Studies of the excited state phenomena due to host-guest interactions of some medically potent small molecules and logic implications

Halder, Dipanjan (2022) Studies of the excited state phenomena due to host-guest interactions of some medically potent small molecules and logic implications. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Dipanjan Halder (16RS046)) 16RS046.pdf - Submitted Version Restricted to Repository staff only Download (11MB)

Abstract

In this dissertation, we have enlightened the host-guest interaction in the excited state. Here we have used flavonols (3-HF, DEPHBC) and Dopamine which are also the medically potent molecules. Flavonol molecules have a unique "dual emission" phenomenon. "Dual emission" of flavonol molecule is observed due to the intramolecular proton transfer occurs in the excited state (ESIPT). "Dual emission" is defined as the emission peak generated in the blue region and also in the green region. The emission peak at blue regions generates due to formation of normal (N*) form of the flavonol molecules and the emission peak of the green region arises because of the formation of tautomeric form (T*) of the probes. The tautomeric form (T*) is enhanced when the micro environment of the flavonol molecules changes from the nonpolar medium to the polar medium. The interaction between flavonol molecules and duplex DNA and G-quadruplex DNA has been studied by applying this concept. In the thesis we have demonstrated the changes in ESIPT of the flavonol molecule when it binds to the minor groove of duplex DNA due to the cationic surfactant induced compaction of DNA. Flavonol molecules detect toxic fluoride radical when it posits in the minor groove of duplex DNA in biological conditions. By using the optical responses of the DNA bound flavonol molecule in excited state we have fabricated the DNA based molecular logic gates. Besides a well-known medically significant molecule, dopamine, doped with carbon nanoparticles, is responsible for photo-induced electron transfer (PET) in the excited state. The PET process is pH-dependent; this leads to the emission of carbon nanoparticles that may increase or decrease due to the change in the pH of the solution. We have constructed molecular logic gate and memory elements by implementing this phenomenon, which may play an essential role in neuronal imaging. Thus, we can say the research work is very significant for photodynamic therapy in the bio medical field.

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