Search results for "ALK"

Influence of Pore-Volume Topology of Zeolite ITQ-7 in Alkylation and Isomerization of Aromatic Compounds

2002

The void structure of zeolite ITQ-7 (ISV structure) is discussed on the basis of catalytic reaction tests. The isomerization and disproportionation of meta-xylene, and the alkylation of benzene or toluene with either ethanol or isopropanol, on the acidic zeolite have been used as model reactions. The dimensions of its three-dimensional system of channels, with pores between 6.1 and 6.3 A and with lower tortuosity than those of beta zeolite, favor higher ratios of isomerization to disproportionation of meta-xylene, and of mono- to dialkylated products and iso- to n-propylbenzene during alkylation of benzene. These effects are enhanced with a partially coked ITQ-7.

Xylene isomerization and aromatic alkylation in zeolites NU-87, SSZ-33, β, and ZSM-5: molecular dynamics and catalytic studies

2004

The unique pore topology of zeolite NU-87, with 10-membered ring (MR) channels intersected by perpendicular 12-MR cavities, can offer new opportunities for alkylaromatics isomerization, as well as for aromatics alkylation. The catalytic performance has been studied for meta-xylene isomerization and disproportionation, as well as toluene alkylation with methanol, ethanol, propanol, and isopropanol. Product distribution was interpreted on the basis of pore topology and compared to zeolites with 12-MR (β), 10- and 12-MR (SSZ-33), and 10-MR (ZSM-5) zeolites. The presence of cavities allows more space for the location of bulky intermediates and/or products, and also traps the molecules, allowing…

On/Off Photoswitching in a Cyanide-Bridged {Fe2Co2} Magnetic Molecular Square

2013

International audience; A repeatable bidirectional paramagnetic ↔ diamagnetic photomagnetic effect has been observed in the cyanide-bridged Fe-Co square complex {[Fe{B(pz)(4)}(CN)(3)](2)[Co(bik)(2)](2)}(ClO(4))(2)*3H(2)O [B(pz)(4) = tetrapyrazolylborate, bik = bis(1-methylimidazol-2-yl)ketone]. Magnetic measurements and low-temperature single-crystal X-ray diffraction experiments have shown that a complete electron transfer from the diamagnetic Fe(II)-Co(III) state to the paramagnetic Fe(III)-Co(II) metastable state is induced by 808 nm laser light irradiation, whereas the diamagnetic state is recovered in an almost quantitative yield under irradiation at 532 nm.

Gold(I)-Catalyzed Intermolecular Cycloaddition of Allenamides with α,β-Unsaturated Hydrazones: Efficient Access to Highly Substituted Cyclobutanes

2014

α,β-Unsaturated N,N-dialkyl hydrazones undergo a mild [2 + 2] cycloaddition to allenamides when treated with a suitable gold catalyst. The method, which represents the first application of N,N-dialkyl hydrazones in gold catalysis, is compatible with a wide variety of substituents at the alkenyl moiety of the hydrazone component, proceeds with excellent levels of regio- and diastereoselectivity, and provides densely substituted cyclobutanes with good to excellent yields.

A Modular Formal Total Synthesis of (±)-Cycloclavine

2016

Cycloclavine is a clavine-type Ergot alkaloid noteworthy for its unique pentacyclic skeleton featuring a 3-azabicyclo[3.1.0]hexane substructure. A short convergent route to the racemic alkaloid is described which comprises only eight linear steps and requires only four chromatographic purifications. The two key building blocks can be prepared in high yield from commercially available starting materials. Two consecutive coupling reactions, namely a selective alkylation of a dienolate and a Heck reaction, are the key steps of the reaction sequence.

Olefin metathesis reactions with fluorinated substrates, catalysts, and solvents.

2014

Efavirenz: What is known about the cellular mechanisms responsible for its adverse effects

2017

The HIV infection remains an important health problem worldwide. However, due to the efficacy of combined antiretroviral therapy (cART), it has ceased to be a mortal condition, becoming a chronic disease instead. Efavirenz, the most prescribed non-nucleoside analogue reverse transcriptase inhibitor (NNRTI), has been a key component of cART since its commercialization in 1998. Though still a drug of choice in many countries, its primacy has been challenged by the arrival of newer antiretroviral agents with better toxicity profiles and treatment adherence. The major side effects related to EFV have been widely described in clinical studies, however the mechanisms that participate in their pat…

Neuronal Bioenergetics and Acute Mitochondrial Dysfunction: A Clue to Understanding the Central Nervous System Side Effects of Efavirenz

2014

Background. Neurological pathogenesis is associated with mitochondrial dysfunction and differences in neuronal/glial handling of oxygen and glucose. The main side effects attributed to efavirenz involve the CNS, but the underlying mechanisms are unclear. Methods. Human cell lines and rat primary cultures of neurons and astrocytes were treated with clinically relevant efavirenz concentration. Results. Efavirenz alters mitochondrial respiration, enhances reactive oxygen species generation, undermines mitochondrial membrane potential, and reduces adenosine triphosphate (ATP) levels in a concentration-dependent fashion in both neurons and glial cells. However, it activates adenosine monophospha…

Profile of stress and toxicity gene expression in human hepatic cells treated with Efavirenz

2012

Hepatic toxicity and metabolic disorders are major adverse effects elicited during the pharmacological treatment of the human immunodeficiency virus (HIV) infection. Efavirenz (EFV), the most widely used non-nucleoside reverse transcriptase inhibitor (NNRTI), has been associated with these events, with recent studies implicating it in stress responses involving mitochondrial dysfunction and oxidative stress in human hepatic cells. To expand these findings, we analyzed the influence of EFV on the expression profile of selected stress and toxicity genes in these cells. Significant up-regulation was observed with Cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1), which indicated m…

[Pharmacogenomics of antiretrovirals].

2008

HIV infection is a serious but treatable disease, yet current treatment is limited by development of resistance and high rates of adverse drug reactions. Antiretroviral therapy is especially suitable for pharmacogenomic investigation as both drug exposure and treatment response can be reliably measured. Increasing knowledge about genes implicated in pharmacokinetics, mode of action, efficacy, and toxicity of drugs has already provided relevant results for clinical practice, for example: The strong association of the abacavir hypersensitivity reaction with HLA-B*5701 permits testing patients for the allele, and if present avoiding the drug and therefore preventing the reaction. Persons with …