Structural organisation of cationic dioctadecyldimethyammonium bromide monolayers in presence of hyaluronic acid.

Langmuir monolayers of dioctadecyldimethyammonium bromide and its interaction with the natural mucopolysaccharide hyaluronic acid are studied using thermodynamic methods and X-ray diffraction at grazing incidence. The 2D crystalline lattice parameters of different phases are determined. The monolayer compressibility, the linear crystalline compressibility components and the thermoelastic expansion coefficient are evaluated.

Structural and electric properties of two semifluorinated alkane monolayers compressed on top of a controlled hydrophobic monolayer substrate.

We investigate the dynamic behavior upon lateral compression of two mixed films made with one of the two semifluorinated alkanes F(CF2)8(CH2)18H and F(CF2)10(CH2)10H and the natural alpha-helix alamethicin peptide. Surface pressure, surface potential versus molecular area isotherms, and grazing-incidence x-ray diffraction were applied to characterize this system. We show that both mixed films demix vertically to form two asymmetric flat bilayers where the lower layer is made of alamethicin and the upper layer is made of semifluorinated molecules.

Analysis of sugar bioprotective mechanisms on the thermal denaturation of lysozyme from Raman scattering and differential scanning calorimetry investigations.

Sugar-induced thermostabilization of lysozyme was analyzed by Raman scattering and modulated differential scanning calorimetry investigations, for three disaccharides (maltose, sucrose, and trehalose) characterized by the same chemical formula (C(12)H(22)O(11)). This study shows that trehalose is the most effective in stabilizing the folded secondary structure of the protein. The influence of sugars on the mechanism of thermal denaturation was carefully investigated by Raman scattering experiments carried out both in the low-frequency range and in the amide I band region.

Evidence of a two-stage thermal denaturation process in lysozyme: a Raman scattering and differential scanning calorimetry investigation.

Raman spectroscopy (in the low-frequency range and the amide I band region) and modulated differential scanning calorimetry investigations have been used to analyze temperature-induced structural changes in lysozyme dissolved in 1H2O and 2H2O in the thermal denaturation process. Low-frequency Raman data reveal a change in tertiary structure without concomitant unfolding of the secondary structure. Calorimetric data show that this structural change is responsible for the configurational entropy change associated with the strong-to-fragile liquid transition and correspond to about 1/3 of the native-denaturated transition enthalpy.

Assembling and compressing a semifluorinated alkane monolayer on a hydrophobic surface: structural and dielectric properties.

We investigate the dynamic behavior upon lateral compression of a semifluorinated alkane F (CF2)8(CH2)18H (denoted F8H18), spread on the hydrophobic top of a suitable amphiphilic monolayer: namely, a natural alpha-helix alamethicin peptide (alam). We show, in particular, the formation of an asymmetric flat bilayer by compressing at the air-water interface a mixed Langmuir film made of F8H18 and alam. The particular chemical structure of F8H18 , the suitable structure of the underlying alam monolayer and its collapse properties, allow for a continuous compression of the upper F8H18 monolayer while the density of the lower alam monolayer remains constant.