NMR-Based Chemosensing via p-H₂ Hyperpolarization: Application to Natural Extracts

Abstract

When dealing with trace analysis of complex mixtures, NMR suffers from both low sensitivity and signal overlap. NMR chemosensing, in which the association between an analyte and a receptor is "signaled" by an NMR response, has been proposed as a valuable analytical tool for biofluids and natural extracts. Such chemosensors offer the possibility to simultaneously detect and distinguish different analytes in solution, which makes them particularly suitable for analytical applications on complex mixtures. In this study, we have combined NMR chemosensing with nuclear spin hyperpolarization. This was realized using an iridium complex as a receptor in the presence of parahydrogen: association of the target analytes to the metal center results in approximately 1000-fold enhancement of the NMR response. This amplification allows the detection, identification, and quantification of analytes at low-micromolar concentrations, provided they can weakly associate to the iridium chemosensor. Here, our NMR chemosensing approach was applied to the quantitative determination of several flavor components in methanol extracts of ground coffee.

NMR Signal Amplification by Reversible Exchange of Sulfur‐Heterocyclic Compounds Found In Petroleum

“…To date, SABRE hyperpolarization of N-heterocycles has been demonstrated successfully by many research groups. [4] Despite being structurally limited to hyperpolarization of N-heterocycles, the SABRE technique has been applied for structural studies [5] of coffee extracts [6] and biofluids, [7] in addition to hyperpolarization of contrast agents for biomedical applications. [4b, 8] …”

Multidimensional NMR approaches towards highly resolved, sensitive and high-throughput quantitative metabolomics

“…The potential of this approach to study mixtures of metabolites has been mainly investigated by Tessari's group through signal amplification by reversible exchange (SABRE) [31,32,33 ]. Briefly, SABRE occurs through the reversible interaction of parahydrogen and a substrate molecule with a metal complex and the transfer of the spin order to the nuclear spins of the substrate, resulting in enhanced NMR signals.…”

“…Since this technique requires species that can reversibly bind to Multidimensional NMR metabolomics Marchand et al 53 an Iridium-based metal complex in solution [32], its application to complex samples is limited. But interestingly, this specificity can be turned into an advantage and applied to perform the selective detection of compounds in natural extracts [33 ]. It should be noted that the short lifetime of the enhanced signals resulting from SABRE makes the use of multidimensional NMR difficult.…”

Quantitative NMR Studies of Multiple Compound Mixtures

“…Aside from as a major analytical tool for structure elucidation of unknown natural products, NMR is also widely used to quantitatively analyze natural products [122] (see Table 2), including (a) small molecular weight chemical compounds such as alcohols [133,134], phenolic acids [125,126], glycosides [124,129], alkaloids [127,130], flavonolignans [131], alkylene [132], heterocyclic compounds [128,141], and terpenoids [123,132] and (b) high molecular weight natural substances such as polysaccharides [142] and lignins [135][136][137][138][139][140]. To obtain accurate quantitative results, it is usually required to optimize qNMR toward given class of compounds.…”