Natural disasters such as drought, extreme temperatures, and flooding can severely impact crop production. Understanding the metabolic response of crops threatened with these disasters provides insights into biological response mechanisms that can influence survival. In this study, a comparative analysis of GC-MS and (1)H NMR results was conducted for wild-type and tolerant rice varieties stressed by up to 3 days of submergence and allowed 1 day of postsubmergence recovery. Most metabolomics studies are conducted using a single analytical platform. Each platform, however, has inherent advantages and disadvantages that can influence the analytical coverage of the metabolome. In this work, a more thorough analysis of the plant stress response was possible through the use of both (1)H NMR and GC-MS. Several metabolites, such as S-methyl methionine and the dipeptide alanylglycine, were only detected and quantified by (1)H NMR. The high dynamic range of NMR, as compared with that of the GC-TOF-MS used in this study, provided broad coverage of the metabolome in a single experiment. The sensitivity of GC-MS facilitated the quantitation of sugars, organic acids, and amino acids, some of which were not detected by NMR, and provided additional insights into the regulation of the TCA cycle. The combined metabolic information provided by (1)H NMR and GC-MS was essential for understanding the complex biochemical and molecular response of rice plants to submergence.

Sulfamate groups (NHSO(3)(-)) are important structural elements in the glycosaminoglycans (GAGs) heparin and heparan sulfate (HS). In this work, proton nuclear magnetic resonance (NMR) line-shape analysis is used to explore the solvent exchange properties of the sulfamate NH groups within heparin-related mono-, di-, tetra- and pentasaccharides as a function of pH and temperature. The results of these experiments identified a persistent hydrogen bond within the Arixtra (fondaparinux sodium) pentasaccharide between the internal glucosamine sulfamate NH and the adjacent 3-O-sulfo group. This discovery provides new insights into the solution structure of the Arixtra pentasaccharide and suggests that 3-O-sulfation of the heparin N-sulfoglucosamine (GlcNS) residues pre-organize the secondary structure in a way that facilitates binding to antithrombin-III. NMR studies of the GlcNS NH groups can provide important information about heparin structure complementary to that available from NMR spectral analysis of the carbon-bound protons.

Although heparin is an important and widely prescribed pharmaceutical anticoagulant, its high degree of sequence microheterogeneity and size polydispersity make molecular-level characterization challenging. Unlike nucleic acids and proteins that are biosynthesized through template-driven assembly processes, heparin and the related glycosaminoglycan heparan sulfate are actively remodeled during biosynthesis through a series of enzymatic reactions that lead to variable levels of O- and N-sulfonation and uronic acid epimers. As summarized in this review, heparin sequence information is determined through a bottom-up approach that relies on depolymerization reactions, size- and charge-based separations, and sensitive mass spectrometric and nuclear magnetic resonance experiments to determine the structural identity of component oligosaccharides. The structure-elucidation process, along with its challenges and opportunities for future analytical improvements, is reviewed and illustrated for a heparin-derived hexasaccharide.