Dynamic nuclear polarization of spherical nanoparticles

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.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).DFG, GRK 1524, Self-Assembled Soft-Matter Nanostructures at Interface

Three-dimensional deuterium-carbon correlation experiments for high-resolution solid-state MAS NMR spectroscopy of large proteins

Well-resolved 2H-13C correlation spectra, reminiscent of 1H-13C correlations, are obtained for perdeuterated ubiquitin and for perdeuterated outer-membrane protein G (OmpG) from E. coli by exploiting the favorable lifetime of 2H double-quantum (DQ) states. Sufficient signal-to-noise was achieved due to the short deuterium T 1, allowing for high repetition rates and enabling 3D experiments with a 2H-13C transfer step in a reasonable time. Well-resolved 3D 2HDQ-13C-13C correlations of ubiquitin and OmpG were recorded within 3.5days each. An essentially complete assignment of 2HDQα shifts and of a substantial fraction of 2HDQβ shifts were obtained for ubiquitin. In the case of OmpG, 2HDQα and 2HDQβ chemical shifts of a considerable number of threonine, serine and leucine residues were assigned. This approach provides the basis for a general heteronuclear 3D MAS NMR assignment concept utilizing pulse sequences with 2HDQ-13C transfer steps and evolution of deuterium double-quantum chemical shift

In-Situ Bulk Polymerization of Dilute Particle/MMA Dispersions

Composites of poly(methyl methacrylate) and various nanoscale inorganic particles (zinc oxide, titanium dioxide, zirconium dioxide, silicon dioxide, and aluminum nitride) were prepared by in-situ bulk polymerization using 2,2‘-azobis(isobutyronitrile) as initiator. The particles of ZnO, TiO2, and ZrO2 were surface-modified by alkylphosphonic acids to render them dispersible in the monomer. The effect of these nanoparticles on the free radical polymerization was investigated. Regardless of chemical nature and size, the particles suppress the autoacceleration which would otherwise occur in the bulk free-radical polymerization of methyl methacrylate (MMA). A degenerative chain transfer is proposed to take place between surface-adsorbed water on the particles and propagating chain radicals. This reaction competes with normal termination. Formation of vinylidene chains ends originating from disproportionation is suppressed. In consequence, thermal stability of PMMA produced in the presence of particles is improved. Aggregation of individual particles upon polymerization has been observed and presumably is due to interparticle depletion attraction, even though the particles are individually dispersed in the monomer. Formation of particle clusters is suppressed when a difunctional monomer (e.g., ethylene glycol dimethacrylate) is used as comonomer. The cross-linked medium slows down the diffusion of the particles and therefore interferes with particle aggregation via a depletion mechanism

Surfactant-assisted formation of organophilic CeO2 nanoparticles

We report a simple one-pot method to prepare organically functionalized CeO 2 nanoparticles by controlled chemical precipitation. The particles were nucleated by mixing aqueous solutions of Ce(NO 3) 3·6H 2O and ammonia at room temperature. Different small organic molecules were chosen as capping agents and injected into the reaction medium at the beginning of the synthesis: 3-(mercaptopropyl) trimethoxy silane (MPS), hexadecyltrimethyl ammonium bromide (CTAB), 3-mercapto propionic acid (3-MPA), and thioglycolic acid (TGA). The resulting nanocrystals were quasi-spherical and had a narrow mean size distribution with an average size smaller than 10nm. Dynamic nuclear polarization enhanced NMR (DNP-NMR) and FTIR measurements suggested a chemical grafting of the surfactant and a homogeneous surface modification. The colloidal stabilities were characterized by dynamic light scattering and zeta potential measurements. The stabilization by aliphatic groups was tested with a frequently used hydrophobic monomer, methyl methacrylate. According to the results, CTAB is the most effective of the used stabilizing surfactant. The mechanism of formation of the organophilic CeO 2 nanoparticles is discussed.TÜBİTAK, project TBAG-109T90

Hyperpolarized MAS NMR of unfolded and misfolded proteins

In this article we give an overview over the use of DNP-enhanced solid-state NMR spectroscopy for the investigation of unfolded, disordered and misfolded proteins. We first provide an overview over studies in which DNP spectroscopy has successfully been applied for the structural investigation of well-folded amyloid fibrils formed by short peptides as well as full-length proteins. Sample cooling to cryogenic temperatures often leads to severe line-broadening of resonance signals and thus a loss in resolution. However, inhomogeneous line-broadening at low temperatures provides valuable information about residual dynamics and flexibility in proteins, and, in combination with appropriate selective isotope labeling techniques, inhomogeneous line-widths in disordered proteins or protein regions may be exploited for evaluation of conformational ensembles. In the last paragraph we highlight some recent studies where DNP-enhanced MAS-NMR-spectroscopy was applied to the study of disordered proteins/protein regions and inhomogeneous sample preparations

Structure, Organization and Dynamics of Functional Supramolecular Materials Studied by Solid-State NMR

I would like to thank my research supervisor, Prof. Hans Wolfgang Spiess for all of his inspiring advises and discussions. I sincerely thank my advisor Dr. Robert Graf for endless NMR explanation and helpful discussions about the projects. I would like to thank also to Prof. Ayhan Bozkurt, Prof. Bryan Coughlin, Dr. Sergio Granados-Focil, Prof. Virgil Percec and Prof. Peter Chu for supplying the samples and fruitful discussions which clarify many key points. I am grateful to all Spiess group members for supplying the friendly research environment. Also I would like to thank to my friends Mihael Mondeshki, Mustafa Diken, and Hamit Erdemi for their proof reading the text and for their support which I feel always. Finally, I am forever indebted to my parents Meliha and Duran and my brother Murat fo