Probing Short-Range Interactions in Isostructural Hydrate and Perhydrate of Dabrafenib by Magic-Angle Spinning Solid-State NMR.

Dabrafenib (), an anticancer drug, exhibits isostructural properties in its hydrate () and perhydrate () forms, as revealed by single-crystal X-ray diffraction. Despite the HO and HO solvent molecules occupying identical locations, the two polymorphs have different thermal behaviors. In general, determination of stoichiometry of HO in the perhydrate crystals is difficult due to the presence of both HO and HO in the same crystal voids.

A facile approach for estimating radio-frequency field strength of low-receptivity nuclei.

Radio-frequency (RF) field calibration is essential in NMR spectroscopy. A common practice is to collect a nutation curve by varying the pulse length in a direct single-pulse excitation experiment or in a cross-polarization magic-angle spinning with a flip-back pulse experiment. From the null points on this curve, one can calculate the RF field strength.

Morphology Tuning via Linker Modulation: Metal-Free Covalent Organic Nanostructures with Exceptional Chemical Stability for Electrocatalytic Water Splitting.

The development of synthetic routes for the formation of robust porous organic polymers (POPs) with well-defined nanoscale morphology is fundamentally significant for their practical applications. The thermodynamic characteristics that arise from reversible covalent bonding impart intrinsic chemical instability in the polymers, thereby impeding their overall potential. Herein, a unique strategy is reported to overcome the stability issue by designing robust imidazole-linked POPs via tandem reversible/irreversible bond formation.

Viscoelastic Covalent Organic Nanotube Fabric via Macroscopic Entanglement.

Covalent organic nanotubes (CONTs) are one-dimensional porous frameworks constructed from organic building blocks via dynamic covalent chemistry. CONTs are synthesized as insoluble powder that restricts their potential applications. The judicious selection of 2,2'-bipyridine-5,5'-dicarbaldehyde and tetraaminotriptycene as building blocks for TAT-BPy CONTs has led to constructing flexible yet robust and self-standing fabric up to 3 μm thickness.

Detection of remote proton-nitrogen correlations by H-detected N overtone solid-state NMR at fast MAS.

Detecting proton and nitrogen correlations in solid-state nuclear magnetic resonance (NMR) is important for the structural determination of biological and chemical systems. Recent advances in proton detection-based approaches under fast magic-angle spinning have facilitated the detection of H-N correlations by solid-state NMR. However, observing remote H-N correlations by these approaches is still a challenge, especially for N sites having large quadrupolar couplings.

Separating an overlapped H peak and identifying its H-H correlations with the use of single-channel H solid-state NMR at fast MAS.

Fast magic-angle spinning (≥60 ​kHz) technique has enabled the acquisition of high-resolution H NMR spectra of solid materials. However, the spectral interpretation is still difficult because the H peaks are overlapped due to the narrow chemical shift range and broad linewidths. An additional C or N or H dimension possibly addresses the issues of overlapped proton resonances, but it leads to the elongated experimental time.

Structure Solution of Nano-Crystalline Small Molecules Using MicroED and Solid-State NMR Dipolar-Based Experiments.

Three-dimensional electron diffraction crystallography (microED) can solve structures of sub-micrometer crystals, which are too small for single crystal X-ray crystallography. However, R factors for the microED-based structures are generally high because of dynamic scattering. That means R factor may not be reliable provided that kinetic analysis is used.

Rhabdoid Meningioma Metastases Cervical Lymph Nodes: A Rare Clinical Case Report and Treatment Outcome.

Meningioma is the most common central nervous system tumor that usually behaves benignly and has a good prognosis after treatment with tumor gross resection and with or without adjuvant therapy. Malignancy in meningioma is very rare and extracranial metastasis to cervical lymph nodes is even rarer. We report a case of a 40-year-old woman diagnosed with metastatic rhabdoid meningioma.

Selective H-H recoupling via symmetry sequences in fully protonated samples at fast magic angle spinning.

Proton-detected solid-state NMR at fast Magic Angle Spinning (MAS) is becoming the norm to characterize molecules. Routinely H-H and H-X dipolar couplings are used to characterize the structure and dynamics of molecules. Selective proton recoupling techniques are emerging as a method for structural characterization via estimation of qualitative and quantitative distances.

