title: A combined binding mechanism of nonionic ethoxylated surfactants to bovine serum albumin revealed by fluorescence and circular dichroism.
abstract: The study systematically investigates aqueous mixtures of fixed bovine serum albumin (BSA) and various ethoxylated nonionic surfactants belonging to a homologous series or not. Mono-disperse tetra-(C12E4), hexa-(C12E6) and octa-ethyleneglycol mono-n-dodecyl ether (C12E8), and poly-disperse eicosa-ethyleneglycol mono-n-tetradecyl ether (C14EO20) are respectively employed. Fluorescence and circular dichroism measurements are performed at surfactant/protein molar ratios (rm)s lower and higher than one. We aim to get new insights into the binding mechanism of these species and to differentiate among the interaction abilities of these surfactants. The relative magnitude of the binding thermodynamic parameters by fluorescence, and the increase of α-helix prove that hydrogen bonding drives the interaction next to the hydrophobic attraction. C12En (n=4,6,8) develop more H bonds with the albumin than C14EO20 owing to a zigzag conformation of their short ethyleneoxide chains. Among the homologous surfactants, C12E6 has a slightly stronger interaction with BSA due to a maximal number of H bonds at a minimal hindering. Static fluorescence and dynamic fluorescence indicate an inter-conversion between the tryptophan (Trp) rotamers which happens around the surfactants critical micellar concentration. For C14EO20, the meander conformation of the polar group determines a less evident conversion of the Trp rotamers and smaller α-helix rise. Binding isotherms of the homologous surfactants and the fluorescence quenching mechanism by C12E6 are also provided.
authors.affiliation: Colloids Chemistry Laboratory, "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Spl. Independentei 202, Sector 6, 060021 Bucharest, Romania.
authors.forename: Alina
authors.initials: A
authors.lastname: Iovescu
authors.affiliation: Colloids Chemistry Laboratory, "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Spl. Independentei 202, Sector 6, 060021 Bucharest, Romania.
authors.forename: Adriana
authors.initials: A
authors.lastname: Băran
authors.affiliation: Colloids Chemistry Laboratory, "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Spl. Independentei 202, Sector 6, 060021 Bucharest, Romania.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Stîngă
authors.affiliation: Colloids Chemistry Laboratory, "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Spl. Independentei 202, Sector 6, 060021 Bucharest, Romania.
authors.forename: Anca Ruxandra
authors.initials: AR
authors.lastname: Cantemir-Leontieş
authors.affiliation: Colloids Chemistry Laboratory, "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Spl. Independentei 202, Sector 6, 060021 Bucharest, Romania.
authors.forename: Monica Elisabeta
authors.initials: ME
authors.lastname: Maxim
authors.affiliation: Colloids Chemistry Laboratory, "Ilie Murgulescu" Institute of Physical Chemistry, Romanian Academy, Spl. Independentei 202, Sector 6, 060021 Bucharest, Romania. Electronic address: danflorin.anghel@gmail.com.
authors.forename: Dan Florin
authors.initials: DF
authors.lastname: Anghel
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry
chemical_list: D013501:Surface-Active Agents; D012710:Serum Albumin, Bovine; D014364:Tryptophan
keywords: Binding thermodynamic parameters; Bovine serum albumin; Ethoxylated nonionic surfactants; Fluorescence; Hydrogen bonding; α-Helix