The Chemical Reactivity of Sol−Gel Materials:  Hydrobromination of Ormosils

Frenkel-Mullerad, Hagit; Avnir, David

doi:10.1021/cm000516h

Cited by 35 publications

(29 citation statements)

References 23 publications

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“…Finally we note that the reaction between the olefin and the bromine solution yields the by-product, hydrobromic acid, which lowers the pH [22], and we already described protection against pH changes elsewhere [16].…”

Section: Exposure Of the Entrapped Enzyme To Bromine And Determinatiosupporting

confidence: 54%

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Frenkel-Mullerad

Ben-Knaz

Avnir

2014

J Sol-Gel Sci Technol

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Chemically reactive sol-gel matrices hold the ability of protecting entrapped enzymes from destruction by external harsh chemicals. We show this concept by exposing alkaline phosphatase (AlP) to a strong oxidizing agent-bromine. In solution, AlP is immediately destroyed by this oxidant. When AlP was entrapped in hybrid silica sol-gel materials carrying double bonds, the reactivity of AlP was preserved after exposure to bromine under conditions which totally destroy it in solution. The matrices studied were vinylated and allylated silicas, and their protectability was compared to n-alkylated silicas and to silica itself. For instance, the reactivity of AlP entrapped in allylated silica after exposure to 25.6 mM bromine solution is 40 times higher than its reactivity when entrapped in pure silica; and in solution the enzyme is totally destroyed at this concentration. Molecular level mechanisms for these observations are proposed.Keywords Sol-gel Á Sol-gel preserved enzymes Á Oxidizing agent Á Ormosil BackgroundAlkaline phosphatase (AlP), like most other enzymes, is totally destructed when exposed to a strong oxidant such as bromine. Here we show how to protect an enzyme when exposed to such conditions. We do so by using the sol-gel materials methodology for enzyme entrapment [1]. Sol-gel entrapped enzymes [2-4] have already been shown to provide significant thermal stability [5][6][7][8], stability to extreme pH values [9][10][11], and stability to non-native environments [12][13][14]. In these earlier studies the protectability was attributed to the encaging itself [15]; here we extend these observations by showing protection against an oxidant due to active chemical scavenging of the destructive chemical by the matrix. Thus when the enzyme is entrapped within sol-gel derived olefinated silicas, and then exposed to bromine solution, the double bonds react with the bromine, and protect the enzyme. By comparing this mode of protection to entrapments in non-reactive matrices-sol-gel derived silicas and sol-gel-derived alkylated silicas-we were able to evaluate the weights of the bromine scavenging and of the physical entrapment to the protection of the enzyme; we find that this relative weight depends on the alkyl and alkenyl chain. Thus, the hybrid sol-gel material we used was based on vinyl (CH 2 =CH-Si; VTS; here and below we use the name of the monomer as the name of the material), or allyl (CH 2 =CH-CH 2 -Si; ATS). In earlier studies we showed these olefinated sol-gel materials are highly reactive towards bromine, undergoing in water an hydrobromination reaction [16,17] which proceeds according to Markovnikov's rule [18], as shown in Scheme 1, resulting in a bromohydrin and HBr. The formation of an acid is an environmental change that the entrapped enzyme can withstand. We recall that we showed that sol-gel entrapped alkaline phosphataseThe online version of the original article can be found under

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Section: Exposure Of the Entrapped Enzyme To Bromine And Determinatiosupporting

confidence: 54%

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Frenkel-Mullerad

Ben-Knaz

Avnir

2014

J Sol-Gel Sci Technol

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“…[17] This conceptÐac-tivity enhancement by catalytic-site isolationÐwas recently shown to have a general validity in heterogeneous catalysis. [26] What happens during in the synthesis of organically modified sol±gel materials [27] is that, at the early stages of the sol±gel process, pseudomicellar aggregates rapidly form in which the R±Si(OH) 3 monomers generated in solution tend to arrange themselves with the polar ±Si(OH) 3 groups at the forefront of the growing sol±gel material and the hydrophobic non-polymerizable ±R residue orientating away from the interfacial, strongly hydrogen-bonding solvent (water/methanol). Thus, the hydrophobic organometallic catalyst is partly entrapped within the micellar core.…”

Section: Resultsmentioning

confidence: 99%

Dynamic Catalysis in Aerobic Oxidation by Sol-Gel Living Materials

Ciriminna¹,

Campestrini²,

Carraro³

et al. 2005

Adv. Funct. Mater.

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The catalytic activity of hybrid organic–inorganic silica glasses doped with the ruthenium species tetra‐n‐propylammonium perruthenate (TPAP) in the aerial oxidation of alcohols to carbonyl compounds, either in toluene or in dense‐phase CO2, substantially increases with time several months after the xerogels' preparation, yielding the most active ruthenium‐based aerobic‐oxidation catalysts reported thus far. The doped sol–gels are living materials, and an explanation of the observed reactivity enhancement is given, which is thought to have general validity for future applications to a wide variety of relevant heterogeneous processes.

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“…This observation can also be explained by the formation of micelle like structures in matrices with high iBu loadings [51], able to accommodate the organic dye. In this case, the photochromic molecules will be trapped in an environment with a much lower polarity.…”

Section: Dynamic Behavior Of the Photochromic Dye Embedded In Ormosilmentioning

confidence: 91%

Thin film photochromic materials: Effect of the sol-gel ormosil matrix on the photochromic properties of naphthopyrans

Pardo

Zayat

Lévy

2009

Comptes Rendus. Chimie

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The Chemical Reactivity of Sol−Gel Materials: Hydrobromination of Ormosils

Cited by 35 publications

References 23 publications

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Dynamic Catalysis in Aerobic Oxidation by Sol-Gel Living Materials

Thin film photochromic materials: Effect of the sol-gel ormosil matrix on the photochromic properties of naphthopyrans

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