Department of Chemical Sciences
School of Natural Sciences

September 15, 2016 at 2.30 pm in AG-80

Title :

Alkyl Chain Tethered Dansyl, 1-Naphthyl and Acridinyl Fluorophores: Synthesis and Photophysical Studies

Abstract :

Conjugated fluorescent molecular probes are known to be efficient in probing structural and dynamical information of a variety of aggregates and organized systems. As these find a definite location into the organized assembly they cause less perturbation to the system. The main advantage of this type of probes is to design such probes as per the demand of the site to be investigated. 1  The hydrophobic tail contains dansylamide, 1-naphthol and 9-aminoacridine derivatives have been synthesized and evaluates towards their fluorescent probe properties. The long hydrophobic chain containing dansylamide derivative (DAN-PA) shows better sensitivity towards solvent polarity as compared to the short hydrophobic chain analogue (DAN-ACYL). DAN-PA can monitor premicellar aggregation of sodium deoxycholate (NaDC) in water. DAN-PA is also found useful to understand the micellization process of surfactants like NaC, SDS and CTAB. 2 DAN-PA shows more affinity towards β-CD as compared to DAN-ACYL. Its fluorescence intensity is quite sensitive towards thermotropic phase changes of lipid bilayer membrane. 1-Naphthol (NpOH) is an excited state proton transfer (ESPT) molecular probe which is a weak acid in the ground state (pKa = 9.2), but a strong acid (pKa* = 0.4) in the excited state. 3 In the aqueous medium, the proton transfer of short hydrophobic tail containing p-5C-NpOH is faster than long tail containing p-13C-NpOH. Shorter chain derivative (p-5C-NpOH) is a better ESPT probe to understand the micellization of CTAB, SDS and Tween-20 as compare to p-13C-NpOH because its proton transfer process shows the significant amount of anionic and neutral intensities in the aqueous medium. Acridine is a good DNA binding probe. In acidic pH, it exists in the protonated form (AcH + ) and in alkaline pH, it exists in neutral form (Ac). 4 The decrease in fluorescence intensity of 9-aminoacridine (AC) and its derivative (AC-PA) (the substrate is bound to DNA) is because of static quenching. 9-aminoacridine upon substitution (AC-PA) binds more efficiently to DNA by an order of magnitudes as compared to the un-substituted 9-aminoacridine (AC). DNA melting studies suggest that both 9-aminoacridine (AC) and its derivative (AC-PA) bind with DNA through intercalation binding.



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3. Mandal, D., Pal, S. K., and Bhattacharyya, K., J. Phys. Chem. A, 1998, 102, 9710–9714.

4. Sayed, M., and Pal, H., Phys. Chem. Chem. Phys., 2015, 17, 9519.