The activation of aryl–Br bonds was achieved by sequential combination of a triplet–triplet annihilation process of the organic dyes, butane‐2,3‐dione and 2,5‐diphenyloxazole, with a ...single‐electron‐transfer activation of aryl bromides. The photophysical and chemical steps were studied by time‐resolved transient fluorescence and absorption spectroscopy with a pulsed laser, quenching experiments, and DFT calculations.
Two‐photon process: The combination of a visible‐to‐UV photon upconversion with a chemical electron‐transfer reaction mechanism has been applied to the reductive aryl–Br σ‐bond activation. Spectroscopic, preparative, and theoretical studies support the operation of a triplet–triplet annihilation process and sequential electron transfer and H‐atom‐transfer steps (see figure).
Abstract
Plasmids can mediate horizontal gene transfer of antibiotic resistance, virulence genes, and other adaptive factors across bacterial populations. Here, we analyze genomic composition and ...pairwise sequence identity for over 10,000 reference plasmids to obtain a global map of the prokaryotic plasmidome. Plasmids in this map organize into discrete clusters, which we call plasmid taxonomic units (PTUs), with high average nucleotide identity between its members. We identify 83 PTUs in the order
Enterobacterales
, 28 of them corresponding to previously described archetypes. Furthermore, we develop an automated algorithm for PTU identification, and validate its performance using stochastic blockmodeling. The algorithm reveals a total of 276 PTUs in the bacterial domain. Each PTU exhibits a characteristic host distribution, organized into a six-grade scale (I–VI), ranging from plasmids restricted to a single host species (grade I) to plasmids able to colonize species from different phyla (grade VI). More than 60% of the plasmids in the global map are in groups with host ranges beyond the species barrier.
Photocatalytic bond activations are generally limited by the photon energy and the efficiency of energy and electron transfer processes. Direct two‐photon processes provide sufficient energy but the ...ultra‐short lifetimes of the excited states prohibit chemical reactions. The commercial dye 9,10‐dicyanoanthracene enabled photocatalytic aromatic substitutions of non‐activated aryl halides. This reaction operates under VIS‐irradiation via sequential photonic, electronic, and photonic activation of the simple organic dye. The resultant highly reducing excited photocatalyst anion readily effected C−H, C−C, C−P, C−S, and C−B bond formations. Detailed synthetic, spectroscopic, and theoretical studies support a biphotonic catalytic mechanism.
Two photons to tango: A highly reducing photocatalytic system was developed that involves the sequential combination of photonic, electronic, and photonic activation of 9,10‐dicyanoanthracene, a simple commercial and soluble organic dye. The ultimately formed excited radical anion DCA.−* enables the reductive activation of various aryl bromides and chlorides under mild conditions and the application to hetero‐biaryl cross‐coupling and heteroatom functionalizations. Detailed spectroscopic and theoretical studies support the postulated dichromatic photocatalytic mechanism.
