Thio-ether-footed resorcin[4]arenes: self-assembly in solution and interaction with gold nanoparticles as viewed by diffusion NMR

In this paper we present the synthesis and characterization of a new family of thio-ether-footed resorcin[4]arenes (2–4). Diffusion NMR was used to follow the self-assembly of 2–4 in CDCl3 and CHCl3 solutions. We found that all three molecules self-assemble into hexameric capsules. These capsules can accommodate both tertiary alkylamines and ammonium salts. From the diffusion NMR data we could conclude that the hexameric capsules of compounds 2–4 are of nearly equal stability and prevail in other organic solvents, such as dichloromethane and benzene but not in tetrahydrofuran (THF). By measuring the diffusion coefficients of 2–4 in different concentrations, we found that further aggregation, beyond the hexameric aggregates, is obtained, especially in the case of 2 at high concentrations. Different diffusion NMR techniques revealed that water molecules are part of the hexameric capsules of 2–4 in chloroform solutions. In addition diffusion NMR was used to examine the interactions of compounds 2–4 with gold nanoparticles in chloroform solution and provided an unequivocal evidence for the attachment of 2–4 to the surface of gold nanoparticles. No evidence was found for the formation of higher aggregates on the gold nanoparticles.