Self-assembly of hydrophobin protein rodlets studied with atomic force spectroscopy in dynamic mode.

We have investigated the self-assembling properties of the class I hydrophobin Vmh2 isolated from the fungus Pleurotus ostreatus. Five different hydrophobin self assembled samples including monolayers, bilayers, and rodlets have been prepared by Langmuir technique and studied at the nanoscale. Local wettability and visco-elasticity of the different hydrophobins samples were obtained from atomic force spectroscopy experiments in dynamic mode performed at different, controlled relative humidity (RH) values. It was found that hydrophobins assembled either in rodlets or in bilayer films, display similar hydropathicity and viscoelasticity in contrast to the case of monolayers, whose hydropathicity and viscoelasticity depend on the adopted preparation method (Langmuir-Blodgett or Langmuir-Schaeffer). The comparison with monolayers properties evidences a rearrangement of the bilayers adsorbed onto solid substrates. It is shown that this rearrangement leads to the formation of a stable hydrophobic film, and that the rodlets structure consists in fragments of restructured proteins bilayers. Our results support the hypothesis that the observed variations in the viscoelastic properties could be ascribed to the localization of the large flexible loop, typical of Class I hydrophobins which appears free at the air interface for LB monolayers but not for the other samples. These findings should now serve future developments and applications of hydrophobin films beyond the archetypal monolayer.

Langmuir-Blodgett film of hydrophobin protein from Pleurotus ostreatus at the air-water interface.

We present results concerning the formation of Langmuir-Blodgett (LB) films of a class I hydrophobin from Pleurotus ostreatus at the air-water interface, and their structure as Langmuir-Blodgett (LB) films when deposited on silicon substrates. LB films of the hydrophobin were investigated by atomic force microscopy (AFM). We observed that the compressed film at the air-water interface exhibits a molecular depletion even at low surface pressure. In order to estimate the surface molecular concentration, we fit the experimental isotherm with Volmer's equation describing the equation of state for molecular monolayers. We found that about (1)/ 10 of the molecules contribute to the surface film formation. When transferred on silicon substrates, compact and uniform monomolecular layers about 2.5 nm thick, comparable to a typical molecular size, were observed. The monolayers coexist with protein aggregates, under the typical rodlet form with a uniform thickness of about 5.0 nm. The observed rodlets appear to be a hydrophilic bilayer and can then be responsible for the surface molecular depletion.

Architecture-controlled "SMART" Calix[6]arene self-assemblies in aqueous solution.

Self-assemblies of a calix[6]arene (1) functionalized at the small rim by three imidazolyl arms and at the large rim by three hydrophilic sulfonato groups have been studied in water. Transmission electron microscopy, atomic force microscopy, and in situ dynamic light scattering showed that 1 forms multilamellar vesicles at a concentration equal to or higher than 10(-4) M. At pH 7.8 and 10(-4) M, the multilamellar vesicles present a relatively large polydispersity (50-250 nm in diameter). However, after sonication unilamellar vesicles of much lower polydispersity and smaller size are obtained. The impact of the pH and the presence of Ag+ ions have also been investigated. Whereas increasing the pH led to the formation of giant vesicles (450 nm), monodisperse vesicules of 50 nm were obtained at a pH (6.5) that is only slightly higher than the pKa of the tris(imidazole) core of 1. Most interestingly, in the presence of silver ions, micelles (2.5 nm large) were obtained instead of vesicles. These observations are attributable to the imidazole core in 1 that is not only sensitive to the presence of protons but also can bind a silver cation. The resulting geometrical change in the monomeric units triggers the collapse of the vesicles into micelles. This shows that the implementation of an acid-base functionality such as an imidazole group in the hydrophobic core of the amphiphilic calix[6]arene makes the aggregation architecture responsive to the pH and to metal ions.