Correlation and dynamics of acyl-chain isomerization rotation in di-myristoyl-phosphatidylcholine bilayers

Interactions of a cationic surfactant--(benzyloxymethyl) dodecyldimethylammonium chloride with model biomembrane systems

Phospholipids are the main components of biological membranes. The aim of the present study was to determine the influence of a cationic surfactant on phospholipid structure and dynamics. Fourier transform infrared (FTIR) and dielectric relaxation (DRS) spectroscopies as well as small-angle X-ray scattering (SAXS) with synchrotron radiation have been used to analyse the structure of fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in the presence of a quaternary ammonium surfactant: (benzyloxymethyl) dodecyldimethylammoniumchloride (BzMDDAC). The presence of the surfactant caused changes in the temperature of the DMPC phase transition, as revealed using FTIR and DRS measurements. This change results from the disappearance of the multilamellar phase of DMPC and the formation of the unilamellar (most likely bicellar) phase, as indicated by the SAXS results.

Structural and dielectric properties of synthetic glycolipids in mixtures with water

Three synthetically produced glycolipids, N-(beta-D-glucopyranosyl)-N-octadecyl-stearoylamide (OSGA), N-(beta-D-glucopyranosyl-N-octadecyl-oleoylamide (OOGA), N-(beta-D-galactopyranosyl)-N-octadecyl-lauroylamide (OLGA) have been studied in different mixtures with water by x-ray diffraction and dielectric measurements with microwaves at 9.4 GHz. The measurements were performed in the temperature range -50-70 degrees C. X-Ray diffraction revealed a direct L(beta') --> H( parallel) transition at 20 degrees C, 60 degrees C, and 45 degrees C depending on the glycolipid species but nearly not on the water content. The hexagonal phases are saturated at a water content of approximately 20 wt%. The lamellar phase absorbs even less water (< 10 wt%). The dielectric data show that in the H( parallel) phase the binding of water is stronger than in the L(beta') phase. In the temperature range below 0 degrees C, OSGA and OOGA show a "subzero transition" due to the freeze-out of water in a separate ice phase. This transition can be seen in an abrupt decrease of the dielectric function because the dielectric response of ice is much smaller at microwave frequencies. OLGA does not show the subzero transition but an additional transition, hexagonal --> distorted hexagonal at 60 degrees C.

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

The influence of general, volatile anesthetics on the dynamic properties of model membranes

The microscopic mechanism of general anesthesia is still not known but it may be located in the membrane region of nerve cells. In the present article microwave experiments on model membrane systems are discussed. At these particular frequencies a significant decrease of the systems' complex dielectric function is measured when it is exposed to volatile anesthetics. This effect is reversible as well as being identical for chemically quite different anesthetics. The corresponding anesthetic concentrations in the samples are relevant for medical anesthesia. The underlying microscopic mechanism is a decrease in the Debye relaxation frequency (and correspondingly an increase in viscosity) of those water molecules which are localized at the membranes' surfaces. General anesthesia might be a consequence of such a viscosity change at hydrophilic surfaces.