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Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids.

ABSTRACT: We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D (13)C-(13)C exchange spectroscopy to probe the peptide backbone torsion angles (?, ?) in a series of selectively (13)C-labeled 40-residue ?-amyloid (A?(1-40)) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39 T and 8 K, using a static double-resonance NMR probe and low-power microwave irradiation at 264 GHz. In frozen solutions of A?(1-40) fibrils doped with DOTOPA-TEMPO, we observe DNP signal enhancement factors of 16-21. We show that the orientation- and frequency-dependent spin polarization exchange between sequential backbone carbonyl (13)C labels can be simulated accurately using a simple expression for the exchange rate, after experimentally determined homogeneous (13)C lineshapes are incorporated in the simulations. The experimental 2D (13)C-(13)C exchange spectra place constraints on the ? and ? angles between the two carbonyl labels. Although the data are not sufficient to determine ? and ? uniquely, the data do provide non-trivial constraints that could be included in structure calculations. With DNP at low temperatures, 2D (13)C-(13)C exchange spectra can be obtained from a 3.5 mg sample of A?(1-40) fibrils in 4 h or less, despite the broad (13)C chemical shift anisotropy line shapes that are observed in static samples.

SUBMITTER: Potapov A

PROVIDER: S-EPMC3660528 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids.

Potapov Alexey A Yau Wai-Ming WM Tycko Robert R

Journal of magnetic resonance (San Diego, Calif. : 1997) 20130227

We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D (13)C-(13)C exchange spectroscopy to probe the peptide backbone torsion angles (φ, ψ) in a series of selectively (13)C-labeled 40-residue β-amyloid (Aβ(1-40)) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39 T and 8 K, using a static double-resonance NMR prob ...[more]

PMID: 23562665

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Project description:Isotopic enrichment of 29Si and DNP-enhanced NMR spectroscopy are combined to determine the detailed surface structure of a silicated alumina catalyst. The significant sensitivity enhancement provided by DNP is vital to the acquisition of multinuclear and multidimensional experiments that provide information on the atomic-level structure of the species present at the surface. Isotopic enrichment not only facilitates spectral acquisition, particularly given the low (1.5 wt %) Si loading, but also enables spectra with higher resolution than those acquired using DNP to be obtained. The unexpected similarity of conventional, CP, and DNP NMR spectra is attributed to the presence of adventitious surface water that forms a sufficiently dense 1H network at the silica surface so as to mediate efficient polarization transfer to all Si species regardless of their chemical nature. Spectra reveal the presence of Si-O-Si linkages at the surface (identified as Q4(3Al)-Q4(3Al)) and confirm that the anchoring of the surface overlayer with the alumina occurs through AlIV and AlV species only. This suggests the presence of Q3/Q4 Si at the surface affects the neighboring Al species, modifying the surface structure and making it less likely AlVI environments are in close spatial proximity. In contrast, Q1/Q2 species, bonded to the surface by fewer covalent bonds, have less of an effect on the surface, and more AlVI species are consequently found nearby. The combination of isotropic enrichment and DNP provides a definitive and fully quantitative description of the Si-modified alumina surface, and we demonstrate that almost one-third of the silicon at the surface is connected to another Si species, even at the low level of coverage used, lowering the propensity for the formation of Brønsted acid sites. This suggests that a variation in the synthetic procedure might be required to obtain a more even coverage for optimum performance. The work here will allow for more rigorous future investigations of structure-function relationships in these complex materials.

Dataset Information

Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids.

Publications

Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids.

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