Natural bond orbital (NBO) analyses and dissected nucleus-independent chemical shifts (NICSπzz) were computed to evaluate the bonding (bond type, electron occupation, hybridization) and aromatic character of the three lowest-lying Si2CH2 (1-Si, 2-Si, 3-Si) and Ge2CH2 (1-Ge, 2-Ge, 3-Ge) isomers. While their carbon C3H2 analogs favor classical alkene, allene, and alkyne type bonding, these Si and Ge derivatives are more polarizable and can favor “highly electron delocalized”? and “non-classical”? structures. The lowest energy Si 2CH2 and Ge 2CH2 isomers, 1-Si and 1-Ge, exhibit two sets of 3–center 2–electron (3c-2e) bonding; a π-3c-2e bond involving the heavy atoms (C–Si–Si and C–Ge–Ge), and a σ-3c-2e bond (Si–H–Si, Ge–H–Ge). Both 3-Si and 3-Ge exhibit π and σ-3c-2e bonding involving a planar tetracoordinated carbon (ptC) center. Despite their highly electron delocalized nature, all of the Si2CH2 and Ge2CH2 isomers considered display only modest two π electron aromatic character (NICS(0)πzz=--6.2 to –8.9 ppm, computed at the heavy atom ring center) compared to the cyclic-C 3H2 (–13.3 ppm).
Two new α‐pyrones (=2H‐pyran‐2‐ones), ficipyrones A and B ( 1 and 2 , resp.), and two new α‐furanones (=2H‐furan‐2‐ones), ficifuranones A and B ( 3 and 4 , resp.), together with three known metabolites, antibiotic F 0368 ( 5 ), hydroxyseiridin ( 6 ), and hydroxyisoseiridin ( 7 ), were isolated from solid cultures of the plant endophytic fungus Pestalotiopsis fici. Their structures were elucidated primarily by NMR spectroscopy, and the absolute configuration of 1 was deduced from the circular‐dichroism (CD) data. Compound 1 showed antifungal activity against the plant pathogen Gibberella zeae (CGMCC 3.2873) with an IC50 value of 15.9 μM . 相似文献
Low-temperature, single crystal X-ray structural characterisations of trans-[NiCl2(HOMe)4], trans-O-[Ni(MeOH)2(μ-Cl)(2/2)2](∞∣∞) · 0.5dioxan and trans-trans-[Ni(H2O)2Cl2(O-dioxan-O)(2/2)](∞∣∞) · dioxan are recorded, offering intriguing insights into O-donor/Ni(II) relativities. All nickel atoms in all structures are located on crystallographic inversion centres, the last two compounds being one-dimensional polymers. 相似文献
A general method for the preparation of 2′-azido-2′-deoxy- and 2′-amino-2′-deoxyarabinofuranosyl-adenine and -guanine nucleosides is described. Selective benzoylation of 3-azido-3-deoxy-1,2-O-isopropylidene-α-d-glucofuranose afforded 3-azido-6-O-benzoyl-3-deoxy-1,2-O-isopropylidene-α-d-glucofuranose (1). Acid hydrolysis of 1, followed by oxidation with sodium metaperiodate and hydrolysis by sodium hydrogencarbonate gave 2-azido-2-deoxy-5-O-benzoyl-d-arabinofuranose (3), which was acetylated to give 1,3-di-O-acetyl-2-azido-5-O-benzoyl-2-deoxy-d-arabinofuranose (4). Compound 4 was converted into the 1-chlorides 5 and 6, which were condensed with silylated derivatives of 6-chloropurine and 2-acetamido-hypoxanthine. The condensation reaction gave α and β anomers of both 7- and 9-substituted purine nucleosides. The structures of the nucleosides were determined by n.m.r. and u.v. spectroscopy, and by correlation of the c.d. spectra of the newly prepared nucleosides with those published for known purine nucleosides. 相似文献
β‐arrestin 1 and 2 (also known as arrestin 2 and 3) are homologous adaptor proteins that regulate seven‐transmembrane receptor trafficking and signalling. Other proteins with predicted ‘arrestin‐like’ structural domains but lacking sequence homology have been indicated to function like β‐arrestin in receptor regulation. We demonstrate that β‐arrestin2 is the primary adaptor that rapidly binds agonist‐activated β2 adrenergic receptors (β2ARs) and promotes clathrin‐dependent internalization, E3 ligase Nedd4 recruitment and ubiquitin‐dependent lysosomal degradation of the receptor. The arrestin‐domain‐containing (ARRDC) proteins 2, 3 and 4 are secondary adaptors recruited to internalized β2AR–Nedd4 complexes on endosomes and do not affect the adaptor roles of β‐arrestin2. Rather, the role of ARRDC proteins is to traffic Nedd4–β2AR complexes to a subpopulation of early endosomes. 相似文献
Adenosine 5-triphosphate receptors are known to be involved in fast excitatory postsynaptic currents in myenteric neurons of the digestive tract. In the present study, the distribution of P2X2 and P2X3 receptor mRNA was examined by in situ hybridisation while P2X2 and P2X3 receptor protein was localised by immunohistochemical methods. In addition, P2X2 and P2X3 receptors were colocalised with calbindin and calretinin in the myenteric and submucosal plexus. P2X2- and P2X3-immunoreactive neurons were found in the myenteric and submucosal plexuses throughout the entire length of the rat digestive tract from the stomach to the colon. Approximately 60%, 70% and 50% of the ganglion cells in the myenteric plexus of the gastric corpus, ileum and distal colon, and 56% and 45% in the submucosal plexus of