Monolayers of lipids

The importance of lipophilicity to bitterness has been well established, both directly and indirectly. The importance of partitioning effects in bitterness perception has been stressed by Rubin and coworkers, and Gardner demonstrated that the threshold concentration of bitter amino acids and peptides correlates very well with molecular connectivity (which is generally regarded as a steric parameter, but is correlated with the octanol-water partition coefficient ). Studies on the surface pressure in monolayers of lipids from bovine, circumvallate papillae also indicated that there is a very good correlation between the concentration of a bitter compound that is necessary in order to give an increase in the surface pressure with the taste threshold in humans. These results and the observations of others suggested that the ability of bitter compounds to penetrate cell membranes is an important factor in bitterness perception. 

It is found that, even a monolayer of lipid (on water), when compressed can undergo various states. In the following text, the various states of monomolecular films will be described as measured from the surface pressure, n, versus area, A, isotherms, in the case of simple amphiphile molecules. On the other hand, the Il-A isotherms of biopolymers will be described separately since these have a different nature. 

The spread mixed lipid monolayer studies provide information about the packing and orientation of such molecules at the water interface. These interfacial characteristics affect many other systems. For instance, mixed surfactants are used in froth flotation. The monolayer surface pressure of a pure surfactant is measured after the injection of the second surfactant. From the change in n, the interaction mechanism can be measured. The monolayer method has also been used as a model biological membrane system. In the latter BLM, lipids are found to be mixed with other lipidlike molecules (such as cholesterol). Hence, mixed monolayers of lipids + cholesterol have been found to provide much useful information on BLM. The most important BLM and temperature melting phenomena is the human body temperature regulation. Normal body temperature is 37°C (98°F), at which all BLM function efficiently. 

The model system for biological membranes is the so-called artificial lipid membrane made of two monolayers of lipid between two (aqueous) electrolyte solutions. The thickness of such a membrane can vary over a wide range and this introduces some ambiguity in deciding what kind of model should be the basis for the mathematical description of ion transport and other properties. Two extreme concepts can be distinguished. 

While the approach curves for monolayers of pure C-16 and DPHC lipids were reproducible, the kf obtained at mixed monolayers of lipids showed larger variations. Some values of kf obtained from different approach curves were very close to those for pure C-16 and DPHC monolayers. This was explained by segregation of lipids in the monolayer into separate do-... 

TiTuch of our understanding of the phase behavior of insoluble - monolayers of lipids at the air-water interface is derived from Adam s studies of fatty acid monolayers (I). It is now clear that the phase behavior of phospholipid monolayers (2) parallels that of the fatty acids we make use of these structure variations in our study of the interactions of phosphatidylcholine (lecithin) monolayers with proteins. Because of the biological significance of the interfacial behavior of lipids and proteins, there is a long history of studies on such systems. When Adam was studying lipid monolayers, other noted contemporary surface chemists were studying protein monolayers (3) and the interactions of proteins with lipid monolayers (4). The latter interaction has been studied by many so-called 4 penetration experiments where the protein is injected into the substrate below insoluble lipid monolayers that are spread on the... 

Figure 9.4 A schematic diagram showing the process of self-assembly for a lipid bilayer on a freshly cleaved metal surface step 1, a metal wire being cut under a lipid droplet with a sharp blade forming an adsorbed monolayer of lipid step 2, upon immersion of the lipid-coated wire tip into aqueous solution, a self-assembled BLM is formed (see [10], [11], [28], and [29] for details).

Apart from its biomolecular thickness, a BLM is a liquid-like, dynamic structure in a metastable state from a self-assembling point of view we conclude that it is difficult to envision how a BLM separating two aqueous solutions can be made from two rigid, solidlike monolayers of lipids without a Plateau Gibbs border. For biosensor development, it is our opinion that a fluid bilayer is of crucial importance. The aim of this section is to describe in sufficient detail how to set up a simple BLM system using the self-assembling techniques [5 10]. 

During the next few seconds, the capacitance is relatively low due to the drop of BLM forming solution on the newly cut surface on the tip of the metallic wires. A monolayer of lipid molecules is irreversibly and rapidly adsorbed onto it. 

The effect of the distance between the active center and the electrode on the reaction rate has been studied using as an example the electrocatalysis of the oxygen reduction reaction by laccase adsorbed on soot. Variation in the distance between the active center and the electroconductive substrate was achieved by inserting an intermediate monolayer of lipid molecules flatly and vertically oriented cholesterol molecules and vertically oriented lecithin molecules (scheme in Figure 36). In this case, the conditions of obtaining compact lipid monolayers were fulfilled. The subsequent setting of laccase did not lead to their desorption. 

Leontidis E, Aroti A (2009) Liquid expanded monolayers of lipids as model systems to understand the anionic Hofmeister series 2. Ion partitioning is mostly a matter of size. J Phys Chem B 113 1460-1467... 

Leontidis E, Aroti A, Belloni L (2009) Liquid expanded monolayers of lipids as model systems to understand the anionic Hofmeister series 1. A tale of model. J Phys Chem B 113 1447-1459 Levitsky VY, Panova AA, Mozhaev VV (1994) Correlation of high-temperamre stability of a-chymotrypsin with salting-in properties of solution. Eur J Biochem 219 231-236 Lipkind GM, Fozzard HA (2008) Voltage-gated Na channel selectivity the role of the conserved domain III lysine residue. J Gen Physiol 131 523-529 Lo Nostro P Fratoni L, Ninham BW, Baglioni P (2002) Water absorbency by wool fibers Hofmeister effect. Biomacromolecules 3 1217-1224... 

In the Langmuir-Schaefer method, a flat substrate is placed horizontally onto a compressed monolayer on the liquid-air interface. When the substrate is lifted horizontally and separated from the water subphase, the monolayer is transferred onto the substrate (Figure 4). The method is useful to transfer viscous films as well as monolayers of lipids and proteins. ... 

INTERACTIONS WITH PHOSPHOLIPID MONOLAYERS OF LIPIDS AND WATER-SOLUBLE COMPOUNDS THAT INDUCE MEMBRANE FUSION... 

Gzyl B, Paluch M Langmuir monolayers of lipids at the water/air interface 245... 

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