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Department of Chemical Biology
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    ABSTRACT: We present a highly sensitive nuclear-magnetic resonance technique to study membrane dynamics that combines the temporary encapsulation of spin-hyperpolarized xenon ((129)Xe) atoms in cryptophane-A-monoacid (CrAma) and their indirect detection through chemical exchange saturation transfer. Radiofrequency-labeled Xe@CrAma complexes exhibit characteristic differences in chemical exchange saturation transfer-driven depolarization when interacting with binary membrane models composed of different molecular ratios of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). The method is also applied to mixtures of cholesterol and POPC. The existence of domains that fluctuate in cluster size in DPPC/POPC models at a high (75-98%) DPPC content induces up to a fivefold increase in spin depolarization time τ at 297 K. In POPC/cholesterol model membranes, the parameter τ depends linearly on the cholesterol content at 310 K and allows us to determine the cholesterol content with an accuracy of at least 5%.
    Biophysical Journal 03/2014; 106(6):1301-8.
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    ABSTRACT: Spherical silica nanoparticles of various particle sizes (∼10 to 100 nm), produced by a modified Stoeber method employing amino acids as catalysts, are investigated using Dynamic Nuclear Polarization (DNP) enhanced Nuclear Magnetic Resonance (NMR) spectroscopy. This study includes ultra-sensitive detection of surface-bound amino acids and their supramolecular organization in trace amounts, exploiting the increase in NMR sensitivity of up to three orders of magnitude via DNP. Moreover, the nature of the silicon nuclei on the surface and the bulk silicon nuclei in the core (sub-surface) is characterized at atomic resolution. Thereby, we obtain unique insights into the surface chemistry of these nanoparticles, which might result in improving their rational design as required for promising applications, e.g. as catalysts or imaging contrast agents. The non-covalent binding of amino acids to surfaces was determined which shows that the amino acids not just function as catalysts but become incorporated into the nanoparticles during the formation process. As a result only three distinct Q-types of silica signals were observed from surface and core regions. We observed dramatic changes of DNP enhancements as a function of particle size, and very small particles (which suit in vivo applications better) were hyperpolarized with the best efficiency. Nearly one order of magnitude larger DNP enhancement was observed for nanoparticles with 13 nm size compared to particles with 100 nm size. We determined an approximate DNP penetration-depth (∼4.2 or ∼5.7 nm) for the polarization transfer from electrons to the nuclei of the spherical nanoparticles. Faster DNP polarization buildup was observed for larger nanoparticles. Efficient hyperpolarization of such nanoparticles, as achieved in this work, can be utilized in applications such as magnetic resonance imaging (MRI).
    Physical Chemistry Chemical Physics 11/2013;
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    ABSTRACT: Chemical Exchange Saturation Transfer (CEST) NMR is an increasingly used technique for generating molecule or microenvironment specific signal contrast. To characterize CEST agents and to extract parameters such as temperature and pH, it is often required to resolve the spectral dimension. This is achieved by recording so called CEST- or z-spectra, where the spectral CEST information is conventionally acquired point by point, leading to long acquisition times. Here, we employ gradient-encoding to substantially accelerate the acquisition process of z-spectra in phantom experiments, reducing it to only two scans. This speedup allows us to monitor dynamic processes such as rapid temperature changes in a PARACEST sample that would be inaccessible with the conventional encoding. Furthermore, we combine the gradient-encoding approach with multi-slice selection, thus reserving one spatial dimension for the simultaneous investigation of heterogeneous PARACEST sample packages within one experiment. Hence, gradient-encoded CEST might be of great use for high-throughput screening of CEST contrast agents.
    Journal of Magnetic Resonance 09/2013; 237C:34-39.


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Nature Cell Biology 03/2003; 5(2):126-36.
Proceedings of the National Academy of Sciences 08/2012; 109(35):14241-6.

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