How pressure enhances the critical temperature of superconductivity in YBa2Cu3O6+y.

High-temperature superconducting cuprates respond to doping with a dome-like dependence of their critical temperature (Tc). But the family-specific maximum Tc can be surpassed by application of pressure, a compelling observation known for decades. We investigate the phenomenon with high-pressure anvil cell NMR and measure the charge content at planar Cu and O, and with it the doping of the ubiquitous CuO2 plane with atomic-scale resolution. We find that pressure increases the overall hole doping, as widely assumed, but when it enhances Tc above what can be achieved by doping, pressure leads to a hole redistribution favoring planar O. This is similar to the observation that the family-specific maximum Tc is higher for materials where the hole content at planar O is higher at the expense of that at planar Cu. The latter reflects dependence of the maximum Tc on the Cu-O bond covalence and the charge-transfer gap. The results presented here indicate that the pressure-induced enhancement of the maximum Tc points to the same mechanism.

Tuning the Mechanism of H/D Exchange for Isobutane on H-BEA by Loading Zn Species in Zeolite.

Kinetics of H/D hydrogen exchange between deuterated isobutane-d10 and Brønsted acid sites (BAS) of three zeolite samples (H-BEA, ZnO/H-BEA, Zn2+ /H-BEA) were monitored with 1 H MAS NMR in situ at 343-468 K. The regioselective H/D exchange in the methyl groups detected on H-BEA can be rationalized in terms of the mechanism of indirect exchange, which involves protonation of the intermediate olefin and further hydride abstraction from the other alkane molecule by the formed carbenium ion. Loading of Zn species in the zeolite results in a decrease of the rate and an increase of the activation energy of the exchange. The loaded Zn species provide the tuning effect on the reaction occurrence, changing the mechanism from the indirect one to the mechanism of the direct exchange.

Quantitative 67Zn, 27Al and 1H MAS NMR spectroscopy for the characterization of Zn species in ZSM-5 catalysts.

67Zn MAS NMR spectroscopy was used to characterize the state of Zn in Zn-modified zeolites ZSM-5. Two 67Zn enriched zeolite samples were prepared: by solid-state exchange with metal 67Zn (Zn2+/ZSM-5 sample) and by ion exchange with zinc formate solution (ZnO/H-ZSM-5 sample), both containing ca. 3.8 wt% Zn. The elemental analysis, TEM, and quantitative BAS and aluminum analyses with 1H and 27Al MAS NMR have shown that Zn2+/ZSM-5 contains zinc in the form of Zn2+ cations, while both ZnO species and Zn2+ cations are present in ZnO/H-ZSM-5 besides BAS. 67Zn MAS NMR has detected the signal of Zn in a tetrahedral environment from ZnO species for both the activated and hydrated ZnO/H-ZSM-5 zeolite. The signal of Zn in an octahedral environment was detected for the hydrated Zn2+/ZSM-5 and ZnO/H-ZSM-5 zeolites. This signal may belong to zinc cation [HOZn]+ or Zn(OH)2 species surrounded by water molecules. Quantitative 67Zn MAS NMR analysis has shown that only 27 and 38% of zinc loaded in the zeolite is visible for the activated and hydrated ZnO/H-ZSM-5 zeolite, and 24% of Zn is visible for the hydrated Zn2+/ZSM-5. Zinc in the form of ZnO species is entirely visible in both the activated and hydrated ZnO/H-ZSM-5 zeolite, while Zn2+ cations are not detected at all for the activated sample and only 29% of Zn2+ cations is visible for the hydrated zeolite. Detection of only a part of Zn2+ cations in the form of [HOZn]+ or Zn(OH)2 species in octahedral environment presumes only partial hydrolysis of the bond of Zn2+ cation with framework oxygen and further solvation of the Zn species formed at hydrolysis by the adsorbed water.

Isobutane Transformation to Aromatics on Zn-Modified Zeolites: Intermediates and the Effect of Zn2+ and ZnO Species on the Reaction Occurrence Revealed by 13 C MAS NMR.

