Theoretical Study on the Photophysical and Photochemical Properties of Elsinochrome A

Abstract

Elsinochrome A (EA) is one of the important perylenequinonoid photosensitizers (PQPs); however, its photophysical and photochemical properties were given less attention in comparsion with other PQPs. In view of the successful use of quantum chemical methods, especially time-dependent density functional theory (TD-DFT), in investigating the photo-physico- chemical characters of various photosensitizers, we attempt to explore the photophysical and photosensitive properties of EA by theoretical methods. Firstly, the absorption spectra and lowest-lying T₁ excitation energy of EA were estimated by TD-DFT calculations. Then, the photosensitizing mechanisms of EA were explored. It was found that EA can photo-generate ¹O₂ through energy transfer in both benzene and DMSO. However, EA gives birth to O₂ ^? only in DMSO, and it is E_A ^.- generated from autoionization reactions that is responsible for the O₂ ^.-- generation, which gains some deeper insights into the photosensitive behaviors of EA.     

Superoxide flux in endothelial cells via the chloride channel-3 mediates intracellular signaling

Reactive oxygen species (ROS) have been implicated in both cell signaling and pathology. A major source of ROS in endothelial cells is NADPH oxidase, which generates superoxide (O(2)(.-)) on the extracellular side of the plasma membrane but can result in intracellular signaling. To study possible transmembrane flux of O(2)(.-), pulmonary microvascular endothelial cells were preloaded with the O(2)(.-)-sensitive fluorophore hydroethidine (HE). Application of an extracellular bolus of O(2)(.-) resulted in rapid and concentration-dependent transient HE oxidation that was followed by a progressive and nonreversible increase in nuclear HE fluorescence. These fluorescence changes were inhibited by superoxide dismutase (SOD), the anion channel blocker DIDS, and selective silencing of the chloride channel-3 (ClC-3) by treatment with siRNA. Extracellular O(2)(.-) triggered Ca(2+) release in turn triggered mitochondrial membrane potential alterations that were followed by mitochondrial O(2)(.-) production and cellular apoptosis. These "signaling" effects of O(2)(.-) were prevented by DIDS treatment, by depletion of intracellular Ca(2+) stores with thapsigargin and by chelation of intracellular Ca(2+). This study demonstrates that O(2)(.-) flux across the endothelial cell plasma membrane occurs through ClC-3 channels and induces intracellular Ca(2+) release, which activates mitochondrial O(2)(.-) generation.     

Protein-cofactor interactions in bacterial reaction centers from Rhodobacter sphaeroides R-26: II. Geometry of the hydrogen bonds to the primary quinone formula by 1H and 2H ENDOR spectroscopy

The geometry of the hydrogen bonds to the two carbonyl oxygens of the semiquinone Q(A)(. -) in the reaction center (RC) from the photosynthetic purple bacterium Rhodobacter sphaeroides R-26 were determined by fitting a spin Hamiltonian to the data derived from (1)H and (2)H ENDOR spectroscopies at 35 GHz and 80 K. The experiments were performed on RCs in which the native Fe(2+) (high spin) was replaced by diamagnetic Zn(2+) to prevent spectral line broadening of the Q(A)(. -) due to magnetic coupling with the iron. The principal components of the hyperfine coupling and nuclear quadrupolar coupling tensors of the hydrogen-bonded protons (deuterons) and their principal directions with respect to the quinone axes were obtained by spectral simulations of ENDOR spectra at different magnetic fields on frozen solutions of deuterated Q(A)(. -) in H(2)O buffer and protonated Q(A)(. -) in D(2)O buffer. Hydrogen-bond lengths were obtained from the nuclear quadrupolar couplings. The two hydrogen bonds were found to be nonequivalent, having different directions and different bond lengths. The H-bond lengths r(OH) are 1.73 +/- 0.03 Angstrom and 1.60 +/- 0.04 Angstrom, from the carbonyl oxygens O(1) and O(4) to the NH group of Ala M260 and the imidazole nitrogen N(delta) of His M219, respectively. The asymmetric hydrogen bonds of Q(A)(. -) affect the spin density distribution in the quinone radical and its electronic structure. It is proposed that the H-bonds play an important role in defining the physical properties of the primary quinone, which affect the electron transfer processes in the RC.     

