Photoinduced Oxidation Research Articles

Towards Copper(I) Clusters for Photo-Induced Oxidation of Biological Thiols in Living Cells.

The cell redox balance can be disrupted by the oxidation of biological peptides, eventually leading to cell death, which provides opportunities to develop cytotoxic drugs. With the aim of developing compounds capable of specifically inducing fatal redox reactions upon light irradiation, we have developed a library of copper compounds. This metal is abundant and considered essential for human health, making it particularly attractive for the development of new anticancer drugs. Copper(I) clusters with thiol ligands (including 5 novel ones) have been synthesized and characterized. Structures were elucidated by X-ray diffraction and showed that the compounds are oligomeric clusters. The clusters display high photooxidation capacity towards cysteine - an essential amino acid - upon light irradiation in the visible range (450 nm), while remaining completely inactive in the dark. This photoredox activity against a biological thiol is very encouraging for the development of anticancer photoredox drugs.The in vitro assay on murine colorectal cancer cells (CT26) did not show any toxicity - whether in the dark or when exposed to 450 nm light, likely because of the poor solubility of the complexes in biological medium.

Oxidation Chemistry of Bicarbonate and Peroxybicarbonate: Implications for Carbonate Management in Energy Storage.

Carbonate formation presents a major challenge to energy storage applications based on low-temperature CO2 electrolysis and recyclable metal-air batteries. While direct electrochemical oxidation of (bi)carbonate represents a straightforward route for carbonate management, knowledge of the feasibility and mechanisms of direct oxidation is presently lacking. Herein, we report the isolation and characterization of the bis(triphenylphosphine)iminium salts of bicarbonate and peroxybicarbonate, thus enabling the examination of their oxidation chemistry. Infrared spectroelectrochemistry combined with time-resolved infrared spectroscopy reveals that the photoinduced oxidation of HCO3- by an Ir(III) photoreagent results in the generation of the short-lived bicarbonate radical in less than 50 ns. The highly acidic bicarbonate radical undergoes proton transfer with HCO3- to furnish the carbonate radical anion and H2CO3, leading to the eventual release of CO2 and H2O, thus accounting for the appearance of H2O and CO2 in both electrochemical and photochemical oxidation experiments. The back reaction of the carbonate radical subsequently oxidizes the Ir(II) photoreagent, leading to carbonate. In the absence of this back reaction, dimerization of the carbonate radical provides entry into peroxybicarbonate, which we show undergoes facile oxidation to O2 and CO2. Together, the results reported identify tangible pathways for the design of catalysts for the management of carbonate in energy storage applications.

Modification of the electronic structure of g-C3N4 using urea to enhance the visible light-assisted degradation of organic pollutants.

Graphitic carbon nitride has been proven to be a good candidate for using solar energy for photo-induced pollutant degradation. However, the high photo-induced holes-electron recombination rate, unfavorable morphology, and textural properties limited their application. In this study, we present a novel g-C3N4 with a novel electronic structure and physiochemical properties by introducing a single nitrogen in the graphitic network of the g-C3N4 through a novel method involving step-by-step co-polycondensation of melamine and urea. Through extensive characterization using techniques such as XPS, UPS-XPS, Raman, XRD, FE-SEM, TEM, and N2 adsorption-desorption, we analyze the electronic and crystallographic properties, as well as the morphology and textural features of the newly prepared g-C3N4 (N-g-C3N4). This material exhibits a lower C/N ratio of 0.62 compared to conventional g-C3N4 and a reduced band gap of 2.63 eV. The newly prepared g-C3N4 demonstrates a distinct valance band maxima that enhances its photo-induced oxidation potential, improving photocatalytic activity in degrading various organic pollutants. We thoroughly investigate the photocatalytic degradation performance of N-g-C3N4 for Congo red (CR) and sulfamethoxazole (SMX), and removal of up to 90 and 86% was attained after 2 h at solution pH of 5.5 for CR and SMX. The influence of different parameters was examined to understand the degradation mechanism and the influence of reactive oxygenated species. The catalytic performance is also evaluated in the degradation of various organic pollutants, and it showed a good performance.

