Study on the preparation of the hierarchical porous CX-TiO2 composites and their selective degradation of PHE solubilized in soil washing eluent.

A series of CX-TiO2(Carbon Xerogel- TiO2) composites with a hierarchical porous structure were obtained through the sol-gel method followed by drying and carbonization, and have been applied to treating solubilizing wastewater containing a high concentration of phenanthrene (PHE). The characterizations demonstrated that the CX-TiO2 exhibits a hierarchical porous structure, with particles of carbon and P25 being uniformly in the matrix. Removal efficiency of CX-TiO2 on PHE in soil washing eluent (SWE) were evaluated under ultraviolet (UV) irradiation or dark condition, and P25 was employed as the reference. The results revealed that CX-TiO2(0.2) had the best removal effect on PHE, with the efficiency as high as 97.8% under UV illumination within 15 h. It demonstrated that in the process of PHE removal by CX-TiO2 whether it was under UV illumination or not, the adsorption plays a dominant role in the early stage. The kinetic behavior of PHE adsorption was fitted using the pseudo-first-order and pseudo-second-order, and Langmuir model and Freundlich models were applied to describe the PHE adsorption isotherms. The results indicating that it was a chemical adsorption process, which was influenced by the interaction between PHE and CX-TiO2, and PHE is adsorbed on the interface of CX-TiO2(0.2) in a single layer form, instead of agglomerating in the admicelle. A possible mechanism of removal of solubilized PHE in SWE was speculated, in which both hierarchical porous structure and appropriate micropores size of CX-TiO2 were indispensable to the selective adsorption and degradation of PHE. Recycling performance certificated that the selective removal efficiency of PHE could still reach 82.09% after five recycles. Thus the excellent performance testified that the CX-TiO2 have great potential in treating SWE containing solubilized PAHs.

Ru(TAP)32+ uses multivalent binding to accelerate and constrain photo-adduct formation on DNA.

Ru(ii)-complexes with polyazaaromatic ligands can undergo direct electron transfer with guanine nucleobases on blue light excitation that results in DNA lesions with phototherapeutic potential. Here we use single molecule approaches to demonstrate DNA binding mode heterogeneity and evaluate how multivalent binding governs the photochemistry of [Ru(TAP)3]2+ (TAP = 1,4,5,8-tetraazaphenanthrene).

Photodegradation of phenanthrene catalyzed by rGO sheets and disk like structures synthesized using sugar cane juice as a reducing agent.

In the present report, rGO sheets (rG1) and disk (rG2) like structures of reduced graphene oxide (rGO) were synthesized using sugar cane juice as green reducing agent. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis.) spectroscopy and photoluminescence (PL) spectroscopy techniques. The transition of electrons localized in different sized sub-domain of the sp2 bonded carbons having different values of highest occupied molecular orbital (HOMO) -lowest unoccupied molecular orbital (LUMO) gap may likely to be responsible for the observed PL emission in rG1 and rG2 at different excitation wavelengths. The rG1 and rG2 were also used as photocatalyst materials for the degradation of phenanthrene (PHE) under the UV irradiation. The rG2 shows better photocatalytic degradation compared to rG1 by degrading the PHE up to 30%.

Effect of low-molecular-weight organic acids on photo-degradation of phenanthrene catalyzed by Fe(III)-smectite under visible light.

The photolysis of polycyclic aromatic hydrocarbons (PAHs) is potentially an important process for its transformation and fate on contaminated soil surfaces. In this study, phenanthrene is employed as a model to explore PAH photodegradation with the assistance of Fe(III)-smectite under visible-light while focusing on roles played by five low-molecular-weight organic acids (LMWOAs), i.e., malic acid, oxalic acid, citric acid, ethylenediaminetetraacetic acid (EDTA), and nitrilotriacetic acid. Our results show that oxalic acid is most effective in promoting the photodegradation of phenanthrene, while only a slight increase in the rate of phenanthrene photodegradation is observed in the presence of malic acid. Electron paramagnetic resonance experiments confirm the formation of CO2(-) radicals in the presence of malic and oxalic acid, which provides strong evidence for generating OH and subsequent photoreaction pathways. The presence of EDTA or nitrilotriacetic acid significantly inhibits both Fe(II) formation and phenanthrene photodegradation because these organic anions tend to chelate with Fe(III), leading to decreases in the electron-accepting potential of Fe(III)-smectite and a weakened interaction between phenanthrene and Fe(III)-smectite. These observations provide valuable insights into the transformation and fate of PAHs in the natural soil environment and demonstrate the potential for using some LMWOAs as additives for the remediation of contaminated soil.

