Minimizing the t 1 -noise when using an indirect 1 H high-resolution detection of unlabeled samples

International audienc

Non-homogeneous distribution of Al³⁺ in doped phosphate glasses revealed by ²⁷Al/³¹P solid state NMR

International audienceSolid state NMR is applied in this contribution on the xAl2O3-(50-x/2)Na2O-(50-x/2)P2O5 composition line (with 0 < x < 5mol%) in order to investigate the distribution of Al3+ ions in Al2O3-doped sodium phosphate glasses. The structure was analysed by (i) 27Al 1D-, 3Q-, DQ- MAS-NMR analysis and (ii) 1D 31P, 27Al(31P) 2D D-HMQC MAS-NMR and 2D 31P R-INADEQUATE technique. The 27Al NMR results confirm the presence of six-coordinated aluminate as major aluminate species and indicate that Al3+ ions are fully dissociated in the glass network. The 31P NMR data show the simultaneous presence of five different phosphate units connected to 0, 1 but also 2 Al3+ ions and offer a new vision of the doping mechanism by highlighting a non-homogeneous distribution of Al3+ ions in the phosphate matrix. This study indicates that the glass networks contain Al3+-rich and -poor domains and present thus a significant structural disorder beyond the local order

Boron isotopes as pH proxy : a new look at boron speciation in deep-sea corals using B-11 MAS NMR and EELs

International audienceDissolved boron in modern seawater occurs in the form of two species, trigonal boric acid B(OH)(3) and tetrahedral borate ion B(OH)(4)(-). One of the key assumption in the use of boron isotopic compositions of carbonates as pH proxy is that only borate ions, B(OH)(4)(-), are incorporated into the carbonate. Here, we investigate the speciation of boron in deep-sea coral microstructures (Lophelia pertusa specimen) by using high field magic angle spinning nuclear magnetic resonance (B-11 MAS NMR) and electron energy-loss spectroscopy (EELS). We observe both boron coordination species, but in different proportions depending on the coral microstructure, i.e. centres of calcification versus fibres. These results suggest that careful sampling is necessary before performing boron isotopic measurements in deep-sea corals. By combining the proportions of B(OH)(3) and B(OH)(4)(-) determined by NMR and our previous ion microprobe boron isotope measurements, we propose a new equation for the relation between seawater pH and boron isotopic composition in deep-sea corals. (C) 2010 Elsevier Ltd. All rights reserved

Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR

We thank EPSRC (EP/E041825/1 and EP/J501542/1) for support, for the award of a studentship to H.C. We also thank the ERC (EU FP7 Consolidator Grant 614290 “EXONMR”).The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging".Publisher PDFPeer reviewe

Simple and Robust Study of Backbone Dynamics of Crystalline Proteins Employing H-1-N-15 Dipolar Coupling Dispersion

International audienceWe report a new solid-state multidimensional NMR approach based on the cross-polarization with variable-contact pulse sequence [Paluch, P.; Pawlak, T.; Amoureux, J.-P.; Potrzebowski, M. J. J. Magn. Reson. 233, 2013, 56], with 1H inverse detection and very fast magic angle spinning (νR = 60 kHz), dedicated to the measurement of local molecular motions of 1H–15N vectors. The introduced three-dimensional experiments, 1H–15N–1H and hCA(N)H, are particularly useful for the study of molecular dynamics of proteins and other complex structures. The applicability and power of this methodology have been revealed by employing as a model sample the GB-1 small protein doped with Na2CuEDTA. The results clearly prove that the dispersion of 1H–15N dipolar coupling constants well correlates with higher order structure of the protein. Our approach complements the conventional studies and offers a fast and reasonably simple method

Klebsiella pneumoniae OmpR facilitates lung infection through transcriptional regulation of key virulence factors.

Bacteria use two-component regulatory systems (TCSs) to adapt to changes in their environment by changing their gene expression. In this study, we show that the EnvZ/OmpR TCS of the clinically relevant opportunistic pathogen Klebsiella pneumoniae plays an important role in successfully establishing lung infection and virulence. In addition, we elucidate the K. pneumoniae OmpR regulon within the host. This work suggests that K. pneumoniae OmpR might be a promising target for innovative anti-infectives

Understanding mechanochemical synthesis of organometallic complexes using solid-state NMR spectroscopy

National audienc

Atomic Description of Catalytic Sites Using Advanced Solid-State NMR Methods

International audienc

An NMR-Driven Crystallography Strategy to Overcome the Computability Limit of Powder Structure Determination: A Layered Aluminophosphate Case

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