Photoinduced One‐Electron Oxidation of Estrone Derivatives: A Combined Steady‐State and Time‐Resolved Spectroscopy Investigation

AbstractA detailed investigation of the photophysics and of the redox properties of a set of selected estrone carboxylate and sulfonate esters was carried out by means of steady‐state and time‐resolved spectroscopies. The observed dual fluorescence was assigned to an efficient intramolecular energy transfer from the aromatic moiety to the carbonyl group. On the other hand, the photoinduced monoelectronic oxidation of R−OX in the presence of persulphate anion is followed by mesolytic fragmentation of the so generated radical cation into the corresponding phenoxyl radical with rate constant values (kfrag) of 104–105 s−1, that depend on the X−O bond dissociation energy values.

Plant Photocatalysts: Photoinduced Oxidation and Reduction Abilities of Plant Leaf Ashes under Solar Light.

Plant leaf ashes were obtained via the high temperature calcination of the leaves of various plants, such as sugarcane, couchgrass, bracteata, garlic sprout, and the yellowish leek. Although the photosynthesis systems in plant leaves cannot exist after calcination, minerals in these ashes were found to exhibit photochemical activities. The samples showed solar light photocatalytic oxidation activities sufficient to degrade methylene blue dye. They were also shown to possess intrinsic dehydrogenase-like activities in reducing the colorless electron acceptor 2,3,5-triphenyltetrazolium chloride to a red formazan precipitate under solar light irradiation. The possible reasons behind these two unreported phenomena were also investigated. These ashes were characterized using a combination of physicochemical techniques. Moreover, our findings exemplify how the soluble and insoluble minerals in plant leaf ashes can be synergistically designed to yield next-generation photocatalysts. It may also lead to advances in artificial photosynthesis and photocatalytic dehydrogenase.

Surface electronic state modulation promotes photoinduced aggregation and oxidation of trace CO for lossless purification of H2 stream

Although photogenerated hydroxyl radicals can oxidize CO without H2 consumption, the nonselective collision severely lowers photocatalytic photon utilization. We here demonstrate that electronic state modification of TiO2 resulted from magnesium doping can promote hydroxyl radical generation by weakening the adsorption of oxygen species and facilitating semiconductor-cocatalyst interfacial electron transfer. Importantly, the partial deprivation of electronic cloud from cationic sites can strengthen σ-donation and π-backdonation that synergistically promote the electrostatic interaction for aggregating CO in the vicinity of semiconductor. The resulted photocatalyst thus exhibits growing superiority over common counterpart in target reaction as CO concentration lowers. By these merits, CO in H2 stream can be reduced to < 1 × 10−6 with efficient photon utilization.

Disproportionation and dimerisation of kynurenic acid under UV light

In this work, we report on the photo-induced oxidation of kynurenic acid (KNA) by the triplet-excited KNA in a neutral aqueous solution. This reaction is confirmed by two different time-resolved methods: optical spectroscopy and chemically induced dynamic nuclear polarization (CIDNP). The disproportionation reaction proceeds with the rate constant of (6.0 ± 1.2) × 107 M−1s−1 via the mechanism of H-atom transfer to the photoexcited KNA in the triplet state, yielding the reduced and oxidized forms of KNA, KNAH2− and KNA(-H)−, respectively. The formation of these radicals is confirmed by a good proportionality relationship between the calculated proton hyperfine coupling constants of both radicals and the signal intensities in 1H CIDNP spectra detected after the recombination of the geminate radical pairs formed immediately after the laser pulse. The oxidized forms of KNA recombine yielding dimeric KNA-KNA products crosslinked via different positions within aromatic systems. The oxidized form of KNA, KNA(-H)−, could be of high biological interest due to its ability to recombine with other electron-deficient radicals, including tryptophan and tyrosine radicals, unravelling a radical pathway for the covalent attachment of KNA to proteins in living tissues.

Disentangling the role of electrons and phonons in the photoinduced CO desorption and CO oxidation on (O,CO)-Ru(0001).

The role played by electronic and phononic excitations in the femtosecond laser induced desorption and oxidation of CO coadsorbed with O on Ru(0001) is investigated using ab initio molecular dynamics with electronic friction. To this aim, simulations that account for both kind of excitations and that only consider electronic excitations are performed. Results for three different surface coverages are obtained. We unequivocally demonstrate that CO desorption is governed by phononic excitations. In the case of oxidation the low statistics does not allow to give a categorical answer. However, the analysis of the adsorbates kinetic energy gain and displacements strongly suggest that phononic excitations and surface distortion also play an important role in the oxidation process.

