Receptor Mediated Circular Dichroism Spectroscopy

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With this award, the Chemical Structure, Dynamics and Mechanisms Program is supporting the research of Professor Babak Borhan (Michigan State University) in the area of chiroptical spectroscopy. With prior NSF CAREER funding, his laboratory has shown that porphyrin tweezers (two metalloporphyrins linked via an alkyl linker) can serve as host systems for chiral guest molecules, which upon complexation lead to an observable circular dichroic (CD) spectrum. The resultant spectrum is easily deciphered to extract stereochemical information of the bound chiral guest molecule. The advantages are that the methodology is non-empirical in assignment of helicity for the interacting porphyrins, it is micro-scale in nature requiring microgram amounts of chiral substrate, it is non-destructive (chiral material can be recovered), has little prep work, and provides the answer in a matter of minutes. Future work will focus on expanding the repertoire of host systems such that a larger subset of chiral organic molecules can succumb to analysis. Most importantly, guest molecules that only have one site of complexation (thus cannot complex with both porphyrins of the tweezer) require a new strategy. It is hypothesized that appropriately designed pseudo-cage host systems with the ability to complex molecules that contain only one site of attachment will predominantly adopt either a P or M helicity upon interaction with chiral guest substrates. The resultant complex is CD active and will provide information required for analysis of absolute stereochemistry. The target chiral molecules for absolute stereochemical determinations are alcohols, amines, diols, diamines, epoxy alcohols, and hydroxy ketones, saturated and unsaturated heterocyclic molecules, and molecules with remote stereochemistry, to name a few. The latter list of compound families is a large subset of chiral molecules that serve as chiral pool reagents for numerous applications in organic synthesis, organic materials, and the medicinal and pharmaceutical arena.A routine, microscale, easy, and reliable method for stereochemical determinations is critical in many areas of chemistry and biology, benefiting a large number of researchers in the latter areas. The nature of the research proposed here is interdisciplinary. Student training will couple chemical synthesis with the design of chromophoric hosts based on a thorough understanding of molecular and structural dynamics. The students will also have to be proficient and knowledgeable spectroscopists. The proposal also has elements that are fit for less accomplished students to participate in research. For the past ten years, the group has organized and directed the Project SEED program at Michigan State University. Continuing to recruit, train, and scientifically stimulate high school students will be a top priority. The training of undergraduate students will be no less important.