Multidimensional Methods for Measuring Kinetics in Complex Materials

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Berg at the University of South Carolina at Columbia is developing new multidimensional spectroscopic methods to study reaction rates (kinetics) and apply the new techniques to materials with complex molecular dynamics. In simple materials, chemical reactions or processes can be experimentally parsed into fundamental steps, each with a well-defined rate. When a material is composed of complex molecules or molecular assemblies, these fundamental steps often appear to have a spread of rates. The multidimensional methods being developed at the Professor Berg's lab help to determine the nature and lifetime of states which cause the spread of rates. The methods being developed here extend to a wide range of processes and materials in biology, chemistry, materials science and engineering. Professor Berg works with graduate and undergraduate students closely on the development of these complex methods of characterizing matter. He is also involved in a number of creative approaches to engage students from underrepresented minority groups in the research project. Three subprojects each address a different material, kinetic problem and technical challenge. The rotation rates of probe molecules inserted into microstructured materials are currently used to measure local viscosity at specific points within the structure. These experiments often yield a range of rotational rates. Six-pulse, polarized optical experiments are being developed to determine whether this range is caused by variability in the microstructure or by local anisotropy in the structure. The green-fluorescent protein (GFP) is a prototype for understanding reaction dynamics within a protein. A multicolor, multidimensional, optical experiment is being developed to determine if the multiple rates observed in GFP kinetics are due to multiple protein substates or due to unresolved intermediate steps in the photocycle. Multidimensional methods of analyzing computer simulations are being developed to understand the formation of long-lived structures within liquids as the liquid is cooled. Although experiments can see these effects at low temperatures, simulations are currently the best approach to probing their initial formation at higher temperatures. Professor Berg intends not only to advance fundamental understanding about molecular reaction kinetics but also to provide students an interdisciplinary training experience, in particular those students from underrepresented minority groups.