フロキサン環への置換基導入反応の開発と光に応答して一酸化窒素を放出するフロキサン分子の創製

Furoxan (1,2,5-oxadiazole-2-oxide), categorized into a heteroaromatic compound, is a potentially useful drug-like molecule. However, due to the vulnerability of furoxan rings to ring-opening under various reaction conditions, there have been sporadic reports on its efficient synthesis; therefore, applied research on furoxan is relatively unexplored. We report herein our recent contribution to this research area. The unique photo-induced nitric oxide donors based on furoxan architecture are also represented.

Modeling the Enzyme Specificity by Molecular Cages through Regulating Reactive Oxygen Species Evolution.

Mimicking the active site and the substrate binding cavity of the enzyme to achieve specificity in catalytic reactions is an essential challenge. Herein, porous coordination cages (PCCs) with intrinsic cavities and tunable metal centers have proved the regulation of reactive oxygen species (ROS) generating pathways as evidenced by multiple photo-induced oxidations. Remarkably, in the presence of the Zn4 -μ4 -O center, PCC converted dioxygen molecules from triplet to singlet excitons, whereas the Ni4 -μ4 -O center promoted the efficient dissociation of electrons and holes to conduct electron transfer towards substrates. Accordingly, the distinct ROS generation behavior of PCC-6-Zn and PCC-6-Ni enables the conversion of O2 to 1 O2 and O2 ⋅- , respectively. In contrast, the Co4 -μ4 -O center combined the 1 O2 and O2 ⋅- together to generate carbonyl radicals, which in turn reacted with the oxygen molecules. Harnessing the three oxygen activation pathways, PCC-6-M (M=Zn/Ni/Co) display specific catalytic activities in thioanisole oxidation (PCC-6-Zn), benzylamine coupling (PCC-6-Ni), and aldehyde autoxidation (PCC-6-Co). This work not only provides fundamental insights into the regulation of ROS generation by a supramolecular catalyst but also demonstrates a rare example of achieving reaction specificity through mimicking natural enzymes by PCCs.

A highly efficient hematite photoelectrochemical fuel cell for solar-driven hydrogen production

Hematite has demonstrated to be a promising photoanode for photoelectrochemical (PEC) hydrogen production because of its narrow band gap and outstanding stability. However, the sluggish water oxidation kinetics on hematite photoanode severely hinder the PEC hydrogen production performance. Herein, we report the construction of a Ti-doped porous hematite-based PEC fuel cell utilizing l-cysteine (L-Cys) oxidation to replace difficult water oxidation for efficient H2 production. The strong complexation interaction between hematite and L-Cys confers the direct photooxidation of L-Cys, producing additional electrons to participate in hydrogen production. As a result, the present Ti-doped porous hematite (Ti-PH) photoanode exhibits a current density of up to 4.45 mA cm−2 at 1.23 V vs. RHE under AM 1.5G illumination. This work provides a new strategy to utilize the additional electron contribution from photoinduced oxidation of organic chemicals for high-efficiency PEC fuel cell and solar fuel production.

Oxidative Probing of the G4 DNA Structure by ZnP1 Porphyrin within Sequences of &lt;i&gt;MYC&lt;/i&gt; and &lt;i&gt;TERT&lt;/i&gt; Promotors

The formation of G4 structures in a DNA double helix competes with the complementary strand, which can change the equilibrium G4 structures studied on single-strand models by classical structural methods. A relevant task is to develop methods for detecting and localizing G4 in extended double-stranded (ds) DNA in the promoter regions of the genome. The porphyrin derivative ZnP1 selectively binds and leads to photo-induced oxidation of guanine in G4 structures on single-stranded (ss) and dsDNA model systems. In this research, we show the oxidative effect of ZnP1 on native sequences of MYC and TERT oncogene promoters that potentially capable to form G4 structures. Single strand breaks in the guanine rich sequence caused by ZnP1 oxidation and subsequent cleavage of the DNA strand by Fpg glycosylase were identified and assigned to the nucleotide sequence. The detected break sites corresponded to sequences potentially capable of forming G4 structures. New data were obtained on the possibility of folding G4 structures in the presence of a complementary strand in the context of the DNA double helix of the natural sequence.

Martin Silicates as Versatile Radical Precursors in Photoredox/ Nickel Dual Catalysis

AbstractA cross-coupling methodology is described based on the nickel-catalyzed connection of an aryl moiety to an alkyl radical generated by photoinduced single-electron oxidation of a silicate formed from a Martin spirosilane. Complementary to the other anionic radical precursors in photoredox catalysis, Martin silicates permit access to highly reactive alkyl radicals directly engageable in smooth C(sp2)–C(sp3) bond-formation reactions.

Visible-light-induced strong oxidation capacity of metal-free carbon nanodots through photo-induced surface reduction for photocatalytic antibacterial and tumor therapy

Biocompatible metal-free carbon dots (CDs) with good photo-induced strong oxidation capacity in aqueous solutions are scarce for high-performance photocatalytic antibacterial and tumor therapy. In this work, we achieved effective visible light-induced cell death and antibacterial performance based on biocompatible metal-free CDs. The visible-light-induced reducing ability of the surface electron-withdrawing structure of the CDs allowed for the remaining photo-induced holes with high oxidation capacity to oxidize water molecules and generate hydroxyl radicals. Antibiotic-resistant bacteria were effectively inhibited by the CDs under xenon lamp irradiation with 450 nm long pass filter. Moreover, CD-based tumor photocatalytic therapy in mice was achieved using a xenon lamp with 450 nm long pass filter (0.3 W cm−2).

Iodine-mediated photoinduced autoinductive tandem chromogenic system for visual colorimetric detection of triacetone triperoxide explosive.

A long-standing challenge in colorimetric detection of triacetone triperoxide (TATP) explosive is low sensitivity. We herein developed an iodine-mediated photoinduced auto-inductive tandem chromogenic system to achieve exponential signal amplification. The strategy employs the KI-TATP reaction and photo-induced autocatalytical oxidation of o-phenylenediamine (OPD) that work in tandem. The resulting I3- from the KI-TATP reaction oxidizes OPD to yellow 2,3-diaminophenazine (DAP) that is further excited by blue light illumination to produce reactive oxygen species (ROS). The obtained ROS, in turn, promotes the oxidation of OPD to gain more DAP, causing the auto-inductive chromogenic reaction processes. This tandem chromogenic system is applied for visual colorimetric detection of TATP, allowing the selective and sensitive detection of TATP down to 42.8μM. Moreover, analyses of TATP in real samples are performed, and the satisfactory recovery results are achieved. Furthermore, a field detection kit is also developed.

4,4′-Difluoro-[3,3′-bi(1,2,5-oxadiazole)] 2,2′-Dioxide

1,2,5-Oxadiazole oxides (furoxans) are well known nitric oxide donors; among them, 4-fluorofuroxans have recently been found to be important photoinduced nitric oxide donors. In this research, it was shown that the reaction of 4,4′-dinitro-[3,3′-bi(1,2,5-oxadiazole)] 2,2′-dioxide with fluoro-containing reagents (tetrabutylammonium fluoride or cesium fluoride) selectively gave the bis-substitution product 4,4′-difluoro-[3,3′-bi(1,2,5-oxadiazole)] 2,2′-dioxide. The structure of the synthesized compound was established by elemental analysis, 13C, 19F-NMR and IR spectroscopy, and mass-spectrometry.

Oxidative Probing of the G4 DNA Structure by Znp1 Porphyrin within Sequences of MYC and TERT Promotors

The formation of G4 structures in a DNA double helix competes with the complementary strand interaction. The local environment in DNA can change equilibrium of G4 structures, which are studied on single-stranded (ss) models by classical structural methods. A relevant task is to develop methods for detecting and localizing G4 structures in extended native double-stranded (ds) DNA in the promoter regions of the genome. The ZnP1 porphyrin derivative selectively binds to G4 structures and leads to photo-induced oxidation of guanine in ssDNA and dsDNA model systems. We have shown the oxidative effect of ZnP1 on native sequences of MYC and TERT oncogene promoters, which can form G4 structures. Single-strand breaks in the guanine-rich sequence because of ZnP1 oxidation and subsequent cleavage of the DNA strand with Fpg glycosylase have been identified and assigned to the nucleotide sequence. The detected break sites have been shown to correspond to sequences capable of forming G4 structures. Thus, we have demonstrated the possibility of using porphyrin ZnP1 for the identification and localization of G4 quadruplexes in extended regions of the genome. Here we have shown the novel data on a possibility of folding G4 structures in the presence of complementary strand in native DNA double helix.

