Silica, immobilization

Synthetic approaches to silica-immobilized aminoalcohol ligands are reported in Scheme 58.310... 

A general review of synthesis and reactivity of silica-immobilized onium catalysts, which deals mainly with phosphonium salts, is available [42]. 

Another factor that remarkably affects the enantioresolution of given enantiomeric pairs has been shown to be the binding chemistry used for the silica immobilization of glycopeptides (see Section 2.2). This was illustrated in the case of ristocetin A, which was covalently bonded to silica microparticles by immobilization onto epoxy-activated silica under mild conditions [22], and compared with the corresponding commercially available CSP, where the macrocycle was immobilized as previously reported for vancomycin, rifamycin B, thiostrepton [7], and teicoplanin [30]. The comparison proved that immobilization of ristocetin A onto epoxy-activated silica could significantly improve the enantioselectivity and the resolution of the corresponding CSP in the separation of a-amino acids under RP conditions [22]. 

We attempted to improve the eatalytic performanee, including stability, of the silica-immobilized Co-POM catalysts by using hydrothermally stable supports, specifically, the mesostructured silicates SBA-15 and MCF, both modified with amino groups by grafting 3-aminopropyltrietoxysilane [97], The physico-chemical properties of three representative NH2-X (X = xerogel, SBA-15 and MSF) supported Co-POM catalysts are given in Table 1. The textural properties of the initial, POM-free supports are shown for comparison. 

Dezotti, M. Innocentini-Mei, L.H. Duran, N. Silica immobilized enzyme catalyzed removal of chlorolignins from eucalyptus Kraft effluent. J. Biotechnol. 1995, 43, 161-167. 

Figure 3. Comparison of pyrolysis products for silica-immobilized and liquid bibenzyl.

Figure 4. Radical chain propagation steps for the pyrolysis of silica-immobilized I, 3-diphenylpropane. Bracket notation denotes species exists in both gas-phase and surface-attached forms.

Duchateau, R. (2003) Silsesquioxanes advanced model supports in developing silica-immobilized polymerization catalysts, in Nanostructured Catalysts, Kluwer Academic/Plenum Publishers, New York, pp. 57-83. 

To illustrate adsorption on silica immobilization of Upases on macioporous silica will be described. 

Lindoy T F, Eaglen P. Ion Complexation by Silica-immobilized Polyethyleneimens, U.S. Patent 5,190,660, Awarded March 2,1993. 

McKittrick, M. W., Yu, K. Q. and Jones, C. W. Effect of metallation protocol on the preparation and performance of silica-immobilized TiCGC-inspired ethylene polymerization catalysts, J. Mol. Catal., A, 2005, 237, 26-35. 

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

Reinhard, S., Soba, P., Rominger, F., and Bluemel, J. (2003) New silica-immobilized nickel catalysts for cyclotrimerizations of acetylenes. Advanced Synthesis and Catalysis, 345, 589-602. 

Several different approaches to preconcentration and matrix elimination have been reported. A commercially available chelation system based on silica-immobilized 8-hydroxyquinoline has been used for on-line preconcentration and matrix separation [315,316]. Detection limits using a 90-fold concentration were 0.04 ng/dm3 for U to 6.3 ng/dm3 for Zn. 

FIGURE 31 A noncovalently silica-immobilized rhodium phosphine catalyst (720). 

R. K. Gilpin, S. E. Ethesham, and R. B. Gregory, Liquid chromatographic studies of the effect of temperature on the chiral recognition of tryptophan by silica-immobilized bovine albumine, A a/. Chem. 63 (1991), 2825. 

Yu K, Jones CW (2003) Silica-immobilized Zinc B-diiminate catalysts for the copolymerization of epoxides and carbon dioxide. OrganometaUics 22 2571... 

All silica immobilized phase transfer catalysts previously reported involve two or more steps for the immobilization. Problems with preparations of this type include the difficulty in obtaining maximum functionality on the substrate and residual substrate bond intermediates which may interfere in final applications. The purpose of this work was to prepare well-characterized functionalized phase transfer catalysts that could be immobilized on siliceous substrates in a single step. As will be shown the preparation of functionalized onium catalysts proceeds readily. The route to facile immobilization of crown ether was not so direct. Avenues for high yield chemistry employing accessible or economic intermediates were not available. A new class of crown ethers which are readily functionalized during synthesis was developed. We have designated than "silacrowns". This report concentrates upon the properties and characterization of these new phase transfer catalysts. 

Metathesis-based grafting techniques have already been successfully applied to the synthesis of other silica-based catalytic supports, e.g. those for heterogeneous ATRP[7, 18] as well as for heterogeneous Heck-type reactions[19]. This tempted us to investigate as to which extent these grafting techniques might be applied to the synthesis of silica-immobilized NHC-precursors. The x-ray structure of such a polymerizable NHC-precursor is shown in Fig. 2. 

Hermansson, J. Grahn, A. Resolution of racemic drugs on a new chiral column based on silica-immobilized cellobiohydrolase. Characterization of the basic properties of the column. J. Chromatogr., 1994, 687, 45-59 [chiral also acebutolol, atenolol, hetaxolol, bisoprolol, carbuterol, cathinone, dobutamine, dopropizine, epanolol, epinephrine, laudanosine, metanephrine, metoprolol, moprolol, norepinephrine, normetanephrine, octopamine, oxybutynine, pamatolol, practolol, prilocaine, propafenone, prox-yphylline, sotalol, talinolol, tetrahydropapaveroline, tetramisole, timolol, tolamolol, toliprolol]... 

M. A. Marshall, Silica-Immobilized 8-Quinolinol Synthesis, Characterization, and Applications in Flow Systems. Diss. Abstr. Int. B, 45 (1985) 3795. 

The PEG-PS supported BINAPs 113 and 115 were used as ligands for Rh-catalyzed asymmetric isomerizations, the metal complexes being formed in situ by reaction of the supported ligands with [Rh(cod)2] [CF3S03]. Both these and their silica-immobilized counterparts were found to be less reactive than their homogenous analogs... 

However, the facile isolation of metallo-silanols allows controlled condensation reactions with organochlorosilanes in the presence of an auxiliary base leading to transition metal substituted oligosiloxanes which can be considered as model compounds for silica-immobilized catalytic systems (Eq. 2a). 

Figure 18. Four possible routes used for preparing silica-immobilized transition metal complexes. [Adapted from (15).]...

ICP-MS is a powerful technique for multi-element trace determinations in water samples. However, its application to the analysis of saline waters is limited to those with dissolved solid contents below 0.2%. in order to avoid instrumental drifts caused by solid deposition on the orifice. The analysis of sea water therefore demands a separation of the salt matrix prior to determination by ICP-MS. Beauchmin and Berman [19] used an on-line column packed with silica immobilized quinolin-8-oI ion-exchanger to separate the matrix and determine Mn, Co, Ni. Cu. Pb and U in the standard reference open ocean water NASS-2 using an isotope dilution technique and a standard addition method. 

---