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Yixuan Li,
Bingwen Hu,
Qun Chen,
Qiang Wang,
Zhengfeng Zhang,
Jun Yang,
Isao Noda,
Julien Trébosc,
Oliver Lafon, Jean-Paul Amoureux,
Feng Deng
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ABSTRACT: Two-dimensional covariance (COV2D) spectroscopy offers an alternative approach to 2D Fourier transformation (FT2D) to obtain homo-nuclear correlation NMR spectra. Considerable saving in experimental time, without loss of resolution, can be achieved by incorporating COV2D with: (i) uniform sampling with a t1 cut-off (CUO) or non-uniform sampling (NUS), and (ii) constant or Gaussian accumulation profiles. We find that covariance treatment, combined with the CUO sampling and Gaussian accumulation profile provides better gain in experimental time, with respect to that required with FT2D NMR. This is in contrast with the maximum entropy (MaxEnt) reconstruction for 2D spectra, which works better with the NUS scheme rather than with the CUO scheme. We further discuss the experimental conditions that define this optimum acquisition, and explain how these parameters can easily be optimized 'on the fly' according to the desired resolution, which is quite sample-dependent.
The Analyst 03/2013; · 4.23 Impact Factor
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ABSTRACT: Just in time: An NMR-driven structure resolution that allows structure determination from the powder diffraction data of a highly complex layered aluminophosphate, and was otherwise not possible despite the high quality of the synchrotron diffraction data, is proposed. This study shows that the strategy is general and allows reduction of the number of free parameters to search for a structure and converge under the limit of the combinatorial explosion of computing time.
Chemistry 03/2013; · 5.93 Impact Factor
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Takeshi Kobayashi,
Olivier Lafon,
Aany S Lilly Thankamony,
Igor I Slowing,
Kapil Kandel,
Diego Carnevale,
Veronika Vitzthum,
Hervé Vezin, Jean-Paul Amoureux,
Geoffrey Bodenhausen,
Marek Pruski
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ABSTRACT: We systematically studied the enhancement factor (per scan) and the sensitivity enhancement (per unit time) in 13C and 29Si cross-polarization magic angle spinning (CP-MAS) NMR boosted by dynamic nuclear polarization (DNP) of functionalized mesoporous silica nanoparticles (MSNs). Specifically, we separated contributions due to: (i) microwave irradiation, (ii) quenching by paramagnetic effects, (iii) the presence of frozen solvent, (iv) the temperature, as well as changes in (v) relaxation and (vi) cross-polarization behaviour. No line-broadening effects were observed for MSNs when lowering the temperature from 300 to 100 K. Notwithstanding a significant signal reduction due to quenching by TOTAPOL radicals, DNP-CP-MAS at 100 K provided global sensitivity enhancements of 23 and 45 for 13C and 29Si, respectively, relative to standard CP-MAS measurements at room temperature. The effects of DNP were also ascertained by comparing with state-of-the-art two-dimensional heteronuclear 1H{13C} and 29Si{1H} correlation spectra, using, respectively, indirect detection or Carr-Purcell-Meiboom-Gill (CPMG) refocusing to boost signal acquisition. This study highlights opportunities for further improvements through the development of high-field DNP, better polarizing agents, and improved capabilities for low-temperature MAS.
Physical Chemistry Chemical Physics 03/2013; · 3.57 Impact Factor
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Chemistry A European Journal. 02/2013;
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ABSTRACT: The origin of the exceptionally high activity of (B, Ag)-codoped TiO2 catalysts under solar-light irradiation has been investigated by XPS and 11B solid-state NMR spectroscopy in conjunction with density functional theory (DFT) calculations. XPS experimental results demonstrated that a portion of the dopant Ag (Ag3+) ions were implanted into the crystalline lattice of (B, Ag)-codoped TiO2 and were in close proximity to the interstitial B (Bint.) sites, forming [Bint.-O-Ag] structural units. In-situ XPS experiments were employed to follow the evolution of the chemical states of the B and Ag dopants during Uv-Vis irradiation. It was found that the [Bint.-O-Ag] units could trap the photoinduced electron to form an unique intermediate structure in the (B, Ag)-codoped TiO2 during the irradiation, which is responsible for the photoinduced shifts of the B 1s and Ag 3d peaks observed in the in-situ XPS spectra. Solid-state NMR experiments including 11B triple-quantum and double-quantum magic angle spinning (MAS) NMR revealed that up to six different boron species were present in the catalysts and only the tri-coordinated interstitial boron (T*) species was in close proximity to the substitutional Ag species, leading to formation of [T*-O-Ag] structural units. Furthermore, as demonstrated by DFT calculations, the [T*-O-Ag] structural units were responsible for trapping the photoinduced electrons, which prolongs the life of the photoinduced charge carriers and eventually leads to a remarkable enhancement in the photocatalytic activity. All these unprecedented findings are expected to be crucial for understanding the roles of B and Ag dopants and their synergy effect in numerous titania-mediated photocatalytic reactions.
