Coumarin-based Low Molecular Weight Hydrogelators:Synthesis,Self-Assembly And Their Biological Applications

Low-molecular-weight hydrogelators?LMHGs?can self-assemble and crosslink in aqueous solution to form supramolecular hydrogels through non-covalent interactions,such as hydrogen bonding,?-?stacking,van der Waals and electrostatic interaction.Due to the properties of biocompatibility,sensitive respond,and designability,supramolecular hydrogels have attracted increasing interest recently as soft materials in the applications of drug delivery,tissue engineering,biosensor,and so on.But so far,the major impediment for designing LMWGs is the lack of understanding of the supramolecular architecture?crystal structure?of the metastable gel fiber in its native?gel?form.Biocompatible micro-or nano-fibers with the merit of fluorescent emission have recently attracted increasing attention due to their practical applications in the field of live cell imaging,e.g.visualizing the interaction between cells and scaffolds.Although of many efforts have been devoted to devolope different types of fluorescent materials,however,these materials are either low fluorescent intensity,time-consuming multistep procedure,or toxicity.Herein,a new serial of 6-substituted coumarin-based isomerichydrogelators without containing amide or long alkyl chains have been designed and synthesized by one-step reaction,where only nitrogen atoms locate at ortho-,meso-,or para-position in pyridine ring,respectively.We have inverstigated the self-assembly mechanisms and properties of isomeric supramolecular hydrogels.To develop the nanofibrous structures with the properties of biocompatibility,strong fluorescent emission,and easy preparation,by changing the position and type of substituent,a new family of7-substituted coumarin-based hydrogelators have been designed and synthesized.Cell imaging study shows that these fluorescent nanofibers are promising scaffolds to elucidate the interaction between substrates and cells in two or three dimensional?2D/3D?environment.Due to the photo-responsiveness of coumarin derivatives,a multi-functional gelator precursor is rationally designed,which can specifically target hepatocellular carcinoma?HCC?cells through receptor-mediated interactions,leading to intracellular self-assembly under UV light and subsequently inducing cancer cell death.The contents and results of thesis are as follows:1.Self-assembly mechanisms of 6-substituted coumarin-pyridine based isomeric hydrogelators1)A new serial of 6-substituted coumarin-based isomeric hydrogelators without containing amide or long alkyl chains have been designed and synthesized by one-step reaction,where only nitrogen atoms locate at ortho-,meso-,or para-position in pyridine ring,respectively.2)SC-XRD analysis proves that isomeric gelators are self-assemble to form 3D crystal networks driving by C-H…O hydrogen bonds and?-?stacking interactions,but their packing modes are completely different.3)We have inverstigated the self-assembly mechanisms and properties of isomeric supramolecular hydrogels.The result implied that the tiny variation of hydrogelators could influence the property of the nanofibrous structures and then induced some differences on cell behaviour.2.7-substituted coumarin-pyridine based hydrogelators for 2D cell imaging1)By changing the position of substituent,a new family of 7-substituted coumarin-based non-conventional hydrogelators have been designed and synthesized by one-step reaction.The entangled nanofibrous structures of the xerogels were observed by SEM and TEM.FM analysis was further used to prove the blue emission of hydrogels under UV light excitation.2)The driving force in self-assembly process is non-conventional C-H…O hydrogen bonds,which is confirmed by a set of techniques including SC-XRD,PXRD,UV-Vis,fluorescence emission spectra,and ¹H NMR.3)In 2D cell cuture,upon switching to fluorescent microscopic channels,an effective imaging of both cells and nanofibers was immediately achieved.After overlaying the images of fluorescent nanofibers and cells,the better visualization of the interaction between the cells and nanofibers was obtained.This implies that these fluorescent nanofibers are promising scaffolds to elucidate the interaction between substrates and cells.3.7-substituted coumarin-benzene based hydrogelators for 3D cell imaging1)By changing the type of substituent,a serial of 7-substituted coumarin-benzene based non-conventional hydrogelators have been designed and synthesized by one-step reaction.The nanofbrous structures can be efficiently excited by UV or NIR light and emit blue light.2)SC-XRD analysis proves that gelators are self-assemble to form 3D crystal networks driving by C-H…O hydrogen bonds and?-?stacking interactions.3)Two-photon images of cell-ECM interactions were detected at various depths in 3D cell culture.It is suggested that the whole images are promising to allow the in situ observation of dynamic single cell-ECM interactions and the degradation of ECM structures.This highlights the NIR excited biomimetic nanofibers are promising scaffolds to allow noninvasive,spatially localized study of 3D dynamic imaging cell behaviors in living systems.3)To develop a coumarin-based molecular platform for cell imaging,we have designed and synthesized a serial of coumarin-benzene/pyridine conjugates hydrogelators.4.Galactose-decorated light-responsive hydrogelator precursor for selectively killing cancer cells1)We have rationally designed and synthesized a multi-functional gelator precursor?Gal-BHMC?in several steps.The chemical structures of all the new compounds were confirmed by ¹H NMR,¹³C NMR,and HRMS.The driving force of BHMC in self-assembly process is O-H…O hydrogen bonds confirmed by SC-XRD and PXRD.2)The cleavage of Gal-BHMC precursors into BHMC hydrogelators in PBS solution was explored by HPLC and UV-Vis absorption under UV light excitation.After the photo-cleavage,the ability to self-assemble into nanofibers for the cleaved BHMC was studied by SEM and TEM.3)The results of FM,TEM,and cell viability analysis suggested that Gal-BHMC can specifically target HCC cells through receptor-mediated interactions,leading to intracellular self-assembly under UV light and subsequently inducing cancer cell death.