To clarify the effects of different Zn species, zeolite topology and acidity (quantity of Brønsted acid sites, BAS) on alkane aromatization, isobutane transformation on Zn2+ /H-ZSM-5, Zn2+ /H-BEA, and ZnO/H-BEA zeolites has been monitored with 13 C MAS NMR. The alkane transformation has been established to occur by aromatization and hydrogenolysis pathways. Zn2+ species is more efficient for the aromatization reaction because aromatic products are formed at lower temperatures on Zn2+ /H-BEA and Zn2+ /H-ZSM-5 than on ZnO/H-BEA. The larger quantity of BAS in ZnO/H-BEA seems to provide a higher degree of the hydrogenolysis pathway on this catalyst. The mechanism of the alkane aromatization is similar for the zeolites of different topology and containing different Zn species, with the main reaction steps being the following: (i) isobutane dehydrogenation to isobutene via isobutylzinc; (ii) isobutene stabilization as a π-complex on Zn sites; (iii) isobutene oligomerization via the alkene insertion into Zn-C bond of methyl-σ-allylzinc formed from the π-complex; (iv) oligomer dehydrogenation with intermediate formation of polyene carbanionic structures; (v) aromatics formation via further polyene dehydrogenation, protonation, cyclization, deprotonation steps with BAS involvement.

Determination of element-deuterium bond lengths in Zintl phase deuterides by 2H-NMR.

The Zintl phase deuterides CaSiD4/3, SrSiD5/3, BaSiD2, SrGeD4/3, BaGeD5/3 and BaSnD4/3 were investigated by nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations to reliably determine element-deuterium bond lengths. These compounds show deuterium bound to the polyanion and deuteride ions in tetrahedral cationic voids. With 2H-NMR experiments we characterised the individual signals of the two distinct crystal sites. Quadrupolar coupling constants (CQ) of the anion-binding site were determined as 58 to 78 kHz (Si compounds), 51 to 61 kHz (Ge compounds) and 38 kHz (Sn compound). These values agree well with the quadrupole couplings derived from DFT using optimized structural models. We further calculated the general element-deuterium distance dependency of CQ using DFT methods that allow an accurate determination of bond lengths via the 2H quadrupole interaction. The thus determined bond lengths are evaluated as d(Si-D) = 1.53-1.59 Å, d(Ge-D) = 1.61-1.65 Å and d(Sn-D) = 1.86 Å. Chemical shifts of the anion-binding site range from 0.3 to 1.3 ppm. The isotropic chemical shifts of the tetrahedral sites are 5.1 ppm (CaSiD4/3), 7.0 to 10.0 ppm (Sr compounds) and 10.7 to 11.6 ppm (Ba compounds).

Revealing the Transient Concentration of CO2 in a Mixed-Matrix Membrane by IR Microimaging and Molecular Modeling.

Through IR microimaging the spatially and temporally resolved development of the CO2 concentration in a ZIF-8@6FDA-DAM mixed matrix membrane (MMM) was visualized during transient adsorption. By recording the evolution of the CO2 concentration, it is observed that the CO2 molecules propagate from the ZIF-8 filler, which acts as a transport "highway", towards the surrounding polymer. A high-CO2 -concentration layer is formed at the MOF/polymer interface, which becomes more pronounced at higher CO2 gas pressures. A microscopic explanation of the origins of this phenomenon is suggested by means of molecular modeling. By applying a computational methodology combining quantum and force-field based calculations, the formation of microvoids at the MOF/polymer interface is predicted. Grand canonical Monte Carlo simulations further demonstrate that CO2 tends to preferentially reside in these microvoids, which is expected to facilitate CO2 accumulation at the interface.

Hydrides of Alkaline Earth-Tetrel (AeTt) Zintl Phases: Covalent Tt-H Bonds from Silicon to Tin.

Zintl phases form hydrides either by incorporating hydride anions (interstitial hydrides) or by covalent bonding of H to the polyanion (polyanionic hydrides), which yields a variety of different compositions and bonding situations. Hydrides (deuterides) of SrGe, BaSi, and BaSn were prepared by hydrogenation (deuteration) of the CrB-type Zintl phases AeTt and characterized by laboratory X-ray, synchrotron, and neutron diffraction, NMR spectroscopy, and quantum-chemical calculations. SrGeD4/3-x and BaSnD4/3-x show condensed boatlike six-membered rings of Tt atoms, formed by joining three of the zigzag chains contained in the Zintl phase. These new polyanionic motifs are terminated by covalently bound H atoms with d(Ge-D) = 1.521(9) Å and d(Sn-D) = 1.858(8) Å. Additional hydride anions are located in Ae4 tetrahedra; thus, the features of both interstitial hydrides and polyanionic hydrides are represented. BaSiD2-x retains the zigzag Si chain as in the parent Zintl phase, but in the hydride (deuteride), it is terminated by H (D) atoms, thus forming a linear (SiD) chain with d(Si-D) = 1.641(5) Å.

113Cd solid-state NMR for probing the coordination sphere in metal-organic frameworks.