Journal of the American Chemical Society 01/2013; · 9.91 Impact Factor
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ABSTRACT: We present a novel cross-polarization MAS NMR pulse sequence to probe proximities between half-integer quadrupolar isotopes. This sequence employs a multi-pulse cross-polarization (MP-CP) transfer, instead of the previous continuous-wave CP (CW-CP) transfer. With respect to CW-CP transfers, our sequence is more robust with respect to offsets and Rotary Resonance Recoupling detrimental effects, especially when taking into account rf-inhomogeneity. Moreover, by using a frequency splitter and a single channel MAS probe, this MP-CP sequence may allow analyzing the through-space connectivities between two isotopes with half-integer spin values and close Larmor frequencies.
Journal of Magnetic Resonance 12/2012; · 2.14 Impact Factor
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ABSTRACT: We show how the (29)Si NMR signals of dispersed inorganic nanoparticles of laponite® 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.
Chemical Communications 12/2012; · 6.17 Impact Factor
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ABSTRACT: It is demonstrated that reliable aluminum-carbon distances can be measured in samples with (13) C natural abundance by NMR spectroscopy. Overcoupled resonators, with only one radio-frequency synthesizer and one amplifier, are used to irradiate in the same pulse sequence (27) Al and (13) C nuclei, which differ by only 3.6 % in Larmor frequencies. The combination of (27) Al saturation pulse with heteronuclear dipolar recoupling yields dipolar dephasing of the (13) C signal, which only depends on the AlC distance and the efficiency of the saturation pulse. Therefore, reliable distances can be obtained by rapid fitting of experimental data to an analytical expression. It is demonstrated that with natural isotopic abundance this approach allows recovery of AlC distances of 216 pm for the covalent bond in lithium tetraalkyl aluminates, commonly used as a co-catalyst in olefin polymerization processes, and which range from 274 to 381 pm for the three carbon atoms in aluminum lactate. The accuracy of the measured internuclear distances is carefully estimated.
ChemPhysChem 09/2012; · 3.41 Impact Factor
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ABSTRACT: We analyze and compare the specifications of TIMES and TIMES(0) proton high-resolution NMR methods for solid-state samples. This comparison is performed in terms of resolution versus magic-angle spinning (MAS) spinning speed, ν(R), rf-field amplitude, ν(1), and tilt-angle for the effective rf-field, θ(p). The chemical-shift and homo-nuclear dipolar scaling factors are calculated for both methods. For all MAS speeds, the best resolution is always observed with rf-field of ν(1)≈120-130kHz. At slow MAS speed (ν(R)⩽10kHz), the best resolution is observed for a tilt-angle of θ(P)≈90°. At moderate spinning speed (15⩽ν(R)⩽35kHz), θ(P)≈55° gives the best resolution. At higher MAS speed (ν(R)⩾60kHz), with TIMES and TIMES(0) the best resolution is obtained for θ(P)⩽40°; but we then recommend TIMES(0), owing to its simpler set-up. We also show that in addition to the usual high rf-field regime (ν(1)≈120-130kHz), another low rf-regime (ν(1)≈40-50kHz) exists at MAS speed higher than ν(R)⩾60kHz, which also gives a good (1)H resolution. This low rf-regime should be useful for multi-dimensional analyses of bio-molecules with (1)H detection under high-resolution, in order to limit the heating of the sample.
