Bulk lipids

Irrespective of the physical form of the carotenoid in the plant tissue it needs to be dissolved directly into the bulk lipid phase (emulsion) and then into the mixed micelles formed from the emulsion droplets by the action of lipases and bile. Alternatively it can dissolve directly into the mixed micelles. The micelles then diffuse through the unstirred water layer covering the brush border of the enterocytes and dissociate, and the components are then absorbed. Although lipid absorption at this point is essentially complete, bile salts and sterols (cholesterol) may not be fully absorbed and are not wholly recovered more distally, some being lost into the large intestine. It is not known whether carotenoids incorporated into mixed micelles are fully or only partially absorbed. 

The other anomalous behavior was the smaller-than-expected permeability of highly branched compounds. This deviation has been explained on the basis that membrane lipids are subject to a more highly constrained orientation (probably a parallel configuration of hydrocarbon chains of fatty acids) than are those in a bulk lipid solvent. As a result, branched compounds must disrupt this local lipid structure of the membrane and will encounter greater steric hindrance than will a straight-chain molecule. This effect with branched compounds is not adequately reflected in simple aqueous-lipid partitioning studies (i.e., in the K0/w value). 

The detached amounts of cadmium octadecanoate LB films at the water surface with various temperatures are shown in Figure 18. The detached amount increased linearly with increasing the subphase temperature. The detachment of LB films is concerned with equilibrium spreading pressure (ESP), which represents the equilibrium between bulk lipid crystals and a lipid monolayer on the water surface [45]. ESPs... 

Chiou chose glyceryl trioleate (triolein) as model lipid because of its similarity to triglycerides which are abundant in organisms [109], Triolein is also a bulk lipid and the good correlation with the bioconcentration factor is restricted to neutral compounds of moderate hydrophobicity. No attempts were made to measure partitioning of ionogenic compounds with the glyceryl trioleate-water partition system. 

Jansson et al. [189] used the conventional approach of blending the solid particles with solvent after which an aliquot was taken to determine the volatile compounds (e.g., phenols and chlorobenzenes). A second fraction was taken after the lipid removal for determination of compounds sensitive to concentrated sulfuric acid. The bulk lipids were removed by oxidative dehydration with Si02 /H2S04 and further cleaned-up with GPC. The chloroparaffins were isolated at this stage. Separation on silica isolated the OCPs, and the organochlorines and organobromines were finally fractionated on active charcoal. 

Solidification of the particles may not be the final step in the formation process of solid lipid particles. Lipidic materials exhibit rich polymorphism [69,70], which may also occur in the dispersed state. In nanoparticles, the polymorphic behavior of the matrix lipids may, however, differ distinctly from that in the bulk material. Polymorphic transitions are usually accelerated in the nanoparticles compared with the bulk lipids [2,62]. In some cases, polymorphic forms not observable in the corresponding bulk materials were detected in lipid nanoparticles [1,65]. Because polymorphism can affect pharmaceutically relevant properties of the particles, such as the drug incorporation capacity [65], corresponding investigations should also be included in the characterization process. As long as polymorphic or other crystalaging phenomena have not terminated, the particle matrix cannot be regarded as static, and alterations of the particle properties may still occur. 

Adi pose ti ssue Extraction, bulk lipid removal, Florisil fracti onati on HRGC/MS 0.1 ng/g No data Mack and Stanley 1984... 

Modern methods of vibrational analysis have shown themselves to be unexpectedly powerful tools to study two-dimensional monomolecular films at gas/liquid interfaces. In particular, current work with external reflection-absorbance infrared spectroscopy has been able to derive detailed conformational and orientational information concerning the nature of the monolayer film. The LE-LC first order phase transition as seen by IR involves a conformational gauche-trans isomerization of the hydrocarbon chains a second transition in the acyl chains is seen at low molecular areas that may be related to a solid-solid type hydrocarbon phase change. Orientations and tilt angles of the hydrocarbon chains are able to be calculated from the polarized external reflectance spectra. These calculations find that the lipid acyl chains are relatively unoriented (or possibly randomly oriented) at low-to-intermediate surface pressures, while the orientation at high surface pressures is similar to that of the solid (gel phase) bulk lipid. 