Conspectus Nature is intrinsically able to control kinetics, conversion, and selectivity of biochemical processes by means of confined reaction environments such as enzyme pockets, bilayer membranes, ...micelles, vesicles, cells, or bioorganic frameworks. The main reason for this fact is the optimal molecular alignment and restricted motion of reactant molecules compared to those found in bulk solution. Under this inspiration, a number of synthetic photo-nanoreactors based on supramolecular self-assembled systems have been developed during the last decades, including mesoporous inorganic materials, microemulsions, micelles, vesicles, lipid bilayer foams, polyelectrolyte nanoparticles, etc. In a broader sense, nanoreactor technology constitutes nowadays a promising tool to enhance organic synthesis under sustainable reaction conditions. In general, nanoreactors change the essential properties of the molecules within them, thus affecting their chemical reactivity. Among the nanoreactor-like systems described in the literature to facilitate photochemical processes, the more recent use of viscoelastic supramolecular gels, typically made of low-molecular-weight (LMW) compounds self-assembled through noncovalent interactions, as compartmentalized reaction media is particularly appealing due to the versatility of these materials in terms of fabrication, properties, and processability. Furthermore, the high specific surface areas found in supramolecular gels, their stimuli-responsive reversibility, good diffusion properties enhancing the interactions between reactants and the three-dimensional (3D) porous network, functional tunability, and blocking effect of external oxygen are some of the most important features that can benefit photoinduced processes carried out in confined gel media. Not surprisingly, the efficiency of photochemical processes inside gel media is largely dependent on the type of reaction, characteristics of the gel network, solvent nature, reactant properties, and reaction conditions. Thus, the main focus of this Account is to provide a concise overview of the most relevant examples reported by us and others in order to illustrate the main advantages associated with the emerging use of gel-based materials as nonconventional reaction media to facilitate and control photochemical reactions. In particular, photodimerization, triplet–triplet annihilation upconversion (TTA-UC) coupled to single electron transfer (SET), photooxidation, photoreduction, and trifluoromethylation reactions will be illustrated during the discussion. These examples suggest that gel-based media can provide a versatile platform for the discovery of new reaction pathways and facilitate the way that photochemical reactions are traditionally carried out in academia and industry in terms of reaction conditions and required infrastructure. In addition, the use of physical or chemical gels as reaction systems may also accelerate high-throughput screening of photocatalysts. Overall, a judicious choice of gelators, reactants, solvent, and reaction conditions for the assembly of these gelators is crucial for controlling conversion, kinetics, and selectivity of intragel photoinduced processes.
The use of transition‐metal complexes as photocatalysts have allowed the performance of diverse organic transformations in an outstanding manner, characterized not only by high yields, TOF, and ...selectivity values, but also by modulating and providing access to novel molecular structures that, without them, would be difficult if not impossible. However, one of the biggest concerns regarding the use of these photocatalysts relies on the difficulties associated with their isolation from reaction media and reutilization once the chemical process ends. The above, besides contaminating reaction products and requiring out tedious purification processes, prompts the inevitable loss of the catalyst, directly affecting its recyclability. In addition, this situation results in negative outcomes from an economic and environmental perspective, since transition‐metal complexes are usually expensive materials, and their unsuccessful recovery could result in leakage into the environment. These drawbacks served as inspiration for the elaboration of the present review focused on the development of novel strategies developed during the last decade for the successful recovery of these species. The strategies summarized herein, whether for homogeneous or heterogeneous systems, are based on the use of thermotropic solvents, changes in the hydrophilic balance of the catalyst, the employment of polymers, copolymers, porous macromolecular structures, and inorganic nanostructures as support of these entities. Moreover, the use of organized and confining media, such as micelles and gels in this context, is also discussed. We hope that this review will motivate the search for new strategies to develop novel catalytic systems, understanding that high performance is based not only on yields but also on recyclability, sustainability, and responsibility to the environment.
Photon upconversion (UC) based on triplet–triplet annihilation (TTA) is considered one of the most attractive methodologies for switching wavelengths from lower to higher energy. This two-photon ...process, which requires the involvement of a bimolecular system, has been widely used in numerous fields such as bioimaging, solar cells, displays, drug delivery, and so on. In the last years, we have witnessed the harnessing of this concept by the organic community who have developed new strategies for synthetic purposes. Interestingly, the generation of high-energetic species by this phenomenon has provided the opportunity not only to photoredox activate compounds with high-energy demanding bonds, expanding the reactivity window that lies outside the energy window of the initial irradiation wavelength, but also to sensitized conventional photocatalysts through energy transfer processes even employing infrared irradiation. Herein, an overview of the principal examples found in literature is described where TTA–UC systems are found to be suitable photosensitizers for several chemical transformations.