Journal of Magnetic Resonance 08/2012; 223:219-27. · 2.14 Impact Factor
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ABSTRACT: I still see you: A new pulse sequence, SHA+, little sensitive to dipolar truncation, allows direct or relayed polarization transfer between (13) C atoms, distant by 3.5-9.6 Å, in amyloid fibrils. SHA+ can also be used in a broadband way with the weak rf-condition of ν(1) /ν(R) ≈0.2-0.3 which permits the investigation of temperature-sensitive biological systems.
ChemPhysChem 08/2012; · 3.41 Impact Factor
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ABSTRACT: We demonstrate that inter-residue (13)C-(13)C proximities (of about 380pm) in uniformly (13)C-labeled proteins can be probed by applying robust first-order recoupling during several milliseconds in single-quantum single-quantum dipolar homo-nuclear correlation (SQ-SQ D-HOMCOR) 2D experiments. We show that the intensity of medium-range homo-nuclear correlations in these experiments is enhanced using broadband first-order finite-pulse radio-frequency-driven recoupling (fp-RFDR) NMR sequence with a nested (XY8)4(1) super-cycling. The robustness and the efficiency of the fp-RFDR-(XY8)4(1) method is demonstrated at high magnetic field (21.1T) and high Magic-Angle Spinning (MAS) speeds (up to 60kHz). The introduced super-cycling, formed by combining phase inversion and a global four-quantum phase cycle, improves the robustness of fp-RFDR to (i) chemical shift anisotropy (CSA), (ii) spread in isotropic chemical shifts, (iii) rf-inhomogeneity and (iv) hetero-nuclear dipolar couplings for long recoupling times. We show that fp-RFDR-(XY8)4(1) is efficient sans(1)H decoupling, which is beneficial for temperature-sensitive biomolecules. The efficiency and the robustness of fp-RFDR-(XY8)4(1) is investigated by spin dynamics numerical simulations as well as solid-state NMR experiments on [U-(13)C]-l-histidine·HCl, a tetra-peptide (Fmoc-[U-(13)C,(15)N]-Val-[U-(13)C,(15)N]-Ala-[U-(13)C,(15)N]-Phe-Gly-t-Boc) and Al(PO(3))(3).
Journal of Magnetic Resonance 07/2012; 223:107-19. · 2.14 Impact Factor
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ABSTRACT: In solids that are spinning about the magic angle, trains of short pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) allow one to improve the efficiency of the excitation of magnetization compared to rectangular pulses. By interleaving N pulse trains with N>1, one obtains 'DANTE-N' sequences comprising N pulses per rotor period that extend over K rotor periods. Optimized interleaved DANTE schemes with N>1 are shorter than basic DANTE-1 sequences with N=1. Therefore, they are less affected by coherent or incoherent decays, thus leading to higher signal intensities than can be obtained with basic DANTE-1 or with rectangular pulses. Furthermore, the shorter length of DANTE-N with N>1 increases the width of the spikelets in the excitation profile, allowing one to cover the range of isotropic chemical shifts and second-order quadrupolar effects typical for side-chain and backbone amide (14)N sites in peptides at B(0)=18.8T. In DANTE-N, spinning sidebands only appear at multiples of the spinning frequency ν(rot), as if the samples were rotating at Nν(rot). We show applications to direct detection of nitrogen-14 nuclei with spin I=1 subject to large quadrupole interactions, using fast magic angle spinning (typically ν(rot)⩾60kHz), backed up by simulations that provide insight into the properties of basic and interleaved DANTE sequences. When used for indirect detection, we show by numerical simulations that even basic DANTE-1 sequences can lead to a four-fold boost of efficiency compared to standard rectangular pulses.
