Ionic immobilized

The regeneration of deactivated immobilized catalysts is not as easy as with conventional supported metal catalysts, where combustion of the deposited material is frequently used. Because such a procedure would destroy the organic ligands, one must resort to washing procedures. However, when this method fails, attempts must be made to recover the metal and the ligand, and to prepare a fresh catalyst. In principle, it is possible to recover the metal complexes from physically and ionically immobilized catalysts. This can also be done from covalently bound catalysts by using an easily hydrolyzable linker. 

The poly(sodium acrylate) hyperbranched graft formed in a simple deprotonation was used to ionically immobilize enzymes. Studies showed that immobihzed glucose oxidase in a 3-poly(sodium acrylate)/Au film retained significant activity on immobihzation and that the enzyme in this ionic assembly remained active for more than 60 days of storage [30]. 

Ionic immobilization of a Mn(lll)-salen complex in the pores of Al-MCM-41 has been reported by Hutchings and coworkers [98, 99]. The catalytically active species was formed in situ by the reaction of the ligand (R,Rj-3,5-di-tert-butylsalen with Mn -ion-exchanged Al-MCM-41. The efficacy of this material as a catalyst for the epoxidation of (Zj-stilbene using PhlO as the oxygen donor was then examined (stilbene PhlO catalyst = 7 1 0.13, 25°C, CH2CI2). When the [Mn(salen )]-Al-... 

Although each method has it own merits, in summary the ionic immobilization might be viewed as the method of choice if the system allows for its application, due to the ease of preparation and regeneration, particularly when thinking of continuous reactors with structured packings. 

Synthesis and Structure of Heparin-Containing Polymers 3.1 Ionic Immobilization... 

In summary, it must be noted that in spite of the wide-spread utility of the methods of ionic immobilization of heparin it is difficult to consider a long-term use of the resultant HCP. All of the reported results indicate that after the contact of HCPs with blood and other physiological media, heparin is qurite rapidly desorbed from the polymeric surface. This does not restrict the use of such heparin-containing polymers for the purposes of a short-term contact with blood. Today such materials are already used to manufacture catheters for perito-venous shunting in Japan, USA, France, and Sweden85 87). 

The thromboresistant properties of polystyrene with ionically immobilized heparin is unambiguously inferior compared to the covalently bound one. For instance, the blood clotting time for some of the covalently immobilized heparincontaining samples was up to 720 min, while for polystyrene, poly-p-aminostyrene, and polytrimethyl aminostyrene with electrostatically bound heparin the blood clotting time did not exceed 35 min. 

The second challenge is the passage through the mucus gel layer. Gl-epithelia are covered by a mucus gel layer, which is 80-200 pm in thickness. The viscosity of mucus affects the diffusion barrier. The presence of sulfate and sialic acid moieties in mucus causes a negative net charge. Hence, the diffusion barrier is even more pronounced for cationic nucleic acid/polymer complexes, which undergo ionical immobilization on the mucus. 

That ionic immobilization is strongly dependent on the pH value and salt concentrations during immobilization and of the reaction mixture in which the enzyme is used cannot be overemphasized. If these parameters are not taken into... 

Fig. 21.2 Nonferrocene diamine ligands (shown on the leji) can be anchored to the inner walls of mesoporous silica using either a covalent or an ionic immobilization approach (right)...

Other immobilization methods are based on chemical and physical binding to soHd supports, eg, polysaccharides, polymers, glass, and other chemically and physically stable materials, which are usually modified with functional groups such as amine, carboxy, epoxy, phenyl, or alkane to enable covalent coupling to amino acid side chains on the enzyme surface. These supports may be macroporous, with pore diameters in the range 30—300 nm, to facihtate accommodation of enzyme within a support particle. Ionic and nonionic adsorption to macroporous supports is a gentle, simple, and often efficient method. Use of powdered enzyme, or enzyme precipitated on inert supports, may be adequate for use in nonaqueous media. Entrapment in polysaccharide/polymer gels is used for both cells and isolated enzymes. 

We showed that these mesoporous silica materials, with variable pore sizes and susceptible surface areas for functionalization, can be utilized as good separation devices and immobilization for biomolecules, where the ones are sequestered and released depending on their size and charge, within the channels. Mesoporous silica with large-pore-size stmctures, are best suited for this purpose, since more molecules can be immobilized and the large porosity of the materials provide better access for the substrates to the immobilized molecules. The mechanism of bimolecular adsorption in the mesopore channels was suggested to be ionic interaction. On the first stage on the way of creation of chemical sensors on the basis of functionalized mesoporous silica materials for selective determination of herbicide in an environment was conducted research of sorption activity number of such materials in relation to 2,4-D. 

