A series of seven functionalized nitroxide biradicals (the bTbK biradical and six derivatives) are investigated as exogenous polarization sources for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and with ca. 100 K sample temperatures. The impact of electron relaxation times on the DNP enhancement (ε) is examined, and we observe that longer inversion recovery and phase memory relaxation times provide larger ε. All radicals are tested in both bulk 1,1,2,2-tetrachloroethane solutions and in mesoporous materials, and the difference in ε between the two cases is discussed. The impact of the sample temperature and magic angle spinning frequency on ε is investigated for several radicals each characterized by a range of electron relaxation times. In particular, TEKPol, a bulky derivative of bTbK with a molecular weight of 905 g·mol(-1), is presented. Its high-saturation factor makes it a very efficient polarizing agent for DNP, yielding unprecedented proton enhancements of over 200 in both bulk and materials samples at 9.4 T and 100 K. TEKPol also yields encouraging enhancements of 33 at 180 K and 12 at 200 K, suggesting that with the continued improvement of radicals large ε may be obtained at higher temperatures.

International audienceWell polarized: Two new polarizing agents PyPol and AMUPol soluble in glycerol/water mixtures are used for dynamic nuclear polarization (DNP) NMR spectroscopy. The enhancement factors (ε) are about 3.5 to 4 times larger than for the established agent TOTAPOL at 263 and 395 GHz. For AMUPol, the temperature dependence of ε allows DNP experiments to be performed at temperatures significantly higher than for typical high-field DNP NMR experiments

Ibuprofen (an anti-inflammatory drug that is a crystalline solid at ambient temperature) has been encapsulated in MCM-41 silica matrices with different pore diameters (35 and 116 Å). Its behavior has been investigated by magic angle spinning (MAS) 1H, 13C, and 29Si solid-state NMR spectroscopy at ambient and low temperature. This study reveals an original physical state of the drug in such materials. At ambient temperature, ibuprofen is not in a solid state (crystalline or amorphous) and is extremely mobile inside the pores, with higher mobility in the largest pores (116 Å). The interaction between ibuprofen and the silica surface is weak, which favors fast drug release from this material in a simulated intestinal or gastric fluid. The quasi-liquid behavior of ibuprofen allows the use of NMR pulse sequences issued from solution-state NMR, such as the INEPT sequence, to characterize these solid-state samples. The solid-state MAS NMR study shows that the proton of the carboxylic acid group of ibuprofen is in a chemical exchange at ambient temperature. Furthermore, at low temperature (down to 223 K), NMR spectroscopy results show that ibuprofen is able to crystallize inside the largest pores (116 Å), whereas a glassy state is obtained for the smallest ones (35 Å).

Buried truth: High‐field magic angle spinning dynamic nuclear polarization (MAS DNP) enhances the sensitivity of solid‐state NMR spectroscopy, but only for protonated surfaces. Direct 29Si DNP using the biradical TOTAPOL (see picture) circumvents this limitation by producing a 30‐fold enhancement of subsurface 29Si NMR signals in mesoporous silica, a material with applications in photonics, nanotechnology and catalysis.

Dimyristoylphophatidylcholine (DMPC) has been entirely or selectively deuterated on the headgroup, glycerol backbone, and acyl chains. Solid-state deuterium and phosphorus NMR was applied to this lipid with the aim to comprehensively depict its structure and dynamics when embedded in bicelles or in liposomes. Molecular mechanics calculations were also accomplished on fully hydrated DMPC bilayers. The main results are fourfold. (a) The local lipid dynamics across the entire membrane thickness could be accurately described:  the glycerol backbone shows a very restricted motional freedom and can be considered as a semirigid “rotula” separating two very fluid zones, the phosphocholine headgroup facing the water medium and the acyl chains constituting the oily bilayer interior. (b) The location of the principal axis of motion of the glycerol backbone of DMPC and its molecular order parameter, S mol, were calculated by making use of NMR, molecular mechanics, and X-ray data reported in earlier studies. Although the later lacks in accurate structural data for hydrogen atoms, there is nonetheless a general trend for an orientation of the glycerol g2−g3 carbon−carbon bond at about 28° with respect to the bilayer normal and for a S mol value of 0.55 for 78% DMPC embedded in bicelles. (c) The two DMPC conformers A and B that were earlier reported in the crystal (Pearson, H.; Parsher, I. Nature 1979, 181, 499−501) also exist in all molecular dynamics runs of fully hydrated DMPC. (d) There is a marked decrease of the DMPC phase transition temperature upon increasing selective deuterium content in the lipid structure. Interestingly, labeling of the five glycerol backbone positions induces the same temperature decrease as a full chain deuteration (54 positions).

Well polarized: Two new polarizing agents PyPol and AMUPol soluble in glycerol/water mixtures are used for dynamic nuclear polarization (DNP) NMR spectroscopy. The enhancement factors (ε) are about 3.5 to 4 times larger than for the established agent TOTAPOL at 263 and 395 GHz. For AMUPol, the temperature dependence of ε allows DNP experiments to be performed at temperatures significantly higher than for typical high‐field DNP NMR experiments.

A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors e ( 1 H) in cross-effect dynamic nuclear polarization (CE DNP) NMR experiments at 9.4 and 14.1 T and 100 K in a DNP-optimized glycerol/water matrix ("DNP juice") have been studied. We observe that e ( 1 H) is strongly correlated with the substituents on the polarizing agents, and its trend is discussed in terms of different molecular parameters: solubility, average e-e distance, relative orientation of the nitroxide moieties, and electron spin relaxation times. We show that too short an e-e distance or too long a T 1e can dramatically limit e ( 1 H). Our study also shows that the molecular structure of AMUPol is not optimal and its e ( 1 H) could be further improved through stronger interaction with the glassy matrix and a better orientation of the TEMPO moieties. A new AMUPol derivative introduced here provides a better e ( 1 H) than AMUPol itself (by a factor of ca. 1.2).

(2017) Surface-sensitive NMR detection of the solid electrolyte interphase layer on reduced graphene oxide. Journal of Physical Chemistry Letters, 8 (5). pp. 1078 -1085 . ISSN 1948 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/42184/1/Leskes%20et%20al.%20-%202017%20-%20Surface %20Sensitive%20NMR%20Detection%20of%20the%20SEI%20Layer%20on%20Reduced %20Graphene%20Oxide.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence. For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk Just Accepted "Just Accepted" manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides "Just Accepted" as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. "Just Accepted" manuscripts appear in full in PDF format accompanied by an HTML abstract. "Just Accepted" manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). "Just Accepted" is an optional service offered to authors. Therefore, the "Just Accepted" Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the "Just Accepted" Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these "Just Accepted" manuscripts. 1Surface Sensitive NMR Detection of the SEI Layer on Reduced Graphene OxideMichal Leskes (1) *, Gunwoo Kim (2,3) , Tao Liu (2) , Alison L. Michan, (2) Fabien Aussenac (4) , Patrick Dorffer (4) , Subhradip Paul (5) , Clare P. Grey Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UKCambridge Graphene Centre, University of Cambridge, Cambridge, CB3 0FA, UKBruker BioSpin, 34 rue de l'Industrie BP 10002, 67166 Wissembourg Cedex, France 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1...