title: Mixed micellization between natural and synthetic block copolymers: β-casein and Lutrol F-127.
abstract: Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, β-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO(101)PO(56)EO(101)), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled β-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above β-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/β-casein micelles. The negative enthalpy of micelle formation (ΔH) and cooperativity increase with raising β-casein concentration in solution. ζ-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of β-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
authors.affiliation: Department of Biotechnology and Food Engineering, Technion - Israel Institute of Technology, Haifa, Israel.
authors.forename: Irina
authors.initials: I
authors.lastname: Portnaya
authors.forename: Rafail
authors.initials: R
authors.lastname: Khalfin
authors.forename: Ellina
authors.initials: E
authors.lastname: Kesselman
authors.forename: Ory
authors.initials: O
authors.lastname: Ramon
authors.forename: Uri
authors.initials: U
authors.lastname: Cogan
authors.forename: Dganit
authors.initials: D
authors.lastname: Danino
mesh_terms: D002151:Calorimetry; D002364:Caseins / Q000737:chemistry*; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D011095:Polyethylenes / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011126:Polypropylenes / Q000737:chemistry*; D011485:Protein Binding; D053838:Scattering, Small Angle; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D002364:Caseins; C510078:Lutrol F 127; D008823:Micelles; D011095:Polyethylenes; D011108:Polymers; D011126:Polypropylenes