RESUMO
Generating sustainable fuel from sunlight plays an important role in meeting the energy demands of the modern age. Herein, we report two-coordinate carbene-metal-amide (cMa, M = Cu(I) and Au(I)) complexes that can be used as sensitizers to promote the light-driven reduction of water to hydrogen. The cMa complexes studied here absorb visible photons (εvis > 103 M-1 cm-1), maintain long excited-state lifetimes (τ â¼ 0.2-1 µs), and perform stable photoinduced charge transfer to a target substrate with high photoreducing potential (E+/* up to -2.33 V vs Fc+/0 based on a Rehm-Weller analysis). We pair these coinage metal complexes with a cobalt-glyoxime electrocatalyst to photocatalytically generate hydrogen and compare the performance of the copper- and gold-based cMa complexes. We also find that the two-coordinate complexes herein can perform photodriven hydrogen production from water without the addition of the cobalt-glyoxime electrocatalyst. In this "catalyst-free" system, the cMa sensitizer partially decomposes to give metal nanoparticles that catalyze water reduction. This work identifies two-coordinate coinage metal complexes as promising abundant metal, solar fuel photosensitizers that offer exceptional tunability and photoredox properties.
RESUMO
A facile one-pot approach for the azidodifluoromethylation of aldehydes via in situ-generated azidodifluoromethenide (N3CF2-) utilizing commercially available TMSCF2Br and NaN3 is disclosed. The formed O-silyl ether products are obtained in yields of up to 91% in short reaction times at ambient temperature. Examples of both inter- and intramolecular [3 + 2] azide-alkyne cycloaddition reactions of the installed azidodifluoromethyl handles are also presented, demonstrating the prospective synthetic and biochemical functionality and utility.
RESUMO
Multidrug resistance (MDR) is one of the major clinical challenges in cancer treatment and compromises the effectiveness of conventional anticancer chemotherapeutics. Among known mechanisms of drug resistance, drug efflux via ATP binding cassette (ABC) transporters, namely P-glycoprotein (P-gp) has been characterized as a major mechanism of MDR. The primary function of ABC transporters is to regulate the transport of endogenous and exogenous small molecules across the membrane barrier in various tissues. P-gp and similar efflux pumps are associated with MDR because of their overexpression in many cancer types. One of the intensively studied approaches to overcome this mode of MDR involves development of small molecules to modulate P-gp activity. This strategy improves the sensitivity of cancer cells to anticancer drugs that are otherwise ineffective. Although multiple generations of P-gp inhibitors have been identified to date, reported compounds have demonstrated low clinical efficacy and adverse effects. More recently, natural polyphenols have emerged as a promising class of compounds to address P-gp linked MDR. This review highlights the chemical structure and anticancer activities of selected members of a structurally unique class of 'biaryl' polyphenols. The discussion focuses on the anticancer properties of ellagic acid, ellagic acid derivatives, and schisandrins. Research reports regarding their inherent anticancer activities and their ability to sensitize MDR cell lines towards conventional anticancer drugs are highlighted here. Additionally, a brief discussion about the axial chirality (i.e., atropisomerism) that may be introduced into these natural products for medicinal chemistry studies is also provided.