Fig. 2: HMT applied to the hydroxyl groups of an α2,8-linked sialic acid tetramer.

a Primary structure of (SiA)₄, depicting the rings’ numbering and the multiple hydroxyl and amide labile ¹Hs. b Magnetic field effect on the appearance of (SiA)₄’s hydroxyl ¹H spectrum. Note how the chemical exchange broadens certain hydroxyl resonances at 600 MHz, whereas at 1 GHz most of the peaks are well-resolved, thanks to field-induced separation of the exchanging sites. c Comparison between a conventional 2D NOESY acquired using 25% non-uniform sampling for a minimal acquisition time with faithful spectral reconstruction, and Hadamard MT NOESY collected with a 600 ms saturation period. Although conventional NOESY only reveals some of the closest neighbors, richer information (coupled to much shorter acquisitions) is provided by the HMT. These 1 GHz spectra were acquired using a Bruker Avance Neo console equipped with a TCI cryoprobe; Table 1 summarizes some of the enhancements observed for this compound. d Conflicts arising between the cross-relaxation peaks observed in the HMT NOESY spectrum (highlighted in c with red fonts and indicated here by dashed lines) and the extended structure proposed for this homopolymer at −10 °C based on non-labile ¹H NOEs⁴⁷. Notice the long distances (in Å) indicated by the dashed lines for some of the new NOESY-derived experimental connectivities. e Revised, compact structure, compatible with the labile ¹H’s NOEs, showing substantial distance shortenings.