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Many popular organic chromophores that catalyze photoinduced proton-coupled electron transfer (PCET) reactions are aromatic in the ground state but become excited-state antiaromatic in the lowest ππ* state. We show that excited-state antiaromaticity makes electron transfer easier. Two representative photoinduced electron transfer processes are investigated: (1) the photolysis of phenol and (2) solar water splitting of a pyridine-water complex. In the selected reactions, the directions of electron transfer are opposite, but the net result is proton transfer following the direction of electron transfer. Nucleus-independent chemical shifts (NICS), ionization energies, electron affinities, and PCET energy profiles of selected [4 n ] and [4 n + 2] π-systems are presented, and important mechanistic implications are discussed.

The antimicrobial potential of two ruthenium(II) polypyridyl complexes, [Ru(phen) 2 L1] 2+ and [Ru(phen) 2 L2] 2+ (phen = 1,10-phenanthroline) containing the 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridilophane (L1) and the 4,4'-bis-[methylen-(1,4,7,10-tetraazacyclododecane)]-2,2' bipyridine (L2) units, is herein investigated. These peculiar polyamine frameworks afford the formation of highly charged species in solution, influence the DNA-binding and cleavage properties of compounds, but they do not undermine their singlet oxygen sensitizing capacities, thus making these complexes attractive 1 O 2 generators in aqueous solution. L1 and L2 also permit to stably host Fenton -active Cu 2+ ion/s, leading to the formation of mixed Ru 2+ /Cu 2+ forms capable to further strengthen the oxidative damages to biological targets. Herein, following a characterization of the Cu 2+ binding ability by [Ru(phen) 2 L2] 2+ , the water-octanol distribution coefficients, the DNA binding, cleavage and 1 O 2 sensitizing properties of [Ru(phen) 2 L2] 2+ and [Cu 2 Ru(phen) 2 L2] 6+ were analysed and compared with those of [Ru(phen) 2 L1] 2+ and [CuRu(phen) 2 L1] 4+ . The antimicrobial activity of all compounds was evaluated against B. subtilis, chosen as a model for gram-positive bacteria, both under dark and upon light-activation. Our results unveil a notable phototoxicity of [Ru(phen) 2 L2] 2+ and [Cu 2 Ru(phen) 2 L2] 6+ , with MIC (minimal inhibitory concentrations) values of 3.12 μM. This study highlights that the structural characteristics of polyamine ligands gathered on highly charged Ru(II)-polypyridyl complexes are versatile tools that can be exploited to achieve enhanced antibacterial strategies., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Ruthenium complexes have been recently reported as potential chemotherapeutic agents that offer tumor selectivity and low tumor resistance. This study investigates the photochemistry and the effect of four strained photoactivatable polypyridyl ruthenium(II) complexes on non-small-cell lung cancer (A549) and triple negative breast cancer (MDA-MB-231) cells. All four ruthenium(II) complexes, [Ru(bpy) 2 dmbpy]Cl 2  (C1) where (bpy = 2,2'-bipyridine and dmbpy = 6,6'-dimethyl-2,2'-bipyridine), [Ru(phen) 2 dmbpy]Cl 2  (C2) where (phen = 1,10-phenanthroline), [Ru(dpphen) 2 dmbpy]Cl 2  (C3) (where dpphen = 4,7-diphenyl-1,10-phenanthroline) and [Ru(BPS) 2 dmbpy]Na 2 (C4) where (BPS = bathophenanthroline disulfonate) eject the dmbpy ligand upon activation by blue light. Determination of the octanol-water partition coefficient (log P) revealed that C3 was the only lipophilic complex (log P = 0.42). LC-MS/MS studies showed that C3 presented the highest cellular uptake. The cytotoxic effect of the complexes was evaluated with and without blue light activation using WST-1 kit. Data indicated that C3 exhibited the highest cytotoxicity after 72 h (MDA-MB-231, IC 50  = 0.73 µM; A549, IC 50  = 1.26 µM) of treatment. The phototoxicity indices of C3 were 6.56 and 4.64 for MDA-MB-230 and A549, respectively. Upon light activation, C3 caused significant ROS production and induced apoptosis in MDA-MB-231 cells as shown by flow cytometry. It also significantly increased Bax/Bcl2 ratio and PERK levels without affecting caspase-3 expression. C3 exhibited poor dark toxicity (IC 50  = 74 μM) on rat mesenchymal stem cells (MSCs). In conclusion, the physical property of the complexes dictated by the variable ancillary ligands influenced cellular uptake and cytotoxicity. C3 may be considered a promising selective photoactivatable chemotherapeutic agent that induces ROS production and apoptosis.

Pyridine and organics containing pyridine rings are widely used but persist in the environment and cause toxic pollution. Due to the attraction of the nitrogen atoms to the electrons in the pi bond, the pyridine ring is difficult to oxidize by oxidant. Here, we propose that ultraviolet (UV) irradiation activates the electrons in the pi bond and enables combination with the hydroxyl radical (OH) originating from hydrogen peroxide (H 2 O 2 ) to eliminate pyridine quickly and mineralize the byproducts. The removal rates of pyridine and total organic carbon (TOC) were compared in different treatments: UV irradiation, UV/H 2 O 2 treatment and Fenton oxidation with different initial pyridine concentrations, pH values and H 2 O 2 concentrations. The UV/H 2 O 2 treatment yielded a higher pyridine removal rate and greater mineralization than the other treatments. The removal rate of pyridine was highest in neutral aqueous solution and H 2 O 2 concentration of 10 mM. At an initial H 2 O 2 concentration of 10 mM, more than 90% of the pyridine was degraded in 10 min, and approximately 70% of the TOC was removed in 60 min. The absorption of UV light at 254 nm by the pi bond of pyridine can accelerate the damage to the stable pyridine structure, especially in the presence of OH. This study provides a promising alternative for the removal and mineralization of pyridine ring-containing materials., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this article, we report the design, synthesis, and characterization of a series of cyclometalated iridium(III) polypyridine complexes containing a perfluorobiphenyl (PFBP) moiety [Ir(N^C) 2 (bpy-PFBP)](PF 6 ) (bpy-PFBP = 4-( S -(perfluoro-(1,1'-biphenyl)-4-yl)- N -mercaptoethylaminocarbonyloxymethyl)-4'-methyl-2,2'-bipyridine; HN^C = 2-phenylpyridine (Hppy) ( 1a ), 2-(4-hydroxymethylphenyl)pyridine (Hppy-CH 2 OH) ( 2a ), 2-((1,1'-biphenyl)-4-yl)pyridine (Hpppy) ( 3a ), 2-((4'-hydroxymethyl-1,1'-biphenyl)-4-yl)pyridine (Hpppy-CH 2 OH) ( 4a ), 2-phenylquinoline (Hpq) ( 5a ), 2-(4-hydroxymethylphenyl)quinoline (Hpq-CH 2 OH) ( 6a )). Their PFBP-free counterparts [Ir(N^C) 2 (bpy-C4)](PF 6 ) (bpy-C4 = 4-( N - n -butylaminocarbonyloxymethyl)-4'-methyl-2,2'-bipyridine; HN^C = Hppy ( 1b ), Hppy-CH 2 OH ( 2b ), Hpppy ( 3b ), Hpppy-CH 2 OH ( 4b ), Hpq ( 5b ), Hpq-CH 2 OH ( 6b )) were also prepared for comparison studies. Upon irradiation, all the complexes displayed intense and long-lived greenish-yellow to orange luminescence in solutions under ambient conditions and in low-temperature alcohol glass. Reactions of the PFBP complexes with peptides containing the FCPF sequence via the π-clamp-mediated cysteine conjugation afforded luminescent peptide conjugates that exhibited rich photophysical properties. Using complex 3a as an example, we demonstrated that the conjugation of complexes to organelle-targeting peptides is an effective means to modulate their intracellular localization behavior, which was further shown to be important to their performance in photodynamic therapy. The results of this work will contribute to the development of photofunctional transition metal complexes as theranostic agents.

