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Johnston C.T.,Purdue University | Premachandra G.S.,Purdue University | Szabo T.,University of Szeged | Lok J.,Purdue University | Schoonheydt R.A.,Center for Surface Science and Catalysis
Langmuir | Year: 2012

The interaction of hen egg white lysozyme (HEWL) with Na- and Cs-exchanged saponite was investigated using sorption, structural, and spectroscopic methods as a model system to study clay-protein interactions. HEWL sorption to Na- and Cs-saponite was determined using the bicinchoninic acid (BCA) assay, thermogravimetric analysis, and C and N analysis. For Na-saponite, the TGA and elemental analysis-derived sorption maximum was 600 mg/g corresponding to a surface coverage of 0.85 ng/mm 2 with HEWL occupying 526 m 2/g based on a cross-sectional area of 13.5 nm 2/molecule. HEWL sorption on Na-saponite was accompanied by the release of 9.5 Na + ions for every molecule of HEWL sorbed consistent with an ion exchange mechanism between the positively charged HEWL (IEP 11) and the negatively charged saponite surface. The d-spacing of the HEWL-Na-saponite complex increased to a value of 4.4 nm consistent with the crystallographic dimensions of HEWL of 3 × 3 × 4.5 nm. In the case of Cs-saponite, there was no evidence of interlayer sorption; however, sorption of HEWL to the "external" surface of Cs-saponite showed a high affinity isotherm. FTIR and Raman analysis of the amide I region of the HEWL-saponite films prepared from water and D 2O showed little perturbation to the secondary structure of the protein. The overall hydrophilic nature of the HEWL-Na-saponite complex was determined by water vapor sorption measurements. The clay retained its hydrophilic character with a water content of 18% at high humidity corresponding to 240 H 2O molecules per molecule of HEWL. © 2011 American Chemical Society.

Bota R.M.,Center for Surface Science and Catalysis | Houthoofd K.,Center for Surface Science and Catalysis | Grobet P.J.,Center for Surface Science and Catalysis | Jacobs P.A.,Center for Surface Science and Catalysis | Leuven K.U.,Center for Surface Science and Catalysis
Catalysis Today | Year: 2010

Mesoporous g-alumina because of its homogeneous pore size distribution, represents a good support for alkali metals. Controlled thermal decomposition of impregnated sodium azide on such support yields a superbasic catalyst for the double bond migration of vinylcyclohexane to ethylidene cyclohexane in continuous liquid flow operation. After slurry impregnation of the azide in methanol, 23Na MAS NMR shows the presence of resonance lines corresponding to Na metal particles and sodium oxide on the support. When dry mixing of the catalyst components is done, only supported sodium oxide is found, in association with decreased catalytic activity. It is concluded that both species are necessary components of the superbasic sites required for the isomerization reaction mentioned. In the transesterification of soybean oil with methanol in a batch reactor, the same differences in activity are encountered. The 23Na MAS NMR spectrum of the former catalyst remained unchanged after the transesterification reaction. © 2010 Elsevier B.V. All rights reserved.

Bajpe S.R.,Center for Surface Science and Catalysis | Breynaert E.,Center for Surface Science and Catalysis | Mustafa D.,Center for Surface Science and Catalysis | Jobbagy M.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | And 3 more authors.
Journal of Materials Chemistry | Year: 2011

HKUST-1 is one of the popular metal-organic frameworks (MOFs). The formation of this MOF is significantly accelerated by adding Keggin polyoxometalate anions to the synthesis solution. In this paper the chemistry behind this observation was investigated. Upon addition of Keggin type H 3PW12O40 heteropolyacid the speciation of Cu2+ cations in ethanol:H2O mixture drastically changes. Combining EPR and XANES measurements with accurate pH measurements and prediction of Cu2+ hydrolysis provides strong evidence for surface induced hydrolysis and consequent dimerisation of monomeric Cu2+ species on Keggin ions in acidic conditions. This enables paddle wheel formation, hence explaining the instantaneous precipitation of Cu 3(BTC)2 at room temperature and the systematic encapsulation of Keggin ions in its pores. © 2011 The Royal Society of Chemistry.

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