Controlled and Reversible Formation of Nanoparticle Aggregates and Films Using Cu²⁺−Carboxylate Chemistry

The controlled and reversible formation of transiently soluble alkanethiolate- and tiopronin-monolayer-protected cluster (MPC) aggregates is demonstrated by using Cu 2+ −carboxylate chemistry to form cluster−Cu 2+ −cluster linkages. The aggregation process and its reversibility were monitored using UV−vis and FTIR spectroscopy. The amount of Cu 2+ required to induce aggregation of dissolved tiopronin-MPCs is a strong function of pH, increasing at lower pH. Cu 2+ −carboxylate chemistry can also be utilized to prepare surface-attached films of tiopronin-MPCs in a manner analogous to alkanethiolate-MPCs, monitoring the film formation using FTIR external reflectance spectroscopy. Experiments exploring the diffusional and capacitive properties of tiopronin-MPCs are also reported.