Changes of the physical properties of the liquid-ordered phase with temperature in binary mixtures of DPPC with cholesterol

Abstract

The structure of the so-called liquid-ordered (lo) phase of binary mixtures of DPPC-d(62) with cholesterol was studied between 20-50 mol% cholesterol using (2)H-NMR, FT-IR, DSC, and neutron specular reflection. Different model systems such as multilamellar vesicles, spherical supported vesicles, and oriented multilayers were used. We observed significant changes of the lo phase structure in the physiological relevant temperature region between 30-45 degrees C. (2)H-NMR in combination with lineshape simulations provides evidence for a drastic effect of cholesterol on the shape of multilamellar vesicles due to magnetic field orientation. Moreover, the data indicates a significant change of the extent of this partial orientation for DPPC-d(62) multilamellar vesicles containing 25 mol% cholesterol between 36-42 degrees C. The semiaxes ratio of the (due to magnetic field orientation) ellipsoidal multilamellar vesicles changes over this temperature range by approximately 25%. (2)H-NMR and FT-IR measurements indicate changes of the average orientational order at the bilayer center in the same temperature range and a significant increase of the number of end-gauche conformers while the majority of the methylene groups remain in an all-trans conformation. Additionally, specular reflection of neutrons shows a concomitant reduction of the bilayer thickness by 4 A. Based on a model of the arrangement of DPPC and cholesterol in the lo phase, a molecular mechanism is proposed in which increasing the temperature between 30 and 45 degrees C has the effect of driving cholesterol from the bilayer center towards the head group region.

Temperature-Dependent In-Plane Structure Formation of an X-Shaped Bolapolyphile within Lipid Bilayers

“…37 °C. [25][26] The band positions of the CH 2 -stretching bands of the B12 lateral alkyl chains (at 20 °C: …”

NMR methods for studying membrane‐active antimicrobial peptides

“…When many labels are introduced simultaneously, these effects can be larger, for example, the gel to liquid crystalline phase transition of fully acyl chain deuterated lipids are found to be 4 -5°C lower than in the protonated case (5). For example, DPPC-d 62 has a T m of 37°C (6), while for the undeuterated DPPC the corresponding value is about 42°C (7). In most cases, only a few isotope labels are introduced, and the isotope-labeled molecule may usually be regarded as identical to the one occurring in nature.…”

Cholesterol and Lipid Phases Influence the Interactions between Serotonin Receptor Agonists and Lipid Bilayers

“…3 and supplemental Fig. 1) arises from non-equivalence of the two aliphatic chains in the L o phase (11,35,36). This occurs be- greatly extends the temperature range in which the methyl peak splittings are observed.…”

“…3. This splitting is the result of the non-equivalency of the two lipid chains (11) and can be used as a reporter for the presence of L o phase (11,35,36). Methyl peak splittings are observed between 293 and 317 K for DPPC-d 62 /cholesterol and over a similar temperature range, just shifted down by a few K (between 287 and 313 K) for DPPC-d 62 /cholesterol/ quipazine.…”