Complementary Fluorescence and Phosphorescence Study of the Interaction of Brompheniramine with Human Serum Albumin

Abstract

Binding of the antihistamine drug brompheniramine (BPA) to human serum albumin (HSA) is studied by measuring quenching of the fluorescence and room temperature phosphorescence (RTP) of tryptophan. The modified Stern-Volmer equation was used to derive association constants and accessible fractions from the steady-state fluorescence data. Decay associated spectra (DAS) revealed three tryptophan fluorescence lifetimes, indicating the presence of three HSA conformations. BPA causes mainly static quenching of the long-living, solvent-exposed conformer. RTP spectra and lifetimes, recorded under deoxygenated conditions in the presence of 0.2 M KI, provided additional kinetic information about the HSA-BPA interactions. Fluorescence DAS that were also recorded in the presence of 0.2 M KI revealed that the solvent-exposed conformer is the major contributor to the RTP signal. The phosphorescence quenching is mostly dynamic at pH 7 and mostly static at pH 9, presumably related to the protonation state of the alkylamino chain of BPA. This provides direct insight into the binding mode of the antihistamine drug, as well as kinetic information at both the nanosecond and the millisecond time scales.

Excited state interactions between flurbiprofen and tryptophan in drug–protein complexes and in model dyads. Fluorescence studies from the femtosecond to the nanosecond time domains

“…Various fluorescence techniques have been used in the past to investigate the interactions between different drugs and proteins, with special attention to HSA. In addition to steady-state fluorescence quenching, [16][17][18][19][20][21][22][23][24] time-resolved measurements [25][26][27] allow the characterisation of the involved dynamic processes. In particular, femtosecond emission [28][29][30][31][32] constitutes a powerful tool for determining the very fast photo-initiated processes.…”

Chiral separation of brompheniramine enantiomers by recycling high‐speed countercurrent chromatography using carboxymethyl‐β‐cyclodextrin as a chiral selector

“…indicated that the D increases with the pH value of aqueous phase. The possible reason is that the amount of molecular BPA increases with the rising of pH and molecular BPA preferentially distributes in organic phase. Simultaneously, α gradually increases with the pH value of aqueous phase when the pH value is lower than 7.50, and then slightly reduces when the pH was over 7.50.…”

pH-Dependent Complexation of Histamine H1 Receptor Antagonists and Human Serum Albumin Studied by UV Resonance Raman Spectroscopy

“…Therefore, it is not possible to conclude whether BPA (in its protonated and neutral form) enters preferably in site I or site II. To answer this question, we investigated the complexation in a separate study of the BPA–HSA system by W214 phosphorescence: a strong quenching by BPA is observed which can be explained assuming a close proximity between BPA and W214 …”