Category Archives: Analytical Chemistry

Chiral Recognition by Dissolution DNP NMR Spectroscopy of 13C-Labeled dl-Methionine

Monteagudo, Eva, Albert Virgili, Teodor Parella, and Míriam Pérez-Trujillo. “Chiral Recognition by Dissolution DNP NMR Spectroscopy of 13C-Labeled Dl-Methionine.” Analytical Chemistry 89, no. 9 (May 2, 2017): 4939–44.

A method based on d-DNP NMR spectroscopy to study chiral recognition is described for the first time. The enantiodifferentiation of a racemic metabolite in a millimolar aqueous solution using a chiral solvating agent was performed. Hyperpolarized 13C-labeled DL-methionine enantiomers were differently observed with a single-scan 13C NMR experiment, while the chiral auxiliary at thermal equilibrium remained unobserved. The method developed entails a step forward in the chiral recognition of small molecules by NMR spectroscopy, opening new possibilities in situations where the sensitivity is limited; e.g. when a low concentration of analyte is available or when the measurement of an insensitive nucleus, like 13C, is required. The advantages and current limitations of the developed method, as well as, future perspectives are discussed.

Hyperpolarized Xenon-Based Molecular Sensors for Label-Free Detection of analytes

Garimella, P.D., et al., Hyperpolarized Xenon-Based Molecular Sensors for Label-Free Detection of analytes. J. Am. Chem. Soc., 2013. 136(1): p. 164-168.

Nuclear magnetic resonance (NMR) can reveal the chemical constituents of a complex mixture without resorting to chemical modification, separation, or other perturbation. Recently, we and others have developed magnetic resonance agents that report on the presence of dilute analytes by proportionately altering the response of a more abundant or easily detected species, a form of amplification. One example of such a sensing medium is xenon gas, which is chemically inert and can be optically hyperpolarized, a process that enhances its NMR signal by up to 5 orders of magnitude. Here, we use a combinatorial synthetic approach to produce xenon magnetic resonance sensors that respond to small molecule analytes. The sensor responds to the ligand by producing a small chemical shift change in the Xe NMR spectrum. We demonstrate this technique for the dye, Rhodamine 6G, for which we have an independent optical assay to verify binding. We thus demonstrate that specific binding of a small molecule can produce a xenon chemical shift change, suggesting a general approach to the production of xenon sensors targeted to small molecule analytes for in vitro assays or molecular imaging in vivo.

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