NMR analysis of succinoglycans from different microbial sources: partial assignment of their 1H and 13C NMR spectra and location of the succinate and the acetate groups

In order to obtain information on the location of succinate and acetate groups, comparative NMR analyses were carried out on succinoglycans from different microbial sources by using conventional and advanced NMR techniques. In particular, one-dimensional 1H and 13C NMR spectra were recorded for qualitative and quantitative analysis on native high-molecular-weight succinoglycans (both in the Na+ salt and free-acid forms) from Pseudomonas sp. NCIB 11592, Agrobacterium radiobacter A201-25, Rhizobium meliloti YE-2, and Rhizobium sp. isolated from Vicia faba and compared with those of the deacylated and deacylated —depyruvated, partially depolymerised exopolysaccharides from Rhizobium meliloti YE-2. Moreover, a series of two-dimensional experiments was performed on all the exopolysaccharides aiming at the partial assignment of the NMR spectra. The NMR data showed that succinate is located on O-6 of either one or both of the two side chain 3-linked β-d-Glc residues, whereas the acetate (when it is present) is located on one of the O-6 of backbone 4-linked β-d-Glc units, but the specific site could not be determined. In addition, the spectral features of the succinate substituent were found to be sensitive to pH changes.