Nanoscale Covalent Organic Frameworks with Donor-Acceptor Structures as Highly Efficient Light-Responsive Oxidase-like Mimics for Colorimetric Detection of Glutathione

Although organic artificial enzymes have been reported as biomimetic oxidation catalysts and are widely used for colorimetric biosensors, developing organic artificial enzymes with high enzymatic activity is still a challenge. Two-dimensional (2D) covalent organic frameworks (COFs) have shown superior potential in biocatalysts because of their periodic π-π arrays, tunable pore size and structure, large surface area, and thermal stability. The interconnection of electron acceptor and donor building blocks in the 2D conjugated COF skeleton can lead to narrower band gaps and efficient charge separation and transportation and thus is helpful to improve catalytic activity. Herein, a donor-acceptor 2D COF was synthesized using tetrakis(4-aminophenyl)pyrene (Py) as an electron donor and thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT) as an electron acceptor. Under visible light irradiation, the donor-acceptor 2D COF exhibited superior enzymatic catalytic activity, which could catalyze the oxidation of chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) by the formation of superoxide radicals and holes. Based on the above property, the photoactivated donor-acceptor 2D COF with enzyme-like catalytic properties was designed as a robust colorimetric probe for cheap, highly sensitive, and rapid colorimetric detection of glutathione (GSH); the corresponding linear range of GSH was 0.4-60 μM, and the limit of detection was 0.225 μM. This study not only presents the construction of COF-based light-activated nanozymes for environmentally friendly colorimetric detection of GSH but also provides a smart strategy for improving nanozyme activity.

All Visible Light Switch Based on the Dimethyldihydropyrene Photochromic Core

Two photoswitchable compounds that can operate under visible light irradiation are prepared and investigated using spectroscopic and computational studies. These all-visible systems are based on the dimethyldihydropyrene (DHP)/cyclophanediene (CPD) photochromic couple connected either to a bipyridine (bpy) unit or to a (tris(bpy)ruthenium(II)) complex through a pyridinium bridge. In these compounds, the DHP to CPD isomerization and the reverse CPD to DHP conversion can be triggered by illumination with red (>630 nm) and blue (460 nm) lights, respectively. The unambiguous and reversible response of these systems triggered by visible light make them potential candidates for biological purposes and electronic devices.

Mechanistic investigation into sunlight-facilitated photodegradation of pyrene in seawater with oil dispersants

This study investigated the effects of 3 model oil dispersants (Corexit EC9500A, Corexit EC9527A and SPC 1000) on photodegradation of pyrene under simulated sunlight. Both Corexit dispersants enhanced photodegradation of pyrene, while SPC1000 slightly inhibited the reaction. Span 80 and Tween 85 were the key ingredients causing the effects, though the underlying mechanisms differed. Span 80 enriches pyrene in the upper layer of water column, whereas Tween 85 induces a photosensitization process. Two reactive oxygen species, ¹O₂ and O₂^-, were found responsible for pyrene photodegradation, though the presence of EC9500A suppressed the ¹O₂ pathway. In terms of photodegradation products, EC9500A enhanced generation of polyaromatic intermediates, i.e., phenaleno[1,9-cd][1,2]dioxine, 1-hydroxypyrene, and 1,8-pyrenequinone, but did not alter the classical photodegradation pathway. The Corexit dispersants were more prone to photochemical decomposition, with multiple by-products detected. The information aids in our understanding of the effects of dispersants on photochemical weathering of oil compositions.

Effect of sunlight irradiation on photocatalytic pyrene degradation in contaminated soils by micro-nano size TiO2

The enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils by micro-nano size TiO(2) in the presence and absence of sunlight was investigated. The results showed that the synergistic effect of sunlight irradiation and TiO(2) was more efficient on pyrene degradation in quartz sand and red and alluvial soils than the corresponding reaction system without sunlight irradiation. In the presence of sunlight irradiation, the photooxidation (without TiO(2)) of pyrene was very pronounced in alluvial and red soils and especially in quartz sand. However, in the absence of sunlight irradiation, the catalytic pyrene degradation by TiO(2) and the photooxidation (without TiO(2)) of pyrene were almost nil. This implicates that ultra-violet (UV) wavelength range of sunlight plays an important role in TiO(2)-enhanced photocatalytic pyrene degradation and in photooxidation (without TiO(2)) of pyrene. The percentages of photocatalytic pyrene degradation by TiO(2) in quartz sand, alluvial and red soils under sunlight irradiation were 78.3, 23.4, and 31.8%, respectively, at 5h reaction period with a 5% (w/w) dose of the amended catalyst. The sequence of TiO(2)-enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils was quartz sand>red soil>alluvial soil, due to different texture and total organic carbon (TOC) contents of the quartz sand and other two soils. The differential Fourier transform infrared (FT-IR) spectra of degraded pyrene in alluvial soil corroborate that TiO(2)-enhanced photocatalytic degradation rate of degraded pyrene was much greater than photooxidation (without TiO(2)) rate of degraded pyrene. Based on the data obtained, the importance for the application of TiO(2)-enhanced photocatalytic pyrene degradation and associated organic contaminants in contaminated soils was elucidated.

