Elucidating the Unique Self-Assembly Behavior of Macroions in Solution From Molecular Level Modeling

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Self-assembly is the process by which specific forces between individual molecular building blocks leads to the spontaneous formation of ordered structures. Molecular self-assembly is ubiquitous in nature from the crystallization of snowflakes to ribosomes and viruses. Molecular self-assembly has emerged as a new approach in chemical synthesis, providing routes to a range of materials that are both scientifically interesting and technologically important. With the support of the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professor Mesfin Tsige of the University of Akron is using computer simulation to investigate the self-assembly behavior of very large molecules with multiple charges (called macroions) in solution. The computer simulation tracks the motion of tens of thousands to hundreds of thousands of beads, each representing a few atoms, as they spontaneously form large complex structures. From these simulations, Professor Tsige and his group are developing a fundamental understanding of the self-assembly of macroions that are almost completely uncharted by theory and simulation. The project involves graduate students and postdoctoral associates at the University of Akron, as well as undergraduate students through the NSF-Research Experiences for Undergraduates (REU) site at the College of Polymer Science and Polymer Engineering, and high school students from the local St. Vincent-St. Mary School. The project complements existing experimental studies by providing information that is difficult or sometimes impossible to get from laboratory measurements. Central to the project is the development of a versatile coarse-grained computer simulation model that is designed for large-scale molecular dynamic simulation. A typical simulation tracks the self-assembly of 25-50 macroions surrounded by 100,000-200,000 solvent molecules into large 'blackberry-like' structures over the course of over 50 million time steps. Together, Professor Tsige and his students are using the computer model to elucidate the mechanism of assembly formation and understand the effects of charge density, charge distribution, macroion size, and solvent polarity on self-assembly behavior. This modeling methodology may advance our understanding of self-assembly in a broad range of macroion solutions, which cover a variety of fields in Chemistry, Material Science, and Biology.