The role of the direct and indirect mechanism in the advanced oxidation process induced degradation of ciprofloxacin

The fluoroquinolone ciprofloxacin occurs worldwide in the aquatic environment and has therefore been listed on the 3rd European union watchlist for monitoring. To eliminate sewage and wastewater treatment plants as entry pathways, advanced oxidation processes have been intensely researched. Hence, photolysis at different pH ranges was studied for its capacity to eradicate ciprofloxacin. High-performance liquid chromatography coupled to high-resolution mass spectrometry was used to identify the degradation products and to monitor all compounds. Ecotoxicity was assessed using quantitative structure-activity relationship analysis comprising the Ecological Structure Activity Relationships tool. Two degradation mechanisms were found active: the direct mechanism, i.e. degradation through ultraviolet absorption by the substance, and the indirect mechanism caused by hydroxyl radicals from water photolysis. The radical scavenger tert-butanol and pH variations revealed that the indirect mechanism predominated in general. The direct photo-induced degradation proceeded about 10 times slower. Products could be attributed to the mechanisms. Based on their chemical structures, all identified products were predicted less toxic by quantitative structure-activity relationship than ciprofloxacin. Mechanistic insight suggested that photo-induced advanced oxidation processes proved efficient for ciprofloxacin elimination when generating hydroxyl radicals. Compounds and pH range hampering their occurrence diminish the efficacy of elimination.

A covalent crosslinking strategy to construct a robust peptide-based artificial esterase.

Peptide-based artificial enzymes derived from the supramolecular assembly of short peptides have attracted growing attention in recent years. However, the stability of these artificial enzymes is still a problem since their noncovalent supramolecular structure is quite sensitive and frail under environmental conditions. In this study, we reported a covalent crosslinking strategy for the fabrication of a robust peptide-based artificial esterase. Inspired by the di-tyrosine bonds in many natural structural proteins, multi-tyrosines were designed into a peptide sequence with histidine as the catalytic residue for the ester hydrolysis reaction. Upon the photo-induced oxidation reaction, the short peptide YYHYY rapidly transferred into nanoparticle-shaped aggregates (CL-YYHYY) and displayed improved esterase-like catalytic activity than some previously reported noncovalent-based artificial esterases. Impressively, CL-YYHYY showed outstanding reusability and superior stability under high temperature, strong acid and alkaline and organic solvent conditions. This study provides a promising approach to improving the catalytic activity and stability of peptide-based artificial enzymes.

From Blue to White: Sustainable Luminescent Metal Organic Framework for Hybrid Light‐Emitting Diodes

AbstractHybrid light‐emitting diodes based on photon down‐converting filters with metal organic frameworks (MOFs) are mainly restricted to cross‐breed materials (i.e., nonemissive MOFs host and guest emitters) due to the lack of highly photostable and luminescent MOFs (LMOFs). This work reports a sustainable and cost‐effective blue‐emitting Zn‐based MOF with the ligand 1,1,2,2‐tetrakis(4‐(pyridin‐4‐yl)phenyl)ethene (Zn‐2‐LMOF) and their host:guest hybrids with Rhodamine B emitter RhB@LMOF toward blue‐ and white‐emitting hybrid light‐emitting diodes (HLEDs). Zn‐2‐LMOF features blue emission (λem = 480 nm) with impressive photoluminescence quantum yield (ϕ) values of 50% (powder) and 70% (polystyrene coatings). Likewise, hybrid RhB@LMOF features a white emission with ϕ of 30–40% in polystyrene coatings. They lead to blue (Zn‐2‐LMOF; x/y CIE color coordinates of 0.28/0.47) and white (RhB@LMOF; x/y CIE color coordinates of 0.31/0.32) HLEDs with stabilities of 20 and 45 h at 50 mA on‐chip under ambient operation, respectively. Though this device performance is average in HLEDs, the device degradation is mainly attributed to the photoinduced oxidation of the ligand in the MOF structure that further leads to the RhB degradation; a key information for future developments in luminescent MOFs.