Hydrophobic effect, with lipids

The squaraine probe 9g was tested for its sensitivity to trace the formation of protein-lipid complexes [57]. The binding of dye 9g to model membranes composed of zwitter-ionic lipid phosphatidylcholine (PC) and its mixtures with anionic lipid cardiolipin (CL) in different molar ratios was found to be controlled mainly by hydrophobic interactions. Lysozyme (Lz) and ribonuclease A (RNase) influenced the association of 9g with lipid vesicles. The magnitude of this effect was much higher... 

A third type of interaction is due to hydrophobic effects. These are the result of nonelectrostatic domains interacting. This type of interaction occurs mainly with the highly lipid-soluble drugs in the lipid part within the cytoplasm of the cell. 

Membrane lipids are strongly amphipathic molecules with a polar hydrophilic head group and an apolar hydrophobic tail. in membranes, they are primarily held together by the hydrophobic effect (see p. 28) and weak Van der Waals forces, and are therefore mobile relative to each other. This gives membranes a more or less fluid quality. 

The dye l-Anilino 8-Naphthalene Sulfonic acid (ANS) has high specificity for protein. It fluoresces only when bound to protein [30]. In smears and handsections (i.e. unembedded materials) we have never observed it to effect emulsion stability in the manner more traditional protein dyes such as Coomassie Brilliant Blue or Fast Green often do. This relative pH independence probably is due to the mode of action of this dye. It becomes fluorescent in hydrophobic pockets on protein molecules [30] in contrast to the ionic bonding necessary for Fast Green FCF and Coommassie Blue [22]. We have not observed a strong cross-reaction with lipids, either, although a fluorescence of different spectral characteristics sometimes is seen. 

Hydrophobic forces The hydrophobic effect is the name given to those forces that cause nonpolar molecules to minimize their contact with water. This is clearly seen with amphipathic molecules such as lipids and detergents which form micelles in aqueous solution (see Topic El). Proteins, too, find a conformation in which their nonpolar side chains are largely out of contact with the aqueous solvent, and thus hydrophobic forces are an important determinant of protein structure, folding and stability. In proteins, the effects of hydrophobic forces are often termed hydrophobic bonding, to indicate the specific nature of protein folding under the influence of the hydrophobic effect. 

Lipid bilayers will spontaneously self-assemble in aqueous solution. The major driving force behind this is the hydrophobic effect - the hydrophobic fatty acid chains avoid coming into contact with the water molecules. Once... 

Artificial membranes are used to study the influence of drug structure and of membrane composition on drug-membrane interactions. Artificial membranes that simulate mammalian membranes can easily be prepared because of the readiness of phospholipids to form lipid bilayers spontaneously. They have a strong tendency to self-associate in water. The macroscopic structure of dispersions of phospholipids depends on the type of lipids and on the water content. The structure and properties of self-assembled phospholipids in excess water have been described [74], and the mechanism of vesicle (synonym for liposome) formation has been reviewed [75]. While the individual components of membranes, proteins and lipids, are made up of atoms and covalent bonds, their association with each other to produce membrane structures is governed largely by hydrophobic effects. The hydrophobic effect is derived from the structure of water and the interaction of other components with the water structure. Because of their enormous hydrogen-bonding capacity, water molecules adopt a structure in both the liquid and solid state. 

One problem with the simulations that was apparent on close inspection of the structures was the presence of hydrophobic cavities which are not properly filled with lipids. Although approximately 90% of the membrane surface were covered with lipids, the remaining 10% might effect the MD simulations. It appears that the surrounding lipids have a great effect on the bci complex not only in vivo and in vitro (see section 3.4), but also in silicio. 

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