In vitro knockout of human p47phox blocks superoxide anion production and LDL oxidation by activated human monocytes

We previously reported that superoxide dismutase (SOD) blocked human monocyte oxidation of LDL and therefore concluded that superoxide anion (O(2)(.-)) was required for oxidation. Others, however, have suggested that SOD may inhibit by mechanisms alternative to the dismutation of O(2)(.-). This study definitively addresses the involvement of O(2)(.-) in monocyte oxidation of LDL. Using an antisense ODN designed to target p47phox mRNA, we found that treatment of monocytes with antisense ODN caused a substantial and selective decrease in expression of p47phox protein, whereas sense ODN was without effect. Corresponding functional assays demonstrated that antisense ODN inhibited production of O(2)(.-). As sense ODN caused no inhibition of O(2)(.-) production, these results suggested that inhibition of p47phox expression caused reduction in O(2)(.-) production. Evaluation of the contribution of O(2)(.-) production to monocyte-mediated oxidation of LDL lipids confirmed that O(2)(.-) production is required for LDL lipid oxidation as antisense ODN treatment significantly inhibited LDL oxidation whereas sense ODN treatment caused no inhibition. This is the first report of the reduction of NADPH oxidase activity in intact human monocytes by directly targeting the mRNA of a significant member of this enzyme complex. Our results provide convincing data that O(2)(.-) is indeed required for monocyte-mediated LDL oxidation.     

Kinetic study on ESR signal decay of nitroxyl radicals,potent redox probes for in vivo ESR spectroscopy,caused by reactive oxygen species

The effect of the chemical structure of nitroxyl spin probes on the rate at which ESR signals are lost in the presence of reactive oxygen species (ROS) was examined. When the spin probes were reacted with either hydroxyl radical (.OH) or superoxide anion radical (O(2)(.-)) in the presence of cysteine or NADH, the probes lost ESR signal depending on both their ring structure and substituents. Pyrrolidine nitroxyl probes were relatively resistant to the signal decay caused by O(2)(.-) with cysteine/NADH. Signal decay rates for these reactions correlated with reported redox potentials of the nitroxyl/oxoammonium couple of spin probes, suggesting that the signal decay mechanism in both cases involves the oxidation of a nitroxyl group. The apparent rate constants of the reactions between the spin probe and .OH and between the spin probe and O(2)(.-) in the presence of cysteine were estimated using mannitol and superoxide dismutase (SOD), respectively, as competitive standards. The rate constants for spin probes and .OH were in the order of 10(9) M(-1) s(-1), much higher than those for the probes and O(2)(.-) in the presence of cysteine (10(3)-10(4) M(-1) s(-1)). These basic data are useful for the measurement of .OH and O(2)(.-) in living animals by in vivo ESR spectroscopy.     

Reactivity of ubiquinone and ubiquinol with superoxide and the hydroperoxyl radical: implications for in vivo antioxidant activity

Endogenous ubiquinones (UQ) such as coenzyme Q(10) are essential electron carriers in the mitochondrial respiratory chain, and the reduced ubiquinol form (UQH(2)) is a chain-breaking antioxidant, decreasing oxidative damage caused by lipid peroxidation within mitochondria. Consequently, exogenous UQ are used as therapies to decrease mitochondrial oxidative damage. The proximal radical produced during mitochondrial oxidative stress is superoxide (O(2)(.-)) and the reaction between UQ and O(2)(.-) to form the ubisemiquinone radical anion (UQ(.-)) may also be important for the scavenging of O(2)(.-) by exogenous UQ. The situation in vivo is that many UQ are predominantly located in the hydrophobic membrane core, from which O(2)(.-) will be excluded but its conjugate acid, HOO(.), can enter. The reactivity of UQ or UQH(2) with HOO(.) has not been reported previously. Here a pulse radiolysis study on the reactions between UQ/UQH(2) and O(2)(.-)/HOO(.) in water and in solvent systems mimicking the surface and core of biological membranes has been undertaken. O(2)(.-) reacts very rapidly with UQ, suggesting that this may contribute to the scavenging of O(2)(.-) in vivo. In contrast, UQH(2) reacts relatively slowly with HOO(.), but rapidly with other oxygen- and carbon-centered radicals, indicating that the antioxidant role of UQH(2) is mainly in preventing lipid peroxidation.     

