Probing the spectral response of a new class of bioactive pyrazoline derivative in homogeneous solvents and cyclodextrin nanocavities: a spectroscopic exploration appended by quantum chemical calculations and molecular docking analysis

Abstract

Time-dependent density functional theory (TD-DFT) calculations and molecular docking analysis provide valuable insights, in addition to experimental evidence, on the newly synthesized pyrazoline derivative 5-(1′-(4-bromophenyl)-3a′,4′,5′,6′,6a′-hexahydrocyclopentapyrazoline)-3-methyl-1-phenyl-1H-pyrazole-4-carbonitrile (PZ) as a fluorescence recognition probe and its photophysical signature in homogeneous and heterogeneous cyclodextrin (CD) environments, in addition to its insertion mechanism inside CD. The spectral trends of PZ do not appear to originate only from changes to the solvent polarity, but also indicate hydrogen bonding interactions with a homogeneous medium. The encapsulation of PZ within supramolecular α-, β- and γ-CD hosts was investigated using fluorescence spectroscopic techniques. The results show the formation of both 1 : 1 and 1 : 2 PZ–CD inclusion complexes with β-CD and only a 1 : 1 complex with γ-CD. The measured lifetimes and steady state anisotropy values also show the same trend and reveal the mode of interaction of the probe with the CD moiety. Furthermore, molecular docking studies performed via molecular mechanics methods (MMC) indicate that the pyrazoline moiety of PZ is most likely oriented towards the dip inside the cyclodextrin cavity. Solvent-dependent spectral data using TD-DFT calculations on the optimized ground and excited state structures of PZ were found to correlate well with the experimental findings.