Theory and Computer Simulations of Polyampholyte-Polyelectrolyte Complexes

University Of Connecticut, Storrs CT

Investigators

Abstract

This award supports theoretical and computational research and education with an aim to develop molecular level models of solutions containing polyampholyte-polyelectrolyte complexes. When a polyelectrolyte is mixed with a polyampholyte (protein) of the same net charge, a soluble complex is formed. The binding occurs in such a way that the oppositely charged amino acids on the protein are close to the polyelectrolyte, causing an electrostatic attraction between the two. With a large excess of polyampholyte, each polyelectrolyte chain is saturated with polyampholytes and the solution is a liquid. As more polyelectrolyte is added, the viscosity steadily increases. Once, enough polyelectrolyte is added, a reversible gel is formed with some polyampholyte molecules acting as temporary crosslinks between polyelectrolyte chains. The research aims to develop molecular models describing the formation of polyampholyte-polyelectrolyte complexes in a wide range of polymer and salt concentrations, solution pH and various properties of polymers like their molecular weight and charge distribution. In dilute solutions the resulting model will provide details of the internal structure of polyampholyte-polyelectrolyte complexes and of the effects of counterion release and condensation on the complex formation. The formation of intercomplex associations and reversible gelation will be studied in semidilute solutions. This will allow prediction of polymer conformations, and solution properties such as viscosity, diffusion coefficient, and relaxation time. The assumptions of the theoretical models will be tested by computer simulation. The results for osmotic coefficient, diffusion coefficient, linear viscoelasticity and steady shear viscosity will be compared with experiments. The molecular models of polyampholyte-polyelectrolyte complexes that will be developed may have far-reaching consequences in the bio-medical area, and in areas utilizing charged macromolecules as rheology modifiers. For example, protein-polyelectrolyte complexes control the rheology and lubrication properties of synovial fluid. A pragmatic industrial use of protein-polyelectrolyte complexes is to use polyelectrolytes to boost the viscosity of protein solution for coating photographic film and paper. In both cases, the associations between the protein and the polyelectrolyte directly control rheology of the complex. The proposed project is well suited for training undergraduate and graduate students in modern analytical and numerical techniques and mentoring is integrated into every aspect of the proposed research. Graduate students will work with undergraduate physics, chemistry or chemical engineering students who will be involved either through independent research for credit or through Research Experience for Undergraduates (REU) programs. The results of the proposed research will be incorporated into a course sequence on Polymer Physics, Polymer Physical Chemistry, as well as into new special topics course, Charged Macromolecules. %%% This award supports theoretical and computational research and education with an aim to develop molecular level models of solutions containing charged polymers, polyampholyte-polyelectrolyte complexes. When a polyelectrolyte (e.g. polyacrylic acid) is mixed with a polyampholyte (e.g. a protein) of the same net charge, a soluble complex is formed. The oppositely charged amino acids on the protein are bound close to the polyelectrolyte, causing an electrostatic attraction between the two. With a large excess of polyampholyte, the solution is a liquid. As more polyelectrolyte is added, the viscosity steadily increases. Once, enough polyelectrolyte is added, a reversible gel is formed. The research aims to develop molecular models describing the formation of polyampholyte-polyelectrolyte complexes under a wide range of conditions. In dilute solutions the resulting model will enable the prediction of polymer conformations, and various solution properties such as viscosity, diffusion coefficient, and relaxation time. The assumptions of the theoretical models will be tested by computer simulation and predictions for various properties will be compared with experiments. The molecular models of polyampholyte-polyelectrolyte complexes that will be developed may have far-reaching consequences in the bio-medical area, and in areas utilizing charged macromolecules as rheology modifiers. For example, protein-polyelectrolyte complexes control the rheology and lubrication properties of synovial fluid. A pragmatic industrial use of protein-polyelectrolyte complexes is to use polyelectrolytes to boost the viscosity of protein solution for coating photographic film and paper. In both cases, the associations between the protein and the polyelectrolyte directly control the rheology of the complex. The proposed project is well suited for training undergraduate and graduate students in modern analytical and numerical techniques and mentoring is integrated into every aspect of the proposed research. Graduate students will work with undergraduate physics, chemistry or chemical engineering students who will be involved either through independent research for credit or through Research Experience for Undergraduates (REU) programs. The results of the proposed research will be incorporated into a course sequence on Polymer Physics, Polymer Physical Chemistry, as well as into new special topics course, Charged Macromolecules. ***