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.