Pascal Miéville

Surface Enhanced NMR Spectroscopy by Dynamic Nuclear Polarization

It is shown that surface NMR spectra can be greatly enhanced using dynamic nuclear polarization. Polarization is transferred from the protons of the solvent to the rare nuclei (here carbon-13 at natural isotopic abundance) at the surface, yielding at least a 50-fold signal enhancement for surface species covalently incorporated into a silica framework.

Fast Characterization of Functionalized Silica Materials by Silicon-29 Surface-Enhanced NMR Spectroscopy Using Dynamic Nuclear Polarization

We demonstrate fast characterization of the distribution of surface bonding modes and interactions in a series of functionalized materials via surface-enhanced nuclear magnetic resonance spectroscopy using dynamic nuclear polarization (DNP). Surface-enhanced silicon-29 DNP NMR spectra were obtained by using incipient wetness impregnation of the sample with a solution containing a polarizing radical (TOTAPOL). We identify and compare the bonding topology of functional groups in materials obtained via a sol-gel process and in materials prepared by post-grafting reactions. Furthermore, the remarkable gain in time provided by surface-enhanced silicon-29 DNP NMR spectroscopy (typically on the order of a factor 400) allows the facile acquisition of two-dimensional correlation spectra.

Dynamic nuclear polarization of quadrupolar nuclei using cross polarization from protons: surface-enhanced aluminium-27 NMR

The surface of γ-alumina nanoparticles can be characterized by dynamic nuclear polarization (DNP) surface-enhanced NMR of (27)Al. DNP is combined with cross-polarization and MQ-MAS to determine local symmetries of (27)Al sites at the surface.

Scavenging Free Radicals To Preserve Enhancement and Extend Relaxation Times in NMR using Dynamic Nuclear Polarization

This enhance-ment arises from thermal mixing, which is brought about bymicrowavesaturationoftheEPRtransitionsofstableradicalsthat are mixed with the sample under investigation beforefreezing. In dissolution DNP, the sample is usually polarizedat low temperatures and moderate magnetic fields (T=1.2 Kand B

Fractional Spin‐Labeling of Polymers for Enhancing NMR Sensitivity by Solvent‐Free Dynamic Nuclear Polarization

Keywords: cross polarization ; dynamic nuclear polarization ; magic angle spinning ; NMR spectroscopy ; peptides ; Range Structural Restraints ; Solid-State Nmr ; Proteins ; Spectroscopy Reference EPFL-ARTICLE-170435doi:10.1002/cphc.201100630View record in Web of Science Record created on 2011-11-29, modified on 2017-05-12

A magnetic tunnel to shelter hyperpolarized fluids

To shield solutions carrying hyperpolarized nuclear magnetization from rapid relaxation during transfer through low fields, the transfer duct can be threaded through an array of permanent magnets. The advantages are illustrated for solutions containing hyperpolarized (1)H and (13)C nuclei in a variety of molecules.

In-Vivo Detection and Tracking of T Cells in Various Organs in a Melanoma Tumor Model by 19F-Fluorine MRS/MRI.

