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Molecular Motion of Tethered Molecules in Bulk and Surface-Functionalized Materials: A Comparative Study of Confinement

Defreese, Jessica L. and Hwang, Son-Jong and Parra-Vasquez, A. Nicholas G. and Katz, Alexander (2006) Molecular Motion of Tethered Molecules in Bulk and Surface-Functionalized Materials: A Comparative Study of Confinement. Journal of the American Chemical Society, 128 (17). pp. 5687-5694. ISSN 0002-7863. doi:10.1021/ja0556474.

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Achieving high degrees of molecular confinement in materials is a difficult synthetic challenge that is critical for understanding supramolecular chemistry on solid surfaces and control of host−guest complexation for selective adsorption and heterogeneous catalysis. In this Article, using ^2H MAS NMR spectroscopy of tethered carbamates as a molecular probe, we systematically investigate the degree of steric confinement within three types of materials:  two-dimensional silica surface, bulk amorphous microporous silica, and bulk amorphous mesoporous silica. The resulting NMR spectra are described with a simple two-site hopping model for motion and prove that the bulk silica network severely limits the molecular mobility of the immobilized carbamate at room temperature to the same degree as surface-functionalized materials at low-temperatures (∼210 K). Raising the temperature of the bulk materials to 413 K still demonstrates the effect of confinement, as manifested in significantly longer characteristic times for the immobilized carbamate relative to surface-functionalized materials at room temperature. The environment surrounding the carbonyl functionality of the immobilized carbamate is investigated using FT-IR spectroscopy, which shows the carbonyl stretching band to be equally shifted for all materials to lower wavenumbers relative to its noninteracting value in carbon tetrachloride solvent. These results suggest that electrostatic interactions between the carbonyl of the immobilized carbamate and silica surface may play an important role in confining the immobilized carbamate and nucleating the formation of a pore wall close to the immobilized carbamate during bulk materials synthesis.

Item Type:Article
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URLURL TypeDescription Information
Hwang, Son-Jong0000-0002-3210-466X
Katz, Alexander0000-0003-3487-7049
Additional Information:© 2006 American Chemical Society. Received August 31, 2005. Publication Date (Web): April 7, 2006. We thank Dr. Maggy Hologne and Dr. Jerome Hirschinger at CNRS, Universite Louis Pasteur, France, and Dr. Sungsool Wi at Virgina Polytechnical Institute and State University for sharing ^2H MAS NMR simulation software. We gratefully acknowledge the National Science Foundation (CTS 0407478) for financial support, as well as a graduate research fellowship for J.L.D. S.-J.H. acknowledges the National Science Foundation under Grant Number 9724240 and the MRSEC Program of the National Science Foundation under Award Number DMR-0080065 for supporting the Caltech Solid State NMR facility.
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NSF Graduate Research FellowshipUNSPECIFIED
Issue or Number:17
Record Number:CaltechAUTHORS:20170510-103157513
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Official Citation:Molecular Motion of Tethered Molecules in Bulk and Surface-Functionalized Materials:  A Comparative Study of Confinement Jessica L. Defreese, Son-Jong Hwang, A. Nicholas G. Parra-Vasquez, and Alexander Katz Journal of the American Chemical Society 2006 128 (17), 5687-5694 DOI: 10.1021/ja0556474
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77340
Deposited By: Tony Diaz
Deposited On:16 May 2017 20:28
Last Modified:15 Nov 2021 17:30

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