A comparative study of the effects of molsidomine and 3-morpholinosydnonimine on the redox status of rat erythrocytes and reticulocytes

After enzymic biotransformation, molsidomine (MO) acts via the metabolite 3-morpholinosydnonimine (SIN-1) through spontaneous liberation of nitric oxide (NO) and superoxide (O(2)(.-)). The aim of this study was to compare the effects of MO and its active metabolite SIN-1 on the redox status of rat erythrocytes and reticulocytes. Rat erythrocyte as well as reticulocyte-rich red blood cell (RBC) suspensions were aerobically incubated (2 h, 37 degrees C) without (control) or in the presence of different concentrations of MO or SIN-1. In rat erythrocytes, biotransformation of MO resulted in the production of NO and nitroxyl (NO(-)). Endogenous superoxide anion (O(2)(.-)) participated in peroxynitrite generation. SIN-1 simultaneously liberated NO and O(2)(.-), which formed peroxynitrite (at least in part), but the liberated NO predominantly reacted with haemoglobin, forming methaemoglobin in erythrocytes. In reticulocytes, MO and SIN-1 caused an increase in the levels of both nitrite and 3-nitrotyrosine (an indicator of peroxynitrite), whereas they decreased the level of O(2)(.-). In reticulocytes, MO was metabolized into SIN-1 which led to the generation of NO, which reacted with O(2)(.-) (endogenous or exogenous) forming reactive nitrogen species. In conclusion, there are two metabolic pathways for MO biotransformation: one causing NO and NO(-) generation predominantly in erythrocytes and the other, via SIN-1 metabolism, in reticulocytes. The main difference between the action of MO and SIN-1 was that the latter caused oxidative damage in RBCs.     

Ras-dependent and -independent regulation of reactive oxygen species by mitogenic growth factors and TGF-beta1.

Mitogenic growth factors and transforming growth factor beta1 (TGF-beta1) induce the generation of reactive oxygen species (ROS) in nonphagocytic cells, but their enzymatic source(s) and regulatory mechanisms are largely unknown. We previously reported on the ability of TGF-beta1 to activate a cell surface-associated NADH:flavin:O(2) oxidoreductase (NADH oxidase) that generates extracellular H(2)O(2). In this study, we compared the ROS-generating enzymatic systems activated by mitogenic growth factors and TGF-beta1 with respect to the primary reactive species produced (O(2)(.-) vs. H(2)O(2)), the site of generation (intracellular vs. extracellular) and regulation by Ras. We find that the mitogenic growth factors PDGF-BB, FGF-2, and TGF-alpha (an EGF receptor ligand) are able to rapidly (within 5 min) induce the generation of intracellular O(2)(.-) without detectable NADH oxidase activity or extracellular H(2)O(2) release. In contrast, TGF-beta1 does not stimulate intracellular O(2)(.-) production and the delayed induction of extracellular H(2)O(2) release is not associated with O(2)(.-) production. Expression of dominant-negative Ras (N17Ras) protein by herpes simplex virus-mediated gene transfer blocks mitogen-stimulated intracellular O(2)(.-) generation but has no effect on TGF-beta1-induced NADH oxidase activation/H(2)O(2) production. These results demonstrate that there are at least two distinctly different ROS-generating enzymatic systems in lung fibroblasts regulated by mitogenic growth factors and TGF-beta1 via Ras-dependent and -independent mechanisms, respectively. In addition, these findings suggest that endogenous production of ROS by growth factors/cytokines may have different biological effects depending on the primary reactive species generated and site of production.     

Involvement of superoxide generation in salicylic acid-induced stomatal closure in Vicia faba.

Salicylic acid (SA), the known mediator of systemic acquired resistance, induced stomatal closure of Vicia faba L. Application of SA to the epidermal peels evoked an elevation of chemiluminescence of Cripridina lucigenin-derived chemiluminescent reagent (CLA) which is sensitive to superoxide anion (O(2)(.-)). The SA-induced generation of chemiluminescence was suppressed by O(2)(.-)-specific scavengers superoxide dismutase (SOD) and 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron). These results suggest that O(2)(.-) was generated in epidermal peels by SA-treatment. A peroxidase inhibitor salicylhydroxamic acid (SHAM) inhibited guaiacol peroxidase activity and suppressed the SA-induced CLA chemiluminescence in the epidermal peels, suggesting that O(2)(.-) generation occurred by the peroxidase-catalyzed reaction as proposed for SA-treated tobacco cell suspension culture [Kawano et al. (1998) Plant Cell Physiol. 39: 721]. SOD, Tiron or SHAM suppressed the SA-induced stomatal closure. Moreover, application of superoxide-generating system also induced stomatal closure. These results support the concept of involvement of reactive oxygen species in signal transduction in SA-induced stomatal closure.     

