Humidity-modulated phase control and nanoscopic transport in supramolecular assemblies.

Supramolecular assembly allows for enhanced control of bulk material properties through the fine modulation of intermolecular interactions. We present a comprehensive study of a cross-linkable amphiphilic wedge molecule based on a sulfonated trialkoxybenzene with a sodium counterion that forms liquid crystalline (LC) phases with ionic nanochannel structures. This compound exhibits drastic structural changes as a function of relative humidity (RH).

Cation and anion transport in a dicationic imidazolium-based plastic crystal ion conductor.

Here we investigate the organic ionic plastic crystal 1,2-bis[N-(N'-hexylimidazolium-d2(4,5))]ethane 2PF6(-) in one of its solid plastic crystal phases by means of multinuclear solid-state (SS) NMR and pulsed-field-gradient NMR diffusometry. We quantify distinct cation and anion diffusion coefficients as well as the Arrhenius diffusion activation energies (Ea) in this dicationic imidazolium-based plastic crystal. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.

Unraveling the local energetics of transport in a polymer ion conductor.

We compare diffusion activation energy measurements in a hydrated perfluorosulfonate ionomer and aqueous solutions of triflic acid. These measurements provide insight into water transport dynamics on sub-nm length scales, and gauge the contribution of the polymer sidechain terminal group. Future membrane materials design will hinge on detailed understanding of transport dynamics.

Hyperpolarized water as an MR imaging contrast agent: feasibility of in vivo imaging in a rat model.

Purpose: To assess the feasibility of a perfusion magnetic resonance (MR) imaging technique that uses Overhauser dynamic nuclear polarization (DNP) to provide contrast during the continuous delivery of hyperpolarized water in rats.

Materials And Methods: Protocols approved by the local institutional animal care and use committees were followed. Twelve male Wistar rats were anesthetized and prepared by placing injection tubing in the subcutaneous layer (n=3), peritoneum (n=3), aorta (n=3), or carotid artery (n=3).

Overhauser dynamic nuclear polarization amplification of NMR flow imaging.

We describe the first study comparing the ability of phase shift velocity imaging and Overhauser dynamic nuclear polarization (DNP)-enhanced imaging to generate contrast for visualizing the flow of water. Prepolarization of water by the Overhauser DNP mechanism is performed in the 0.35T fringe field of an unshielded 2.

Continuous flow Overhauser dynamic nuclear polarization of water in the fringe field of a clinical magnetic resonance imaging system for authentic image contrast.

We describe and demonstrate a system to generate hyperpolarized water in the 0.35 T fringe field of a clinical 1.5 T whole-body magnetic resonance imaging (MRI) magnet.

Heisenberg spin exchange effects of nitroxide radicals on Overhauser dynamic nuclear polarization in the low field limit at 1.5mT.

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) at very low magnetic fields (0.05-20mT) have gained interest due to the simple and portable magnet design and newly emerging applications outside of the usual laboratory setting. A method to enhance the NMR signal is needed due to the low thermal polarization of nuclear spins at these fields; dynamic nuclear polarization (DNP) via the Overhauser effect from free radicals is an attractive option.

Dynamic nuclear polarization of 13C in aqueous solutions under ambient conditions.

The direct enhancement of the (13)C NMR signal of small molecules in solution through Overhauser-mediated dynamic nuclear polarization (DNP) has the potential to enable studies of systems where enhanced signal is needed but the current dissolution DNP approach is not suitable, for instance if the sample does not tolerate a freeze-thaw process or if continuous flow or rapid re-polarization of the molecules is desired. We present systematic studies of the (13)C DNP enhancement of (13)C-labeled small molecules in aqueous solution under ambient conditions, where we observe both dipolar and scalar-mediated enhancement. We show the role of the three-spin effects from enhanced protons on (13)C DNP through DNP experiments with and without broadband (1)H decoupling and by comparing DNP results with H(2)O and D(2)O.

Portable X-band system for solution state dynamic nuclear polarization.

This paper concerns instrumental approaches to obtain large dynamic nuclear polarization (DNP) enhancements in a completely portable system. We show that at fields of 0.35 T under ambient conditions and at X-band frequencies, 1H enhancements of >100-fold can be achieved using nitroxide radical systems, which is near the theoretical maximum for 1H polarization using the Overhauser effect at this field.

Hyperpolarized water as an authentic magnetic resonance imaging contrast agent.

Pure water in a highly (1)H spin-polarized state is proposed as a contrast-agent-free contrast agent to visualize its macroscopic evolution in aqueous media by MRI. Remotely enhanced liquids for image contrast (RELIC) utilizes a (1)H signal of water that is enhanced outside the sample in continuous-flow mode and immediately delivered to the sample to obtain maximum contrast between entering and bulk fluids. Hyperpolarization suggests an ideal contrast mechanism to highlight the ubiquitous and specific function of water in physiology, biology, and materials because the physiological, chemical, and macroscopic function of water is not altered by the degree of magnetization.