¹⁴N overtone transition in double rotation solid-state NMR

Solid-state NMR transitions involving outer energy levels of the spin-1 14N nucleus are immune, to first order in perturbation theory, to the broadening caused by the nuclear quadrupole interaction. The corresponding overtone spectra, when acquired in conjunction with magic-angle sample spinning, result in lines, which are just a few kHz wide, permitting the direct detection of nitrogen compounds without the need for labeling. Despite the success of this technique, “overtone” resonances are still broadened due to indirect, second order effects arising from the large quadrupolar interaction. Here we demonstrate that another order of magnitude in spectral resolution may be gained by using double rotation. This brings the width of the 14N solid-state NMR lines much closer to the region commonly associated with high-resolution solid-state NMR spectroscopy of 15N and demonstrates the improvements in resolution that may be possible through the development of pulsed methodologies to suppress these second order effects

K-edge X-ray absorption spectra in transition metal oxides beyond the single particle approximation: shake-up many body effects

The near edge structure (XANES) in K-edge X-ray absorption spectroscopy (XAS) is a widely used tool for studying electronic and local structure in materials. The precise interpretation of these spectra with the help of calculations is hence of prime importance, especially for the study of correlated materials which have a complicated electronic structure per se. The single particle approach, for example, has generally limited itself to the dominant dipolar cross-section. It has long been known however that effects beyond this approach should be taken into account, both due to the inadequacy of such calculations when compared to experiment and the presence of shake-up many-body satellites in core-level photoemission spectra of correlated materials. This effect should manifest itself in XANES spectra and the question is firstly how to account for it theoretically and secondly how to verify it experimentally. By using state-of-the-art first principles electronic structure calculations and 1s photoemission measurements we demonstrate that shake-up many-body effects are present in K-edge XAS dipolar spectra of NiO, CoO and CuO at all energy scales. We show that shake-up effects can be included in K-edge XAS spectra in a simple way by convoluting the single-particle first-principles calculations including core-hole effects with the 1s photoemission spectra. We thus describe all features appearing in the XAS dipolar cross-section of NiO and CoO and obtain a dramatic improvement with respect to the single-particle calculation in CuO. These materials being prototype correlated magnetic oxides, our work points to the presence of shake-up effects in K-edge XANES of most correlated transition metal compounds and shows how to account for them, paving the way to a precise understanding of their electronic structure.Comment: 6 pages, 4 picture

Strategies for 1H-Detected Dynamic Nuclear Polarization Magic-Angle Spinning NMR Spectroscopy

© 2020 The Authors. Published by Wiley-VCH GmbH Combining dynamic nuclear polarization with proton detection significantly enhances the sensitivity of magic-angle spinning NMR spectroscopy. Herein, the feasibility of proton-detected experiments with slow (10 kHz) magic angle spinning was demonstrated. The improvement in sensitivity permits the acquisition of indirectly detected 14N NMR spectra allowing biomolecular structures to be characterized without recourse to isotope labelling. This provides a new tool for the structural characterization of environmental and medical samples, in which isotope labelling is frequently intractable

Diagnostic accuracy of MRI in the differential diagnosis between uterine leiomyomas and sarcomas: A systematic review and meta-analysis

Background: Differential diagnosis between uterine leiomyomas and sarcomas is challenging. Magnetic resonance imaging (MRI) represents the second-line diagnostic method after ultrasound for the assessment of uterine masses. Objectives: To assess the accuracy of MRI in the differential diagnosis between uterine leiomyomas and sarcomas. Search Strategy: A systematic review and meta-analysis was performed searching five electronic databases from their inception to June 2023. Selection Criteria: All peer-reviewed observational or randomized clinical trials that reported an unbiased postoperative histologic diagnosis of uterine leiomyoma or uterine sarcoma, which also comprehended a preoperative MRI evaluation of the uterine mass. Data Collection and Analysis: Sensitivity, specificity, positive and negative likelihood ratios, diagnostic odds ratio, and area under the curve on summary receiver operating characteristic of MRI in differentiating uterine leiomyomas and sarcomas were calculated as individual and pooled estimates, with 95% confidence intervals (CI). Results: Eight studies with 2495 women (2253 with uterine leiomyomas and 179 with uterine sarcomas), were included. MRI showed pooled sensitivity of 0.90 (95% CI 0.84–0.94), specificity of 0.96 (95% CI 0.96–0.97), positive likelihood ratio of 13.55 (95% CI 6.20–29.61), negative likelihood ratio of 0.08 (95% CI 0.02–0.32), diagnostic odds ratio of 175.13 (95% CI 46.53–659.09), and area under the curve of 0.9759. Conclusions: MRI has a high diagnostic accuracy in the differential diagnosis between uterine leiomyomas and sarcomas

Understanding the Role of Designed Solid Acid Sites in the Low-Temperature Production of ϵ-Caprolactam

Modern society is placing increasing demands on commodity chemicals, driven by the ever‐growing global population and the desire for improved standards of living. As the polymer industry grows, a sustainable route to ϵ‐caprolactam, the precursor to the recyclable nylon‐6 polymer, is becoming increasingly important. To this end, we have designed and characterized a recyclable SAPO catalyst using a range of characterization techniques, to achieve near quantitative yields of ϵ‐caprolactam from cyclohexanone oxime. The catalytic process operates under significantly less energetically demanding conditions than other widely practiced industrial processes

Direct Enhancement of Nuclear Singlet Order by Dynamic Nuclear Polarization

Hyperpolarized singlet order is available immediately after dissolution DNP, avoiding need for additional preparation steps. We demonstrate this procedure on a sample of [1,2–13C2]pyruvic aci

Understanding the role of molecular diffusion and catalytic selectivity in liquid-phase Beckmann rearrangement

ABSTRACT: Understanding the role of diffusion in catalysis is essential in the design of highly active, selective, and stable industrial heterogeneous catalysts. By using a combination of advanced in situ spectroscopic characterization tools, particularly quasi-elastic and inelastic neutron scattering, we outline the crucial differences in diffusion modes and molecular interactions of active sites within solid-acid catalysts. This, coupled with 2D solid-state NMR and probe-based FTIR spectroscopy, reveals the nature of the active site in our SAPO- 37 catalyst and affords detailed information on the evolution of solid-acid catalysts that can operate at temperatures as low as 130 °C, for the Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam (precursor for Nylon-6). The versatility of this approach leads to structure−property correlations that contrast the dynamics of the diffusion process in the different materials studied. Our results illustrate the power of these techniques in unravelling the interplay between active site and molecular diffusion in single-site heterogeneous catalysts, which can play a vital role in designing low-temperature, sustainable catalytic processes