Design, Synthesis And Properties Of Novel Helical Architectures

The high-level structures are responsible for the various complicated and delicate functions inliving system. For example, DNA double helix structure achieves the storage and transfer ofgenetic information by replication, transcription and translation. Variety of proteins in organismspresents the unique functions in the life cycle which mainly result from differences of thesecondary structures consisting of the-helices and β-sheets. Inspired by these biologicalmacromolecules and macromolecular assemblies, it has been becoming a key research topic inthe fields of chemistry and materials that rationally and intentionally designing the covalent andnoncovalent artificial helical structures to mimic their functions and develop their potentialapplications in sensors, optics devices, information storage, enantiomer separation, asymmetriccatalysis and materials science. Diverse chemical structures, ample driving forces and powerfulcomputer simulation provided an ideal platform and effective guidance for the design of thehelical structures. At the same time, with the innovation of various characterization techniques,especially the combination of X-ray crystal diffraction, nuclear magnetic resonance spectrometer,imaging technology and circular dichroism spectrometer makes them possible that parsing theprecise structure of helices and investigating the folding mechanism of helical structures,aggregation behavior and the control of chirality at the molecular level. Herein, quinolinederivatives and their analogues were used as ideal scaffolds to build two types of new helicalstructures and thus explore the relationship between the structure and property of helix.1. Construction of STM-Visualized Aromatic Helical PolymersThe conventional characterization methods of helical structures mainly include crystallographyand spectral technologies. However, the characterization of helical polymers, in particular thatthe corroboration of their helical conformations strongly relied on the evidence of circulardichroism spectroscopy. Recently, single-molecule imaging technique which has been made greatprogress in the characterization of molecular structures at extraordinary levels will provide moredirect proof regarding the helical structure. As known, the outside morphologies of helicalpolymers can be clearly observed by AFM. Nevertheless, the direct observation of inside patternsof helical polymer is restricted due to the contact mode of AFM. In order to achieve a morein-depth observation of helical polymer from outside morphology to inner backbone, weestablished a new type of aromatic helical polymers consisting of1,8-diaza-9-methyl-2,7-anthracenedicarboxylic acid as structural motif and1,3,4-oxadiazole aslinker. By STM, we successfully observed the inner backbones of helical polymer with a pattern of π-π stacking at a single molecule level, which is the smallest helical architecture observed thusfar (diameter ca.1.3nm). These single helical structures could form double helices byintermolecular π-π interactions. In the STM images, we firstly identified the single and doublehelical structures, and observed the interconversion of single and double helices. Interconversionof single and double helices is controllable by temperature and the concentration. The new typeof aromatic helical structures can be used for controllable self-assembly and design of potentialfunctional materials. These results also provided a new method for the characterization ofcomplicated and highly-ordered structures at single molecule level.2. Construction of Novel Multi-Responsive Aliphatic-Aromatic Helical Polymers andTheir Assembly BehaviourControllable switching of helical structures by external stimuli will make their function diverseand intelligent. Here, according to the well-studied crystal structures and conformation analysisby molecular simulation, we built a novel aliphatic-aromatic hybrid helical polymer with partialflexibility by using Boc-protected8-aminomethyl-4-isobutoxyquinoline-2-carboxylic acid and8-amino-4-isobutoxyquinoline-2-carboxylate as structure motifs. The folding and unfolding ofthe helical polymers could be controlled by pH and redox as well. The formation of organogelwas achieved by heating and then annealing. Finally we performed the self-assembly study in thearea-confined microevironment (e. g. emulsion) and successfully constructed a number ofsupramolecular nanostructures including nanotubes, vesicles, polygonal nanorings, fusiformnanorings by controlling the aggregating conditions. The helical polymers as a kind of intelligentmaterials will be of broad application prospects. Additionally, helix-based self-assembly alsoprovided a new method for construction of hierarchical structures.3. Chirality Transfer in Helical StructuresBased on two kinds of helical structures established successfully, we explored the handednessof helical molecules. In the aliphatic-aromatic helical structures, the right and left handness ofhelices were induced by S and R chiral molecules at the C terminals, respectively. And the helicalstructure presented a phenomenon of chirality amplification as the helix length increases.However, the handedness inversion of helix took place when the chiral molecules wereincorporated into the N terminal. Further analyses suggested that the folding of helical structurewas launched from C terminal. Furthermore, to investigate the chirality transfer from one helix toanother helix, we prepared a C2-symmetrical helices within2,2’-selenodiethanamine as the linker.We found a chiral amplification phenomenon of “1+1>2”. Finally, we used the aromatic helicalpolymers to study the supramocular chirality based on the interconversion between single anddouble helices. The formation of double helices induced different supramolecular chirality from the single helices that are remarkable intensity decrease and large bathochromic shift. Theseresults provided new insights into the chirality transfer rules from chiral carbon tosupramolecular chirality.