Development of environmentally responsive hydrogels with metal affinity behavior

Abstract

This work describes initial efforts to incorporate affinity ligands within an environmentally responsive hydrogel. Metal affinity ligands were chosen as model affinity groups and thermally responsive N-isopropyl acrylamide/acrylamide copolymers were used as the base hydrogels. The À ÀNH 2 group of the acrylamide serves as a reactive group for functionalization with metal affinity ligands. The gels were synthesized by free radical polymerization and Cu 2þ was bound to the gel via 1,4-butanediol diglycidyl ether (BDE) as a linker and iminodiacetic acid (IDA) as a chelating ligand. The base acrylamide gels were also functionalized with metal affinity ligands to allow for comparison with thermally responsive affinity gels. The results show the effectiveness of this technique for both these types of gels, and an improved method to immobilize metal affinity groups on to thermally sensitive N-isopropyl acrylamide gels was also developed. It was seen that the yields for the reaction with BDE decreased with increased reaction time in both kinds of gels, whereas reaction with IDA showed a decrease in yields with increase in temperature for N-isoporpyl acrylamide gels and increase in yields for acrylamide gels. Further techniques were developed to overcome diffusional resistances and stresses in the thermally responsive N-isopropyl acrylamide gels so as to improve the distribution of Cu 2þ ions.

Controlling Phase Transition Behavior of Thermally Responsive Metal Affinity Hydrogels: A Molecular Design Approach

“…7 The PT was broader and shifted to higher temperatures when copolymerized with acrylamide, which agrees with reported results. 2,8 Further, when the gel was grafted with iminodiacetic acid and chelated with Cu 2+ as a metal affinity group (Scheme 1A), the sharp PT behavior was lost.…”

“…The gel was immersed in DI water for at least 3 days with water changes at least 3 times a day to remove any unreacted monomers. In a similar manner, free-standing thin film gels were synthesized by transferring gel solution between two glass plates coated with dimethyldichlorosilane and separated by a 0.5 mm spacer using a syringe . The gels were cut into round pieces of 1.6 cm diameter using a cork punch before further use.…”

“…The higher BCC in the bulk gels suggested that there could be some entrapment of copper 7,23 in the tortuous structure of the gel. When the bulk gels were swollen and shrunk 2-3 times by decreasing and increasing the temperature, the excess copper was eluted and the BCC reduced to 73 ( 5%, which is comparable to that of the thin film gels.…”

“…Visual comparison of the distribution of copper in affinity hydrogels: (a) gels functionalized using a grafting technique7 showing an uneven distribution and (b) gels synthesized by in-situ polymerization in this study showing an even distribution.…”

Poly(N‐isopropylacrylamide) Networks Conjugated with Gly–Gly–His via a Merrifield Solid‐Phase Peptide Synthesis Technique for Metal‐Ion Recognition

“…12 °C) in the phase transition of the conjugated gel upon exposure to Cu 2+ and Ni 2+ ions, suggesting selective recognition through complexation between the ion and cyclam functional group. Although the incorporation of such chelating moieties into stimuli‐responsive polymers has allowed for the identification and collection of heavy metal ions, there still remain difficulties in the identification of a wide range of heavy metal ions.…”