Precise In Vivo Inflammation Imaging Using In Situ Responsive Cross‐linking of Glutathione‐Modified Ultra‐Small NIR‐II Lanthanide Nanoparticles

To improve the bioimaging signal‐to‐noise ratio (SNR), long‐term imaging capability, and decrease the potential biotoxicity, an in vivo cross‐linking strategy was developed by using sub‐10 nm, glutathione‐modified, lanthanide nanoprobes. After administration, the nanoprobes cross‐link in response to reactive oxygen species (ROS) at the inflamed area and enable the quick imaging of ROS in the second near‐infrared (NIR‐II) window. These nanoprobes could be rapidly excreted due to their ultra‐small size. This strategy may also be applied to other ultra‐small contrast agents for the precise bioimaging by in situ lesion cross‐linking.     

A Glutathione‐Activated Phthalocyanine‐Based Photosensitizer for Photodynamic Therapy

A zinc(II) phthalocyanine substituted with a 2,4‐dinitrobenzenesulfonate group has been prepared. Its fluorescence emission and reactive oxygen species generation can be greatly enhanced by glutathione in phosphate‐buffered saline and inside MCF‐7 cells. This compound thus functions as a highly efficient molecular‐based activatable photosensitizer.     

Protective Properties of Novel S‐Acyl‐Glutathione Thioesters Against Ultraviolet‐induced Oxidative Stress

UV‐induced toxicity is characterized by marked oxidative stress, accompanied by the depletion of key cellular antioxidants, particularly glutathione (GSH). Replenishing cellular GSH may represent a means of counteracting UV‐induced toxicity: however, treatment with free GSH is not therapeutically effective due to its unfavorable pharmacokinetic properties. In this study, we show that S‐acyl‐glutathione (acyl‐SG) derivatives, which consist of an acyl chain (of variable length and saturation) linked via a thioester bond to GSH, increase intracellular levels of reduced GSH in primary skin fibroblasts, adenocarcinoma HeLa and neuroblastoma SH‐SY5Y cells. Consistent with this, acyl‐SG derivatives protect against UV‐induced reactive oxygen species (ROS) production and UV‐B/C‐mediated lipid peroxidation and caspase‐3 activation in the analyzed cell lines, with unsaturated thioesters displaying a significantly greater protective effect. Taken together, our findings suggest that acyl‐SG thioesters may be therapeutically effective in the treatment of UV‐related skin disorders and oxidative stress‐mediated conditions in general.     

Aggregation‐Induced Emission Gold Clustoluminogens for Enhanced Low‐Dose X‐ray‐Induced Photodynamic Therapy

The use of gold nanoparticles as radiosensitizers is an effective way to boost the killing efficacy of radiotherapy while drastically limiting the received dose and reducing the possible damage to normal tissues. Herein, we designed aggregation‐induced emission gold clustoluminogens (AIE‐Au) to achieve efficient low‐dose X‐ray‐induced photodynamic therapy (X‐PDT) with negligible side effects. The aggregates of glutathione‐protected gold clusters (GCs) assembled through a cationic polymer enhanced the X‐ray‐excited luminescence by 5.2‐fold. Under low‐dose X‐ray irradiation, AIE‐Au strongly absorbed X‐rays and efficiently generated hydroxyl radicals, which enhanced the radiotherapy effect. Additionally, X‐ray‐induced luminescence excited the conjugated photosensitizers, resulting in a PDT effect. The in vitro and in vivo experiments demonstrated that AIE‐Au effectively triggered the generation of reactive oxygen species with an order‐of‐magnitude reduction in the X‐ray dose, enabling highly effective cancer treatment.     

Iron‐Catalyzed Direct Oxidative Alkylation and Hydroxylation of Indolin‐2‐ones with Alkyl‐Substituted N‐Heteroarenes

Presented herein is the first direct alkylation and hydroxylation reaction between two different C(sp³)?H bonds, indolin‐2‐ones and alkyl‐substituted N‐heteroarenes, through an oxidative cross‐coupling reaction. The reaction is catalyzed by a simple iron salt under mild ligand‐free and base‐free conditions. The reaction is environmentally benign, employs air (molecular oxygen) as the terminal oxidant and oxygen source for the synthesis of O‐containing compounds, and produces only water as the byproduct.     

