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Xanthan belongs to a special class of bacterial polysaccharides by having on one hand a oligosaccharide repeating unit and on the other higher order structures resulting in an unusually large chain rigidity. It is further characterized with an ionic strength, pH, and solvent-dependent cooperative conformational (order-disorder) transition. The ordered state is predominantly double-stranded, but partially denatured, fully or aggregated forms may coexist, depending on the sample history. In this chapter, we have reviewed the literature on chemical modifications of xanthan, and the resulting physical properties resulting from the modifications. It appears that research has been carried out without fully recognizing the complex conformational issues and possible degradations (depolymerizations) accompanying the modifications of xanthan. However, in recent years this issue has been more systematically dealt with, including studies on hydrophobization in both the ordered and disordered state.

Biomaterials based on peptide-coupled alginates must provide both optimal biological environments and tuneable stability/degradation profiles. The present work investigates the degradation pattern and kinetics of peptide-coupled alginates prepared via the periodate oxidation reductive amination route. Alginates degrade slowly (non-enzymatically) under physiological conditions by acid-catalysed hydrolysis and alkali-catalysed β-elimination, both operating simultaneously but dominated by the latter. While periodate oxidation alone largely increases the rate of β-elimination, substitution restores the susceptibility towards β-elimination to that of the parent alginate. For acid hydrolysis the rate of depolymerization is proportional to the degree of substitution, being approximately one order of magnitude larger than the parent alginate, but still lower than for the corresponding materials with fully reduced dialdehydes. Results also suggest a composition-dependent preference for substitution at C2 or C3. These results demonstrate how the various chemistries introduced by the coupling provide useful means to tune the biodegradability profiles. © 2016. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Carboxylated schizophyllan (sclerox) samples of different degrees of oxidation were molecularly characterized by size exclusion chromatography equipped with a multi-angle light scattering detector (SEC-MALS) in 0.10 M aqueous NaCl solution. The molar mass distribution obtained by SEC-MALS shows that sclerox of low degree of oxidation is dissolved mainly as the trimer, whereas the trimer and single chain coexist in solution of sclerox of high degree of oxidation. The trimer of sclerox is much more flexible than the fully ordered triple helix of the parent schizophyllan and easily dissociates into single chains upon heating. © 2015. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Xanthan exists under most conditions in an extended double-stranded conformation, but may dissociate into disordered, single strands. The influence of both the chemical structure and the conformational state on properties such as solubility, viscosity, salt tolerance, stability towards chemical degradation, depolymerization kinetics and gel formation, are briefly discussed.