Adipose tissue Extract with methylene chloride, remove bulk lipid by gel permeation chromatography, fractionate on Florisil (elute with diethyl ether/ hexane) HRGC/MS 9 ng/g No data EPA 1986f... 

Analysis of the results and comparison with the lipid phase transition observed iq the bulk lipid/water systems allows to conclude that the lowest temperature during heating at which measurable diffusion occurred correlates with the onset of formation of the lamellar Ln liquid crystalline phase of the given phospholipid. Therefore, the data support a correlation between the surface and bulk phase transitions. This was confirmed in recent studies where the lipid surface phase transition was successfully measured for the first time in foam film by independent means involving the detailed investigations of the temperature dependences of the W(C) curve for the foam film and its thickness. 

Wood, G. W. and Schroeder, F. Membrane effects of ethanol Bulk lipid versus lipid domains. Life Sciences 4i(6) 467-475, 1988. 

Timm-Heinrich, M. Skall Nielsen, N. Xu, X. Jacobsen, C. Oxidative stability of structured lipids containing C18 0, C18 l, C18 2, C18 3 or CLA in sn2-position - as bulk lipids and in milk drinks. Innovat. Food Sci Emerg. Technol. 2004, J (2), 249-261. 

The positive heats of mixing for lecithin-cholesterol mixtures indicate that interactions between unlike molecules are smaller than the interactions between like molecules, i.e., the hydrocarbon chain interactions with cholesterol are smaller than in each of the pure phases. If the excess heats of mixing become large enough, phase separation will occur. It may occur when the surface pressure is increased (i.e., as the films are compressed). The point at which phase separation occurs is difficult to predict, measure, or detect however, evidence of phase separation can be deduced from the following experiment. If excess amounts of two lipids are placed in water, the equilibrium surface pressure should reflect whether the surface film is a mixture. According to the phase rule (11,12, 13,14), if two bulk lipid phases are present, only one surface phase can be present at the air—water surface. Thus the composition of the equi-... 

Interaction of small molecules and ions with lipid bilayers is of importance from the point of view of membrane transport and other processes such as aaion of drugs and anesthetics on membranes. This includes a number of antibiotics and fatty acids also. The effect of these perturbations on the lipid bilayer in terms of differences in the structure and dynamics of the lipids close to the perturbative group versus the bulk lipids is also interesting and may... 

MD simulations of ionophore/channel molecules intercalated into a lipid bilayer would require a large number of lipid molecules to ensure that the ionophore/channel molecule does not interact with its periodic images. Still, comparisons between boundary and bulk lipids may have to be done from independent simulations to get an accurate view of how these molecules affea bilayer dynamics. Typical channels like gramicidin show ion transport times of —10 s, which is a time scale that is presently unattainable in typical MD simulations. However, one can obtain insights into the molecular aspects of the energy barriers involved in the translocation of small molecules and ions from PMF calculations, particularly when there is no ambiguity about the path of the solute movement. Moreover, short time scale (10 s) simulations can... 

TRXRD represents an important recent innovation in the experimental study of bulk lipid phase transition kinetics. The method provides direct structural information continuously throughout the course of the transition and offers useful insights into the transition mechanism. Although several successful experiments have been performed, the full potential of the method has yet to be realized. As indicated above, many of the limitations are of a technical nature. Next, I address some of the factors which, in my opinion, warrant attention if these limitations are to be removed and the potential of the TRXRD method fully exploited. 

Membrane enzymes often show a transition in the Arrhenius plot of the enzyme activity, which is usually attributed to a change in the lipid configuration. (K" " -h H" ")-ATPase preparations show such a transition at 27-28°C [71,86]. However, a transition in the polarisation signal of a lipid viscosity probe (diphenylhexatriene), was not observed in this region [71], indicating that the transition in the ATPase activity is either due to a change in the rate-limiting step of the reaction or to the presence of an annulus of specific lipids with physical properties different from those of the bulk lipids. 

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