Adsorbed layer, activity thickness

For lipase, initial activity corresponds to the amount of protein that was adsorbed. Specific activity is constant at 1 mmoFs gE for this carrier-enzyme system, which compares to 27% of the free enzyme activity. The trypsin system shows a lower specific activity that is only 10% of the free enzyme. The reason for the lower recovered activity of this system is not known. To rule out possible internal diffusion limitations, the Wheeler-Weisz modulus was estimated, assuming a carrier layer thickness of 0.1 mm for all carriers. Using the data of the experiments performed at 150 rpm, one finds ... 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

Kawaguchi et al.125) prepared an ionene-oxyethylene-ionene (IEI) triblock copolymer with the molecular weight 72 X 103 and measured its surface tension in aqueous KBr. They also determined by ellipsometry the adsorbance and the thickness of the adsorbed polyelectrolyte layer at the air-KBr solution interface as a function of the KBr concentration. The data obtained indicate that this copolymer is surface-active and that the effect of added KBr on the surface tension is stronger than in the case of polyoxyethylene (POE). 

Figure 8a Importance of interfacial effects according to Eq. (3) as a function of temperature for a membrane thickness of 50 p,m. Activation energy difference between exit from the pores to the externally adsorbed layer and intracrystalline diffusion is varied. If N N = 1, interfacial effects are not important.

The measured adsorption effect at the electrode is influenced by all dissolved and/or dispersed surface-active substances according to their concentration in the solution, adsorbability at the electrode, kinetics of adsorption, structure of the adsorbed layer, and some other factors. Adsorption of organic molecules on electrodes causes a change of the electrode double-layer capacitance. It is the result of an exchange between the counterions and water molecules from solution, followed by changes in the dielectric properties and the thickness of the double layer on the electrode surface, that is, parameters that determine the electrode capacitance (Bockris et al., 1963 Damaskin and Petrii, 1971). 

FIGURE 19.7. Interfacial activity in a Type I blend of an A-B diblock copolymer added to a blend of A and B homopolymers [A = SPB(89) and B = SPB(63)]. A/a = 4,230 and A/b = 3,600 for the homopolymers, while A/Ab = 790 and Nsb = 730 for the block copolymer. Symbols show experimental measurements using secondary-ion mass spectrometry (SIMS), and curves show SCFT predictions using x and / values from Tables 19.1 and 19.2. (a) Volume fraction profile in loglinear format of the diblock copolymer for a sample with 0.07 volume% block copolymer with an A/B interface at z = 190 nm. (b) Volume fraction profile in linear-linear format of the diblock copolymer for a sample with 0.07 volume% block copolymer with an A/B interface at z = 190 nm. The cross-hatched area represents the adsorbed amount, F. (c) Adsorption isotherm the dependence of the adsorbed amount, r, on the copolymer volume fraction in the A-rich phase ab/a- (d) The thickness of the adsorbed layer (standard deviation of the volume fraction profile near the peak), a, plotted versus the amount adsorbed, F. 

In the case of methanol-n.amyl alcohol on the original charcoal, the thickness of the adsorbed layer is only 1.48. This has been attributed to the fact that methanol and amyl alcohol have the same polar group in their molecules, so they both compete for the active CO2 complex sites present on the charcoal snrface. As the alcohol molecnles lay flat on the carbon snrface, the larger hydrocarbon portion in amyl alcohol occnpies more than one active site, renderingthem inaccessible to interaction with the OH gronp of the alcohols. 

The adsorption from binary solutions on sohd adsorbents in general and on activated carbons in particular is discussed in Chapter 3. The nature and types of adsorption and adsorption isotherms from dilute solutions and from completely miscible binary solutions are described. The composite isotherm equation is derived. The shapes and classification of composite isotherms and the influence of adsorbate-adsorbent interactions, the heterogeneity of the carbon surface, and the size and orientation of the adsorbed molecules on the shapes are examined. The thickness of the adsorbed layer and the determination of individual adsorption isotherms from a composite isotherm are also described. 