Spectroscopic techniques are a powerful tool for structure determination, especially if single-crystal material is unavailable. (113)Cd solid-state NMR is easy to measure and is a highly sensitive probe because the coordination number, the nature of coordinating groups, and the geometry around the metal ion is reflected by the isotropic chemical shift and the chemical-shift anisotropy. Here, a detailed investigation of a series of 27 cadmium coordination polymers by (113)Cd solid-state NMR is reported. The results obtained demonstrate that (113)Cd NMR is a very sensitive tool to characterize the cadmium environment, also in non-single-crystal materials. Furthermore, this method allows the observation of guest-induced phase transitions supporting understanding of the structural flexibility of coordination frameworks.

Water-mediated proton conduction in a robust triazolyl phosphonate metal-organic framework with hydrophilic nanochannels.

The development of water-mediated proton-conducting materials operating above 100 °C remains challenging because the extended structures of existing materials usually deteriorate at high temperatures. A new triazolyl phosphonate metal-organic framework (MOF) [La3L4(H2O)6]Cl⋅x H2O (1, L(2-) = 4-(4H-1,2,4-triazol-4-yl)phenyl phosphonate) with highly hydrophilic 1D channels was synthesized hydrothermally. Compound 1 is an example of a phosphonate MOF with large regular pores with 1.9 nm in diameter. It forms a water-stable, porous structure that can be reversibly hydrated and dehydrated. The proton-conducting properties of 1 were investigated by impedance spectroscopy. Magic-angle spinning (MAS) and pulse field gradient (PFG) NMR spectroscopies confirm the dynamic nature of the incorporated water molecules. The diffusivities, determined by PFG NMR and IR microscopy, were found to be close to that of liquid water. This porous framework accomplishes the challenges of water stability and proton conduction even at 110 °C. The conductivity in 1 is proposed to occur by the vehicle mechanism.

Synthesis, crystal structure, and solid-state NMR investigations of heteronuclear zn/co coordination networks--a comparative study.

Synthesis and solid-state NMR characterization of two isomorphous series of zinc and cobalt coordination networks with 1,2,4-triazolyl benzoate ligands are reported. Both series consist of 3D diamondoid networks with four-fold interpenetration. Solid-state NMR identifies the metal coordination of the ligands, and assignment of all (1)H and (13)C shifts was enabled by the combination of (13)C editing, FSLG-HETCOR spectra, and 2D (1)H-(1)H back-to-back (BABA) spectra with results from NMR-CASTEP calculations. The incorporation of Co(2+) replacing Zn(2+) ions in the MOF over the full range of concentrations has significant influences on the NMR spectra. A uniform distribution of metal ions is documented based on the analysis of (1)H T1 relaxation time measurements.

Investigation of the spin-lattice relaxation of 13CO and 13CO2 adsorbed in the metal-organic frameworks Cu3(btc)2 and Cu(3-x)Zn(x)(btc)2.

The (13)C nuclear spin-lattice relaxation time of (13)CO and (13)CO2 molecules adsorbed in the metal-organic frameworks (MOFs) Cu2.97Zn0.03(btc)2 and Cu3(btc)2 is investigated over a wide range of temperatures at resonance frequencies of 75.468 and 188.62 MHz. In all cases a mono-exponential relaxation is observed, and the (13)C spin-lattice relaxation times (T1) reveal minima within the temperature range of the measurements and both frequencies. This allows us to carry out a more detailed analysis of the (13)C spin relaxation data and to consider the influence due to the spectral functions of the thermal motion. In a model-free discussion of the temperature dependence of the ratios T1 (T)∕T1,min we observe a motional mechanism that can be described by a single correlation time. In relation to the discussion of the relaxation mechanisms this can be understood in terms of dominating translational motion with mean jump distance being larger than the minimum distances between neighboring adsorption sites in the MOFs. A more detailed discussion of the jump-like motion observed here might be carried out on the basis of self-diffusion coefficients. From the present spin relaxation measurements activation energies for the local motion of the adsorbed molecules in the MOFs can be estimated to be 3.3 kJ∕mol and 2.2 kJ∕mol, for CO and CO2 molecules, respectively. Finally, our findings are compared with our recent results derived from the (13)C line shape analysis.

Eigenmodes in the long-time behavior of a coupled spin system measured with nuclear magnetic resonance.

The many-body quantum dynamics of dipolar coupled nuclear spins I=1/2 on an otherwise isolated cubic lattice are studied with nuclear magnetic resonance. By increasing the signal-to-noise ratio by 2 orders of magnitude compared with previous reports for the free induction decay (FID) of (19)F in CaF(2) we obtain new insight into its long-time behavior. We confirm that the tail of the FID is an exponentially decaying cosine, but our measurements reveal a second decay mode with comparable frequency but twice the decay constant. This result is in agreement with a recent theoretical prediction for the FID in terms of eigenvalues for the time evolution of chaotic many-body quantum systems.

Five-year long-term clinical follow-up of the XIENCE V everolimus eluting coronary stent system in the treatment of patients with de novo coronary artery lesions: the SPIRIT FIRST trial.

BACKGROUND: Drug-eluting stents have shown to be superior over bare metal stents in clinical and angiographic outcomes after percutaneous treatment of coronary artery stenosis. However, long-term follow-up data are scarce and only available for sirolimus- and paclitaxel-eluting stents. AIM: To assess the feasibility and performance of the XIENCE V everolimus-eluting stent (EES) versus an identical bare metal stent after a 5-year follow-up period. METHODS: SPIRIT FIRST was a First in Man, multicentre, prospective, single-blind, clinical trial, randomizing 60 patients with a single de novo coronary artery lesion in a ratio of 1:1 to either an everolimus eluting or a bare metal control stent. RESULTS: At 5-year clinical follow-up, data were available in 89% and 86% of patients in the everolimus and control arm, respectively. In the everolimus arm, no additional death, myocardial infarction, clinically driven target lesion revascularization (TLR), or clinically driven target vessel revascularization (TVR) events were observed between 1- and 5-year follow-up. The 5-year hierarchical major adverse cardiac events (MACE) and target vessel failure (TVF) rates for the everolimus arm were 16.7% (4/24) for both endpoints. In the control group, no additional cardiac death, myocardial infarction, or clinically driven TLR events were observed between 2- and 5-year follow-up. No additional clinically driven TVR events were observed between 3- and 5-year follow-up. The 5-year hierarchical MACE and TVF rates for the control arm were 28.0% (7/25) and 36.0% (9/25), respectively. No stent thromboses were observed in either the everolimus arm or the control arm up to 5 years. CONCLUSION: The favorable 5-year long term clinical outcome of the EES is consistent with the results from other studies of the EES with shorter follow-up.

Unusual 209Bi NMR quadrupole effects in topological insulator Bi2Se3.

Three-dimensional topological insulators are an important class of modern materials, and a strong spin-orbit coupling is involved in making the bulk electronic states very different from those near the surface. Bi2Se3 is a model compound, and 209Bi NMR is employed here to investigate the bulk properties of the material with focus on the quadrupole splitting. It will be shown that this splitting measures the energy band inversion induced by spin-orbit coupling in quantitative agreement with first-principle calculations. Furthermore, this quadrupole interaction is very unusual as it can show essentially no angular dependence, e.g., even at the magic angle the first-order splitting remains. Therefore, it is proposed that the magnetic field direction is involved in setting the quantization axis for the electrons, and that their life time leads to a new electronically driven relaxation mechanism, in particular for quadrupolar nuclei like 209Bi. While a quantitative understanding of these effects cannot be given, the results implicate that NMR can become a powerful tool for the investigation of such systems.

Comparison of a polymer-free rapamycin-eluting stent (YUKON) with a polymer-based paclitaxel-eluting stent (TAXUS) in real-world coronary artery lesions.

BACKGROUND: In selected patient cohorts the polymer-free rapamycin-eluting YUKON stent (A) has demonstrated noninferiority compared with the polymer-based paclitaxel-eluting TAXUS stent (B). To test for equivalency in unselected real-world patients with coronary lesions of various complexities, we retrospectively compared both stent designs. METHODS: A total of 410 patients with symptomatic CAD were successfully treated with A (n = 205) or with B (n = 205). Baseline clinical characteristics, coronary lesion location, lesion length, and the number of stents implanted per lesion were equally distributed between the treatment groups. All patients underwent QCA-analysis at baseline. Clinical follow-up with assessment of MACE and noncardiac deaths was obtained at 30 days and 6 months. RESULTS: Nominal stent diameter was 2.96 +/- 0.38 mm in Group A vs. 3.05 +/- 0.42 mm in Group B (P = 0.2); nominal length of stented segmentwas 22.97 +/-13.0 mm vs. 23.63 +/- 10.0 (P = 0.56). Analysis of MACE after 6 months resulted in one angiographically documented stent thrombosis causing MI in B (0.2%) vs. none in A. No other MI or cardiac deaths occurred in either group, while two noncardiac deaths in A (1.0%) were reported. Fifteen target lesion revascularizations (7.3%) were performed in A vs. 7 (3.4%) in B. Differences in study endpoints at 6 months did not reach statistical significance (P > 0.05). CONCLUSIONS: Up to 6 months after PCI of real-world coronary lesions, there were no statistically significant differences in MACE between patients treated with the polymer-free rapamycin-eluting YUKON stent and the polymer-based paclitaxel-eluting TAXUS stent.

Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy.

Pulsed field gradient (PFG) NMR is successfully applied to trace the diffusion of methyl oleate (MO) inside the mesopores of hierarchically structured titanium silicalite-1 (TS-1)-based catalysts. Introduction of mesoporosity by post-synthetic treatment of initially microporous TS-1 provides additional active surface to improve catalytic activity in the epoxidation of MO. The present study provides experimental evidence of the accessibility of mesopores for MO resulting from alkaline treatment of TS-1. The self-diffusion coefficients of MO inside the pores of hierarchically structured TS-1 catalysts are up to two orders of magnitude lower compared to the values in the bulk liquid phase. Additionally, the methodological capability of PFG NMR for measuring self-diffusion coefficients of long-chain hydrocarbons (up to C19) confined to narrow mesopores of catalytically active is demonstrated for the first time.

Correction: Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy.

[This corrects the article DOI: 10.1039/C8RA07434H.].

Investigation of room temperature multispin-assisted bulk diamond 13C hyperpolarization at low magnetic fields.

In this work we investigated the time behavior of the polarization of bulk 13C nuclei in diamond above the thermal equilibrium. This nonthermal nuclear hyperpolarization is achieved by cross relaxation between two nitrogen related paramagnetic defect species in diamond in combination with optical pumping. The decay of the hyperpolarization at four different magnetic fields is measured. Furthermore, we use the comparison with conventional nuclear resonance measurements to identify the involved distances of the nuclear spin with respect to the defects and therefore the coupling strengths. Also, a careful look at the linewidth of the signal give valuable information to piece together the puzzle of the hyperpolarization mechanism.

Four-year results after brachytherapy for diffuse coronary in-stent restenosis: will coronary radiation therapy survive?

BACKGROUND: Prior to the introduction of drug-eluting stents (DES), diffuse coronary in-stent restenosis (ISR) was mainly treated by brachytherapy (BT), with good short-term and mid-term results. However, there exist limited data on the long-term effects of BT that justify its continuous use. MATERIALS AND METHODS: Two hundred patients with diffuse ISR treated with intravascular BT were retrospectively followed over 4 years. Group A (n=134) was treated with the noncentered (90)Sr/Y BetaCath radiation system, whereas Group B (n=66) was treated with the centered 32P Galileo source wire system. Primary endpoints after 4 years were target lesion restenosis (TLS) and target lesion revascularization (TLR). Secondary endpoints were target vessel revascularization (TVR) and nontarget vessel revascularization (NTVR), as well as major adverse cardiac events (MACE). RESULTS: Follow-up at 4 years yielded a TLS rate of 37.6% (Group A, 40.8%; Group B, 31.1%; P=.48). TLR was performed in 34.8% of patients (37.5% in Group A vs. 29.5% in Group B; P=.55). Ten percent of patients underwent coronary bypass surgery. Percutaneous coronary intervention was performed more often in Group A (27.5%) than in Group B (19.7%), while TVR was less frequent in Group A (10.0%) than in Group B (18.0%). NTVR was undertaken in 25.0% of Group A patients versus 21.3% of Group B patients, and MACE occurred in 1.7% of Group A patients versus 3.3% of Group B patients. These differences were not statistically significant (P>.05). CONCLUSIONS: While excellent short-term and mid-term results after coronary BT are widely accepted, a high TLS rate can be observed after 4 years. The potential superiority of DES to BT will depend on the availability of long-term clinical data.

Perspective on the phase diagram of cuprate high-temperature superconductors.

Universal scaling laws can guide the understanding of new phenomena, and for cuprate high-temperature superconductivity the influential Uemura relation showed, early on, that the maximum critical temperature of superconductivity correlates with the density of the superfluid measured at low temperatures. Here we show that the charge content of the bonding orbitals of copper and oxygen in the ubiquitous CuO2 plane, measured with nuclear magnetic resonance, reproduces this scaling. The charge transfer of the nominal copper hole to planar oxygen sets the maximum critical temperature. A three-dimensional phase diagram in terms of the charge content at copper as well as oxygen is introduced, which has the different cuprate families sorted with respect to their maximum critical temperature. We suggest that the critical temperature could be raised substantially if one were able to synthesize materials that lead to an increased planar oxygen hole content at the expense of that of planar copper.