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Studies
of molecular structure and dynamics with NMR spectroscopy
Dr. Boyd
Goodson
One
of our primary research initiatives concerns the exploration of
molecular structure, dynamics, and interactions of inclusion complexes
and proteins using novel nuclear magnetic resonance (NMR) and
optical/nuclear double resonance (ONDR) techniques.vi These studies
will use liquid-crystalline matrices and/or laser-polarization methods
to “amplify” the interactions between nuclear spins of the
involved molecules. The signatures of weak (but specific) interactions
between host and guest molecules would be registered in restored
dipolar couplings,vii manifested either as splittings in the NMR
spectra, or detected via magnetization transfer between guest and host
spins. Anticipated increases in (structural and dynamical) selectivity
(and detection sensitivity) would provide a new, direct probe of a wide
variety of macromolecular systems, particularly those that participate
in weak but specific interactions that underlie a host of chemical and
biological phenomena.
Undergraduate Research Component.
As an integral part of this research initiative, undergraduate
researchers will investigate the preparation, stability, ordering, and
general magnetic resonance properties of organic (thermotropic)viii and
aqueous (lyotropic)ix nematic liquid-crystalline (LC) solutions
containing various complex-forming molecules. Xenon-binding systems are
of particular interest due to their direct application in planned ONDR
experiments. This research will involve the systematic study of the
dependences of spectral features (e.g., chemical shifts, splittings,
and relaxation rates) on concentration, temperature, ligand
partitioning, and other parameters (primarily utilizing 13C, 129Xe, 1H,
and 2H nuclei) in order to characterize the behavior of a given complex
aligned within a LC environment. A number of inclusion complexes with
association constants varying between ~1 to 104 M-1 are under study,
beginning with those constructed from (weakly-binding) cyclodextrins,
calixarenes, and (strongly-binding) cryptophanes;x a variety of
cryptophane derivatives (differing, e.g., by their cavity size,
bridging group and capping group functionalization) are being
synthesized by the research group of Jean-Pierre Dutasta (ENS Lyon,
France) and provided in collaboration for our studies.
In order
to have realistic expectations for project completion within one
summer—and still allow adequate time for learning and instrument
training—the scope of the project for a given undergraduate
researcher would be limited to the study of one chosen molecular
complex and one type of liquid crystalline matrix. Alternatively,
particularly motivated students with strong interests in physics and/or
lasers would also have the opportunity to perform optical pumping
experiments to generate “laser-polarized” xenonxi (via an
in-house polarizing apparatus) for use in ONDR experiments. A primary
aspect of undergraduate research in the Goodson laboratory is NMR
training. Students are trained how to use the state-of-the-art Varian
Unity Inova 400 MHz NMR spectrometer in the Goodson Lab, as well as
various modern software packages involved in data acquisition,
processing, analysis, and presentation.
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