Background 19F-MRI and 19F-MRS can identify specific cell types after in-vitro or in-vivo 19F-labeling. Knowledge on the potential to track in-vitro 19F-labeled immune cells in tumor models by 19F-MRI/MRS is scarce. Aim To study 19F-based MR techniques for in-vivo tracking of adoptively transferred immune cells after in-vitro 19F-labeling, i.e. to detect and monitor their migration non-invasively in melanoma-bearing mice. Methods Splenocytes (SP) were labeled in-vitro with a perfluorocarbon (PFC) and IV-injected into non-tumor bearing mice. In-vitro PFC-labeled ovalbumin (OVA)-specific T cells from the T cell receptor-transgenic line OT-1, activated with anti-CD3 and anti-CD28 antibodies (Tact) or OVA-peptide pulsed antigen presenting cells (TOVA-act), were injected into B16 OVA melanoma-bearing mice. The distribution of the 19F-labelled donor cells was determined in-vivo by 19F-MRI/MRS. In-vivo 19F-MRI/MRS results were confirmed by ex-vivo 19F-NMR and flow cytometry. Results SP, Tact, and TOVA-act were successfully PFC-labeled in-vitro yielding 3x1011-1.4x1012 19F-atoms/cell in the 3 groups. Adoptively transferred 19F-labeled SP, TOVA-act, and Tact were detected by coil-localized 19F-MRS in the chest, abdomen, and left flank in most animals (corresponding to lungs, livers, and spleens, respectively, with highest signal-to-noise for SP vs TOVA-act and Tact, p<0.009 for both). SP and Tact were successfully imaged by 19F-MRI (n = 3; liver). These in-vivo data were confirmed by ex-vivo high-resolution 19F-NMR-spectroscopy. By flow cytometric analysis, however, TOVA-act tended to be more abundant versus SP and Tact (liver: p = 0.1313; lungs: p = 0.1073; spleen: p = 0.109). Unlike 19F-MRI/MRS, flow cytometry also identified transferred immune cells (SP, Tact, and TOVA-act) in the tumors. Conclusion SP, Tact, and TOVA-act were successfully PFC-labeled in-vitro and detected in-vivo by non-invasive 19F-MRS/MRI in liver, lung, and spleen. The portion of 19F-labeled T cells in the adoptively transferred cell populations was insufficient for 19F-MRS/MRI detection in the tumor. While OVA-peptide-activated T cells (TOVA-act) showed highest infiltration into all organs, SP were detected more reliably by 19F-MRS/MRI, most likely explained by cell division of TOVA-act after injection, which dilutes the 19F content in the T cell-infiltrated organs. Non-dividing 19F-labeled cell species appear most promising to be tracked by 19F-MRS/MRI.

Filterable Agents for Hyperpolarization of Water, Metabolites, and Proteins.

Hyperpolarization is generated by dissolution dynamic nuclear polarization (d-DNP) using a polymer-based polarizing agent dubbed FLAP (filterable labeled agents for polarization). It consists of a thermo-responsive poly(N-isopropylacrylamide), also known as pNiPAM-COOH, labeled with nitroxide radicals. The polymer powder is impregnated with an arbitrary solution of interest and frozen as is. Dissolution is followed by a simple filtration, leading to hyperpolarized solutions free from any contaminants. We demonstrated the use of FLAP to hyperpolarize partially deuterated water up to P((1) H)=6 % with a long relaxation T1 >36 s characteristic of high purity. Water hyperpolarization can be transferred to drugs, metabolites, or proteins that are waiting in an NMR spectrometer, either by exchange of labile protons or through intermolecular Overhauser effects. We also show that FLAPs are suitable polarizing agents for (13) C-labeled metabolites such as pyruvate, acetate, and alanine.

A spinning thermometer to monitor microwave heating and glass transitions in dynamic nuclear polarization

As previously demonstrated by Thurber and Tycko, the peak position of 79Br in potassium bromide (KBr) allows one to determine the temperature of a spinning sample. We propose to adapt the original design by using a compact KBr tablet placed at the bottom of the magic angle spinning rotor, separated from the sample under investigation by a thin disk made of polytetrafluoroethylene (or ‘Teflon’®). This design allows spinning the sample up to at least 16 kHz. The KBr tablet can remain in the rotor when changing the sample under investigation. Calibration in the range of 98 < T < 320 K has been carried out in a static rotor by inserting a platinum thermometer. The accuracy is better than ± 0.9 K, even in the presence of microwave irradiation. Irradiation with 5 W microwaves at 263 GHz leads to a small temperature increase of 3.6 ± 1.4 K in either static or spinning samples. The dynamic nuclear polarization enhancement decreases with increasing temperature, in particular when a frozen glassy sample undergoes a glass transition. Copyright

Surface functionalization of alumina ceramic foams with organic ligands.

Different anchoring groups have been studied with the aim of covalently binding organic linkers to the surface of alumina ceramic foams. The results suggested that a higher degree of functionalization was achieved with a pyrogallol derivative--as compared to its catechol analogue--based on the XPS analysis of the ceramic surface. The conjugation of organic ligands to the surface of these alumina materials was corroborated by DNP-MAS NMR measurements.