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.
The reasons for capacity fading of LiCoPO
4 cathodes in 1
M LiPF
6 EC/DMC 1:1 electrolyte solutions were investigated using
19F,
31P NMR and XPS spectroscopy. The origin of the poor performance of ...LiCoPO
4 cathodes in LiPF
6 containing electrolyte solutions is a nucleophilic attack of F
− anions in solution on the P atoms, resulting in the breaking of the P―O bonds of the phosphate anions and the formation of soluble LiPO
2F
2 moieties.
► Reasons for capacity fading of LiCoPO
4 cathodes in LiPF
6 containing electrolytes. ► Nucleophilic attack of F
− anions on the P atoms of LiCoPO
4. ► Breaking of the P―O bonds of the phosphate anions with the formation of LiPO
2F
2.
The yttrium gallabenzene complex (1‐Me‐3,5‐tBu2−C5H3Ga)(μ‐Me)Y(2,4‐dtbp) is accessible from Y(GaMe4)3 and K(2,4‐dtbp) via a tandem salt metathesis/methane elimination ...(2,4‐dtbp=2,4‐di‐tert‐butyl‐pentadienyl). The pentadienyl ligand in (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(2,4‐dtbp) (E=Al, Ga) is easily displaced by salt metathesis with KC5Me5 and KTpMe,Me (TpMe,Me=tris(pyrazolyl‐Me2‐3,5)borato) affording (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(TpMe,Me) and (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(C5Me5). The yttrium center in (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(2,4‐dtbp) readily forms adducts with neutral Lewis bases like 4‐DMAP (4‐dimethylaminopyridine), PMe3, DMPE (1,2‐bis(dimethylphosphino)ethane), and DME (1,2‐dimethoxyethane). In stark contrast, addition of TMEDA (N,N,N’,N’‐tetramethylethylenediamine) results in methyl/pentadienyl exchange between aluminum and yttrium resulting in (1‐(2,4‐dtbp)‐1‐Me‐3,5‐tBu2−C5H3Al)Y(Me)(tmeda). The bonding features of the newly synthesized complexes are analyzed by single‐crystal X‐ray diffraction (SCXRD) and heteronuclear (89Y, 31P) NMR spectroscopy.
The gallabenzene‐type yttrium complex (1‐Me‐3,5‐tBu2−C5H3Ga)(μ‐Me)Y(2,4‐dtbp) (A) is readily formed from one‐pot‐reactions using mixtures YMe3n/GaMe3/K(2,4‐dtbp) (2,4‐dtbp=2,4‐di‐tert‐butyl‐pentadienyl), while the remaining pentadienyl ligand gets easily displaced by pentamethylcyclopentadienyl affording B, showcasing the strong interaction of the heterobenzene ligand with the rare‐earth‐metal center. Distinct ligand bonding is revealed by 89Y NMR chemical shifts.
NHCs go nano: Ruthenium nanoparticles were formed from (cyclooctadiene)(cyclooctatriene)ruthenium(0) and stabilized by N‐heterocyclic carbenes (NHCs). Solid‐state NMR spectroscopy revealed both the ...coordination of the NHC ligands on the surface of the particles and their surface reactivity.
NMR Signatures of the Active Sites in Sn-β Zeolite Wolf, Patrick; Valla, Maxence; Rossini, Aaron J. ...
Angewandte Chemie (International ed.),
September 15, 2014, Volume:
53, Issue:
38
Journal Article
Peer reviewed
Open access
Dynamic nuclear polarization surface enhanced NMR (DNP‐SENS), Mössbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active‐site speciation in Sn‐β ...zeolite. This approach unambiguously shows the presence of framework SnIV‐active sites in an octahedral environment, which probably correspond to so‐called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).
Open and closed: The Sn‐β zeolite spectroscopic signatures obtained from 119Sn Mössbauer and DNP‐SENS NMR spectroscopy combined with DFT calculations on a T site model indicate that the active sites correspond to two types of octahedral SnIV sites: one with two water molecules coordinated to the framework Sn atom (closed site) and one where an Sn‐O‐Si bridge was opened by one of the water molecules (open site).
Solid-state NMR spectroscopy is an emerging tool for structural studies of crystalline, membrane-associated, sedimented, and fibrillar proteins. A major limitation for many studies is still the ...large amount of sample needed for the experiments, typically several isotopically labeled samples of 10-20mg each. Here we show that a new NMR probe, pushing magic-angle sample rotation to frequencies around 100kHz, makes it possible to narrow the proton resonance lines sufficiently to provide the necessary sensitivity and spectral resolution for efficient and sensitive proton detection. Using restraints from such spectra, a well-defined de novo structure of the model protein ubiquitin was obtained from two samples of roughly 500µg protein each. This proof of principle opens new avenues for structural studies of proteins available in microgram, or tens of nanomoles, quantities that are, for example, typically achieved for eukaryotic membrane proteins by in-cell or cell-free expression.
Supplementary cementitious materials (SCM) are increasingly used in concrete for economical and environmental reasons. However, the durability of reinforced concretes against, for example, corrosion ...induced by carbonation varies. Here, the phase assemblage of various cement pastes with/without SCM (slag, fly ash and metakaolin), carbonated in accelerated conditions (1.5% CO2 and 65% RH) or not, has been investigated by various technics (XRD, TGA/DTA and 29Si as well as 27Al nuclear magnetic resonance spectroscopy) and compared.
Results show that, after carbonation, anhydrous phases are less decalcified than hydrated phases. In cement pastes with slag, most of the calcium remains in the non-hydrated part of the slag. In contrast, the C-A,S-H phase is deeply modified and results show a coupling between C-A,S-H and hydrated aluminate phases during carbonation. In all carbonated materials, these phases tend to become an aluminosilicate gel, a very amorphous/disordered phase, containing less water than the original hydrates.
Martin Dračínský
European journal of organic chemistry,
October 9, 2018, Volume:
2018, Issue:
37
Journal Article
Peer reviewed
“The Dračínský group research involves many aspects of experimental NMR spectroscopy in solution and solid state, molecular modelling, and theoretical calculations of spectroscopic parameters.” Find ...out more about this author's research at https://doi.org/10.1002/ejoc.201800506.
“The Dračínský group research involves many aspects of experimental NMR spectroscopy in solution and solid state, molecular modelling, and theoretical calculations of spectroscopic parameters.” Find out more about this author's research at https://doi.org/10.1002/ejoc.201800506.
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