Photochemical Sciences Ph.D. Dissertations

Photochemistry of Fe(III)-carboxylates in polysaccharide-based materials with tunable mechanical properties

Date of Award

2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Alexis Ostrowski (Advisor)

Second Advisor

Michael Geusz (Committee Member)

Third Advisor

George Bullerjahn (Committee Member)

Fourth Advisor

R. Marshall Wilson (Committee Member)

Abstract

We present the formulation and study of light-responsive materials based on carboxylate-containing polysaccharides. The functional groups in these natural polymers allow for strong interactions with transition metal ions such as Fe(III). The known photochemistry of hydroxycarboxylic acids in natural waters inspired us in exploring the visible light induced photochemistry of the carboxylates in these polysaccharides when coordinated to Fe(III) ions. Described in this dissertation are the design and characterization of the Fe(III)-polysaccharide materials, specifically the mechanistic aspects of the photochemistry and the effects that these reactions have on the structure of the polymer materials.

We present a study of the quantitative photochemistry of different polysaccharide systems, where the presence of uronic acids was important for the photoreaction to take place. Alginate (Alg), pectate (Pec), hyaluronic acid (Hya), xanthan gum (Xan), and a polysaccharide extracted from the Noni fruit (NoniPs), were among the natural uronic acid-containing polysaccharide (UCPS) systems we analyzed. Potato starch, lacking of uronate groups, did not present any photochemistry in the presence of Fe(III); however, we were able to induce a photochemical response in this polysaccharide upon chemical manipulation of its functional groups. Important structure-function relationships were drawn from this study. The uronate moiety present in these polysaccharides is then envisioned as a tool to induce response to light in a variety of materials.

Following this approach, we report the formulation of materials for controlled drug release, able to encapsulate and release different drug models only upon illumination with visible light. Furthermore, hybrid hydrogels were prepared from UPCS and non-responsive polymers. Different properties of these materials could be tuned by controlling the irradiation time, intensity and location. These hybrid gels were evaluated as scaffolds for tissue engineering showing great promise, as changes in the behavior of the growing cells were observed as a result of the photochemical treatment of the material.

We present these natural and readily available, polysaccharide-based, metal-coordination materials as convenient building blocks in the formulation of new stimuli responsive materials. The photochemical methods developed here can be used as convenient tools for creating advanced materials with tailored patterns and gradients of mechanical properties.

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