Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 162
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
IEEE Trans Cybern ; 2020 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-32112691

RESUMO

This article investigates a fuzzy adaptive two-bit-triggered control for uncertain nonlinear systems with actuator failures and dead-zone constraint. Actuator failures and dead-zone constraint exist frequently in practical systems, which will affect the system performance greatly. Based on the improved fuzzy-logic systems (FLSs), a fuzzy adaptive compensation control is established to address these issues. The approximation error is introduced to the control design as a time-varying function. In addition, for the limited transmission resources of the practical system, a two-bit-triggered control mechanism is proposed to further save system transmission resources. It is proved that the proposed method can guarantee the system tracking performance and all the signals are bounded. Its effectiveness is verified by the simulation examples.

2.
Artigo em Inglês | MEDLINE | ID: mdl-32220963

RESUMO

The small GTPase RABL3 is an oncogene of unknown physiological function. Homozygous knockout alleles of mouse Rabl3 were embryonic lethal, but a viable hypomorphic allele (xiamen [xm]) causing in-frame deletion of four amino acids from the interswitch region resulted in profound defects in lymphopoiesis. Impaired lymphoid progenitor development led to deficiencies of B cells, T cells, and natural killer (NK) cells in Rabl3 xm/xm mice. T cells and NK cells exhibited impaired cytolytic activity, and mice infected with mouse cytomegalovirus (MCMV) displayed elevated titers in the spleen. Myeloid cells were normal in number and function. Biophysical and crystallographic studies demonstrated that RABL3 formed a homodimer in solution via interactions between the effector binding surfaces on each subunit; monomers adopted a typical small G protein fold. RABL3xm displayed a large compensatory alteration in switch I, which adopted a ß-strand configuration normally provided by the deleted interswitch residues, thereby permitting homodimer formation. Dysregulated effector binding due to conformational changes in the switch I-interswitch-switch II module likely underlies the xm phenotype. One such effector may be GPR89, putatively an ion channel or G protein-coupled receptor (GPCR). RABL3, but not RABL3xm, strongly associated with and stabilized GPR89, and an N-ethyl-N-nitrosourea (ENU)-induced mutation (explorer) in Gpr89 phenocopied Rabl3 xm.

4.
Int J Mol Sci ; 21(5)2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-32120830

RESUMO

Nano Ag has excellent antibacterial properties and is widely used in various antibacterial materials, such as antibacterial medicine and medical devices, food packaging materials and antibacterial textiles. Despite the many benefits of nano-Ag, more and more research indicates that it may have potential biotoxic effects. Studies have shown that people who ingest nanoparticles by mouth have the highest uptake in the intestinal tract, and that the colon area is the most vulnerable to damage and causes the disease. In this study, we examined the toxic effects of different concentrations of Ag-NPs on normal human colon cells (NCM460) and human colon cancer cells (HCT116). As the concentration of nanoparticles increased, the activity of the two colon cells decreased and intracellular reactive oxygen species (ROS) increased. RT-qPCR and Western-blot analyses showed that Ag NPs can promote the increase in P38 protein phosphorylation levels in two colon cells and promote the expression of P53 and Bax. The analysis also showed that Ag NPs can promote the down-regulation of Bcl-2, leading to an increased Bax / Bcl-2 ratio and activation of P21, further accelerating cell death .This study showed that a low concentration of nano Ag has no obvious toxic effect on colon cells, while nano Ag with concentrations higher than 15 µg/mL will cause oxidative damage to colon cells.

5.
Proc Natl Acad Sci U S A ; 117(9): 4894-4901, 2020 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-32071239

RESUMO

γ-secretase is an intramembrane protease complex that catalyzes the proteolytic cleavage of amyloid precursor protein and Notch. Impaired γ-secretase function is associated with the development of Alzheimer's disease and familial acne inversa in humans. In a forward genetic screen of mice with N-ethyl-N-nitrosourea-induced mutations for defects in adaptive immunity, we identified animals within a single pedigree exhibiting both hypopigmentation of the fur and diminished T cell-independent (TI) antibody responses. The causative mutation was in Ncstn, an essential gene encoding the protein nicastrin (NCSTN), a member of the γ-secretase complex that functions to recruit substrates for proteolysis. The missense mutation severely limits the glycosylation of NCSTN to its mature form and impairs the integrity of the γ-secretase complex as well as its catalytic activity toward its substrate Notch, a critical regulator of B cell and T cell development. Strikingly, however, this missense mutation affects B cell development but not thymocyte or T cell development. The Ncstn allele uncovered in these studies reveals an essential requirement for NCSTN during the type 2 transitional-marginal zone precursor stage and peritoneal B-1 B cell development, the TI antibody response, fur pigmentation, and intestinal homeostasis in mice.