Development of new photosensitizers (PSs) with high photodynamic efficacy and minimal side effects is of great interest in photodynamic therapy (PDT). In this work, we reported several pyridine-embedded phenothiazinium (pyridophenothiazinium) dyes, which could be conveniently synthesized in a few short steps and acted as highly efficient and potent PSs to selectively localize to lysosomes and photosensitively kill cancer cells. Among them, compound 5 , which possessed the ability of promoting intracellular reactive oxygen species (ROS) upon light irradiation by almost 40-fold higher than that of methylene blue (MB, a general phenothiazinium-based PS), exhibited a remarkable phototherapeutic index (PI = 53.8) against HT29 cancer cells, leading to eradication of large solid tumors (∼300 mm 3 ) in a xenograft mouse model without apparent side effects. These results suggest that the pyridophenothiazinium dyes developed herein, especially compound 5 , may serve as promising lysosome-targeted PSs for efficient photodynamic antitumor therapy.

Bioactive oxazolopyridine unit was used in the synthesis of fluorescent markers for specific organelles in this paper. The compounds 1a-c are linked with double bond between oxazolopyridine ring and photogenic precursors (3a-c). Compound 1a showed higher fluorescence yield (0.86 in THF), compounds 1b-c showed larger stokes shifts in DMSO. In lipid vesicles environment, they also showed good optical properties. In addition, the three compounds are biomarkers with lower cytotoxicity. Among them, compound 1a based on oxazolopyridine and coumarin unit is a dual targetable fluorescent marker for mitochondria and lipid droplets; while the other two compounds 1b-c are only biomarkers for lipid droplets., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Due to acquired resistance or limitations of the currently approved drugs against cancer, there is an urgent need for the development of new classes of compounds. Among others, there is an increasing attention towards the use of Ru(II) polypyridyl complexes. Most studies in the literature were made on complexes based on the coordination of N-donating bidentate ligands to the ruthenium core whereas studies on 2,2':6', 2″-terpyridine (terpy) coordinating ligands are relatively scare. However, several studies have shown that [Ru(terpy)2] 2+ derivatives are able bind to DNA through various binding modes making these compounds potentially suitable as chemotherapeutic agents. Additionally, light irradiation of these compounds was shown to enable DNA cleavage, highlighting their potential use as photosensitizers (PSs) for photodynamic therapy (PDT). In this work, we present the systematic investigation of the potential of 7 complexes of the type [Ru(terpy)(terpy-X)]2+ (X = H (1), Cl (2), Br (3), OMe (4), COOH (5), COOMe (6), NMe2 (7)) as potential chemotherapeutic agents and PDT PSs. Importantly, six of the seven complexes were found to be stable in human plasma as well as photostable in acetonitrile upon continuous light irradiation (480 nm). The determination of the distribution coefficient logP values for the 7 complexes revealed their good water solubility. Complex 7 was found to be cytotoxic in the micromolar range in the dark as well as to have some phototoxicity upon light exposure at 480 nm in non-cancerous retinal pigment epithelium (RPE-1) and cancerous human cervical carcinoma (HeLa) cells. SYNOPSIS: The systematic investigation of the potential of 7 complexes of the type [Ru(terpy)(terpy-X)] 2+ (terpy: 2,2':6', 2″-terpyridine; X = H (1), Cl (2), Br (3), OMe (4), COOH (5), COOMe (6), NMe2 (7)) as potential chemotherapeutic agents and photosensitizers for photodynamic therapy is presented., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Here, we developed a novel non-enzymatic rapid testing method for determination of organophosphate pesticide (malathion) in water. In principle, target molecule can block the Fluorescence resonance energy transfer (FRET) between chemical fluorescent probe (energy donor) and β-cyclodextrin-coated silver nanoparticles (@AgNP) (receptor). The effects of malathion on the dynamics of fluorescent probe and β-cyclodextrin@AgNP were evaluated and their properties were further characterized. The current methodology showed a good sensitivity of 0.01 μg/mL represented as a limit of detection (LOD) and the calibration curve was linear over the concentration range of 0.1-25 μg/mL. Recovery rate from water samples spiked at 3 different concentration levels (0.3, 0.4, and 0.6 μg/mL) showed satisfactory range between 83% and 101%., (Copyright © 2018. Published by Elsevier B.V.)

A novel three-dimensional microporous framework, [Tb(pddb)phen(ox) 0.5 ] n (Tb-MOF), was synthesized hydrothermally with V-shaped 4,4'-(pyridine-2,6-diyl)dibenzoic acid (H 2 pddb), oxalate (ox), and 1,10-phenanthroline (phen). The framework of Tb-MOF features one-dimensional channels functionalized with pyridine-N Lewis base groups and the absence of coordinated and lattice water molecules in the structure. The Tb-MOF exhibits high thermostability (up to 385 °C) and chemical stability in a wide pH range (4-11) and common organic solvents as well as boiling water. The luminescence investigations of the Tb-MOF in common solvents, water with different pH values, and inorganic ions were performed. Results show that the Tb-MOF has high luminescence stability and the ability to probe Fe 3+ ions. Significantly, the Tb-MOF with particularly high water stability can be first developed as a highly selective and sensitive luminescent sensor for the biomarker 2-thiazolidinethione-4-carboxylic acid (TTCA) via fluorescence quenching. The low detection limit (1 ppm), reusability, and high antidisturbance together make the Tb-MOF become a promising sensor for the practical detection of TTCA in urine systems, and for the first time realize the detection of urinary TTCA through fluorescence spectrometry based on an Ln-MOF sensor.

