Tight-binding parameters for charge transfer along DNA

We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The $\pi$ molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are discussed and then used for calculating the corresponding wavefunctions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessary parameters for a tight-binding phenomenological description based on the $\pi$ molecular overlap. We find that usually the hopping parameters for holes are higher in magnitude compared to the ones for electrons, which probably indicates that hole transport along DNA is more favorable than electron transport. Our findings are also compared with existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table

Intramolecular charge transport along isolated chains of conjugated polymers: Effect of torsional disorder and polymerization defects: Effect of torsional disorder and polymerization defects

Recently, it has become possible to measure the mobility of charges along isolated chains of conjugatedpolymers. The mobility of holes along poly(phenylenevinylene) and polythiophene backbones were reportedto be 0.43 and 0.02 cm 2 V-1 s-1, respectively. The large difference between the mobility of holes on poly-(phenylenevinylene) and polythiophene chains can be attributed to deviations from the coplanar alignment ofstructural units in the polymer backbone. The effect of such torsional disorder on intramolecular hole transportis studied theoretically in this paper using a model based on the tight-binding approximation. The calculatedratio of hole mobilities along poly(phenylenevinylene) and polythiophene chains was found to be in agreementwith experimental findings. For both polymers, estimated mobilities become consistent with the experimentalvalues if polymerization defects and chain end effects are included in the calculations. This suggests thateven higher mobilities than those reported here can be realized by improving the effective conjugation alongthe polymer chai

Absolute rates of hole transfer in DNA

Absolute rates of hole transfer between guanine nucleobases separated by one or two A:T base pairs in stilbenedicarboxamide-linked DNA hairpins were obtained by improved kinetic analysis of experimental data. The charge-transfer rates in four different DNA sequences were calculated using a density-functional-based tight-binding model and a semiclassical superexchange model. Site energies and charge-transfer integrals were calculated directly as the diagonal and off-diagonal matrix elements of the Kohn-Sham Hamiltonian, respectively, for all possible combinations of nucleobases. Taking into account the Coulomb interaction between the negative charge on the stilbenedicarboxamide linker and the hole on the DNA strand as well as effects of base pair twisting, the relative order of the experimental rates for hole transfer in different hairpins could be reproduced by tight-binding calculations. To reproduce quantitatively the absolute values of the measured rate constants, the effect of the reorganization energy was taken into account within the semiclassical superexchange model for charge transfer. The experimental rates could be reproduced with reorganization energies near 1 eV. The quantum chemical data obtained were used to discuss charge carrier mobility and hole-transport equilibria in DNA. © 2005 American Chemical Society

Curvature expansion for the background-induced gluondynamics string

Using the cumulant expansion for an averaged Wilson loop we derive an action of the gluodynamics string in the form of a series in powers of the correlation length of the vacuum. In the lowest orders it contains the Nambu-Goto term and the rigidity term with corresponding coupling constants computed from the bilocal correlator of gluonic fields. Some higher derivative corrections are also calculated. (orig.)Available from TIB Hannover: RA 2999(96-134) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman