Preadsorbent layers

Fig. XVII-21. Continued) (c) Isosteric heats of adsorption of n-hexane on ice powder Vm = 0.073 cm STP. (From Ref. 125). (d) Isosteric heats of adsorption of Ar on graphitized carbon black having the indicated number of preadsorbed layers of ethylene. (From Ref. 126.)...

UPD generally involves the reductive deposition of an atomic layer of one element on a second. It has clearly been shown, however, that if there is a preadsorbed atomic layer of a third element, the UPD process may involve reactions with both the substrate and the preadsorbed layer. 

The similar dependencies are observed when the preadsorbed layer was formed from 10-2 g/1 CSDAPM solution (Fig. 5). 

The comparison of results of the SDS adsorption on the CSDAPM and PDADMAC preadsorbed layers shows that in the second case the adsorption of anionic surfactant also leads to the overcharge of the surface and increases with the increasing of surfactant concentration. Whereas the time of SDS adsorption on different polyelectrolytes is various. For example, when SDS 10 4M adsorbs on... 

Adsorption of oppositely charged SDS on preadsorbed PE layer resulted in the surface overcharge. The bilayer deformation study showed the increase in deformation values as a result of SDS adsorption, hence the anionic surfactant caused swelling of the preadsorbed layer. 

Fig. 5 The area for an undisturbed PEO coil divided by the area per adsorbed PEO chain as a function of the concentration of the polymer sample in the solution. The unfilled circle illustrates the result after allowing a preadsorbed layer to desorb in 100 mM NaCl for 12 hours...

Ultrahigh vacuum techniques (basic pressure xl02 Pa) enable adsorption studies to be made on stringently clean solid surfaces whereas degassing under moderate vacuum conditions, as normally applied in surface area determinations, leave the adsorbent covered with a preadsorbed layer of impurities and/or the adsorbate. On subsequent adsorption (e.g. of N2 or noble gases) completion of the physisorbed monolayer is usually reached at p/pn 0.1 whereas on clean surfaces this state occurs at p/p° values which may be smaller by orders of magnitude. However, as mentioned above, it should be kept in mind that linearity of the BET plot does not in itself provide conclusive evidence for the validity of njj,. 

The polyelectrolyte AM-MAPTAC-1 has only 1% of the segments charged. In this case no swelling of the preadsorbed layer on the mica surface is observed when SDS is added to the solution. The data obtained for an SDS concentration of 0.1 cmc are essentially the same as observed prior to the addition of SDS (Figure 23) and are dominated by a steric repulsion. We conclude that hardly any SDS is present in the adsorbed layer. However, when the SDS concentration is increased to 0.3 cmc, the range of the steric force is less than at the lower SDS concentration. A further increase in surfactant concentration results in a progressive decrease in the range of the... 

As sketched in Fig. 10 and mentioned before, the cells anchor to adhesive proteins that are immobilized on the surface. When cells are cultured for a certain time, they even produce their own adhesive proteins and secrete it into the space between membrane and substratum. Thus, we tried to address whether or not these adhesive proteins underneath the cell body may contribute to the total QCM readout of a confluent cell layer. Instead of limiting the analysis to preadsorbed layers of one or two purified proteins, we tried to study the complex extracellular material underneath the cells (extracellular matrix or ECM) by removing the cell bodies but leaving the macromolec-ular network of proteins and sugars behind on the substrate. The protocol required a combination of hypotonic stress and detergent extraction [16]. Microscopic inspection of reference substrates revealed that this procedure hfted the cell bodies effectively off the substrate. The surface was, however, still decorated with proteins as revealed by immunocytochemical staining. 

