Immobilization effects

Fig. 5. Effect of solvent on stability of sol-gel-immobilized CPO. The highest stability displayed in 200-A pore sol-gel may be owing to immobilization of the enzyme within the pores of the sol-gel, whereas it may have been immobilized effectively only on the surface in the case of the other pore sizes.

At the upper limit of the ci range, v decreases to a minimum as the molecules are progressively immobilized, effectively making good and poor solvents functionally indistinguishable. In this regime, viscosity merges into elasticity, P becomes independent of c, and the dispersion simulates the behavior of a molten polymer. 

If is obtained from experiments in stirred suspension or microcarrier cultures, as described above, then, it may be possible to estimate from Q- lqu- However, care must be exercised because can be altered by changes in the culture environment. For example, qy for cells immobilized in agarose beads or hollow fibres may be different from qy for the same cells grown in the same medium in a stirred suspension reactor (Shirai et al, 1988 Wohlpart et al, 1991). In addition, qy may change over time due to changes in cell, nutrient and byproduct concentrations. Analysis of cell density and immobilization effects is complicated by the presence of nutrient concentration gradients. However, stirred vessels with cells immobilized... 

Putting on a cyclopropyl group gives a very powerful antagonist called diprenorphine (Fig. 12.31), which is 100 times more potent than nalorphine and can be used to reverse the immobilizing effects of etorphine (see above). Diprenorphine has no analgesic activity. 

The measurable activity reflects the biocatalytic efficiency of an immobilized enzyme. In homogeneous solution the initial rate of substrate conversion rises linearly with enzyme concentration. The reaction rate is influenced by substrate diffusion only at extremely large degrees of conversion. With immobilized enzymes the measured reaction rate depends not only on the substrate concentration and the kinetic constants Km and vmax but also on so-called immobilization effects. These effects are due to the following alterations of the enzyme by the immobilization process (Kobayashi and Laidler, 1974). 

All zirconium based solids synthesized share in common a number of features which are responsible for their catalytic properties and their stability. Thus, zirconium is anchored to a silica surface via a Zr-Oj bond, known to be a strong bond. This bond intervenes in two ways it stabilizes Zr as a mononuclear species (dimerization is further prevent from by the fact that the hydroxyl groups on the surface are isolated) it leads to a very reactive species, formally an 8e species. Thus the siloxy ligand shows an immobilizing effect and an electronic effect. 

In brief, unlike solubility, the effects of crystallinity on the effective diffusivity intimately involve the details of the polymer morphology. Because of the chain immobilization effect, crystallinity may cause an increase in the activation energy of diffusion. However, observed decreases for the activation energy of diffusion for helium in semicrystalline materials have been attributed to "grain boundary" effects (22.) For a first approximation, some authors have found it sufficient to use the following relationship for the correlation of amorphous volume fraction and effective diffusivity,... 

Fig. 2 Common immobilization effects during the coupling of affinity ligands to solid supports.

The polymer networks (Figure 9.1(c)) represent promising molecular structmes compared to a coil conformation based on the possible additional immobilization effects which are clearly illustrated if we consider a network given by a copolymeric structure of rigid and flexible segments. Recently, molecular composites by semi-interpenetrating polymer networks have been reported [62]. 

The /3 relaxation is very broad compared with that in completely amorphous polymers due to the immobilizing effect of the crystals on the amorphous fraction. 

Electrode modification can be carried out by methods that vary greatly. A reaction can be affected simply by addition to the electrolysis solution of a substance that is readily adsorbed onto the electrode surface. Thus, additimi of a thiocyanate salt to the medium diverts the anodic oxidatimi of carboxylates frran decarboxylative dimerization (Kolbe reaction) to peracid formation [1]. Often, a polymer solutimi containing an electrocatalyst is placed on a surface, and the solvent evaporated or a monomer is electrochemicaUy polymerized in situ from solution mito the surface. Electrocatalysts deposited in this manner include organometallic electrocatalyst complexes such as vitamin B12 [2], oxidizable heterocycles such as pyrrole or thiophene, or metal ions [3]. Successive layers of complementary materials may be laid down on an electrode to achieve the desired immobilization effect. Thus, a polymer (PDAA polydimethyldiallyl ammonium chloride) bearing... 

Based on the rigidification concept, Mahajan [25] has developed an approach in which the Maxwell model is used twice. The polymer region in the vicinity of the CMS particle is assumed to have reduced permeabihty due to the immobilization effect. This is an extension of the concept given for the semi-crystalline polymer. When crystallites are present within an amorphous phase the chain mobility of the amorphous phase appears to be reduced leading to high activation energy of diffusion. Michaels et al. introduced chain irmnobilization factor p by which the overall diffusion coefficient ) is given by... 

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