An infrared reflectance spectroscopic study of a pH-tunable network of nanoparticles linked by hydrogen bonding

This paper presents novel findings of the pH-tunable structural properties of a hydrogen-bonded nanoparticle network using an infrared reflectance spectroscopic (IRS) technique. Gold nanoparticles encapsulated with thiolates and alkylthiols terminated with carboxylic groups were utilized as building blocks and molecular linkers, respectively, for assembling the network film. The IRS bands associated with the reactivities of the carboxylic acid groups on the nanoparticles allowed us to analyze the structures during surface titration of the network thin films. IRS data have revealed that the network, linked by predominantly head-to-head hydrogen bonding, could be reversibly tuned between the neutral protonated and the ionic deprotonated states. This protonation/deprotonation process was also found to exhibit membrane-type properties, as supported by open-circuit potential measurement of the membrane. These findings have important implications to designing nanoparticle-based functional nanostructures for molecular recognition.