Binding interaction of phenazinium-based cationic photosensitizers with human hemoglobin: Exploring the effects of pH and chemical structure

Deciphering the fluorescence quenching mechanism of a flavonoid drug following interaction with human hemoglobin

“…Herein, we endeavor to quantify the QCT–Hb interaction through elucidation of the binding constant on the basis of the following equation [ 41,56–58 ] : where K denotes the binding constant and n the number of binding sites. The determination of the drug–protein binding constant is crucial in this context because the therapeutic efficiency of a drug critically depends on the binding capacity and the ensuing impact on the stability of the protein.…”

“…At pH 7.4, the far‐UV CD profile of native Hb is composed of two characteristic negative peaks at ~208 and 222 nm indicative of a α‐helix‐rich secondary structure of Hb. [ 25,56,58–61 ] The CD spectra are presented here in the form of mean residue ellipticity (MRE in deg cm 2 mol −1 ) according to the equation [ 58,62–64 ] in which θ 222 designates the observed ellipticity (in mdeg.) at λ = 222 nm, n is the number of amino acid residues in the protein (n = 574 for Hb [ 56,58 ] ), l is the optical path length (0.1 cm), and the term [Hb] indicates the molar concentration of Hb.…”

“…[ 25,56,58–61 ] The CD spectra are presented here in the form of mean residue ellipticity (MRE in deg cm 2 mol −1 ) according to the equation [ 58,62–64 ] in which θ 222 designates the observed ellipticity (in mdeg.) at λ = 222 nm, n is the number of amino acid residues in the protein (n = 574 for Hb [ 56,58 ] ), l is the optical path length (0.1 cm), and the term [Hb] indicates the molar concentration of Hb. The α‐helicity content of the protein is then estimated from the MRE value using the following relationship [ 62–64 ] : Figure 6 reveals a gradual lowering of the CD signal (in terms of MRE) of the native protein with no discernible shift of the peak positions with incremental addition of QCT.…”

“…AutoDock‐based molecular docking simulation has extensively been utilized in the literature to predict the probable binding locus of drug molecules within the complex microheterogeneous environment of various biomacromolecules. [ 33,53,58,66 ] The optimized (or minimum energy) docked conformation of QCT within Hb providing a rational evaluation of the probable binding location of the drug within the protein scaffolds is presented in Figure 7. In order to elucidate an unbiased result to this effect, the AutoDock‐based blind docking strategy has been employed in the present work.…”

“…In order to elucidate an unbiased result to this effect, the AutoDock‐based blind docking strategy has been employed in the present work. [ 33,53,58,66 ] The residues of native Hb in the close vicinity (within 4.0 Å) of bound drug molecule are also highlighted in Figure 7. The protein residues surrounding (within 4.0 Å) the bound QCT are as follows: Arg141 (belonging to Chain 1), Ala120, Ala123, Ser124, Lys127 (belonging to Chain 3), Leu32, Val33, Val34, Pro36, Gln39, Leu48, Ser49, Thr50, Pro51, Val54 (belonging to Chain 4).…”