Natural α-, β- and γ- cyclodextrins as effective traps of cyanotoxins

Cyanotoxins are considered to be a major environmental threat, due to their extreme toxicity for most life forms. Various classes of cyanotoxins have been detected worldwide, especially in lakes. Removal of particularly stable cyanotoxins from irrigation or drinking water is a challenging project, done primarily by nanofiltration, adsorption or chemical oxidation. The prospect of removal using cyclodextrins (CD) has been recently considered. The interactions of three abundant and powerful toxins, microcystin-LR, microcystin-RR and nodularin-R with α-, β- and γ- CDs in aqueous solutions were examined at the semi-empirical PM7(COSMO) level of theory. The results indicate that these cyclic peptide toxins interact with CDs in a similar fashion, namely by insertion of their phenylalkyl side chain into the hydrophobic CD cavity, preferably via the secondary side of CD. Furthermore, the interaction strength was found to increase with the size of cyclodextrin. The theoretical data agree with experimental data obtained by 1H-NMR, suggesting that PM7 is a computationally affordable theoretical method for the study of cyanotoxin interactions with CDs. The PM7-COSMO calculated structure of the most stable complexes between microcystin-LR with three natural CDs is shown in Figure 2.

Figure 2. Structure of the most stable inclusion complexes between microcystin-LR with α, β, and γ-CD in aqueous solution at the PM7(COSMO) level of theory.