Temperature-modulated interaction changes with adenosine nucleotides on intelligent cationic, thermoresponsive surfaces

Thin layer poly(N-isopropylacrylamide-co-n-butyl-methacrylateco-N,N-dimethylaminopropylacrylamide) (IBD) copolymer gels are covalently introduced to initiator immobilized silica bead surfaces to create thermally sensitive intelligent cationic surfaces. The surface shows thermoresponsive changes in charge density as well as hydrophilic/hydrophobic character. The polymer chains dehydrate and inter-/intra-molecular aggregation occurs due to weakly deprotonated cationic amino groups in the hydrophobized circumstances, resulting in the surface charge density decrease. This was corroborated by the thermoresponsive pKa shift of dimethylamino side groups in the copolymers as well as the surface potential changes at elevated temperature. The unique characteristics of the IBD copolymer-immobilized surfaces were applied to regulate adenosine nucleotides retention in high-performance liquid chromatography using aqueous mobile phase by thermal stimulus. At lower temperature, adenosine nucleotides showed higher retention which was primarily driven by ionic interaction with positively charged surfaces. With increasing temperatures, their retention was shortened and a drastic change was observed above the polymer transition temperatures. This is strong evidence that the solute interaction is being regulated by the thermoresponsive surface charge density changes and hydrophobic alterations. Furthermore, we confirmed the modulation of nucleotide retention by step-temperature gradient without changing mobile phase composition. These findings should be beneficial in utilizing this stimuli responsive surface for the separation of bioactive compounds in aqueous system and environmental impact.