Macromolecular Self-Assembly Based On Multiple Supramolecular Interactions

Macromolecular self-assembly has attracted great attention due to its functional diversity and various potential applications in drug delivery, catalysis, template synthesis etc. The research field has been developed rapidly since the end of the last century, but the mechanisms of self-assembly of some kind of macromolecules still remain unclear because of the complexity and diversity of macromolecular structures and architectures. Here, two main research aspects in the field of macromolecular self-assembly interest our research group mostly:One is the investigation of the detailed mechanisms of the known self-assembly phenomena, which would provide more precise strategies to control the self-assembly behavior. Another one is dealing with expanding the scope of building blocks and assembly mechanisms in order to construct novel assemblies with attractive functions. This thesis is written along these two directions:In the first part, the mechanism of thermoresponsive self-assembly of conventional random copolymer is investigated. And in the second part, a novel crystalline self-assembly based on a protein is pursued by introducing multiple supramolecular interactions.(1) Investigation of the self-assemble mechanism of cyclodextrin-containing thermoresponsive random copolymersDue to the practicality of the random copolymers such as easy productivity and low cost, their self-assembly behavior has been of interest for a long time. However, since their molecular structure is more complicated than that of block copolymers, only a few of systematic studies on their self-assembly, especially from the aspect of the kinetics were reported. Our group previously conducted primary research on the thermoresponsive self-assembly of a cyclodextrin-containing random copolymer and found that the copolymer in solution led to different self-assembly morphologies such as solid micelles and vesicles depending on the heating rate. Thus, in order to study the detailed mechanism of this heating rate-dependent self-assembly, in the current work, cyclodextrin-containing monomer AEMACD is synthesized to obtain random copolymer P(NIPAM-co-AEMACD) (PNiCD). With dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM), the heating rate-dependent self-assembly behavior of PNiCD has been found:It forms relatively small micelles (radius of ca.53 nm) at a fast heating rate, while forms relatively large micelles (ca.136 nm) accompanied by plenty amount of tiny particles (ca.10 nm) at a slow heating rate. Further tracking the size distribution evolution during the heating process with DLS reveals that at the slow heating rate PNiCD firstly forms tiny particles around its LCST (-38 ℃), and the particles aggregate again into large secondary micelles along further heating. While at the fast heating rate it directly assembles into solid micelles. Based on all of these results, two different mechanisms have been suggested for this self-assembly:At the slow heating process, a PNiCD chain has enough time to rearrange its chain conformation forming a relatively stable unimolecular micelle, i.e. the tiny particle, and then re-aggregates into large secondary micelles to reduce their surface, while at the fast heating process PNiCD chains directly entangle to each other and then form stable micelles. These new mechanisms will arouse new interest on the self-assembly mechanism of amphiphilic copolymers with more complicated and ill-defined structures.Besides, guest macromolecules for the cyclodextrin, namely adamantane mono-end substituted poly(ethylene glycol) (MPEG-ADA) and azobenzene mono-end substituted poly(ethylene glycol) (MPEG-Azo) are synthesized, and the formation of macromolecular complexes between PNiCD and the guests are demonstrated with DLS measurement. The results of the thermal-induced aggregation of the supramolecularly graft macromolecules indicate the self-assembly behavior can be controlled by the host-guest interactions of cyclodextrin and guest molecules.(2) New crystalline self-assembly behavior of Concanavalin AIn the last decade, the research interest on self-assembly with proteins as building blocks gradually increased with emphasis on the ordered protein assembly through mutation of surface residues. For example, Tezcan et al. reported the metal-coordination-mediated self-assembly of cb562 mutant proteins, which formed various morphologies such as tube-like structure and crystal, demonstrating the utility of the supramolecular chemistry as a driving force in protein assembly.In our work, a inducing ligand Rh3Man composed of rhodamine B (RhB) moiety and mannose (Man) moiety is designed and synthesized. Precipitate aggregation of concanavalin A (ConA) in buffer induced by Rh3Man was found. Through a combination of measurements including UV-vis, circular dichroism spectroscopy, fluorescence lifetime measurement, TEM, AFM, and optical microscopy, the aggregation is revealed as a crystal structur with a equal molar amount of Rh3Man and ConA. The detailed crystalline structure was determined by X-ray diffraction, i.e. cell parameters:a= 84.00 A, b= 116.03 A, c= 84.10 A, α= 90.00 °, β= 95.03 °, γ= 90.00 °; space group:P21. Such structure was demonstrated to be induced by the sugar-protein interaction and crosslinking of ConA via Rh3Man dimerization. The crystal contains exceptionally a large amount of bulk water (68.7%) and ITC measurement showed a large negative enthalpy, so this self-assembly crystallization is featured by the two unusual factors in ordinary protein crystals.In order to investigate the universality of this process, a inducing ligand Rh3Glu in which the Man group of Rh3Man was substituted by glucose, and also inducing ligands with different spacer length between RhB moiety and Man group, namely, Rh1Man, Rh2Man, Rh4Man, and Rh5Man, were synthesized. Among these ligands, Rh3Glu, Rh2Man, and Rh4Man successfully induced crystalline self-assembly of Con A. The crystal formed by Rh3Glu was similar to that with Rh3Man (cell parameter:84.16 A, b= 116.01 A, c= 84.24 A, α= 90.00 °, β= 95.98 °, γ= 90.00 °; space group:P21), while that formed by Rh4Man was quite different from that from Rh3Man (cell parameter:a= 84.16 A, b= 116.01 A, c= 84.24 A, α= 90.00 °, β= 95.98 °, γ= 90.00 °; space group:P21212) with low bulk water content (39.1%).The protein crystalline self-assembly found in this thesis differs substantially from the conventional protein crystallization process, i.e., this assembly can produce protein crystal at a high rate, with a high conversion ratio from the solution with a high protein concentration, thus it makes the large amount production of protein crystal possible. Besides, as the slow crystallization rate has been the bottle-neck process of protein crystallography, this new high-rate crystalline self-assembly might open a new window to the study of the optimization of protein crystallization process.