Demystifying and Unravelling the Factual Molecular Structure of the Biopolymer Sporopollenin
Sporopollenin is a natural highly cross-linked biopolymer composed of carbon, hydrogen, and oxygen which forms the outer wall of pollen grains. Sporopollenin is resilient to chemical degradation. Because of this stability, its exact chemical structure and the biochemical pathways involved in its biosynthesis remains a mystery and unresolved. It is obvious that a well-conceived coherent study of the sporopollenin structure details will help immensely scientists in better understanding the chemistry of their current applications of sporopollenin exines such as drug delivery, peptide synthesis, micro-reactors, and wastewater purification. As well, it may also lead to the discovery of newer biomedical applications in the next coming years. We have identified and characterized the molecular structure of the clean, intact sporopollenin using mass spectrometric and nuclear magnetic resonance techniques. These analyses showed that sporopollenin is composed of a circular polyhydroxylated tetraketide polymer rigid backbone and a poly(hydroxyacid) branched network. The poly(hydroxyacid) network chains are attached by covalantly ether bonds to the polyhydroxylated tetraketides rigid backbone, forming the scaffold of the spherical sporopollenin.