Interaction of acridinedione dye with a globular protein in the presence of site selective and site specific binding drugs: Photophysical techniques assisted by molecular docking methods.

Photophysical investigations and molecular docking studies of photoinduced electron transfer (PET) based fluorophores of acridine family with a globular protein, Bovine Serum Albumin (BSA) bound to non-narcotic drugs like phenylbutazone (PB) and flufenamic acid (FA) were carried out in aqueous solution. PB and FA are site specific and site selective drugs, wherein PB predominantly binds at the site (I) whereas FA selectively orients towards site (II) of BSA. Acridinedione (AD) dyes, both resorcinol and dimedone based are hydrophobic in nature and exhibits a combination of both hydrophobic and hydrogen-bonding interactions that are based on the binding sites in BSA. The extent of displacement of AD from the binding sites of BSA by PB and FA are elucidated and established from variation in the fluorescence lifetime and relative amplitude distribution of free and dye bound in site (I) and site (II). The extent of binding affinity of PB-BSA and FA-BSA in the presence of AD is minimal when compared to other site I and II drugs. This is attributed to AD dye bound to several amino acid residues present in BSA such that the dye prefers multiple binding sites in BSA even in the presence of FA and PB. Further, the dye bound to several amino acid residues of BSA ascertains the combination of hydrogen-bonding, hydrophobic interactions, pi-pi and pi-alkyl interaction apart from the binding through sites (I) and (II) from molecular docking methods. The combination of fluorescence tools with molecular modelling techniques provides an excellent approach in determining the stability of these complexes containing competitive guest molecules in the presence of a fluorescence probe and the binding characteristics of dye in a micro heterogeneous environment.

Fluorescence Spectral Studies on the Interaction of Alanine and Valine with Resorcinol-Based Acridinedione Dyes in Aqueous Solution: A Comparative Study with Glycine.

Photophysical studies were carried out for simple amino acids like alanine and valine with resorcinol-based aqueous acridinedione (ADDR) dyes. ADDR dyes exhibit interesting excited-state characteristics on altering the substituents at the 9th and 10th sites (Scheme 1). The longest-wavelength absorption maxima remain the same on adding the amino acids to the fluorophore, whereas the excited-state behavior varies significantly mostly based on the nature of the substituent at the 9th position. The absence of fluorescence enhancement was observed with addition of ß-alanine, l-alanine, and l-valine to ADDR1 dye (photoinduced electron transfer, PET), whereas addition of glycine exhibits enhancement accompanied with a shift toward a longer-wavelength region. Interestingly, the addition of amino acids to non-PET dyes results in a fluorescence quenching accompanied with a larger shift toward the shorter-wavelength region. The properties of fluorophore and nonfluorophore dyes in the presence of alanine or valine are found to be entirely different from those of glycine. The interaction of alanine with ADDR dyes is predominantly through H-bonding, but the structural aspects of H-bonding interactions of alanine and water are completely different from those of glycine and water. The time-correlated single-photon counting method portrays the existence of fluorophore in two distinguishable microenvironments in the presence of amino acids. The fluorescence spectral technique used as a tool in elucidating the mode of interaction of dye with neutral amino acids in aqueous solution is illustrated in the present study.