Enhanced mitochondrial superoxide in hyperglycemic endothelial cells: direct measurements and formation of hydrogen peroxide and peroxynitrite

Hyperglycemic challenge to bovine aortic endothelial cells (BAECs) increases oxidant formation and cell damage that are abolished by MnSOD overexpression, implying mitochondrial superoxide (O(2)(.-)) as a central mediator. However, mitochondrial O(2)(.-) and its steady-state concentrations have not been measured directly yet. Therefore, we aimed to detect and quantify O(2)(.-) through different techniques, along with the oxidants derived from it. Mitochondrial aconitase, a sensitive target of O(2)(.-), was inactivated 60% in BAECs incubated in 30 mM glucose (hyperglycemic condition) with respect to cells incubated in 5 mM glucose (normoglycemic condition). Under hyperglycemic conditions, increased oxidation of the mitochondrially targeted hydroethidine derivative (MitoSOX) to hydroxyethidium, the product of the reaction with O(2)(.-), could be specifically detected. An 8.8-fold increase in mitochondrial O(2)(.-) steady-state concentration (to 250 pM) and formation rate (to 6 microM/s) was estimated. Superoxide formation increased the intracellular concentration of both hydrogen peroxide, measured as 3-amino-2,4,5-triazole-mediated inactivation of catalase, and nitric oxide-derived oxidants (i.e., peroxynitrite), evidenced by immunochemical detection of 3-nitrotyrosine. Oxidant formation was further evaluated by chloromethyl dichlorodihydrofluorescein (CM-H(2)DCF) oxidation. Exposure to hyperglycemic conditions triggered the oxidation of CM-H(2)DCF and was significantly reduced by pharmacological agents that lower the mitochondrial membrane potential, inhibit electron transport (i.e., myxothiazol), and scavenge mitochondrial oxidants (i.e., MitoQ). In BAECs devoid of mitochondria (rho(0) cells), hyperglycemic conditions did not increase CM-H(2)DCF oxidation. Mitochondrial O(2)(.-) formation in hyperglycemic conditions was associated with increased glucose metabolization in the Krebs cycle and hyperpolarization of the mitochondrial membrane.     

Relevance of molecular weight of chitosan and its derivatives and their antioxidant activities in vitro

The antioxidant potency of different molecular weight (DMW) chitosan and sulfated chitosan derivatives was investigated employing various established in vitro systems, such as superoxide (O(2)(.-))/hydroxyl ((-.)OH) radicals scavenging, reducing power, iron ion chelating. As expected, we obtained several satisfying results, as follows: firstly, low molecular weight chitosan had stronger scavenging effect on O(2)(.-) and (-.)OH than high molecular weight chitosan. For example the O(2)(.-) scavenging activity of low molecular weight chitosan (9 kDa) and high molecular weight chitosan (760 kDa) were 85.86% and 35.50% at 1.6 mg/mL, respectively. Secondly, comparing with DMW chitosan, DMW sulfated chitosans had the stronger inhibition effect on O(2)(.-). At 0.05 mg/mL, the scavenging activity on O(2)(.-) reached 86.26% for low molecular weight chitosan sulfate (9 kDa), but that of low molecular weight chitosan (9 kDa) was 85.86% at 1.6 mg/mL. As concerning chitosan and sulfated chitosan of the same molecular weight, scavenging activities of sulfated chitosan on superoxide and hydroxyl radicals were more pronounced than that of chitosan. Thirdly, low molecular weight chitosan sulfate had more effective scavenging activity on O(2)(.-) and (-.)OH than that of high molecular weight chitosan sulfate. Fourthly, DMW chitosans and sulfated chitosans were efficient in the reducing power, especially LCTS. Their orders were found to be LCTS>CTS4>HCTS>CTS3>CTS2>CTS1>CTS. Fifthly, CTS4 showed more considerable ferrous ion-chelating potency than others. Finally, the scavenging rate and reducing power of DMW chitosan and sulfated derivatives increased with their increasing concentration. Moreover, change of DMW sulfated chitosans was the most pronounced within the experimental concentration. However, chelating effect of DMW chitosans were not concentration dependent except for CTS4 and CTS1.     

