Penetration into monolayers

Penetration into Monolayers at the Air-Water and Oil-Water Interface. Membrane extracts as described above penetrate monolayers at the air-water interface reaching equilibrium surface pressures in 10-30 minutes depending on the protein concentration in the substrate. Figure 8 shows the equilibrium spreading... 

Mechanism of Proteolioid Vesicle Penetration into Monolayers. The principle conclusion from the penetration studies at the air-water and oil-water interfaces is that intrinsic membrane protein in vesicles greatly facilitates the transfer of material into monolayers. In marked contrast lipid vesicles do not penetrate monolayers to any appreciable extent although some exchange of lipid between a monolayer and the outer lipid layer of a liposome can occur (48.49). It is established that both glycophorin (50) and the anion transporter (51) increase the rate of "flip-flop" when incorporated into bilayers. Thus in the initial encounter between the proteolipid vesicles and the monolayer the protein-enhanced rate of "flip-flop" between the inner and outer halves of the vesicle bilayer would facilitate lipid transfer to the monolayer. The process of redistribution of lipid between vesicle and monolayer would bring the protein into intimate contact with the monolayer leading to penetration. 

Influence of Intermolecular Spacing on Enzymic Hydrolysis of Lecithin Monolayers. When snake venom phospholipase A is injected under a lecithin monolayer, it splits lecithin into lysolecithin and free fatty acid. The change in polar groups of the monolayer results in a change of surface potential. However, if prior to injection of enzyme into the subsolution, a lecithin monolayer is compressed to such a surface pressure that the active site of the enzyme is unable to penetrate the monolayer, hydrolysis does not proceed. For monolayers of dipalmitoyl, egg, soybean, and dioleoyl lecithins the threshold surface pressure values at which hydrolysis does not proceed are 20, 30, 37, and 45 dynes per cm., respectively (40). This is also the same order for area per molecule in their surface pressure-area curves, indicating that enzymic hydrolysis of lecithin monolayers is influenced by the unsaturation of the fatty acyl chains and hence the intermolecular spacing in monolayers (40). 

Our results show that there is a clear difference between the sorption of /ert-butyl alcohol by the microporous phenyl-modified silica compared with the sorption of w-butyl alcohol. Comparison of total pore volumes and monolayer capacities with those for other sorptives leads us to conclude that sorption of the straight-chained isomer is significantly more sterically hindered than its branched analogue. This may be explained by the difference in the shapes of the two molecules. The spherical ten-butyl alcohol molecule is able to easily penetrate into the micropores of the unswollen sample without blocking the pore-entrance, while the straight-chain w-butyl alcohol molecule may block the pores upon adsorption. 

Another type of interaction is the penetration of a surface-active constituent of the substrate into a spread monolayer. Penetration effects can be studied by injecting a solution of the surface-active material into the substrate immediately beneath the monolayer a) if there is no association between the injected material and the monolayer, tt and AK will both remain unaltered (b) if the injected material adsorbs on to the underside of the monolayer without actual penetration, AK will change appreciably but tt will alter very little (c) if the injected material penetrates into the monolayer (i.e. when there is association between both polar and non-polar parts of the injected and original monolayer materials), ir will change significantly and A V will assume an intermediate value between AV of the original monolayer and AV of a monolayer of injected material. Penetration is less likely to occur when the monolayer is tightly packed. 

For SAMs of HS(CH2)i60H or HS(CH2)i60CH3on Au 111, it was found that vapor-deposited Al inserts only with the OH SAM to form an -O-Al-H product while with the OCH3 SAM, the metal was either deposited on top of the SAM as an overlayer, or the Al atoms penetrated into the SAM to the monolayer/Au interface.60... 

Fig. 4. Immunocytochemistry of formalin fixed 147L) cell cultures using a-PR-A anti-receptor MAb (left) and a control MAb (right). Immunocytochemistry was performed with T47D breast cancer cells grown as monolayers in chamber slides. Cells were fixed for 15 min with 3.7% buffered formalin, followed by a permeabilization step with Triton X-100 (0.1%) for antibody penetration into the cell. Immunocytochemistry was performed by the indirect avidin-biotin immunoperoxidase method using diaminobenzi-dine as the chromagen.

For A n = 0.2-50eV, surface penetration into the first monolayers reduces the temperature for epitaxy and yields a higher density of structures. These processes dominate in sputtering and PLD at higher background pressures of 0.05-0.5mbar. 

When complexes are formed on penetration, the length and the stereochemical configuration of the hydrocarbon chains in the penetrating and the monolayer molecules are important long chains penetrate more easily than short, and if double bonds are present, penetration into, or by, sub-... 

If the standard BET procedure is to be used, it should be established that monolayer-multilayer formation is operative and is not accompanied by micropore filling (Section 11.2.1.8.C), which is usually associated with an increase in the value of C (>200, say). It should be appreciated that the BET analysis does not take into account the possibility of micropore filling or penetration into cavities of molecular size. These effects can thus falsify the BET surface areas and in case of doubt their absence should be checked by means of an empirical method of isotherm analysis or by using surface area reference samples (see Section 11.2.1.6.B). 

Data on emulsion film formation from insoluble surfactant monolayer are rather poor. It is known, however, that such films can be obtained when a bubble is blown at the surface of insoluble monolayers on an aqueous substrate [391,392]. Richter, Platikanov and Kretzschmar [393] have developed a technique for formation of black foam films which involves blowing a bubble at the interface of controlled monolayer (see Chapter 2). Experiments performed with monolayers from DL-Py-dipalmitoyl-lecithin on 510 3 mol dm 3 NaCl aqueous solution at 22°C gave two important results. Firstly, it was established that foam films, including black films, with a sufficiently long lifetime, formed only when the monolayer of lecithin molecules had penetrated into the bubble surface as well, i.e. there are monolayers at both film surfaces on the contrary a monolayer, however dense, formed only at one of the film surfaces could not stabilize it alone and the film ruptured at the instant of its formation. Secondly, relatively stable black films formed at rather high surface pressures of the monolayer at area less than 53A2 per molecule, i.e. the monolayer should be close-packed, which corresponds to the situation in black films stabilized with soluble surfactants. 

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