Determination of thiol compounds by HPLC and fluorescence detection with 1,3,5,7‐tetramethyl‐8‐bromomethyl‐difluoroboradiaza‐s‐indacene

Altered levels of thiols in biological fluids are considered to be an important indicator for several diseases. In this article, 1,3,5,7‐tetramethyl‐8‐bromomethyl‐difluoroboradiaza‐s‐indacene is proposed as a fluorescent derivatization reagent for the determination of thiols including glutathione, cysteine, N‐acetylcysteine, and homocysteine by HPLC. Under the optimized derivatization and separation conditions, a baseline separation of all the four derivatives has been achieved using isocratic elution on an RP C₈ column within 26 min. With fluorescence detection at 505 and 525 nm for the excitation and emission, respectively, the LODs (S/N = 3) are from 0.2 nM (glutathione) to 0.8 nM (cysteine). The feasibility of this method in real samples has been evaluated by the determination of thiols in human plasma from the healthy persons and hypertensive patients with recoveries of 92–105.3%.     

A Copper‐Catalyzed Aerobic [1,3]‐Nitrogen Shift through Nitrogen‐Radical 4‐exo‐trig Cyclization

A novel radical [1,3]‐nitrogen shift catalyzed by copper diacetate under an oxygen atmosphere (1 atm) has been developed for the construction of a diverse range of indole derivatives from α,α‐disubstituted benzylamine. In this reaction, oxygen was used as a clean terminal oxidant, and water was produced as the only by‐product. Five inert bonds were cleaved, and two C−N bonds and one C−C double bond were constructed in one pot during this transformation. This unique method demonstrated broad application protential for the late‐stage modification of biologically active natural products and drugs. Mechanistic investigations indicate that a unique 4‐exo ‐trig cyclization of an aminyl radical onto a phenyl ring is involved in the catalytic cycle.     

A Native‐Chemical‐Ligation‐Based Turn‐on Fluorescent Probe for Selective Detection of Cysteine

Selective and quantitative detection of biological thiols such as cysteine, homocysteine, and glutathione is often necessary because abnormal levels of such thiols can cause some diseases. Here, we report that bis(pentafluorophenyl) 1,4‐benzenedicarbothionic acid diester can serve as a turn‐on fluorescent probe for selective detection of cysteine vis‐a‐vis homocysteine and glutathione. When cysteine was added to a mixture of the diester and a sodium phosphate buffer solution with THF (60 vol%), which is non‐fluorescent, the mixture became green‐fluorescent. In contrast, addition of homocysteine or glutathione did not make the mixture fluorescent. A native‐chemical‐ligation‐based mechanism is proposed.     

Enzyme‐MOF Nanoreactor Activates Nontoxic Paracetamol for Cancer Therapy

Prodrug activation, by exogenously administered enzymes, for cancer therapy is an approach to achieve better selectivity and less systemic toxicity than conventional chemotherapy. However, the short half‐lives of the activating enzymes in the bloodstream has limited its success. Demonstrated here is that a tyrosinase‐MOF nanoreactor activates the prodrug paracetamol in cancer cells in a long‐lasting manner. By generating reactive oxygen species (ROS) and depleting glutathione (GSH), the product of the enzymatic conversion of paracetamol is toxic to drug‐resistant cancer cells. Tyrosinase‐MOF nanoreactors cause significant cell death in the presence of paracetamol for up to three days after being internalized by cells, while free enzymes totally lose activity in a few hours. Thus, enzyme‐MOF nanocomposites are envisioned to be novel persistent platforms for various biomedical applications.     

Multifunctional Antioxidants: Regenerable Radical‐Trapping and Hydroperoxide‐Decomposing Ebselenols

Regenerable, multifunctional ebselenol antioxidants were prepared that could quench peroxyl radicals more efficiently than α‐tocopherol. These compounds act as better mimics of the glutathione peroxidase enzymes than ebselen. Production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in human mononuclear cells was considerably decreased upon exposure to the organoselenium compounds. At a concentration of 25 μm , the ebselenol derivatives showed minimal toxicity in pre‐osteoblast MC3T3 cells.     

The Copper(II)‐Catalyzed Oxidation of Glutathione

The kinetics and mechanisms of the copper(II)‐catalyzed GSH (glutathione) oxidation are examined in the light of its biological importance and in the use of blood and/or saliva samples for GSH monitoring. The rates of the free thiol consumption were measured spectrophotometrically by reaction with DTNB (5,5′‐dithiobis‐(2‐nitrobenzoic acid)), showing that GSH is not auto‐oxidized by oxygen in the absence of a catalyst. In the presence of Cu²⁺, reactions with two timescales were observed. The first step (short timescale) involves the fast formation of a copper–glutathione complex by the cysteine thiol. The second step (longer timescale) is the overall oxidation of GSH to GSSG (glutathione disulfide) catalyzed by copper(II). When the initial concentrations of GSH are at least threefold in excess of Cu²⁺, the rate law is deduced to be ?d[thiol]/dt=k[copper–glutathione complex][O₂]^0.5[H₂O₂]^?0.5. The 0.5^th reaction order with respect to O₂ reveals a pre‐equilibrium prior to the rate‐determining step of the GSSG formation. In contrast to [Cu²⁺] and [O₂], the rate of the reactions decreases with increasing concentrations of GSH. This inverse relationship is proposed to be a result of the competing formation of an inactive form of the copper–glutathione complex (binding to glutamic and/or glycine moieties).     

