2H-NMR-spectroscopic investigations of phospholipid bilayers

The influence of headgroup structure and fatty acyl chain saturation of phospholipids on monolayer behavior: a comparative rheological study

This paper compares six phospholipidic monolayers at the water/chloroform interface by performing dilational rheological measurements with a drop tensiometer apparatus. The chosen lipids differ both in their headgroup structure and fatty acyl chain saturation or symmetry. The study concentrated on monolayers formed with DPPC, DPPE, DOPC, DOPE, POPC and POPE. Using a generalized Maxwell rheological model, transposed at the interface, the intimate intermolecular interactions between amphiphilic molecules are studied on and off the monolayer plane. The equilibrium and nonequilibrium phenomena are analyzed and, respectively, correlated with monolayer cohesion and with monolayer/sub-surface interactions. The purpose of this work is to gain further insights into the influences (as slight as they are) of the weak changes in phospholipid structure and on the behavior of the monolayers. The results, widely described, provide further details on nuances existing between very similar molecules, and likewise, on the synergies created between the different effects.

An index of lipid phase diagrams

There is a growing awareness of the utility of lipid phase behavior data in studies of membrane-related phenomena. Such miscibility information is commonly reported in the form of temperature-composition (T-C) phase diagrams. The current index is a conduit to the relevant literature. It lists lipid phase diagrams, their components and conditions of measurement, and complete bibliographic information. The main focus of the index is on lipids of membrane origin where water is the dispersing medium. However, it also includes records on acylglycerols, fatty acids, cationic lipids, and detergent-containing systems. The miscibility of synthetic and natural lipids with other lipids, with water, and with biomolecules (proteins, nucleic acids, carbohydrates, etc.) and non-biological materials (drugs, anesthetics, organic solvents, etc.) is within the purview of the index. There are 2188 phase diagram records in the index, the bulk (81%) of which refers to binary (two-component) T-C phase diagrams. The remainder is made up of more complex (ternary, quaternary) systems, pressure-T phase diagrams, and other more exotic miscibility studies. The index covers the period from 1965 through to July, 2001.

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.

Miscibility of phospholipids with identical headgroups and acyl chain lengths differing by two methylene units: effects of headgroup structure and headgroup charge

We have investigated the influence of the chemical structure and charge of the hydrophillic headgroup on the miscibility of saturated phospholipids with acyl chain lengths differing by two methylene units, namely DMPA/DPPA, DMPC/DPPC, DMPE/DPPE and DMPG/DPPG (0.1 M NaCl). All four mixtures were analysed by DSC at pH 7. To study the influence of a change in headgroup charge, we additionally investigated DMPA/DPPA mixtures at pH 4 and 12, and DMPG/DPPG mixtures at pH 2. The experimental DSC thermograms were fitted using methods described before [Johann et al., Biophys. J. 71 (1996), 3215-3228] to obtain the temperatures of onset and end of melting and first approximations for the non-ideality parameters as a function of composition. The resulting phase diagrams were then fitted using a four non-ideality parameter model for non-ideal, non-symmetric mixing in both phases. The phase diagram of the system DMPG/DPPG has a lens-like shape, the non-ideality parameters rhog and rhol for the gel and the liquid-crystalline phase, respectively, are zero, indicating ideal mixing in both phases. For the other mixtures, differences in miscibility are observed depending on the structure of the headgroup. At pH 7, rhog > rhol, i.e., the miscibility in the liquid-crystalline phase is more ideal than in the gel state. All rhog values are positive and the sequence for rhog observed is PA>PE>PC>PG. Partial protonation of PA at pH 4 or complete deprotonation at pH 12 leads to negative non-ideality parameters for both phases, indicating a preference for mixed pair formation. Protonation of PG in DMPG/DPPG mixtures at pH 2 leads to positive non-ideality parameters for both phases, indicating a tendency for demixing. The results show, that the miscibility of phospholipids with identical headgroups but chain lengths differing by two methylene groups is dependent on headgroup structure and on headgroup charge.

Phases and phase transitions of the hydrated phosphatidylethanolamines

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Here, a review of the LIPIDAT data subset referring to hydrated phosphatidylethanolamines (PE) is presented together with an analysis of these data. The PE subset represents 14% of all LIPIDAT records. It includes data collected over a 38-year period and consists of 1511 records obtained from 203 articles in 35 different journals. An analysis of the data in the subset has allowed us to identify trends in synthetic PE phase behavior reflecting changes in lipid chain length, chain unsaturation (number, isomeric type and position of double bonds), chain asymmetry and branching, type of chain-glycerol linkage (ether vs. ester) and headgroup modification. Also included is a summary of the data concerning the effect of pH, stereochemical purity, and different additives such as salts, saccharides, alcohols, amino adds and alkanes on PE phase behavior. Information on the phase behavior of biologically derived PE is also presented. This review includes 236 references.