Mesoporous Silica Nanoparticles Loaded with Surfactant: Low Temperature Magic Angle Spinning 13C and 29Si NMR Enhanced by Dynamic Nuclear Polarization

We show that dynamic nuclear polarization (DNP) can be used to enhance NMR signals of13C and 29Si nuclei located in mesoporous organic/inorganic hybrid materials, at several hundreds of nanometers from stable radicals (TOTAPOL) trapped in the surrounding frozen disordered water. The approach is demonstrated using mesoporous silica nanoparticles (MSN), functionalized with 3-(N-phenylureido)propyl (PUP) groups, filled with the surfactant cetyltrimethylammonium bromide (CTAB). The DNP-enhanced proton magnetization is transported into the mesopores via 1H–1H spin diffusion and transferred to rare spins by cross-polarization, yielding signal enhancements εon/off of around 8. When the CTAB molecules are extracted, so that the radicals can enter the mesopores, the enhancements increase to εon/off ≈ 30 for both nuclei. A quantitative analysis of the signal enhancements in MSN with and without surfactant is based on a one-dimensional proton spin diffusion model. The effect of solvent deuteration is also investigated

Le bloc paravertébrale dans la chirurgie carcinologique du sein, étude du relais antalgique

LYON1-BU Santé (693882101) / SudocSudocFranceF

Indirect and direct ²⁹Si dynamic nuclear polarization of dispersed nanoparticles

We show how the 29Si NMR signals of dispersed inorganic nanoparticles of laponite® can be enhanced by Dynamic Nuclear Polarization (DNP). The direct DNP enhances the signals of 29Si nuclei near unpaired electrons, whereas the indirect DNP via 1H enhances the signals of more remote sites

Does a strong pynocline impact organic-matter preservation and accumulation in an anoxic setting ? The case of the Orca Basin, Gulf of Mexico