7.
Sci Immunol ; 5(43)2020 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-31980486

RESUMO

T follicular helper cells (TFH) participate in germinal center (GC) development and are necessary for B cell production of high-affinity, isotype-switched antibodies. In a forward genetic screen, we identified a missense mutation in Prkd2, encoding the serine/threonine kinase protein kinase D2, which caused elevated titers of immunoglobulin E (IgE) in the serum. Subsequent analysis of serum antibodies in mice with a targeted null mutation of Prkd2 demonstrated polyclonal hypergammaglobulinemia of IgE, IgG1, and IgA isotypes, which was exacerbated by the T cell-dependent humoral response to immunization. GC formation and GC B cells were increased in Prkd2-/- spleens. These effects were the result of excessive cell-autonomous TFH development caused by unrestricted Bcl6 nuclear translocation in Prkd2-/- CD4+ T cells. Prkd2 directly binds to Bcl6, and Prkd2-dependent phosphorylation of Bcl6 is necessary to constrain Bcl6 to the cytoplasm, thereby limiting TFH development. In response to immunization, Bcl6 repressed Prkd2 expression in CD4+ T cells, thereby committing them to TFH development. Thus, Prkd2 and Bcl6 form a mutually inhibitory positive feedback loop that controls the stable transition from naïve CD4+ T cells to TFH during the adaptive immune response.

8.
J Exp Bot ; 71(4): 1527-1539, 2020 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-31680166

RESUMO

Plasma membrane proton pumps play a crucial role in maintaining ionic homeostasis in salt-resistant Populus euphratica under saline conditions. High levels of NaCl (200 mM) induced PeHA1 expression in P. euphratica roots and leaves. We isolated a 2022 bp promoter fragment upstream of the translational start of PeHA1 from P. euphratica. The promoter-reporter construct PeHA1-pro::GUS was transferred to tobacco plants, demonstrating that ß-glucuronidase activities increased in root, leaf, and stem tissues under salt stress. DNA affinity purification sequencing revealed that PeWRKY1 protein targeted the PeHA1 gene. We assessed the salt-induced transcriptional response of PeWRKY1 and its interaction with PeHA1 in P. euphratica. PeWRKY1 binding to the PeHA1 W-box in the promoter region was verified by a yeast one-hybrid assay, EMSA, luciferase reporter assay, and virus-induced gene silencing. Transgenic tobacco plants overexpressing PeWRKY1 had improved expression of NtHA4, which has a cis-acting W-box in the regulatory region, and improved H+ pumping activity in both in vivo and in vitro assays. We conclude that salt stress up-regulated PeHA1 transcription due to the binding of PeWRKY1 to the W-box in the promoter region of PeHA1. Thus, we conclude that enhanced H+ pumping activity enabled salt-stressed plants to retain Na+ homeostasis.

9.
Sensors (Basel) ; 19(24)2019 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-31842415

RESUMO

In the present work, a novel electrochemical sensor was developed for the detection of trace cadmium with high sensitivity and selectivity in an easy and eco-friendly way. Firstly, a glassy carbon electrode (GCE) was modified with nontoxic sodium carboxymethyl cellulose (CMC) by a simple drop-casting method, which was applied to detect cadmium by differential pulse anodic stripping voltammetry (DPASV) in a solution containing both target cadmium and eco-friendly bismuth ions, based on a quick electro-codeposition of these two metal ions on the surface of the modified electrode (CMC-GCE). Investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR), both CMC (with good film-forming ability) and bismuth (with well-defined stripping signal) were found to be well complexed with target cadmium, leading to vital signal amplification for cadmium detection at a sub-nanomolar level. Under the optimal conditions, the proposed sensor exhibited a good linear stripping signal response to cadmium (Ⅱ) ion, in a concentration range of 0.001 µmol/L-1 µmol/L with a limit of detection of 0.75 nmol/L (S/N = 3). Meanwhile, the results demonstrate that this novel electrochemical sensor has excellent sensitivity and reproducibility, which can be used as a promising detection technique for testing natural samples such as tap water.

