Synthesis and characterisation of L-DOPA-modified methyl glycol chitosan (MeGlyChi-DOPA) Ioannis Manolakis 1 , Trinidad Velasco-Torrijos 2 1 Atlantic Technological University, ATU Sligo, Ash Lane, F91 YW50 Sligo, Ireland 2 Department of Chemistry, Maynooth University, Maynooth, Ireland As part of a recent RSC Research Enablement Grant project, we have been investigating the feasibility of a mussel-inspired polyol esterification chemistry using L -3,4-dihydroxyphenylalanine ( L -DOPA) [1-2] to modify polysaccharide substrates, and chitosan and its derivatives in particular. The proposed chemistry has been particularly effective in esterifying primary hydroxyl groups [1-2] and we were interested to study the feasibility and potential selectivity of this approach in polysaccharide substrates. In this work we focus on the results from the attempted modification of methyl glycol chitosan (MeGlyChi) with L -DOPA (Scheme 1).
Scheme 1. Synthesis of MeGlyChi-DOPA The synthesised MeGlyChi-DOPA derivative exhibited significantly different spectroscopic and thermal properties compared to its precursor MeGlyChi (Table 1), with a clear T g at 81 o C, no melting transition and evidence of a newly formed ester bond by FTIR (new band at 1733 cm -1 ). MeGlyChi-DOPA was also shown to produce self-standing hydrogels in Tris HCl buffer (pH 8.5), with the addition of small quantities of a strong base solution (1.0 M NaOH). This provided indirect evidence of the presence of covalently bound catechol moieties on the polysaccharide backbone, able to induce oxidative crosslinking via catechol-to-quinone transformation and to form gels.
Figure 1. Photograph (left) and SEM image (right) of MeGlyChi-DOPA hydrogels References
1. Manolakis, I.; Noordover, B.A.J.; Vendamme, R.; Eevers, W. Novel L-DOPA-Derived Poly (ester amide)s: Monomers, Polymers, and the First L-DOPA-Functionalized Biobased Adhesive Tape. Macromol . Rapid Commun. 2014 , 35, 71 2. Shannon, A.; Manolakis, I. A Facile Route to Bio-Inspired Supramolecular Oligo(Ethylene Glycol) Catecholates. Macromol . Chem. Phys. 2018 , 220, 1800412
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