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lecture13 - Today's Lecture 13 Mon Oct 30 Assignments I a...

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A. S. Edison University of Florida 2006 Today’s Lecture 13) Mon, Oct 30: Assignments: I a. Important homonuclear (e.g. 1 H) experiments b. Small molecules c. Peptide assignments
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A. S. Edison University of Florida 2006 Homonuclear 2D Experiments Name Type of correlation Notes COSY Co rrelated S pectroscopy 1 H atoms separated by 2 or 3 covalent bonds and mediated by J-coupling (sometimes up to 5 bonds). Several variants available. Only pairs of coupled atoms (compare to TOCSY). Cross peaks antiphase. TOCSY To tal Co rrelation S pectroscopy 1 H atoms separated by 2 or 3 covalent bonds and mediated by J-coupling. All 1 H in a network of coupled spins will be correlated Correlations between networks of coupled spins. Very useful for side-chains in peptides/proteins. Cross peaks in phase. NOESY N uclear O verhauser E ffect S pectroscopy 1 H atoms up to ~5 Å in space mediated by dipolar interactions. The NOE is highly dependent on molecular correlation time: Small molecules have positive NOE and large molecules are negative. Larger molecules have faster transfer rates. Intermediate sized molecules (~500 Da) do not work with NOESY. Crude but important measure of atomic distances; generally categorize into “strong” (<2.5 Å), “medium” (<4 Å), “weak” (>4 Å). Spin diffusion can cause problems in accurate measurements. ROESY R otating Frame O verhauser E ffect S pectroscopy 1 H atoms up to ~5 Å in space mediated by dipolar interactions. Unlike NOESY, ROESY is the same sign regardless of correlation time. This is especially useful for intermediate MW where NOESY doesn’t work. ROESY uses a transverse spin lock and is very similar to TOCSY. For this reason, ROESY experiments often have more artifacts than NOESY.
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A. S. Edison University of Florida 2006 DQF-COSY: Double quantum filtered COSY to clean up diagonal and reduce solvent Dossey, A. T., Walse, S. S., Rocca, J. R., & Edison, A. S. “Single Insect NMR: A New Tool to Probe Chemical Biodiversity” ACS Chemical Biology, 1 (8), 511–514 (2006).
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A. S. Edison University of Florida 2006 TOCSY: 60 ms DIPSI-2 mixing time
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A. S. Edison University of Florida 2006 ROESY: 400 ms cw mixing time
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A. S. Edison University of Florida 2006 TOCSY and COSY comparison
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A. S. Edison University of Florida 2006 ROESY and COSY comparison
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A. S. Edison
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