Browsing by Author "Mohammed, Mohiuddin"

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Construction of self-assembled nanostructure-based tetraphenylethylene dipeptides: supramolecular nanobelts as biomimetic hydrogels for cell adhesion and proliferation
(2020-09-07)
Talloj, Satish Kumar
;
Mohammed, Mohiuddin
;
Lin, Hsin-Chieh
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Supramolecular fluorescent materials with aggregation-induced emission (AIE) characteristics have promising applications as fluorescent probes for bio and chemosensors. In this study, a versatile low molecular weight tetraphenylethylene dipeptide hydrogelator (TPE-YY) with efficient AIE characteristics was developed, which was able to form hydrogels in a broad pH range from 3.7 to 10.2. The self-assembly of this hydrogel is completely pH-dependent, with significant structural transitions from high to low pH. At a relatively high pH value (10.2), a weak transparent hydrogel with an entangled network of nanofibers was obtained, while upon neutralization (pH 7.2) with dilute HCl, a stable semi-transparent gel with twisted nanobelts was formed. When the pH of the hydrogel was reduced to below 5.7, a turbid viscous gel and precipitation appeared with the thickening of the nanobelts. Surprisingly, the hydrogel resulting from the glucono-delta-lactone triggered gel showed only nanofibers independent of pH. The nature of the hydrogels and the nanostructures at different pH values were thoroughly examined and discussedviaoscillatory rheology, electron microscopy and various spectroscopic techniques {(HNMR)-H-1,D-2-NMR, Fourier transform infrared (FTIR) and Circular dichroism (CD)}. Interestingly, the self-assembled hydrogel exhibited excellent biocompatibility over 95% using hydrogel leachables on two different cell lines, 3A6 (human MSCs) and L929 (mouse fibroblast cells). Moreover, the self-assembled nanobelts formed at neutral pH showed excellent cell adhesion and proliferation of 3A6 cells, whereas the nanofibers showed poor cell adhesion and proliferation. Overall, we demonstrate the importance of chemical design for the formation of self-assembled nanobelts and supramolecular hydrogels at physiological pH with selective cell adhesion and proliferation, presenting a promising applications in tissue engineering and regenerative medicine.
Enzyme Instructed Self-assembly of Naphthalimide-dipeptide: Spontaneous Transformation from Nanosphere to Nanotubular Structures that Induces Hydrogelation
(1970-01-01)
Chakravarthy, Rajan Deepan
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Mohammed, Mohiuddin
;
Lin, Hsin-Chieh
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Understanding the structure-morphology relationships of self-assembled nanostructures is crucial for developing materials with the desired chemical and biological functions. Here, phosphate-based naphthalimide (NI) derivatives have been developed for the first time to study the enzyme-instructed self-assembly process. Self-assembly of simple amino acid derivativeNI-Ypresulted in non-specific amorphous aggregates in the presence of alkaline phosphatase enzyme. On the other hand,NI-FYpdipeptide forms spherical nanoparticles under aqueous conditions which slowly transformed into partially unzipped nanotubular structures during the enzymatic catalytic process through multiple stages which subsequently resulted in hydrogelation. The self-assembly is driven by the formation of beta-sheet type structures stabilized by offset aromatic stacking of NI core and hydrogen bonding interactions which is confirmed with PXRD, Congo-red staining and molecular mechanical calculations. We propose a mechanism for the self-assembly process based on TEM and spectroscopic data. The nanotubular structures ofNI-FYpprecursor exhibited higher cytotoxicity to human breast cancer cells and human cervical cancer cells when compared to the nanofiber structures of the similar Fmoc-derivative. Overall this study provides a new understanding of the supramolecular self-assembly of small-molecular-weight hydrogelators.