M. D. Mitov

Temperature and Chain Length Effects on Bending Elasticity of Phosphatidylcholine Bilayers

A strong decrease of the bilayer bending elastic modulus, kc, has been experimentally established for dimyristoyl and dipalmitoyl phosphatidylcholine, when the liquid-crystal-gel phase transition temperature is approached from above. This phenomenon may be due to local-curvature-induced changes in the transition temperature. In the liquid-crystal phase, the bending modulus, kc, significantly increases as a function of the lipid chain length for dilauryl, dimyristoyl and dipalmitoyl phosphatidylcholine.

Sugars in the Aqueous Phase Change the Mechanical Properties of Lipid Mono- and Bilayers

ABSTRACT We applied two independent methods to measure the bending elasticity of SOPC lipid membranes in the presence of different sucrose concentrations in the aqueous phase. The micropipette technique was used to study the membrane bending rigidity in the concentration range of (0.11–0.30) mol/l of sucrose, while for sucrose concentrations 0 mol/l and 0.05 mol/l the thermal fluctuation analysis of quasi-spherical vesicles was applied. Both methods revealed a strong reduction of the bending elastic modulus, when sucrose is present in the water. Using micromanipulation of emulsion droplets, we investigated the sucrose influence on the stretching elasticity of SOPC lipid monolayers at the oil-water interface. Our results showed an almost two-fold reduction of the stretching elasticity modulus of the lipid monolayer in the presence of 0.18 mol/l of sucrose in the aqueous phase. The experimental results, reported here, reveal a strong influence of sugar molecules on the elasticity of lipid mono- and bilayers.

Dynamics of Fluctuating Vesicles

A method is described which allows to characterize experimentally the dynamic behaviour of thermal fluctuations of giant lipidic vesicles observed by optical microscopy, and to evaluate the time correlation functions of their spherical harmonics.The obtained results demonstrate the validity of the theoretical model for the hydrodynamic of the fluctuations recently proposed by Milner and Safran.

Mechanoformation of neutral giant phospholipid vesicles in high ionic strength solution

We present new and simple method for formation of giant unilamellar vesicles (GUVs) in high ionic strength solutions, such as phosphate buffered saline (PBS). Mechanoformation method is an alternative method to electroformation method. The advantage of the mechanoformation procedure is that there are no limitations with respect to the ionic strength of the aqueous solutions, because there is no applied electric potential thus no current flow through the formation cell and no electrolysis is induced.

Deformation of giant vesicles in AC electric fields —Dependence of the prolate-to-oblate transition frequency on vesicle radius

The electrodeformation of giant vesicles is studied as a function of their radii and the frequency of the applied AC field. At low frequency the shape is prolate, at sufficiently high frequency it is oblate and at some frequency, fc, the shape changes from prolate to oblate. A linear dependence of the prolate-to-oblate transition inverse frequency, 1/fc, on the vesicle radius is found. The nature of this phenomenon does not change with the variation of both the solution conductivity, ?, and the type of the fluid enclosed by the lipid membrane (water, sucrose or glucose aqueous solution). When ? increases, the value of fc increases while the slope of the line 1/fc(r) decreases. For vesicles in symmetrical conditions (the same conductivity of the inner and the outer solution) a linear dependence between ? and the critical frequency, fc, is obtained for conductivities up to ?=114??S/cm. For vesicles with sizes below a certain minimum radius, depending on the solution conductivity, no shape transition could be observed.

Does maltose influence on the elasticity of SOPC membrane

Thermally induced shape fluctuations of giant quasi-spherical lipid vesicles are used to study the influence of the disaccharide maltose, dissolved in the aqueous solution, on the curvature elasticity kc of a lipid membrane. The influence of the carbohydrate solute is investigated throughout a considerably wide interval of concentrations. The values of the bending elastic modulus for 200 mM and 400 mM of maltose in the water solution are obtained. The data for kc in presence of maltose is compared with previously obtained results for this constant for the most popular hydrocarbons: monosaccharides glucose and fructose and disaccharides sucrose and trehalose. It is shown that the presence of maltose, dissolved in the aqueous phase surrounding the membrane does not influence on the bending elasticity with the increase of its concentration in the aqueous solution. Up to our knowledge this is the first sugar that does not show decrease of the bending elastic modulus of the lipid membrane, when present in the water surrounding it in concentration up to 400mM.

Bending elasticity of lipid membranes in presence of beta 2 glycoprotein I in the surrounding solution

Thermally induced shape fluctuations of giant quasi/spherical lipid vesicles are used to study the bending elasticity modulus kc of a phospholipid (PHLP) membranes in presence of beta 2 glycoprotein I (β2/GPI) in the aqueous solution which surrounds the vesicles membrane. The bending elastic modulus kc of PHLP - protein membrane was obtained for different mass concentrations of β2/GPI for pure neutral SOPC membranes and for mixed SOPC: Cardiolipin negatively charged membranes. The experimental results for the bending elastic modulus kc of the PHLP membranes does not show dependence on the concentration of β2/GPI in the range from 5.5 to 55 >g/ml, when β2/GPI is present in the aqueous solution surrounding the vesicles membrane. Obtained results are in good agreement with predictions, based on different experiments, explaining the mechanism of binding of β2/GPI to neutral membranes.