Exchangeable cations-mediated photodegradation of polycyclic aromatic hydrocarbons (PAHs) on smectite surface under visible light.

Clay minerals saturated with different exchangeable cations are expected to play various roles in photodegradation of polycyclic aromatic hydrocarbons (PAHs) via direct and/or indirect pathways on clay surfaces. In the present study, anthracene and phenanthrene were selected as molecule probes to investigate the roles of exchangeable cations on their photodegradation under visible light irradiation. For five types of cation-modified smectite clays, the photodegradation rate of anthracene and phenanthrene follows the order: Fe(3+)>Al(3+)>Cu(2+)>>Ca(2+)>K(+)>Na(+), which is consistent with the binding energy of cation-π interactions between PAHs and exchangeable cations. The result suggests that PAHs photolysis rate depends on cation-π interactions on clay surfaces. Meanwhile, the deposition of anthracene at the Na(+)-smectite and K(+)-smectite surface favors solar light absorption, resulting in enhanced direct photodecomposition of PAHs. On the other hand, smectite clays saturated with Fe(3+), Al(3+), and Cu(2+) are highly photoreactive and can act as potential catalysts giving rise to oxidative radicals such as O2(-) , which initiate the transformation of PAHs. The present work provides valuable insights into understanding the transformation and fate of PAHs in the natural soil environment and sheds light on the development of technologies for contaminated land remediation.

Aqueous phenanthrene toxicity after high-frequency ultrasound degradation.

Given that polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene (PH), possess a potent risk for aquatic biota, a great attempt to develop and apply advanced oxidation processes, such as ultrasound (US), is of great concern nowadays. However, because US PAH-derived toxic intermediates are difficult to detect, the present study investigates aqueous PH toxicity before and after high-frequency US degradation, in hemocytes of mussel Mytilus galloprovincialis. Specifically, cell viability (with the use of neutral red uptake/NRU method), and oxidative-stress indices in terms of superoxide anions, (O2(-)), nitric oxides (NO, in terms of nitrites), lipid peroxidation products (in terms of malondialdehyde/MDA content) and DNA damage (with the use of Comet assay method) were investigated in mussel hemocytes exposed to environmentally relevant concentrations of PH (0.01, 0.1, 1 and 10 µg L(-1)), before and after US treatment for 120 min (at a frequency of 582 kHz). According to the results, the NRU method showed a significant attenuation of PH-induced mortality in US PH-treated hemocytes in all cases. Moreover, the increased levels of O2(-) and NO generation, as well as MDA content measured in PH-treated hemocytes, were drastically decreased after US degradation in any case. Similarly, the disturbance of DNA integrity (in terms of % DNA in tail, OM and TM), was negligible in case of US PH-treated hemocytes. Although further in vitro and in vivo studies are needed, the present study showed for the first time that high frequency US could be applied as a highly efficient and "environmentally friendly" process for degrading low molecular weight PAH, such as PH.

Visible light photodegradation of phenanthrene catalyzed by Fe(III)-smectite: role of soil organic matter.

In the present study, phenanthrene is employed as a model to explore the roles played by three soil organic matter (SOM) fractions, i.e., dissolved organic matter (DOM), humic acid (HA), and fulvic acid (FA), in its photodegradation with assistance of Fe(III)-smectite under visible-light. Slight decrease in phenanthrene photodegradation rate was observed in the presence of DOM, which is explained in terms of oxidative-radical competition between DOM and target phenanthrene molecules due to the high electron-donor capacity of phenolic moieties in DOM. On the other hand, a critic content is observed with FA (0.70mg/g) and HA (0.65mg/g). Before reaching the critic content, the removal of phenanthrene is accelerated; while after that, the photodegradation rate is suppressed. The acceleration of phenanthrene degradation can be attributed to the photosensitization of FA and HA. Due to the strong interaction between phenanthrene and the phenyl rings, however, the retention of phenanthrene on SOM-Fe(III)-smectite in the presence of high content of HA or FA is enhanced, thus slowing down its photodegradation. Those observations provide valuable insights into the transformation and fate of PAHs in the natural soil environment and open a window for using clay-humic substances complexes for remediation of contaminated soil.

Photocatalytic degradation of phenanthrene on soil surfaces in the presence of nanometer anatase TiO2 under UV-light.

The effect of nanometer anatase TiO2 was investigated on the photocatalytic degradation of phenanthrene on soil surfaces under a variety of conditions. After being spiked with phenanthrene, soil samples loaded with different amounts of TiO2 (0 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, and 4 wt.%) were exposed to UV-light irradiation for 25 hr. The results indicated that the photocatalytic degradation of phenanthrene followed the pseudo first-order kinetics. TiO2 significantly accelerated the degradation of phenanthrene with the half-life reduced from 45.90 to 31.36 hr for TiO2 loading of 0 wt.% and 4 wt.%, respectively. In addition, the effects of H2O2, light intensity and humic acid on the degradation of phenanthrene were investigated. The degradation of phenanthrene increased with the concentration of H2O2, light intensity and the concentration of humic acids. It has been demonstrated that the photocatalytic method in the presence of nanometer anatase TiO2 was a very promising technology for the treatments of soil polluted with organic substances in the future.

Photostability and toxicity of pentachlorophenol and phenanthrene.

Fate of organic contaminants under UV irradiation as environmental variable was studied. Aqueous solutions of pentachlorophenol and phenanthrene were subjected to simulated solar radiation and monitored during ≤ 93 h. Immobilization tests were conducted using Daphnia magna neonates in pre-irradiated water for the assessment of photoproduct-mediated toxicity. We observed a time-dependent decrease in exposure concentrations following irradiation, which correlated positively with reduced immobilization of the animals. A complete disappearance of the lowest and highest concentrations of pentachlorophenol was noted after 25 h and 75 h, respectively. Survivorship of the animals increased until 100% and correlated positively with irradiation time. However, phenanthrene was rather persistent under irradiation, with less than 25% decline in exposure concentrations after 93 h. Neonates were not immobilized at maximum aqueous solubility of phenanthrene. Rate constants (k) for the photodegradation of pentachlorophenol at 0.41, 0.59, 1.1, and 2.1 mg l(-1) were in the range of 7.2 × 10(-2) and 4.9 × 10(-2)h(-1), showing a slight decrease with increasing initial pentachlorophenol concentration. Nonetheless, pentachlorophenol degradation in the studied concentration range could still be described by the pseudo-first-order kinetics. K values for phenanthrene at 0.12 and 0.22 mg l(-1) were 2.9 × 10(-3)h(-1) and 4.2 × 10(-3)h(-1), respectively.

Photodegradation of phenanthrene by N-doped TiO2 photocatalyst.

The photodegradation of phenanthrene has been catalyzed by nanostructures of TiO2 doped with nitrogen, N-doped TiO2. The N-doped TiO2 was prepared from the sol-gel reaction of Titanium(IV) bis(ethyl acetoacetato)diisopropoxide with 25% ammonia solution. The N-doped TiO2 was calcined at various temperatures from 300 to 700 degrees C. X-ray diffraction (XRD) results showed that N-doped TiO2 remained amorphous at 300 degrees C but anatase-to-rutile transformation started at 400 degrees C and was complete at 700 degrees C. The average particle size calculated from Scherrer's equation was in the range of 9-51 nm with surface area (S(BET)) of 253.7-4.8 m2/g. X-ray photoelectron spectroscopy (XPS) results confirmed the incorporation of nitrogen atoms (Ti-N bond) in the N-doped catalyst. Moreover, the percentage of nitrogen determined by Elemental analysis was 0.236% of N-doped calcined at 400 degrees C. UV-Vis reflection spectra indicated that N-doped TiO2 calcined at 400 degrees C shifted to the higher absorption edge in the range of visible light. N-doped TiO2 calcined at 400 degrees C successfully catalyzed the photodegradation of phenanthrene (80% conversion) whereas N-doped TiO2 calcined at 500 degrees C and P25 TiO2 failed as catalysts.

