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Elucidating the binding mode of carboxylate-containing ligands to gold nanoparticles (AuNPs) is crucial to understand their stabilizing role. A detailed picture of the three-dimensional structure and coordination modes of citrate, acetate, succinate and glutarate to AuNPs is obtained by 13 C and 23 Na solid-state NMR in combination with computational modelling and electron microscopy. The binding between the carboxylates and the AuNP surface is found to occur in three different modes. These three modes are simultaneously present at low citrate to gold ratios, while a monocarboxylate monodentate (1 κO 1 ) mode is favoured at high citrate:gold ratios. The surface AuNP atoms are found to be predominantly in the zero oxidation state after citrate coordination, although trace amounts of Au δ + are observed. 23 Na NMR experiments show that Na + ions are present near the gold surface, indicating that carboxylate binding occurs as a 2e − L-type interaction for each oxygen atom involved. This approach has broad potential to probe the binding of a variety of ligands to metal nanoparticles. The manner in which carboxylates bind to the surface of nanoparticles has been an important question in materials science. Now, multinuclear magnetic resonance experiments — alongside DFT calculations, XPS and TEM measurements — have elucidated the three-dimensional ligand structures of gold nanoparticles capped with various ratios of carboxylate-containing ligands, and enabled the determination of the most probable binding modes.

Nuclear spin hyperpolarization of 13 C-labelled metabolites by dissolution dynamic nuclear polarization can enhance the NMR signals of metabolites by several orders of magnitude, which has enabled in vivo metabolic imaging by MRI. However, because of the short lifetime of the hyperpolarized magnetization (typically <1 min), the polarization process must be carried out close to the point of use. Here we introduce a concept that markedly extends hyperpolarization lifetimes and enables the transportation of hyperpolarized metabolites. The hyperpolarized sample can thus be removed from the polarizer and stored or transported for use at remote MRI or NMR sites. We show that hyperpolarization in alanine and glycine survives 16 h storage and transport, maintaining overall polarization enhancements of up to three orders of magnitude. MRI imaging can be significantly enhanced by injecting highly magnetized chemical agents, but the short magnetization lifetime requires processing at the point of use. Here, the authors demonstrate a method that could extend the lifetime from seconds to hours, enabling remote preparation.

Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by dissolution dynamic nuclear polarization (D-DNP) usually involves saturating the ESR transitions of polarizing agents (PAs; e.g., persistent radicals embedded in frozen glassy matrices). This approach has shown enormous potential to achieve greatly enhanced nuclear spin polarization, but the presence of PAs and/or glassing agents in the sample after dissolution can raise concerns for in vivo MRI applications, such as perturbing molecular interactions, and may induce the erosion of hyperpolarization in spectroscopy and MRI. We show that D-DNP can be performed efficiently with hybrid polarizing solids (HYPSOs) with 2,2,6,6-tetramethyl-piperidine-1-oxyl radicals incorporated in a mesostructured silica material and homogeneously distributed along its pore channels. The powder is wetted with a solution containing molecules of interest (for example, metabolites for MRS or MRI) to fill the pore channels (incipient wetness impregnation), and DNP is performed at low temperatures in a very efficient manner. This approach allows high polarization without the need for glass-forming agents and is applicable to a broad range of substrates, including peptides and metabolites. During dissolution, HYPSO is physically retained by simple filtration in the cryostat of the DNP polarizer, and a pure hyperpolarized solution is collected within a few seconds. The resulting solution contains the pure substrate, is free from any paramagnetic or other pollutants, and is ready for in vivo infusion. Significance Hyperpolarization by dissolution dynamic nuclear polarization can dramatically enhance signal intensities in MRI and NMR, notably for metabolic tracers for imaging and diagnosis. It is applicable to a variety of substrates for in vivo imaging and chemistry but requires the use of contaminants (glassing agents and free radicals) that may interact with cells and proteins and can have potential side effects. These contaminants can sometimes be eliminated by precipitation followed by filtration or solvent extraction, but these methods are substrate-specific, are usually time-consuming, and typically result in signal loss. Here, production of pure hyperpolarized liquids free of contaminants is shown by a simple wetting–polarization–filtration sequence for a solid silica matrix containing homogeneously distributed persistent radicals.

We have established Meloidogyne hapla as a tractable model plant-parasitic nematode amenable to forward and reverse genetics, and we present a complete genome sequence. At 54 Mbp, M. hapla represents not only the smallest nematode genome yet completed, but also the smallest metazoan, and defines a platform to elucidate mechanisms of parasitism by what is the largest uncontrolled group of plant pathogens worldwide. The M. hapla genome encodes significantly fewer genes than does the free-living nematode Caenorhabditis elegans (most notably through a reduction of odorant receptors and other gene families), yet it has acquired horizontally from other kingdoms numerous genes suspected to be involved in adaptations to parasitism. In some cases, amplification and tandem duplication have occurred with genes suspected of being acquired horizontally and involved in parasitism of plants. Although M. hapla and C. elegans diverged >500 million years ago, many developmental and biochemical pathways, including those for dauer formation and RNAi, are conserved. Although overall genome organization is not conserved, there are areas of microsynteny that may suggest a primary biological function in nematodes for those genes in these areas. This sequence and map represent a wealth of biological information on both the nature of nematode parasitism of plants and its evolution.