10.
Phys Rev E ; 100(5-1): 052126, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31870038

RESUMO

We consider the finite-time performance of a quantum Otto engine working between a hot squeezed and a cold thermal bath at inverse temperatures ß_{h} and ß_{c}(>ß_{h}) with (k_{B}≡1)ß=1/T. We derive the analytical expressions for work, efficiency, power, and power fluctuations, in which the squeezing parameter is involved. By optimizing the power output with respect to two frequencies, we derive the efficiency at maximum power as η_{mp}=(η_{C}^{gen})^{2}/[η_{C}^{gen}-(1-η_{C}^{gen})ln(1-η_{C}^{gen})], where the generalized Carnot efficiency η_{C}^{gen} in the high-temperature or small squeezing limit simplifies to an analytic function of squeezing parameter γ: η_{C}^{gen}=1-ß_{h}/[ß_{c}cosh(2γ)]. Within the context of irreversible thermodynamics, we demonstrate that the expression of efficiency at maximum power satisfies a general form derived from nonlinear steady state heat engines. We show that, the power fluctuations are considerably increased, although the engine efficiency is enhanced by squeezing.

11.
Cell Death Dis ; 10(12): 887, 2019 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-31767864

RESUMO

Chordoma is a malignant primary osseous spinal tumor with pronounced chemoresistance. However, the mechanisms of how chordoma cells develop chemoresistance are still not fully understood. Cytokeratin 8 (KRT8) is a molecular marker of notochordal cells, from which chordoma cells were believed to be originated. In this study, we showed that either doxorubicin or irinotecan promoted KRT8 expression in both CM319 and UCH1 cell lines, accompanied by an increased unfolded protein response and autophagy activity. Then, siRNA-mediated knockdown of KRT8 chemosensitized chordoma cells in vitro. Mechanistic studies showed that knockdown of KRT8 followed by chemotherapy aggravated endoplasmic reticulum stress through PERK/eIF2α arm of unfolded protein response and blocked late-stage autophagy. Moreover, suppression of the PERK/eIF2α arm of unfolded protein response using PERK inhibitor GSK2606414 partially rescued the apoptotic chordoma cells but did not reverse the blockage of the autophagy flux. Finally, tumor xenograft model further confirmed the chemosensitizing effects of siKRT8. This study represents the first systematic investigation into the role of KRT8 in chemoresistance of chordoma and our results highlight a possible strategy of targeting KRT8 to overcome chordoma chemoresistance.

12.
Artigo em Inglês | MEDLINE | ID: mdl-31780357

RESUMO

OBJECTIVE: To investigate the prevalence, risk factors, and clinical outcomes associated with early fluid overload (FO) in a special group of pediatric patients undergoing repair of anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA). DESIGN: It was a retrospective study performed with multiple variable regression analysis. SETTING: A single cardiac surgical institution. PARTICIPANTS: Eighty-eight patients younger than 18 years of age undergoing ALCAPA surgical repair with cardiopulmonary bypass were recruited at the authors' institution from June 2010 to September 2017. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: Of 88 pediatric patients with ALCAPA after surgical repair, 37.5% developed early FO, defined as fluid accumulation ≥5% within the period from surgery until midnight of postoperative day 1. Patients with early FO were younger, weighed less, and had worse preoperative cardiac dysfunction. With logistic regression analysis, being underweight was confirmed to be a risk factor for FO development (odds ratio, 8.66; 95% confidence interval, 2.83-26.52; p < 0.001). Early FO also predicted severe acute kidney injury, respiratory morbidity, and low cardiac output syndrome after reimplantation procedure. Patients with early FO also had significantly longer mechanical ventilation hours (p  <  0.001), intensive care unit length of stay (p = 0.003), and hospital length of stay (p = 0.009). CONCLUSION: Early FO ≥5% has been linked to adverse postoperative outcomes in pediatric patients undergoing repair for ALCAPA. The use of restrictive fluid management is crucial for patients who have lower weight and poor myocardial function before and after complex surgical procedures such as in ALCAPA settings.

