Radical-Smiles Rearrangement by a Vitamin B2-Derived Photocatalyst in Water.

Herein, we report a catalytic radical-Smiles rearrangement system of arene migration from ether to carboxylic acid with riboflavin tetraacetate (RFT), a readily available ester of natural vitamin B2, as the photocatalyst and water as a green solvent, being free of external oxidant, base, metal, inert gas protection, and lengthy reaction time. Not only the known substituted 2-phenyloxybenzoic acids substrates but also a group of naphthalene- and heterocycle-based analogues was converted to the corresponding aryl salicylates for the first time. Mechanistic studies, especially a couple of kinetic isotope effect (KIE) experiments, suggested a sequential electron transfer-proton transfer processes enabled by the bifunctional flavin photocatalyst.

Additive-free oxychlorination of unsaturated C-C bonds with tert-butyl hypochlorite and water.

Herein we report an additive-free protocol for the facile synthesis of α,α-dichloroketones and α-chlorohydrins from various aryl terminal, diaryl internal, and aliphatic terminal alkynes and alkenes, respectively. The commercially available tert-butyl hypochlorite (tBuOCl) was employed as a suitable chlorinating reagent, being accompanied by the less harmful tBuOH as the by-product. In addition, the oxygen atoms in the products came from water rather than molecular oxygen, based on the 18O-labelling experiments. Meanwhile, the diastereoselectivity of the Z- and the corresponding E-alkenes has been compared and rationalized. Using a group of control experiments, the possible mechanisms have been proposed as the initial electrophilic chlorination of unsaturated C-C bonds in a Markovnikov-addition manner in general followed by a nucleophilic addition with water. This work simplified the oxychlorination method with a mild chlorine source and a green oxygen source under ambient conditions.

Alkyne Oxidation by a Vitamin B2-Based Photocatalytic System with Both H2O and O2 as the Oxygen Source.

The employment of readily available photocatalysts and green oxygen atom sources is recognized as a promising strategy to develop sustainable catalysis for oxidation reactions. We herein reported a sacrificial reagent-free system consisting of riboflavin tetraacetate (RFT), an ester of natural vitamin B2 as the photocatalyst, and Sc(OTf)3 and NaCl as the cocatalysts for alkyne oxidation under blue light or even sunlight irradiation to produce 1,2-diketone in which the oxygen atoms were from both water and molecular oxygen, respectively. A major Cl-/Cl• cycle was proposed to be involved and achieved by the excited [RFT-2Sc3+]* complex via single electron transfer for the first time, distinguished from the OCl- active species by a two-electron process in previous flavin-halide photo-oxidation systems.

Visible-light-induced aerobic epoxidation with vitamin B2-based photocatalyst.

Herein we described the catalytic epoxidation of α,ß-enone, with peroxide in situ generated, via a predominant single electron transfer and a minor energy transfer pathway. We use inexpensive natural vitamin B2 (riboflavin, RF) or its simple ester (riboflavin tetraacetate, RFT) as the photocatalysts, commonly used 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) as both the electron source and organic base, and ambient air as the terminal oxidant, under visible-light irradiation and room temperature.

Catalyst-Free and Transition-Metal-Free Approach to 1,2-Diketones via Aerobic Alkyne Oxidation.

A catalyst-free and transition-metal-free method for the synthesis of 1,2-diketones from aerobic alkyne oxidation was reported. The oxidation of various internal alkynes, especially more challenging aryl-alkyl acetylenes, proceeded smoothly with inexpensive, easily handled, and commercially available potassium persulfate and an ambient air balloon, achieving the corresponding 1,2-diketones with up to 85% yields. Meanwhile, mechanistic studies indicated a radical process, and the two oxygen atoms in the 1,2-diketons were most likely from persulfate salts and molecular oxygen, respectively, rather than water.

Cerium Ammonium Nitrate-Mediated Access to Biaryl Lactones: Substrate Scopes and Mechanism Studies.

