Lipid property

The link from lipid properties to mechanical properties of the bilayers is now feasible within the SCF approach. The next step is to understand the phase behaviour of the lipid systems. It is likely that large-scale (3D) SCF-type calculations are needed to prove the conjectures in the field that particular values of the Helfrich parameters are needed for processes like vesicle fusion, etc. In this context, it may also be extremely interesting to see what happens with the mechanical parameters when the system is molecularly complex (i.e. when the system contains many different types of molecules). Then there will be some hope that novel and deep insights may be obtained into the very basic questions behind nature s choice for the enormous molecular complexity in membrane systems. 

Table 5.3. Alteration of Membrane Lipid Properties and the Resultant Approximate Directions of Changes of Fluorescence Parameters of a Typical Membrane Fluorophore Probe of the Fatty Acyl Chain Region0...

Cevc, G. (1992). Lipid properties as a basis for membrane modeling and rational liposome ddairps[Pg.410]

To rigorously test the phase transition model, one must demonstrate that surface lipids actually do melt at the critical temperature, and that melted lipids are in fact more permeable to water than solid ones. A variety of biophysical techniques have been applied to this problem (Table 6.1). These have included direct biophysical measurements of lipid properties, and associated measurements of water-loss. In general, these studies have supported... 

The majority of publications on cuticular lipids involve analyses of lipid composition. Which compounds are present, and what is their function Correlations between lipid composition and water-loss have provided indirect tests of the phase transition hypothesis, under the assumption that changes in lipid composition predictably affect lipid properties. In this section, we summarize available information on how specific structural changes affect the physical properties of pure surface lipids, as well as how different lipids interact with each other. 

Nowadays, several solution structures of membrane-bound peptides and protein fragments have been reported (33,34). More important is that bicelles have been used successfully to investigate the effect of bioactive peptides on lipid properties, such as order and dynamics, and at the same time of the dynamics of the peptides themselves (35,36). 

Potts and Guy concluded that lipid properties of chemicals account for permeability through the stratum corneum of the skin and that permeability is a function of the K of a compound. Bowman and Maibach showed... 

Lipids are not covalently bound in membranes but rather interact dynamically to form transient arrangements with asymmetry both perpendicular and parallel to the plane of the lipid bilayer. The fluidity, supermolecular-phase propensity, lateral pressure and surface charge of the bilayer matrix is largely determined by the collective properties of the complex mixture of individual lipid species, some of which are shown in Fig. 8.1. Lipids also interact with and bind to proteins in stiochiometric amounts affecting protein structure and function. The broad range of lipid properties coupled with the dynamic organization of lipids in membranes multiplies their functional diversity in modulating the environment and therefore the function of membrane proteins. 

Many lipid-based foods show time-dependent rheological behavior and a combination of these, for example, viscous-elastic and viscous-plastic. In general, lipids, from a rheological point of view, can be classified as Newtonian and non-Newtonian, as depicted in Figure 4.1. To characterize lipid properties, such as Newtonian and non-Newtonian behavior, several approaches can be taken and the stress-strain relationships obtained. 

Since the first attempt of Chapman and co-workers in 1966 [860], IR spectroscopy has become one of the most frequently used tools for elucidating lipid properties and the mutual effects of different lipids and proteins, which are of interest for different aspects of bioscience and biosensor design (see Refs. [333, 748, 861-864] for review). The IR methods used are transmission, ATR (MIR), and IRRAS for model monolayer, bilayer, and multibilayer membranes and biological membranes. To perform in situ measurements on the membranes of intact individual cells (e.g., as a function of cell membrane potential), planar miniature waveguides can be used instead of the ATR optics [865]. PM-IRRAS has been applied to obtain high-performance spectra of model membranes at the AW interface [866-875]. The experimental data focus mainly on the correlation between the structure of the matrix amphiphile or phospholipid film and the structure of the constituent species, the subphase composition, the surface pressure, and other external conditions, as well as the interaction of such monolayers with peptides and proteins (for reviews, see Refs. [332-334, 876, 877]). 

The glycosylated GPLs comprise the well-established PI lipid anchors and the newly discovered glucosylation products of the aminophospholipids. Despite the glycation these PLs retain their lipid properties, which is essential for their function. 

Lipid Properties and the Orientation of Aromatic Residues in OmpF, Influenza M2, and Alamethicin Systems Molecular Dynamics Systems. 

Tieleman PD, Forest LR, Samsom MSP, Berendsen HJC (1998) Lipid properties and the orientation of aromatic residues in OmpF, influenza M2, and alamethicin systems molecular dynamics simulations. Biochemistry 37(50) 17554-17561... 

As a first requirement, the sample analyzed should represent as closely as possible the lipid composition of the whole matrix from which it was taken furthermore, sample preparation should be carried out in such an environment as to minimize any changes in lipid properties prior to analysis. In food analysis, proper sampling of the lipid fraction requires knowledge of the physical structure and location of the major lipids in the sample, and the choice of the most adequate procedure depends on the t)q)e of food being analyzed, the nature of the lipid fraction, as well as the analytical procedure applied for the extraction. Foods consisting almost entirely of lipids, such as vegetable oils, often require little, if any, sample preparation prior to analysis. Qn the other hand, for more complex foods, such as meat or milk, extraction and purification of the lipid fraction is necessary prior to analysis. Official methods have been developed, which recommend the sample preparation and extraction procedures to be followed for a specific t)q5e of food. Solvent extraction methods are usually used, to separate lipids from water-soluble food components, prior to chromatographic analysis these are described in the sections that follow. A number of steps are usually required, prior to the solvent xtraction of lipids from a matrix ... 

Uses Emollient, conditioner, o/w emulsifier, gellant, moisturizer, solubilizer used In aq. or dilute alcoholic preparations (shampoos, aftershaves, cleansers) solubilizer and carrier for nail care preps. solubilizer for perfumes and lipids Properties Golden yel. soft wax faint char, odor sol. in water sol. cloudy in anhyd. ethanol partly sol. in castor oil si. sol. in min. oil, IPM drop pt. 42-50 C acid no. 5 max. sapon. no. 20-36 flash pt. > 100 C pH 3.5-8.0 (5% aq.)... 

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