Dynamic nuclear polarization for sensitivity enhancement in modern solid-state NMR.

Magnetic resonance (MR) is one of the most versatile and useful physical effects used for human imaging, chemical analysis, and the elucidation of molecular structures. However, its full potential is rarely used, because only a small fraction of the nuclear spin ensemble is polarized, that is, aligned with the applied static magnetic field. Hyperpolarization methods seek other means to increase the polarization and thus the MR signal. A unique source of pure spin order is the entangled singlet spin state of dihydrogen, parahydrogen (pH2 ), which is inherently stable and long-lived. When brought into contact with another molecule, this "spin order on demand" allows the MR signal to be enhanced by several orders of magnitude. Considerable progress has been made in the past decade in the area of pH2 -based hyperpolarization techniques for biomedical applications. It is the goal of this Review to provide a selective overview of these developments, covering the areas of spin physics, catalysis, instrumentation, preparation of the contrast agents, and applications.

Parahydrogen-Based Hyperpolarization for Biomedicine

Metallo-oxide (MO)-based bioinorganic nanocomposites promise unique structures, physicochemical properties, and novel biochemical functionalities, and within the past decade, investment in research on materials such as ZnO, TiO2, SiO2, and GeO2 has significantly increased. Besides traditional approaches, the synthesis, shaping, structural patterning, and postprocessing chemical functionalization of the materials surface is inspired by strategies which mimic processes in nature. Would such materials deliver new technologies? Answering this question requires the merging of historical knowledge and current research from different fields of science. Practically, we need an effective defragmentation of the research area. From our perspective, the superficial accounting of material properties, chemistry of the surfaces, and the behavior of biomolecules next to such surfaces is a problem. This is particularly of concern when we wish to bridge between technologies in vitro and biotechnologies in vivo. Further, be...

Interactions between Metal Oxides and Biomolecules: from Fundamental Understanding to Applications

Protein magic angle spinning (MAS) NMR spectroscopy has generated structural models of several amyloid fibril systems, thus providing valuable information regarding the forces and interactions that confer the extraordinary stability of the amyloid architecture. Despite these advances, however, obtaining atomic resolution information describing the higher levels of structural organization within the fibrils remains a significant challenge. Here, we detail MAS NMR experiments and sample labeling schemes designed specifically to probe such higher order amyloid structure, and we have applied them to the fibrils formed by an eleven-residue segment of the amyloidogenic protein transthyretin (TTR(105−115)). These experiments have allowed us to define unambiguously not only the arrangement of the peptide β-strands into β-sheets but also the β-sheet interfaces within each protofilament, and in addition to identify the nature of the protofilament-to-protofilament contacts that lead to the formation of the complete fibril. Our efforts have resulted in 111 quantitative distance and torsion angle restraints (10 per residue) that describe the various levels of structure organization. The experiments benefited extensively from the use of dynamic nuclear polarization (DNP), which in some cases allowed us to shorten the data acquisition time from days to hours and to improve significantly the signal-to-noise ratios of the spectra. The β-sheet interface and protofilament interactions identified here revealed local variations in the structure that result in multiple peaks for the exposed N- and C-termini of the peptide and in inhomogeneous line-broadening for the residues buried within the interior of the fibrils.

Higher Order Amyloid Fibril Structure by MAS NMR and DNP Spectroscopy

A novel series of hydrogen-bonded solid 1 : 1 acid–base complexes of 15N-labeled 2,4,6-trimethylpyridine (collidine) with carboxylic acids and their hydrogen bond deuterated analogs were synthesized and studied by 1H magic angle spinning (MAS) and 15N cross-polarization NMR with and without MAS. Not only zwitterionic complexes with the H-bond proton closer to nitrogen than to oxygen but also molecular complexes have been observed, where the proton is located closer to oxygen. For these complexes, the isotropic 1H and 15N chemical shifts and the 15N chemical shielding tensor elements were measured (the latter by lineshape simulation of the static powder spectra) as a function of the hydrogen bond geometry. For the deuterated analogs 1H/2H isotope effects on the isotropic 15N chemical shifts were obtained under MAS conditions. Lineshape simulations of the static 15N powder spectra revealed the dipolar 2H,15N couplings and hence the corresponding distances. The results reveal several hydrogen bond geometry–NMR parameter correlations which are analyzed in terms of the valence bond order model. (1) The collidine and apparently other pyridines isotropic 15N chemical shifts depend in a characteristic way on the nitrogen–hydrogen distance. This correlation can be used in the future to evaluate hydrogen bond geometries and solid-state acidities in more complicated systems. (2) A correlation of the 1H with the 15N isotropic chemical shifts is observed which corresponds to the well-known hydrogen bond geometry correlation indicating a strong decrease of the A· · ·B distance in an AHB hydrogen bond when the proton is shifted to the hydrogen bond center. This contraction is associated with a low-field 1H NMR chemical shift. (3) The 15N chemical shift anisotropy principal tensor elements dt, dr and d? (tangential, radial and perpendicular with respect to the pyridine ring) exhibit a linear relation with the isotropic 15N chemical shifts. A crossing point of dt = dr is observed. Further correlations of the hydrogen bond geometry with the geometric H/D isotope effects on the 15N chemical shifts and with the pKa values of the associated acids are reported. Copyright  2001 John Wiley & Sons, Ltd.

coupling and hydrogen bond geometry correlations in a novel series of hydrogen-bonded acid-base complexes of collidine with carboxylic acids

PHIP-label: parahydrogen-induced polarization in propargylglycine-containing synthetic oligopeptides

Synthesis and solid state NMR characterization of novel peptide/silica hybrid materials.

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PHIP-label: parahydrogen-induced polarization in propargylglycine-containing synthetic oligopeptides

Synthesis and solid state NMR characterization of novel peptide/silica hybrid materials.