Heteronuclear DNP of H and F nuclei using BDPA as a polarizing agent.

This work explores the dynamic nuclear polarization (DNP) of 1H and 19F nuclei in a sample of 25/75 (% v/v) fluorobenzene/toluene containing the radical 1,3-bisphenylene-2-phenylallyl radical (BDPA) as a polarizing agent. Previously, heteronuclear effects in DNP were studied by analysing the shapes of DNP spectra, or by observing cross-relaxation between nuclei of different types. In this work, we report a rather specific DNP spectrum, where 1H and 19F nuclei obtain polarizations of opposite signs upon microwave (MW) irradiation.

DNP-NMR of surface hydrogen on silicon microparticles.

Dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR) offers a promising route to studying local atomic environments at the surface of both crystalline and amorphous materials. We take advantage of unpaired electrons due to defects close to the surface of the silicon microparticles to hyperpolarize adjacent H nuclei. At 3.

Developing Mn-doped lead sulfide quantum dots for MRI labels.

Magnetic interactions of Mn ions in lead sulfide (PbS) nanocrystals with protons in water are probed by NMR and MRI. A thin layer of capping molecules enables free solvent diffusion to the nanocrystal surface resulting in a decrease of proton relaxation times. Magnetic resonance imaging of neuronal cell pellets exposed to (PbMn)S at non-toxic concentrations demonstrates their prospects as MRI-labels.

Solid effect DNP polarization dynamics in a system of many spins.

We discuss the polarization dynamics during solid effect dynamic nuclear polarization (DNP) in a central spin model that consists of an electron surrounded by many nuclei. To this end we use a recently developed formalism and validate first its performance by comparing its predictions to results obtained by solving the Liouville von Neumann master equation. The use of a Monte Carlo method in our formalism makes it possible to significantly increase the number of spins considered in the model system.

Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents.

Many approaches are now available for achieving high levels of nuclear spin polarization. One of these methods is based on the notion that as the temperature is reduced, the equilibrium nuclear polarization will increase, according to the Boltzmann distribution. The main problem with this approach is the length of time it may take to approach thermal equilibrium at low temperatures, since nuclear relaxation times (characterized by the spin-lattice relaxation time T1) can become very long.

Reliable gamma aminobutyric acid measurement using optimized PRESS at 3 T.

Gamma aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the central nervous system and there is strong interest in noninvasive measurement of GABA levels to assess GABAergic dysfunction in a number of psychiatric and neurological diseases. GABA detection by proton MR spectroscopy is challenging due to its low concentration as well as its strong overlap with more highly concentrated metabolites; therefore, editing techniques are typically required. In this study, the parameters of a standard point resolved spectroscopy (PRESS) sequence were optimized through repeated simulations to reliably and simultaneously detect GABA and glutamate at 3 T.

Preparation of highly polarized nuclear spin systems using brute-force and low-field thermal mixing.

Over the years, several strategies have been developed for generating highly polarized nuclear spin systems, including dynamic nuclear polarization, optical pumping, and methods exploiting parahydrogen. Here, we present an alternative strategy, using an enhanced 'brute-force' approach (i.e.

Conversion of parahydrogen induced longitudinal two-spin order to evenly distributed single spin polarisation by optimal control pulse sequences.

Strongly enhanced spin polarization in the form of longitudinal spin order can be generated on target molecules by using parahydrogen in a catalyzed hydrogenation reaction. An optimal control algorithm was used to generate radiofrequency pulse sequences which convert the arising longitudinal two-spin order into single-spin Zeeman order with high efficiency and distribute it evenly between three coupled spins within the same molecule. The pulses are designed to be very robust towards variations in the B(0) and B(1) fields.

Quantum mechanical simulation of solid effect dynamic nuclear polarisation using Krylov-Bogolyubov time averaging and a restricted state-space.

A strategy is described for simulations of solid effect dynamic nuclear polarisation that reduces substantially the dimension of the quantum mechanical problem. Averaging the Hamiltonian in the doubly rotating frame is used to confine the active space to the zero quantum coherence subspace. A further restriction of the Liouville space is made by truncating higher spin order states, which are weakly populated due to the presence of relaxation processes.

Quantifying the transfer and settling in NMR experiments with sample shuttling.

Nuclear magnetic resonance (NMR) in combination with pulsed magnetic field gradients has proven very successful for measuring molecular diffusion, where the correlation time of the motion is much shorter than the timescale of the experiment. In this article, it is demonstrated that a single-scan NMR technique to measure molecular diffusion can be employed to also study incoherent random motions over macroscopic length scales that show correlation times similar to the timescale of the experiment. Such motions are observed, for example, after the mixing of two components or after transferring a sample from one container into another.

A dedicated spectrometer for dissolution DNP NMR spectroscopy.

Using low temperature dynamic nuclear polarisation (DNP) in conjunction with dissolution makes it possible to generate highly polarised nuclear spin systems for liquid state applications of nuclear magnetic resonance spectroscopy. However, in its current implementation, which requires the transfer of the solute between two different magnets, the hyperpolarisation strategy is limited to spin systems with relatively long longitudinal relaxation time constants. Here we describe the design and construction of a dedicated spectrometer for DNP applications that is based on a magnet with two isocentres.

Slice-selective single scan proton COSY with dynamic nuclear polarisation.

