Adsorption Behavior of Hydrophobin and Hydrophobin/Surfactant Mixtures at the Air–Water Interface

Abstract

The adsorption of the surface-active protein hydrophobin, HFBII, and the competitive adsorption of HFBII with the cationic, anionic, and nonionic surfactants hexadecyltrimethylammonium bromide, CTAB, sodium dodecyl sulfate, SDS, and hexaethylene monododecyl ether, C(12)E(6), has been studied using neutron reflectivity, NR. HFBII adsorbs strongly at the air-water interface to form a dense monolayer ∼30 Å thick, with a mean area per molecule of ∼400 Å(2) and a volume fraction of ∼0.7, for concentrations greater than 0.01 g/L, and the adsorption is independent of the solution pH. In competition with the conventional surfactants CTAB, SDS, and C(12)E(6) at pH 7, the HFBII adsorption totally dominates the surface for surfactant concentrations less than the critical micellar concentration, cmc. Above the cmc of the conventional surfactants, HFBII is displaced by the surfactant (CTAB, SDS, or C(12)E(6)). For C(12)E(6) this displacement is only partial, and some HFBII remains at the surface for concentrations greater than the C(12)E(6) cmc. At low pH (pH 3) the patterns of adsorption for HFBII/SDS and HFBII/C(12)E(6) are different. At concentrations just below the surfactant cmc there is now mixed HFBII/surfactant adsorption for both SDS and C(12)E(6). For the HFBII/SDS mixture the structure of the adsorbed layer is more complex in the region immediately below the SDS cmc, resulting from the HFBII/SDS complex formation at the interface.

Molecular Dynamics Simulation of Protein Biosurfactants

“…MD simulations of both HFBI and HFBII found that the protein secondary and tertiary structures are largely unchanged at the air-water interface [81,83]. This is consistent with circular dichroism [85] and neutron reflectivity measurements [86], which show limited changes in at the air-water interface. A greater change in the structure of HFBI was found at the water-decane interface [81].…”

Production and characterization of stable foams with fine bubbles from solutions of hydrophobin HFBII and its mixtures with other proteins

“…The hydrophobin molecules are "sticky" -they adhere to each other [8,38], as well as to other macromolecules and solid walls [30,39]. These adhesive interactions lead to irreversible aggregation of the HFBII molecules in the bulk of solution.…”

Hydrophobins as aqueous lubricant additive for a soft sliding contact

“…Based on the comparison of amino acid residue sequence, hydrophobins are classified into two groups, type I and type II [1][2][3][4][5][6][7]. Surface-active properties of hydrophobins have drawn particular interests in self-assembled adsorption behavior of hydrophobins at air/water [8][9][10], water/oil [11][12][13][14], and water/solid interfaces [15][16][17][18][19][20][21][22]. This, in turn, sparked intensive researches to utilize hydrophobins as coating materials for biomedical, technical, and personal care products [23][24][25][26][27][28].…”