无溶剂条件下磷酸锆纳米粒子作为固体酸催化剂催化苯酚选择性烷基化(英文)

A facile synthesis of α-zirconium phosphate(ZP) nanoparticles as an effective, eco-friendly, and recyclable solid acid catalyst is reported. Polyvinylpyrrolidone(PVP) and polyvinyl alcohol(PVA) were used as organic matrix as dispersing agents and served as a template for the nanoparticles. Hydrogen bonds between ZP and PVA or PVP, along the polymer chains, appear to play an important role for improving the dispersion of in situ formed ZP. Following calcination of PVA/ZP or PVP/ZP, pure hexagonal ZP nanoparticles were obtained. The catalysts were characterized by nitrogen sorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy, and transmission electron microscopy. Pyridine-FTIR and temperature-programmed desorption of NH3 suggest the presence of Brnsted acid sites. The acidic properties of the catalyst were studied in Friedel-Crafts alkylation of phenol by tert-butanol, producing 2-tert-butylphenol, 4-tert-butylphenol, and 2,4-ditert-butylphenol. The alkylation reaction was performed in the presence of catalysts P2O5/Al2O3, P2O5/SiO2, α-ZrP(prepared in the absence of the polymers), and various ionic liquids. The use of the hexagonal ZP nanoparticle catalyst afforded an excellent phenol conversion(86%) and selectivity towards 4-tert-butylphenol(83%) under optimized reaction conditions. The catalyst was easily recovered from the reaction mixture, regenerated, and reused at least four times without significant loss in the catalytic activity.     

Acetylation of alcohols and phenols under solvent-free conditions using copper zirconium phosphate

Copper zirconium phosphate nanoparticles have been used as an efficient catalyst for the acetyla‐tion of a wide range of alcohols and phenols with acetic anhydride in good to excellent yields under sol...     

Immobilized Pd nanoparticles on Tris-modified SiO2：Synthesis,characterization, and catalytic activity in Heck cross-coupling reactions

The preparation of supported Pd nanoparticles on Tris (tris(hydroxymethyl)aminomethane)- modified SiO₂ gel and their catalytic application in Heck coupling are investigated. The catalyst was characterized using a combination of X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. The supported Pd nanoparticles were found to be a highly active and reusable catalyst for the Heck reaction at a low Pd loading (0.02 mol%) because of stabilization by the Tris moieties. Several reaction parameters, including the type and amount of solvent, base, and temperature, were evaluated. The heterogeneity of the catalytic system was investigated using different approaches, and showed that slight Pd leaching into the reaction solution occurred under the reaction conditions. Despite this metal leaching, the catalyst can be reused seven times without significant loss of its activity.     

Reactivity of Diruthenium and Dirhodium Analogues of Pentaborane(9): Agostic versus Boratrane Complexes

A series of novel Cp*‐based (Cp*=η⁵‐C₅Me₅) agostic, bis(σ‐borate), and boratrane complexes have been synthesized from diruthenium and dirhodium analogues of pentaborane(9). The synthesis and structural characterization of the first neutral ruthenadiborane(6) analogue are also reported. This new route offers a very efficient method for the isolation of bis(σ‐borate) and agostic complexes from diruthenapentaborane(9).     

Naturally occurring esterification reactions with bryostatin

Bryostatin structures share a commonality of a central bryophan ring, but each differs due to two groups (R(1) and R(2)) that are attached to the bryophan ring via ester bonds. This research examines the impact that conditions such as UV light, acidic and basic conditions can have on the bryostatin structure in the presence of octanoic acid and water. Mass spectrometry (MS) measurements suggest that bryostatin can easily rearrange into various structures under natural conditions by reacting with carboxylates that are ubiquitous in nature. A second set of measurements suggest bryostatin can be hydrolyzed by water, a reaction that has significant implications in both medicinal applications and extraction procedures.     

