Ammonia Borane Dehydrogenation Catalyzed by (κ⁴-EP<inf>3</inf>)Co(H) [EP<inf>3</inf> = E(CH<inf>2</inf>CH<inf>2</inf>PPh<inf>2</inf>)<inf>3</inf>; E = N, P] and H<inf>2</inf> Evolution from Their Interaction with NH Acids

© 2017 American Chemical Society.Two Co(I) hydrides containing the tripodal polyphosphine ligand EP3, (κ4-EP3)Co(H) [E(CH2CH2PPh2)3; E = N (1), P (2)], have been exploited as ammonia borane (NH3BH3, AB) dehydrogenation catalysts in THF solution at T = 55 °C. The reaction has been analyzed experimentally through multinuclear (11B, 31P{1H}, 1H) NMR and IR spectroscopy, kinetic rate measurements, and kinetic isotope effect (KIE) determination with deuterated AB isotopologues. Both complexes are active in AB dehydrogenation, albeit with different rates and efficiency. While 1 releases 2 equiv of H2 per equivalent of AB in ca. 48 h, with concomitant borazine formation as the final "spent fuel", 2 produces 1 equiv of H2 only per equivalent of AB in the same reaction time, along with long-chain poly(aminoboranes) as insoluble byproducts. A DFT modeling of the first AB dehydrogenation step has been performed, at the M06//6-311++G∗ level of theory. The combination of the kinetic and computational data reveals that a simultaneous B-H/N-H activation occurs in the presence of 1, after a preliminary AB coordination to the metal center. In 2, no substrate coordination takes place, and the process is better defined as a sequential BH3/NH3 insertion process on the initially formed [Co]-NH2BH3 amidoborane complex. Finally, the reaction of 1 and 2 with NH-acids [AB and Me2NHBH3 (DMAB)] has been followed via VT-FTIR spectroscopy (in the -80 to +50 °C temperature range), with the aim of gaining a deeper experimental understanding of the dihydrogen bonding interactions that are at the origin of the observed H2 evolution

Amine Boranes Dehydrogenation Mediated by an Unsymmetrical Iridium Pincer Hydride: (PCN) vs (PCP) Improved Catalytic Performance

© 2018 American Chemical Society. The IrIII hydride (tBuPCN)IrHCl (1) containing the tridendate unsymmetrical pincer ligand tBuPCN- {tBuPCN(H) = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole} has been exploited as ammonia borane (NH3BH3, AB) and amine boranes dehydrogenation catalyst in THF solution at ambient temperature. 1 releases one H2 equivalent per AB equivalent, with concomitant cyclic poly(aminoboranes) formation [B-(cyclotriborazanyl)-amine-borane (BCTB) and cyclotriborazane (CTB)] as the final "spent fuel". 1 has been found to have superior catalytic activity than its symmetrical analogue (tBuPCP)IrHCl, with recorded TOF values of 580 h-1 (AB in THF) and 401 h-1 (DMAB in toluene) at ambient temperature. The reaction has been analyzed experimentally through multinuclear [11B, 31P{1H}, 1H] NMR and IR spectroscopy, kinetic rate measurements, and kinetic isotope effect determination with deuterated AB isotopologues. The hydride/borohydride intermediate (tBuPCN)IrH(η2-BH4) (2) is the catalyst resting state formed during the dehydrogenation process; it is detected by a variableerature multinuclear NMR of the reaction course (in the 190-323 K range). A DFT modeling of the reaction mechanism using DMAB as substrate has been performed with the geometry optimization in toluene at the M06 level of theory. The combination of the kinetic and computational data reveals that a simultaneous B-H/N-H activation occurs in the presence of 1, after the preliminary amine borane coordination to the metal center

Phase formation and relaxor properties of lead-free perovskite ceramics on the base of sodium-bismuth titanate

The work was supported by the Russian Foundation for Basic Research (Projects 16-53-48009, 17-03-00542)

Probiotic consortiums: Structure and antagonistic activity against opportunistic bacteria and human normobiota (using the example of <i>Escherichia coli</i>) <i>in vitro</i>

