145 research outputs found
Mechanism of Alkyl Migration in Diorganomagnesium 2,6-Bis(imino)pyridine Complexes: Formation of Grignard-Type Complexes with Square-Planar Mg(II) Centers
Dialkylmagnesium compounds [MgR2L2] (R = n-Bu, L = none or R = Bn, L = THF) react with 2,6-bis(imino)pyridines (BIP) to afford different types of Mg(II) alkyl complexes, depending on the nature of R. For R = n-Bu, thermally stable products resulting from selective alkyl transfer to the pyridine nitrogen (N1) atom are obtained. However, NMR studies showed that the reaction of [Mg(Bn)2THF2] with iPrBIP at â65 °C leads to a thermally unstable product arising from benzyl migration to position C2 in the pyridine ring. Above +5 °C, this compound rearranges, cleanly yielding a mixture of two isomeric complexes, in which the benzyl group has migrated to positions C3 or C4 of the central ring, respectively. Similar isomeric mixtures were obtained when [Mg(Bn)2THF2] was reacted with iPrBIP or MesBIP at room temperature. Such mixtures are thermally stable below 80 °C, but at this temperature, the 3-benzyl isomer converts into the thermodynamically favored 4-benzyl product, albeit not quantitatively. An alternate route was devised for the selective syntheses of the latter type of compounds. The X-ray diffraction structure of one of them provided an unusual example of a square-planar alkylmagnesium(II) center.Ministerio de EconomĂa e InnovaciĂłn CTQ2015-68978-
Oxygen-Induced Dimerization of Alkyl-Manganese(II) 2,6-Bisiminopyridine Complexes: Selective Synthesis of a New Ditopic NNN-Pincer Ligand
The outcome of the reaction of manganese(II) dialkyls with 2,6-bisiminopyridine (BIP) ligands is dramatically altered by the presence of very small amounts of oxygen (< 0.5 mol %), leading to binuclear species. These arise from the dimerization of the initial product, a Mn(II) 4-alkyl-2,6-bisiminodihydropyridinate alkyl complex. Cleavage of the binuclear Mn products with methanol affords the free dimeric bases, which can be regarded as a special type of ditopic NNN pincer ligand with an unusual tricyclic framework. The coordinative ability of the new ligands has been probed with the syntheses of Zn and Pd organometallic derivativesMinisterio de EconomĂa e InnovaciĂłn TQ2015- 68978-
The cadherinâcatenin complex in nasopharyngeal carcinoma
Abnormal Wnt signaling and impaired cellâcell
adhesion due to abnormal E-cadherin and b-catenin func tion have been implicated in many cancers, but have not
been fully explored in nasopharyngeal carcinoma. The aim
of this study was to analyze b-Catenin cellular location and
E-cadherin expression levels in nasopharyngeal carcinoma.
E-cadherin expression levels were also correlated with
clinical data and underlying pathology. b-Catenin and
E-cadherin expression were examined in 18 nasopharyn geal carcinoma and 7 non-tumoral inflammatory pharynx
tissues using immunohistochemical methods. Patient clin ical data were collected, and histological evaluation was
performed by hematoxylin/eosin staining. b-catenin was
detected in membrane and cytoplasm in all cases of naso pharyngeal carcinoma, regardless of histological type; in
non-tumoral tissues, however, b-catenin was observed only
in the membrane. As for E-cadherin expression levels,
strong staining was observed in most non-tumoral tissues,
but staining was only moderate in nasopharyngeal carci noma tissues. E-cadherin expression was associated with
b-catenin localization, study group, metastatic disease, and
patient outcomes. Reduced levels of E-cadherin protein
observed in nasopharyngeal carinoma may play an
important role in invasion and metastasis. Cytoplasmic
b-catenin in nasopharyngeal carcinoma may impair cellâ
cell adhesion, promoting invasive behavior and a metastatic
tumor phenotype
[2,6-Bis(di-tert-butylÂphosphinomethÂyl)ÂphenÂyl-Îș3 P,C 1,PâČ](nitrato-ÎșO)nickel(II)
The NiII atom in the title compound, [Ni(C24H43P2)(NO3)], adopts a distorted square-planar geometry with the P atoms in a trans arrangement. The compound contains a twofold rotational axis with the nitrate group offset from this axis, except for an O atom of the nitrate group, generating two positions of 50% occupancy for the other atoms of the nitrate group
Protonolysis of FeâC bonds of a diiminopyridineiron(II) dialkyl complex by acids of different strengths: Influence of monoanionic ligands on the spectroscopic properties of diiminopyiridine-FeY2 complexes
Fortalecimiento de gestiones a través del Centro de Información de Actividades Porcinas (CIAP) para el desarrollo sustentable de pequeños y medianos productores porcinos familiares de la zona de influencia de la Facultad de Ciencias Agrarias de la Universidad Nacional de Rosario
Fortalecimiento de gestiones a través del Centro de Información de Actividades Porcinas (CIAP) para el desarrollo sustentable de pequeños y medianos productores porcinos familiares de la zona de influencia de la Facultad de Ciencias Agrarias de la Universidad Nacional de RosarioFil: Silva, Patricia. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentin
Cross-Dehydrogenative Couplings between Indoles and ÎČ-Keto Esters : Ligand-Assisted Ligand Tautomerization and Dehydrogenation via a Proton-Assisted Electron Transfer to Pd(II)