Click‐Assembled,Oxygen‐Sensing Nanoconjugates for Depth‐Resolved,Near‐Infrared Imaging in a 3 D Cancer Model

Hypoxia is an important contributing factor to the development of drug‐resistant cancer, yet few nonperturbative tools exist for studying oxygenation in tissues. While progress has been made in the development of chemical probes for optical oxygen mapping, penetration of such molecules into poorly perfused or avascular tumor regions remains problematic. A click‐assembled oxygen‐sensing (CAOS) nanoconjugate is reported and its properties demonstrated in an in vitro 3D spheroid cancer model. The synthesis relies on the sequential click‐based ligation of poly(amidoamine)‐like subunits for rapid assembly. Near‐infrared confocal phosphorescence microscopy was used to demonstrate the ability of the CAOS nanoconjugates to penetrate hundreds of micrometers into spheroids within hours and to show their sensitivity to oxygen changes throughout the nodule. This proof‐of‐concept study demonstrates a modular approach that is readily extensible to a wide variety of oxygen and cellular sensors for depth‐resolved imaging in tissue and tissue models.     

Construction of hole‐transported MoO3‐x coupled with CdS nanospheres for boosting photocatalytic performance via oxygen‐defects‐mediated Z‐scheme charge transfer

The establishment of Z‐scheme charge transfer between semiconductors is an effective method to improve the performance of hybridized semiconductor photocatalysts. Herein, the novel photocatalysts consisting of MoO_3‐x and varying amounts of cadmium sulfide (CdS) nanospheres were successfully prepared via the one‐pot hydrothermal method in the presence of polyvinylpyrrolidone (PVP). It is indicated that the PVP not only served as the reducing agent for the formation of oxygen defects in MoO_3‐x, but also the cross‐linking agent for the coupling between MoO_3‐x and CdS. The CdS/MoO_3‐x composite allowed for higher visible‐light photocatalytic performance for enhanced removal of methylene blue and tetracycline with an efficiency of 97.6% and 85.5%, respectively. The improved performance of the CdS/MoO_3‐x composite was found to be mainly attributable to the remarkable charge carrier separation and transfer between CdS and MoO_3‐x based on the favorable hole‐transporting nature and oxygen deficiencies of MoO_3‐x. In addition, the hole‐oxidized photocorrosion of CdS was efficiently suppressed due to the presence of hole‐attractive MoO_3‐x. At the solid interface, an oxygen‐defects‐mediated Z‐scheme charge carrier transfer pathway was proposed as the underlying mechanism for the superior photocatalytic reaction.     

Copper‐Modified Covalent Triazine Frameworks as Non‐Noble‐Metal Electrocatalysts for Oxygen Reduction

The electrochemical oxygen reduction reaction (ORR) is an important cathode reaction of various types of fuel cells. The development of electrocatalysts composed only of abundant elements is a key goal because currently only platinum is a suitable catalyst for ORR. Herein, we synthesized copper‐modified covalent triazine frameworks (CTF) hybridized with carbon nanoparticles (Cu‐CTF/CPs) as efficient electrocatalysts for the ORR in neutral solutions. The ORR onset potential of the synthesized Cu‐CTF/CP was 810 mV versus the reversible hydrogen electrode (RHE; pH 7), the highest reported value at neutral pH for synthetic Cu‐based electrocatalysts. Cu‐CTF/CP also displayed higher stability than a Cu‐based molecular complex at neutral pH during the ORR, a property that was likely as a result of the covalently cross‐linked structure of CTF. This work may provide a new platform for the synthesis of durable non‐noble‐metal electrocatalysts for various target reactions.     

Copper‐Mediated Selenazolidine Deprotection Enables One‐Pot Chemical Synthesis of Challenging Proteins

While chemical protein synthesis has granted access to challenging proteins, the synthesis of longer proteins is often limited by low abundance or non‐strategic placement of cysteine residues, which are essential for native chemical ligations, as well as multiple purification and isolation steps. We describe the one‐pot total synthesis of human thiosulfate:glutathione sulfurtransferase (TSTD1). WT‐TSTD1 was synthesized in a C‐to‐N synthetic approach involving multiple NCL reactions, Cu^II‐mediated deprotection of selenazolidine (Sez), and chemoselective deselenization. The seleno‐analog Se‐TSTD1, in which the active site Cys is replaced with selenocysteine, was also synthesized with a kinetically controlled ligation with an N‐to‐C synthetic approach. The catalytic activity of the two proteins indicated that Se‐TSTD1 possessed only four‐fold lower activity than WT‐TSTD1, thus suggesting that selenoproteins can have physiologically comparable sulfutransferase activity to their cysteine counterparts.     

