Proton-coupled carbon-13 sample spinning NMR studies of macromolecules and ordered systems
Chung, John
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/22541
Description
Title
Proton-coupled carbon-13 sample spinning NMR studies of macromolecules and ordered systems
Author(s)
Chung, John
Issue Date
1991
Doctoral Committee Chair(s)
Oldfield, Eric
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
"We have studied a variety of macromolecular systems such as lipid/water lyotropic phases and elastomeric polymers, and in addition a thermotropic liquid-crystal displaying macroscopic orientational ordering behavior, by Carbon-13 ($\sp{13}$C) nuclear magnetic resonance (NMR) spectroscopy. We find that under ""magic angle"" spinning (MAS) these systems display high resolution due to extensive motions, and therefore traditional proton-decoupling is not necessary. In the absence of proton decoupling, i.e., proton-coupled MAS (PCMAS), we find that these systems display scalar hyperfine-coupled $\sp{13}$C splittings with radically asymmetric linewidths and shapes. We attribute these effects to cross-correlation terms between two or more different relaxation mechanisms, (dipolar/chemical shift anisotropy (DD/CSA) relaxations) at the high magnetic fields employed."
Since the DD/CSA effects are quite novel and have not been treated in detail experimentally or theoretically, we have extended the previous theories to a more realistic anisotropic motional model and have attempted to explain the proton-coupled $\sp{13}$C longitudinal relaxation data in two elastomers by fitting it to the simple model. The data does not explain the model in an intuitively reasonable fashion; and it is concluded that more work needs to be done in order to study a system with more experimental measurables which would allow for fitting to a more elaborate theory of restricted motions.
"We have also tried to extend the usefulness of PC-MAS relaxation cross-correlation study to a thermotropic liquid crystal; and in the process we have determined the effects which sample spinning in a magnetic field can have on an ordered phase such as the nematic phase of a liquid crystal. Our findings indicate that rapid spinning of the sample can lead to destruction of the macroscopic order-director alignment along the sample spinner axis. In order to avoid this difficulty ""off-axis"" spinning experiments are done to show that the stability of the order director can be maintained. With the added precaution we show that proton-coupled $\sp{13}$C relaxation study is feasible in the nematic phase; and from the measured relaxation time constants we obtain macroscopic cross-correlation spectral densities, although the interpretation of these spectral densities is dependent on the of knowledge of the accurate static tensor elements."
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