Production of reactive oxygen intermediates (O(2)(.-), H(2)O(2), and (.)OH) by maize roots and their role in wall loosening and elongation growth

Cell extension in the growing zone of plant roots typically takes place with a maximum local growth rate of 50% length increase per hour. The biochemical mechanism of this dramatic growth process is still poorly understood. Here we test the hypothesis that the wall-loosening reaction controlling root elongation is effected by the production of reactive oxygen intermediates, initiated by a NAD(P)H oxidase-catalyzed formation of superoxide radicals (O(2)(.-)) at the plasma membrane and culminating in the generation of polysaccharide-cleaving hydroxyl radicals ((.)OH) by cell wall peroxidase. The following results were obtained using primary roots of maize (Zea mays) seedlings as experimental material. (1) Production of O(2)(.-), H(2)O(2), and (.)OH can be demonstrated in the growing zone using specific histochemical assays and electron paramagnetic resonance spectroscopy. (2) Auxin-induced inhibition of growth is accompanied by a reduction of O(2)(.-) production. (3) Experimental generation of (.)OH in the cell walls with the Fenton reaction causes wall loosening (cell wall creep), specifically in the growing zone. Alternatively, wall loosening can be induced by (.)OH produced by endogenous cell wall peroxidase in the presence of NADH and H(2)O(2). (4) Inhibition of endogenous (.)OH formation by O(2)(.-) or (.)OH scavengers, or inhibitors of NAD(P)H oxidase or peroxidase activity, suppress elongation growth. These results show that juvenile root cells transiently express the ability to generate (.)OH, and to respond to (.)OH by wall loosening, in passing through the growing zone. Moreover, inhibitor studies indicate that (.)OH formation is essential for normal root growth.     

Prooxidant and antioxidant action of 4-(4-phenoxybenzoyl)benzoic acid derivatives

4-(4-Phenoxybenzoyl)benzoic acid derivatives (PBADs) were found to inhibit rat and human alpha-reductase isozymes 1 and 2 in vitro. Chemiluminescence (CL), electron spin resonance, spin trapping techniques, and spectrophotometry were used to examine the effect of PBADs on reactive oxygen species (superoxide radical, O(2)(.-); hydroxyl radical, HO(*); singlet oxygen, (1)O(2)) generating systems. All test compounds at a concentration of 0.5 mM enhanced the CL from O(2)(.-) up to fivefold, which was recorded as the light sums during 1 min. At 0.38 mM PBAD enhanced production of HO(*) from H(2)O(2) in the presence of Co(II) up to 90%, as measured by a deoxyribose assay. Using the spin trap agent 5,5-dimethyl-1-pyrroline-N-oxide, it was found that the amplitude of the signal arising from the Fenton-like reaction [Co(II)/H(2)O(2)] was significantly diminished by the test compounds. The compounds also inhibited the (1)O(2) dependent 2,2,6,6-tetramethylpiperidine-N-oxide radical, which is generated in the acetonitrile/H(2)O(2) system. The measured rate constants of (1)O(2)-dimol quenching by PBAD were in the range of (0.8-2.6) x 10(8) M(-1) s(-1). The interaction between PBAD and (1)O(2) was also checked using a spectrophotometry method based on bleaching of p-nitrosodimethylaniline. These results indicate that PBAD may directly scavenge HO(*) and (1)O(2), but not O(2)(.-). However, the compounds that were examined had prooxidant ability under some reaction conditions.     

