Abstract
For compounds dissolved in non-polar solvents, nuclear magnetic resonance spectroscopic investigations have benefited greatly from the advent of cryogenically cooled probes. Unfortunately the allure of significant increases in sensitivity may not be realized for compounds such as metabolites that are dissolved in solvents with high ionic-strengths such as solutions typically utilized for metabolomic or biomolecular investigations. In some cases there is little benefit from a cryogenically cooled probe over a conventional room temperature probe. Various sample preparation methods have been developed to minimize the detrimental effects of salt; for large numbers of metabolomic samples these preparation methods tend to be onerous and impractical. An alternative to manipulating the sample, is to utilize a probe that is designed to have a higher tolerance for solutions with high ionic-strengths. In order to acquire high-quality optimal data and choose the appropriate probe configuration (especially important for comparative quantitative investigations) the effects of salts and buffers on cryogenic probe performance must be understood. Herein we detail sample considerations for two cryogenic probes, a standard 5 mm and a narrow diameter 1.7 mm, in an effort to identify via integrals, intensities and noise levels the optimal choice for biomolecular investigations.
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Notes
In previous investigations with hundreds of metabolomic samples, as long as the height of the samples were consistent, the automated shimming routine described within the supplemental information produced a very homogeneous field with replicates in different tubes having marginal differences in line-widths for both probes. Only when the height of the sample was low did the shimming routine fail.
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Acknowledgements
This work was supported by a Natural Sciences and Engineering Research Council Discovery grant to RTS through his adjunct appointment with Dalhousie University. Magnetic resonance data was collected at the Biomolecular Magnetic Resonance Facility (BMRF) housed at the National Research Council of Canada’s Institute for Marine Biosciences in Halifax. The cryogenic probes were provided by Dalhousie University through an Atlantic Canada Opportunities Agency (ACOA) Grant. We thank Ian Burton, John Walter and Tobias Karakach for stimulating and insightful discussions.
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Biswas, Z., Merkley, N. & Syvitski, R.T. Biomolecular sample considerations essential for optimal performance from cryogenic probes. Metabolomics 10, 607–615 (2014). https://doi.org/10.1007/s11306-013-0620-z
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DOI: https://doi.org/10.1007/s11306-013-0620-z