Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance
In the first part of the dissertation, spider dragline silk is studied by solid state NMR techniques. The dependence of NMR frequency on molecular orientation is exploited using the DECODER experiment to determine the orientation of the protein backbone within the silk fibre. Practical experiment...
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ndltd-UBC-oai-circle.library.ubc.ca-2429-171232018-01-05T17:38:44Z Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance Eles, Philip Thomas In the first part of the dissertation, spider dragline silk is studied by solid state NMR techniques. The dependence of NMR frequency on molecular orientation is exploited using the DECODER experiment to determine the orientation of the protein backbone within the silk fibre. Practical experimental considerations require that the silk fibres be wound about a cylindrical axis perpendicular to the external magnetic field, complicating the reconstruction of the underlying orientation distribution and necess-itating the development of numerical techniques for this purpose. A two-component model of silk incorporating static b-sheets and polyglycine II helices adequately fits the NMR data and suggests that the b-sheets are well aligned along the silk axis (20 FWHM) while the helices are poorly aligned (68 FWHM). The effects of fibre strain, draw rate and hydration on orientation are measured. Measurements of the time-scale for peptide backbone motion indicate that when wet, a strain-dependent frac-tion of the poorly aligned component becomes mobile. This suggests a mechanism for the supercontraction of silk involving latent entropic springs that undergo a local straindependent phase transition, driving supercontraction. In the second part of this dissertation a novel method is developed for exciting NMR and nuclear quadrupole resonance (NQR) by rf irradiation at multiple frequencies that sum to (or differ by) the resonance frequency. This is fundamentally different than traditional NMR experiments where irradiation is applied on-resonance. With excitation outside the detection bandwidth, two-photon excitation allows for detection of free induction signals during excitation, completely eliminating receiver dead-time. A theoretical approach to describing two-photon excitation is developed based on average Hamiltonian theory. An intuition for two-photon excitation is gained by analogy to the coherent absorption of multiple photons requiring conservation of total energy and momentum. It is shown that two-photon excitation efficiency impro-ves when the two applied rf frequencies deviate from half-resonance. For two-photon NQR, it is shown that observable magnetization appears perpendicular to the excita-tion coil, requiring a second coil for detection, and that double quantum coherences are also generated. Several model systems and experimental geometries are used to demonstrate the peculiarities of two-photon excitation in NMR and NQR. Science, Faculty of Physics and Astronomy, Department of Graduate 2009-12-23T00:55:33Z 2009-12-23T00:55:33Z 2005 2005-11 Text Thesis/Dissertation http://hdl.handle.net/2429/17123 eng For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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NDLTD |
language |
English |
sources |
NDLTD |
description |
In the first part of the dissertation, spider dragline silk is studied by solid state NMR techniques.
The dependence of NMR frequency on molecular orientation is exploited using the
DECODER experiment to determine the orientation of the protein backbone within the silk
fibre. Practical experimental considerations require that the silk fibres be wound about a
cylindrical axis perpendicular to the external magnetic field, complicating the reconstruction
of the underlying orientation distribution and necess-itating the development of numerical
techniques for this purpose. A two-component model of silk incorporating static b-sheets and
polyglycine II helices adequately fits the NMR data and suggests that the b-sheets are well
aligned along the silk axis (20 FWHM) while the helices are poorly aligned (68 FWHM). The
effects of fibre strain, draw rate and hydration on orientation are measured. Measurements
of the time-scale for peptide backbone motion indicate that when wet, a strain-dependent
frac-tion of the poorly aligned component becomes mobile. This suggests a mechanism for
the supercontraction of silk involving latent entropic springs that undergo a local straindependent
phase transition, driving supercontraction.
In the second part of this dissertation a novel method is developed for exciting NMR and
nuclear quadrupole resonance (NQR) by rf irradiation at multiple frequencies that sum to
(or differ by) the resonance frequency. This is fundamentally different than traditional NMR
experiments where irradiation is applied on-resonance. With excitation outside the detection
bandwidth, two-photon excitation allows for detection of free induction signals during
excitation, completely eliminating receiver dead-time. A theoretical approach to describing
two-photon excitation is developed based on average Hamiltonian theory. An intuition for
two-photon excitation is gained by analogy to the coherent absorption of multiple photons
requiring conservation of total energy and momentum. It is shown that two-photon excitation
efficiency impro-ves when the two applied rf frequencies deviate from half-resonance.
For two-photon NQR, it is shown that observable magnetization appears perpendicular to
the excita-tion coil, requiring a second coil for detection, and that double quantum coherences
are also generated. Several model systems and experimental geometries are used to
demonstrate the peculiarities of two-photon excitation in NMR and NQR. === Science, Faculty of === Physics and Astronomy, Department of === Graduate |
author |
Eles, Philip Thomas |
spellingShingle |
Eles, Philip Thomas Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
author_facet |
Eles, Philip Thomas |
author_sort |
Eles, Philip Thomas |
title |
Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
title_short |
Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
title_full |
Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
title_fullStr |
Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
title_full_unstemmed |
Peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
title_sort |
peptide backbone orientation and dynamics in spider dragline silk and two-photon excitation in nuclear magnetic and quadrupole resonance |
publishDate |
2009 |
url |
http://hdl.handle.net/2429/17123 |
work_keys_str_mv |
AT elesphilipthomas peptidebackboneorientationanddynamicsinspiderdraglinesilkandtwophotonexcitationinnuclearmagneticandquadrupoleresonance |
_version_ |
1718590441861939200 |