Roles of the reactive oxygen species-generating peroxidase reactions in plant defense and growth induction

Extracellularly secreted plant peroxidases (POXs) are considered to catalyze the generation of reactive oxygen species (ROS) coupled to oxidation of plant hormone indole-3-acetic acid (IAA) and defense-related compounds salicylic acid (SA), aromatic monoamines (AMAs) and chitooligosaccharides (COSs). This review article consists of two parts, which describe H(2)O(2)-dependent and H(2)O(2)-independent mechanisms for ROS generation, respectively. Recent studies have shown that plant POXs oxidize SA, AMAs and COSs in the presence of H(2)O(2) via a conventional POX cycle, yielding the corresponding radical species, such as SA free radicals. These radical species may react with oxygen, and superoxide (O(2)(.-)) is produced. Through the series of reactions 2 moles of O(2)(.-) can be formed from 1 moles of H(2)O(2), thus leading to oxidative burst. It has been revealed that the ROS induced by SA, AMAs and COSs triggers the increase in cytosolic Ca(2+) concentration. Actually POXs transduce the extracellular signals into the redox signals that eventually stimulate the intracellular Ca(2+) signaling required for induction of defense responses. On the other hand, IAA can react with oxygen and plant POXs in the absence of H(2)O(2), by forming the ternary complex enzyme-IAA-O(2), which readily dissociates into enzyme, IAA radicals and O(2)(.-). This article covers the recent reports showing that extracellularly produced hydroxy radicals derived from O(2)(.-) mediate the IAA-induced cell elongation. Here a novel model for IAA signaling pathway mediated by extracellular ROS produced by cell-wall POXs is proposed. In addition, possible controls of the IAA-POX reactions by a fungal alkaloid are discussed.     

Folic acid conjugates with photosensitizers for cancer targeting in photodynamic therapy: Synthesis and photophysical properties

Recent researches in photodynamic therapy have focused on novel techniques to enhance tumour targeting of anticancer drugs and photosensitizers. Coupling a photosensitizer with folic acid could allow more effective targeting of folate receptors which are over-expressed on the surface of many tumour cells. In this study, different folic acid–OEG-conjugated photosensitizers were synthesized, characterized and their photophysical properties were evaluated. The introduction of an OEG does not significantly improve the hydrophilicity of the FA–porphyrin. All the FA-targeted photosensitizers present good to very good photophysical properties. The best one appears to be Ce6. Molar extinction coefficient, fluorescence and singlet oxygen quantum yields were determined and were compared to the corresponding photosensitizer alone.     

Salicylic acid mediated by the oxidative burst is a key molecule in local and systemic responses of cotton challenged by an avirulent race of Xanthomonas campestris pv malvacearum

We analyzed the production of reactive oxygen species, the accumulation of salicylic acid (SA), and peroxidase activity during the incompatible interaction between cotyledons of the cotton (Gossypium hirsutum) cv Reba B50/Xanthomonas campestris pv malvacearum (Xcm) race 18. SA was detected in petioles of cotyledons 6 h after infection and 24 h post inoculation in cotyledons and untreated leaves. The first peak of SA occurred 3 h after generation of superoxide (O(2)(.-)), and was inhibited by infiltration of catalase. Peroxidase activity and accumulation of SA increased in petioles of cotyledons and leaves following H(2)O(2) infiltration of cotyledons from 0.85 to 1 mM. Infiltration of 2 mM SA increased peroxidase activity in treated cotyledons and in the first leaves, but most of the infiltrated SA was rapidly conjugated within the cotyledons. When increasing concentrations of SA were infiltrated 2. 5 h post inoculation at the beginning of the oxidative burst, the activity of the apoplastic cationic O(2)(.-)-generating peroxidase decreased in a dose-dependent manner. We have shown that during the cotton hypersensitive response to Xcm, H(2)O(2) is required for local and systemic accumulation of SA, which may locally control the generation of O(2)(.-). Detaching cotyledons at intervals after inoculation demonstrated that the signal leading to systemic accumulation of SA was emitted around 3 h post inoculation, and was associated with the oxidative burst. SA produced 6 h post infection at HR sites was not the primary mobile signal diffusing systemically from infected cotyledons.     

Synthesis, photophysical and photochemical studies of new water-soluble indium(III) phthalocyanines.

The preparation of water-soluble indium(III)phthalocyanine complexes is described for the first time in this study. Peripherally and non-peripherally 3-hydroxypyridine tetrasubstituted indium(III) phthalocyanines (5a, 6a) and their quaternarized derivatives (5b, 6b) have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy, electronic spectroscopy and mass spectra. The quaternarized compounds (5b, 6b) show excellent solubility in water, which makes them potential photosensitizers for use in photodynamic therapy (PDT) applications. Photochemical and photophysical measurements were conducted on 3-pyridyloxy appended indium(III) phthalocyanines in dimethylsulfoxide (DMSO) for non-ionic (5a, 6a) and in both DMSO and water for quaternarized (5b, 6b) derivatives. General trends are described for quantum yields of photodegradation, fluorescence lifetimes, fluorescence quantum yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds. The singlet oxygen quantum yields (Phi(Delta)), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) are very high (Phi(Delta) > 0.55). Thus, these complexes may be useful as Type II photosensitizers.     

