Carbon-Carbon Distance Measurement via C7 and R14 sequences in Solid State NMR,

M. Carravetta, M. Edén, A. Brinkmann, P. J. E. Verdegem, J. Lugtenburg, and M. H. Levitt,
41st Experimental NMR Conference, Asilomar, California, USA (Apr. 2000), poster.

Solid state NMR can be used as a tool for obtaining molecular structural information, such as torsional angles, distances, molecular conformations and so on. Internuclear distances are directly related to the dipolar coupling value but such information is lost under MAS-conditions: proper recoupling techniques need to be applied in order to bring this information back into the spectrum. Experiments have been performed on doubly 13C-labelled model compounds, using C7 and R14 methods for homonuclear dipolar recoupling and double quantum filtration to get rid of the natural abundance background.

Our aim is:

(i) test and improve the efficiency of this approach for extracting distances, particularly in the presence of large chemical shift anisotropies (CSA),

(ii) measure distances in systems which are difficult to handle with other techniques, such as membrane proteins. Both for carbon atoms which are one bond apart [distances from 0.13nm to 0.16 nm] and for longer distances [about 0.3 nm] this method yields distances with a deviation of 3% or less from the values obtained with other techniques. This level of precision is sufficient for estimating the bond order in conjugated carbon chains (for example, retinal). These discrepancies are probably due to interference with other interactions, such as CSA and rf-inhomogeneity. There is a need for sequences with better compensation properties. The stability of different sequences with respect to RF-amplitude errors and to chemical shifts has been studied via computer simulation.

Dr. Andreas Brinkmann
National Research Council Canada
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Ottawa, Ontario K1A 0R6
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