Pyrene-assisted efficient photolysis of disulfide bonds in DNA-based molecular engineering

An efficient pyrene-assisted method has been developed for the photolysis of disulfide bonds, with 77% of disulfides cleaved after only 20 min of irradiation (0.3W) at 350 nm. By employing a DNA framework, it was possible to observe both a distance-dependent cleavage pathway and a radical-forming photoreaction mechanism. To demonstrate the biomedical applications of such pyrene disulfide molecular assemblies, a DNA micelle structure and DNAzyme analog were further studied. Rapid photodriven disassembly of DNA micelles was achieved, allowing the further design of controlled pharmaceutical release at the target region and at a specific time. The DNAzyme analog can carry out multiple turnover reactions that follow the Michaelis-Menten equation, with a kcat of 10.2 min(-1) and a KM of 46.3 μM (0.3W 350 nm light source), comparable to that of common DNAzymes, e.g., 8-17 DNAzyme.

Photodegradation of pyrene on soil surfaces under UV light irradiation

The rates of photodegradation of pyrene (Pyr) on soil surfaces under UV light have been studied. Different parameters such as temperature, soil particle sizes, soil depth, and humic acid (HA) concentration responsible for photodegradation have been monitored. The results obtained indicated that Pyr photodegradation follows pseudo-first-order kinetics. Pyr degradation was fastest at 30 degrees C, while the photodegradation rate was increased with the temperature from 20 to 30 degrees C. The degradation loss was about 35% at 30 degrees C, 30% at 25 degrees C and 25% at 20 degrees C, respectively. The rates of Pyr photodegradation at different soil particle sizes followed the order: less than 1mm>less than 0.45 mm>less than 0.25 mm. The results showed that the relationship of Pyr half-life with soil depth was linear (significant correlation, p<0.01). When the soil depth increased from 1 to 4mm, the half-life increased from 19.80 to 37.46 d. HA treatments significantly increased the photodegradation of Pyr on soil surfaces under UV light. However the concentration of HA increased from 5 to 40 mg kg(-1), the pseudo-first-order rates of Pyr decreased due to the shielding effect of HA.

Effects of UVA and visible light on the photogenotoxicity of benzo[a]pyrene and pyrene

This study investigated the role of UVA/visible light (U, 320-800 nm) and visible light (V, 400-800 nm) in the phototoxicity and photogenotoxicity of two ubiquitous polycyclic aromatic hydrocarbons (PAH): benzo[a]pyrene (BaP) and Pyrene (Pyr). These mechanisms were evaluated by the WST-1 test and the comet assay on normal human keratinocytes (NHK) and by the micronucleus test on CHO cells. The production of reactive oxygen species (ROS) was assessed through the induction of 8-oxodeoxyguanine (8-oxodG) lesions by immunofluorescence staining in NHK. Results of the WST-1 test revealed the phototoxic properties of BaP and Pyr after irradiation with U and V lights. BaP presented the highest phototoxic properties. Results of the comet assay showed that U- and V-irradiated BaP and Pyr induced increasing rates of DNA single-strand breaks in NHK, in a dose dependent manner. The tested PAH could also induce increased levels of micronuclei in CHO cells after U and V irradiations. Increasing 8-oxodG levels were detected after U and V irradiations in BaP- and Pyr-treated keratinocytes and confirmed the involvement of ROS in the photogenotoxicity of PAH. Overall, this study highlighted the existence of an alternative pathway of PAH genotoxicity that is induced by UVA and/or visible light. Visible light is suggested to photoactivate PAH by a mechanism which is mainly based on oxidative reactions.

DNA photocleavage and biological activity of a pyrene dihydrodioxin

A pyrene dihydrodioxin has been synthesized, shown to bind to duplex DNA by intercalation, and cleave the phiX 174 supercoiled plasmid upon irradiation with UV light. This compound also exhibits cytotoxic activity at the micromolar range in a number of human cancer cell lines.

