Coating particle-immobilizing

Figure C 1.5.6. Single Ag nanoparticles imaged with evanescent-wave excitation. (A) Unfiltered photograph showing scattered laser light (514.5 nm) from Ag particles immobilized on a polylysine-coated surface. (B) Bandpass filtered (540-580 nm) photograph taken from a blank Ag colloid sample incubated witli 1 mM NaCl and...

The next two examples illustrate more complex surface reaction chemistry that brings about the covalent immobilization of bioactive species such as enzymes and catecholamines. Poly [bis (phenoxy)-phosphazene] (compound 1 ) can be used to coat particles of porous alumina with a high-surface-area film of the polymer (23). A scanning electron micrograph of the surface of a coated particle is shown in Fig. 3. The polymer surface is then nitrated and the arylnitro groups reduced to arylamino units. These then provided reactive sites for the immobilization of enzymes, as shown in Scheme III. 

Figure 10. An hypothetical model for a cyclic water splitting system, based on a semiconductor particle immobilized in a polymerized membrane and having access to both aqueous solutions on each side of the membrane. Specific and selective coating by catalysts leads to simultaneous and separate hydrogen and oxygen generation on each side of the polymerized membrane.

Fig. 20.23 SEM image of a quartz plate coated with immobilized Ag/Pd particles...

In Novozym 435, the enzyme is not covalently linked to the carrier, but merely adsorbed. Therefore, as mentioned, enzyme leaching is a known issue with this product. The problem has been addressed by several authors [20, 21], Even though the enzyme performance has been satisfactory, there has been a need specifically for a non-leaching immobilized formulation. It has been shown that several physical and chemical treatments such as coating the immobilized particles can enhance the stability of Novozym 435 [20-22],... 

Lipases are manufactured by fermentation of selected microorganisms followed by a purification process. The enzymatic interesterification catalysts are prepared by the addition of a solvent such as acetone, ethanol, or methanol to a slurry of an inorganic particulate material in buffered lipase solution. The precipitated enzyme coats the inorganic material, and the lipase-coated particles are recovered by filtration and dried. Various support materials have been used to immobilize lipases. Generally, porous particulate materials with high surface areas are preferred. Typical examples of the support materials are ion-exchange resins, silicas, macroporous polymers, clays, etcetera. Effective support functionality requirements include (i) the lipase must adsorb irreversibly with a suitable structure for functionality, (ii) pore sizes must not restrict reaction rates, (iii) the lipase must not contaminate the finished product, (iv) the lipase must be thermally stable, and (v) the lipase must be economical. The dried particles are almost inactive as interesterification catalyst until hydrated with up to 10% water prior to use. 

Coated particle waste is especially effective for immobilizing cesium, which readily leaches from glassified waste because of its high solubility and tendency to partition into leachable phases. 

The 50% maximal theoretical yield of KR processes may be overruled by DKR to achieve 100% of the desired product if a fast racemization process for the substrate can be coupled to the KR in situ. A mixture of CaLB immobilized onto IL-coated particles and an acidic zeolite are allowed to carry out DKR in a one-pot under scCOj flow conditions (50 C, lOMPa) [133]. In this way, acylation of rac-23i with vinyl propionate in a DKR gave the propionate of (R)-23i in 92% yield and >99.9% ee. 

The process of deposition of particles at interfaces which occurs in many industrial processes, such as surface coating, is described at a fundamental level. Particle deposition can be conveniently split into three major steps (i) transfer of particles from the bulk dispersion over macroscopic distances to the surface (ii) transfer of the particles through the boundary layer adjacent to the interface (hi) formation of a permement adhesive contact with the surface or previously deposited particles leading to particle immobilization (attachment). The role of interparticle interactions on deposition is described in terms of double layer repulsion and van der Waals attraction. Particular attention is given to the effect of addition of electrolytes on particle deposition. The measurement of particle deposition using rotating disc and cyhnder techniques is described. The effect of nonionic polymers and polyelectrolytes (both anionic and cationic) on particle deposition at interlaces is described. The most universal and convenient methods for measuring particle deposition are the indirect methods. 

FIGURE 3 Scanning electron micrograph (1200x magnification) of the surface of a porous alumina particle coated with poly(diphenoxy-phosphazene). Surface nitration, reduction, and glutaric dialdehyde coupling immobilized enzyme molecules to the surface. (From Ref. 23.)... 

Third, a poly[bis(phenoxy)phosphazene] has been coated on porous alumina particles, surface nitrated, reduced to the amino-derivative, and then coupled to the enzyme glucose-6-phosphate dehydrogenase or trypsin by means of glutaric dialdehyde. The immobilized enzymes were more stable than their counterparts in solution, and they could be used in continuous flow enzyme reactor equipment (25). 

H. Zhang and M.E. Meyerhoff, Gold-coated magnetic particles for solid-phase immunoassays enhancing immobilized antibody binding efficiency and analytical performance. Anal. Chem. 78, 609-616 (2006). 

The possibility to use the YI sensor for virus detection was explored by monitoring the interaction between a-HSV-1 gG antibody and HSV-1 virus particles. To this end, channel 1 was coated with protein pA as described in Sect. 10.4.2 followed by the immobilization of a a-HSV-1 gG layer on the sensing surface of channel 1. Channel 4 was used as a reference channel. Finally a solution with HSV-1 virus particles at a concentration of 105 particles/ml was added to channel 1. Figure 10.2 shows the phase change measured between channel 1 and reference channel 4, clearly demonstrating the detection of virus particles by the YI sensor (Fig. 10.15). 

Various forms of macro- and microelements differ in their ability to migrate and redistribute among the soil profile. The elements contained in clastic minerals are practically immobile. The elements, bound to finely dispersed clay minerals, are either co-transported with clay particles, or are involved in sorption-desorption processes. Part of the elements are found in concretions and also in very thin coating films of hydrated iron oxides some elements make a part of specially edaphic organic compounds. 

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