Theoretical model of biomacromolecule through nanopore including effects of electrolyte and excluded volume

A theoretical model for the translocation process of biomacromolecule is developed based on the self-consistent field theory （SCFT）, where the biomacromolecule is regarded as a self-avoiding polymer chain actuated by the external potential. In this theoretical model, the external potential, the Coulomb electrostatic potential of the charged ions （the electrolyte effect）, and the attractive interaction between the polymer and the nanopore （the excluded volume effect） are all considered, which have effects on the free energy landscape and conformation entropy during the translocation stage. The result shows that the entropy barrier of the polymer in the solution with high valence electrolyte is much larger than that with low valence electrolyte under the same condition, leading to that the translocation time of the DNA molecules in the solution increases when the valence electrolyte increases. In addition, the attractive interaction between the polymer and the nanopore increases the free energy of the polymer, which means that the probability of the translocation through the nanopore increases. The average translocation time decreases when the excluded volume effect parameter increases. The electrolyte effect can prolong the average translocation time. The simulation results agree well with the available experimental results.

VISCOMETRIC INVESTIGATIONS OF POLYVINYLPYRROLIDONE IN MIXED SOLVENTS AND WITH VARYING TEMPERATURE

The viscosity behavior of polyvinylpyrrolidone(PVP)has been determined at 25℃ in mixed solvents comprising water/dimethylformamide(DMF)and water/methanol(MeOH).Analysis of the data has considered the PVP as being both host and guest polymer in solution.The intrinsic viscosity of PVP in DMF is higher than in water and in MeOH,but also increases in a mixed solvent with high water content because of the effect of polymer-solvent interactions.It was also found that the intrinsic viscosity of PVP at finite concentration,[η_(pvp)]_c decreases with an increase in the concentration of PVP in solution.The viscosity behavior of PVP in a mixed solvent is affected by the concentration-dependent intermolecular excluded volume effect,which can be quantitatively expressed by the parameter,b_Y,which reflects the shrinkage of PVP chain coils,resulting in a decrease of[η_(pvp)]_c.The effect of temperature on the viscosity behavior of PVP in MeOH shows that the interaction parameter increases up to a maximum value,and then decreases after a certain temperature.

Macromolecular Crowding Enhances Thermal Stability of Rabbit Muscle Creatine Kinase

The effect of dextran on the conformation （or secondary structure） and thermal stability of creatine kinase （CK） was studied using the far-ultraviolet （UV） circular dichroism （CD） spectra. The results showed that lower concentrations of dextran （less than 60 g/L） induced formation of the secondary CK structures. However, the secondary structure content of CK decreased when the dextran concentrations exceeded 60 g/L. Thermally induced transition curves were measured for CK in the presence of different concentrations of dextran by far-UV CD. The thermal transition curves were fitted to a two-state model by a nonlinear, least-squares method to obtain the transition temperature of the unfolding transition. An increase in the transition temperature was observed with the increase of the dextran concentration. These observations qualitatively accord with predictions of a previously proposed model for the effect of intermolecular excluded volume （macromolecular crowding） on protein stability and conformation. These findings imply that the effects of macromolecular crowding can have an important influence on our understanding of how protein folding occurs in vivo.