2 research outputs found
Light-Responsive Iron(III)–Polysaccharide Coordination Hydrogels for Controlled Delivery
Visible-light
responsive gels were prepared from two plant-origin polyuronic acids
(PUAs), alginate and pectate, coordinated to FeÂ(III) ions. Comparative
quantitative studies of the photochemistry of these systems revealed
unexpected differences in the photoreactivity of the materials, depending
on the polysaccharide and its composition. The roles that different
functional groups play on the photochemistry of these biomolecules
were also examined. Mannuronic-rich alginates were more photoreactive
than guluronic acid-rich alginate and than pectate. The microstructure
of alginates with different mannuronate-to-guluronate ratios changed
with polysaccharide composition. This influenced the gel morphology
and the photoreactivity. Coordination hydrogel beads were prepared
from both Fe–alginate and Fe–pectate. The beads were
stable carriers of molecules as diverse as the dye Congo Red, the
vitamin folic acid, and the antibiotic chloramphenicol. The photoreactivity
of the hydrogel beads mirrored the photoreactivity of the polysaccharides
in solution, where beads prepared with alginate released their cargo
faster than beads prepared with pectate. These results indicate important
structure–function relationships in these systems and create
guidelines for the design of biocompatible polysaccharide-based materials
where photoreactivity and controlled release can be tuned on the basis
of the type of polysaccharide used and the metal coordination environment
Mössbauer Spectroscopic Characterization of Iron(III)–Polysaccharide Coordination Complexes: Photochemistry, Biological, and Photoresponsive Materials Implications
While polycarboxylates and hydroxyl-acid
complexes have long been known to be photoactive, simple carboxylate
complexes which lack a significant LMCT band are not typically strongly
photoactive. Hence, it was somewhat surprising that a series of reports
demonstrated that materials synthesized from ironÂ(III) and polysaccharides
such as alginate (polyÂ[guluronan-<i>co</i>-mannuronan])
or pectate (polyÂ[galacturonan]) formed photoresponsive materials that
convert from hydrogels to sols under the influence of visible light.
These materials have numerous potential applications in areas such
as photopatternable materials, materials for controlled drug delivery,
and tissue engineering. Despite the near-identity of the functional
units in the polysaccharide ligands, the reactivity of ironÂ(III) hydrogels
can depend on the configuration of some chiral centers in the sugar
units and in the case of alginate the guluronate to mannuronate block
composition, as well as pH. Here, using temperature- and field-dependent
transmission Mössbauer spectroscopy, we show that the dominant
iron compound detected for both the alginate and pectate gels displays
features typical of a polymeric (Fe<sup>3+</sup>O<sub>6</sub>) system.
The Mössbauer spectra of such systems are strongly dependent
on temperature, field, size, and crystallinity, indicative of superparamagnetic
relaxation of magnetically ordered nanoparticles. Pectate and alginate
hydrogels differ in the size distribution of the iron oxyhydroxy nanoparticles,
suggesting that in general smaller nanoparticles are more reactive.
Potential biological implications of these results are also discussed