13.
Sci Total Environ ; 688: 1155-1161, 2019 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-31726546

RESUMO

Although oily sludge has tremendous resource recovery value, its high water content has hindered its treatment and reuse. This study systematically explored the technical feasibility of using Fe(II)-activated persulfate oxidation (Fe2+/S2O82-) to enhance the dewaterability of oily sludge. To identify the main factors controlling sludge dewatering, this study measured changes in chemical oxygen demand, ammonia nitrogen (NH4+-N) and extracellular polymeric substances (EPS). Results showed that at 0.1 mmol-Fe2+/g-VSS and 0.08 mmol-S2O82-/g-VSS, capillary suction time (s) was reduced by roughly 36.1% within 1 min and dewaterability was strengthened strongly. Sulfate radicals originating from Fe2+/S2O82- oxidized a large amount of EPS, leading to liberation of EPS-bound water. A similar declining trend in NH4+-N was evident as a result of the strong oxidizing ability of sulfate radicals. Further analysis via scanning electron microscopy and thermogravimetric-Fourier transform infrared spectrometry revealed that Fe2+/S2O82- oxidation destroyed the water-oil-gel-like structure of the oily sludge, thereby accelerating the separation of solids and water while reducing CO2 emissions during the subsequent pyrolysis. Therefore, oily sludge dewatering was enhanced significantly by the Fe2+/S2O82- process.

14.
Phys Rev E ; 100(1-1): 012105, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31499858

RESUMO

We investigate the finite-power performance of quantum heat engines working in the linear response regime where the temperature gradient is small. The engine cycles with working substances of ideal harmonic systems consist of two heat transfer and two adiabatic processes, such as the Carnot cycle, Otto cycle, and Brayton cycle. By analyzing the optimal protocol under maximum power we derive the explicitly analytic expression for the irreversible entropy production, which becomes the low dissipation form in the long duration limit. Assuming the engine to be endoreversible, we derive the universal expression for the efficiency at maximum power, which agrees well with that obtained from the phenomenological heat transfer laws holding in the classical thermodynamics. Through appropriate identification of the thermodynamic fluxes and forces that a linear relation connects, we find that the quantum engines under consideration are tightly coupled, and the universality of efficiency at maximum power is confirmed at the linear order in the temperature gradient.

15.
Artigo em Inglês | MEDLINE | ID: mdl-31295127

RESUMO

This paper presents a novel nonlinear dictionary learning (DL) model to address the energy disaggregation (ED) problem, i.e., decomposing the electricity signal of a home to its operating devices. First, ED is modeled as a new temporal DL problem where a set of dictionary atoms is learned to capture the most representative temporal features of electricity signals. The sparse codes corresponding to these atoms show the contribution of each device in the total electricity consumption. To learn powerful atoms, a novel deep temporal DL (DTDL) model is proposed that computes complex nonlinear dictionaries in the latent space of a long short-term memory autoencoder (LSTM-AE). While the LSTM-AE captures the deep temporal manifold of electricity signals, the DTDL model finds the most representative atoms inside this manifold. To simultaneously optimize the dictionary and the deep temporal manifold, a new optimization algorithm is proposed that alternates between finding the optimal LSTM-AE and the optimal dictionary. To the best of authors' knowledge, DTDL is the only DL model that understands the deep temporal structures of the data. Experiments on the Reference ED Data Set show an outstanding performance compared with the recent state-of-the-art algorithms in terms of precision, recall, accuracy, and F-score.

