Hemin–G-quadruplex-crosslinked poly-N-isopropylacrylamide hydrogel: a catalytic matrix for the deposition of conductive polyaniline†
A G-rich nucleic acid-tethered acrylamide/N-isopropylacrylamide (NIPAM) copolymer is prepared. The nucleic acid-modified pNIPAM chains assemble, in the presence of K+ ions, into a stimuli-responsive G-quadruplex-crosslinked pNIPAM hydrogel undergoing cyclic and reversible solution/hydrogel/solid transitions. Addition of kryptofix [2.2.2], CP, to the K+-stabilized G-quadruplex-crosslinked hydrogel eliminates the K+ ions from the crosslinking units, resulting in the transition of the hydrogel into a pNIPAM solution. In turn, heating the pNIPAM hydrogel from 25 °C to 40 °C results in the transition of the hydrogel to the solid state, and cooling the solid to 25 °C restores the hydrogel state. Incorporation of hemin into the G-quadruplex-crosslinked hydrogel results in a catalytic hydrogel that catalyzes the oxidation of aniline by H2O2 to form polyaniline. The polyaniline/pNIPAM hydrogel hybrid doped with 2 M HCl forms an emeraldine salt, which exhibits an electrical conductivity of 9 × 10−4 [cm Ω]−1.