Journal of Magnetic Resonance 06/2012; 223:228-36. · 2.14 Impact Factor
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ABSTRACT: The multiple-quantum dipolar refocused-INEPT (MQ-D-R-INEPT) NMR experiment is presented. This new pulse sequence allows the generation of two-dimensional through-space NMR correlation spectra between spin-½ and quadrupolar nuclei under high-resolution. Compared to the existing sequences, the MQ-D-R-INEPT sequence benefits from increased robustness, due to the reduced sensitivity to offsets and radio-frequency field inhomogeneity of the R-INEPT recoupling scheme as compared to the classical cross-polarization transfer involving a quadrupolar nucleus, and applicability to quadrupolar nuclei with any half-integer spin value. Here, the heteronuclear dipolar couplings have been reintroduced using the rotary resonance recoupling (R(3)) sequence, chosen because it is γ-encoded, and thus robust to spinning speed instabilities and to radio-frequency inhomogeneities in the case of nuclei subjected to large chemical shift anisotropy (e.g., (31)P). In the course of the article, a new definition of γ-encoding is introduced, more general and practical than the previous ones, as it does not depend on the implementation of the recoupling sequence, and is independent of the considered frame. The efficiency of the MQ-D-R-INEPT experiment is demonstrated for the observation of (31)P-(27)Al proximities. It is first tested on AlPO(4)-VPI-5, and then applied to a complex aluminophosphate AlPO(4)-(Al(5)P(7))-DAE of incompletely established structure. For this latter sample, the high-resolution provided by the MQMAS filter allows the resolution of a large number of (31)P-(27)Al correlations, which represent an essential step towards the determination of its structural model.
Physical Chemistry Chemical Physics 04/2012; · 3.57 Impact Factor
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Physical Chemistry Chemical Physics 04/2012; 14:7112-7119. · 3.57 Impact Factor
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ABSTRACT: To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica, polymers and nanoparticles. For the same purpose, we describe a general and facile method to immobilize palladium bis(phosphine) complexes on the basis of the technique widely used for metal-organic framework (MOF) synthesis, yielding a mesoporous coordination polymer palladium-CP1. Although palladium complexes are generally not stable enough to allow further manipulation, we succeeded in preparation of a palladium coordination polymer without by-product Pd clusters or nanoparticles. The fresh palladium-CP1 catalyst exhibits a yield close to 55% for tolane at room temperature and 24 h in Sonogashira coupling of iodobenzene and phenylacetylene, as compared with a yield of 89% for its homogeneous counterpart [Pd(PPh(3))(2)Cl(2)]. Furthermore, this catalyst is stable enough to be reused more than four times with no Pd and Zn leaching. Therefore this new immobilization method offers great promise for the produce of recyclable palladium heterogeneous catalysts with higher activity and higher thermal and chemical stability in the future.
Dalton Transactions 03/2012; 41(15):4692-8. · 3.84 Impact Factor
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ABSTRACT: We present a detailed analysis of the Symmetry-based Resonance-Echo Saturation-Pulse DOuble-Resonance (S-RESPDOR) method in order to measure the inter-nuclear distances between spin-1/2 and quadrupolar nuclei. This recently introduced sequence employs a symmetry-based recoupling scheme on the observed spin-1/2 channel and a saturation pulse on the quadrupolar channel. This method requires a low radio-frequency (rf) field, is compatible with high MAS frequency and allows a rapid determination of inter-nuclear distances by fitting the experimental signal fraction to an analytical expression. Here, we analyze in detail the influence of the various experimental and spin-interaction parameters on the S-RESPDOR signal fraction and the measured distance. We show that the S-RESPDOR signal fraction only depends on the quadrupole interaction and the inter-nuclear distance. We demonstrate that the required rf-field on the quadrupolar channel is smaller than that required for an adiabatic-passage pulse in REAPDOR-type experiments. The only limitation of the method is the requirement of accurate rotor synchronization between the two parts of the dipolar recoupling sequences. Using S-RESPDOR, we have quantitatively measured a (31)P-(51)V distance of 357 pm in a mono-vanadium-substituted polyoxo-tungstate, K(4)PVW(11)O(40), from the Keggin family and a (13)C-(67)Zn distance of 286 pm in [80%-(67)Zn]zinc [1-(13)C]acetate. These results show that S-RESPDOR can be employed in the challenging cases of quadrupolar nuclei exhibiting a high spin number and either large chemical-shift anisotropy ((51)V) or low gyromagnetic ratio ((67)Zn).