Cross-dehydrogenative coupling reactions between -ketoesters and electron-rich arenes, such as indoles, proceed with high regiochemical fidelity with a range of -ketoesters and indoles. The mechanism of the reaction between a prototypical -ketoester, ethyl 2-oxocyclopentanonecarboxylate and N-methylindole, has been studied experimentally by monitoring the temporal course of the reaction by 1H NMR, kinetic isotope effect studies, and control experiments. DFT calculations have been carried out using a dispersion-corrected range-separated hybrid functional (B97X-D) to explore the basic elementary steps of the catalytic cycle. The experimental results indicate that the reaction proceeds via two catalytic cycles. Cycle A, the dehydrogenation cycle, produces an enone intermediate. The dehydrogenation is assisted by N-methylindole, which acts as a ligand for Pd(II). The compu-tational studies agree with this conclusion, and identify the turnover-limiting step of the dehydrogenation step, which involves a change in the coordination mode of the -keto ester ligand from an O,Oâ-chelate to an C-bound Pd enolate. This ligand tautom-erization event is assisted by the -bound indole ligand. Subsequent scission of the â-CâH bond takes place via a proton-assisted electron transfer mechanism, where Pd(II) acts as an electron sink and the trifluoroacetate ligand acts as a proton acceptor, to pro-duce the Pd(0) complex of the enone intermediate. The coupling is completed in cycle B, where the enone is coupled with indole. Pd(TFA)2 and TFA-catalyzed pathways were examined experimentally and computationally for this cycle, and both were found to be viable routes for the coupling step
The cadherinâcatenin complex in laryngeal squamous cell carcinoma
Abnormal Wnt signaling and impaired cellâcell adhesion due to abnormal E-cadherin and ÎČ-catenin function have been implicated in many cancers, but have not been fully explored in laryngeal squamous cell carcinoma. In this study, ÎČ-catenin cellular location and E-cadherin expression levels were analyzed in 16 laryngeal squamous cell carcinomas (LSCCs) (9 glottic and 7 supraglottic) and 11 samples of non-tumoral inflammatory larynx tissue, using immunohistochemical methods. All non-tumoral tissues showed equally strong membranous expression of ÎČ-catenin, while cytoplasmic expression was found in only 3 of the 11 samples. By contrast, whereas 8/9 glottic LSCCs exhibited only membranous expression of ÎČ-catenin, 6/7 supraglottic LSCCs displayed both membranous and cytoplasmic expression (p = 0.003). Strong E-cadherin staining was observed in 9/11 non-tumoral tissues and 7/9 glottic LSCCs, whereas 4/7 supraglottic LSCCs exhibited weak expression. Reduced membrane expression of E-cadherin and cytoplasmic retention of ÎČ-catenin in supraglottic LSCC seems to be related with more aggressive biological behavior which has been described in clinical studies. Further research is required to clarify the involvement of ÎČ-catenin in the mechanism associated with malignant transformation in laryngeal tissues
The cadherinâcatenin complex in nasopharyngeal carcinoma
Abnormal Wnt signaling and impaired cellâcell adhesion due to abnormal E-cadherin and ÎČ-catenin function have been implicated in many cancers, but have not been fully explored in nasopharyngeal carcinoma. The aim of this study was to analyze ÎČ-Catenin cellular location and E-cadherin expression levels in nasopharyngeal carcinoma. E-cadherin expression levels were also correlated with clinical data and underlying pathology. ÎČ-Catenin and E-cadherin expression were examined in 18 nasopharyngeal carcinoma and 7 non-tumoral inflammatory pharynx tissues using immunohistochemical methods. Patient clinical data were collected, and histological evaluation was performed by hematoxylin/eosin staining. ÎČ-catenin was detected in membrane and cytoplasm in all cases of nasopharyngeal carcinoma, regardless of histological type; in non-tumoral tissues, however, ÎČ-catenin was observed only in the membrane. As for E-cadherin expression levels, strong staining was observed in most non-tumoral tissues, but staining was only moderate in nasopharyngeal carcinoma tissues. E-cadherin expression was associated with ÎČ-catenin localization, study group, metastatic disease, and patient outcomes. Reduced levels of E-cadherin protein observed in nasopharyngeal carinoma may play an important role in invasion and metastasis. Cytoplasmic ÎČ-catenin in nasopharyngeal carcinoma may impair cellâcell adhesion, promoting invasive behavior and a metastatic tumor phenotype
R-Allyl Nickel(II) Complexes with Chelating N-Heterocyclic Carbenes: Synthesis, Structural Characterization, and Catalytic Activity
The N-heterocyclic carbene (NHC) nickel complexes [(L)Ni(NHC)][BArF4] (ArF = 3,5-bis(trifluoromethyl)-
phenyl; L = allyl (1), methylallyl (2); NHC = 1-(2-picolyl)-3-methylimidazol-2-ylidene (a), 1-(2-picolyl)-3-isopropylimidazol-2-ylidene (b), 1-(2-picolyl)-3-n-butylimidazol-2-ylidene (c), 1-(2-picolyl)-3-phenylimidazol-2-ylidene (d), 1-(2-picolyl)-3- methylbenzoimidazol-2-ylidene (e), 1-(2-picolyl)-4,5-dichloro-3-methylimidazol-2-ylidene (f)) have been obtained in high yields and characterized by NMR spectroscopy. Furthermore, 1d was unambiguously characterized by single-crystal X-ray crystallography. Complexes 1aâf/2aâf have shown catalytic activity toward dimerization and hydrosilylation of styrenes. In particular, 1a proved to be the most efficient catalyst in the dimerization of styrene derivatives in the absence of cocatalyst. Also, complexes 1a,d showed high selectivity and moderate to good yields in hydrosilylation reactions
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