Two-photon interactions at single fluorescent molecule level

Single-molecule spectroscopy and single-molecule detection are emerging areas that have many applications when combined with scanning, imaging, and spectroscopy techniques. We have combined a commercial confocal scanning head, to a Ti:sapphire laser and to an inverted microscope, for the detection of single molecule fluorescence of varies dyes by two-photon excitation. We collected spot images of fluorescent molecules that have been deposited on a substrate considering both blinking and photobleaching behavior of fluorescent spots. Here, we report data related to two-photon interactions that occur with the following fluorescent molecules: Indo-1, Rhodamine 6G, Fluorescein, and Pyrene. The choice of these specific dyes is based upon their wide use in biological and medical applications together with the varying complexity of their chemical structure that increases from Pyrene to Indo-1. Moreover, we report some data about single molecule studies related to denaturation of an enhanced green fluorescent protein, GFPmut2, under one photon excitation regime, that show a very similar trend to that observed for the already mentioned fluorescent molecules.

Selectivity and efficiency of pyrene attachment to alkanes induced by broadband X-rays

Bombardment of pyrene-doped n-heneicosane (C21H44) in its orthorhombic solid phase with <1.3> MeV broadband X-rays results in the formation of both mono- and di-heneicosylpyrenes, whereas the same dose in liquid cyclohexane yields only monosubstituted pyrene. In both cases, the reaction efficiency decreases as pyrene concentration is increased from 10-5 to 10-2 M. Qualitatively, the overall attachment efficiency is higher in orthorhombic n-heneicosane than in liquid cyclohexane, but the selectivity of attachment is greater in cyclohexane. Differences between these results and those from irradiations of the same samples with eV range photons are discussed.

Photocatalytic reactions of pyrene at TiO2/water interfaces

The photocatalytic oxidation of pyrene preadsorbed on TiO2 is examined in aqueous suspension under UV irradiation. Chemical oxygen demand measurements, UV-VIS spectrophotometer, infrared spectrometer and GC-MS analytical techniques were used to monitor the formed intermediates. During the oxidation processes, the ring-open reaction, hydroxylation and ketolysis occurred to produce some intermediate products (4-oxapyrene-5-one, 1,6- or 1,8-pyrenediones, 4,5-phenanthrenedialdehyde, cyclopenta[def]phenanthrene). Some factors affecting the photodegradation rate were also studied. The results were different from other studies: The pH of the dispersion, ratio of Py/TiO2:water had little effect on the photooxidation rate of pyrene catalyzed by TiO2, while the surface coverage, addition of Fe3+ affected it greatly.

UVA-Induced DNA single-strand cleavage by 1-hydroxypyrene and formation of covalent adducts between DNA and 1-hydroxypyrene

1-Hydroxypyrene (HOP), a metabolite found in the urine of humans and laboratory animals exposed to polycyclic aromatic hydrocarbons (PAHs), is known to be both acutely toxic and genotoxic. It has been widely used as a biomarker for studying PAH exposure. In this research, we have found that, upon UVA irradiation, HOP causes DNA single-strand cleavages and forms HOP-DNA covalent adducts. The UVA-induced cleavage of supercoiled plasmid PhiX174 DNA is dependent upon both HOP concentration and UVA dosage. A longer irradiation time or higher HOP concentration induces more DNA cleavage. Results of the photocleavage experiments carried out in the presence of reactive oxygen species scavengers, histidine, sodium azide, mannitol, SOD, and desferal indicate that both the superoxide free radical and singlet oxygen are likely involved in causing DNA single-strand cleavage. The photocleavage is inhibited by the presence of an excited singlet-state quencher, KI, indicating that it is an excited-state reaction. Along with light-induced DNA cleavage, HOP also forms DNA covalent adducts while being degraded upon light irradiation. Light-induced degradation of 20 microM HOP follows first-order reaction kinetics in a 10% methanolic buffer (10 mM phosphate) solution in the absence or presence of 40 microM calf thymus DNA, with degradation half-lives of 20 or 15 min, respectively. The shorter degradation half-life in the presence of DNA is due to the formation of the HOP-DNA covalent adduct. The formation of the HOP-DNA covalent adduct is evidenced by comparing the UV-vis absorption and fluorescence emission spectra of the pure HOP with those of the HOP-DNA adduct. The covalent HOP-DNA adduct produced due to irradiation was purified by either extensive dialysis (3 x 500 mL buffer solutions), phenol and chloroform extraction followed by ethanol precipitation, or chloroform extraction alone. The isolated HOP-DNA adduct has an absorption peak at 353 nm, which is 8 nm red-shifted compared to that of free HOP. The fluorescence emission for HOP-DNA is at least 70 times weaker than that for free HOP in solution. In summary, the findings with HOP reveal that, in addition to metabolic activation that eventually leads to the formation of alkylated DNA adducts or other forms of DNA damage, HOP may be activated by light to produce DNA single-strand cleavage and covalent DNA adducts. These DNA lesions can be sources of toxicity.

