81 research outputs found

    Homoleptic Divalent Dialkyl Lanthanide-Catalyzed Cross-Dehydrocoupling of Silanes and Amines

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    The rare-earth bis(alkyl) compound Sm{C(SiHMe2)3}2THF2 (1b) is prepared by the reaction of samarium(II) iodide and 2 equiv of KC(SiHMe2)3. This synthesis is similar to that of previously reported Yb{C(SiHMe2)3}2THF2 (1a), and compounds 1a,b are isostructural. Reactions of 1b and 1 or 2 equiv of B(C6F5)3 afford SmC(SiHMe2)3HB(C6F5)3THF2 (2b) or Sm{HB(C6F5)3}2THF2 (3b), respectively, and 1,3-disilacyclobutane {Me2Si-C(SiHMe2)2}2 as a byproduct. Bands from 2300 to 2400 cm–1 assigned to νBH in the IR spectra and highly paramagnetically shifted signals in the 11B NMR spectra of 2b and 3b provided evidence for Sm-coordinated HB(C6F5)3. Compounds 1a,b react with the bulky N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazol-2-ylidene (ImtBu) to displace both THF ligands and give three-coordinate monoadducts Ln{C(SiHMe2)3}2ImtBu (Ln = Yb (4a), Sm (4b)). Complexes 4a,b catalyze cross-dehydrocoupling of organosilanes with primary and secondary amines at room temperature to give silazanes and H2, whereas 1a,b are not effective catalysts under these conditions. Second-order plots of ln{[Et2NH]/[Ph2SiH2]} vs time for 4a-catalyzed dehydrocoupling are linear and indicate first-order dependences on silane and amine concentrations. However, changes in the experimental rate law with increased silane concentration or decreased amine concentration reveal inhibition by silane. In addition, excess ImtBu or THF inhibit the reaction rate. These data, along with the structures of 4a,b, suggest that the bulky carbene favors low coordination numbers, which is important for accessing the catalytically active species

    Seasonal abundance and host plants of coconut stick insect (Graeffea crouanii Le Guillou) in coconut plantations of Fiji islands

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    Field survey conducted in major coconut growing regions in the three Fiji islands viz., Viti Levu, Vanua Levu, and Taveuni, revealed the presence of only one pest species of stick insect, Graeffea crouanii. Temperature had a significant effect on the level of infestation in the farms surveyed, while the effect of rainfall and humidity on the infestation was insignificant. Severe infestation was observed in isolated pockets, and the pest distribution was discontinuous in the surveyed areas. On a damage scale index, the insect infestation on coconut palms ranged from 0 to 4 grades. The peak increase of G. crouanii populations was from November to April in wet season at each of the three hotspots: Namaumada (Viti Levu), Dawara (Vanua Levu), and Salialevu (Taveuni). The occurrence of G. crouanii at varying damage levels in the present study may be attributed to the presence of sparse coconut palms in isolated coconut plantations. The field survey identified many alternate host plants of G. crouanii in the two plant families viz., Arecaceae and Pandanaceae. The information on the seasonal abundance and infestation levels of G. crouanii and its alternate host plants are discussed in formulating location-specific pest management strategies

    Caspase-3, myogenic transcription factors and cell cycle inhibitors are regulated by leukemia inhibitory factor to mediate inhibition of myogenic differentiation

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    <p>Abstract</p> <p>Background</p> <p>Leukemia inhibitory factor (LIF) is known to inhibit myogenic differentiation as well as to inhibit apoptosis and caspase-3 activation in non-differentiating myoblasts. In addition caspase-3 activity is required for myogenic differentiation. Therefore the aim of this study was to further investigate mechanisms of the differentiation suppressing effect of LIF in particular the possibility of a caspase-3 mediated inhibition of differentiation.</p> <p>Results</p> <p>LIF dependent inhibition of differentiation appeared to involve several mechanisms. Differentiating myoblasts that were exposed to LIF displayed increased transcripts for c-fos. Transcripts for the cell cycle inhibitor p21 as well as muscle regulatory factors myoD and myogenin were decreased with LIF exposure. However, LIF did not directly induce a proliferative effect under differentiation conditions, but did prevent the proportion of myoblasts that were proliferating from decreasing as differentiation proceeded. LIF stimulation decreased the percentage of cells positive for active caspase-3 occurring during differentiation. Both the effect of LIF inhibiting caspase-3 activation and differentiation appeared dependent on mitogen activated protein kinase and extracellular signal regulated kinase kinase (MEK) signalling. The role of LIF in myogenic differentiation was further refined to demonstrate that myoblasts are unlikely to secrete LIF endogenously.</p> <p>Conclusions</p> <p>Altogether this study provides a more comprehensive view of the role of LIF in myogenic differentiation including LIF and receptor regulation in myoblasts and myotubes, mechanisms of inhibition of differentiation and the link between caspase-3 activation, apoptosis and myogenic differentiation.</p

