Solvent-induced stable pseudopolymorphism of Au(i)–thiolate lamellar assemblies: a model system for understanding the environment acclimation of biomacromolecules

Abstract

A unique coordination polymer of Au(I)–thiolate has been used as a model system to study the molecular-level pseudopolymorphism in hierarchical assemblies and help understand the environment acclimation of biomacromolecules. Two lamellar pseudopolymorphs of the coordination polymer Au(I)–3-mercaptopropionic acid (MPA) have been successfully prepared in two solvents, water and ethylene glycol (EG), at appropriate pH values. The two pseudopolymorphs have distinct differences in optical properties, morphology and thermal stability. By analyzing their composition and structure in detail, it is suggested that the large change in the dissociation ability of –COOH and –COONa species in MPA ligands plays an important role in enabling the solvent-induced pseudopolymorphism. Based on the above conclusion, a series of water/EG binary solvents and pH values have been used to induce the formation of other possible polymorphs, and a third pseudopolymorph has been discovered. However, it cannot be separated from the above two polymorphs. The two obtained pseudopolymorphs exhibit high structure preservation and cannot inter-convert to each other either in solution or in the solid state because of the collective interactions. Based on the above results and other studies, reflections on how biomacromolecules realize the environment acclimation chemically are finally discussed.