Tridentate NacNac Tames T-Shaped Nickel(I) Radical.

The reaction of a nickel(II) chloride complex containing a tridentate ß-diketiminato ligand with a picolyl group [2,6-iPr2 -C6 H3 NC(Me)CHC(Me)NH(CH2 py)]Ni(II)Cl (1)] with KSi(SiMe3 )3 conveniently afforded a nickel(I) radical with a T-shaped geometry (2). The compound's metalloradical nature was confirmed through electron paramagnetic resonance (EPR) studies and its reaction with TEMPO, resulting in the formation of a highly unusual three-membered nickeloxaziridine complex (3). When reacted with disulfide and diselenide, the S-S and Se-Se bonds were cleaved, and a coupled product was formed through carbon atom of the pyridine-imine group. The nickel(I) radical activates dihydrogen at room temperature and atmospheric pressure to give the monomeric nickel hydride.

Tridentate NacNac Stabilized Tin and Nickel Complexes: Access to a Monomeric Nickel Hydride and Its Catalytic Application.

The transmetalation reaction of picolyl-supported tridentate nacnac germylene monochloride [2,6-iPr2-C6H3NC(Me)CHC(Me)NH(CH2py)]GeCl (1) (py = pyridine) with SnCl2 results in an analogous stannylene chloride (2). The three-coordinated stannylenium cation [{2,6-iPr2-C6H3NC(Me)CHC(Me)NH(CH2py)}Sn]+ with SnCl3- as a counteranion (3) has been generated through the abstraction of chloride ligand from 2 using an additional equivalent of SnCl2. Instead of forming a donor-acceptor complex, 2 undergoes a facile redox transmetalation reaction with Ni(COD)2 (COD = cyclooctadiene) and CuCl to afford analogous nickel and copper complexes [2,6-iPr2-C6H3NC(Me)CHC(Me)NH(CH2py)]MCl [M = Ni (4) and Cu (5)]. The reactions of 4 with potassium tri-sec-butylborohydride (commonly known as K-selectride) and AgSbF6 provide access to monomeric Ni(II) hydride, [2,6-iPr2-C6H3NC(Me)CHC(Me)NH(CH2py)]NiH (6) and a Ni(II) cation, [{2,6-iPr2-C6H3NC(Me)CHC(Me)NH(CH2py)}Ni][SbF6] (7), respectively. 6 was found to be an effective catalyst for the hydroboration of amides.

1H NMR with Partial Transition Selectivity.

1H NMR has unique strengths, owing, for one, to 1H being the most sensitive NMR nucleus. However, the limited frequency range of 1H chemical shifts implies spectral crowding, leading to difficulties in assignment and interpretation of the spectra. Homonuclear broadband decoupling has been developed as a means of simplifying 1H NMR spectra but clearly leads to the inevitable and complete loss of precious information on homonuclear scalar couplings in solution state. A novel experiment is introduced in this work, which leads to partial 1H multiplet selectivity, thereby reducing spectral crowding, while at the same time permitting couplings to be inferred. The present one-dimensional (1D) experiment relies on two-way coherence transfer starting from 1H to coupled 13C carbons at natural abundance and ending finally with 1H detection. The experiment may be termed CArbon Single transition EDited (CASED) 1H NMR. The unusual spectral patterns that result are summarized, demonstrated, and rationalized for various molecular fragments. Artifacts in the present version of the CASED experiment are also described, and an application to the 1H NMR of a disaccharide is demonstrated as a first practical example.

A direct nuclear magnetic resonance method to investigate lysine acetylation of intrinsically disordered proteins.

Intrinsically disordered proteins are frequent targets for functional regulation through post-translational modification due to their high accessibility to modifying enzymes and the strong influence of changes in primary structure on their chemical properties. While lysine Nε-acetylation was first observed as a common modification of histone tails, proteomic data suggest that lysine acetylation is ubiquitous among both nuclear and cytosolic proteins. However, compared with our biophysical understanding of the other common post-translational modifications, mechanistic studies to document how lysine Nε-acetyl marks are placed, utilized to transduce signals, and eliminated when signals need to be turned off, have not kept pace with proteomic discoveries. Herein we report a nuclear magnetic resonance method to monitor Nε-lysine acetylation through enzymatic installation of a13C-acetyl probe on a protein substrate, followed by detection through 13C direct-detect spectroscopy. We demonstrate the ease and utility of this method using histone H3 tail acetylation as a model. The clearest advantage to this method is that it requires no exogenous tags that would otherwise add steric bulk, change the chemical properties of the modified lysine, or generally interfere with downstream biochemical processes. The non-perturbing nature of this tagging method is beneficial for application in any system where changes to local structure and chemical properties beyond those imparted by lysine modification are unacceptable, including intrinsically disordered proteins, bromodomain containing protein complexes, and lysine deacetylase enzyme assays.

Pathogen-specific antimicrobials engineered de novo through membrane-protein biomimicry.

Precision antimicrobials aim to kill pathogens without damaging commensal bacteria in the host, and thereby cure disease without antibiotic-associated dysbiosis. Here we report the de novo design of a synthetic host defence peptide that targets a specific pathogen by mimicking key molecular features of the pathogen's channel-forming membrane proteins. By exploiting physical and structural vulnerabilities within the pathogen's cellular envelope, we designed a peptide sequence that undergoes instructed tryptophan-zippered assembly within the mycolic acid-rich outer membrane of Mycobacterium tuberculosis to specifically kill the pathogen without collateral toxicity towards lung commensal bacteria or host tissue. These mycomembrane-templated assemblies elicit rapid mycobactericidal activity and enhance the potency of antibiotics by improving their otherwise poor diffusion across the rigid M. tuberculosis envelope with respect to agents that exploit transmembrane protein channels for antimycobacterial activity. This biomimetic strategy may aid the design of other narrow-spectrum antimicrobial peptides.

Crystal structure of a 1:1 co-crystal of the anti-cancer drug gefitinib with azelaic acid.

In the title co-crystal, C22H24ClFN4O3·C9H16O4, gefitinib (GTB; systematic name: quinazolin-4-amine) co-crystallizes with azelaic acid (AA; systematic name: nona-nedioic acid). The co-crystal has the monoclinic P21/n centrosymmetric space group, containing one mol-ecule each of GTB and AA in the asymmetric unit. A structure overlay of the GTB mol-ecule in the co-crystal with that of its most stable polymorph revealed a significant difference in the conformation of the morpholine moiety. The significant deviation in the conformation of one of the acidic groups of azelaic acid from its usual linear chain structure could be due to the encapsulation of one acidic group in the pocket formed between the two pincers of GTB namely, the morpholine and phenyl moieties. Both GTB and AA mol-ecules form N-H⋯O, O-H⋯N, C-H⋯O hydrogen bonds with C-H⋯F close contacts along with off-stacked aromatic π-π inter-actions between the GTB mol-ecules.

Hydrothermal Synthesis and Structure of a Dinuclear Molybdenum(III) Hydroxy Squarate with a Mo-Mo Bond.

The reaction of molybdenum(II) and chromium(II) acetates with squaric acid in degassed and deionized water under hydrothermal conditions at 150 °C is described. The products have been formulated as M2(µ-OH)2(µ-C4O4)2(H2O)4·2H2O, where M = Cr (1) and Mo (2), based on combustion elemental analysis, infrared spectroscopy, magic angle spinning (MAS) solid-state carbon-13 nuclear magnetic resonance (NMR), and single-crystal X-ray diffraction. The edge-shared bioctahedral structures involve doubly bridging hydroxide ligands and µ-squarate ligands. The chromium compound lacks a direct metal-metal-bonding interaction, while in contrast the molybdenum compound contains a Mo-Mo bond [2.491(2) Å]. The nature of the Mo-Mo-bonding interaction is compared with that of other similar d3-d3 dimers.

Correction: Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy.

Correction for 'Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy' by Janne Soetbeer et al., Phys. Chem. Chem. Phys., 2018, 20, 25506-25517.

Modular, triple-resonance, transmission line DNP MAS probe for 500 MHz/330 GHz.

We describe the design and construction of a modular, triple-resonance, fully balanced, DNP-MAS probe based on transmission line technology and its integration into a 500 MHz/330 GHz DNP-NMR spectrometer. A novel quantitative probe design and characterization strategy is developed and employed to achieve optimal sensitivity, RF homogeneity and excellent isolation between channels. The resulting three channel HCN probe has a modular design with each individual, swappable module being equipped with connectorized, transmission line ports. This strategy permits attachment of a mating connector that facilitates accurate impedance measurements at these ports and allows characterization and adjustment (e.g. for balancing or tuning/matching) of each component individually. The RF performance of the probe is excellent; for example, the 13C channel attains a Rabi frequency of 280 kHz for a 3.2 mm rotor. In addition, a frequency tunable 330 GHz gyrotron operating at the second harmonic of the electron cyclotron frequency was developed for DNP applications. Careful alignment of the corrugated waveguide led to minimal loss of the microwave power, and an enhancement factor ε = 180 was achieved for U-13C urea in the glassy matrix at 80 K. We demonstrated the operation of the system with acquisition of multidimensional spectra of cross-linked lysozyme crystals which are insoluble in glycerol-water mixtures used for DNP and samples of RNA.

Experimental and theoretical charge density, intermolecular interactions and electrostatic properties of metronidazole.

Metronidazole is a radiosensitizer; it crystallizes in the monoclinic system with space group P21/c. The crystal structure of metronidazole has been determined from high-resolution X-ray diffraction measurements at 90 K with a resolution of (sin θ/λ)max = 1.12 Å-1. To understand the charge-density distribution and the electrostatic properties of metronidazole, a multipole model refinement was carried out using the Hansen-Coppens multipole formalism. The topological analysis of the electron density of metronidazole was performed using Bader's quantum theory of atoms in molecules to determine the electron density and the Laplacian of the electron density at the bond critical point of the molecule. The experimental results have been compared with the corresponding periodic theoretical calculation performed at the B3LYP/6-31G** level using CRYSTAL09. The topological analysis reveals that the N-O and C-NO2 exhibit less electron density as well as negative Laplacian of electron density. The molecular packing of crystal is stabilized by weak and strong inter- and intramolecular hydrogen bonding and H...H interactions. The topological analysis of O-H...N, C-H...O and H...H intra- and intermolecular interactions was also carried out. The electrostatic potential of metronidazole, calculated from the experiment, predicts the possible electrophilic and nucleophilic sites of the molecule; notably, the hydroxyl and the nitro groups exhibit large electronegative regions. The results have been compared with the corresponding theoretical results.

Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy.

The chemical structure of polarizing agents critically determines the efficiency of dynamic nuclear polarization (DNP). For cross-effect DNP, biradicals are the polarizing agents of choice and the interaction and relative orientation of the two unpaired electrons should be optimal. Both parameters are affected by the molecular structure of the biradical in the frozen glassy matrix that is typically used for DNP/MAS NMR and likely differs from the structure observed with X-ray crystallography. We have determined the conformations of six bis-nitroxide polarizing agents, including the highly efficient AMUPol, in their DNP matrix with EPR spectroscopy at 9.7 GHz, 140 GHz, and 275 GHz. The multi-frequency approach in combination with an advanced fitting routine allows us to reliably extract the interaction and relative orientation of the nitroxide moieties. We compare the structures of six bis-nitroxides to their DNP performance at 500 MHz/330 GHz.

A Comparison of Measurements of Change in Respiratory Status in Spontaneously Breathing Volunteers by the ExSpiron Noninvasive Respiratory Volume Monitor Versus the Capnostream Capnometer.

BACKGROUND: Current respiratory monitoring technologies such as pulse oximetry and capnography have been insufficient to identify early signs of respiratory compromise in nonintubated patients. Pulse oximetry, when used appropriately, will alert the caregiver to an episode of dangerous hypoxemia. However, desaturation lags significantly behind hypoventilation and alarm fatigue due to false alarms poses an additional problem. Capnography, which measures end-tidal CO2 (EtCO2) and respiratory rate (RR), has not been universally used for nonintubated patients for multiple reasons, including the inability to reliably relate EtCO2 to the level of impending respiratory compromise and lack of patient compliance. Serious complications related to respiratory compromise continue to occur as evidenced by the Anesthesiology 2015 Closed Claims Report. The Anesthesia Patient Safety Foundation has stressed the need to improve monitoring modalities so that "no patient will be harmed by opioid-induced respiratory depression." A recently available, Food and Drug Administration-approved noninvasive respiratory volume monitor (RVM) can continuously and accurately monitor actual ventilation metrics: tidal volume, RR, and minute ventilation (MV). We designed this study to compare the capabilities of capnography versus the RVM to detect changes in respiratory metrics. METHODS: Forty-eight volunteer subjects completed the study. RVM measurements (MV and RR) were collected simultaneously with capnography (EtCO2 and RR) using 2 sampling methods (nasal scoop cannula and snorkel mouthpiece with in-line EtCO2 sensor). For each sampling method, each subject performed 6 breathing trials at 3 different prescribed RRs (slow [5 min], normal [12.6 ± 0.6 min], and fast [25 min]). All data are presented as mean ± SEM unless otherwise indicated. RESULTS: Following transitions in prescribed RRs, the RVM reached a new steady state value of MV in 37.7 ± 1.4 seconds while EtCO2 changes were notably slower, often failing to reach a new asymptote before a 2.5-minute threshold. RRs as measured by RVM and capnography during steady breathing were strongly correlated (R = 0.98 ± 0.01, bias = Capnograph-based RR - RVM-based RR = 0.21 ± 1.24 [SD] min). As expected, changes in MV were negatively correlated with changes in EtCO2. However, large changes in MV following transitions in prescribed RR resulted in relatively small changes in EtCO2 (instrument sensitivity = ΔEtCO2/ΔMV = -0.71 ± 0.11 and -0.55 ± 0.11 mm Hg per 1 L/min for nasal and in-line sampling, respectively). Nasal cannula EtCO2 measurements were on average 4 mm Hg lower than in-line measurements. CONCLUSIONS: RVM measurements of MV change more rapidly and by a greater degree than capnography in response to respiratory changes in nonintubated patients. Earlier detection could enable earlier intervention that could potentially reduce frequency and severity of complications due to respiratory depression.

Developmental patterning and segregation of alkaloids in areca nut (seed of Areca catechu) revealed by magnetic resonance and mass spectrometry imaging.

Areca nut (seed of Areca catechu) is consumed by people from different parts of Asia, including India. The four major alkaloids present in areca nut are arecoline, arecaidine, guvacoline and guvacine. Upon cutting, the nut reveals two kinds of regions; white and brown. In our present study, we have monitored the formation of these two regions within the nut during maturation, using the non-invasive techniques of magnetic resonance imaging (MRI) and volume localized magnetic resonance spectroscopy (MRS). Electrospray ionization mass spectrometry (ESI MS) and desorption electrospray ionization mass spectrometry (DESI MS) imaging have been used to study the associated change in the alkaloid contents of these two regions during the growth of the nut. Our study reveals that white and brown regions start forming within the nut when the liquid within starts solidifying. At the final stage of maturity, arecoline, arecaidine and guvacoline get segregated in the brown region whereas guvacine gets to the white region of the nut. The transport of molecules with maturity and corresponding pattern formation are expected to be associated with a multitude of physiochemical changes.

Chemical-shift-resolved ¹9F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy.

Overhauser-DNP-enhanced homonuclear 2D (19)F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000 MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra. This powerful general approach avoids the rather stiff excitation, detection, and other special requirements of high-field (19)F NMR spectroscopy.

ADEQUATE CR: 13C connectivity mapping in indirect detection mode with composite refocusing.

We report a novel rare spin correlation experiment termed ADEQUATE with composite refocusing (CR), which is the (1)H-detected version of 2D INADEQUATE CR. ADEQUATE CR begins with a polarization transfer from protons to the attached carbon, followed by (13)C-(13)C double-quantum (DQ) preparation. Unlike the ADEQUATE class of experiments, (13)C DQ coherence is converted after evolution to single-quantum single transitions (SQ-STs) by CR. (13)C SQ-ST is then transferred back to the coupled protons by a coherence order selective reconversion. The present sequence produces partial transition selectivity in the (1)H dimension as does (1)H Indirect detected (13)C Low-Abundance Single-transition correlation Spectroscopy (HICLASS), thereby mitigating the reduction in sensitivity enhancement because of the presence of homonuclear proton couplings. However, unlike HICLASS (which is an experiment that involves SQ-TS evolution), no homonuclear zero quantum mixing is required on the (13)C channel in the present experiment. Experimental results are demonstrated on a variety of samples, establishing the efficiency of the proposed method.

1H Indirect detected 13C Low-Abundance Single-transition correlation Spectroscopy (HICLASS)-13C homonuclear correlation at natural abundance.

A novel proton-detected (13)C homonuclear correlation experiment is reported at natural abundance, viz., (1)H Indirect detected (13)C Low-Abundance Single-transition correlation Spectroscopy (HICLASS). HICLASS is based on the evolution of (13)C single-quantum single transitions, followed by their mixing, and (1)H detection subsequent to heteronuclear transfer. Reduced relaxation losses during the evolution time and partial selectivity in the (1)H multiplet structure result in enhanced sensitivity of HICLASS. The superior performance of HICLASS is demonstrated for (1)H-detected (13)C correlation work.

(119/117/115)Sn low-abundance single-transition correlation spectroscopy (LASSY): sensitivity-enhanced homonuclear correlation experiments for Sn NMR.

We report the implementation of our novel rare-spin homonuclear correlation experiment, namely, Low-Abundance Single-transition correlation SpectroscopY (LASSY), for (119/117/115)Sn NMR at natural abundance. Our pulse sequence results in diagonal suppressed COSY-style display and outperforms the optimal homonuclear correlation experiment for rare spins, which involves double quantum evolution (INADEQUATE CR). The new experiment maximizes efficiency both in respect of pulse transformations as well as relaxation effects, and gives rise to a simplified two-dimensional (2D) spectrum with considerably reduced crowding, exhibiting only one transition in each cross peak, instead of four. Performance optimization of LASSY is carried out in light of the relatively 'large' line widths typical of Sn NMR in solution state. The superior performance of the sequence is demonstrated on dimeric tetraorganodistannoxane samples.

Postharvest ripening study of sweet lime (Citrus limettioides) in situ by volume-localized NMR spectroscopy.

Spatially resolved NMR--especially volume-localized spectroscopy (VLS)is useful in various fields including clinical diagnosis, process monitoring, etc. VLS carries high significance because of its ability to identify molecular species and hence track molecular events. This paper reports the application of VLS at 200 MHz to study the postharvest ripening of sweet lime ( Citrus limettioides ) in situ, including a comparative study of normal and acetylene-mediated ripening. Localization to a cubic voxel of 64 microL was achieved with point-resolved spectroscopy (PRESS). Glucose, sucrose, fructose, and citric acid are found to be among the main constituents in the fruit. In the natural process, the sugar to acid ratio increases with ripening. Ethanol generation is seen to occur at a faster rate in acetylene-mediated ripening. Whereas NMR imaging experiments including parametric imaging (e.g., T(1) or T(2) maps) may be employed for "macro" monitoring of processes such as these, this work demonstrates that the molecular imprint of the process may be tracked noninvasively by VLS.

CD28 activation does not down-regulate Cbl-b expression in aged rat T-lymphocytes.

It is well known that T-lymphocyte proliferation declines ex vivo with age, and is associated with decreased expression and/or activity of stimulatory intracellular signaling proteins. However, the role of inhibitory intracellular signaling molecules like the ubiquitin ligase Cbl-b in regulating T-lymphocyte function in aging is largely unknown. Therefore, we tested the hypothesis that T-lymphocyte proliferation declines with age, in part, due to increased expression of Cbl-b. We show that young splenic T-lymphocytes reduced Cbl-b expression when stimulated with anti-CD3 and anti-CD28 antibodies, while in aged T-lymphocytes the CD28-dependent Cbl-b down-regulation did not occur. This effect did not appear to be due to reduced CD28 receptor expression on aged T-lymphocytes. The mechanism for lack of Cbl-b down-regulation may involve the proteasome since blocking proteasomal activity in young T-lymphocytes prevented Cbl-b down regulation while there was no effect in aged T-lymphocytes on Cbl-b expression. These data provide evidence for a novel mechanism by which aging reduces T-lymphocyte function.