Despite extensive studies in gold catalysis, σ-allenylgold species have not been invoked as catalytic intermediates and their reactivities not studied. This work reports for the first time they are ...generated in situ and undergo nucleophilic addition to activated aldehydes in a bifunctional phosphine ligand-enabled gold catalysis. This development reveals a broad range of opportunities to achieve propargylic C–H functionalization for the first time under catalytic and mild conditions. The homopropargylic alcohols generated undergo ligand-enabled cycloisomerizations involving an unexpected silyl migration.
Phenols are widely used as starting materials in both industrial and academic society. Dearomatization reactions of phenols provide an efficient way to construct highly functionalized ...cyclohexadienones. The main challenge to make them asymmetric by catalytic methods is to control the selectivity while overcoming the loss of aromaticity. In this tutorial review, an up to date summary of recent progress in CADA reactions of phenol and aniline derivatives is presented.
User-generated content is a valuable resource for capturing all aspects of our environment and lives, and dedicated Volunteered Geographic Information (VGI) efforts such as OpenStreetMap (OSM) have ...revolutionized spatial data collection. While OSM data is widely used, considerably little attention has been paid to the quality of its Point-of-interest (POI) component. This work studies the accuracy, coverage, and trend worthiness of POI data. We assess the accuracy and coverage using another VGI source that utilizes editorial control. OSM data is compared to Foursquare data by using a combination of label similarity and positional proximity. Using the example of coffee shop POIs in Manhattan we also assess the trend worthiness of OSM data. A series of spatio-temporal statistical models are tested to compare change in the number of coffee shops to home prices in certain areas. This work overall shows that, although not perfect, OSM POI data and specifically its temporal aspect (changeset) can be used to drive urban science research and to study urban change.
A simple synthetic route for the preparation of functional nanoscale graphene oxide (NGO), a novel nanocarrier for the loading and targeted delivery of anticancer drugs, is reported. The NGO is ...functionalized with sulfonic acid groups, which render it stable in physiological solution, followed by covalent binding of folic acid (FA) molecules to the NGO, thus allowing it to specifically target MCF‐7 cells, human breast cancer cells with FA receptors. Furthermore, controlled loading of two anticancer drugs, doxorubicin (DOX) and camptothecin (CPT), onto the FA‐conjugated NGO (FA–NGO) via π–π stacking and hydrophobic interactions is investigated. It is demonstrated that FA–NGO loaded with the two anticancer drugs shows specific targeting to MCF‐7 cells, and remarkably high cytotoxicity compared to NGO loaded with either DOX or CPT only. Considering that the combined use of two or more drugs, a widely adopted clinical practice, often displays much better therapeutic efficacy than that of a single drug, the controlled loading and targeted delivery of mixed anticancer drugs using these graphene‐based nanocarriers may find widespread application in biomedicine.
Nanoscale graphene oxide (NGO) with good biocompatibility and physiological stability is synthesized by functionalization with sulfonic acid groups and conjugation with folic acid. In the delivery of multiple drugs, cellular‐uptake experiments show the targeted delivery of the anticancer drugs doxorubicin and camptothecin into cells (see picture) by the NGO via receptor‐mediated endocytosis.
The first efficient intermolecular reaction of gold carbene intermediates generated via gold-catalyzed alkyne oxidation has been realized using nitriles as both the reacting partner and the reaction ...solvent, offering a generally efficient synthesis of 2,5-disubstituted oxazoles with broad substrate scope. The overall reaction is a 2 + 2 + 1 annulation of a terminal alkyne, a nitrile, and an oxygen atom from an oxidant. The reaction conditions are exceptionally mild, and a range of functional groups are easily tolerated. With complex and/or expensive nitriles, only 3 equiv could be sufficient to achieve serviceable yields in the absence of any solvent and using only 1 mol % BrettPhosAuNTf2 as the catalyst.
The treatment of readily available propargylic indole-3-acetates with a catalytic amount of AuCl(PPh3)/AgSbF6 leads to tandem activations of the propargylic esters and the in situ generated allenylic ...esters, resulting in expeditious access to highly functionalized cyclobutanes with fused 2,3-indoline and γ-lactone rings and an exocyclic E-double bond through sequential 3,3-rearrangement and 2 + 2 cyclization.
For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, ...due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C–C triple bond a surrogate of an α-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the α-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The α-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of “gold rush”.
Fundamental understanding of pore‐scale methane hydrate dissociation in porous media is important to evaluate submarine slope stability and potential utilization of methane resources. In this paper, ...a general pore‐scale framework based on the lattice Boltzmann (LB) method is established for reactive transport coupled with nonisothermal multiple physicochemical processes in porous media. The framework combines the gas hydrate dissociation kinetic model, the single‐phase flow LB model, the mass transport LB model, and the conjugate heat transfer LB model. The pore‐scale framework is validated by several benchmark problems and then employed to investigate the endothermic dissociation process of methane hydrate with pore‐filling and grain‐coating habits in porous media. The methane hydrate endothermic dissociation behavior coupled with nonlinear nonisothermal multiple physicochemical processes involving intrinsic dissociation dynamics, gas flow, mass transport, phase change heat transfer, and conjugate heat transfer is well captured by the framework. The phase change of methane hydrate dissociation and pore structure evolution for different pore habits of hydrate are well depicted, and some insights about the dissociation front advancement and temperature distributions are also obtained. In addition, the effects of temperature field, inlet temperature, and inlet pressure on methane hydrate dissociation are investigated. The pore‐scale methane hydrate dissociation helps to advance our understanding of permeability‐saturation variation relation for continuum models.
Key Points
A pore‐scale lattice Boltzmann model for reactive transport in porous media is established
Methane hydrate dissociation induced dissociation front evolution and variation of transport properties in porous media are studied
Effects of temperature and pressure on pore‐scale dissociation process of pore‐filling and grain‐coating methane hydrates are emphasized
0D lead‐free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs3Cu2X5 ...(X = I, Br, and Cl) NCs with orthorhombic structure and well‐defined morphologies. All these Cs3Cu2X5 NCs exhibit broadband blue‐green photoluminescence (PL) emissions in the range of 445–527 nm with large Stokes shifts, which are attributed to their intrinsic self‐trapped exciton (STE) emission characteristics. The high PL quantum yield of 48.7% is obtained from Cs3Cu2Cl5 NCs, while Cs3Cu2I5 NCs exhibit considerable air stability over 45 days. Intriguingly, as X is changed from I to Br and Cl, Cs3Cu2X5 NCs exhibit a continuous redshift of emission peaks, which is contrary to the blueshift in CsPbX3 perovskite NCs.
0D all‐inorganic Cs3Cu2X5 (X = I, Br, and Cl) nanocrystals (NCs) with orthorhombic structure and well‐defined morphologies are produced. The NCs exhibit a continuous redshift of broadband blue‐green photoluminescence emissions in the range of 445–527 nm as X is changed from I to Br and Cl, which are attributed to their intrinsic self‐trapped exciton emission characteristics.
Loading and delivery of Bcl‐2‐targeted short interfering RNA (siRNA) and anticancer drug doxorubicin (DOX) by polyethylenimine (PEI)‐conjugated graphene oxide (PEI‐GO) is studied. A higher knockdown ...efficiency of siRNA delivered by PEI‐GO than by PEI is achieved. Sequential delivery of siRNA and DOX by the PEI‐GO nanocarrier shows a synergistic effect, which leads to significantly improved chemotherapy efficacy.
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