Iron-Centered Star Polymer Synthesis
Metallobiomaterials result when bioactive dibenzoylmethane (dbm) is combined with iron, and poly(lactic acid) (PLA) a bioderived, biocompatible and biodegradable polymer.
Initially we explored chelation routes to polymeric dbmPLA metal complexes. That is, alcohol functionalized dbm ligands were employed as initiators to produce dbmPLA macroligands which were subsequently coordinated to metals such as europium, to generate metal-centered stars. However, reactions were slow and good control was only possible to ~10 kDa for dbmPLA. Thus, protecting group strategies were explored.
In fact, metals can serve “ligand protecting groups” during polymerization reactions and can be subsequently removed to liberation free macroligands. Thus, trifunctional Fe(dbmOH)3 complexes were prepared and tested as metalloinitiators in tin catalyzed lactide and caprolactone ring opening polymerizations. Reactions were considerably faster and more controlled than for the unprotected dbmOH. What is more, we discovered that the tin catalyst is not even needed! Iron tris(dbm) also serves as a catalyst for ring opening polymerization and Fe(dbmPLA)3 "grows itself." That is, iron serves multiple functions: as a protecting group, metalloinitiator, catalyst, chromophore and stimuli responsive center in the material. The resulting red-orange iron polymers, Fe(dbmPLA)3 and Fe(dbmPCL)3 can be demetallated with dilute acid, to produce dbmPLA and dbmPCL for subsequent coordination to other metal centers.
Images coming soon
“Iron Tris(dibenzoylmethane)-centered Polylactide Stars: Multiple Roles for the Metal Complex in Lactide Ring Opening Polymerization” Gorczynski, J. L.; Chen, J.; Fraser, C. L. J. Am. Chem. Soc. 2005, 127, 14956-7.
Iron Tris(dbm) Nanoparticles
Recently we have fabricated Fe(dbmPLA)3 as nanoparticles and explored the two-stage degradation properties of these materials, at the metal center and along the polyester backbone, as a function of pH and buffer conditions. Macroligand dissociation from the metal center is more facile at low pH, whereas polyester hydrolysis is faster at higher pH.
Images coming soon
“Two-stage pH Sensitive Degradation of Iron Tris(Dibenzoylmethane-Polylactide) Nanoparticles” Chen, Y. J.; Pfister, A.; Fraser, C. L. In preparation.