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Development of a Combined DNP/EPR Spectrometer for the Investigation of Small Volume Samples by Solid State NMR.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Development of a Combined DNP/EPR Spectrometer for the Investigation of Small Volume Samples by Solid State NMR./
作者:	Carroll, Anne Munroe.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	175 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-08, Section: B.
Contained By:	Dissertations Abstracts International80-08B.
標題:	Physical chemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13841638
ISBN:	9780438902527

Development of a Combined DNP/EPR Spectrometer for the Investigation of Small Volume Samples by Solid State NMR.
Carroll, Anne Munroe.

Development of a Combined DNP/EPR Spectrometer for the Investigation of Small Volume Samples by Solid State NMR. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 175 p.

Source: Dissertations Abstracts International, Volume: 80-08, Section: B.

Thesis (Ph.D.)--Yale University, 2018.

This item must not be added to any third party search indexes.

Solid state nuclear magnetic resonance spectroscopy (ssNMR) is an important tool in the structural and dynamic studies of large bio-molecules, like proteins and nucleic acid chain. It offers a more adaptable sample environment than either solution NMR or X-ray crystallography. As researchers continue to look at more complex molecular systems, they require both better resolution and higher sensitivity. Unfortunately, the high dimension correlation spectra needed to resolve large molecules can take longer to acquire than the experiments can be stably maintained. Dynamic Nuclear Polarization (DNP) is a method of enhancing the NMR signal by transferring magnetization from unpaired electrons to the nuclei by exciting an electron paramagnetic resonance (EPR) transition. DNP instruments for magic angle spinning (MAS) ssNMR were introduced in the 1980s, and advancements in instrumentation, sample preparation, and theory have continued since. This dissertation presents the development and early optimization of a compact DNP instrument for the investigation of small samples in a 7 T magnet. Diode sources are the most compact and least expensive sources of the 198 GHz needed at excite EPR transitions at 7 T, but their low power output dictates careful optimization of the microwave path and sample geometry. In this work, a quasi-optical system has been used to transport the microwaves from the source to a corrugated waveguide and the sample at the center of the magnet. This system has low loss, can be rearranged and modified to optimize microwave transmission, and changes little with frequency within the 6 GHz range of the source. The capacity to sweep the microwave source has enabled the use of EPR as a time efficient method of system optimization. ERP saturation behavior also provides a quantitative metric of microwave transmission, unlike DNP enhancement. Early work focused on finding a suitable sample with which to test efficient transmission of microwaves. Common EPR samples, including DPPH, BDPA, and a crystal of perylene, were used to demonstrate the ability to perform resonator-free EPR, but were unsuitable for DNP. Synthetic high-pressure high-temperature (HPHT) diamond has proved to be a suitable sample on which to optimize both EPR and DNP. Single substituted nitrogen, called P1 centers, provide EPR active electrons as well as a source from which to polarize the 13C nuclei. The diamond's crystal structure produces long electron relaxation times, which enable EPR saturation and DNP enhancement at room temperature. With diamond as the test sample, several combined EPR/DNP probes were built. These probes, both static and magic angle spinning (MAS), incorporated a Bo-field modulation coil to enable EPR detecting on the same sample and configuration used for DNP. Optimizations into the MAS probes focused on the optical nature of the microwaves. Dielectric waveguides and lenses were designed to transmit and focus the microwaves into the small sample region, creating the high microwave intensity needed for EPR saturation. NMR coils were designed to take advantage of the microwave polarization in a novel fashion. The probe built with these innovations outperformed previous investigations of the direct DNP polarization of 13C nuclei. This dissertation is divided into six chapters. Chapter one gives important background in the field of solid state NMR in biological samples and the rise of DNP. Chapter two introduces much of the instrumentation of the current system, including the static EPR/DNP probe. The development of EPR detection, particularly the use of EPR saturation behavior as a metric of microwave intensity, is described in chapter three. Preliminary work with dielectric waveguide is illustrated in chapter four, while chapter five chronicles the development of the MAS probes capable of both EPR and DNP. Chapter six focuses on DNP results in diamond, concluding with a future goal for DNP sample preparation inspired by this work.

ISBN: 9780438902527Subjects--Topical Terms:

1981412
Physical chemistry.

Development of a Combined DNP/EPR Spectrometer for the Investigation of Small Volume Samples by Solid State NMR.
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506 $a This item must not be added to any third party search indexes.
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520 $a Solid state nuclear magnetic resonance spectroscopy (ssNMR) is an important tool in the structural and dynamic studies of large bio-molecules, like proteins and nucleic acid chain. It offers a more adaptable sample environment than either solution NMR or X-ray crystallography. As researchers continue to look at more complex molecular systems, they require both better resolution and higher sensitivity. Unfortunately, the high dimension correlation spectra needed to resolve large molecules can take longer to acquire than the experiments can be stably maintained. Dynamic Nuclear Polarization (DNP) is a method of enhancing the NMR signal by transferring magnetization from unpaired electrons to the nuclei by exciting an electron paramagnetic resonance (EPR) transition. DNP instruments for magic angle spinning (MAS) ssNMR were introduced in the 1980s, and advancements in instrumentation, sample preparation, and theory have continued since. This dissertation presents the development and early optimization of a compact DNP instrument for the investigation of small samples in a 7 T magnet. Diode sources are the most compact and least expensive sources of the 198 GHz needed at excite EPR transitions at 7 T, but their low power output dictates careful optimization of the microwave path and sample geometry. In this work, a quasi-optical system has been used to transport the microwaves from the source to a corrugated waveguide and the sample at the center of the magnet. This system has low loss, can be rearranged and modified to optimize microwave transmission, and changes little with frequency within the 6 GHz range of the source. The capacity to sweep the microwave source has enabled the use of EPR as a time efficient method of system optimization. ERP saturation behavior also provides a quantitative metric of microwave transmission, unlike DNP enhancement. Early work focused on finding a suitable sample with which to test efficient transmission of microwaves. Common EPR samples, including DPPH, BDPA, and a crystal of perylene, were used to demonstrate the ability to perform resonator-free EPR, but were unsuitable for DNP. Synthetic high-pressure high-temperature (HPHT) diamond has proved to be a suitable sample on which to optimize both EPR and DNP. Single substituted nitrogen, called P1 centers, provide EPR active electrons as well as a source from which to polarize the 13C nuclei. The diamond's crystal structure produces long electron relaxation times, which enable EPR saturation and DNP enhancement at room temperature. With diamond as the test sample, several combined EPR/DNP probes were built. These probes, both static and magic angle spinning (MAS), incorporated a Bo-field modulation coil to enable EPR detecting on the same sample and configuration used for DNP. Optimizations into the MAS probes focused on the optical nature of the microwaves. Dielectric waveguides and lenses were designed to transmit and focus the microwaves into the small sample region, creating the high microwave intensity needed for EPR saturation. NMR coils were designed to take advantage of the microwave polarization in a novel fashion. The probe built with these innovations outperformed previous investigations of the direct DNP polarization of 13C nuclei. This dissertation is divided into six chapters. Chapter one gives important background in the field of solid state NMR in biological samples and the rise of DNP. Chapter two introduces much of the instrumentation of the current system, including the static EPR/DNP probe. The development of EPR detection, particularly the use of EPR saturation behavior as a metric of microwave intensity, is described in chapter three. Preliminary work with dielectric waveguide is illustrated in chapter four, while chapter five chronicles the development of the MAS probes capable of both EPR and DNP. Chapter six focuses on DNP results in diamond, concluding with a future goal for DNP sample preparation inspired by this work.
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