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Demystifying and unravelling the molecular structure of the biopolymer sporopollenin
Author(s) -
Mikhael Abanoub,
Jurcic Kristina,
Schneider Celine,
Karr David,
Fisher Gregory L.,
Fridgen Travis D.,
DiegoTaboada Alberto,
Georghiou Paris E.,
Mackenzie Grahame,
Banoub Joseph
Publication year - 2020
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8740
Subject(s) - sporopollenin , biopolymer , chemistry , monomer , two dimensional nuclear magnetic resonance spectroscopy , polymer , organic chemistry , pollen , stereochemistry , botany , biology
Rationale We report the unsolved molecular structure of the complex biopolymer sporopollenin exine extracted from Lycopodium clavatum pollen grains. Methods TOF‐SIMS and CID‐MS/MS, MALDI‐TOF‐MS and CID‐TOF/TOF‐MS/MS were used for the analysis of this complex biopolymer sporopollenin exine extracted from Lycopodium clavatum pollen grains . Solid‐state 1 H‐ and 13 C‐NMR, 2D 1 H‐ 1 H NOESY, Rotor‐synchronized 13 C{ 1 H} HSQC, and 13 C{ 1 H} multi CP‐MAS NMR experiments were used to confirm the structural assigments revealed by MS and MS/MS studies. Finally, high‐resolution XPS was used to check for the presence of aromatic components in sporopollenin. Results The combined MS and NMR analyses showed that sporopollenin contained poly(hydroxy acid) dendrimer‐like networks with glycerol as a core unit, which accounted for the sporopollenin empirical formula. In addition, these analyses showed that the hydroxy acid monomers forming this network contained a β‐diketone moiety. Moreover, MALDI‐TOF‐MS and MS/MS allowed us to identify a unique macrocyclic oligomeric unit composed of polyhydroxylated tetraketide‐like monomers. Lastly, high‐resolution X‐ray photoelectron spectroscopy (HR‐XPS) showed the absence of aromaticity in sporopollenin. Conclusions We report for the first time the two main building units that form the Lycopodium clavatum sporopollenin exine. The first building unit is a macrocyclic oligomer and/or polymer composed of polyhydroxylated tetraketide‐like monomeric units, which represents the main rigid backbone of the sporopollenin biopolymer. The second building unit is the poly(hydroxy acid) network in which the hydroxyl end groups can be covalently attached by ether links to the hydroxylated macrocyclic backbone to form the sporopollenin biopolymer, a spherical dendrimer. Such spherical dendrimers are a typical type of microcapsule that have been used for drug delivery applications. Finally, HR‐XPS indicated the total absence of aromaticity in the sporopollenin exine.