The influence of specific proteins in the complex mixture in the adsorbed layer on cellular reactions has yet to be demonstrated directly, but purified proteins preadsorbed to surfaces and then exposed to blood provide information on the potential of various proteins to influence cellular events. A much more comprehensive study of this type which includes proteins such as von Willebrand factor and a2-macroglobulin is presented in this volume (63). The ability of proteins to enhance or repress cellular reactions when used as pure preadsorbates does not indicate the magnitude of the role played by the protein when present in the complex layer adsorbed from plasma. The protein may be present in very small amounts in the plasma-derived adsorbate relative to the purified preadsorbed layer. For example, von Willebrand factor is present at very low concentrations in plasma (10-15 xg/mL) and is therefore probably present at very low levels in the absorbed layer formed on polymers exposed to plasma. Thus, although von Willebrand factor undoubtedly could be an important factor in surface thrombosis, its influence at the very low adsorption levels likely to exist in vivo must be demonstrated. However, the knowledge of which proteins are potentially important, derived from preadsorption studies, is extremely useful in focusing attention on specific proteins to study in the actual adsorbed layer. 

In our experience, unless the preadsorbed protein has a specific (enzyme/substrate, antigen/antibody) relationship with the dissolved one, the preadsorbed protein will adsorb little or no other protein. Where the ellipsometer shows increased optical film thickness upon exposure of, e.g., a preadsorbed layer of albumin to fibrinogen, such interactions occur at the expense of the ability of the preadsorbed albumin to adsorb antibody to albumin (14). This indicates that exchange - in this case by the larger species - took place. A notable exception may be the ability of plasma to deposit a thus far unidentified protein onto preadsorbed immunoglobulins (IgG) (15), but here too, some specific interactions may take place. 

In this equation, the radius is corrected for the thickness of one preadsorbed layer. 4.6.3 Modified Antoine Equation... 

Exposure of a preadsorbed layer of PLL(375)-g[5.6]-PEG-(5) to a solution with a pH value outside of the pH range where adsorption is observed or to a solution with a high ionic strength causes a gradual desorption of the polymer. Therefore, the adsorption of PLL(375)-g[5.6]-PEG(5) and the stability of this adsorbed polymer layer require that the contacting solution be limited to the pH range between the isoelectric point of the surface and the pA/a of the polymer, and to low ionic strengths. 

PLL(375)-g[5.6]-PEG(5) was also found to adsorb onto a preadsorbed layer of serum proteins. After a typical adsorption of serum protein (that is, about 260 ng/cm ), subsequent exposure to a 1 mg/mL solution of PLL(375)-g[5.6]-PEG(5) effected an overlayer of polymer with a surface areal density of approximately 90 ng/cm. ... 

Application of a solution of the sample on a preadsorbent layer, followed by direct development... 

The use of preparative plates with a preadsorbent zone reduces the amount of care necessary to produce a narrow band. Sample in this case is applied to the relatively inert preadsorbent layer as a crude streak across the plate. Even so. it is best to exercise some care and apply the sample evenly across the plate, because a high local sample concentration can cause an overloading effect in the corresponding region of the plate. 

Figure 3.5 Sequence of separation on a preadsorbent layer. (Photograph courtesy of Analtech.)...

Fielden, M. L., Claesson, P. M. and Schillen, K., Investigation of a 31% charged cationic polyelectrolyte interacting with sodium dodecyl sulfate in bulk solution and as a preadsorbed layer on mica. Low ionic strength, Langmuir, 14, 5366-5375 (1998). 

The forces acting between mica surfaces carrying a preadsorbed layer of AM-MAPTAC-30 (obtained by adsorp-... 

Polyvinylidene difluoride (PVDF), 428 Polyzonal TLC, 154-156 Porphyrins, 737-740 distribution, 738 practical eiqieriments, 739-740 structure, 737-738 TLC of, 738-739 Positioning sensors, 376-377 Postchromatographic derivatization, 145-146 of carbohydrates, 498-499,500 Preadsorbent layers, 17-18 Prechromatographic derivatization, 145 of carbohydrates, 498... 

Investigation of the replacement adsorption shows [63] that the rate of this process is close to the rate of the second stage of polymer adsorption, but depends on the age of the pre-adsorbed layer (Fig. 34). The rate of the replacement adsorption decreases when the age of the preadsorbed layer increases. 

Malinauskas A, Niaura G, Bloxham S, Ruzgas T, Gorton L. Electropolymerization of preadsorbed layers of some azine redox dyes on graphite. J Colloid Interface Sci 2000 230 122-127. 

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