ESR and UV-Vis studies of semiquinone radical anion and hydroquinone generated by irradiation of 15-deacetyl-13-glycine substituted hypocrellin B

15-Deacetyl-13-glycine substituted hypocrellin B (GDHB) is a new type of hypocrellin derivative with enhanced red absorption longer than 600 nm and water solubility. When an anaerobic DMSO or DMSO-buffer (pH 7.4) solution of GDHB was illuminated with >470 nm light, a strong electron spin resonance (ESR) signal was formed. The ESR signal was assigned to the semiquinone anion radical of GDHB (GDHB*-) based on a series of experiments. GDHB*- was predominantly photoproducted via the self-electron transfer between the excited- and ground-state species. Decay of this species, both in the presence and absence of electron donor, was consistent with second-order kinetics. In aqueous solution, the TEMPO counter-spin experiment indicated the formation of GDHB*- that could not be detected by ESR method directly. The formation of GDHB*- and hydroquinone of GDHB (GDHBH*-) was also confirmed by spectrometric method. These findings suggested that GDHB was at least a favorable type I phototherapeutic agent.

[Sensitized photomodification of DNA with binary systems of oligonucleotide conjugates. III. Double-quantum sensitization]

Site-specific modification of single-stranded DNA by oligonucleotide derivatives of p-azido-O-(4-aminobutyl)tetrafluorobenzaldoxime sensitized by an oligonucleotide derivative of pyrenylethylamine was studied. Upon irradiation with the long-wave UV light (365-390 nm) of a DNA target-oligonucleotide reagent complementary complex, a considerable increase in the rate of sensitized photomodification at the G11 residue of the target relative to the direct photomodification was observed owing to the singlet-single energy transfer from the sensitizer onto the photoreagent. Upon simultaneous irradiation of the complex with UV and visible light in the region of the triplet-triplet absorption of pyrene (360-580 nm), an additional increase in the modification rate and a change in its site-direction (from the G11 to T13 residue) occurred through the two-photon triplet-triplet sensitization. The total extent of the structure photomodification amounted to 80%.

Increased polycyclic aromatic hydrocarbon toxicity following their photomodification in natural sunlight: impacts on the duckweed Lemna gibba L. G-3

The authors previously demonstrated that simulated solar radiation (SSR), with a fluence rate of only 40 mumol m-2 sec-1, increased polycyclic aromatic hydrocarbon (PAH) toxicity to the duckweed Lemna gibba and that PAHs photomodified in SSR (generally oxygenation of the ring system) are more toxic than the parent compounds (Huang et al., Environ. Toxicol. Chem., 1993, 12, 1067-1077). It is not known, however, to what extent toxicity of PAHs can increase due to photomodification. Thus, natural sunlight, which has a high fluence rate (approximately 2000 mumol m-2 sec-1), was used to photomodify anthracene, benzo[a]pyrene, fluoranthene, phenanthrene, and pyrene. Toxicity was based on growth inhibition of L. gibba, measured as the rate of production of new leaves over an 8-day period. Initially, the toxicity of the PAHs applied in intact form was probed, with the compounds demonstrating greater toxicity in sunlight than in SSR. Next the PAHs were photomodified in sunlight prior to incubation with the plants. The half-lives of the PAHs in sunlight ranged from 12 min to 30 hr. Although most of the products of PAH photomodification are not yet identified, the degree that PAH toxicity increased following photomodification in sunlight could still be probed. The mixtures of photomodified chemicals that were derived from each PAH in sunlight were applied of L. gibba and growth inhibition under 100 mumol m-2 sec-1 of SSR was determined. The LC50s for the PAH photoproducts generated in sunlight were an order of magnitude lower than the LC50s for the PAHs applied in intact form.

Isothermal annealing kinetics of X-irradiated pyrene by electron paramagnetic resonance

The annealing behavior of X-irradiated stable free radicals found in pyrene (C16H10) single crystals was studied by electron paramagnetic resonance. Two processes of thermal decay kinetics were found, both with the same activation energy: 1.9 +/- 0.1 eV.

