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NMR study of proton transfer to strong bases on inner surfaces of MCM-41

Ip, B. C. K. and Andreeva, D. V. and Buntkowsky, G. and Akcakayiran, D. and Findenegg, G. H. and Shenderovich, I. G. (2010):
NMR study of proton transfer to strong bases on inner surfaces of MCM-41.
In: Microporous and Mesoporous Materials, pp. 22-28, 134, (1-3), [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

Variable temperature (1)H and (15)N NMR techniques have been used to study the interaction of (15)N enriched 4-dimethylaminopyridine (AP) and 4-diethyl-2,6-di-tert-butylaminopyridine (TBAP) with the surface of MCM-41 silica Both bases become protonated on the surface. AP-H(+) and TBAP-H(+) remain immobilized on the surface at room temperature, but are free to rotate around the molecular C(2) axis The concentration of the protonated species is not affected by the presence of water and water is not involved in or coordinated around the protonated species We propose that strong electrostatic interactions can affect the local structure of the inner surfaces of MCM-41 that result in mutual interactions of neighboring silanol groups which enables proton transfer to the guests There are good reasons to suggest that three surface silanol groups are involved in each cluster with one protonated base The N H distance in the AP-H(+) cation is lengthened by a hydrogen bond to the deprotonated silanol group The N H distance in the TBAP-H(+) cation is shorter and the interaction to the anion is purely electrostatic. In the presence of water and an excess of AP, 2.1 AP, water complexes are formed, with one water bonded between two bases and the N H distances of about 1 7 angstrom. The reorientation of these complexes and the molecular exchange among different species are slow at room temperature. TBAP does not interact with water on the silica surface (C) 2010 Elsevier Inc. All rights reserved

Item Type: Article
Erschienen: 2010
Creators: Ip, B. C. K. and Andreeva, D. V. and Buntkowsky, G. and Akcakayiran, D. and Findenegg, G. H. and Shenderovich, I. G.
Title: NMR study of proton transfer to strong bases on inner surfaces of MCM-41
Language: English
Abstract:

Variable temperature (1)H and (15)N NMR techniques have been used to study the interaction of (15)N enriched 4-dimethylaminopyridine (AP) and 4-diethyl-2,6-di-tert-butylaminopyridine (TBAP) with the surface of MCM-41 silica Both bases become protonated on the surface. AP-H(+) and TBAP-H(+) remain immobilized on the surface at room temperature, but are free to rotate around the molecular C(2) axis The concentration of the protonated species is not affected by the presence of water and water is not involved in or coordinated around the protonated species We propose that strong electrostatic interactions can affect the local structure of the inner surfaces of MCM-41 that result in mutual interactions of neighboring silanol groups which enables proton transfer to the guests There are good reasons to suggest that three surface silanol groups are involved in each cluster with one protonated base The N H distance in the AP-H(+) cation is lengthened by a hydrogen bond to the deprotonated silanol group The N H distance in the TBAP-H(+) cation is shorter and the interaction to the anion is purely electrostatic. In the presence of water and an excess of AP, 2.1 AP, water complexes are formed, with one water bonded between two bases and the N H distances of about 1 7 angstrom. The reorientation of these complexes and the molecular exchange among different species are slow at room temperature. TBAP does not interact with water on the silica surface (C) 2010 Elsevier Inc. All rights reserved

Journal or Publication Title: Microporous and Mesoporous Materials
Volume: 134
Number: 1-3
Uncontrolled Keywords: hydrogen bond proton transfer nmr spectroscopy mcm-41 host-guest systems mesoporous silica materials hydrogen-bonded complexes water pyridine catalysts sba-15 diffusion acidity sites metal
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:50
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
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633OO Times Cited:11 Cited References Count:41

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