16.
Planta ; 250(4): 1073-1088, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31165231

RESUMO

MAIN CONCLUSION: The 5-leaf-stage rape seedlings were more insensitive to Pi starvation than that of the 3-leaf-stage plants, which may be attributed to the higher expression levels of ethylene signaling and sugar-metabolism genes in more mature seedlings. Traditional suppression subtractive hybridization (SSH) and RNA-Seq usually screen out thousands of differentially expressed genes. However, identification of the most important regulators has not been performed to date. Here, we employed two methods, namely, a two-round SSH and two-factor transcriptome analysis derived from the two-factor ANOVA that is commonly used in the statistics, to identify development-associated inorganic phosphate (Pi) starvation-induced genes in Brassica napus. Several of these genes are related to ethylene signaling (such as EIN3, ACO3, ACS8, ERF1A, and ERF2) or sugar metabolism (such as ACC2, GH3, LHCB1.4, XTH4, and SUS2). Although sucrose and ethylene may counteract each other at the biosynthetic level, they may also work synergistically on Pi-starvation-induced gene expression (such as PT1, PT2, RNS1, ACP5, AT4, and IPS1) and root acid phosphatase activation. Furthermore, three new transcription factors that are responsive to Pi starvation were identified: the zinc-finger MYND domain-containing protein 15 (MYND), a Magonashi family protein (MAGO), and a B-box zinc-finger family salt-tolerance protein. This study indicates that the two methods are highly efficient for functional gene screening in non-model organisms.


Assuntos
Brassica napus/genética , Regulação da Expressão Gênica de Plantas , Fosfatos/deficiência , Transdução de Sinais , Fatores de Transcrição/genética , Transcriptoma , Análise de Variância , Brassica napus/crescimento & desenvolvimento , Brassica napus/fisiologia , Etilenos/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Fosfatos/metabolismo , Reguladores de Crescimento de Planta/metabolismo , Folhas de Planta/genética , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/fisiologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Análise de Sequência de RNA , Técnicas de Hibridização Subtrativa , Fatores de Transcrição/metabolismo
17.
Aging (Albany NY) ; 11(11): 3463-3486, 2019 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-31160541

RESUMO

Mounting evidence points to alterations in the gut microbiota-neuroendocrine immunomodulation (NIM) network that might drive Alzheimer's Disease (AD) pathology. In previous studies, we found that Liuwei Dihuang decoction (LW) had beneficial effects on the cognitive impairments and gastrointestinal microbiota dysbiosis in an AD mouse model. In particular, CA-30 is an oligosaccharide fraction derived from LW. We sought to determine the effects of CA-30 on the composition and function of the intestinal microbiome in the senescence-accelerated mouse prone 8 (SAMP8) mouse strain, an AD mouse model. Treatment with CA-30 delayed aging processes, ameliorated cognition in SAMP8 mice. Moreover, CA-30 ameliorated abnormal NIM network in SAMP8 mice. In addition, we found that CA-30 mainly altered the abundance of four genera and 10 newborn genera. Advantageous changes in carbohydrate-active enzymes of SAMP8 mice following CA-30 treatment, especially GH85, were also noted. We further found that seven genera were significantly correlated with the NIM network and cognitive performance. CA-30 influenced the relative abundance of these intestinal microbiomes in SAMP8 mice and restored them to SAMR1 mouse levels. CA-30 ameliorated the intestinal microbiome, rebalanced the NIM network, improved the AD-like cognitive impairments in SAMP8 mice, and can thus be a potential therapeutic agent for AD.

18.
Biomed Res Int ; 2019: 6723849, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31211141

RESUMO

The security of engineering Saccharomyces cerevisiae is becoming more focused on industrial production in consideration of the public concern regarding genetically modified organisms. In this work, a rapid and highly efficient system for seamless gene deletion in S. cerevisiae was developed through two-step integration protocol combined with endonuclease I-SCEI expression. The factors affecting the frequency of the second homologous recombination were optimized, and studies indicated that the mutant strains with 500 bp direct repeats and that have been incubating in galactose (0.5 g/100 mL) medium at 30°C and 180 r/min for 24 h permit high frequency (6.86 × 10-4) of the second homologous recombination. Furthermore, DNA sequence assays showed only self-DNA in native location without any foreign genes after deletion using this method. The seamless gene deletion method was applied to the construction of the engineering strains with BAT2 (encoding aminotransferase) deletion and ATF1 (alcohol acetyltransferases) overexpression. The mutants exhibited significant effects on higher alcohol reduction and ester improvement after Baijiu fermentation. The engineered strains can be used in industrial production in security, thereby meeting the requirements of modern science and technology.