Photochemical instability of 1-nitropyrene, 3-nitrofluoranthene, 1,8-dinitropyrene and their parent polycyclic aromatic hydrocarbons

The environmental contaminants pyrene, 1-nitropyrene, 1,8-dinitropyrene, fluoranthene, and 3-nitrofluoranthene were exposed to light (greater than or equal to 310 nm) either in DMSO, or following coating onto silica. Under all conditions tested the pyrenyl were less stable than the fluoranthenyl compounds. During irradiation in DMSO or on silica, 1-nitropyrene had half-lives of 1.2 and 6 days, while those of 3-nitrofluoranthene were 12.5 and greater than 20 days, respectively. The photodecomposition of 1,8-dinitropyrene resembled that of 1-nitropyrene with half-lives of 0.7 and 5.7 days. A principle photodecomposition product of 1,8-dinitropyrene was identified as 1-nitropyren-8-ol. It was also found that when the nitroarenes were exposed to light, the loss of compound was associated with a concomitant loss of mutagenicity in Salmonella typhimurium strain TA98. The mechanism of nitrated polycyclic aromatic hydrocarbon decomposition and 1-nitropyren-8-ol formation, and the relevance to the atmospheric disposition of these compounds are discussed.

1-Nitropyrene: a mutagenic product induced by the action of near ultraviolet light on 1-aminopyrene

A solution of 1-aminopyrene in dimethyl sulfoxide exposed to an artificial source of near ultraviolet light (600 kJ/m2) induced significant direct-acting mutagenicity in the Ames/Salmonella plating assay utilizing strain TA98. High-performance liquid chromatography of this solution resulted in a fraction that was mutagenic on TA98 but inactive on a nitroreductase-deficient strain of Salmonella (TA98NR). This observation suggested the presence of a nitro-containing compound. Mass spectral analysis confirmed that 1-nitropyrene was the active photoproduct in this fraction. These data implicate photochemical transformation of primary aromatic amines as an alternative mechanism by which nitroaromatic compounds can be formed in the environment.

[Inductive-resonance energy transfer between chromophores localized in different parts of irradiated and nonirradiated erythrocyte ghosts]

A study was made of the inductive-resonance energy transfer between chromophore pairs, tryptophan--pyren, tryptophan--1.8-anilinonaphthalene sulfonate (ANS), puren--1.8-ANS, diphenylhexatrien--ethidium, and 1,8-ANS--ethidium, in irradiated (250 Gy) and nonirradiated preparations of erythrocytic membranes. The radiation--induced decrease in the energy transfer was noted in the pairs in which one of the chromophores was localized in a lipid phase. On the basis of the data obtained it is suggested that irradiation of membranes causes the lesions in them which lead to a reduction of the effective thickness of a hydrophobic part of the lipid bilayer.

Photodecomposition of 1-nitropyrene and other direct-acting mutagens extracted from diesel-exhaust particulates

The effect of irradiation with wavelengths of 320-418 nm on direct-acting mutagenicity of 1-nitropyrene (1-NP) and particulate-matter extracts of a direct-injecting diesel engine was examined. The activity of samples in the Ames test with and without addition of S9 mix in Salmonella typhimurium strain TA98, TA100 and TA1538 decreased with increasing irradiation energy. Visible light was sufficient to destroy the mutagenicity of a 0.1-mM 1-NP solution. The same was true for particulate matter crude extracts as well as the transitional and oxygenate subfractions isolated by column chromatography. UV spectroscopy, thin-layer chromatography and GC-MS analysis were performed to characterize the irradiation products of 1-NP. The mechanism of photodecomposition of 1-NP at different wavelengths and the significance of this finding for the evaluation of health risks from diesel vehicles are discussed.

Mutagenicity of photochemical reaction products of polycyclic aromatic hydrocarbons with nitrite

Six kinds of polycyclic aromatic hydrocarbons (PAHs) were subjected to ultraviolet light irradiation with nitrite for 1, 4, 8 and 24 h, and the irradiated samples were tested for mutagenicity towards Salmonella typhimurium TA 98, TA 100 and TA 1538. Irradiated samples of pyrene, fluoranthene and benzo[a]pyrene showed marked mutagen responses towards TA 98 and TA 1538, especially in the absence of S9 mix. The direct-acting mutagenic activity of these samples, showing high activities at 1-8 h, decreased greatly with the development of irradiation. Further, these direct-acting mutagens were mostly present in the neutral fraction. On the other hand, the mutagenicity of the irradiated sample of 5,6-benzoquinoline was high both with and without S9 mix, and was mostly present in the basic fraction because of its authentic characteristic. There was no correlation between the yield of 1-nitropyrene and the mutagenic activity of the photochemical reaction product of pyrene with nitrite. Further studies by TLC separation suggested that a considerable number of direct-acting mutagens formed in this experiment were more polar than nitrated PAH such as 1-nitropyrene.