A general approach to triphenylenes and azatriphenylenes: total synthesis of dehydrotylophorine and tylophorine.

A convergent and flexible synthesis of substituted triphenylenes, azatriphenylenes, and the cytotoxic alkaloids dehydrotylophorine and tylophorine has been developed.

Direct one-pot synthesis of phenanthrenes via Suzuki-Miyaura coupling/aldol condensation cascade reaction.

We have developed an efficient cascade reaction, a Suzuki-Miyaura coupling followed by an aldol condensation, for the construction of phenanthrene derivatives using microwave irradiation. For example, the reaction of methyl 2-bromophenylacetamide with 2-formylphenylboronic acid in the presence of a palladium catalyst and a base provided a biaryl intermediate, which underwent in situ cyclization to afford the corresponding phenanthrene in high yield.

Photooxygenation of alkynylperylenes. Formation of dibenzo[jk,mn]phenanthrene-4,5-diones.

3-(1-Alkynyl)perylenes undergo oxygenation when subjected to irradiation with visible light under aerated conditions. The structures of novel oxygenated products formed in this manner are assigned as regioisomeric dibenzo[jk,mn]phenanthrene-4,5-diones.

Photophysical and photochemical processes of 9,10-dihydro-9-silaphenanthrene derivatives: photochemical formation and electronic structure of 9-silaphenanthrenes.

Photophysical and photochemical processes of 9-methyl- and 9-phenyl-9,10-dihydro-9-silaphenanthrene derivatives have been studied at room temperature and 77 K in comparison with the carbon analogue, 9,10-dihydrophenanthrene. These 9,10-dihydro-9-silaphenanthrene derivatives show smaller fluorescence quantum yield and remarkably larger Stokes shifts than those of the carbon analogue. In contrast, their phosphorescence quantum yields are two times larger than those of the carbon analogue, although the absolute value is not so large (approximately 0.1). Reaction products and intermediates produced by the 266 nm light photolysis have been studied, and it has been confirmed that 9-methyl- and 9-phenyl-9-silaphenanthrenes have been photochemically formed in methylcyclohexane at 77 K, in addition to the formation of radical cations of 9,10-dihydro-9-silaphenanthrene derivatives and the carbon-centered radical: 9-hydro-9-silaphenanthrenyl radical.

Light-driven molecular motors: stepwise thermal helix inversion during unidirectional rotation of sterically overcrowded biphenanthrylidenes.

To investigate the unidirectional rotation of chiral overcrowded biphenanthrylidenes in more detail, the size of the substituent next to the double bond responsible for the unidirectionality of rotation was varied. The thermal and photochemical isomerization of three sterically overcrowded alkenes is described. The behavior of the biphenanthrylidenes with methyl and ethyl substituents is rather similar, and these compounds undergo a unidirectional 360 degrees rotation around the central double bond in a four-step sequence involving two photochemical cis-trans isomerizations and two thermal helix inversions. The only difference between these two true molecular motors was a small entropic effect, which causes the ethyl substituted molecular motor to rotate slightly faster. The behavior of the i-propyl substituted compound differs significantly from that of the other two. Although not all different isomers of the i-propyl substituted molecular motor were detected spectroscopically, experimental data led to the conclusion that this compound can also be considered as a molecular motor and is capable of performing a 360 degrees unidirectional rotation. (1)H NMR and X-ray analysis show a meso-like form as an intermediate in the unidirectional rotation, which proves that the thermal helix inversion is a stepwise process.

Pre-column derivatization of rofecoxib for determination in serum by HPLC.

An HPLC method for determination of rofecoxib in human serum is presented. The method is based on pre-column derivatization of analyte to a phenanthrene derivative of the drug. Rofecoxib and the internal standard were extracted from serum using liquid-liquid extraction. Upon exposure to UV light, the drug was found to undergo a photocyclization reaction, giving a species with high absorbance. Validation of the method has been studied in the concentration range 10-500 ng ml(-1).

