Wide-range pKa tuning of proton imprinted nanoparticles for reversible protonation of target molecules via thermal stimuli

Abstract

pK_a tuning of Brønsted acids in synthetic nano-materials is of great importance for the design of ion exchange and bio-/molecular-separation media and polymer catalysis. It has been reported that hydrogel nanoparticles with carboxylic acids that show large and reversible pK_a shifts in response to thermal stimuli can be prepared by copolymerization of N-isopropylacrylamide (NIPAm), acrylic acids (AAc) and N,N′-methylene bisacrylamide (BIS) via the proton imprinting polymerization process. However, the reported range of pK_a shifts is limited to the range of 5.3 to 7.5. In this study, we report a procedure to prepare proton imprinted NPs that show pK_a shifts in the tuned pK_a range and demonstrate applications of the NPs. pK_a values ranging from 4.3 to 8.7 were achieved by designing the structure of monomers containing carboxylic acids and applying the proton imprinting procedure. It was demonstrated that proton-imprinted NPs with different pK_a values could be used for the reversible and selective protonation of target molecules which have specific pK_a values. Our results establish the generality of the proton imprinting procedure and provide a guide for designing stable and inexpensive materials for sophisticated purification processes.