Accelerated acquisition of wideline solid-state NMR spectra of spin 3/2 nuclei by frequency-stepped indirect detection experiments.

73% of all NMR-active nuclei are quadrupolar nuclei with a nuclear spin I > 1/2. The broadening of the solid-state NMR signals by the quadrupolar interaction often leads to poor sensitivity and low resolution. In this work we present experimental and theoretical investigations of magic angle spinning (MAS) 1H{X} double-echo resonance-echo saturation-pulse double-resonance (DE-RESPDOR) and Y{X} J-resolved solid-state NMR experiments for the indirect detection of spin 3/2 quadrupolar nuclei (X = spin 3/2 nuclei, Y = spin 1/2 nuclei). In these experiments, the spectrum of the quadrupolar nucleus is reconstructed by plotting the observed dephasing of the detected spin as a function of the transmitter offset of the indirectly detected spin. Numerical simulations were used to investigate the achievable levels of dephasing and to predict the lineshapes of indirectly detected NMR spectra of the quadrupolar nucleus. We demonstrate 1H, 31P and 207Pb detection of 35Cl, 81Br, and 63Cu (I = 3/2) nuclei in trans-Cl2Pt(NH3)2 (transplatin), (CH3NH3)PbCl3 (methylammonium lead chloride, MAPbCl3), (CH3NH3)PbBr3 (methylammonium lead bromide, MAPbBr3) and CH3C(CH2PPh2)3CuI (1,1,1-tris(diphenylphosphinomethyl)ethane copper(I) iodide, triphosCuI), respectively. In all of these experiments, we were able to detect megahertz wide central transition or satellite transition powder patterns. Significant time savings and gains in sensitivity were attained in several test cases. Additionally, the indirect detection experiments provide valuable structural information because they confirm the presence of dipolar or scalar couplings between the detected nucleus and the quadrupolar nucleus of interest. Finally, numerical simulations suggest these methods are also potentially applicable to abundant spin 5/2 and spin 7/2 quadrupolar nuclei.

Phosphine Ligand Binding and Catalytic Activity of Group 10-14 Heterobimetallic Complexes.

Heterobimetallic complexes have attracted much interest due to their broad range of structures and reactivities as well as unique catalytic abilities. Additionally, these complexes can be utilized as single-source precursors for the synthesis of binary intermetallic compounds. An example is the family of bis(pyridine-2-thiolato)dichloro-germanium and tin complexes of group 10 metals (Pd and Pt). The reactivity of these heterobimetallic complexes is highly tunable through substitution of the group 14 element and the neutral ligand bound to the transition metal. Here, we study the binding energies of three different phosphorous-based ligands, PR3 (R = Bu, Ph, and OPh) by density functional theory and restricted Hartree-Fock methods. The PR3 ligand-binding energies follow the trend of PBu3 > PPh3 > P(OPh)3, in agreement with their sigma-bonding ability. These results are confirmed by ligand exchange experiments monitored with 31P NMR spectroscopy, in which a weaker binding PR3 ligand is replaced with a stronger one. Furthermore, we demonstrate that the heterobimetallic complexes are active catalysts in the Negishi coupling reaction, where stronger binding PR3 ligands inhibit access to an active site at the metal center. Similar strategies could be applied to other complexes to better understand their ligand-binding energetics and predict their reactivity as both precursors and catalysts.

A new approach for the acquisition of trauma surgical skills: an OSCE type of simulation training program.

BACKGROUND: Worldwide, trauma-related deaths are one of the main causes of mortality. Appropriate surgical treatment is crucial to prevent mortality, however, in the past decade, general surgery residents' exposure to trauma cases has decreased, particularly since the COVID-19 pandemic. In this context, accessible simulation-based training scenarios are essential. METHODS: A low-cost, previously tested OSCE scenario for the evaluation of surgical skills in trauma was implemented as part of a short training boot camp for residents and recently graduated surgeons. The following stations were included bowel anastomosis, vascular anastomosis, penetrating lung injury, penetrating cardiac injury, and gastric perforation (laparoscopic suturing). A total of 75 participants from 15 different programs were recruited. Each station was videotaped in high definition and assessed in a remote and asynchronous manner. The level of competency was assessed through global and specific rating scales alongside procedural times. Self-confidence to perform the procedure as the leading surgeon was evaluated before and after training. RESULTS: Statistically significant differences were found in pre-training scores between groups for all stations. The lowest scores were obtained in the cardiac and lung injury stations. After training, participants significantly increased their level of competence in both grading systems. Procedural times for the pulmonary tractotomy, bowel anastomosis, and vascular anastomosis stations increased after training. A significant improvement in self-confidence was shown in all stations. CONCLUSION: An OSCE scenario for training surgical skills in trauma was effective in improving proficiency level and self-confidence. Low pre-training scores and level of confidence in the cardiac and lung injury stations represent a deficit in residency programs that should be addressed. The incorporation of simulation-based teaching tools at early stages in residency would be beneficial when future surgeons face extremely severe trauma scenarios.

Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy.

Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D 113Cd and 77Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. 113Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe3O, CdSe2O2, and CdSeO3 Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear 113Cd-113Cd and 77Se-77Se and heteronuclear 113Cd-77Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, 77Se{113Cd} scalar heteronuclear multiple quantum coherence (J-HMQC) experiments were used to selectively measure one-bond 77Se-113Cd scalar coupling constants (1J(77Se, 113Cd)). With knowledge of 1J(77Se, 113Cd), heteronuclear 77Se{113Cd} spin echo (J-resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. The J-resolved experiments directly confirmed that major Cd and Se surface species have CdSe2O2 and SeCd4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.

Validity Argument for a Simulation-Based Objective Structured Clinical Examination Scenario for Evaluation of Surgical Skills in Trauma.

BACKGROUND: Trauma is one of the main causes of death globally, and appropriate surgical care is crucial to impact mortality. However, resident-performed trauma cases have diminished in the last 10 years. Simulation-based tools have proven to be effective to evaluate practical skills in a variety of settings. However, there is a lack of evidence regarding proper validation of trauma surgery models. OBJECTIVE: The aim of this study was to evaluate under a contemporary validity framework, an objective structured clinical evaluation (OSCE) scenario for the assessment of basic and advanced surgical skills in trauma and emergency surgery. METHODS: An OSCE-type simulation assessment program was developed incorporating six stations representing basic and advanced surgical skills that are essential in trauma surgery. Each station was designed using ex-vivo animal tissue. The stations included basic knots and sutures, bowel resection and anastomosis, vascular end-to-end anastomosis, lung injury repair, cardiac injury repair, and laparoscopic suturing. Eight postgraduate year 2 (PY-2), eight recently graduated surgeons (RGS), and 3 experts were recruited, and their performance was blindly assessed by experts using the validated general rating scale OSATS (Objective Structured Assessment of Technical Skills) as well as the time taken to complete the procedure. RESULTS: Significant differences were identified among groups. The average OSATS score was 82 for the PY2 group, 113 for the RGS group, and 147 for the experts (P < 0.01). The average procedural time to complete all the stations was 98 minutes for the PY2 group, 68 minutes for the RGS group, and 35 minutes for the expert surgeons (P < 0.01). CONCLUSION: An OSCE scenario designed using ex-vivo tissue met 4 out of 5 criteria of the Messick validity framework: content, relation to other variables, response process and consequences of the test. The results show it is a valid strategy for the evaluation of practical skills in trauma surgery.

All Single-Mode-Fiber Supercontinuum Source Setup for Monitoring of Multiple Gases Applications.

In this paper, a gas sensing system based on a conventional absorption technique using a single-mode-fiber supercontinuum source (SMF-SC) is presented. The SC source was implemented by channeling pulses from a microchip laser into a one kilometer long single-mode fiber (SMF), obtaining a flat high-spectrum with a bandwidth of up to 350 nm in the region from 1350 to 1700 nm, and high stability in power and wavelength. The supercontinuum radiation was used for simultaneously sensing water vapor and acetylene gas in the regions from 1350 to 1420 nm and 1510 to 1540 nm, respectively. The experimental results show that the absorption peaks of acetylene have a maximum depth of approximately 30 dB and contain about 60 strong lines in the R and P branches, demonstrating a high sensitivity of the sensing setup to acetylene. Finally, to verify the experimental results, the experimental spectra are compared to simulations obtained from the Hitran database. This shows that the implemented system can be used to develop sensors for applications in broadband absorption spectroscopy and as a low-cost absorption spectrophotometer of multiple gases.

Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials.

