Carbohydrate structural determination by NMR spectroscopy: modern methods and limitations

The emerging field of metabolomics, in which a large number of small-molecule metabolites from body fluids or tissues are detected quantitatively in a single step, promises immense potential for early diagnosis, therapy monitoring and for understanding the pathogenesis of many diseases. Metabolomics methods are mostly focused on the information-rich analytical techniques of NMR spectroscopy and mass spectrometry (MS). Analysis of the data from these high-resolution methods using advanced chemometric approaches provides a powerful platform for translational and clinical research and diagnostic applications. In this review, the current trends and recent advances in NMR- and MS-based metabolomics are described with a focus on the development of advanced NMR and MS methods, improved multivariate statistical data analysis and recent applications in the area of cancer, diabetes, inborn errors of metabolism and cardiovascular diseases.

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Metabolomics-based methods for early disease diagnostics.

A scheme enabling the complete sampling of multidimensional NMR domains within a single continuous acquisition is introduced and exemplified. Provided that an analyte's signal is sufficiently strong, the acquisition time of multidimensional NMR experiments can thus be shortened by orders of magnitude. This could enable the characterization of transient events such as proteins folding, 2D NMR experiments on samples being chromatographed, bring the duration of higher dimensional experiments (e.g., 4D NMR) into the lifetime of most proteins under physiological conditions, and facilitate the incorporation of spectroscopic 2D sequences into in vivo imaging investigations. The protocol is compatible with existing multidimensional pulse sequences and can be implemented by using conventional hardware; its performance is exemplified here with a variety of homonuclear 2D NMR acquisitions.

https://www.pnas.org/content/pnas/99/25/15858.full.pdf

The acquisition of multidimensional NMR spectra within a single scan

Based on a brief revision of what constitutes state-of-the-art “quantitative experimental conditions” for 1H quantitative NMR (qHNMR), this comprehensive review contains almost 200 references and covers the literature since 1982 with emphasis on natural products. It provides an overview of the background and applications of qHNMR in natural products research, new methods such as decoupling and hyphenation, and analytical potential and limitations, and compiles information on reference materials used for and studied by qHNMR. The dual status of natural products, being single chemical entities and valuable biologically active agents that need to be purified from complex matrixes, results in an increased analytical demand when testing their deviation from the singleton composition ideal. The outcome and versatility of reported applications lead to the conclusion that qHNMR is currently the principal analytical method to meet this demand. Considering both 1D and 2D 1H NMR experiments, qHNMR has proved to be h...

Quantitative 1H NMR: development and potential of a method for natural products analysis.

Comparing and combining NMR spectroscopy and mass spectrometry in metabolomics

B. Reduction in Saddle-Type Coil Size 5 C. Solenoidal Coils and Magic Angle Spinning 5 D. Microcoils 6 E. Microfabrication 7 F. Direct Comparisons of Probe Sensitivity 8 V. Microliter-Volume Static NMR Spectroscopy 9 A. Natural Product Extracts 9 B. Analysis of Combinatorial Chemistry Products 10 VI. Nanoliter-Volume Static NMR Spectroscopy 10 VII. NMR Detection of Capillary Separations 12 A. Flow Effects 12 B. HPLC−NMR 13 C. SFC−NMR 15 D. CE−NMR 15 E. CEC−NMR 17 VIII. Conclusions 18 IX. Acknowledgments 19 X. References 19

High-Resolution NMR Spectroscopy of Sample Volumes from 1 nL to 10 μL

An HPLC NMR system is presented that integrates a commercial microbore HPLC system using a 0.5-mm column with a 500-MHz proton NMR spectrometer using a custom NMR probe with an observe volume of 1.1 μL and a coil fill factor of 68%. Careful attention to capillary connections and NMR flow cell design allows on-line NMR detection with no significant loss in separation efficiency when compared with a UV chromatogram. HPLC NMR is performed on mixtures of amino acids and small peptides with analyte injection amounts as small as 750 ng; the separations are accomplished in less than 10 min and individual NMR spectra are acquired with 12 s time resolution. Stopped-flow NMR is achieved by diversion of the chromatographic flow after observation of the beginning of the analyte band within the NMR flow cell. Isolation of the compound of interest within the NMR detection cell allows multidimensional experiments to be performed. A stopped-flow COSY spectrum of the peptide Phe-Ala is acquired in 3.5 h with an injected a...

/pdf/a-microcoil-nmr-probe-for-coupling-microscale-hplc-with-on-4vyyhhwp09.pdf

A microcoil NMR probe for coupling microscale HPLC with on-line NMR spectroscopy.

Typical high-resolution natural-abundance 13C NMR experiments require milligrams of material. In this study, solenoidal microcoil direct and inverse detection probes have been designed to explore improvements in the limits of detection (LOD) for 13C NMR at 11.7 T. A direct-detection radio frequency probe with an observe volume (Vobs) of 1 microL has been developed with carbon observe, deuterium lock, and proton decouple channels. The nonspinning line width of a decoupled [3-13C]-L-alanine (99%) peak achieved is 1.3 Hz. The natural-abundance 13C3 sigma LOD for sucrose for a 90-min acquisition time is 18 micrograms (52 nmol). The 3 sigma LOD for [3-13C]-L-alanine (99%) is 375 ng (4.2 nmol) for an acquisition time less than 30 s. The inverse detection probe has proton observe and carbon decouple channels and a Vobs of 550 nL. The 3 sigma LOD for sucrose from a 1 D 13C decoupled HMQC spectrum is 1.6 micrograms (4.5 nmol) for a 14-min acquisition time.

Design of solenoidal microcoils for high-resolution 13C NMR spectroscopy.

Department of Chemistry, Department of Electrical andComputer Engineering, Beckman Institute for AdVancedScience and Technology, UniVersity of Illinois atUrbana-Champaign, 405 North Mathews AVenueUrbana, Illinois 61801ReceiVed December 10, 1998ReVised Manuscript ReceiVed February 3, 1999Nuclear magnetic resonance (NMR) is a powerful analyticaltool capable of determining three-dimensional structures formolecules as complicated as large proteins. It suffers, however,from an inherently low sensitivity compared to almost all otheranalytical methods. Studies of mass-limited samples such as minorcomponents of drug metabolites, microseparation eluates, andpheromone isolates are extremely difficult with current NMRdetectors. A number of approaches have been taken to improvethe intrinsic sensitivity of an NMR experiment. The primarysolution has been to perform the experiment at a higher staticmagnetic field (B

Raju Subramanian

Papers

High-Resolution NMR Spectroscopy of Sample Volumes from 1 nL to 10 μL

A microcoil NMR probe for coupling microscale HPLC with on-line NMR spectroscopy.

Design of solenoidal microcoils for high-resolution 13C NMR spectroscopy.

Rapid Two-Dimensional Inverse Detected Heteronuclear Correlation Experiments with <100 nmol Samples with Solenoidal Microcoil NMR Probes

High‐Resolution NMR Spectroscopy of Sample Volumes from 1 nL to 10 μL