Assuntos
Álcoois/metabolismo , Ésteres/metabolismo , Deleção de Genes , Proteínas/genética , Proteínas de Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae , Transaminases/genética , Recombinação Homóloga , Proteínas/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Transaminases/metabolismo
19.
Eur J Cardiothorac Surg ; 56(5): 883-890, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31005966

RESUMO

OBJECTIVES: Acute kidney injury (AKI) is a prevalent complication after the surgical repair of paediatric cardiac defects and is associated with poor outcomes. Insufficient renal perfusion secondary to severe myocardial dysfunction in neonates is most likely an independent risk factor in patients undergoing repair for anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA). We retrospectively investigated the epidemiology and outcomes of children with ALCAPA who developed AKI after repair. METHODS: Eighty-nine children underwent left coronary reimplantation. The paediatric-modified risk, injury, failure, loss and end-stage (p-RIFLE) criteria were used to diagnose AKI. RESULTS: The incidence of AKI was 67.4% (60/89) in our study. Among the patient cohort with AKI, 23 (38.3%) were diagnosed with acute kidney injury/failure (I/F) (20 with acute kidney injury and 3 with acute kidney failure). Poor cardiac function (left ventricular ejection fraction < 35%) prior to surgery was a significant contributing factor associated with the onset of AKI [odds ratio (OR) 5.55, 95% confidential interval (CI) 1.39-22.13; P = 0.015], while a longer duration from diagnosis to surgical repair (OR 0.97, 95% CI 0.95-1.00; P = 0.049) and a higher preoperative albumin level (OR 0.83, 95% CI 0.70-0.99; P = 0.041) were found to lower the risk of AKI. Neither the severity of preoperative mitral regurgitation nor mitral annuloplasty was associated with the onset of AKI. After reimplantation, there was 1 death in the no-AKI group and 2 deaths in the AKI/F group (P = 0.356); the remaining patients survived until hospital discharge. The median follow-up time was 46.5 months (34.0-63.25). During follow-up, patients in the AKI cohort were seen more often by specialists and reassessed more often by echocardiography. CONCLUSIONS: Paediatric AKI after ALCAPA repair occurs at a relatively higher incidence than that suggested by previous reports and is linked to poor clinical outcomes. Preoperative cardiac dysfunction (left ventricular ejection fraction < 35%) is strongly associated with AKI. The beneficial effect of delaying surgery seen in some of our cases warrants further investigation, as it is not concordant with standard teaching regarding the timing of surgery for ALCAPA.

20.
Dalton Trans ; 48(19): 6473-6483, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-30993295

RESUMO

A ruthenium carbene catalyst chelated with a 3,4-dioxocyclobut-1-ene-1,2-dithiolate ligand was synthesized and its molecular structure was determined by single-crystal X-ray diffraction. The Ru catalyst had excellent catalytic activity with high yields and good Z/E ratios for the ring opening metathesis polymerization (ROMP) of norbornene (yield: 96%/Z/E: 86 : 14) and 1,5-cyclooctadiene (yield: 86%/Z/E: 91 : 9) and for ring opening cross metathesis (ROCM) reactions of norbornene/5-norbornene-2-exo, 3-exo-dimethanol with styrene (yields: 64%-92%/Z/E: 97 : 3-98 : 2) or 4-fluorostyrene (yield: 46%-94%/Z/E: 98 : 2). The catalyst also had high Z-stereoretentivity (91 : 9-98 : 2) for cross-metathesis (CM) reactions of terminal olefins with (Z)-2-butene-1,4-diol. More importantly, the catalyst had moderate Z-stereoselectivity for homometathesis reactions of terminal olefins giving cis-olefins as the major products (Z/E ratios of 70 : 30-77 : 23). Like other Ru carbene complexes, the catalyst tolerates many different functional groups. The presented data, supported by DFT calculations, show that our catalyst, bearing a chelating 3,4-dioxocyclobut-1-ene-1,2-dithiolate ligand, exhibits higher stability towards air than Hoveyda's stereoretentive complex systems.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA