Site-Specific Iron Substitution in STA-28, a Large Pore Aluminophosphate Zeotype Prepared by Using 1, 10-Phenanthrolines as Framework-Bound Templates

An AlPO4 zeotype has been prepared using the aromatic diamine 1, 10-phenanthroline and some of its methylated analogues as templates. In each case the two template N atoms bind to a specific framework Al site to expand its coordination to the unusual octahedral AlO4N2 environment. Furthermore, using this framework-bound template, Fe atoms can be included selectively at this site in the framework by direct synthesis, as confirmed by annular dark field scanning transmission electron microscopy and Rietveld refinement. Calcination removes the organic molecules to give large pore framework solids, with BET surface areas up to 540 m2 g-1 and two perpendicular sets of channels that intersect to give pore space connected by 12-ring openings along all crystallographic directions

"Razne vijesti"

The present work shows the synthesis of nano-sized hybrid zeolitic imidazolate frameworks (ZIFs) with the rho topology based on a mixture of the linkers benzimidazole (bIm) and 4-methyl-5-imidazolecarboxaldehyde (4-m-5-ica). The hybrid ZIF was obtained by post-synthetic modification of ZIF-93 in a bIm solution. The use of different solvents, MeOH and N, N-dimethylacetamide (DMAc), and reaction times led to differences in the quantity of bIm incorporated to the framework, from 7.4 to 23 % according to solution-state NMR spectroscopy. XPS analysis showed that the mixture of linkers was also present at the surface of the particles. The inclusion of bIm to the ZIF-93 nanoparticles improved the thermal stability of the framework and also increased the hydrophobicity according to water adsorption results. N2 and CO2 adsorption experiments revealed that the hybrid material has an intermediate adsorption capacity, between those of ZIF-93 and ZIF-11. Finally, ZIF-93/11 hybrid materials were applied as fillers in polybenzimidazole (PBI) mixed matrix membranes (MMMs). These MMMs were used for H2/CO2 separation (at 180 °C) reaching values of 207 Barrer of H2 and a H2/CO2 selectivity of 7.7 that clearly surpassed the Robeson upper bound (corrected for this temperature)

Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial

Background: Many patients with COVID-19 have been treated with plasma containing anti-SARS-CoV-2 antibodies. We aimed to evaluate the safety and efficacy of convalescent plasma therapy in patients admitted to hospital with COVID-19. Methods: This randomised, controlled, open-label, platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]) is assessing several possible treatments in patients hospitalised with COVID-19 in the UK. The trial is underway at 177 NHS hospitals from across the UK. Eligible and consenting patients were randomly assigned (1:1) to receive either usual care alone (usual care group) or usual care plus high-titre convalescent plasma (convalescent plasma group). The primary outcome was 28-day mortality, analysed on an intention-to-treat basis. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936. Findings: Between May 28, 2020, and Jan 15, 2021, 11558 (71%) of 16287 patients enrolled in RECOVERY were eligible to receive convalescent plasma and were assigned to either the convalescent plasma group or the usual care group. There was no significant difference in 28-day mortality between the two groups: 1399 (24%) of 5795 patients in the convalescent plasma group and 1408 (24%) of 5763 patients in the usual care group died within 28 days (rate ratio 1·00, 95% CI 0·93–1·07; p=0·95). The 28-day mortality rate ratio was similar in all prespecified subgroups of patients, including in those patients without detectable SARS-CoV-2 antibodies at randomisation. Allocation to convalescent plasma had no significant effect on the proportion of patients discharged from hospital within 28 days (3832 [66%] patients in the convalescent plasma group vs 3822 [66%] patients in the usual care group; rate ratio 0·99, 95% CI 0·94–1·03; p=0·57). Among those not on invasive mechanical ventilation at randomisation, there was no significant difference in the proportion of patients meeting the composite endpoint of progression to invasive mechanical ventilation or death (1568 [29%] of 5493 patients in the convalescent plasma group vs 1568 [29%] of 5448 patients in the usual care group; rate ratio 0·99, 95% CI 0·93–1·05; p=0·79). Interpretation: In patients hospitalised with COVID-19, high-titre convalescent plasma did not improve survival or other prespecified clinical outcomes. Funding: UK Research and Innovation (Medical Research Council) and National Institute of Health Research

