Unstable monolayer

In principle, compressing a monolayer should produce more domains of radius J eq. however McConnell shows that in practice, domains grow to exceed this radius. Once a domain grows to A = it becomes unstable toward... 

Formation of the first layer (a monolayer) of passivating oxide film on a denuded metal surface occurs very simply by the loss of protons from the adsorbed intermediate oxidation products, such intermediates being common to both dissolution and passivation processes . Thus for example, the first oxidative step in the anodic oxidation of nickel is the formation of the unstable adsorbed intermediate NiOH by... 

In situ absorption spectra for PS I monolayers on different concentrations of NaCI subphase surface was also investigated (Figures not shown). The results indicate that no obvious band can be recorded for PS I monolayer on the surface of NaCI subphase with its concentration above 1 mol/L, which may be attributed to that the protein, PS I, becomes unstable on the surfaces containing high concentrations of salt. 

In LB films [1], the arrangement of the various functional moieties is considered to be controlled spatially across the films at molecular dimensions as described above. As one of functional moieties, various polycyclic aromatic hydrocarbons were used [55,56]. Some of the compounds were mixed with arachidic acid to form stable monolayers [37], because the amphiphilc derivatives of aromatic hydrocarbons themselves often form unstable monolayers on the subphase [40], For preparation of stable monolayers of polycyclic aromatic amphiphiles, Steven et al. investigated the effects of the length of alkyl chain and the composition and pH of the subphase [57],... 

Shimomura and Kunitake have reported that stable monolayers and LB films were obtained by electrostatic interaction of water soluble anionic polymers with cationic amphiphiles [58]. This polyion-complexation was also a useful method for stabilization of monolayers of unstable [59] or water soluble anionic surfactants [60]. Mixtures of water soluble cationic and anionic surfactants (1 1) also formed stable Langmuir monolayers at the air/ water interface [60]. 

The same way with PPV LB films was not applicable to MOPPV, because its polyion complex was unstable in solid state. The elimination reaction of a sulfbnium leaving group in the polyion complex rapidly progressed in solid state even at room temperature and the complex consequently became insoluble in the conventional organic solvents. Then, there is no way to form the polyion complex monolayer at the air/water interface. 

Concerning the mode of formation of ES, we prefer the concept that the substrate in a monolayer is chemisorbed to the active center of the enzyme protein, just as the experimental evidence pertaining to surface catalysis by inorganic catalysts indicates that in these reactions chemisorbed, not physically adsorbed, reactants are involved. Such a concept is supported by the demonstration of spectroscopically defined unstable intermediate compounds between enzyme and substrate in the decomposition by catalase of ethyl hydroperoxide,11 and in the interaction between peroxidase and hydrogen peroxide.18 Recently Chance18 determined by direct photoelectric measurements the dissociation con-... 

In a similar fashion, the Rotello group reported several protein-mediated assemblies of nanoparticles (Srivastava, Verma, et al. 2005 Verma et al. 2005). Unstable proteins such as chymotrypsin are readily denatured upon prolonged interaction with functionalized nanoparticles because of the exposure of proteins to the hydrophobic layer (Srivastava, Verma, et al. 2005). Addition of a hydrophilic portion to the monolayer by inserting a short tetraethylene glycol between the charged terminal group and hydro-phobic aliphatic chain circumvented this denaturation problem (Hong et al. 2004). 

Electron beam damage effects followed the general rule that molecular groups in intimate contact with the metal substrate and aromatic groups appear relatively stable. Thus in the monolayer, alanine, with a methyl group likely sticking out from the surface, was the only molecule found to be unstable. In multilayer films, only tryptophan with the aromatic indole group to stabilize the molecule was found to yield multilayers stable under electron beam irradiation. 

The mixed lipid-cholesterol monolayers are unstable. Recent studies of these systems show that for molecular fractions of cholesterol larger than 30% the cholesterol separates from the film, as if there were a limited misability in two dimensions. 

Even closer to cell membranes than monolayers and bilayers are organized surfactant structures called black lipid membranes (BLMs). Their formation is very much like that of an ordinary soap bubble, except that different phases are involved. In a bubble, a thin film of water — stabilized by surfactants — separates two air masses. In BLMs an organic solution of lipid forms a thin film between two portions of aqueous solution. As the film drains and thins, it first shows interference colors but eventually appears black when it reaches bilayer thickness. The actual thickness of the BLM can be monitored optically as a function of experimental conditions. Since these films are relatively unstable, they are generally small in area and may be formed by simply brushing the lipid solution across a pinhole in a partition separating two portions of aqueous solution. 

If the slightly soluble, surface-active compound is spread as a mono-layer, the film is unstable and desorbs from the surface. Analysis of the kinetics of desorption follows the treatment given by Ter Minassian-Saraga (29). Immediately upon spreading the monolayer, film molecules... 

Specific properties of polysilanes have been linked to the method of synthesis.35 For example, in the case of anionic polymerization of poly[l-(6-methoxy-hexyl)-l,2,3-trimethyldisilanylene] a new type of chromism was induced in the polysilane film by the difference in the surface properties of substrates and was termed a surface-mediated chromism. The polysilane exhibited thermochromism with an absorption maximum at 306 nm at 23°C, but <15°C a band at 328 nm began to appear. A monolayer of the polysilane was transferred onto both a clean hydrophilic quartz plate and a hydrophobic one treated with hexamethyldisilazane by the vertical dipping method. With the hydrophobic plate, a broad UV absorption at 306 nm is obtained, whereas the absorption on a hydrophilic plate shifts to 322 nm. The conformation of the polysilane is preserved by hydrogen bonding between the silica surface and the ether section of the substituent on the hydrophilic plate. The polysilane is attached to the hydrophobic surface only by van der Waals forces, and this weaker interaction would not sustain the thermodynamically unstable conformational state that is attained on the water surface. 

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