Irreversible Macroscopic Supramolecular Assembly Based On Cyclodextrins And Ferrocene

Supramolecular assembly is an important method to construct an ordered structure from the bottom to up, which is based on supramolecular interactions. This method can be used in multidimensional preparation of highly precise ordered structure under mild condition, and parallel to achieve large amounts of building blocks to assemble, is expected to promote the field of supramolecular research into commercial applications. However, traditional supramolecular research focused on molecular or nano-level, like supramolecular polymers, supramolecular surfactants and so on. For some large scale preparation will require development of supramolecular materials millimeter and above millimeter macroscopic supramolecular assembly. Currently, research on macroscopic supramolecular Assembly is still at an early stage, facing a lot of problems and difficulties, such as macroscopic building blocks’surface roughness, surface functional groups of distribution and interaction, interface, primitive control movements, etc. These difficulties lead to the force is not enough to achieve the construction of macroscopic assembly result from only part of host-guest interaction.In order to solve these problems, we put forward the concept of "flexible spacer layer", which is to construct polyelectrolyte multilayers (PEI/PAA-PDDA/PSS) on surface of macroscopic building block of millimeter scale by layer-by-layer technology. The coating with a certain thickness and mobility in the rigid blocks’surface and it can make up for the surface roughness and increase the rate of supramolecuiar interaction functional groups. This mechanism of macroscopic supramolecular assembly based on flexible spacer is explained by "multiple interaction" (multivalency), which means that when two units with many interaction sites approach, one of the sites interacts at first and then the interaction probability of the other sites will be highly increased. It causes elevation of local concentration, thus improving the building blocks between the apparent binding constants, the enhancement of binding force.However, like other ordinary polyelectrolyte multilayers, the components for flexible spacer layer are relatively complex, and easy to be influenced by various factors, such as pH, ionic concentration and strength. In order to simplify the process of film-forming and enhance the relative stability of the flexible layer, we use macroscopic scale PDMS cube as building block, cyclodextrin and ferrocene molecules as molecular recognition system, with glutaraldehyde cross-linking treatment on the high flow of multilayer film (PEI/PAA). This method proposed a new flexible spacer layer which can be used for macroscopic supramolecular assembly and highly improves the stability of assembly. Aldehyde and amino of glutaraldehyde can quickly react and form the stable Schiff base structure in the buffer which is a simple and effective method for crosslinking polymer and commonly used in biological systems. Amino of PEI can react with glutaraldehyde and partially cross-link flexible spacer layer, which shortens the film-forming time, simplifies the film-forming conditions, enhances the stability of the flexible spacer layer, and guarantees the liquidity of the macro assembly. Therefore it realizes macroscopic supramolecular assembly by multiple interactions.In addition, according to the characteristics of oxidation and reduction of the ferrocene molecule, we regulate valence of ferrocene through the external redox stimulation. The ferrocene valence change binding constants between ferrocene and cyclodextrin in order to accomplish controllable supramolecular assembly and disassembly. This work provides a new idea for the macro dynamic supramolecular assembly.