Selective H-N Distance Measurements by N Overtone Solid-State NMR Spectroscopy at Fast MAS.

Accurate distance measurements between proton and nitrogen can provide detailed information on the structures and dynamics of various molecules. The combination of broadband phase-modulated (PM) pulse and rotational-echo saturation-pulse double-resonance (RESPDOR) sequence at fast magic-angle spinning (MAS) has enabled the measurement of multiple H-N distances with high accuracy. However, complications may arise when applying this sequence to systems with multiple inequivalent N nuclei, especially a single H sitting close to multiple N atoms.

Protein Phosphatase Type 2C Functions in Phytohormone-Dependent Pathways and in Plant Responses to Abiotic Stresses.

Plants, as sessile organisms, are susceptible to a myriad of stress factors, especially abiotic stresses. Over the course of evolution, they have developed multiple mechanisms to sense and transduce environmental stimuli for appropriate responses. Among those, phosphorylation and dephosphorylation, regulated by protein kinases and protein phosphatases, respectively, are considered crucial signal transduction mechanisms.

Ectopic expression of GmHP08 enhances resistance of transgenic Arabidopsis toward drought stress.

Ectopic expression of Glycine max two-component system member GmHP08 in Arabidopsis enhanced drought tolerance of transgenic plants, possibly via ABA-dependent pathways. Phosphorelay by two-component system (TCS) is a signal transduction mechanism which has been evolutionarily conserved in both prokaryotic and eukaryotic organisms. Previous studies have provided lines of evidence on the involvement of TCS genes in plant perception and responses to environmental stimuli.

On the use of radio-frequency offsets for improving double-quantum homonuclear dipolar recoupling of half-integer-spin quadrupolar nuclei.

Detecting proximities between nuclei is crucial for atomic-scale structure determination with nuclear magnetic resonance (NMR) spectroscopy. Different from spin-1/2 nuclei, the methodology for quadrupolar nuclei is limited for solids due to the complex spin dynamics under simultaneous magic-angle spinning (MAS) and radio-frequency irradiation. Herein, the performances of several homonuclear rotary recoupling (HORROR)-based homonuclear dipolar recoupling sequences are evaluated for Al (spin-5/2).

α-Cyclodextrin Encapsulation of Bicyclo[1.1.1]pentane Derivatives: A Storable Feedstock for Preparation of [1.1.1]Propellane.

The bicyclo[1.1.1]pentane (BCP) scaffold is useful in medicinal chemistry, and many protocols are available for synthesizing BCP derivatives from [1.

Accuracy of H-H distances measured using frequency selective recoupling and fast magic-angle spinning.

Selective recoupling of protons (SERP) is a method to selectively and quantitatively measure magnetic dipole-dipole interaction between protons and, in turn, the proton-proton distance in solid-state samples at fast magic-angle spinning. We present a bimodal operator-based Floquet approach to describe the numerically optimized SERP recoupling sequence. The description calculates the allowed terms in the first-order effective Hamiltonian, explains the origin of selectivity during recoupling, and shows how different terms are modulated as a function of the radio frequency amplitude and the phase of the sequence.

Can proton-proton recoupling in fully protonated solids provide quantitative, selective and efficient polarization transfer?

Dipolar recoupling sequences have been used to probe spatial proximity of nuclear spins and were traditionally designed to probe rare spins such as C and/or N nuclei. The multi-spin dipolar-coupling network of the rare spins is weak due to smaller couplings and large chemical shift dispersion. Therefore, the recoupling approaches were tailored to design offset compensated or broadband sequences.

Heterologous Expression of a Soybean Gene Conferred Improved Drought Resistance of Transgenic .

Two-component systems (TCSs) have been identified as participants in mediating plant response to water deficit. Nevertheless, insights of their contribution to plant drought responses and associated regulatory mechanisms remain limited. Herein, a soybean response regulator (RR) gene , which is the potential drought-responsive downstream member of a TCS, was ectopically expressed in the model plant for the analysis of its biological roles in drought stress response.

Borohydride-containing coordination polymers: synthesis, air stability and dehydrogenation.

Control of the reactivity of hydride (H) in crystal structures has been a challenge because of its strong electron-donating ability and reactivity with protic species. For metal borohydrides, the dehydrogenation activity and air stability are in a trade-off, and control of the reactivity of BH has been demanded. For this purpose, we synthesize a series of BH -based coordination polymers/metal-organic frameworks.

Accurate H-N distance measurements by phase-modulated RESPDOR at ultra-fast MAS.

The combination of a phase-modulated (PM) saturation pulse and symmetry-based dipolar recoupling into a rotational-echo saturation-pulse double-resonance (RESPDOR) sequence has been employed to measure H-N distances. Such a measurement is challenging owing to the quadrupolar interaction of N nucleus and the intense H-H homonuclear dipolar interactions. Thanks to the recent advances in probe technology, the homonuclear dipolar interaction can be sufficiently suppressed at a fast MAS frequency (ν ≥ 60 kHz).

Synthesis of porous coordination polymers using carbon dioxide as a direct source.

Porous coordination polymers (PCPs) were synthesized by using CO and metal borohydrides as precursors. Borohydrides converted CO into bridging ligands such as formate (HCO) or formylhydroborate ([BH(OCHO)]) which are available to construct porous architectures; one of them shows 380 m g surface area.

Resolution enhancement and proton proximity probed by 3D TQ/DQ/SQ proton NMR spectroscopy under ultrafast magic-angle-spinning beyond 70 kHz.

Proton nuclear magnetic resonance (NMR) in solid state has gained significant attention in recent years due to the remarkable resolution and sensitivity enhancement afforded by ultrafast magic-angle-spinning (MAS). In spite of the substantial suppression of H-H dipolar couplings, the proton spectral resolution is still poor compared to that of C or N NMR, rendering it challenging for the structural and conformational analysis of complex chemicals or biological solids. Herein, by utilizing the benefits of double-quantum (DQ) and triple-quantum (TQ) coherences, we propose a 3D single-channel pulse sequence that correlates proton triple-quantum/double-quantum/single-quantum (TQ/DQ/SQ) chemical shifts.

Crystal melting and glass formation in copper thiocyanate based coordination polymers.

Crystal melting and glass formation of coordination polymers (CPs) and metal-organic frameworks (MOFs) are rare thermal events. To expand the library of melting CP/MOFs, we utilized anti-crystal engineering in ionic liquids to construct CPs. A combination of Cu+ and 4,4'-bipyridin-1-ium derivatives afforded four melting CPs showing stable liquid and glassy states.

Synthesis and Structural Characterization of a Pure ZnAl(OH)(SO)·2.6HO Layered Double Hydroxide.

The phase purity of a series of ZnAl(OH)SO· nHO layered double hydroxides (ZnAl-LDH) obtained from a reaction of bayerite (Al(OH)) with an excess of zinc(II) sulfate under hydrothermal conditions was investigated as a function of the reaction temperature, the duration of the hydrothermal treatment, and the zinc(II) concentration. The product quality, i.e.

Improved sensitivity and quantification for Si NMR experiments on solids using UDEFT (Uniform Driven Equilibrium Fourier Transform).

We demonstrate the possibility to use UDEFT (Uniform Driven Equilibrium Fourier Transform) technique in order to improve the sensitivity and the quantification of one-dimensional Si NMR experiments under magic-angle spinning (MAS). We derive an analytical expression of the signal-to-noise ratios of UDEFT and single-pulse (SP) experiments subsuming the contributions of transient and steady-state regimes. Using numerical spin dynamics simulations and experiments on Si-enriched amorphous silica and borosilicate glass, we show that 5929859 refocusing composite π-pulse and the adiabatic inversion using tanh/tan modulation improve the robustness of UDEFT technique to rf-inhomogeneity, offset, and chemical shift anisotropy.

Determination of the N chemical shift anisotropy in natural abundance samples by proton-detected 3D solid-state NMR under ultrafast MAS of 70 kHz.

Chemical shift anisotropy (CSA) is a sensitive probe of electronic environment at a nucleus, and thus, it offers deeper insights into detailed structural and dynamic properties of different systems, for example, chemical, biological, and materials. Over the years, massive efforts have been made to develop recoupling methods that reintroduce CSA interaction under magic angle spinning (MAS) conditions. Most of them require slow or moderate MAS (≤20 kHz) and isotopically enriched samples.