Involvement Of Singlet Oxygen Research Articles

Kinetics of Active Oxygen Species with Implications for Atmospheric Ozone Chemistry

Photochemical processes involving singlet oxygen (O2(a1Δ)), oxygen atoms, and ozone are critical in determining atmospheric ozone concentrations. Here we report on kinetic measurements and modeling that examine the importance of the reactions of vibrationally excited ozone. Oxygen atoms and O2(a1Δ) were produced by UV laser photolysis of ozone. Time-resolved absorption spectroscopy was used for O3 concentration measurements. It was found that vibrationally excited ozone formed by O + O2 + M O3(ν) + M recombination reacts effectively with O2(a1Δ) and O atoms. The reaction O3(υ) + O2(a1Δ) O + 2O2 results in a reduction of the ozone recovery rate due to O atom regeneration, whereas the reaction O3(υ) + O 2O2 removes two odd oxygen species, resulting in incomplete ozone recovery. The possible impact of these reactions on the atmospheric O2(a1Δ) and O3 budgets at altitudes in the range of 80–100 km is considered.

Mixed-ligand copper(II) phenolate complexes: Synthesis, spectral characterization, phosphate-hydrolysis, antioxidant, DNA interaction and cytotoxic studies

A series of phenol-based mixed-ligand copper(II) complexes of the type [CuL1–4(diimine)] (1–8), where L1–4=N1,N2-bis(5-substituted-2-hydroxybenzylidene)-1,2-ethylene/phenylenediimine and diimine=2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen), have been isolated and fully characterized by analytical and spectral techniques. Electronic spectra of complexes suggest Cu(II) cation has a d9 electronic configuration, adopting distorted octahedral geometry with axial elongation, due to Jahn–Teller effect. Electrochemical studies of complexes evidenced one-electron irreversible reduction wave in the cathodic region. The observed rate constant (k) values for the hydrolysis of 4-nitrophenylphosphate (4-NPP) are in the range of 0.25–3.82×10−2min−1. The obtained room temperature magnetic moment values (1.79–1.90BM) lies within the range observed for octahedral copper(II) complexes. Antioxidant studies revealed that these complexes possess considerable radical scavenging potency against DPPH. The binding studies of complexes with calf thymus DNA (CT-DNA) revealed intercalation with minor-groove binding, and the complex 4 exhibits highest binding activity than the other complexes. The cleavage activity on supercoiled pBR322 DNA revealed the involvement of hydroxyl radical and singlet-oxygen as reactive oxygen species, and complexes encourage binding to minor-groove. Further, the cytotoxicity of complex 4 on human hepatocellular liver carcinoma HepG2 cell line implies the cell death through apoptosis.

Mixed-ligand binuclear copper(II) complex of 5-methylsalicylaldehyde and 2,2′-bipyridyl: Synthesis, crystal structure, DNA binding and nuclease activity

A new mixed-ligand binuclear copper(II) complex [Cu(MS)(bpy)]2.(ClO4)2, built of 5-methylsalicylaldehyde and 2,2′-bipyridyl has been synthesized and characterized by using elemental analysis, IR and UV-Vis spectroscopy. Crystal structure of the complex shows that copper(II) ion lies in a square pyramidal coordination environment. The structure consists of two symmetrical half units in which the copper(II) ion of one half unit connected with the phenolate oxygen atom of other half unit along with one perchlorate anion in the crystal lattice as free molecule. Presence of uncoordinated perchlorate anion was also confirmed by IR spectroscopy. Absorption spectroscopy exhibits d-d transition at 628 nm, which further supports the square pyramidal geometry around the copper(II) ions. EPR spectrum of the copper(II) complex at room temperature shows a broad signal without any splitting pattern at g || = 2.26,g ⊥ = 2.03 and the magnetic moment (μ eff= 1.31 BM) obtained at room temperature indicate an antiferromagnetic interaction between the two copper(II) ions through phenoxide-bridge. Binding studies reveal that the complex possesses good binding propensity (K b = 5.2 ± 1.7 × 104 M−1) and bind to nitrogenous bases of DNA through intercalation. Nuclease activity of the complex with pBR322 DNA shows that the effect of hydrolytic cleavage is dose-dependent and the oxidative cleavage indicates the involvement of hydroxyl radical and singlet-oxygen as reactive oxygen species. Mixed-ligand binuclear copper(II) complex was isolated and characterized. The binding studies of the complex suggest the intercalation mode of binding with CTDNA. The nuclease activity with pBR322 DNA shows that the hydrolytic cleavage is dose-dependent and the oxidative mechanism implies the involvement of hydroxyl radical and singlet-oxygen as reactive oxygen species.