Surface characterization is crucial for understanding how the atomic-level structure affects the chemical and photophysical properties of semiconducting nanoparticles (NPs). Solid-state nuclear magnetic resonance spectroscopy (NMR) is potentially a powerful technique for the characterization of the surface of NPs, but it is hindered by poor sensitivity. Dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) has previously been demonstrated to enhance the sensitivity of surface-selective solid-state NMR experiments by 1-2 orders of magnitude. Established sample preparations for DNP SENS experiments on NPs require the dilution of the NPs on mesoporous silica. Using hexagonal boron nitride (h-BN) to disperse the NPs doubles DNP enhancements and absolute sensitivity in comparison to standard protocols with mesoporous silica. Alternatively, precipitating the NPs as powders, mixing them with h-BN, and then impregnating the powdered mixture with radical solution leads to further 4-fold sensitivity enhancements by increasing the concentration of NPs in the final sample. This modified procedure provides a factor of 9 improvement in NMR sensitivity in comparison to previously established DNP SENS procedures, enabling challenging homonuclear and heteronuclear 2D NMR experiments on CdS, Si, and Cd3P2 NPs. These experiments allow NMR signals from the surface, subsurface, and core sites to be observed and assigned. For example, we demonstrate the acquisition of DNP-enhanced 2D 113Cd-113Cd correlation NMR experiments on CdS NPs and natural isotropic abundance 2D 13C-29Si HETCOR of functionalized Si NPs. These experiments provide a critical understanding of NP surface structures.

Unveiling the Photo- and Thermal-Stability of Cesium Lead Halide Perovskite Nanocrystals.

Lead halide perovskites possess unique characteristics that are well-suited for optoelectronic and energy capture devices, however, concerns about their long-term stability remain. Limited stability is often linked to the methylammonium cation, and all-inorganic CsPbX3 (X=Cl, Br, I) perovskite nanocrystals have been reported with improved stability. In this work, the photostability and thermal stability properties of CsPbX3 (X=Cl, Br, I) nanocrystals were investigated by means of electron microscopy, X-ray diffraction, thermogravimetric analysis coupled with FTIR (TGA-FTIR), ensemble and single particle spectral characterization. CsPbBr3 was found to be stable under 1-sun illumination for 16 h in ambient conditions, although single crystal luminescence analysis after illumination using a solar simulator indicates that the luminescence states are changing over time. CsPbBr3 was also stable to heating to 250 °C. Large CsPbI3 crystals (34±5 nm) were shown to be the least stable composition under the same conditions as both XRD reflections and Raman bands diminish under irradiation; and with heating the γ (black) phase reverts to the non-luminescent δ phase. Smaller CsPbI3 nanocrystals (14±2 nm) purified by a different washing strategy exhibited improved photostability with no evidence of crystal growth but were still thermally unstable. Both CsPbCl3 and CsPbBr3 show crystal growth under irradiation or heat, likely with a preferential orientation based on XRD patterns. TGA-FTIR revealed nanocrystal mass loss was only from liberation and subsequent degradation of surface ligands. Encapsulation or other protective strategies should be employed for long-term stability of these materials under conditions of high irradiance or temperature.

Solution-Grown Sodium Bismuth Dichalcogenides: Toward Earth-Abundant, Biocompatible Semiconductors.

Many technologically relevant semiconductors contain toxic, heavily regulated (Cd, Pb, As), or relatively scarce (Li, In) elements and often require high manufacturing costs. We report a facile, general, low-temperature, and size tunable (4-28 nm) solution phase synthesis of ternary APnE2 semiconductors based on Earth-abundant and biocompatible elements (A = Na, Pn = Bi, E = S or Se). The observed experimental band gaps (1.20-1.45 eV) fall within the ideal range for solar cells. Computational investigation of the lowest energy superstructures that result from "coloring", caused by mixed cation sites present in their rock salt lattice, agrees with other better-known members of this family of materials. Our synthesis unlocks a new class of low cost and environmentally friendly ternary semiconductors that show properties of interest for applications in energy conversion.

Soft Chemistry, Coloring and Polytypism in Filled Tetrahedral Semiconductors: Toward Enhanced Thermoelectric and Battery Materials.

Filled tetrahedral semiconductors are a rich family of compounds with tunable electronic structure, making them ideal for applications in thermoelectrics, photovoltaics, and battery anodes. Furthermore, these materials crystallize in a plethora of related structures that are very close in energy, giving rise to polytypism through the manipulation of synthetic parameters. This Minireview highlights recent advances in the solution-phase synthesis and nanostructuring of these materials. These methods enable the synthesis of metastable phases and polytypes that were previously unobtainable. Additionally, samples synthesized in solution phase have enhanced thermoelectric performance due to their decreased grain size.

