5,615 research outputs found
Obtenção, caracterização e avaliação da atividade de um nanocatalisador de Pd(0) sintetizado in situ sob a superfície de Fe3O4@dextrana para redução do 4-nitrofenol
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Química, Florianópolis, 2015.O objetivo principal deste trabalho é a preparação, caracterização e avaliação da atividade catalítica das nanopartículas (NPs) de Pd impregnadas no suporte magnético magnetita e estabilizada por dextrana. As NPs-Pd foram preparadas por crescimento in situ sob a superfície de nanopartículas superparamagnéticas (NPSMs) (Fe3O4@dextrana/Pd(0)). O controle do crescimento das NPs-Pd foi feito com o auxílio de NaBH4, como agente redutor. O catalisador de Fe3O4@dextrana/Pd foi totalmente caracterizado por diversas técnicas tais como espectroscopia de infravermelho, espalhamento de luz dinâmico, espalhamento de raios-X a baixos ângulos, microscopia eletrônica de transmissão e varredura, e difração de raios-X de pó. A caracterização mostrou que o catalisador é constituído de um suporte feito de Fe3O4@dextrana composto por unidades de nanocristais com tamanho de 9,7 nm, formando nanoclusters de 105,6 nm, contendo as NPs-Pd de 7,8 nm impregnadas em sua superfície. Os estudos cinéticos foram realizados por UV-vis, sendo que a atividade catalítica foi avaliada pela reação modelo de redução do p-nitrofenol (Nip), utilizando NaBH4. Aplicando um modelo de reação de superfície pseudo-molecular, a reação foi investigada pelo modelo teórico de isoterma de adsorção, revelando ser uma reação bimolecular que segue o mecanismo de Langmuir-Hinshelwood. A atividade catalítica do nanocatalisador Fe3O4@ dextrana/Pd com área superficial de 3,33 m2L-1x10-3 (0, 0053 mg L-1 de Pd) pode ser efetivamente analisada, e foi possível obter os parâmetros cinéticos kL, KBH4- e KNip. Os resultados mostraram que as moléculas de Nip possuem afinidade de adsorção muito maior do que BH4- pela superfície das NPs-Pd, resultado da influência do caráter hidrofóbico do Nip sob a constante de adsorção do substrato. Um novo parâmetro de atividade catalítica ??? foi proposto e utilizado com sucesso na comparação com outros catalisadores reportados na literatura. As NPSMs de Fe3O4@dextrana/Pd apresentaram um valor de ? = 3,65 L mg-1 s-1, superior ao citado na literatura. O estudo do reuso de Fe3O4@dextrana/Pd demonstrou que é possível reutilizar as mesmas por até 5 vezes com cerca de 99% de conversão do Nip e valor alto de TOF, 692 h-1.Abstract : The aim of this work was the preparation, characterization and evaluation of catalytic activity of Pd nanoparticles (NPs) impregnated in magnetite and stabilized by dextran. The Pd NPs were prepared by the in situ growth under the surface of superparamagnetic nanoparticles. The growth control of Pd NPs was made with the aid of NaBH4, as reducing agent. The catalyst Fe3O4@dextran/Pd was fully characterized by several techniques such as: infrared spectroscopy, dynamic light scattering, X-ray scattering at small angle, transmission and scanning electron microscopy , and diffraction X-ray powder. The characterization revealed that the catalyst consisted of a support made of Fe3O4@dextran nanocrystals composed of units with 9.7 nm in size, forming nanoclusters of 105.6 nm containing NPs of Pd with 7.8 nm diameter, impregnated in the surface. The kinetic studies were performed by UV-vis spectrocopy, and the catalytic activity was evaluated by the model reaction of the p-nitrophenol (Nip) reduction, using NaBH4 as a reducing agent. Applying a pseudo-molecular surface reaction approach, the reduction reaction could be investigated by means of a theoretical adsorption model, revealing that the reaction is bimolecular and followed the Langmuir-Hinshelwood mechanism.The catalytic activity of nano-catalyst of Fe3O4@dextran/Pd, with a surface area of 3.33m2L-1x103 (0.0053 mg L-1Pd), could be effectively determined, obtaining the kinetic parameters kL, KBH4- and KNip. These kinetics results showed that the Nip molecules have higheraffinity for the catalyst surface than the molecules of BH4-, as a result of the influence of the Nip hydrophobic character. A new catalytic activity parameter "?" was proposed and effectively used for comparison with other recent reported catalysts. The reuse studies showed that could be reused up to 5 times with about 99% conversion of Nip and a high TOF value, 692 h-1
