Thermomechanical properties of planar myelin multilayers

JULIO M. PUSTERLA; BRUNO DEMÉ; LEIDE P. CAVALCANTI; SCHNECK, EMMANUEL; RAFAEL G. OLIVEIRA

Buenos Aires

Congreso; I Congreso Argentino de Técnicas Neutrónicas; 2017

Comisión Nacional de Energía Atómica

There are numerous works about diffraction/dispersion in myelin, mainly nerve and isolated membranes. None of the above work has attempted to separate the specular and non-specular components of the scattering. Such separation allows to study mechanical properties such as bending regidity and transverse compressibility between layers (Schneck et al., 2009). With this purpose, we deposit myelin multilayers and their lipid fraction on Si/SiO2 planar substrate and perform rocking scan curves in different environmental conditions to which myelin is sensitive. Measurements were made in the D16 beamline of the Laue Langevin Institute´s neutron source that allows controlling environmental variables and even measuring under water. The myelin lipid diffractograms (stacked with 20 mM CaCl2) showed values of compressibility (transverse) B = 3.7 MPa and bending rigidity ($kappa$) of 8.2 kT. These are values comparable to other lipids in the fluid phase. For the entire myelin membrane the system may have one or two phases depending on the environmental conditions. The thicker (~ 8 nm and protein enriched) phase is shown to be comparatively compact as demonstrated by the high specular / non-specular signal ratio (higher Caillé parameter) compared to the finer phase (~6 nm) lipid-enriched, which is more disordered (higher non-specular/specular ratio), in other words with higher Caillé parameter. The properties of the lipid phase are altered by the presence of the protein phase with which it is continuous transversely. We are currently trying to correlate these data with more accessible techniques such as SAXS and AFM.