Indirectly detected chemical shift correlation NMR spectroscopy in solids under fast magic angle spinning [electronic resource]

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Ngôn ngữ: eng

Ký hiệu phân loại: 621.36 Optical engineering

Thông tin xuất bản: Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2011

Mô tả vật lý: Size: 121 p. : , digital, PDF file.

Bộ sưu tập: Metadata

ID: 268530

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The development of fast magic angle spinning (MAS) opened up an opportunity for the indirect detection of insensitive low-? nuclei (e.g., 
13
C and 
15
N) via the sensitive high-{gamma} nuclei (e.g., 
1
H and 
19
F) in solid-state NMR, with advanced sensitivity and resolution. In this thesis, new methodology utilizing fast MAS is presented, including through-bond indirectly detected heteronuclear correlation (HETCOR) spectroscopy, which is assisted by multiple RF pulse sequences for 
1
H-
1
H homonuclear decoupling. Also presented is a simple new strategy for optimization of 
1
H-
1
H homonuclear decoupling. As applications, various classes of materials, such as catalytic nanoscale materials, biomolecules, and organic complexes, are studied by combining indirect detection and other one-dimensional (1D) and two-dimensional (2D) NMR techniques. Indirectly detected through-bond HETCOR spectroscopy utilizing refocused INEPT (INEPTR) mixing was developed under fast MAS (
- Chapter 2). The time performance of this approach in 
1
H detected 2D 
1
H{l_brace}
13
C{r_brace} spectra was significantly improved, by a factor of almost 10, compared to the traditional 
13
C detected experiments, as demonstrated by measuring naturally abundant organic-inorganic mesoporous hybrid materials. The through-bond scheme was demonstrated as a new analytical tool, which provides complementary structural information in solid-state systems in addition to through-space correlation. To further benefit the sensitivity of the INEPT transfer in rigid solids, the combined rotation and multiple-pulse spectroscopy (CRAMPS) was implemented for homonuclear 
1
H decoupling under fast MAS (
- Chapter 3). Several decoupling schemes (PMLG5
m

$\bar{x}$
, PMLG5
mm

$\bar{x}$x
and SAM3) were analyzed to maximize the performance of through-bond transfer based on decoupling efficiency as well as scaling factors. Indirect detection with assistance of PMLG
m

$\bar{x}$
during INEPTR transfer proved to offer the highest sensitivity gains of 3-10. In addition, the CRAMPS sequence was applied under fast MAS to increase the 
1
H resolution during t
1
evolution in the traditional, 
13
C detected HETCOR scheme. Two naturally abundant solids, tripeptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (f-MLF-OH) and brown coal, with well ordered and highly disordered structures, respectively, are studied to confirm the capabilities of these techniques. Concomitantly, a simple optimization of 
1
H homonuclear dipolar decoupling at MAS rates exceeding 10 kHz was developed (
- Chapter 4). The fine-tuned decoupling efficiency can be obtained by minimizing the signal loss due to transverse relaxation in a simple spin-echo experiment, using directly the sample of interest. The excellent agreement between observed decoupling pattern and earlier theoretical predictions confirmed the utility of this strategy. The properties of naturally abundant surface-bound fluorocarbon groups in mesoporous silica nanoparticles (MSNs) were investigated by the above-mentioned multidimensional solid-state NMR experiments and theoretical modeling (
- Chapter 5). Two conformations of (pentafluorophenyl)propyl groups (abbreviated as PFP) were determined as PFP-prone and PFP-upright, whose aromatic rings are located above the siloxane bridges and in roughly upright position, respectively. Several 1D and 2D NMR techniques were implemented in the characterizations, including indirectly detected 
1
H{l_brace}
13
C{r_brace} and 
19
F{l_brace}
13
C{r_brace} 2D HETCOR, Carr-Purcell-Meiboom-Gill (CPMG) assisted 
29
Si direct polarization and 
29
Si
19
F 2D experiments, 2D double-quantum (DQ) 
19
F MAS NMR spectra and spin-echo measurements. Furthermore, conformational details of two types of PFP were confirmed by theoretical calculation, operated by Dr. Takeshi Kobayashi. Finally, the arrangement of two surfactants, cetyltrimetylammoium bromide (CTAB) and cetylpyridinium bromide (CPB), mixed inside the MSN pores, was studied by solid-state NMR (
- Chapter 6). By analyzing the 
1
H-
1
H DQMAS and NOESY correlation spectra, the CTAB and CPB molecules were shown to co-exist inside the pores without forming significant monocomponent domains. A 'folded-over' conformation of CPB headgroups was proposed according to the results from 
1
H-
29
Si 2D HETCOR.

1. 01 coal, lignite, and peat
2. 36 materials science
3. Aromatics
4. Bromides
5. Brown coal

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