New functional materials comprising the plant polymer sporopollenin

Abstract

"Sporopollenin is a plant polymer present in the exine of pollen grains. It possesses remarkable mechanical, thermal and chemical stability, and is also highly recalcitrant to hydrolysis. Recent works have provided insight into its molecular structure. Nevertheless, it remained to be fully clarified, since its solubilization is hindered by its extreme inertness. Even after harsh isolation procedures, sporopollenin is recovered as modified/degraded fragments of the native polymer. In this work, we tested both acetolysis and ionic liquid (IL) reaction on bee pollen (BP). The obtained fractions were analyzed by infrared spectroscopy (FTIR) that showed that both methods rendered sporopollenin enriched fractions, regardless of the introduction of acetate on the acetolyzed BP and the incomplete removal of non-sporopollenin material by the ILs. The same workflow was employed for sunflower pollen (SP), plus an innovative approach of combining acetolyzed sunflower pollen (AcetSP) and IL reaction. The SP + IL reaction allowed to obtain endexine capsules. Nuclear magnetic resonance (NMR) and/or FTIR data showed signals for aromatics, primary aliphatic esters and acetals in both precipitated and soluble fractions, indicating that sporopollenin can be partially hydrolyzed with ILs. Polysaccharides and proteins were found as contaminants in the IL-isolated fractions, similar as in BP.(...)"