Herein we described an access to biaryl lactones from ortho-aryl benzoic acids via intramolecular O-H/C-H oxidative coupling with the commonly used cerium ammonium nitrate (CAN) as the one-electron oxidant under a thermal condition. The radical interrupting experiment suggested a radical process, while the kinetic isotope effect (KIE) showed that the C-H cleavage likely was not involved in the rate-determining step. Competitive reactions, especially the strikingly different ρ values of Hammett equations, indicated that the reaction rate was more sensitive to the electronic properties on the aryl moiety rather than the carboxylic moiety, which corresponded to the first single electron transfer (SET) step. In addition, the quite negative ρ values (-4.7) of the aryl moiety unveiled the remarkable electrophilic nature of the second intramolecular radical addition process, which was also consistent with product yields and regioselectivity. Moreover, control experiments disclosed that the single electron in the third step was also transferred to CeIV instead of molecular oxygen. Besides, the possible role of co-solvents trifluoroethanol (TFE) and its influences on the CeIV species were discussed. This work elucidated the possible mechanism by proposing the step that had more effects on the total reaction rate and the species that was responsible for the last single electron transfer.

A Biomimetic Lubricating Nanosystem with Responsive Drug Release for Osteoarthritis Synergistic Therapy.

Osteoarthritis (OA) is associated with lubrication failure of articular cartilage and severe inflammatory response of joint capsule. Synergistic therapy combining joint lubrication and anti-inflammation emerges as a novel treatment of OA. In this study, bioinspired by ultralow friction of natural articular synovial fluid and mussel adhesion chemistry, a biomimetic nanosystem with dual functions of enhanced lubrication and stimuli-responsive drug release is developed. A dopamine mediated strategy realizes one step biomimetic grafting of hyaluronic acid (HA) on fluorinated graphene. The polymer modified sheets exhibit highly efficient near-infrared absorption, and show steady lubrication with a long time under various working conditions, in which the coefficient of friction is reduced by 75% compared to H2 O. Diclofenac sodium (DS) with a high loading capacity of 29.2% is controllably loaded, and responsive and sustained drug release is adjusted by near-infrared light. Cell experiments reveal that the lubricating nanosystem is taken up by endocytosis, and anti-inflammation results confirm that the nanosystem inhibits osteoarthritis deterioration by upregulating cartilage anabolic gene and downregulating catabolic proteases and pain-related gene. This work proposes a promising biomimetic approach to integrate polymer modified fluorinated graphene as a dual-functional nanosystem for effective synergistic therapy of OA.

Rational Construction of Fluorescence Turn-Off Fluorinated Carbon Fiber/Ag Composites and Their Anticancer and Antibacterial Activities.

Although fluorinated carbon fiber/Ag composites possess unique structure and special charge distribution and exhibit great potential in numerous fields, their synthesis has long been a headache because of inert chemistry bonds, low surface energy, and easy aggregation. Herein, we first demonstrate a fresh concept of constructing the nanoscale hydrosoluble fluorinated carbon fiber oxide (FCO)/Ag composite and then integrate it as a highly effective targeting nanocarrier and photothermal therapy and antibacterial agent. Chemical introduction of oxygen allows us to controllably deposit Ag nanoparticles (AgNPs) for the first time and further facilitates surface modification with folic acid prelinked bovine serum albumin to induce targeted endocytosis toward tumor cells. The structure adjustment of FCO into nanosize and the decoration of AgNPs endow the composite with much better photothermal property than fluorinated carbon materials, and FCO/Ag also serves as an effective fluorescence quencher for doxorubicin, realizing visual monitor of drug adsorption processes by "turn-off" fluorescence. Meanwhile, both in vitro and in vivo results reveal greatly improved cancer therapeutic effects than single therapy. What is more is that the synergistic interactions of lipophilic fluorine and AgNPs also ensure highly effective antibacterial activity. Our study integrates FCO/Ag as an emerging drug carrier that exhibits excellent targeted efficiency and high photothemal property and reports its unprecedented experimental example in both antibacterial- and anticancer-combined chemo-photothermal therapy.