PD-L1 expression predicts longer disease free survival in high risk head and neck cutaneous squamous cell carcinoma
No full textProgrammed cell death (PD-1) and its ligand (PD-L1) inhibitors have shown clinical response in many tumours. PD-L1 data are limited in head and neck cutaneous squamous cell carcinoma (HNcSCC) and no clinical trials of PD-1/PD-L1 inhibitors are published. We performed PD-L1 immunohistochemistry on 74 cases of high risk HNcSCC with 38 matched metastases and evaluated clinicopathological associations, prognostic significance and heterogeneity in matched metastases. We observed PD-L1 expression in >5% of primary tumour cells in 29 cases (39.2%), primary tumour infiltrating lymphocytes (TILs) in 40 cases (70.2%), metastatic tumour cells in 15 cases (39.5%), and metastatic TILs in 18 cases (47.4%). PD-L1 expression in >5% of primary tumour cells was associated with an inflammatory phenotype (p = 0.04), and in primary TILs with clear margins (p = 0.05). PD-L1 expression in >5% of primary tumour cells (p = 0.01), primary TILs (p = 0.001), and metastatic TILs (p = 0.02) was associated with improved disease free survival. PD-L1 expression in >5% of tumour cells was heterogeneous between primary and metastatic tumours in 13 cases (34.2%). PD-L1 expression is common in HNcSCC supporting the rationale for a clinical trial of PD-1/PD-L1 inhibitors. PD-L1 expression in tumour cells or TILs predicts longer disease free survival and demonstrates temperospatial heterogeneity
Pd-Catalyzed Chemoselective O‑Benzylation of Ambident 2‑Quinolinone Nucleophiles
No full textWe have discovered and developed a highly chemoselective
O-benzylation
of ambident 2-quinolinone nucleophiles via Pd-catalysis. Detailed
reaction analysis using direct-injection high resolution mass spectrometry
(DI-HRMS) combined with in situ 31P NMR implicate a phosphine
mono-oxide Pd(II) η1-benzyl complex as a key intermediate
on the catalytic cycle. Extrapolation of this method to selectively
O-alkylate a series of substituted 2-quinolinones using several benzylic
electrophiles is demonstrated providing 2-benzyloxy quinolines in
good yields and high O:N selectivities (up to 100:1) utilizing as
little as 1 mol % Pd-catalyst to achieve these results
Pd-Catalyzed Chemoselective O‑Benzylation of Ambident 2‑Quinolinone Nucleophiles
No full textWe have discovered and developed a highly chemoselective
O-benzylation
of ambident 2-quinolinone nucleophiles via Pd-catalysis. Detailed
reaction analysis using direct-injection high resolution mass spectrometry
(DI-HRMS) combined with in situ 31P NMR implicate a phosphine
mono-oxide Pd(II) η1-benzyl complex as a key intermediate
on the catalytic cycle. Extrapolation of this method to selectively
O-alkylate a series of substituted 2-quinolinones using several benzylic
electrophiles is demonstrated providing 2-benzyloxy quinolines in
good yields and high O:N selectivities (up to 100:1) utilizing as
little as 1 mol % Pd-catalyst to achieve these results
Pd-Catalyzed Four-Component Sequential Reaction Delivers a Modular Fluorophore Platform for Cell Imaging
No full textA Pd-catalyzed
cascade reaction of four versatile privileged synthons
is described. The sequential reaction involves the formation of five
new chemical bonds by concatenating three distinct chemical steps.
One of the derivatives exhibited absorption in the visible region,
fluorescence with a high quantum yield, and excellent photostability.
Its application is explored in live cell imaging, which exhibited
cytoplasmic and mitochondrial specific staining with no toxicity
Pd-Catalyzed Four-Component Sequential Reaction Delivers a Modular Fluorophore Platform for Cell Imaging
No full textA Pd-catalyzed
cascade reaction of four versatile privileged synthons
is described. The sequential reaction involves the formation of five
new chemical bonds by concatenating three distinct chemical steps.
One of the derivatives exhibited absorption in the visible region,
fluorescence with a high quantum yield, and excellent photostability.
Its application is explored in live cell imaging, which exhibited
cytoplasmic and mitochondrial specific staining with no toxicity
Adipose PD-L1 Modulates PD-1/PD-L1 Checkpoint Blockade Immunotherapy Efficacy in Breast Cancer.