Iron and Cobalt Diazoalkane Complexes Supported by ß-Diketiminate Ligands: A Synthetic, Spectroscopic, and Computational Investigation.

Diazoalkanes are interesting redox-active ligands and also precursors to carbene fragments. We describe a systematic study of the binding and electronic structure of diphenyldiazomethane complexes of ß-diketiminate supported iron and cobalt, which span a range of formal d-electron counts of 7-9. In end-on diazoalkane complexes of formally monovalent three-coordinate transition metals, the electronic structures are best described as having the metal in the +2 oxidation state with an antiferromagnetically coupled radical anion diazoalkane as shown by crystallography, spectroscopy, and computations. A formally zerovalent cobalt complex has different structures depending on whether potassium binds; potassium binding gives transfer of two electrons into the η2-diazoalkane, but the removal of the potassium with crown ether leads to a form with only one electron transferred into an η1-diazoalkane. These results demonstrate the influence of potassium binding and metal oxidation state on the charge localization in the diazoalkane complexes. Interestingly, none of these reduced complexes yield carbene fragments, but the new cobalt(II) complex LtBuCoPF6 (LtBu = bulky ß-diketiminate) does catalyze the formation of an azine from its cognate diazoalkane, suggesting N2 loss and transient carbene formation.

Photoinduced Trans-to-cis Phase Transition of Polycrystalline Azobenzene at Low Irradiance Occurs in the Solid State.

The ability to produce large-scale, reversible structural changes in a variety of materials by photoexcitation of a wide variety of azobenzene derivatives has been recognized for almost two decades. Because photoexcitation of trans-azobenzene produces the cis-isomer in solution, it has generally been inferred that the macroscopic structural changes occurring in materials are also initiated by a similar large-amplitude trans-to-cis isomerization. This work provides the first demonstration that a trans-to-cis photoisomerization occurs in polycrystalline azobenzene, and is consistent with the previously hypothesized nature of the trigger in the photoactuated mechanisms of the materials in question. It is also demonstrated that under low irradiance, trans-to-cis isomerization occurs in the solid (not via a pre-melted phase); and the presence of the cis-isomer thus lowers the melting point of the sample, providing a liquid phase. A variety of experimental techniques were employed, including X-ray diffraction measurements of polycrystalline azobenzene during exposure to laser irradiation and fluorescence measurements of the solid sample. A practical consequence of this work is that it establishes trans-azobenzene as an easily obtainable and well-defined control for monitoring photoinduced structural changes in X-ray diffraction experiments, using easily accessible laser wavelengths.

Polytypism and Unique Site Preference in LiZnSb: A Superior Thermoelectric Reveals Its True Colors.

The first example of polytypism in the I-II-V semiconductors has been demonstrated with the synthesis of cubic LiZnSb by a low-temperature solution-phase method. This phase exhibits a unique coloring pattern that is novel for this class of compounds. The choice of site configuration has a considerable impact on the band structure of these materials, which in turn affects the transport properties. While the hexagonal polytype has been suggested as a promising n-type and extremely poor p-type thermoelectric material, the cubic analogue is calculated to have high efficiencies for both the n- and p-type derivatives (1.64 and 1.43, respectively, at 600 K). Furthermore, the cubic phase is found to be the energetically favored polytype. This surprising result provides a rationale for the lack of success in synthesizing the hexagonal polytype in either stoichiometric or n-type compositions.

Large Scale Nanoparticle Screening for Small Molecule Analysis in Laser Desorption Ionization Mass Spectrometry.

Nanoparticles (NPs) have been suggested as efficient matrixes for small molecule profiling and imaging by laser-desorption ionization mass spectrometry (LDI-MS), but so far there has been no systematic study comparing different NPs in the analysis of various classes of small molecules. Here, we present a large scale screening of 13 NPs for the analysis of two dozen small metabolite molecules. Many NPs showed much higher LDI efficiency than organic matrixes in positive mode and some NPs showed comparable efficiencies for selected analytes in negative mode. Our results suggest that a thermally driven desorption process is a key factor for metal oxide NPs, but chemical interactions are also very important, especially for other NPs. The screening results provide a useful guideline for the selection of NPs in the LDI-MS analysis of small molecules.