The transfer of protons and electrons is key to energy conversion and storage, from photosynthesis to fuel cells. Increased understanding and control of these processes are needed. A new anthracene-phenol-pyridine molecular triad was designed to undergo fast photoinduced multiple-site concerted proton-electron transfer (MS-CPET), with the phenol moiety transferring an electron to the photoexcited anthracene and a proton to the pyridine. Fluorescence quenching and transient absorption experiments in solutions and glasses show rapid MS-CPET (3.2 × 10 10 s -1 at 298 K). From 5.5 to 90 K, the reaction rate and kinetic isotope effect (KIE) are independent of temperature, with zero Arrhenius activation energy. From 145 to 350 K, there are only slight changes with temperature. This MS-CPET reaction thus occurs by tunneling of both the proton and electron, in different directions. Since the reaction proceeds without significant thermal activation energy, the rate constant indicates the magnitude of the electron/proton double tunneling probability.

Metal complexes have many proven applications in the caging and photochemical release of biologically active compounds. Photocaging groups derived from Ru(II) traditionally have been composed of ancillary ligands that are planar and bi- or tridentate, such as 2,2'-bipyridine (bpy), 2,2':6',2″-terpyridine (tpy), and 1,10-phenanthroline (phen). Complexes bearing ancillary ligands with denticities higher than three represent a new class of Ru(II)-based photocaging groups that are grossly underdeveloped. Because high-denticity ancillary ligands provide the ability to increase the structural rigidity and control the stereochemistry, our groups initiated a research program to explore the applications of such ligands in Ru(II)-based photocaging. Ru(TPA), bearing the tetradentate ancillary ligand tris(2-pyridylmethyl)amine (TPA), has been successfully utilized to effectively cage nitriles and aromatic heterocycles. Nitriles and aromatic heterocycles caged by the Ru(TPA) group show excellent stability in aqueous solutions in the dark, and the complexes can selectively release the caged molecules upon irradiation with light. Ru(TPA) is applicable as a photochemical agent to offer precise spatiotemporal control over biological activity without undesired toxicity. In addition, Ru(II) polypyridyl complexes with desired photochemical properties can be synthesized and identified by solid-phase synthesis, and the resulting complexes show properties to similar to those of complexes obtained by solution-phase synthesis. Density functional theory (DFT) calculations reveal that orbital mixing between the π* orbitals of the ancillary ligand and the Ru-N dσ* orbital is essential for ligand photodissociation in these complexes. Furthermore, the introduction of steric bulk enhances the photoliability of the caged molecules, validating that steric effects can largely influence the quantum efficiency of photoinduced ligand exchange in Ru(II) polypyridyl complexes. Recently, two new photocaging groups, Ru(cyTPA) and Ru(1-isocyTPQA), have been designed and synthesized for caging of nitriles and aromatic heterocycles, and these complexes exhibit unique photochemical properties distinct from those derived from Ru(TPA). Notably, the unusually greater quantum efficiency for the ligand exchange in [Ru(1-isocyTPQA)(MeCN) 2 ](PF 6 ) 2 , Φ 400 = 0.033(3), uncovers a trans-type effect in the triplet metal-to-ligand charge transfer ( 3 MLCT) state that enhances photoinduced ligand exchange in a new manner. DFT calculations and ultrafast transient spectroscopy reveal that the lowest-energy triplet state in [Ru(1-isocyTPQA)(MeCN) 2 ](PF 6 ) 2 is a highly mixed 3 MLCT/ 3 ππ* excited state rather than a triplet metal-centered ligand-field ( 3 LF) excited state; the latter is generally accepted for ligand photodissociation. In addition, Mulliken spin density calculations indicate that a majority of the spin density in [Ru(1-isocyTPQA)(MeCN) 2 ](PF 6 ) 2 is localized on the isoquinoline arm, which is opposite to the cis MeCN, rather than on the ruthenium center. This significantly weakens the Ru-N6 ( cis MeCN) bond, which then promotes the ligand photodissociation. This newly discovered effect gives a clearer perception of the interplay between the 3 MLCT and 3 LF excited states of Ru(II) polypyridyl complexes, which may be useful in the design and applications of ruthenium complexes in the areas of photoactivated drug delivery and photosensitizers.

Photocaging allows for precise spatiotemporal control over the release of biologically active compounds with light. Most photocaged molecules employ organic photolabile protecting groups; however, biologically active compounds often contain functionalities such as nitriles and aromatic heterocycles that cannot be caged with organic groups. Despite their prevalence, only a few studies have reported successful caging of nitriles and aromatic heterocycles. Recently, Ru(ii)-based photocaging has emerged as a powerful method for the release of bioactive molecules containing these functional groups, in many cases providing high levels of spatial and temporal control over biological activity. This Feature Article discusses recent developments in applying Ru(ii)-based photocaging towards biological problems. Our groups designed and synthesized Ru(ii)-based platforms for the photoinduced delivery of cysteine protease and cytochrome P450 inhibitors in order to achieve selective control over enzyme inhibition. We also reported Ru(ii) photocaging groups derived from higher-denticity ancillary ligands that possess photophysical and photochemical properties distinct from more traditional Ru(ii)-based caging groups. In addition, for the first time, we are able to rapidly synthesize and screen Ru(ii) polypyridyl complexes that elicit desired properties by solid-phase synthesis. Finally, our work also defined steric and orbital mixing effects that are important factors in controlling photoinduced ligand exchange.

The methodology of experimental research was carried out using the MODDE 6.0 software to study the acetamiprid photodegradation depending on the operating parameters, such as the initial concentration of acetamiprid, concentration and type of the used catalyst and the initial pH of the medium. The results showed the importance of the pollutant concentration effect on the acetamiprid degradation rate. On the other hand, the amount and type of the used catalyst have a considerable influence on the elimination kinetics of this pollutant. The degradation of acetamiprid as an environmental pesticide pollutant via UV irradiation in the presence of titanium dioxide was assessed and optimized using response surface methodology with a D-optimal design. The acetamiprid degradation ratio was found to be sensitive to the different studied factors. The maximum value of discoloration under the optimum operating conditions was determined to be 99% after 300 min of UV irradiation.

Nuclear spin hyperpolarization overcomes the sensitivity limitations of traditional NMR and MRI, but the most general method demonstrated to date (dynamic nuclear polarization) has significant limitations in scalability, cost, and complex apparatus design. As an alternative, signal amplification by reversible exchange (SABRE) of parahydrogen on transition metal catalysts can hyperpolarize a variety of substrates, but to date this scheme has required transfer of the sample to low magnetic field or very strong RF irradiation. Here we demonstrate "Low-Irradiation Generation of High Tesla-SABRE" (LIGHT-SABRE) which works with simple pulse sequences and low power deposition; it should be usable at any magnetic field and for hyperpolarization of many different nuclei. This approach could drastically reduce the cost and complexity of producing hyperpolarized molecules., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Incorporating the visual discrimination of 2,2'-bipyridine and self-healing properties, a novel photo-switchable metallo-hydrogel system is fabricated using a pincer-type Cu(II) complex and 2,2'-azopyridine.