No full textProgrammed death-ligand 1 (PD-L1) and its receptor programmed cell death protein 1 (PD-1) modulate antitumor immunity and are major targets of checkpoint blockade immunotherapy. However, clinical trials of anti-PD-L1 and anti-PD-1 antibodies in breast cancer demonstrate only modest efficacy. Furthermore, specific PD-L1 contributions in various tissue and cell compartments to antitumor immunity remain incompletely elucidated. Here we show that PD-L1 expression is markedly elevated in mature adipocytes versus preadipocytes. Adipocyte PD-L1 prevents anti-PD-L1 antibody from activating important antitumor functions of CD8+ T cells in vitro. Adipocyte PD-L1 ablation obliterates, whereas forced preadipocyte PD-L1 expression confers, these inhibitory effects. Pharmacologic inhibition of adipogenesis selectively reduces PD-L1 expression in mouse adipose tissue and enhances the antitumor efficacy of anti-PD-L1 or anti-PD-1 antibodies in syngeneic mammary tumor models. Our findings provide a previously unappreciated approach to bolster anticancer immunotherapy efficacy and suggest a mechanism for the role of adipose tissue in breast cancer progression
PD trending and TVA test readings are good indicators of the condition of aged stator bar insulation.
No full textIncludes bibliographical references.Keeping generators available on-line is a major factor in achieving maximum productivity in power generation. During operation, generator components are continuously exposed to thermal, electrical, mechanical and environmental stresses. The complex interactions of these stresses degrade the components resulting in a reduction of useful life. An integral part of satisfactory operation of high voltage (HV) electrical rotating plant relies upon the integrity of the electrical HV insulation of both the rotor and stator. The combined effect of the above mentioned stresses results in ageing of the insulation, which if not detected, results in premature failure in service. Deterioration of the stator bar insulation is a leading factor for determining the serviceability of hydro generators. Unexpected and expected stator bar failure can result in forced outages and costly emergency repairs. This research will deal with the deterioration of stator bar insulation in air-cooled hydro generators only
Surpassing the Limited Coordination Affinity of Native Amides by Introducing Pyridone-Pd-AgOAc Clusters to Promote Distal γ‑C(sp<sup>3</sup>)–H Arylation
No full textThe
utilization of weak coordination in promoting site-selective
C(sp3)–H functionalization is of immense importance.
Herein, we report a Pd-catalyzed distal γ-C(sp3)–H
arylation that harnesses the weak coordination affinity of keto groups
with the native noncoordinating amide moiety. The current protocol
overcomes one of the major challenges associated with the diversification
of synthetic modular frameworks of quaternary centers: controlling
the mono- vs difunctionalization of chemically equivalent C–H
bonds. The developed condition overrides the interference of the acidic
α-hydrogen for possible side reactions of amides and delivers
the exclusive formation of the γ-monoarylated product. The association
of 2-hydroxy pyridine ligands bearing electron-withdrawing substituents
demonstrated the best partnership with the Pd–Ag hetero-bimetallic
complex to achieve this distal γ-C(sp3)–H
activation of a range of noncoordinating aliphatic amides in the absence
of any other exogenous ligand. Here, an array of mechanistic measurements
helped us to realize the role of the ligand. A density functional
theory (DFT) study was performed on four different computational models
to elucidate the working principle of a single pyridone ligand in
the absence of any externally installed strong chelating donor motifs.
The reaction proceeds sequentially through three primary stages: initial
C–H activation of the γ-C(sp3)–H bond
of the amide, succeeded by the oxidative addition of the aryl halide,
culminating in reductive elimination, which facilitates the C(sp2)–C(sp3) coupling between the aryl and the
aliphatic amide moieties. The role of the silver salt remained essential
not only for successful C–H activation but also for turning
over the catalytic cycle
Degradation processes of voids in solid dielectrics under AC applied fields
No full textThis Thesis is concerned with an experimental study into the degradation processes that occur when voids in solid dielectric materials experience high applied electric fields. A method has been developed for manufacturing 2 mm thick samples of silicone rubber that contain a single gas void of around 1mm diameter. Samples are simultaneously electrically stressed under an applied ac sinusoidal voltage of 11-12kV for 6 hours that is then increased to 12-17kV. During the stressing period, partial discharge (PD) data is regularly acquired. The samples are then inspected for signs of degradation. Degraded samples that have not suffered catastrophic failure and contain pits or evidence of damage were then cut open using an RMC MT-7 ultra- microtome equipped with a C R-21 cryo-system set at -110ºC in order to provide a surface containing open segments that can be assessed using spectroscopic techniques.The experiment is repeatable and the obtained degraded samples and the degradation areas of microtomed samples have been analysed using Raman spectroscopy to identify the chemical content of the degraded areas and obtained improved images using a scanning electron microscope (S EM) at the void /silicone rubber interface. In addition, the obtained PD patterns have been used to make a comparison between measurement and simulation results obtained using a physical model implemented in Matlab
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