Photophysical and molecular docking studies of photoinduced electron transfer (PET) and non-PET based fluorophores of acridinedione derivatives with a glycoprotein: Ovalbumin

Photophysical studies of resorcinol-based family of acridinedione (ADR) dyes with a glycoprotein, ovalbumin (OVA) were carried out in water. Addition of OVA to photoinduced electron transfer (PET) based dye (ADR1) resulted in a considerable red shift of emission maxima with a slight increase in the fluorescence intensity, whereas no significant variation in the fluorescence intensity or shift of emission maxima results in the case of a non-PET dye. Fluorescence lifetime studies illustrates that the PET lifetime component enhances by several fold on the introduction of OVA which is accompanied with the formation of multi lifetime components in the aqueous phase of varying distribution as observed in well-known globular protein, bovine serum albumin (BSA). Interestingly, a decrease in the fluorescence lifetime of non-PET dye (ADR2) with the evolution of more than one distinct lifetime species results with OVA. This behaviour ascertains the presence of at least two different micro environment of dye residing in aqueous phase on the addition of OVA. The introduction of OVA induces the formation of several distinguishable micro environments around the close vicinity of the dye molecule that are subjected to various binding forces. Further, the dye bound to several amino acid residues through conventional and non-conventional hydrogen-bonding interactions accompanied with hydrophobic interactions, pi-pi, pi-alkyl interactions and weak van der Waals forces also coexist. The variation in binding energies of various dye-OVA conformations are established from molecular docking (MD) techniques. The combination of docking techniques validates and authenticates the origin of multi decay characteristics of dye-OVA complex that correlates dye bound to different binding sites in protein. A combined approach of fluorescence techniques along with MD methods and Isothermal Calorimetric Titration (ITC) studies provides an excellent approach in determining the nature of interaction and binding stability of dye-protein system in a micro heterogeneous environment.