One-dimensionally periodic block copolymer photonic lamellar gels with full-color tunability as a result of a direct exchange of counteranions were fabricated via a two-step procedure comprising the self-assembly of a hydrophobic block-hydrophilic polyelectrolyte block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), followed by sequential quaternization of the P2VP layers in 1-bromoethane solution. Depending on the hydration characteristics of each counteranion, the selective swelling of the block copolymer lamellar structures leads to large tunability of the photonic stop band from blue to red wavelengths. More extensive quaternization of the P2VP block allows the photonic lamellar gels to swell more and red shift to longer wavelength. Here, we investigate the dynamic swelling behavior in the photonic gel films through time-resolved in situ measurement of UV-vis transmission. We model the swelling behavior using the transfer matrix method based on the experimentally observed reflectivity data with substitution of appropriate counterions. These tunable structural color materials may be attractive for numerous applications such as high-contrast displays without using a backlight, color filters, and optical mirrors for flexible lasing.

Pyridine, a complex nitrogen-containing heterocyclic compounds, is usually difficult to degrade by means of single biological method. The internal loop photobiodegradation reactor (ILPBR) was used for degradation of pyridine in batch and continuous experiments following three protocols: photolysis alone (P), biodegradation alone (B), and intimately coupled photolysis and biodegradation (P&B) to investigate the regularity of pyridine degradation. The experimental results indicated that pyridine removal rate by P&B was fastest among three protocols in batch experiment, in which protocol B was faster than P. For initial pyridine concentration of 100 mg L(-1), the pyridine removal rates were respectively 4.95, 10.2 and 14.58 mg (L x h)(-1) corresponding to protocol P, B and P&B. Pyridine degradation kinetic equations were established based on Monod model, and the saturation constants decreased from 1920.4 mg x L(-1) for protocol B to 1094.1 mg x L(-1) for protocol P&B. Protocols P, B and P&B were also used for pyridine degradation in continuous flow and influent pyridine concentration increased from 50 to 300 mg x L(-1), and their average removal rates were respectively 15.8 mg (L x h)(-1) for protocol P, 23.1 mg x (L x h)(-1) for protocol B and 24.9 mg x (L x h)(-1) for protocol P&B, in which the removal rates were higher than that in batch. Experiments suggested that the inhibition of pyridine to biofilm could be relieved due to UV irradiation in process of intimately coupled UV photolysis and biodegradation, and biofilm had kept its bioactivity degrading pyridine and enhanced pyridine removal rates.

UV light can degrade pyridine to ammonia nitrogen at room temperature. The decomposition of pyridine under UV irradiation with the help of aluminum oxide powders was rarely studied. While with the assist of alumina, fast photo-catalytic degradation of pyridine to 100 percentage ammonia nitrogen was realized within an hour. The promising promotion phenomena were confirmed in opening other nitrogen heterocyclic compounds (NHCs) such as quinoline and 2,2'-bipyridine. Scanning electron microscopy images showed the alumina powder was about 100 nm in size. X-ray diffraction results indicated that the sample was mainly a-Al203. Specific surface area of the sample was about 280 m(2)/g determined by BET method. The optimum dosages of catalysts and effects of pH value were also tested. There was no clear absorbance of the alumina sample showed in the range of 200-420 nm. It is believed that the interaction between pyridine and alumina surface hydroxyl caused by chemisorptions weakened the carbon-nitrogen bond and led to the promotion of the decomposition., (Copyright © 2011 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.)

The variation in structural, thermal and colorant properties of 2,6-diaminopyridine were studied using differential scanning calorimetry (DSC), UV-visible, NMR spectroscopies and powder X-ray diffraction techniques, before and after fast neutrons irradiation with 2.12 and 3.50 kGy and gamma irradiation with 136.16 Gy doses. Under fast neutron irradiation, the sample enthalpy values, and melting and boiling temperatures were varied with increase in the irradiation dose. But the variation in boiling temperature was more pronounced than that of the melting point. However, there was no drastic change in these transition temperatures. The kinetic parameters were calculated using free isoconversional and Kissinger analysis methods. Moreover, UV-visible spectra showed that fast neutron and gamma irradiations had destroyed the color of the title compound. The gamma irradiation showed similar effect on structural and thermal properties. Results are also shown where the intensity of XRD patterns strongly depends on the irradiation dose. According to the NMR results, it seems that the collision occurs between para-hydrogen of 2,6-DAP and fast neutrons., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Combining TiO(2) photocatalysis with inorganic oxidants (such as O(3) and H(2)O(2)) or transition metal ions (Fe(3+), Cu(2+) and Ag(+)) often leads to a synergic effect. Electron transfer between TiO(2) and the oxidant is usually involved. Accordingly, the degree of synergy could be influenced by TiO(2) surface area. With this in mind, the disappearance of thiacloprid, a neonicotinoid insecticide, was studied applying various photochemical AOPs and different TiO(2) photocatalysts. In photocatalytic ozonation experiments, synergic effect of three different TiO(2) photocatalysts was quantified. Higher surface area resulted in a more pronounced synergic effect but an increasing amount of TiO(2) did not influence the degree of the synergy. This supports the theory that the synergy is a consequence of adsorption of ozone on the TiO(2) surface. No synergy was observed in photocatalytic degradation of thiacloprid in the presence of dissolved iron(III) species performed under varied experimental conditions (concentration, age of iron(III) solution, different TiO(2) films, usage of TiO(2) slurries). This goes against the literature for different organic compounds (i.e., monuron). It indicates different roles of iron(III) in the photodegradation of different organic molecules. Moreover, TiO(2) surface area did not affect photodegradation efficiency in iron(III)-based experiments which could confirm absence of electron transfer between TiO(2) photocatalyst and iron(III)., (Copyright (c) 2009 Elsevier B.V. All rights reserved.)

We evaluated the acute toxicities of the metal pyrithiones (MePTs)--copper pyrithione (CuPT) and zinc pyrithione (ZnPT)--to four species of marine algae and a marine crustacean (Tigriopus japonicus). We also performed acute toxicity tests using six of the main MePT photodegradation products: pyridine-N-oxide (PO); 2-mercaptopyridine (HPS); pyridine-2-sulfonic-acid (PSA); 2-mercaptopyridine-N-oxide (HPT); 2,2'-dithio-bis-pyridine ([PS](2)); and 2,2'-dithio-bis-pyridine-N-oxide ([PT](2))-and three marine organisms representing three trophic levels: an alga (Skeletonema costatum), a crustacean (T. japonicus), and a fish (Pagrus major). The acute toxicity values (72-h EC(50)) of CuPT, ZnPT, HPT, (PT)(2), (PS)(2), HPS, PO, and PSA for S. costatum, which was the most sensitive of the test organisms to the chemicals tested, were 1.5, 1.6, 1.1, 3.4, 65, 730, >100,000, and >100,000 microg l(-1), respectively. CuPT was detected in the growth media used for S. costatum tests and in seawater containing HPT or (PT)(2); the concentration of CuPT in seawater containing HPT was highly dependent on the Cu(2+) concentration. These results indicate that in the presence of sufficient Cu(2+), the toxicities of HPT and (PT)(2) should be assessed as CuPT because in Japan MePTs are most frequently used as antifouling booster biocides in conjunction with cuprous oxide.

