Theoretical investigation of microcystin-LR, microcystin-RR and nodularin-R complexation with α-, β-, and γ-cyclodextrin as a starting point for the targeted design of efficient cyanotoxin traps

• Structure of complexes between cyclodextrins and cyclic peptide cyanotoxins.
• Efficiency trends in the complexation of cyclic peptide cyanotoxins by cyclodextrins.
• Reliability assessment of PM7(COSMO) in modeling complexation by cyclodextrins.
• A sustainable chemistry tool for the screening of cyanotoxin filtration agents.

The interactions of three abundant cyanotoxins, namely microcystin-LR, microcystin-RR and nodularin-R with α-, β-, and γ-cyclodextrin in water were structurally and thermodynamically investigated by a computationally affordable methodology using the semi-empirical PM7 method in conjunction with an implicit treatment of solvent effects by the conductor-like screening model (COSMO). As an in silico methodology, PM7(COSMO) offers the advantage of being more environment-friendly than experimental approaches, provided that its computational accuracy limitations are properly accounted for. The results suggest the formation of 1:1 complexes via partial inclusion of the hydrophobic side-chain of cyanotoxins inside the cyclodextrin cavity preferably via the wider opening, further stabilized by hydrogen bonds between hydrophilic groups of the interacting molecules. Enthalpy and entropy changes upon complexation result in a binding efficiency increasing with cyclodextrin size, along with an increase dependent on cyanotoxin, in the order nodularin-R

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