Browsing by Author "Chakravarthy, Rajan Deepan"

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Enzyme Instructed Self-assembly of Naphthalimide-dipeptide: Spontaneous Transformation from Nanosphere to Nanotubular Structures that Induces Hydrogelation
(1970-01-01)
Chakravarthy, Rajan Deepan
;
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.
Fluorescent supramolecular hydrogels self-assembled from tetraphenylethene (TPE)/single amino acid conjugates
(2018-01-01)
Chu, Nien-Tzu
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Chakravarthy, Rajan Deepan
;
Shih, Nai-Chia
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Lin, Yen-Hsu
;
Liu, Yen-Chu
Herein, we report the synthesis of simple TPE/single amino acid conjugates, TPE-Ser and TPE-Asp with side-chains featuring functional groups that may provide an additional hydrogen bonding network for hydrogelation in aqueous medium. TPE-Ser, which has the lowest molecular weight, containing hydroxyl groups undergoes self-assembly into supramolecular hydrogels under physiological pH conditions. TPE-Asp with a carboxylic group side chain undergoes the self-assembly and hydrogelation processes under slightly acidic conditions (pH = 6.0). UV-vis, IR, PL and rheological studies clearly indicate the formation, stability and fluorescence properties of TPE-amino acid hydrogels. TEM micrographs of the hydrogels indicate that the compounds are self-assembled into a nanosheet morphology with random size and shape. Further, in vitro analysis of TPE-Ser and TPE-Asp with 3A6 cells shows that the compounds exhibit unique fluorescence signals in microcellular environments thus making them suitable candidates for bioimaging applications. Overall, these findings highlight the importance of the structure-hydrogelation relationship and provide new insights into the design of single amino-acid-based supramolecular hydrogels.
Reverse thermo-responsive hydrogels prepared from Pluronic F127 and gelatin composite materials
(2017-01-01)
Yeh, Mei-Yu
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Zhao, Jiong-Yao
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Hsieh, Yi-Ru
;
Lin, Jhong-Hua
;
Chen, Fang-Yi
Gelatin is an important hydrocolloid which has widespread applications in the pharmaceutical industry and biomedical science. However, despite its significance, clinical applications of gelatin are largely limited because of its gel-to-solution transition around human body temperature. In this work, we developed a series of F127-gelatin composite hydrogels with reverse thermo-responsive properties. The stiffness of F127-gelatin hydrogels can be adjusted by varying the types and contents of gelatin (type A, GA and type B, GB). The results of rheological data showed that F127-GA gels have higher gel strengths than those of F127-GB, which might be due to different isoelectric points between GA and GB. In addition, F127-gelatin gels showed significant cell viability and biocompatibility for human mesenchymal stem cells, indicating that these discovered hydrogels can serve as potential biomaterials and implantable scaffolds for applications in tissue engineering and regenerative medicine.
Self-assembly of single amino acid/pyrene conjugates with unique structure-morphology relationship
(2017-12-07)
Nelli, Srinivasa Rao
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Chakravarthy, Rajan Deepan
;
Xing, Yue-Ming
;
Weng, Jen-Po
;
Lin, Hsin-Chieh
This article describes the self-assembly of pi-conjugated building blocks composed of single amino acid and pyrene (Py) moieties. In aqueous conditions, the Py-capped amino acids undergo self-assembly through various non-covalent interactions such as hydrogen-bonding, pi-pi stacking as well as electrostatic interactions to form supramolecular nanostructures in acidic and basic conditions. Interestingly, we found that the blend of different Py-gelators with oppositely charged amino acids (Py-Glu and Py-Lys) displays unique nano-structural morphologies and gelation properties of the resulting hydrogels at physiological pH when compared with single Py conjugates, which was attributed to additional electrostatic interactions. Overall, this report illustrates the importance of two-component supramolecular co-assembled hydrogels and their structure-morphology relationship, improved mechanical properties, and biocompatibility and thus provides a new insight into the design of self-assembled nanomaterials.
The role of amino acids on supramolecular co-assembly of naphthalenediimide-pyrene based hydrogelators
(2018-01-01)
Nelli, Srinivasa Rao
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Chakravarthy, Rajan Deepan
;
Mohiuddin, Mohammed
;
Lin, Hsin-Chieh
;
材料科學與工程學系
This report describes the two component self-assembly of -capped amino acid hydrogelators (serine (S), aspartic acid (D), glutamic acid (E) or lysine (K)) prepared from pyrene (Py) based donor and naphthalenediimide (NDI) based acceptor molecules. The co-assembly can be triggered to form hydrogels by varying the pH conditions and the major driving forces behind the hydrogelation were found to be the formation of a strong charge-transfer (CT) complex and hydrogen bonding interactions at suitable pH conditions. The NDI-Py blends with matched donor/acceptor amino acid pairs undergo self-assembly under acidic pH conditions, whereas the blend (NDI-S + Py-K) with a mismatched amino acid pair forms a stable hydrogel under physiological pH conditions. UV-Vis, FTIR and rheological studies clearly indicate the formation and the stability of these CT-induced hydrogels. These hydrogels are of nanofibrous morphology with an average diameter of about 6-9 nm as evidenced by TEM analysis. In addition, this novel NDI-Py mixed component system exhibited good biocompatibility towards PC3 cells. Overall, since hydrogels based on CT-mediated two-component assemblies are very rare, our newly discovered NDI-Py hydrogels provide chemical insights into the design of a CT-induced hydrogelator and might facilitate various applications in biomedical engineering.
The role of aromatic side chains on the supramolecular hydrogelation of naphthalimide/dipeptide conjugates
(2018-03-21)
Hsu, Shu-Min
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Chakravarthy, Rajan Deepan
;
Cheng, Hsun
;
Wu, Fang-Yi
;
Lai, Tsung-Sheng
Herein, the influence of an amino acid side chain on the structural and functional properties of hydrogels has been described. In this study, four new hydrogelators based on the conjugates of dipeptides and naphthalimide (NI) have been designed, synthesized, and examined. Homopeptide 1 (NI-FF) of the phenylalanine residue forms a weak hydrogel or a viscous solution of worm-like micelles under basic conditions. On the other hand, dipeptide conjugates of 2 (NI-FY), 3 (NI-YF), and 4 (NI-YY), containing additional hydroxyl groups as tyrosine residues, can self-assemble into supramolecular hydrogels under physiological pH conditions. UV-vis, IR, and rheological studies clearly indicate the formation and stability of these dipeptide hydrogels. The TEM results revealed that the hydrogels (1-4) self-assembled into a nanofibrous morphology. Furthermore, the cell culture results show that NI-YF has better cell compatibility as compared to NI-FY and NI-YY and thus shows potential to be used as a hydrogel biomaterial. Overall, this study highlights the importance of the structure-hydrogelation relationship and provides new insights into the design of self-assembled peptide amphiphiles.