Interactions of bovine serum albumin with cationic imidazolium and quaternary ammonium gemini surfactants: Effects of surfactant architecture

Amino acid-based cationic gemini surfactant–protein interactions

“…Fluorescence of BSA is usually dominated by the contribution of its aromatic amino acid residues, namely tyrosine (Tyr), tryptophan (Trp) and phenylalanine (Phe), the emission of the latter one being negligible in most cases [26][27][28]50,57]. The variations in the fluorescence spectra obtained by exciting the protein at 295 nm have been attributed to the presence of tryptophan residues while the changes that result from protein excitation at 280 nm are associated with both tryptophan and tyrosine residues [26,28].…”

“…Fluorescence quenching may occur as a result of collision between the fluorophore and the quencher in the excited state or from ground-state complex formation, thus involving dynamic or static quenching mechanisms, respectively [23,[26][27][28]50,57]. There are several ways to distinguish static from dynamic quenching, which include determination of the bimolecular quenching rate constant value, comparison of the values of the Stern-Volmer quenching constant obtained at different temperatures, and comparison of protein absorption spectra in the presence and in the absence of surfactant (quencher) [23,[26][27][28]50,57,64,65].…”

“…There are several ways to distinguish static from dynamic quenching, which include determination of the bimolecular quenching rate constant value, comparison of the values of the Stern-Volmer quenching constant obtained at different temperatures, and comparison of protein absorption spectra in the presence and in the absence of surfactant (quencher) [23,[26][27][28]50,57,64,65]. Higher temperature results in faster diffusion thus enhancing dynamic quenching, and the Stern-Volmer quenching constant increases, while for a static quenching process the Stern-Volmer constant decreases with increasing temperature due to reduced stability of the complex [23,[26][27][28]50,57,64]. The UV-vis absorption spectra can help distinguish both processes because collisional quenching only affects the excited states of the fluorophores, which do not perturb the UV absorption spectra, a situation that is in marked contrast to ground-state complex formation [26,27,50,66].…”

“…Higher temperature results in faster diffusion thus enhancing dynamic quenching, and the Stern-Volmer quenching constant increases, while for a static quenching process the Stern-Volmer constant decreases with increasing temperature due to reduced stability of the complex [23,[26][27][28]50,57,64]. The UV-vis absorption spectra can help distinguish both processes because collisional quenching only affects the excited states of the fluorophores, which do not perturb the UV absorption spectra, a situation that is in marked contrast to ground-state complex formation [26,27,50,66].…”

“…This mechanism is on the basis of their employment as denaturing agents in the extraction and purification of proteins from biological matrixes as well as on protein characterization [24,25]. Recent investigations showed that gemini surfactants interact more efficiently with proteins when compared to traditional single-chain surfactants [26][27][28][29]. Our report on the interaction between bovine serum albumin (BSA) and anionic amino acid-based gemini surfactants also revealed that surfactant stereochemistry influenced the binding to the protein, as well as external conditions, such as pH, ionic strength and temperature [29].…”