Research

	Protein-Polyelectrolyte Complexes	*Simulation*s
The objective of this research is to develop molecular level models of the solutions containing protein-polyelectrolyte complexes using a combination of analytical and numerical techniques. The molecular models of protein-polyelectrolyte complexes will have far-reaching consequences in the bio-medical area, and in the 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 utilize 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 mixtures. Dr. Dobrynin's plan is to develop molecular models describing the formation of protein-polyelectrolyte complexes in a wide range of polymer and salt concentrations, solution pH and such properties of polymers as their molecular weight and charge distribution. Using our molecular model of protein/polyelectrolyte mixtures we will be able to predict the polymer conformations, and solution properties such as viscosity, diffusion coefficient, and relaxation time. This research is sponsored by National Science Foundation. more details

	Ordered Monolayers of Adsorbed Charged Macromolecules on Charged Surfaces
During the last decade, polymer chemistry has opened new avenues in the preparation of macromolecules with well defined three dimensional shapes and a rich functionality of the molecular surface. Molecules like cylindrically shaped brushes, dendrimers monodendron jacketed polymers are of particular interest for the future of nanotechnology. The adsorption of these polymers from the solutions onto a solid substrate can be used as a substitute for the standard semiconductor lithography techniques in devices where simple periodic patterning is sufficient. Various applications of nanometer periodic patterning would include the creation of a periodic electric potential in a two dimensional electron gas system, fabrication of quantum dots and antidots, synthesis of DNA electrophoresis media and fabrication of high-density magnetic recording devices. Dr. Dobrynin's group is primarily interested in the development of an analytical theory and in computer simulations of the adsorption of charged dendrimers, and cylindrically shaped brushes on charged surfaces. The main stream lines of this research are: adsorption diagram of the 3-D shaped polymers on a charged surface as a function of the polymer concentration, the polymer and the surface charge density, the ionic strength of a solution and kinetics of polymer adsorption on a charged substrate. This research is sponsored by the Petroleum Research Fund.

	Layered Nanoarchitecutre via Self-assembly of Polyion-Polycation Molecules	Simulations
Recently a new self-assembly technique based on the long-range electrostatic attraction between oppositely charged molecules has been introduced for ultra thin film preparation. Layer-by-layer deposition of multiple materials leads to multilayer films in which orientation and distance between different compounds can be controlled with higher accuracy. The key to a successful deposition of multilayer assemblies in a layer-by-layer fashion is the inversion and subsequent reconstruction of surface properties. For the polyelectrolyte films this is achieved by alternating the deposition of polyanions and polycations from their aqueous solutions. The successful refunctionalization of the surface properties depends not only on the surface roughness, charge density but also on the parameters such as polyelectrolyte concentration, adsorption time, pH or charge density along polymer backbone. The development of a quantitative model able to predict the optimal range of the parameters for the layer-by-layer adsorbed polyanion-polycation films is an important step towards understanding the nature of the long-range order of the adsorbed layers. The specific techniques that we use to solve this problem include analytical theory, self-consistent field calculations, molecular dynamics and Monte Carlo simulations. This research is sponsored by National Science Foundation. more details

Bateria Gliding Motility

Molecular engines converting chemical energy of polymerization reactions into mechanical force play an important role in the motility of cells and bacteria. The most studied example is the pathogenic bacteria, Listeria monocytogenes, which propels itself through the cell by polymerizing a network of host cell actin filaments. The actin is polymerized by proteins at the posterior end of the bacteria, leading to the formation of an actin tail trapped in the host cytoskeleton. Asymmetric location of the nucleation sites on the bacteria surface leads to its directional motion with a velocity matching the rate of actin polymerization. The polymerization mechanism for bacteria motility is also supported by the study of biomimetic systems where Listeria was replaced by polymeric beads covered with actin polymerization sites. The detailed mechanism of force production in a polymerizing actin network is still debated. Polymerization is also a driving force for motility of myxobacteria, cyanobacteria, and flexibacteria. For example, filamentous cyanobacteria Phormidium uncinatum and Anabaena variabilis have nozzle-like pores, 14-16 nm outer diameter and about 7nm inner diameter, near the septa that separate the cells of a filament. The pores extrude polysaccharide secretion with a rate similar to the rate of filament gliding. There is an important similarity between the polymerization-assisted motion of Listeria and cyanobacteria. Our plan is to investigate the mechanism of bacterial gliding motility using molecular dynamics simulations and analytical methods. Our recent simulations have confirmed the fact that the chain polymerization leading to chain compression is indeed a driving force for the nozzle directional motion. We find a simple linear relationship between chain polymerization rate and average nozzle velocity with proportionality coefficient being dependent on the geometric characteristics of the nozzle such as its length and friction coefficient. This model supports the slime secretion mechanism for motility of Myxobacteria and filamentous cyanobacteria. It also provides physical foundation for the molecular propulsion engine based on the chain polymerization reaction. This research is sponsored by National Science Foundation. more details

MOLECULAR DYNAMICS SIMULATIONS OF A MOLECULAR NOZZLE
Movie (18MB), PDF (1.8MB)

MOLECULAR DYNAMICS SIMULATIONS OF LISTERIA
Movie (16MB)