Millee and Kiechnee [168] had also suggested activation of the adsorbent layer back in 1953. They achieved this by drying the chromatogram strips over phosphorus pentoxide in a vacuum desiccator at 3 mm mercury pressure. Since the danger of inactivation by air humidity is so great with the standard sizes used today and the standard 250 [i thicknesses, the procedure is of no more than historical interest. 

An adsorbent layer ( NORIT activated carbon powder d 0.01 mm) in the suspension form with starch was smeared. The layer thickness - after a drying at 150° C temperature - rises as highly as 0.1 0.2 mm. 

Fig. 39 shows the dependence of hydrodynamic thickness 3 of an adsorbed saturated PEO layer on the tangential shear stress t = r APjlL acting on the peripheric part of the layer, where r is the capillary radius and L is the length of the capillary. The obtained dependence is reversible. This points to elastic or viscoelastic deformation of adsorbed layers. Thin quartz capillaries represent a simple model system that may be effectively used for investigation of both electrosurface phenomena and mechanical properties of adsorbed layers of surface-active polymers. 

The same enzsrme was studied extensively by Harkins, Folurt and Fourt (15). However, most of their work was carried out with adsorbed enzyme. They adsorbed catalase molecules on plates conditioned with thorium nitrate. An increase in thickness of 55 A followed the adsorption. The activity of the adsorbed catalase when tested in 0.008 M hydrogen peroxide proved to be 1/5 to 1/10 that of the original material. The same authors in addition carried out some immunological tests with alternate adsorbed layers of catalase and anticatalase which will be reviewed later. Some of the data, however, are of some concern for the enzymatic activity of successive layers. First, an anticatalase layer 50 to A thick, adsorbed on the catalase, did not diminish the activity of the enzjrme. Second, the thickness of a second layer of catalase adsorbed on the anticatalase was only 10 A, the order of an unfolded protein. Third, the activity of the system catalase—anticatalase—catalase was the same as that of catalase—anticatalase. One might conclude that the second layer of catalase 10 A thick was inactive. 

The statistical thermodynamics of block copolymer adsorption was considered elsewhere.Many theories attempt to characterize adsorption by smface density, block segment distribution profile, and the thickness of adsorbed layer. As a rule, an adsorbed diblock copolymer has one block adsorbed on the surface in a rather flat conformation, whereas the other block, having a lower surface activity, forms dangling tails. Because of their freely dangling blocks, adsorbed diblock copolymers are often interpenetrated. The adsorption of block copolymers leads to the segregation of blocks in the adsorption layer. It was found that both kinetic and equilibrium features of the block copolymer adsorption are intimately related to the phase behavior of the block copolymer solution. In particular, a very strong increase in the adsorbed amount is observed when the system approaches the phase boundary. As a consequence, a partial phase separation phenomenon may proceed in the surface zone. 

Table 6.8 shows some adsorbents used to prepare the stationary phase in the chromatographic separation of carotenoids by TLC. The choice between them depends on the solvent or mixture of solvents to be used as eluent phase. The adsorbent layer is placed on the glass plate (normally 20 X 20 cm) as a slurry, with a thickness that is variable but small (0.2-0.7 mm). The adsorbent is allowed to air-dry and is activated in the oven at 110°C. The pigment extract is applied to the base of the plate, and the plate is put into a tank containing the eluent. Development is usually carried out upwards, and when complete, the band or bands of interest are selected, scraped off, and eluted from the silica with either diethyl ether (in the case of polar carotenoids) or acetone or ethanol (if the polarity is medium), and filtered to remove the sihca. 

Certain highly porous solid materials selectively adsorb certain molecules. Examples are silica gel for separation of aromatics from other hydrocarbons, and activated charcoal for removing liquid components from gases. Adsorption is analogous to absorption, but the principles are different. Layers of adsorbed material, only a few molecules thick, are formed on the extensive interior area of the adsorbent - possibly as large as 50,000 sq. ft./lb of material. 

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