Formation of a multilayer

Compression of the PS II membrane monolayer shows that the monolayer collapses at a relatively low surface pressure, at around 20mN/m. This can be attributed to the formation of a multilayered structure [8] and some of PS II membrane fragments diffuse into the subphase. This observation further indicates that PS II membranes can only marginally stay at the air-water interface and one must be very careful in choosing the experimental parameters. 

Negatively charged species such as carboxylic acid group in acid-treated CNTs can attract positively charged enzymes from solution as long as the pH value of the enzyme solution is controlled to be lower than the iso-electric point of the enzyme thus, multilayer films of the enzyme can be formed by the layer-by-layer technique. For example, five layers of GOx can be immobilized on the electrode surface by alternatively dipping a poly(diallyldimethylammonium chloride (PDDA))-functionalized GC into a CNT solution and a GOx solution (pH 3.8). Figure 15.15 illustrates the preparation process for the formation of a multilayer film of GOx on the electrode. 

By size of pore one can mean the diameter of an equivalent cylindrical or the distance between the sides of a slit-shaped pore (i.e., in general a diameter of the largest circle that can be inscribed in a flat cross section of a pore of arbitrary form). The basis of this classification is that each of the size ranges corresponds to characteristic adsorption effect that is manifested in the isotherm of adsorption [53,115], In micropores, the interaction potential is significantly higher than in wider pores, owing to the proximity of the walls. This explains that such pores become totally full with adsorbate at low relative pressures. In mesopores, one will observe formation of mono- and then multilayer molecular film forming over the walls. After formation of a multilayer molecular film,... 

Those Dps proteins that bind DNA do so nonspecifically via positive residues at the N-terminus of the protein. When a cell is under prolonged stress. Dps cocrystallizes with DNA in vivo. This process is favored because it occurs spontaneously and does not deplete the cell s ATP levels. The formation of a multilayered complex provides a physical barrier around the DNA in addition to the hydrogen peroxide detoxification that accompanies iron oxidation. ... 

Figure 4.37. Formation of a multilayer film based on the self-assembly method...

Porosity of nanoporous carbonaceous materials is usually analyzed on the basis of nitrogen adsorption isotherms, which reflect the gradual formation of a multilayer film on the pore walls followed by capillary condensation in the unfilled pore interior. The pressure-dependence of the film thickness is affected by the adsorbent surface. Hence, an accurate estimation of the pore-size distribution (i.e., pore-size analysis) requires a correction for the thickness of the film formed on the pore walls. The latter (so-called t-curve) is determined on the basis of adsorption isotherms on non-porous or macroporous adsorbents of the surface properties analogous to those for the adsorbent studied. 

From changes in the series resonant frequency of 80 Hz due to binding of the thrombin to the aptamer at 30 nM, it is possible to calculate the surface density of the protein. Using equation (5.1) and the molecular mass of a-thrombin (33.6 kD), we can calculate the number of thrombin molecules attached to the aptamer layer Athrombin = 5 x 10 (here again a correction factor of 2 was used). On the other hand, on the base of the crystal strucmre of the thrombin (Malkowski et al., 1997) the cross-sectional area of this molecule is approximately 20 mn. Therefore, approximately 1.0 x 10 thrombin molecules are required to cover the electrode surface. Thus, the value obtained suggests that at 30 nM the thrombin covers a substantial part of the sensor surface. However, further decrease in the frequency after addition of a higher thrombin concentration may demonstrate the aggregation of thrombin molecules and the formation of a multilayer strucmre. 

Figure 4 shows the results of the kinetic tests on asphaltene films, where the variation in surface pressure is measured against time while the area is kept constant. The f]—t curves for asphaltenes spread from 20%/80% toluene/hexane are markedly different from the H— curves for asphaltenes spread from pure toluene. Asphaltenes spread from solvents containing less than 20% toluene give rise to an increase in surface pressure with increasing bulk concentration of asphaltenes (Fig. 4). Amul-tilayer structure may exist on the surface when the solvent contains less toluene (< 20%). When the amount of toluene in the spreading solvent is high, even 8mg/ml asphaltenes may be dissolved, and no change in the surface pressure is observed. This may be explained as a result of the asphaltene fraction being dissolved in the aromatic solvent, preventing formation of a multilayer.

Assuming the formation of a multilayer of adsorbed molecules, Brunauer, Emmett, and Teller (BET) modified the Langmuir approach of balancing the rates of adsorption and desorption for the various molecular layers. The BET model assumes that the adsorption of the first monolayer has a characteristic heat of adsorption but that subsequent layers are controlled by the heat of condensation of the vapor in question, A//l. 

Williams, S. K., Carter, T., Park, P. K., Rose, D. G., Schneider, T., and Jarrell, B. E., Formation of a multilayer cellular lining on a polyurethane vascular graft following endothelial cell sodding, J. Biomed. Mater. Res., 1992 26(1) 103-117. 

The process of formation of a multilayer film on the ITO coated glass from sequential addition of PABA/RNA bilayers was observed with UV-Vis Spectroscopy as shown in Figure 3.34. The film growth observed with the deposition of additional bilayers suggests that the multilayer formation of PABA/RNA is reproducible with sequential deposition. All spectra exhibit an intense and sharp peak attributed to the w-tt and bipolaron band transitions. The bipolaron absorption band at 800 nm, associated with complexation of RNA with PABA, increases linearly with the number of PABA/RNA bilayers (Figure 3.34 inset). The linear relationship between absorbance and the number of deposited bilayers indicates that the deposition was reproducible from layer to layer, i.e., the amount of PABA adsorbed in each bilayer was the same. In addition to these results, multilayer formation was observed with ellipsometric and X-ray photoelectronic spectroscopy. The linear increase in film thickness with number of PABA/RNA bilayers was observed using ellipsometry. The average thickness of the PABA/RNA bilayer built up on a silicon substrate was approximately 10 nm. Additionally, X-ray photoelectron... 

The Langmuir equation and the method of solid surface area determination based on it can be applied for the systems in which the adsorption process is not complicated by formation of a multilayer as well as by adsorption in micropores and capillary condensation. Adsorption of gases at the temperatures higher than the critical temperature on nonporous or wideporous adsorbents is an example of such cases. Despite this limitation, the Langmuir equation is used in technical adsorption for calculations of kinetics and dynamics of impurities uptake from the gas medium or diluted solutions. 

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