Stability of cationic and amphoteric derivatives of mannan from the yeast Candida albicans

Infection with Candida albicans can prove lethal in immuno-compromised patients. It is imperative to develop a vaccine against this common organism. The amphoteric derivatives of the mannan component of the Candida cell wall may present a prospective target for the development of such a vaccine; however, the radical processing by antigen-presenting cells of the immune system is not fully understood. In this work a set of tailor-made cationic and amphoteric derivatives of three different degrees of quaternization (DS_Q 0.14-0.38) has been prepared by chemical modification of ultrasonically-treated mannan and three carboxymethylated mannan derivatives (DS_CM 0.13-0.32). These were exposed to free-radical attack by OH, generated in situ by the Fenton reaction. Potential changes in composition, DS_Q, and molar mass distribution due to free-radical degradation were monitored by elemental analysis, NMR and FTIR spectroscopies, and size exclusion chromatography. A protective effect of quaternization against OH degradation was found. Non-isothermal thermogravimetric analysis found that the thermal stability of this mannan was also improved by chemical modification.