Cooperative Mesoscopic Transitions in Finite Systems

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

TECHNICAL SUMMARY This award supports research and education to develop computational and analytical tools to advance theoretical understanding of structural transitions in folding, aggregation, and adsorption processes of polymers and proteins in a thermal environment. These studies are prerequisites for the design of novel materials and biomimetic technological applications such as biosensors. The PI aims to develop a systematic identification of structural transitions and the classification of their properties by means of computer simulations of simplified, coarse-grained models and subsequent thermodynamic statistical analyses. The challenge for a thorough investigation lies in the precise description of the cooperative behavior of interacting monomers, lining up in linear polymer chains, under the influence of dominant finite-size effects. Hence, the transition behavior has to be studied on mesoscopic length scales, which, because of system complexity, neither allow for a quantum nor for a classical mechanics approach. The development of efficient simulation methods is an essential prerequisite for this project. Primarily, sophisticated generalized-ensemble Monte Carlo methods such as parallel tempering, multicanonical sampling, and the Wang-Landau method will be used. For time-resolved information molecular dynamics simulations will be performed. The major research fields in this project are: 1. Polymer crystallization and protein folding. By means of computer simulations of simple models for homopolymers, nucleation effects and conformational phases are studied and classified for flexible and semiflexible polymers. Changes in freezing behavior due to disorder effects caused by different types of monomers are investigated in simulations of generic heteropolymer models, resembling structural properties of proteins. 2. Aggregation. The formation of polymer and protein clusters is simulated and thermodynamically analyzed for simplified coarse-grained and also for atomistic models. Of particular interest is the understanding of first-order-like transitions by means of microcanonical statistical analyses. 3. Adsorption at substrates. The influence of competing energetic and entropic effects on structure formation in adsorption processes of polymers at attractive soft and solid substrates is investigated on different levels of model abstraction. This award supports graduate and postdoctoral training in the interdisciplinary fields of polymer science and biophysics. This includes the development of skills in computational and statistical physics and the ability to present and communicate research results. The junior scientists become familiar with high-performance computing on compute clusters of various scales, including most modern architectures such as graphics processing units. NONTECHNICAL SUMMARY This award supports research and education in the interdisciplinary field of soft condensed matter and aims at a better understanding of the significant structural changes polymers, which are long chain-like molecules, and proteins experience in structure formation processes such as folding, aggregation, and adsorption at surfaces of materials. Folding and aggregation of biomolecules are essential processes in biological systems that enable cell functionality. However, misfolding and nonfunctional aggregation are known to be serious factors in epidemic diseases such as Alzheimer's. On the technological side, the understanding of adsorption properties of polymers on the surfaces of materials is potentially interesting for the design of novel materials with specific mechanical and electronic properties, which is particularly interesting for future technological applications. In this project, properties of these structural transformations are investigated by means of computer simulations of appropriate models and by performing a systematic analysis of the statistical mechanics that triggers these processes. Structural phase diagrams give insight into the competition between intrinsic effects in the molecular system and the influence of the external environment. The understanding of the origin of qualitative structural changes in molecular systems and their dependence on environmental parameters, such as the temperature, pressure, and electromagnetic fields is the key to their control and eventual future biomimetic applications. Graduate students and postdoctoral researchers who are involved in this project learn how to develop and specialize models, algorithms, and data analysis tools. They use most modern resources needed for highly parallel computing, which besides conventional computer systems also includes graphics processing units.