A novel class of derivatized acetylacetonate (acac) linkers for robust functionalization of TiO2 nanoparticles (NPs) under aqueous and oxidative conditions is reported. The resulting surface adsorbate anchors are particularly relevant to engineering photocatalytic and photovoltaic devices since they can be applied to attach a broad range of photosensitizers and photocatalytic complexes and are not affected by humidity. Acac is easily modified by CuI-mediated coupling reactions to provide a variety of scaffolds, including substituted terpy complexes (terpy = 2,2':6,2''-terpyridine), assembled with ligands coordinated to transition-metal ions. Since Mn-terpy complexes are known to be effective catalysts for oxidation chemistry, functionalization with Mn(II) is examined. This permits visible-light sensitization of TiO2 nanoparticles due to interfacial electron transfer, as evidenced by UV-vis spectroscopy of colloidal thin films and aqueous suspensions. The underlying ultrafast interfacial electron injection is complete on a subpicosecond time scale, as monitored by optical pump-terahertz probe transient measurements and computer simulations. Time-resolved measurements of the Mn(II) EPR signal at 6 K show that interfacial electron injection induces Mn(II) --> Mn(III) photooxidation, with a half-time for regeneration of the Mn(II) complex of ca. 23 s.

Septet 3,5-difluoropyridyl-2,4,6-trinitrene along with quintet 2-azido-3,5-difluoropyridyl-4,6-dinitrene, quintet 4-azido-3,5-difluoropyridyl-2,6-dinitrene, triplet 2,6-diazido-3,5-difluoropyridyl-4-nitrene, and triplet 2,4-diazido-3,5-difluoropyridyl-6-nitrene have been obtained by photolysis of 2,4,6-triazido-3,5-difluoropyridine in solid argon at 4 K. The electronic and magnetic properties of the matrix-isolated nitrenes were studied using electron paramagnetic resonance (EPR) spectroscopy in combination with density functional theory (DFT) calculations. The fine-structure parameters of the nitrenes were determined with high accuracy from computer spectral simulations. All signals in the EPR spectra of the nitrenes randomly oriented in the solid phase were unambiguously assigned on the basis of eigenfield calculations of the Zeeman energy levels and angular dependencies of resonance fields from the direction of the applied magnetic field.

We have studied nonsteroidal ligands of the human androgen receptor (hAR) and have shown elsewhere that when photoactivated by visible light they collide with O2 to yield singlet oxygens (1O2) in vitro. Here we report cell killing after brief light activation (405 nm) of 1,2,3,4-tetrahydro-2,2-dimethyl-6-(trifluoromethyl)-8-pyridono[5,6-g]quinoline (TDPQ) in human prostate tumor cells. TDPQ/AR complexes were required for the death response because AR-positive LNCaP cells were killed, whereas AR-negative PC-3 cells were resistant. Excess dihydrotestosterone (DHT) blocked the TDPQ effect when the two were added together; irradiation of cells containing DHT alone had no effect. When LNCaP AR expression was suppressed using small interfering oligonucleotides targeting AR, photocytotoxicity was diminished. Conversely, stable transfection of hAR into PC-3 cells made the cells photosensitive to TDPQ. Similar results were obtained using a structural isomer of TDPQ, and also the synthetic steroidal AR ligand R1881. Cell death occurred via apoptosis as demonstrated by annexin V immunostaining, nuclear condensation, and caspase inhibition. Death involved oxidative stress, because it was prevented by addition of the antioxidant ascorbic acid during photoactivation. Detection of elevated levels of 8-hydroxy-2'-deoxyguanosine in nuclei of irradiated cells indicated oxidative DNA damage. Apoptosis spread into adjacent nonirradiated cells by direct cell-cell contacts, indicative of a bystander effect. Other photoactivatable ligands are described, implying a general method for ablation of cells bearing specific nuclear hormone receptors.

Persistence of two neonicotinoids viz thiacloprid and acetamiprid in soil as affected by UV and sunlight exposure was studied. Treated soil was placed in petri-plates, brought to field capacity moisture and then exposed to UV and sunlight. Dissipation for both the pesticides followed monophasic first order kinetics under sunlight, however under UV-light biphasic dissipation was recorded. Residues of acetamiprid and thiacloprid in soil dissipated with half-lives of 11.1 and 12.8 days under UV light and 25.1 and 19.1 days under sunlight, respectively. Residues of both the neonicotinoids dissipated quickly under UV light as compared to sunlight. Exposure of thin film of acetamiprid and thiacloprid to UV and sunlight revealed that acetamiprid is more photo labile than thiacloprid. More than 95% acetamiprid dissipated within 24 h as compared to approximately 70% dissipation observed for thiacloprid.

The six isomeric trideuteriopyridines and the three isomeric tetradeuteriopyridines undergo phototransposition upon S0 --> S2 (pi, pi*) excitation in the vapor phase at 254 nm. On the basis of the products formed, the six trideuteriopyridine isomers can be divided into two triads. Similarly, the three isomeric tetradeuteriopyridines also constitute a triad. Irradiation of any one member of each triad results in the formation of the other two members of that triad. These isomerizations are consistent with a mechanism involving photocyclization, nitrogen migration around the five sides of the cyclopentenyl ring, and rearomatization.

The high resolution X-band electron para magnetic resonance (EPR) spectrum of quintet pyridyl-2,6-dinitrene was recorded after the photolysis of 4-amino-2,6-diazido-3,5-dichloropyridine in solid argon matrix at 15 K. This spectrum represents a new type of powder EPR spectra that are characteristic for quintet spin states with zero-field splitting parameters |E(q)/D(q)| approximately 1/4. All EPR lines of the quintet dinitrene were unambiguously assigned based on the eigenfield calculations of the Zeeman energy levels and angular dependencies of resonance magnetic fields. Owing to the high resolution of the experimental EPR spectrum, zero-field splitting parameters of the quintet dinitrene were determined with a high accuracy: D(q)=0.2100+/-0.0005 cm(-1) and E(q)=-0.0560+/-0.0002 cm(-1). These parameters provide correct information regarding the molecular angle Theta and distance r between two triplet sites in the molecule of quintet dinitrene. The measured molecular angle Theta=114.2 degrees+/-0.2 degrees is in excellent agreement with results of the density functional theory calculations. The analysis of the magnetic parameters shows that the spin population on the nitrene units in the quintet dinitrene is greater than that on the nitrene unit in the triplet nitrene.