Diving seals: are they a model for coping with oxidative stress?

The diving lifestyle of seals depends upon cardiovascular adjustments that result in frequent vasoconstriction of numerous organs. With the first post-dive breath, reperfusion allows for eliminating accumulated carbon dioxide (CO(2)) and reloading oxygen (O(2)) stores. Reintroduction of oxygenated blood raises the potential for production of reactive oxygen species (ROS) and the possibility that they may overwhelm the antioxidant defenses. This study addresses the question of possible adaptive responses that allow ringed seal (Phoca hispida) tissues to tolerate repeated cycles of ischemia and reperfusion, and thus protect them from oxidative insult. We obtained samples of ringed seal heart, muscle and kidney through the cooperation of native subsistence hunters at Barrow, Alaska. Samples were subjected to oxidative stress by addition of xanthine oxidase. Production of superoxide radical (O(2)(.-)), lipid peroxidation (as determined by the presence of thiobarbituric acid reactive substances, TBARS) and antioxidant capacity (AOX) were quantified by spectrophotometric analysis. Similarly treated pig tissues were anticipated to be more susceptible to oxidative stress. Contrary to expectations, pig tissues revealed less O(2)(.-) and TBARS compared with ringed seal tissues. These results show that ringed seal muscle, heart and kidney can be induced in vitro to generate ROS, and suggest that the living seal's protective defenses may depend upon O(2)(.-) production, similar to the protective effect of experimental preconditioning, or on enhanced intermediate scavenging, as evidenced by the larger AOX found in ringed seal tissues.     

痂囊腔菌素A对动物实体肿瘤的光动力治疗

从生物学角度研究了痂囊腔菌素A（EA）对黑色素瘤B-16实体肿瘤的光敏生物活性,实验结果显示,EA对黑色素瘤B-16实体肿瘤生长具有良好的抑制、杀伤效果,表明EA具有光敏抗肿瘤活性。     

Effect of structural modifications on photosensitizing activities of hypocrellin dyes: EPR and spectrophotometric studies.

Mono-substituted hypocrellin B (MHB) and di-substituted hypocrellin B (DHB) by mercaptoacetic acid are new photosensitizers synthesized to improve the red absorption and water solubility of the parent hypocrellin B (HB). The photochemistries (Type I and/or Type II) of MHB and DHB have been studied in homogeneous solutions using electron paramagnetic resonance (EPR) and spectrophotometric methods. In anaerobic homogeneous DMSO solution, DHB*- (or MHB*-) was predominantly photoproduced via self-electron transfer between the excited- and ground-state species. The presence of an electron donor significantly promotes the formation of the reduced form of DHB (or MHB). As compared with hypocrellin B, the efficiencies of DHB*- and MHB*- generation was enhanced obviously. When oxygen-saturated solutions of DHB (or MHB) were illuminated with 532 nm light, singlet oxygen (1O2), superoxide anion radical (O2*-), hydroxyl radical (*OH) and hydrogen peroxide (H2O2) were formed. DHB and MHB generate 1O2 with quantum yields of 0.18 and 0.22, respectively, which are much lower than that of HB (0.76) in chloroform. The superoxide anion radical was significantly enhanced by the presence of electron donors. The rate of O2*- production was also dependent on the concentration of DHB or MHB. Moreover, O2*- upon disproportionation can generate H2O2 and ultimately the highly reactive *OH via the Fenton reaction and other pathway with the involvement of DHB*- (or MHB*-). As in the case of DHB*- (or MHB*-), the efficiencies of O2*- and *OH generation by DHB and MHB were also enhanced obviously, consistent with the fact that DHB*- (or MHB*-) acts as the precursor of O2* and thus *OH. These findings suggest that the photodynamic actions of DHB and MHB may proceed via enhanced Type I mechanism and reduced Type II mechanism as compared with that of HB.