arXiv subjects

Kinga Bochenek

Publications and source records attributed to Kinga Bochenek.

3 recordsLinked to original sources

arXiv2004

Hopping Models of Charge Transfer in a Complex Environment: New Class of Coupled Memory Continous-Time Random Walks

Charge transport processes in disordered complex media are accompanied by anomalously slow relaxation for which usually a broad distribution of relaxation times is adopted. To account for those properties of the environment, a standard kinetic approach in description of the system is addressed either in the framework of continuous-time random walks (CTRW) or fractional diffusion. In this paper the power of the CTRW approach is illustrated by use of the probabilistic formalism and limit theorems that allow to predict the limiting distributions of the paths traversed by charges and to derive effective relaxation properties of the entire system of interest. Application of the method is discussed for non-exponential electron-transfer processes controlled by dynamics of the surrounding medium.

cond-mat.stat-mech↗

arXiv2003

Electronic Properties of Random Polymers: Modelling Optical Spectra of Melanins

Melanins are a group of complex pigments of biological origin, widely spread in all species from fungi to man. Among diverse types of melanins, the human melanins, eumelanins,are brown or black nitrogen-containing pigments, mostly known for their photoprotective properties in human skin. We have undertaken theoretical studies aimed to understand absorption spectra of eumelanins and their chemical precursors. The structure of the biopigment is poorly defined, although it is believed to be composed of cross-linked heteropolymers based on indolequinones. As a basic model of the eumelanin structure, we have chosen pentamers containing hydroquinones (HQ) and/or 5,6-indolequinones (IQ) and/or semiquinones (SQ) often listed as structural melanin monomers. The eumelanin oligomers have been constructed as random compositions of basic monomers and opitimized for the energy of bonding. Absorption spectra of model assemblies have been calculated within the semiempirical intermediate neglect of differential overlap (INDO) approximation. Model spectrum of eumelanin has been further obtained by sum of independent spectra of singular polymers. By comparison with experimental data it is shown that the INDO/CI method manages to reproduce well characteristic properties of experimental spectrum of synthetic eumelanins.

physics.bio-ph↗

arXiv2003

Fundamental building blocks of eumelanins: electronic properties of indolequinone-dimers

We present results from the theoretical INDO calculations of the electronic structure for stacked eumelanins' monomers. As basic indolic components of the eumelanin structure 5,6-dihydroxyindole (DHI or HQ) and its oxidized forms (SQ and IQ) were chosen. The results reveal dependency of electronic properties of such aggregates on monomers' redox states. They point out also a tendency to localize an extra charge on one of dimer's subunits that could be suggestive of an electron hopping as a model mechanism forthe electron transfer in eumelanins.

physics.bio-ph↗