Herein, the direct covalent functionalization of single‐walled carbon nanotubes (SWNT) is presented with an amino‐decorated phenyl‐phenothiazine (PTH‐NH2) organophotocatalyst through the diazonium ...chemistry protocol. Three different SWNT‐PTH hybrids are prepared by varying the amount of PTH‐NH2 and diazonium agent and are fully characterized. These hybrids differ not only in the degree of functionalization, but also in the chemical structure and the photophysical properties. The study shows that these features affect the photoredox activity of the materials in the photo‐debromination of aromatic halides. Thus, sample SWNT‐PTH‐5, a functionalized nanotube with a 5% wt loading of PTH, surpasses the catalytic performance of homogeneous PTH in 11 different substrates, finishing the reaction in shorter times, in a recyclable manner and without catalyst leaching. This study demonstrates the importance of controlling the functionalization degree of SWNT with photocatalysts to prepare photocatalytic materials with even higher catalytic activity than that presented by the homogeneous PTH catalyst.
The control on the direct functionalization of single‐walled carbon nanotubes with the organophotocatalyst PTH allowed the creation of hybrid materials with enhanced charge transfer properties able to overcome homogeneous counterparts in the photoreductive debromination of aromatic halides with a robust character toward the stability during operation, including wide scope and synthetic utility.
A novel visible light promoted formation of CAryl‐S bonds through electron donor‐acceptor (EDA) complexes of alkylamines with 5‐ and 6‐membered (hetero)arene halides is presented. This represents the ...first EDA‐based thiolation method not relying on π‐π or a thiolate‐anion‐π interactions and provides a facile access to heteroarene radicals, which can be suitably trapped by disulfide derivatives to form the corresponding versatile arylsulfides. Mechanistic investigations on the aspects of the whole process were conducted by spectroscopic measurements, demonstrating the hypothesized EDA complex formation. Moreover, the strength of this method has been proven by a gram‐scale synthesis of thiolated products and the late‐stage derivatization of an anticoagulant drug.
An effective approach for the direct thiolation of five‐membered heteroarenes involving visible‐light‐absorbing EDA complexes is reported. The reaction takes place from an EDA complex between an alkylamine and the heteroarene halide. Selective photolysis to the EDA complex has allowed to generate the heteroarene radical that is suitably trapped by disulfide derivatives, providing a potent synthetic versatility.
Abstract Background Diet represents 30–35% of risk factors that contribute to the onset of cancer. Some foods and dietary patterns have been linked to the risk of various cancers. However ...epidemiological available data are not consistent for many foods and the associations with cancer risk remain unclear. The concerns about this issue are considered like a “Hot topic” for oncologists and general population. Objective The aim of this report is to present a review of the published epidemiologic research to date reflecting the most current scientific evidence related to diet and cancer risk. Design EMBASE and PubMed-NCBI were searched for relevant articles up to October 2013 that identified potentials interactions between foods or dietary patterns with cancer risk. Results There is no conclusive evidence as an independent risk factor for isolated nutrients versus adoption of dietary patterns for cancer risk. Moderate physical activity after breast cancer diagnosis contributes to 40% reduction of recurrence/disease-specific mortality. Cancer colon risk derived from meat intake is influenced by both total intake and its frequency. The interaction of phenolic compounds on metabolic and signaling pathways like P450, MAP kinase, PI3 kinase, IGF-1, NF-kB and ROS seems to exert an inhibitory effect on cell proliferation and tumor metastasis and induces apoptosis in various types of cancer cells, including colon, lung, prostate, hepatocellular or breast cancer. Conclusions There is a direct relationship between unhealthy diet and lifestyle with the increase of tumor development and cancer risk. For this reason, a good nutritional status based on a balanced diet constitutes one of the main preventive factors from tumors. However the mixed results from epidemiologic studies hinder to get unequivocal and consistent evidence about the interaction between diet and cancer risk. More epidemiological studies will be needed in the future to clarify this issue.
Highlights • We review studies that have examined possible interactions between dietary phytochemicals and cancer prevention. • A diet rich in phytochemicals is associated with a reduction in the ...risk of cancer. • A cancer prevention strategy based on dietary intake of natural phytochemicals is a realistic option for the general population.
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