Fig. 10 shows the radial particle densities, electrolyte solutions in nonpolar pores. Fig. 11 the corresponding data for electrolyte solutions in functionalized pores with immobile point charges on the cylinder surface. All ion density profiles in the nonpolar pores show a clear preference for the interior of the pore. The ions avoid the pore surface, a consequence of the tendency to form complete hydration shells. The ionic distribution is analogous to the one of electrolytes near planar nonpolar surfaces or near the liquid/gas interface (vide supra). 

Immobilized ionic liquids Chloroaluminate ionic liquids on inorganic supports IGI, UK 2001 27... 

Transition metal catalysis in liquid/liquid biphasic systems principally requires sufficient solubility and immobilization of the catalysts in the IL phase relative to the extraction phase. Solubilization of metal ions in ILs can be separated into processes, involving the dissolution of simple metal salts (often through coordination with anions from the ionic liquid) and the dissolution of metal coordination complexes, in which the metal coordination sphere remains intact. 

The ability of iron(III) chloride genuinely to catalyze Friedel-Crafts acylation reactions has also been recognized by Holderich and co-workers [97]. By immobilizing the ionic liquid [BMIM]Cl/FeCl3 on a solid support, Holderich was able to acetylate mesitylene, anisole, and m-xylene with acetyl chloride in excellent yield. The performance of the iron-based ionic liquid was then compared with that of the corresponding chlorostannate(II) and chloroaluminate(III) ionic liquids. The results are given in Scheme 5.1-67 and Table 5.1-5. As can be seen, the iron catalyst gave superior results to the aluminium- or tin-based catalysts. The reactions were also carried out in the gas phase at between 200 and 300 °C. The acetylation reac-... 

Since no special ligand design is usually required to dissolve transition metal complexes in ionic liquids, the application of ionic ligands can be an extremely useful tool with which to immobilize the catalyst in the ionic medium. In applications in which the ionic catalyst layer is intensively extracted with a non-miscible solvent (i.e., under the conditions of biphasic catalysis or during product recovery by extraction) it is important to ensure that the amount of catalyst washed from the ionic liquid is extremely low. Full immobilization of the (often quite expensive) transition metal catalyst, combined with the possibility of recycling it, is usually a crucial criterion for the large-scale use of homogeneous catalysis (for more details see Section 5.3.5). 

It was recently found that the modification of neutral phosphine ligands with cationic phenylguanidinium groups represents a very powerful tool with which to immobilize Rh-complexes in ionic liquids such as [BMIM][PFg] [76]. The guani-dinium-modified triphenylphosphine ligand was prepared from the corresponding iodide salt by anion-exchange with [NH4][PFg] in aqueous solution, as shown in Scheme 5.2-15. The iodide can be prepared as previously described by Stelzer et al. [73]. 

While unmodified xanthene ligands (compound a in Figure 5.2-4) show highly preferential solubility in the organic phase in the biphasic l-octene/[BMIM][PFg] mixture even at room temperature, the application of the guanidinium-modified xanthene ligand (compound b in Figure 5.2-4) resulted in excellent immobilization of the Rh-catalyst in the ionic liquid. 

In comparison with traditional biphasic catalysis using water, fluorous phases, or polar organic solvents, transition metal catalysis in ionic liquids represents a new and advanced way to combine the specific advantages of homogeneous and heterogeneous catalysis. In many applications, the use of a defined transition metal complex immobilized on a ionic liquid support has already shown its unique potential. Many more successful examples - mainly in fine chemical synthesis - can be expected in the future as our loiowledge of ionic liquids and their interactions with transition metal complexes increases. 

Figure 5.4-3 shows the results of a lifetime study for Wilke s catalyst dissolved, activated, and immobilized in the [EMIM][(CF3S02)2N]/compressed CO2 system. Over a period of more than 61 h, the active catalyst showed remarkably stable activity while the enantioselectivity dropped only slightly. These results clearly indicate - at least for the hydrovinylation of styrene with Wilke s catalyst - that an ionic liquid catalyst solution can show excellent catalytic performance in continuous product extraction with compressed CO2. 

The combination of ionic liquids and compressed CO2 - at opposite extremes of the volatility and polarity scales - offers a new and intriguing immobilization technique for homogeneous catalysis. 

Ambient-temperature ionic liquids have received much attention in both academia and industry, due to their potential as replacements for volatile organic compounds (VOCs) [1-3]. These studies have utilized the ionic liquids as direct replacements for conventional solvents and as a method to immobilize transition metal catalysts in biphasic processes. 

The cationic nature of the copper(I) catalyst means that it is immobilized in the ionic liquid. This permits the PMMA product to be obtained, with negligible copper contamination, by a simple extraction procedure with toluene (in which the ionic liquid is not miscible) as the solvent. The ionic liquid/catalyst solution was subsequently reused. 

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