the ileum and distal colon, respectively, showed positive immunoreactivity to the P2X2 receptor. Approximately 10%, 2% and 15% of the ganglion cells in the myenteric plexus of the gastric corpus, ileum and distal colon, and 62% and 40% in the submucosal plexus of the ileum and distal colon, respectively, showed positive immunoreactivity to the P2X3 receptor. Double-labelling studies showed that about 10–25% of the neurons with P2X2 immunoreactivity in myenteric plexus and 30–50% in the submucosal plexus were found to express calbindin or calretinin. About 80% of the neurons with P2X3 receptor immunoreactivity in the myenteric plexus and about 40% in the submucosal plexus expressed calretinin. Approximately 30–75% of the neurons with P2X3 receptor immunoreactivity in the submucosal plexus expressed calbindin, while none of them were found to express calbindin in the myenteric plexus. 相似文献
Computations have been performed to find an adequate definition of exact two-sided probabilities in 2times2 contingency tables. It turns out, that both uncorrected χ2 and Yates' correction for continuity give only unsatisfactory approximations to the exact probabilities of the hypergeometric distribution. The latter are therefore recommended for general use. 相似文献
An experimental study has been carried out on the stability of adenine (one of the five nucleic acid bases) under hydrothermal conditions. The experiments were performed in sealed autoclaves at 300 degrees C under fugacities of CO(2), N(2) and H(2) supposedly representative of those in marine hydrothermal systems on the early Earth. The composition of the gas phase was obtained from the degradation of oxalic acid, sodium nitrite and ammonium chloride, and the oxidation of metallic iron. The results of the experiments indicate that after 200 h, adenine is still present in detectable concentration in the aqueous phase. In fact, the concentration of adenine does not seem to be decreasing after approximately 24 h, which suggests that an equilibrium state may have been established with the inorganic constituents of the hydrothermal fluid. Such a conclusion is corroborated by independent thermodynamic calculations. 相似文献
In brain mitochondria succinate activates H2O2 release, concentration dependently (starting at 15 μM), and in the presence of NAD dependent substrates (glutamate, pyruvate,
β-hydroxybutyrate). We report that TCA cycle metabolites (citrate, isocitrate, α-ketoglutarate, fumarate, malate) individually
and quickly inhibit H2O2 release. When they are present together at physiological concentration (0.2, 0.01, 0.15, 0.12, 0.2 mM respectively) they
decrease H2O2 production by over 60% at 0.1–0.2 mM succinate. The degree of inhibition depends on the concentration of each metabolite.
Acetoacetate is a strong inhibitor of H2O2 release, starting at 10 μM and acting quickly. It potentiates the inhibition induced by TCA cycle metabolites. The action
of acetoacetate is partially removed by β-hydroxybutyrate. Removal is minimal at 0.1 mM acetoacetate, and is higher at 0.5 mM
acetoacetate. We conclude that several inhibitors of H2O2 release act jointly and concentration dependently to rapidly set the required level of H2O2 generation at each succinate concentration. 相似文献
The sensitivity of phytoplankton species for hydrogen peroxide (H2O2) was analyzed by pulse amplitude modulated (PAM) fluorometry. The inhibition of photosynthesis was more severe in five tested
cyanobacterial species than in three green algal species and one diatom species. Hence the inhibitory effect of H2O2 is especially pronounced for cyanobacteria. A specific damage of the photosynthetic apparatus was demonstrated by changes
in 77 K fluorescence emission spectra. Different handling of oxidative stress and different cell structure are responsible
for the different susceptibility to H2O2 between cyanobacteria and other phytoplankton species. This principle may be potentially employed in the development of new
agents to combat cyanobacterial bloom formation in water reservoirs. 相似文献
A density functional theory (DFT) study of cct-As, ccc, and cct-CO isomers of the ruthenium dihydride complex RuH2(CO)2(AsMe2Ph)2 is reported (see Scheme for the labeling isomer 34 structures of RuH2(CO)2(AsMe2Ph)2). Complex geometries and relative energies of different isomers have been calculated with both B3LYP and M06-2X functionals. The results show that the B3LYP calculated Boltzmann populations of cct-As, ccc, and cct-CO isomers are 65.5, 34.2, and 0.3%, respectively. These are in better agreement with the experimental data than those calculated at the M06-2X level. However, the calculations of 1H NMR chemical shifts were found to be better described with M06-2X than with B3LYP or with HF level of theories. In addition, a transition state between the two most stable isomers was determined through DFT/(B3LYP or M06-2X) calculations.