A combination of cobalt(II) complexes and pyridine ligands carrying organic spins, aminoxyl and carbene, provided single-molecule magnets with Stotal = 3/2 in diluted frozen solutions.

[3]- and [5]-ladderanes obtained by way of template-controlled syntheses conducted in the organic solid state have been characterized via He I photoelectron (PE) spectroscopy. The results provide a first correlation with X-ray crystallographic structure data and establish the reliability of quantum chemical DFT (B3LYP/6-31G*) and ab initio HF calculations in predicting geometrical and electronic structures of molecular ladder frameworks.

The degradation of 2-chloropyridine (2-CPY) and its degradation primary product 2-hydroxypyridine (2-HPY) was studied by means of ultraviolet (UV) irradiation at 254nm. Photolytic and photocatalytic experiments were conducted on 2-CPY and 2-HPY aqueous solutions in a batch reactor with internal recycle in laminar and turbulent conditions at 50 degrees C in a closed but not airtight system with and without additional aeration, at solution ambient pH and at controlled pH conditions, with use and in the absence of radical scavenger. The solution volume was 0.4L and initial substrate concentrations were approximately 2.6mmol/L (0.25-0.3g/L depending on the substrate). Where applicable 1g/L TiO(2) (P-25) was used, suspended in the liquid in a form of turbulent slurry or using a glass tube around the UV-lamp on which a fixed TiO(2) catalytic layer had been deposited. At the aforementioned conditions 2-CPY readily degrades photolytically, the catalytic path having very little influence. In all cases 2-CPY produces 2-HPY which further degrades to other products. Aeration, pH and the presence of catalyst and/or radical scavengers do not affect the rate of decomposition of 2-CPY, but have a strong influence on the further decomposition of the produced 2-HPY. 2-HPY decomposition proceeds both catalytically and photolytically following oxygen dependent and oxygen independent pathways.

The abiotic degradation of the new antifouling agent, triphenylborane pyridine (TPBP), was investigated in buffer solutions having different pH values (pH 5, 7, and 9), and in artificial and natural seawater to estimate environmental fate of TPBP. The TPBP in these waters was decomposed by a seven-day hydrolysis process at 50 degrees C both in the dark and a photolysis process under UV-A irradiation using a high-pressure mercury lamp for periods up to 24h. TPBP hydrolysis was significantly enhanced by acidic pH solutions. The photolysis rate of TPBP was higher in acidic pH solutions than in neutral or basic pH solutions, and was highest in natural seawater, which could have contained naturally dissolved organic matter. Two degradation products, phenol and an unknown substance (Peak #1), were observed during the hydrolysis and photolysis studies of TPBP. The concentration of these substances after a one-day photolysis treatment was higher than after a seven-day hydrolysis treatment. The degradation rate of TPBP in the five test water samples was related to the simultaneous photolysis formation of phenol and Peak #1. However, the degradation rate of TPBP was not related to the formation of the hydrolysis products. Therefore, it is suggested that photodegradation of TPBP follows a different pathway to the hydrolysis degradation of TPBP. Our results indicate the chemical and photochemical reaction of TPBP in water occurs in natural aquatic environments.

The photochemical behavior of the antifouling agent zinc pyrithione (ZnPT) was studied in aqueous media of different composition under simulated solar irradiation using a xenon light source. The influence of important constituents of natural water (dissolved organic matter and nitrate) was also examined using a multivariate kinetic model. It was found that photodegradation proceeds via a pseudo first-order reaction. Kinetic experiments were monitored by LC-MS and photolytic half-lives ranging between 9.2 and 15.1 min have been observed. The increasing concentration of dissolved organic matter (DOM) accelerates the photolysis reaction, while the effect of nitrate ions was also positive since it increased the degradation rate, but to a lesser extent. Irradiation of the aqueous ZnPT solutions gave rise to several transformation products that were isolated by means of solid-phase extraction using poly(styrene-divinylbenzene) extraction disks. These byproducts were identified using liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry. Besides 2-pyridinesulfonic-acid, other degradation products formed included pyridine-N-oxide, 2-mercaptopyridine, 2,2'-dithiobis(pyridine-N-oxide), 2,2-dipyridyl disulfide and the pyridine/pyrithione mixed disulfide, 2,2'-dithiobispyridine mono-N-oxide (PPMD).

The potential energy surfaces corresponding to the photochemical reactions of pyridine, phosphinine, and arsabenzene have been investigated by employing the CAS(6,6)/6-311G(d,p) and MP2-CAS-(6,6)/6-311++G(3df,3pd)//CAS(6,6)/6-311G(d,p) methods. The thermal (or dark) reactions of these reactant species have also been examined using the same level of theory. The mechanisms of drastic structural change in the excited- and ground-state reactions of pyridine, phosphinine, and arsabenzene and the differences between them are elucidated. The theoretical investigations suggest that conical intersections play a crucial role in their photoisomerization reactions. The results obtained allow a number of predictions to be made.

Gas phase complexes Mg*+ (2,6-difluoropyridine) (1) and Mg*+ (pentafluoropyridine) (2) have been subjected to photodissociation in the spectral range of approximately 230-440 nm. Except for the evaporative photofragment Mg*+ , the primary photoproduct for is C(5)H(3)N*(+), which is associated with the rupture of two C-F bonds by the photoexcited Mg*+ , forming very stable MgF(2). In contrast, the direct loss of MgF(+) is more favorable for due to fluorine substitution. Given enough energy, C(5)H(3)N*(+) can undergo decomposition to form C(4)H(2)*(+) and HCN. These results are very different from those for Mg*+ (2-fluoropyridine), highlighting the significance of the additional F at C6 of and . Density functional theory (DFT) calculations have been employed to examine the geometries and energetics of the complexes as well as relevant reaction mechanisms. All of the complexes feature the direct attachment of Mg*+ to the N atom. The key intermediate is found to be FMg(+) (C(5)H(x)F(4-x)N) (x = 3 or 0), which can lead to the formation of MgF(+) directly or MgF(2) through activation of another C-F bond adjacent to N, producing the pyridyne radical cations. However, hydrogen-transfer prior to the rupture of the second C-F bond followed by ring-opening of C(5)H(3)N*(+) may result in the formation of chain forms of C(5)H(3)N*(+). The influence of the fluorine substitution on the competition of the two routes have been demonstrated.