Antimicrobial DNA-binding photosensitizers from the common rush, Juncus effusus.

Our continuing survey of phototoxins from higher plants has led to the isolation and identification from the common rush, Juncus effusus L., of the phenanthrene, dehydroeffusol (1), and the dihydrophenanthrene, juncusol (2), compounds that display enhanced antimicrobial activities in light. The antimicrobial activities (minimum inhibitory concentrations) for these compounds against methicillin-resistant and -sensitive Staphylococcus aureus and Candida albicans were increased 16- and two-fold, respectively, by irradiation with ultraviolet A (UVA). Photosensitized DNA-binding activities (as possible covalent bond formation) of these compounds were determined by using restriction enzymes and a specially prepared 1.5 kb DNA fragment. Under UVA irradiation, dehydroeffusol strongly inhibited all the restriction enzymes (KpnI, XbaI, PmeI, DraI, PacI and BciVI) that have at least one 5'-TpA sequence in their recognition sites. Weak inhibitions were found for the restriction enzymes EcoRI, SacI, BamHI, SalI, PstI and HindIII, which do not possess a 5'-TpA sequence at their restriction sites and the restriction site sequences of which consist of all bases, A, T, G and C. Trace or no inhibition was found for AscI and SmaI, the restriction site sequences of which are composed of only C and G. The results indicate the necessity of thymine (adenine) for the photosensitized DNA-binding activity of dehydroeffusol. A strong inhibition against SphI, which does not have a 5'-TpA sequence in the restriction sequence, indicates that there are possibly other binding sequence(s) for dehydroeffusol. With juncusol and UVA, strong inhibitions for KpnI and BciVI and trace inhibitions for PacI, XbaI, PmeI and DraI were found. This result also showed a preference of juncusol for 5'-TpA, but the preference could be more selective than that of dehydroeffusol depending on the surrounding sequences of 5'-TpA in the respective restriction sites. A strong inhibition of SphI by juncusol with UVA also indicated the existence of an unknown binding sequence for this compound. Generally, the DNA-binding activity of this compound was weaker than that of dehydroeffusol.

In-vitro study of interaction between photooxidation and biodegradation of 2-methylphenanthrene by Sphingomonas SP. 2MPII.

This work reports a study of interactions between reactions of photooxidation and reactions of bacterial degradation of an alkylated polyaromatic hydrocarbon (2-methylphenanthrene). Bacterial growth was carried out using artificial sunlight as light source. Among the various products detected, the major product was identified as the 2-methylphenanthrene aldehyde. Sunlight allows accelerated elimination of the substrate. This enhancement of the biodegradation rate of 2 methylphenanthrene is due to the use of assimilable photoproducts by the bacterium.

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.

Photo-induced electron transfer from nucleotides to ruthenium-tris-1,4,5,8-tetraazaphenanthrene: model for photosensitized DNA oxidation.

The luminescence quenching of ruthenium-tris-1,4,5,8-tetraazaphenanthrene [Ru(tap)3(2+)] by nucleotides approaches the diffusion rate only with guanosine-5'-monophosphate (GMP), the most reducing nucleotide, and leads to an electron transfer with the production of the monoreduced complex and the oxidized base. The resulting deprotonated GMP(-H).radical recombines with the monoreduced complex according to a bimolecular equimolar process. The pH dependence of the decay of the transient reduced complex, in the presence of an oxidant (oxygen or benzoquinone) indicates the formation of Ru(tap)2(tapH)2+, i.e. the reduced protonated species, subsequent to the electron transfer, with a pKa of 7.6 as confirmed from pulse radiolysis experiments. As the non-protonated reduced complex, Ru(tap)2(tap-.)+, has a higher reducing power than the protonated one, oxygen is able to reoxidize only the non-protonated species, whereas benzoquinone reoxidizes both species but with different rate constants. The flash photolysis of Ru(tap)3(2+) in the presence of DNA and the effect of Mg2+ ions and GMP as supplementary additives also show the existence of a photo-induced electron transfer with the nucleic acid, which can be correlated to the photosensitized cleavage of DNA by this complex.