Click‐Assembled,Oxygen‐Sensing Nanoconjugates for Depth‐Resolved,Near‐Infrared Imaging in a 3 D Cancer Model

Hypoxia is an important contributing factor to the development of drug‐resistant cancer, yet few nonperturbative tools exist for studying oxygenation in tissues. While progress has been made in the development of chemical probes for optical oxygen mapping, penetration of such molecules into poorly perfused or avascular tumor regions remains problematic. A click‐assembled oxygen‐sensing (CAOS) nanoconjugate is reported and its properties demonstrated in an in vitro 3D spheroid cancer model. The synthesis relies on the sequential click‐based ligation of poly(amidoamine)‐like subunits for rapid assembly. Near‐infrared confocal phosphorescence microscopy was used to demonstrate the ability of the CAOS nanoconjugates to penetrate hundreds of micrometers into spheroids within hours and to show their sensitivity to oxygen changes throughout the nodule. This proof‐of‐concept study demonstrates a modular approach that is readily extensible to a wide variety of oxygen and cellular sensors for depth‐resolved imaging in tissue and tissue models.     

Photo‐oxidation of poly(2,6‐dimethyl‐1,4‐phenylene oxide): A reinvestigation

Reinvestigation of poly(2,6‐dimethyl‐1,4‐phenylene oxide) photodegradation at wavelengths > 290 nm shows that both methyl groups and aromatic rings are sites of oxidation with their relative rates dependent on exposure conditions, based on infrared spectroscopy. The methyl group loss is linear with exposure and apparently proceeds by direct abstraction of a benzylic hydrogen by oxygen. The aromatic ring loss and carbonyl growth in the IR spectra appear to be auto‐accelerating and seem to proceed by electron transfer to oxygen, either sensitized or through a direct reaction with oxygen, and recombination of the polymer radical cation and superoxide to result in oxygen addition to the ring. Molecular weight loss in solution occurs to a significant degree only in the presence of oxygen, even in the presence of a hydrogen‐donating solvent, indicating that aryl ether photolysis is not a major pathway. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2318–2331     

Yoctoliter Thermometry for Single‐Molecule Investigations: A Generic Bead‐on‐a‐Tip Temperature‐Control Module

A new temperature‐jump (T‐jump) strategy avoids photo‐damage of individual molecules by focusing a low‐intensity laser on a black microparticle at the tip of a capillary. The black particle produces an efficient photothermal effect that enables a wide selection of lasers with powers in the milliwatt range to achieve a T‐jump of 65 °C within milliseconds. To measure the temperature in situ in single‐molecule experiments, the temperature‐dependent mechanical unfolding of a single DNA hairpin molecule was monitored by optical tweezers within a yoctoliter volume. Using this bead‐on‐a‐tip module and the robust single‐molecule thermometer, full thermodynamic landscapes for the unfolding of this DNA hairpin were retrieved. These approaches are likely to provide powerful tools for the microanalytical investigation of dynamic processes with a combination of T‐jump and single‐molecule techniques.     

Enzyme‐Triggered Fluorescence Turn‐on: A Probe for Specifically Imaging Ovarian‐Cancer‐Related γ‐Glutamyltranspeptidase

A fluorescent turn‐on probe for specifically targeting γ ‐glutamyltranspeptidase (GGT ) was designed and synthesized by integrating boron‐dipyrromethene (BODIPY ) as a chromophore and glutathione (GSH ) as the GGT substrate. GGT ‐catalyzed the cleavage of the γ ‐glutamyl bond and generated the aromatic hydrocarbon transfer between the sulfur and the nitrogen atom in BODIPY , leading to distinct optical changes. Such specific responsiveness provides an easily distinguishable fluorescence signal to visualize the GGT activity in living cells and differentiate GGT ‐positive cancer cells from GGT ‐negative cells.     

Room‐Temperature‐Phosphorescence‐Based Dissolved Oxygen Detection by Core‐Shell Polymer Nanoparticles Containing Metal‐Free Organic Phosphors

The highly sensitive optical detection of oxygen including dissolved oxygen (DO) is of great interest in various applications. We devised a novel room‐temperature‐phosphorescence (RTP)‐based oxygen detection platform by constructing core–shell nanoparticles with water‐soluble polymethyloxazoline shells and oxygen‐permeable polystyrene cores crosslinked with metal‐free purely organic phosphors. The resulting nanoparticles show a very high sensitivity for DO with a limit of detection (LOD) of 60 nm and can be readily used for oxygen quantification in aqueous environments as well as the gaseous phase.