Zinc pyrithione (ZnPT) or copper pyrithione (CuPT) have been effectively used as ship-antifouling agents, as an alternative to organotin compounds. Because of their instability in light and a lack of suitable analytical procedures, there is little data on their residue levels in environmental matrices. It is possible to investigate the fate of such compounds by toxicity alteration with certain treatments. The purpose of this study was to evaluate the degradation of pyrithiones through toxicity reduction by near ultraviolet (UV-A) irradiation. Metal pyrithiones dissolved in acetonitrile were irradiated with a UV-A lamp for 0, 0.5, 1, and 2 h, and were subjected to UV spectral measurement and toxicity evaluation using both sea urchin and freshwater rotifer bioassays. For the bioassays, photolyzed samples were dissolved in dimethyl sulfoxide after evaporation of the acetonitrile. The changes in UV spectra of photolyzed ZnPT or CuPT showed a time-dependent degradation, and the UV spectra at 2 h irradiation suggested substantial decomposition. Toxicities of ZnPT and CuPT were 12 and 5 microg/L as 24 h LC50 to the survival of rotifers and 10(-6) ng/L and 2.3 ng/L as 27 h EC50 to normal pluteus formation, respectively. By evaporation of the acetonitrile, the EC50 of ZnPT was 2.2 ng/L, which was the same as that of CuPT. The EC50s of ZnPT or CuPT for both species increased with longer irradiation times. Photolyzed ZnPT or CuPT demonstrated substantial degradation in the UV spectra, but possessed marked toxicity, which is probably due to toxic degradation products. One reason why photolyzed CuPT was toxic to rotifers was explained by the high toxicity of copper ions formed by UV-A irradiation., (Copyright 2006 Wiley Periodicals, Inc.)

Fluoropyridyl derivatives of [3,2-c]pyrazolo-corticosteroids have high affinity for the glucocorticoid receptor (GR) and are highly active glucocorticoids. They are thus considered to be excellent candidates for PET imaging of GR containing tissues when labeled with fluorine-18 (t(1/2)=110 min). Previously reported syntheses of these fluorinated glucocorticoids were accomplished by conventional thermal nucleophilic halogen exchange reactions with chloropyridyl precursors. These reactions were found to proceed at rates too slow for feasible application to radiosynthesis using [(18)F]fluoride. We have applied microwave-heating methods to these reactions and found that significant rate enhancements can be realized. Kinetic experiments showed an average relative rate ratio of 3/1 for microwave versus conventional heating and preparative experiments showed an average relative conversion ratio of 4.5/1 during the initial 120 min, a period approximating one half-life of the isotope. The microwave method described was used to prepare previously unreported 2'-(2-fluoro-4-pyridyl)-11beta,17,21-trihydroxy-16alpha-methyl-20-oxo-pregn-4-eno-[3,2-c]-pyrazole, which was evaluated for biological activity.

A simple and efficient synthesis of 2-amino pyrido[2,3-d]pyrimidine derivatives was accomplished via a three-component reaction under microwave irradiation without catalyst. This method had many dramatic advantages such as the short reaction time, high yield, and broad substrate scope, as well as convenient operation. We provide new series of potential biologically active compounds as inhibitors of Cdk4.

Microwave reaction of RuCl3 with 2,2'-bipyridinyl-4,4'-dicarboxylic acid diethyl ester (debpy) in ethylene glycol generated Ru(bpy)3(2+) instead of the expected Ru(debpy)3(2+). Gas chromatography-mass spectrometry analysis of the headspace revealed CO2, and Ru(bpy)3(2+) was recovered from the filtrate. Further experiments suggest that RuCl3 decarboxylates debpy during microwave synthesis.

One-electron guanine oxidation in DNA has been investigated in anionic reverse micelles (RMs). A photochemical method for generating Ru3+ from the ruthenium polypyridyl complex tris(2-2'-bipyridine)ruthenium(II) chloride ([Ru(bpy)3]Cl2) is combined with high-resolution polyacrylamide gel electrophoresis (PAGE) to quantify piperidine-labile guanine oxidation products. As characterized by emission spectroscopy of Ru(bpy)3(2+), the addition of DNA to RMs containing Ru(bpy)3(2+) does not perturb the environment of Ru(bpy)3(2+). The steady-state quenching efficiency of Ru(bpy)3(2+) with K3[Fe(CN)6] in buffer solution is approximately 2-fold higher than that observed in RMs. Consistent with the difference in quenching efficiency in the two media, a 1.5-fold higher yield of piperidine-labile damage products as monitored by PAGE is observed for duplex oligonucleotide in buffer vs RMs. In contrast, a 13-fold difference in the yield of PAGE-detected G oxidation products is observed when single-stranded DNA is the substrate. Circular dichroism spectra showed that single-stranded DNA undergoes a structural change in anionic RMs. This structural change is potentially due to cation-mediated adsorption of the DNA phosphates on the anionic headgroups of the RMs, leading to protection of the guanine from oxidatively generated damage.

Mono- and binuclear complexes of (Re(CO)3Cl) with dipyrido[2,3-a:3',2'-c]-6,7-dimethylphenazine (ppbMe2) were synthesised and their photophysical properties probed using picosecond time-resolved infrared spectroscopy (TRIR). Excitation of these complexes in solution at 400 nm produces short-lived excited states. The IR spectrum of the excited state of the mononuclear [Re(CO)3Cl(ppbMe2)] have nu(CO) bands shifted to higher wavenumber relative to those of the ground state. This is consistent with formation of a (3)MLCT excited state. The IR spectrum of the excited state of the bimetallic [(Re(CO)3Cl)2(micro-ppbMe2)] shows the formation of two distinct groups of nu(CO) bands. This is interpreted as the formation of two distinct Re sites arising from a localised MLCT state with formally oxidised Re centre and a formally reduced bridging ligand. The nu(CO) bands of the adjacent Re centre are affected by the reduction of the bridging ligand. On the IR timescale the excited state structure is best formulated as [Cl(CO)3Re(II)(micro-ppbMe2 *-)Re(I)(CO)3Cl].

[2.n](2,6)Pyridinocrownophanes (3a-e) were efficiently prepared by intramolecular [2 + 2] photocycloaddition of vinylpyridine derivatives under irradiation using a 400-W high-pressure mercury lamp through a Pyrex filter. They were of cis-configuration with respect to the cyclobutane ring, which was proven by the specific methine proton NMR resonances at delta 3.98-4.08. From ESI-MS analysis 3a-e were found to form 1:1 complexes with Ag+ cation. In a liquid-liquid extraction, 3 showed the highest affinity toward Ag+ cation among several heavy metal nitrates. In this series, 3c possessing four ethereal oxygen atoms was found to show the highest Ag+ affinity, according to the liquid-liquid extraction and determination of stability constant with the cation. The photoreactivity of precursor vinylpyridines is discussed by the predictor gamma(r(c)) proposed by Caldwell.