Short acquisition time and single scan capability of gradient-assisted ultrafast multidimensional spectroscopy makes it possible to record 2D spectra of highly polarised spin systems in the liquid state using dynamic nuclear polarization (DNP) in conjunction with fast dissolution. We present a slice selective experiment, suitable for back-to-back acquisition of two independent single-scan 2D experiments from different sample volumes. This scheme maximizes the amount of information obtainable from a sample that is prepolarised with a non-repeatable DNP technique.

Symmetries of the master equation and long-lived states of nuclear spins.

In terms of the master equation of relaxation, long-lived states in systems of n interacting spin-1/2 nuclei are described as those with eigenvalues much less than the characteristic T(1) rate. It is demonstrated that degeneracies of correlations between interacting dipole-dipole pairs are responsible for their presence. The case n=3 is considered in full detail.

The transport of sugars to developing embryos is not via the bulk endosperm in oilseed rape seeds.

The fate of sucrose (Suc) supplied via the phloem to developing oilseed rape (Brassica napus) seeds has been investigated by supplying [(14)C]Suc to pedicels of detached, developing siliques. The method gives high, sustained rates of lipid synthesis in developing embryos within the silique comparable with those on the intact plant. At very early developmental stages (3 d after anthesis), the liquid fraction that occupies most of the interior of the seed has a very high hexose-to-Suc ratio and [(14)C]Suc entering the seeds is rapidly converted to hexoses.

Image-based characterization of foamed polymeric tissue scaffolds.

Tissue scaffolds are integral to many regenerative medicine therapies, providing suitable environments for tissue regeneration. In order to assess their suitability, methods to routinely and reproducibly characterize scaffolds are needed. Scaffold structures are typically complex, and thus their characterization is far from trivial.

A low-cost implementation of EPR detection in a dissolution DNP setup.

The implementation of electron paramagnetic resonance (EPR) detection in a low-temperature dissolution dynamic nuclear polarization (DNP) setup is presented. Using a coil oriented parallel to the static magnetic field, the change of the longitudinal magnetization of free radicals is measured upon resonant irradiation of an amplitude or frequency modulated microwave (mw) field. The absorption EPR spectrum is measured if the amplitude of the mw field is modulated, whilst the first derivative of the spectrum is obtained with frequency modulation.

Craniofacial growth in fetal Tarsius bancanus: brains, eyes and nasal septa.

The tarsier skull has been of particular interest in studies of primate taxonomy and functional morphology for several decades. Despite this, there remains no comprehensive data on how the tarsier skull develops, especially in relation to the soft-tissues of the head. Here we have documented for the first time fetal development of the skull and brain as well as the nasal septum and eyes in T.

Water mobility in the endosperm of high beta-glucan barley mutants as studied by nuclear magnetic resonance imaging.

(1)H NMR imaging (MRI) was used as a noninvasive technique to study water distribution and mobility in hydrated barley (Hordeum vulgare L.) seeds of accessions with varying content of beta glucan (BG), a highly hygroscopic cell wall component. High contents of BG in barley are unfavorable in malting where it leads to clotting of filters and hazing of beer as well as in animal feed where it hinders the rapid uptake of energy.

A simple approach for phase-modulated single-scan 2D NMR spectroscopy.

Conventional NMR spectroscopy techniques require long acquisition times due to the recovery time between the repeated excitations necessary for each increment of the evolution times in the indirectly detected dimensions. Here we outline a pulse sequence element for gradient-assisted ultrafast multidimensional NMR spectroscopy using frequency-modulated 'chirp' pulses to generate phase-modulated magnetization in an indirectly detected spectral dimension. The potential of this sequence element is demonstrated by acquiring a correlation spectroscopy (COSY) spectrum in 96 ms.

Investigating the coating-dependent release mechanism of a pulsatile capsule using NMR microscopy.

Chronopharmaceutical capsules, ethylcellulose-coated to prevent water ingress, exhibited clearly different release characteristics when coated by organic or aqueous processes. Organic-coated capsules produced a delayed pulse release, whereas aqueous-coated capsules exhibited less delayed and more erratic release behaviour. Nuclear magnetic resonance microscopy was used to elucidate the internal mechanisms underlying this behaviour by studying the routes of internal water transport and the timescale and sequence of events leading to the pulse.

Metabolizable and non-metabolizable sugars activate different signal transduction pathways in tomato.

To gain insight into the regulatory mechanisms of sugar signaling in plants, the effect of derivatives of the transport sugar sucrose (Suc), the Suc isomers palatinose and turanose, and the Suc analog fluoro-Suc were tested. Photo-autotrophic suspension culture cells of tomato (Lycopersicon peruvianum) were used to study their effect on the regulation of marker genes of source and sink metabolism, photosynthesis, and the activation of mitogen-activated protein kinases (MAPKs). Suc and glucose (Glc) resulted in reverse regulation of source and sink metabolism.

1H detected (13)C echo planar imaging.

Cyclic J cross polarisation (CYCLCROP) is a sensitive method for the noninvasive monitoring of (13)C distributions and fluxes. The PRAWN rotating frame Hartmann-Hahn mixing sequence ameliorates problems associated with sensitivity to Hartmann-Hahn mismatch and reduces RF power deposition. The combination of CYCLCROP with echo planar imaging (EPI) for spatial encoding of the proton detected carbon signal allows efficient use of the available signal to be made, permitting a significant improvement in the temporal resolution of any study.