Mechanistic Study And Imaging Of Biomolecule-instructed Self-assembly Of Supramolecular Hydrogels

Self-assembly/disassembly is ubiquitous in nature.In biology,cell uses small molecules to self-assemble/disassemble nano-or micro-sized,or superstructural biological complexes for its development,functionality,and death.For examples,intracellular self-assembly/disassembly of small molecules into highly ordered structures is essential to maintain the cytoskeleton(e.g.,cytoplasmic microtubules),regulate cell mitosis(e.g.,spindle fibers),or dominate a disease(e.g.,?-amyloid in Alzheimer's disease).Most of the self-assembly/disassembly processes in nature were found to be regulated by enzymes.This has fascinated and inspired researchers to exploit Nature's principles by developing and studying similar self-assembly/disassembly processes using enzymatic transformation in the past decade for a wide range of applications in biology and biomedicine.To date,a variety of techniques,such as nuclear magnetic resonance,electron microscopy,X-ray crystallography,mass spectrometry,and optical spectroscopy,have been reported to characterize the morphology and structures of the molecular self-assembly/disassembly.However,due to its dynamic property of self-assembly,developing new analytical methods to sensitively monitor this process remains challenging.In this dissertation,the author focuses on the design of novel imaging method for the sensing of several important biomarker-instructed self-assembly processes.In the second part of this dissertation,using a homebuilt liquid-phase scanning tunneling microscopy(L-STM)with ultrahigh stability,the author directly visualized enzymatic self-assembly/disassembly of oligopeptide nanofibers in real time for the first time.Static high-resolution L-STM images clearly showed the molecular packing details in the supramolecular nanofiber and the diameter of the nanofiber was consistent with that in cryo transmission electron microscopy(cryo-TEM)observations.Moreover,self-repairing behavior of the supramolecular nanofibers was also directly observed at high resolution for the first time.This work unprecedentedly revealed new insights into Nature-mimic self-assembly and disassembly at molecular level.It also illustrates the potential of our homebuilt L-STM in studying delicate biological processes in physiological solution with high resolution.In the second part of this dissertation,we rationally designed a hydrogelator Nap-Phe-Phe(CF3)-Glu-Tyr-Ile-OH(la)whose supramolecular hydrogel(i.e.,Gel la)can be subjected to tyrosine kinase-directed disassembly,and its phosphate precursor Nap-Phe-Phe(CF3)-Glu-Tyr(H2PO3)-Ile-OH(1b)which can be subjected to alkaline phosphatase(ALP)-instructed self-assembly to form supramolecular hydrogel Gel lb,respectively.Disassembly/self-assembly of their corresponding supramolecular hydrogels conferring respective "On/Off" 19F NMR/MRI signals were employed to sense the activity of these two important enzymes in vitro and in cell lysates for the first time.We anticipate that our new 19F NMR/MRI method would facilitate pharmaceutical researchers to screen new inhibitors for these two enzymes without steric hindrance.In the fourth part of this dissertation,we rationally designed an iodinated hydrogelator precursor Nap-Phe-Phe(I)-Tyr(H2PO3)-OH(1P)which self-assembles into nanofibers to form hydrogel under the catalysis of ALP.With this property of concentrating iodine atoms at the locations of ALP,1P was successfully applied for direct nano-computed tomography(nano-CT)imaging ALP activity in bacteria for the first time.We envision that,based on this pioneering work,new hydrogelators containing more iodine atoms(e.g.,five iodine atoms in 1P)will be designed for better nano-CT imaging of ALP activity with higher CT contrast in the near future.In the fifth part of this dissertation,with the knowledge that the extracellualr environment of some cancer cells contains large amount of alkaline phosphatase(ALP)while their intracellular environment is glutathione(GSH)-abundant in mind,we rationally designed a precursor Cys(SEt)-Glu-Tyr(H2PO3)-Phe-Phe-Gly-CBT(1)which can efficiently yield amphiphilic 2 and 2-D to self-assemble into two different nanofibers in hydrogels under the sequential treatment of ALP and GSH.We envision that,by employing a click condensation reaction,this work offers a platform for facilely post modulation of supramolecular nanofibers,and the versatile precursor 1 could be used to kill two birds with one stone.