Data related to the pH-dependent photophysics of a class of rhenium complexes containing the hydroxypyridine ligand are presented. Data include ground-state pK(a) values, emission energies, and lifetimes. The complexes all have ground-state pK(a) values near 7.0 and exhibit a dramatic change in emission intensity near this pH. The lifetimes of these complexes, however, are constant over this pH range. A model is presented to account for the observed photophysical behavior. The pH-dependent emission properties of these species make them good candidates for luminescence-based pH probes, especially in the environmental and biomedical fields.

Four-carbon-tethered pyridones undergo photocycloaddition to give exclusively trans-[4 + 4] products. The presence of a tether alcohol engenders a solvent-dependent diastereoselectivity for the cycloaddition by intramolecular hydrogen bonding to the adjacent pyridone. Following cycloaddition, the alcohol can deliver a carbonyl group to the proximal, hindered amide nitrogen, leading to a very facile amide hydrolysis.

The back thermal cis-trans isomerization reaction of stilbazole betaine in the presence of metmyoglobin was studied. The catalytic effect of metmyoglobin heme on the back thermal cis-trans isomerization reaction of stilbazole betaine was observed.

In this study, the mitochondrial phototoxicity of the cationic rhodacyanine MKT-077 was investigated by comparing its effects on the inhibition of mitochondrial respiration and the structural integrity of mitochondrial DNA (mtDNA) in the presence and absence of added high-intensity visible light (7.5 J/cm2). Results indicate that photoirradiation significantly enhances the mitochondrial toxicity of MKT-077 at both the biochemical and DNA levels. For example, the concentration of MKT-077 required to achieve one-half maximal inhibition of ADP-stimulated respiration was observed to be 6-fold lower in the presence versus absence of high-intensity light (one-half maximal inhibition at 2.5 versus 15 microg MKT-077/ mg, respectively). In addition, photoirradiation produced a 25-fold increase in inhibition of succinate-cytochrome c reductase activity by MKT-077 (one-half maximal inhibition at 2 versus 50 microg MKT-077/ml, +/-light, respectively) and a 6-fold increase in inhibition of cytochrome oxidase activity (one-half maximal inhibition at 5 versus 30 microg MKT-077/ml, +/-light, respectively). Furthermore, the combination of 25 microg/ml MKT-077 and 7.5 J/cm2 visible light caused significant degradation of mtDNA in isolated rat liver mitochondria, whereas the same concentration of dye in the absence of light had only a modest effect on mtDNA. Evaluation of light-induced MKT-077 lipid peroxidation in mitochondrial membrane fragments by the thiobarbituric acid test and by measurement of nonrespiratory-linked oxygen uptake suggests that mitochondrial phototoxicity by MKT-077 may be the result of lipid peroxidation via reactive oxygen species. These results have important implications with regard to the potential use of MKT-077 in photochemotherapy.

The grafting of 4-vinyl pyridine (VP) to styrene-butadienestyrene triblock copolymer (SBS) by radiation-induced graft copolymerization was studied. The cohesive properties such as cohesive energy (Ecoh), molar volume (V), solubility parameter (delta), molar molecular weight (WM), specific volume (Vg), and density (1/Vg) of SBS-g-VP graft copolymer were calculated according to the group contribution of Fedors. The morphology of SBS-g-VP was studied by optical polarizing microscopy. We also measured the glass transition temperature and the mechanical properties of SBS-g-VP graft copolymer. Contact angle and blood-clotting time experiments were also performed to evaluate the biocompatibility of SBS-g-VP. A second domain was found in the SBS-g-VP graft copolymer, which resulted in different properties between SBS-g-VP and SBS. The blood compatibility of SBS-g-VP as measured by the Lee-White clotting test was better than that of SBS and polystyrene.

N-Hydroxypyridine-2-thione (2-HPT), known to release hydroxyl radicals on irradiation with visible light, and two related compounds, viz. N-hydroxypyridine-4-thione (4-HPT) and N-hydroxyacridine-9-thione (HAT), were tested for their potency to induce DNA damage in L1210 mouse leukemia cells and in isolated DNA from bacteriophage PM2. DNA single-strand breaks and modifications sensitive to various repair endonucleases (Fpg protein, endonuclease III, exonuclease III, T4 endonuclease V) were quantified. Illumination of cell-free DNA in the presence of 2-HPT and 4-HPT gave rise to damage profiles characteristic for hydroxyl radicals, i.e. single-strand breaks and the various endonuclease-sensitive modifications were formed in the same ratios as after exposure to established hydroxyl radical sources. In contrast, HAT plus light gave rise to a completely different DNA damage profile, namely that characteristic for singlet oxygen. Experiments with various scavengers (t-butanol, catalase, superoxide dismutase) and in D2O as solvent confirmed that hydroxyl radicals are directly responsible for the DNA damage caused by photoexcited 2-HPT and 4-HPT, while the damage by HAT plus light is mediated by singlet oxygen and type I reactions. The type of DNA damage characteristic of hydroxyl radicals was also observed in L1210 mouse leukemia cells when treated with 2-HPT plus light or with H2O2 at 0 degrees C. t-Butanol (2%) inhibited the cellular DNA damage by approximately 50%. A dose of 2-HPT plus light that generated single-strand breaks at a frequency of 5 x 10(-7)/bp was associated with 50% cell survival. No DNA damage and cytotoxicity was observed after treatment with 2-HPT in the dark. We propose that 2-HTP and 4-HTP may serve as new agents to study the consequences of DNA damage induced by hydroxyl radicals in cells. In addition, the data provide direct evidence that hydroxyl radicals are ultimately responsible for the genotoxic effects caused by H2O2 in the dark.

We studied the effects of gamma irradiation on the dimensions, mechanical and material properties, and mature hydroxypyridinium crosslink density of collagen in goat patellar tendon-bone specimens. Left and right patellar tendon-bone units were removed from 10 adult female goats and were bisected longitudinally. Each tendon half was frozen, and then the left halves were exposed to 4, 6, or 8 Mrad (40,000, 60,000, or 80,000 Gy) of gamma irradiation. The contralateral tendon halves served as controls (no irradiation). Each specimen then was loaded to failure in tension, and its soft-tissue midsubstance was processed to measure collagen content and hydroxypyridinium crosslink density. Dose-dependent reductions in the mechanical properties were found, including 46% (p < 0.01) and 18% (p < 0.05) reductions in maximum force and stiffness, respectively, at 4 Mrad. Similar reductions were noted in material properties, including 37% (p < 0.005) and 8% (p > 0.05) reductions in maximum stress and modulus, respectively, at 4 Mrad. These results are consistent with our previous report involving 2 and 3 Mrad (20,000 and 30,000 Gy) of exposure. We also found significant decreases in hydroxypyridinium crosslink density with 6 Mrad of irradiation (p < 0.05). However, since only one biomechanical parameter (modulus) correlated significantly with only one biochemical measure (hydroxypyridinium crosslink density) (p < 0.05), other possible mechanisms also are being explored to more fully explain these dose-dependent changes.