Synthesis of tetrazole based donor-acceptor type fluorescent molecules and their interaction with transport protein bovine serum albumin.

Tetrazole derivatives are profoundly used in pharmaceutical and agricultural chemistry as their bioactivity is governed by the possible strong interaction with protein molecules. For this purpose, two tetrazole based donor-acceptor type fluorophores N, N-diphenyl-4-(1 H-tetrazol-5-yl)aniline (DPTA) and N-(4-(1 H-tetrazol-5-yl)phenyl)-N-(naphthalen-2-yl)naphthalen-2-amine (TPNNA) were synthesised and their detailed photophysical behaviour were explored using absorption, emission and fluorescence lifetime measurement in different polar medium. Structurally TPNNA is expected to be more non-polar than DPTA due to the presence of more hydrophobic units in the donor part. Both molecules show local and a polarity dependent charge transfer emission. Upon interaction with transport protein Bovine serum albumin (BSA), both molecules show a significant change in their emission behaviour, where DPTA shows a ratiometric change in the emission spectra and TPNNA shows a rapid blue shift (~ 38 nm) in the emission spectra. Stronger binding interaction of TPNNA than DPTA with BSA is reflected by the calculated binding constants of 1.25 × 106 M- 1 and 3.33 × 105 M- 1, respectively. Interaction phenomena are reflected by a consistent disappearance of the charge transfer component along with building-up of a fast lifetime component with increasing concentration of BSA in the medium. This strong protein-ligand binding interaction was also supported by Time resolved anisotropy measurement and circular dichroism study. Molecular docking study revealed that hydrogen bonding and van der Waals interactions are the prevailing forces for binding of DPTA and TPNNA with BSA.