43923-AC7
Transitional Properties of a Polymer Chain
Capillary rise of polymer in thin tubes approximately 40-100 nanometers in diameter, comparable to the size of individual polymer molecule) shows anomalous molecular weight dependency. We had shown that microfluidics (actually we discuss nanofluidics, but we use here the term micro as opposite to macro, as microscopic mechanism as opposed to coarse grained macroscopic) of highly entangled melts is not properly described by Stokes flow where the macroscopic viscosity is inserted. We suggested that this dependence reveals breakdown of macroscopic hydrodynamics characterized by the bulk viscosity and propose a new microscopic mechanism for transport along thin capillary based on the reptation of a single polymer chain. A chain in a melt is constrained by other chains, allowing the motion only along the ”reptation tube”. The chain is pushed through the reptation tube by the difference in hydrostatic pressure between the ends of the chain. We also discuss nonlinear effects (which might be relevant at the onset of capillary rise flow) and the crossover from microscopic to macroscopic flow for larger capillaries.
Another direction of our research is related to the elasticity of cisplatin-bound DNA molecules. Cisplatin was incidentally discovered to suppress cell division and became one of the most successful anti-tumor drugs. It is therapeutically active upon binding to DNA and locally kinking it. We demonstrate that after a bimodal modeling, the degree of platination of a single DNA molecule can be consistently and reliably estimated from elasticity measurements performed with magnetic tweezers. We predicted and measured for the first time two separate persistence lengths of kinked DNA at high and low tensions. We also directly observed that the degree of platination of DNA strongly depends on the concentration of sodium chloride as required for cisplatin's intracellular activity. Our study shows that micromanipulation techniques accurately reveal the degree of chemical modification of DNA which can be used for a new type of structure-sensitive biosensors.