Journal of Magnetic Resonance 02/2012; 215:34-49. · 2.14 Impact Factor
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Florence Babonneau,
Christian Bonhomme,
Christel Gervais,
Thierry Azais,
Guillaume Laurent,
Olivier Lafon,
Lionel Montagne,
Julien Trebosc,
Laurent Delevoye,
Gregory Tricot, Jean-Paul Amoureux,
Thibault Charpentier,
Frederic Angeli,
Franck Fayon,
Michael Deschamps,
Sylvian Cadars,
Pierre Florian,
Dominique Massiot
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ABSTRACT: Nuclear spins as spies to explore the structure of materials This article illustrates how solid state NMR, which is by nature a local spectroscopic technique, is also able to establish dialogs between nuclear spins over distances up to few nanometers. Access to such length scales is possible through one-dimensional and multidimensional experiments that give chemical signatures not only from one unique atom in relation with its environment, but from groups of atoms chemically bonded or spatially close. In that sense, solid state NMR appears as a perfect investigation tool for materials with more and more complex compositions and structures. The selected examples belong to families of materials that have been developed for applications in the fields of energy (glasses for nuclear waste management), health (hybrid materials for controlled release of drugs) and sustainable development (heterogeneous catalysts).
L'Actualité chimique 01/2012; · 0.12 Impact Factor
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Olivier Lafon,
Aany Sofia Lilly Thankamony,
Takeshi Kobayashi,
Diego Carnevale,
Veronika Vitzthum,
Igor I. Slowing,
Kapil Kandel,
Hervé Vezin, Jean-Paul Amoureux,
Geoffrey Bodenhausen,
Marek Pruski
The Journal of Physical Chemistry C. 01/2012;
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ABSTRACT: We study the QUantitative Cross-Polarization (QU-CP) method proposed by Hou et al. (Chem. Phys. Lett. 421 (2006) 356) under the moderate MAS speed of 23 kHz, re-examining its two building blocks, namely, the CP polarization transfer from (1)H to (13)C, and the thermal equalization of the (13)C magnetizations. We show that the nuclear-integrated cross-polarization (NI-CP) scheme is conveniently used for (1)H-(13)C polarization transfer, because of its simplicity, robustness to rf-mismatch, and compatibility with fast sample spinning. In the mixing part, in addition to dipolar-assisted rotational-resonance (DARR) recoupling, we examine the Phase-Alternated Recoupling Irradiation Schemes (PARIS and PARIS(xy)), and Second-order Hamiltonian among Analogous Nuclei Generated by Hetero-nuclear Assistance Irradiation (SHANGHAI) sequences, and show that SHANGHAI gives the best performances in equalizing the (13)C magnetizations.
Journal of Magnetic Resonance 11/2011; 214(1):340-5. · 2.14 Impact Factor
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ABSTRACT: Three (1)H-(1)H homonuclear dipolar decoupling schemes for (1)H indirect detection measurements at very fast MAS are compared. The sequences require the following conditions: (i) being operable at very fast MAS, (ii) a long T(2)(') value, (iii) a large scaling factor, (iv) a small number of adjustable parameters, (v) an acquisition window, (vi) a low rf-power requirement, and (vii) a z-rotation feature. To satisfy these conditions a modified sequence named TIlted Magic-Echo Sandwich with zero degree sandwich pulse (TIMES(0)) is introduced. The basic elements of TIMES(0) consist of one sampling window and two phase-ramped irradiations, which realize alternating positive and negative 360° rotations of (1)H magnetization around an effective field tilted with an angle θ from the B(0) axis. The TIMES(0) sequence benefits from very large chemical shift scaling factors at ultra-fast MAS that reach κ(cs)=0.90 for θ=25° at ν(r)=80kHz MAS and only four adjustable parameters, resulting in easy setup. Long κ(cs)T(2)(') values, where T(2)(') is a irreversible proton transverse relaxation time, greatly enhance the sensitivity in (1)H-{(13)C} through-bond J-HMQC (Heteronuclear Multiple-Quantum Coherence) measurements with (1)H-(1)H decoupling during magnetization transfer periods. Although similar sensitivity can be obtained with through-space D-HMQC sequences, in which (13)C-(1)H dipolar interactions are recoupled, J-HMQC experiments incorporating (1)H-(1)H decoupling benefit from lower t(1)-noise, more uniform excitation of both CH, CH(2) and CH(3) moieties, and easier identification of through-bond connectivities.
Journal of Magnetic Resonance 11/2011; 214(1):151-8. · 2.14 Impact Factor
