Physical immobilization

Polymer-based stabilization/solidification (S/S) is a technology for the ex situ treatment of radioactive, mixed, and hazardous wastes. It is a process in which polymers are created within the waste matrix to solidify and physically immobilize the hazardous constituents of contaminated materials. The goal is to prevent the migration of contaminants into the environment by forming a solid mass. 

Stabilization (admixing) Physical immobilization Chemical fixation in a cementious or pozzolanic mixture... 

W. Norde and T. Zoungrana, Surface-induced changes in the structure and activity of enzymes physically immobilized at solid/liquid interfaces, Biotechnol. Appl. Biochem. 28, 133-143 (1998). 

Physical immobilization methods there is no chemical modification of the enzyme. 

For DMDBT oxidation, CPO physically immobilized on SBA-16 of 90 A had a higher thermostability than the free enzyme, retaining 50% of its activity at 45°C after 187 h while the free enzyme was half-inactivated after 68 h. This could be due to the restricted movement of the immobilized enzyme confined in the pores of this material. In contrast, the immobilization in material with a larger pore of 117 A did not improve the thermostability of the enzyme, probably due to the fact that larger pores did not prevent the increased conformational flexibility of the enzyme at this temperature. 

Another limitation in the industrial application of peroxidases is the low stability to H202 (see Chap. 12). Here, an improvement for H202 inactivation through the physical immobilization of CPO on the mesoporous sieve SBA-15 of 130 A for the oxidation of indole to 2-oxoindole has been reported [8]. The performance of the immobilized enzyme was enhanced to that of the native CPO with respect to maximum conversion. According to the authors, the superior performance of... 

The interaction between biotin and avidin/SA is also used to immobilize DNA. Usually, avidin/SA is physically immobilized on the substrate, where the specific binding sites of avidin/SA allow the immobilization of biotinylated ssDNA as the probe [21-27]. It is of great advantage that a chemically stable DNA chip can be readily prepared by this technique. 

Either the CO2 formation is followed potemiometrically (243) or the O2 consumption is measured amperometrically at an oxygen electrode (245). In the first method, the enzyme is physically immobilized with a dialysis membrane. The response is linear in the range 5-300 pg/mL of salicylate. The second technique uses chemically immobilized enzyme (GA -F BSA) attached to a pig intestine mounted on the tip of the O 2 electrode. Samples containing from 10 pM to 2 mM salicylate were analyzed. An elegant microelectrode (244) has the enzyme and the cofactor immobilized in the electrode matrix (carbon paste) and the catechol formation is monitored at -F 300 mV versus Ag/AgCl. The electrode consists of a disposable strip, allowing measurements to be made on a drop of blood within 1 min. 

Organotransition metal complexes are physically immobilized on a solid when there is no direct covalent or ionic interaction between the complex and the sohd. The complex may, for example, be dissolved in a stationary phase on a solid or entrapped with a sohd matrix. 

Polymers can also be used for the physical immobilization of metal complexes. For example, the degree of swelling observed for 1% crosslinked polystyrene varies with solvents more swelling is observed in THF than in methanol. Thus, the cationic complex [(diphos)Rh(NBD)]PF6 can be adsorbed onto polystyrene in THF. When dried and extracted with methanol, the complex is bound within the polystyrene matrix. The immobilized complex is a catalyst for the hydrogenation of 1-hexene in methanol. ... 

Butadiene is polymerized by rhodium compounds in aqueous or alcoholic solution [178]. It is generally accepted that the active species is a TT-allyl rhodium complex of low valency [28, 179] which is not rapidly terminated by reaction with water or alcohol. No clear kinetic pattern was observed in the earlier papers but a recent investigation [180] has shown the rate and molecular weight data to be accommodated by a scheme involving monomer transfer and physical immobilization of the active centres in precipitated polymer. In the initial stages the polymerization is first order in rhodium and, at constant monomer concentration, is (pseudo) zero order E = 14.8 kcal mole" ). This is followed by a declining rate which is almost independent of temperature. Molecular weights rise slowly to a maximum value with time (ca. 4000 after 22 h at 70°C). 

Physical immobilization methods do not involve covalent bond formation with the enzyme, so that the native composition of the enzyme remains unaltered. Physical immobilization methods are subclassified as adsorption, entrapment, and encapsulation methods. Adsorption of proteins to the surface of a carrier is, in principle, reversible, but careful selection of the carrier material and the immobilization conditions can render desorption negligible. Entrapment of enzymes in a cross-linked polymer is accomplished by carrying out the polymerization reaction in the presence of enzyme the enzyme becomes trapped in interstitial spaces in the polymer matrix. Encapsulation of enzymes results in regions of high enzyme concentration being separated from the bulk solvent system by a semipermeable membrane, through which substrate, but not enzyme, may diffuse. Physical immobilization methods are represented in Figure 4.1 (c-e). 

The behavior of immobilized enzymes differs from that of dissolved enzymes because of the effects of the support material, or matrix, as well as conformational changes in the enzyme that result from interactions with the support and covalent modification of amino acid residues. Properties observed to change significantly upon immobilization include specific activity, pH optimum, Km, selectivity, and stability.23 Physical immobilization methods, especially entrapment and encapsulation, yield less dramatic changes in an enzyme s catalytic behavior than chemical immobilization methods or adsorption. The reason is that entrapment and encapsulation result in the enzyme remaining essentially in its native conformation, in a hydrophilic environment, with no covalent modification. 

FRRPP Physical immobilization of free radicals to reinitiate polymerization... 

The most convenient and most popular analytical methodology to assess enantiomer purity is the direct separation of enantiomers on so-called chiral stationary phases (CSPs). CSPs consist of an (ideally) inert chromatographic support matrix incorporating chemically or physically immobilized SO species. CSPs may be created by a variety of SO immobilization techniques, including (i) covalent attachment onto fhe surface of suitably pre-functionalized carrier materials, (ii) physical fixation employing coating techniques, and (iii) incorporation into polymeric networks by copolymerization, or combinations of these procedures. 

As it was difficult to bind MCLA covalently to polymer microsphere, physical immobilization was studied. Figure 1 shows the typical time course of the CL intensity of MCLA-ms dispersion compared with that of the filtrate of the same dispersion when incubated with the same ROS generator. The accumulated values of the CL intensity in these measurements are shown in Table 1. The ratio of the accumulated value of the filtrate to that of the dispersion was 2.6%. The desorption of MCLA from the carrier polymer microsphere can be substantially neglected, although very weak CL was observed due to slight desorption. 

Deterioration of gradients could be avoided by physical immobilization of the functional groups of the buffer. This has been accomplished in analytical gels (12) through the use of Innobilines (Tradename of LKB Produkter, A.B., Bronma, Sweden) but these have not yet found application in free solutions. 

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