Effect of biological confinement on the photophysics and dynamics of a proton-transfer phototautomer: an exploration of excitation and emission wavelength-dependent photophysics of the protein-bound drug

The present work demonstrates the effect of biological confinement on the photophysics and dynamics of a bio-active drug molecule viz., 5-chlorosalicylic acid (5ClSA). 5ClSA is a potential candidate exhibiting Excited-State Intramolecular Proton Transfer (ESIPT) reaction and thereby generating the phototautomer (i.e. proton transferred keto form) in the excited state. Given the pK(a) of 5ClSA (around 2.64), the anionic form of the drug molecule is expected to be the interacting species with the protein under the experimental conditions (buffered solution of pH 7.40). The ESIPT photophysics of the drug (5ClSA anion) is found to be remarkably modified within the confined bio-environment of a model transport protein Bovine Serum Albumin (BSA) in terms of remarkable emission intensity enhancement coupled with a discernible red-shift of the emission maximum wavelength. Such considerable modification of the ESIPT photophysics of the 5ClSA anion has been exploited to determine the drug-protein binding strength (as characterized by the binding constant K (±10%) = 6.11 × 10(2) M(-1)). The present work also delves into evaluation of the probable binding location of the drug within the biomacromolecular assembly of the protein by a blind docking simulation technique, which reveals hydrophobic subdomain IIA to be the probable binding site of the drug. Circular dichroism (CD) spectroscopy delineates the effect of drug binding on the protein secondary structure in terms of decrease of α-helical content of BSA with increasing drug concentration. Apart from this, the excitation-emission matrix fluorescence technique is found to hint at the effect on protein tertiary structure upon binding to the drug. Chaotrope-induced protein denaturation has been explored to complement the findings on the binding interaction process. The modulated dynamics of the proton transfer phototautomer of the 5ClSA anion within the biological confinement is also investigated in this context to explore the slower rate of solvent-relaxation dynamics.     

Spectral deciphering of the interaction between an intramolecular hydrogen bonded ESIPT drug, 3,5-dichlorosalicylic acid, and a model transport protein

The present work demonstrates a detailed characterization of the interaction of a bio-active drug molecule 3,5-dichlorosalicyclic acid (3,5DCSA) with a model transport protein Bovine Serum Albumin (BSA). The drug molecule is a potential candidate exhibiting Excited-State Intramolecular Proton Transfer (ESIPT) reaction and the modulation of ESIPT photophysics within the bio-environment of the protein has been exploited spectroscopically to monitor the drug-protein binding interaction. Apart from evaluating the binding constant (K (±10%) = 394 M(-1)) the probable location of the neutral drug molecule within the protein cavity (hydrophobic subdomain IIA) is explored by AutoDock-based blind docking simulation. The rotational relaxation dynamics of the drug within the protein has been interpreted on the lexicon of the two-step and wobbling-in-cone model. Circular dichroism (CD) spectroscopy delineates the effect of drug binding on the protein secondary structure in terms of decrease of α-helical content of BSA with increasing drug concentration. Also the esterase activity of the drug:protein conjugate system is found to be reduced in comparison to the native protein.     

On finite groups with exactly seven element centralizers

For a finite groupG, #Cent(G) denotes the number of centralizers of its elements. A groupG is calledn-centralizer if #Cent(G) =n, and primitive n-centralizer if $\# Cent(G) = \# Cent\left( {\frac{G}{{Z(G)}}} \right) = n$ . The first author in [1], characterized the primitive 6-centralizer finite groups. In this paper we continue this problem and characterize the primitive 7-centralizer finite groups. We prove that a finite groupG is primitive 7-centralizer if and only if $\frac{G}{{Z(G)}} \cong D_{10} $ orR, whereR is the semidirect product of a cyclic group of order 5 by a cyclic group of order 4 acting faithfully. Also, we compute#Cent(G) for some finite groups, using the structure ofG modulu its center.     

5-Methoxybenzothiophene-2-Carboxamides as Inhibitors of Clk1/4: Optimization of Selectivity and Cellular Potency

Clks have been shown by recent studies to be promising targets for cancer therapy, as they are considered key regulators in the process of pre-mRNA splicing, which in turn affects every aspect of tumor biology. In particular, Clk1 and -4 are overexpressed in several human tumors. Most of the potent Clk1 inhibitors reported in the literature are non-selective, mainly showing off-target activity towards Clk2, Dyrk1A and Dyrk1B. Herein, we present new 5-methoxybenzothiophene-2-carboxamide derivatives with unprecedented selectivity. In particular, the introduction of a 3,5-difluoro benzyl extension to the methylated amide led to the discovery of compound 10b (cell-free IC₅₀ = 12.7 nM), which was four times more selective for Clk1 over Clk2 than the previously published flagship compound 1b. Moreover, 10b showed an improved growth inhibitory activity with T24 cells (GI₅₀ = 0.43 µM). Furthermore, a new binding model in the ATP pocket of Clk1 was developed based on the structure-activity relationships derived from new rigidified analogues.