New NMR techniques for the study of quadrupolar nuclei

The recently-developed multiple-quantum MAS (MQMAS) NMR experiment allows the acquisition of high-resolution, isotropic spectra of half-integer quadrupolar nuclei through the removal of the second-order quadrupolar broadening. Much interest has been generated in the combination of this high-resolution experiment with methods for obtaining structural information, such as cross-polarization. This technique, used with great success in the NMR of spin I = 1/2 nuclei, provides information on the spatial proximity of atoms. However, cross-polarization involving quadrupolar nuclei is an inherently more complex process, the mechanism of which is poorly understood. This thesis is concerned with further developments in the high-resolution NMR of quadrupolar nuclei in solids using the MQMAS experiment and, in particular, with novel techniques involving the combination of MQMAS with cross-polarization. The application of cross-polarization to quadrupolar nuclei is considered and the novel possibility of cross-polarization directly to the multiple-quantum coherences of a quadrupolar nucleus in a powdered sample is proposed. A theoretical and experimental investigation of both single- and multiple-quantum cross-polarization in static samples is undertaken. The intensity and lineshape variations observed in cross-polarized NMR spectra are modelled by computer simulations and the relationship between cross-polarization and quadrupolar nutation is demonstrated. The effects of MAS upon the cross-polarization process are then discussed in the light of these findings using both simulations and experimental methods. The combination of direct multiple-quantum cross-polarization with MQMAS in novel two-dimensional techniques is demonstrated, allowing spectral editing of the high-resolution NMR spectra of quadrupolar nuclei. Examples of cross-polarization to triple-, five- and seven-quantum coherences of "2"3Na, "1"7O,"2"7Al and "4"5Sc are shown. Additional two-dimensional techniques involving cross-polarization to single-quantum coherences are also discussed. The MQMAS and cross-polarized MQMAS experiments are then applied to systems of geochemical and industrial interest. An "1"7O NMR study of silicate minerals and an "2"7Al NMR study of amorphous alumino silicates are undertaken, and the ability of these techniques to provide additional insights into the nature of these materials is investigated. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:D211272 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Multiple-quantum cross-polarization and two-dimensional MQMAS NMR of quadrupolar nuclei

Cross-polarization from H-1 to the multiple-quantum coherences of a quadrupolar nucleus is used in combination with the two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR experiment in order to extract high-resolution CPMAS NMR spectra. The technique is demonstrated on Na-23 (S = 3/2), O-17, Al-27 (both S = 5/2), and Sc-45 (S = 7/2) nuclei, showing the applicability of multiple-quantum cross-polarization to systems with differing spin quantum number, gyromagnetic ratio, and relative nuclide abundance. The utility of this two-dimensional MAS NMR experiment for spectral editing and site-specific measurement of crosspolarization intensities is demonstrated. The possibility of direct cross-polarization to higher order multiple-quantum coherences is also considered and three-, five-, and seven-quantum cross-polarized Sc-45 MAS NMR spectra are presented. (C) 2000 Academic Press.</p

Quadrupolar coupling: an introduction and crystallographic aspects

The quadrupolar coupling interaction is discussed in the context of the recent interest in determining crystallographic information by solid-state NMR. First, the nature of the quadrupolar interaction is reviewed and the first-principles calculation and experimental NMR measurement of quadrupolar couplings are discussed. Then, with these foundations in place, we describe how quadrupolar coupling parameters can be used to provide information about the arrangement of atoms in a crystalline solid. The topics discussed in this section include the effect of crystal symmetry, local structure, and solid-state dynamics upon quadrupolar parameters and how comparison of calculated and experimental parameters might be used to refine crystal structures derived from powder diffraction data

Rotor-synchronized acquisition of quadrupolar satellite-transition NMR spectra: practical aspects and double-quantum filtration

The very broad resonances of quadrupolar (spin I &#62; 1/2) nuclei are resolved by magic angle spinning (MAS) into a large number of spinning sidebands, each of which often remains anisotropically broadened. The quadrupolar interaction can be removed to a first-order approximation if the MAS NMR spectrum is acquired in a rotor-synchronized fashion, aliasing the spinning sidebands onto a centreband and thereby increasing the signal-to-noise ratio in the resulting, possibly second-order broadened, spectrum. We discuss the practical aspects of this rotor-synchronization in the direct (t2) time domain, demonstrating that the audiofrequency filters in the receiver section of the spectrometer have a significant impact on the precise timings needed in the experiment. We also introduce a novel double-quantum filtered rotor-synchronized experiment for half-integer spin quadrupolar (spin I = 3/2, 5/2, etc.) nuclei that makes use of central-transition-selective inversion pulses to both excite and reconvert double-quantum coherences and yields a simplified spectrum containing only the ST1 (mI = ± 1/2 ↔ ± 3/2) satellite-transition lineshapes. For spin I = 5/2 nuclei, such as 17O and 27Al, this spectrum may exhibit a significant resolution increase over the conventional central-transition spec