    The relation of serum GGT level in patients with non valvular atrial fibrillation and normal sinus rhythm

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    Background: The primary objective of the study was to assess and compare the relation of serum GGT level in patients with non valvular atrial fibrillation and normal sinus rhythm. The fundamental mechanisms underlying AF remains poorly understood. Oxidative stress is hypothesized to induce and maintain nonvalvular atrial fibrillation particularly in elderly patients. GGT levels are increased in patients with chronic inflammation. Increased serum levels of GGT are found in chronic nonvalvular atrial fibrillation (AF) patients as compared with patients in sinus rhythm.Methods: We included 75 patients of nonvalvular atrial fibrillation and 75 patients of sinus rhythm after applying exclusion criteria. Serum level of gamma glutamyl transrerase (GGT) of both the groups was compared.Results: Presence of coronary artery disease, hypertension, gender, hyperlipidemia, diabetes mellitus and smoking status were comparable between the 2 groups (P > 0.05 for all). Serum gamma glutamyl transferase activity in 75 cases was 71.45±26.21 with maximum being 147 IU/L more than the normal range for age, whereas in controls it was 19.68±5.53 i.e. much within the normal range for age.Conclusions: At the end of the study we concluded that serum GGT levels were significantly higher in patients with chronic nonvalvular atrial fibrillation (AF) patients as compared with patients in sinus rhythm

    Integrative analyses identify modulators of response to neoadjuvant aromatase inhibitors in patients with early breast cancer

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    Introduction Aromatase inhibitors (AIs) are a vital component of estrogen receptor positive (ER+) breast cancer treatment. De novo and acquired resistance, however, is common. The aims of this study were to relate patterns of copy number aberrations to molecular and proliferative response to AIs, to study differences in the patterns of copy number aberrations between breast cancer samples pre- and post-AI neoadjuvant therapy, and to identify putative biomarkers for resistance to neoadjuvant AI therapy using an integrative analysis approach. Methods Samples from 84 patients derived from two neoadjuvant AI therapy trials were subjected to copy number profiling by microarray-based comparative genomic hybridisation (aCGH, n = 84), gene expression profiling (n = 47), matched pre- and post-AI aCGH (n = 19 pairs) and Ki67-based AI-response analysis (n = 39). Results Integrative analysis of these datasets identified a set of nine genes that, when amplified, were associated with a poor response to AIs, and were significantly overexpressed when amplified, including CHKA, LRP5 and SAPS3. Functional validation in vitro, using cell lines with and without amplification of these genes (SUM44, MDA-MB134-VI, T47D and MCF7) and a model of acquired AI-resistance (MCF7-LTED) identified CHKA as a gene that when amplified modulates estrogen receptor (ER)-driven proliferation, ER/estrogen response element (ERE) transactivation, expression of ER-regulated genes and phosphorylation of V-AKT murine thymoma viral oncogene homolog 1 (AKT1). Conclusions These data provide a rationale for investigation of the role of CHKA in further models of de novo and acquired resistance to AIs, and provide proof of concept that integrative genomic analyses can identify biologically relevant modulators of AI response

    The GYMSSA trial: a prospective randomized trial comparing gastrectomy, metastasectomy plus systemic therapy versus systemic therapy alone

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    <p>Abstract</p> <p>Background</p> <p>The standard of care for metastatic gastric cancer (MGC) is systemic chemotherapy which leads to a median survival of 6-15 months. Survival beyond 3 years is rare. For selected groups of patients with limited MGC, retrospective studies have shown improved overall survival following gastrectomy and metastasectomies including peritoneal stripping with continuous hyperthermic peritoneal perfusion (CHPP), liver resection, and pulmonary resection. Median survival after liver resection for MGC is up to 34 months, with a five year survival rate of 24.5%. Similarly, reported median survival after pulmonary resection of MGC is 21 months with long term survival of greater than 5 years a possibility. Several case reports and small studies have documented evidence of long-term survival in select individuals who undergo CHPP for MGC.</p> <p>Design</p> <p>The GYMSSA trial is a prospective randomized trial for patients with MGC. It is designed to compare two therapeutic approaches: gastrectomy with metastasectomy plus systemic chemotherapy (GYMS) versus systemic chemotherapy alone (SA). Systemic therapy will be composed of the FOLFOXIRI regimen. The aim of the study is to evaluate overall survival and potential selection criteria to determine those patients who may benefit from surgery plus systemic therapy. The study will be conducted by the Surgery Branch at the National Cancer Institute (NCI), National Institutes of Health (NIH) in Bethesda, Maryland. Surgeries and followup will be done at the NCI, and chemotherapy will be given by either the local oncologist or the medical oncology branch at NCI.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov ID. NCT00941655</p
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