Background. Using probiotic preparations based on consortia of microorganisms not only helps to restore the balance of the intestinal microbiota, but also increases the therapeutic effect of probiotics. Promising sources for obtaining probiotic consortia are milk products that have undergone natural fermentation with the help of spontaneously formed microbial consortia. The aim. To study the structure of five microbial consortia with probiotic properties from naturally fermented milk products and to assess in vitro their antagonistic activity against opportunistic bacteria and a representative of the human normobiota – Escherichia coli. Materials and methods. The structure of bacterial consortia was analyzed by sequencing methods. The antagonistic activity of the consortia was assessed by the disk diffusion method. Results. It has been established that the studied microbial consortiums are represented by Enterococcus spp. and Streptococcus spp. bacteria. In consortiums No. 1, No.  2, and No.  3, Enterococcus bacteria dominated, while in consortiums No.  4 and No. 5, Streptococcus dominated. Antagonistic activity was shown against four isolates of opportunistic bacteria: Klebsiella pneumoniae No.  493, Enterobacter hormaechei No. 372, Staphylococcus aureus No. 4 and Pseudomonas aeruginosa No. 25 IMB, as well as against one representative of the human normobiota – Escherichia coli No. 495. The highest growth delay zone is found in E. coli No. 495 isolate. Three test cultures (K. pneumoniae No. 509, E. coli ATCC25922 and P. aeruginosa No. 3 IMB) exhibited more dense growth around probiotic consortia. Conclusion. The results of the study showed that the effect of probiotic consortia differing in the composition of microorganisms can be neutral and bactericidal. The presence of antagonistic activity in the studied microbial consortia against multiresistant isolates of opportunistic bacteria is a prospect for creating probiotics with antibacterial properties

Isolation and whole genome sequencing of a lipophilic anaerobic bacterium, a representative of the species complex <i>Corynebacterium tuberculostearicum</i>, from a tuberculosis focus

Background. The study of the lower respiratory tract microbiome has been actively developed inrecent years with the help of whole genome sequencing (WGS) methods. Due to this, it became clear that the nature of the lungs microbiota is very different from other microbial communities inhabiting the human body. One of the important directions in the study of pathological lungs biocenosis is the study of the role of the satellite microbiota of the tuberculosis focus. The aim of the work. To isolate and characterize oxygen-tolerant anaerobes from the necrotic contents of tuberculomas. Materials and methods. Biopsy material from 5 patients with pulmonary tuberculosis was obtained during a planned surgical treatment of tuberculoma. A pure culture was isolated from one sample during anaerobic cultivation. Lipase activity of strain was determined by plating on brain heart infusion agar (HIMEDIA, India) supplemented with 0.1 % Tween-80 and 10 mM of CaCl2. Antibiotic susceptibility was determined by RAPMYCO and SLOWMYCO of TREK Diagnostic Systems (Thermo Fisher Scientific, USA). DNA from the sediment of the broth culture was isolated by the CTAB chloroform method. Whole genome sequencing was performed on a DNBSeq-G400 NGS sequencer by Genomed (Russia). Results. Based on WGS results and phylogenetic analysis, the strain was identified as Corynebacterium kefirresidentii. The strain was characterized by high lipase activity and resistance only to Isoniazid, Ethionamide and Trimethoprim/Sulfamethoxazolin. Conclusion. The isolation of a lipophilic anaerobic representative of the Corynebacterium tuberculostearicum species complex from a tuberculous focus indicates a  possible role of the non-tuberculous microbiota in the liquefaction of caseous necrosis. We assumed that in some cases, favorable conditions are created inside the tuberculous focus for the development of satellite anaerobic lipophilic microbiota

Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively

The Magnitude and Mechanism of Charge Enhancement of CH∙∙O H-bonds

Quantum calculations find that neutral methylamines and thioethers form complexes, with N-methylacetamide (NMA) as proton acceptor, with binding energies of 2–5 kcal/mol. This interaction is magnified by a factor of 4–9, bringing the binding energy up to as much as 20 kcal/mol, when a CH3+ group is added to the proton donor. Complexes prefer trifurcated arrangements, wherein three separate methyl groups donate a proton to the O acceptor. Binding energies lessen when the systems are immersed in solvents of increasing polarity, but the ionic complexes retain their favored status even in water. The binding energy is reduced when the methyl groups are replaced by longer alkyl chains. The proton acceptor prefers to associate with those CH groups that are as close as possible to the S/N center of the formal positive charge. A single linear CH··O hydrogen bond (H-bond) is less favorable than is trifurcation with three separate methyl groups. A trifurcated arrangement with three H atoms of the same methyl group is even less favorable. Various means of analysis, including NBO, SAPT, NMR, and electron density shifts, all identify the +CH··O interaction as a true H-bond