as a molecular wire. Interestingly, hole transfer proceeded exceptionally fast for some sequences in which G/C's are located close to each other, an observation that we cannot explain by a simple sequential hole transfer between G/C's but rather through hole delocalization over the nucleobases. To further investigate and refine the factors that affect kHT, we examined various artificial nucleobases. We clearly demonstrated that kHT depends strongly on the HOMO energy gap between the bases (ΔHOMO), and that kHT can be increased with decreasing ΔHOMO. We reduced ΔHOMO between the two type of base pairs by replacing adenines (A's) with deazaadenines ((z)A's) or diaminopurines (D's) and showed that the hole transfer rate through the G/C and A/T mix sequence increased by more than 3 orders of magnitude. We also investigated how DNA flexibility affects kHT. Locked nucleic acid (LNA) modification, which makes DNA more rigid, lowered kHT by more than 2 orders of magnitude. On the other hand, 5-Me-2'-deoxyzebularine (B) modification, which increases DNA flexibility, increased kHT by more than 1 order of magnitude. These new insights in hole transfer kinetics obtained from modified DNAs may aid in the design of new molecular-scale conducting materials.

Dynamical treatment of charge transfer through duplex nucleic acids containing modified adenines

We address the issue of whether chemical alterations of nucleobases are an effective tool to modulate charge transfer through DNA molecules. Our investigation uses a multilevel computational approach based on classical molecular dynamics and quantum chemistry. We find yet another piece of evidence that structural fluctuations are a key factor to determine the electronic structure of double-stranded DNA. We argue that the electronic structure and charge transfer ability of flexible polymers is the result of a complex intertwining of various structural, dynamical and chemical factors. Chemical intuition may be used to design molecular wires, but this is not the sole component in the complex charge transfer mechanism through DNA.

Detection of single-nucleotide variations by monitoring the blinking of fluorescence induced by charge transfer in DNA

Charge transfer dynamics in DNA: Photo-induced charge separation and charge-recombination dynamics in DNA was assessed by monitoring the blinking of fluorescence. Single nucleotide variations, mismatch and one base deletion, were differentiated based on the length of the off-time of the blinking, which corresponds to the lifetime of the charge-separated state.

The single-molecule conductance and electrochemical electron-transfer rate are related by a power law

This study examines quantitative correlations between molecular conductances and standard electrochemical rate constants for alkanes and peptide nucleic acid (PNA) oligomers as a function of the length, structure, and charge transport mechanism. The experimental data show a power-law relationship between conductances and charge transfer rates within a given class of molecules with the same bridge chemistry, and a lack of correlation when a more diverse group of molecules is compared, in contrast with some theoretical predictions. Surprisingly, the PNA duplexes exhibit the lowest charge-transfer rates and the highest molecular conductances. The nonlinear rate-conductance relationships for structures with the same bridging chemistries are attributed to differences in the charge-mediation characteristics of the molecular bridge, energy barrier shifts and electronic dephasing, in the two different experimental settings.

Dynamics and efficiency of photoinduced charge transport in DNA: Toward the elusive molecular wire

Experimental investigations of photoinduced charge transport in synthetic DNA capped hairpins possessing electron acceptor and donor stilbene chromophores at either end have established the mechanism, dynamics, and efficiency of charge transport in DNA. The mechanism for charge transport in repeating A-T base pairs (A-tracts) was found to change from single-step superexchange at short distances to multistep incoherent hole hopping at longer distances. The rate constants for base-to-base hole hopping in longer A- and G-tract sequences are 1.2 × 109 s–1 and 4.3 × 109 s–1, respectively, considerably slower than the rate constants associated with molecular wires. Even slower rate constants are observed for alternating or random base sequences such as those encountered in natural DNA. The efficiency of charge separation in capped hairpins with A-tract sequences is also low as a consequence of the competition of hole hopping with charge recombination. Significantly higher efficiencies for charge separation are possible using diblock purine base sequences consisting of two or three adenines followed by a larger number of guanines. The short A-block serves as a molecular rectifier, slowing down charge recombination. More efficient charge separation can also be achieved using non-natural bases or by using the triplet acceptor anthraquinone for hole injection.

Between superexchange and hopping: an intermediate charge-transfer mechanism in poly(A)-poly(T) DNA hairpins

We developed a model for hole migration along relatively short DNA hairpins with fewer that seven adenine (A):thymine (T) base pairs. The model was used to simulate hole migration along poly(A)-poly(T) sequences with a particular emphasis on the impact of partial hole localization on the different rate processes. The simulations, performed within the framework of the stochastic surrogate Hamiltonian approach, give values for the arrival rate in good agreement with experimental data. Theoretical results obtained for hairpins with fewer than three A:T base pairs suggest that hole transfer along short hairpins occurs via superexchange. This mechanism is characterized by the exponential distance dependence of the arrival rate on the donor/acceptor distance, k(a) ≃ e(-βR), with β = 0.9 Å(-1). For longer systems, up to six A:T pairs, the distance dependence follows a power law k(a) ≃ R(-η) with η = 2. Despite this seemingly clear signature of unbiased hopping, our simulations show the complete delocalization of the hole density along the entire hairpin. According to our analysis, the hole transfer along relatively long sequences may proceed through a mechanism which is distinct from both coherent single-step superexchange and incoherent multistep hopping. The criterion for the validity of this mechanism intermediate between superexchange and hopping is proposed. The impact of partial localization on the rate of hole transfer between neighboring A bases was also investigated.

Solution, surface, and single molecule platforms for the study of DNA-mediated charge transport

The structural core of DNA, a continuous stack of aromatic heterocycles, the base pairs, which extends down the helical axis, gives rise to the fascinating electronic properties of this molecule that is so critical for life. Our laboratory and others have developed diverse experimental platforms to investigate the capacity of DNA to conduct charge, termed DNA-mediated charge transport (DNA CT). Here, we present an overview of DNA CT experiments in solution, on surfaces, and with single molecules that collectively provide a broad and consistent perspective on the essential characteristics of this chemistry. DNA CT can proceed over long molecular distances but is remarkably sensitive to perturbations in base pair stacking. We discuss how this foundation, built with data from diverse platforms, can be used both to inform a mechanistic description of DNA CT and to inspire the next platforms for its study: living organisms and molecular electronics.