International audienceWe show how the 29 Si NMR signals of dispersed inorganic nano-particles of laponite s can be enhanced by Dynamic Nuclear Polarization (DNP). The direct DNP enhances the signals of 29 Si nuclei near unpaired electrons, whereas the indirect DNP via 1 H enhances the signals of more remote sites. As a local and non-destructive technique, solid-state nuclear magnetic resonance (NMR) provides precious insight into the atomic-scale structure and dynamics of nanoparticles (NPs), i.e. materials with three external dimensions sized between 1 and 100 nm. 1,2 Nevertheless, the low sensitivity of NMR can preclude the observation of diluted species, such as the edge, corner, grafting or surface sites. The sensitivity limitation of NMR is even more acute for nuclei with long longitudinal relaxation times (T 1n), low natural abundance and/or low gyromagnetic ratio, such as 29 Si. 3,4 Herein, we show how the NMR signals of inorganic NPs dispersed in a frozen solution containing TOTAPOL 5 can be enhanced at high static magnetic field, B 0 , and under magic-angle spinning (MAS) using dynamic nuclear polarization (DNP). 3-12 Enhancements of 29 Si NMR signals in the order of 10 are reported in direct polarization (DP) and 1 H-29 Si cross-polarization (CP) experiments for laponite s (1), an industrial synthetic clay NP (see Fig. 1), with applications for hybrid materials and soft matter (cleanser, coating). 13-15 Hereafter, the DP and CP experiments with microwave irradiation are referred to as direct and indirect DNP, respectively. This protocol should become a standard for the DNP of NPs, since they are often dispersed in a liquid phase to prevent their aggregation. 16 The dispersion is supplementary to impregnation 4,17 and co-condensation, 18 which have been employed for high-field MAS DNP of porous solids or particle aggregates. 3,4,17-19 Hitherto, dispersion in frozen 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)-propan-2-ol (TOTAPOL) solutions has only been demonstrated for indirect 13 C and 15 N DNP of biological systems, such as bacteriophage or peptide mesocrystals. 10,11 We also show the complementarity of indirect and direct 29 Si DNP: in indirect DNP, 1 H spin diffusion distributes the polarization within the whole sample, whereas direct DNP enhances the signals of 29 Si sites nearer to TOTAPOL. The polarization buildups in direct and indirect DNP are compared and the polarization leakage is discussed. Fig. 2a shows how the indirect 29 Si DNP results in a 14-fold enhancement of 29 Si NMR signals of 1 dispersed in TOTAPOL solution. The concentration in unpaired electrons of 1 is lower than 100 nm (see the EPR spectrum in Fig. S1a, ESI †). Hence, in indirect DNP, the polarization is transferred from an exogenous TOTAPOL radical in the matrix to 29 Si nuclei of 1 via 1 H spin diffusion and 1 H-29 Si CP. The 29 Si NMR spectrum enhanced by indirect DNP displays two resolved 29 Si NMR signals. The intense peak at À94 ppm corresponds to the (SiO) 3 Si(OMg) (Q 3) sites, located inside the silicate framework, whereas the weak peak at À85 ppm is assigned to the (SiO) 2 Si(OMg)OH (Q 2) sites. 15 Fig. 1 (a) Schematic representation of 1 NPs, which are disk-shaped crystallites with a diameter of ca. 25-30 nm. 20 The specific surface area of 1 is 370 m 2 g À1. (b and c) Atomic-scale structures of the circular (b) and lateral (c) surfaces. The sheet of octahedrally coordinated magnesium atoms is sandwiched by two sheets of silicate.The Orca Basin (an intraslope depression located in the Gulf of Mexico) collects sedimentary particles of terrestrial origin (clastic and organic particles mainly supplied by the Mississippi River) and of marine origin (biogenic productivity). The basin is partly filled with dense brines leached from salt diapirs cropping out on the sea floor, and is permanently stratified. A strong pycnocline induces anoxic bottom conditions, expectedly favorable to organic matter (OM) preservation. Here, we report on OM in the upper 750 cm below sea floor of Core MD02-2552 (Holocene). The organic content is dominated by marine-derived amorphous OM. The organic assemblage is unexpectedly degraded to some extent, which may be accounted for by a relatively long residence time of organic particles at the halocline-pycnocline at 2240 m. Thus the organic particles are temporarily trapped and kept in contact with the dissolved oxygen-rich overlying water mass. Lastly, the land-derived organic fraction shows co-variations with the land-derived clay mineral supply. To cite this article: N. Tribovillard et al., C. R. Geoscience 341 (2009). # 2008 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved. Résumé Une pycnocline concentrée at -elle un impact sur la préservation de la matière organique et sur son accumulation dans un dépôt anoxique ? Le bassin d'Orca, petite dépression située dans le Golfe du Mexique, reçoit des particules sédimentaires d'origine continentale (clastiques et organiques), véhiculées par le Mississippi principalement, et d'origine marine (productivité). Le bassin est partiellement rempli par des saumures issues du lessivage de diapirs salifères affleurant dans les fonds marins. La colonne d'eau y est très fortement stratifiée et le corps d'eau situé sous la halocline-pycnocline est totalement anoxique. Cette anoxie est a priori favorable à la préservation de la matière organique (MO). Nous étudions ici le contenu organique des premiers 750 cm de la carotte MD02-2552 déposés au cours de l'Holocène. Le contenu organique est dominé par la MO amorphe d'origine marine. L'état de préservation de la MO est étonnamment mauvais, compte tenu du contexte de dépôt. Cela est dû au fait que la MO est retenue durablement à l'interface de densité à 2240 m de profondeur, ce qui permet un long séjour dans des conditions encore relativement riches en oxygène dissous. Enfin, les particules organiques terrigènes montrent une distribution relativement bien corrélée à celle des minéraux argileux. Pour citer cet article : N. Tribovillard et al., C. R. Geoscience 341 (2009). # 2008. Publié par Elsevier Masson SAS. Tous droits réservés