A variety of applications of 8‐alkynylated nucleosides has prompted the synthesis of new purine analogues. Bromination of unprotected 2‐amino‐2′‐deoxyadenosine with Br2/AcOH/AcONa gives 2‐amino‐8‐bromo‐2′‐deoxyadenosine (87%). The brominated derivative is converted to 8‐alkynylated 2‐amino‐2′‐deoxyadenosines by palladium‐catalyzed Sonogashira cross‐coupling reaction via microwave assistance (81 – 95%). The resulting compounds are further transformed to 8‐alkynylated 2′‐deoxyisoguanosines (52 – 70%). The physical properties of new compounds are investigated. 相似文献
A Monte Carlo simulation was conducted in order to determine the size and power of two proposed tests (the covariance and correlation tests) for three-factor interaction in 2 × 2 × 2 contingency tables. Results were compared to the log-odds ratio test statistic. Simulation showed the correlation test to be more conservative than the covariance test, but less so than the log-odds ratio test. However, the correlation test was the most powerful among the three tests. 相似文献
Li2S is a fully lithiated sulfur‐based cathode with a high theoretical capacity of 1166 mAh g?1 that can be coupled with lithium‐free anodes to develop high‐energy‐density lithium–sulfur batteries. Although various approaches have been pursued to obtain a high‐performance Li2S cathode, there are still formidable challenges with it (e.g., low conductivity, high overpotential, and irreversible polysulfide diffusion) and associated fabrication processes (e.g., insufficient Li2S, excess electrolyte, and low reversible capacity), which have prevented the realization of high electrochemical utilization and stability. Here, a new cathode design composed of a homogeneous Li2S‐TiS2‐electrolyte composite that is prepared by a simple two‐step dry/wet‐mixing process is demonstrated, allowing the liquid electrolyte to wet the powder mixture consisting of insulating Li2S and conductive TiS2. The close‐contact, three‐phase boundary of this system improves the Li2S‐activation efficiency and provides fast redox‐reaction kinetics, enabling the Li2S‐TiS2‐electrolyte cathode to attain stable cyclability at C/7 to C/3 rates, superior long‐term cyclability over 500 cycles, and promising high‐rate performance up to 1C rate. More importantly, this improved performance results from a cell design attaining a high Li2S loading of 6 mg cm?2, a high Li2S content of 75 wt%, and a low electrolyte/Li2S ratio of 6. 相似文献
Vanadium is an environmentally toxic metal with peculiar and sometimes contradictory cellular effects. It is insulin-mimetic,
it can either stimulate cell growth or induce cell death, and it has both mutagenic and antineoplastic properties. However,
the mechanisms involved in those effects are poorly understood. Several studies suggest that H2O2 is involved in vanadate-induced cell death, but it is not known whether cellular sensitivity to vanadate is indeed related
to H2O2 generation. In the present study, the sensitivity of four cell lines from different origins (K562, K562-Lucena 1, MDCK, and
Ma104) to vanadate and H2O2 was evaluated and the production of H2O2 by vanadate was analyzed by flow cytometry. We show that cell lines very resistant to H2O2 (K562, K562-Lucena 1, and Ma104 cells) are much more sensitive to vanadate than MDCK, a cell line relatively susceptible
to H2O2, suggesting that vanadate-induced cytotoxicity is not directly related to H2O2 responsiveness. In accordance, vanadate concentrations that reduced cellular viability to approximately 60–70% of the control
(10 μmol/L) did not induce H2O2 formation. A second hypothesis, that peroxovanadium (PV) compounds, produced once vanadate enters into the cells, are responsible
for the cytotoxicity, was only partially confirmed because MDCK cells were resistant to both vanadate and PV compounds (10 μmol/L
each). Therefore, our results suggest that vanadate toxicity occurs by two distinct pathways, one dependent on and one independent
of H2O2 production. 相似文献