디티로신의 공유 자가 조립을 통한 단백질 기반 나노구조체 합성

Abstract

Self-assembly phenomena were one of the most focused region by chemical or biological regions. Small building molecules assembled into nano-, micro- or macro- structure by only themselves. Self-assembled structures showed different their properties unlike their precursors, and changed their properties by self-assembly methods. Untill now, researches about self-assembly of organic chemical block co-polymers had been received attention and self-assembly of bio-inspired materials processed mainly with non-covalent bonds among building molecules. The non-covalently self-assembled structures did not show durable and reliable properties because of weak chemical and mechanical intrinsic stability of non-covalent bonds. To overcome these weak instability, previous researches reported self-assembly based on covalent bonds, but they used this to enhance mechanical strength of hydrogels or to improve the shell of drug carriers, did not report many covalently self-assembled bio- nanostructures This thesis presented various self-assembled nanostructures using dityrosine bonds between tyrosine amino acids, with enhanced chemical and mechanical stability. YYAYY peptide sequence was used as the model monomer, which had two tyrosine groups at both ends. This sequence was able to produce network structure under UV-irradiated radical polymerization. Monomers integrated into small oligomeric patches, then the patches grow into lateral direction continuously, and made nano-sized sheet. This sheet grew into nanostructures of which morphology could be controlled by solution pH and type. First, pH 10 buffer aqueous solution, produced nanocapsules, showing a diameter with 155.1 ± 46.13 nm and the wall thickness with 2.43 ± 1.3 nm. These nanocapsules show blue fluorescence as reported. UV-Vis spectra and 1H-NMR spectra confirmed the existence of dityrosine bonds in the nanocapsules. Second, pH 13 0.1 M NaOH aqueous solution produced smaller nanocapsules showing diameters less than 100 nm. High pH increased high radical concentration, accelerating polymerization, and giving smaller sized nanocapsules. Third, pH 13 0.1 M NaOH methanol solution produced nanofilms which had few micrometer size and 4 nm thickness. Increased interaction between methanol and self-assembled intermediate maintained the flat morphology. Also, the nanofilms show elastic modulus with 29.88 ± 1.43 GPa and hardness with 740 ± 0.12 MPa superior to non-covalently self-assembled sturctures. Stability tests performed on the nanoflims, in 80℃ for a week, pH4 buffer for a day and 1N HCl aqueous solution for a day. As the result, nanofilms had just stacked up with each other due to change of ionic concentration, and did not show any deformation or degeneration. Through this research, self-assembled nanostructure with superior mechanical strength and chemical stability had been fabricated without any template or post treatments. Only small change in reaction medium control the morphology and size of the nanostructures. This could be applied on more stable support for cell or enzymes, or drug carriers.