Role of reactive oxygen species in ultra-weak photon emission in biological systems

Ultra-weak photon emission originates from the relaxation of electronically excited species formed in the biological systems such as microorganisms, plants and animals including humans. Electronically excited species are formed during the oxidative metabolic processes and the oxidative stress reactions that are associated with the production of reactive oxygen species (ROS). The review attempts to overview experimental evidence on the involvement of superoxide anion radical, hydrogen peroxide, hydroxyl radical and singlet oxygen in both the spontaneous and the stress-induced ultra-weak photon emission. The oxidation of biomolecules comprising either the hydrogen abstraction by superoxide anion and hydroxyl radicals or the cycloaddition of singlet oxygen initiate a cascade of oxidative reactions that lead to the formation of electronically excited species such as triplet excited carbonyl, excited pigments and singlet oxygen. The photon emission of these electronically excited species is in the following regions of the spectrum (1) triplet excited carbonyl in the near UVA and blue–green areas (350–550nm), (2) singlet and triplet excited pigments in the green–red (550–750nm) and red-near IR (750–1000nm) areas, respectively and (3) singlet oxygen in the red (634 and 703nm) and near IR (1270nm) areas. The understanding of the role of ROS in photon emission allows us to use the spontaneous and stress-induced ultra-weak photon emission as a non-invasive tool for monitoring of the oxidative metabolic processes and the oxidative stress reactions in biological systems in vivo, respectively.

Oxidative cleavage of DNA by pentamethine carbocyanine dyes irradiated with long-wavelength visible light

Here we report the synthesis of seven symmetrical carbocyanine dyes in which two nitrogen-substituted benz[e]indolium rings are joined by a pentamethine bridge that is meso-substituted with chlorine or bromine versus hydrogen. The heteroatom of benz[e]indolium is modified with a phenylpropyl, methyl, or cationic quaternary ammonium group. In reactions containing micro molar concentrations of halogenated dye, irradiation at 575, 588, 623, or 700nm produces good photocleavage of plasmid DNA. UV–visible spectra show that the carbocyanines are in their H-aggregated and monomeric forms. Scavenger experiments point to the involvement of singlet oxygen and hydroxyl radicals in DNA photocleavage.

De Novo Generation of Singlet Oxygen and Ammine Ligands by Photoactivation of a Platinum Anticancer Complex

De Novo Generation of Singlet Oxygen and Ammine Ligands by Photoactivation of a Platinum Anticancer Complex

Silicon and Germanium Nanoparticles with Tailored Surface Chemistry as Novel Inorganic Fiber Brightening Agents

Low-molecular-weight organic molecules, such as coumarins and stilbenes, are used commercially as fluorescent whitening agents (FWAs) to mask photoyellowing and to brighten colors in fabrics. FWAs achieve this by radiating extra blue light, thus changing the hue and also adding to the brightness. However, organic FWAs can rapidly photodegrade in the presence of ultraviolet (UV) radiation, exacerbating the yellowing process through a reaction involving singlet oxygen species. Inorganic nanoparticles, on the other hand, can provide a similar brightening effect with the added advantage of photostability. We report a targeted approach in designing new inorganic silicon- and germanium-based nanoparticles, functionalized with hydrophilic (amine) surface terminations as novel inorganic FWAs. When applied on wool, by incorporation in a sol-gel Si matrix, the inorganic FWAs improved brightness properties, demonstrated enhanced photostability toward UV radiation, especially the germanium nanoparticles, and also generated considerably lower levels of reactive oxygen species compared to a commercial stilbene-based organic FWA, Uvitex NFW.

Spectroscopy of mixed molybdenum-vanadium oxides and catalytic oxidation of toluene

The EPR, FTIR, and XRD techniques are used to examine individual and mixed vanadiummolybdenum oxides of composition (1 − x)V2O5: xMoO3 prepared by coprecipitation. The phase and structural heterogeneity of these oxides is characterized. The oxidation of toluene with air oxygen to maleic anhydride on V2O5 and mixed oxides involves singlet oxygen 1O2. A correlation between the content of V(IV) ions in the mixed catalysts and the amount desorbed 1O2 is observed. It is demonstrated that the oxidation of toluene causes changes in the spatial distribution of the V(IV) ions in the matrix and the phase composition of the samples.

Copper(ii) complex of methionine conjugated bis-pyrazole based ligand promotes dual pathway for DNA cleavage

Three Cu(II) complexes of bis-pyrazole based ligands have been synthesized and structurally characterized by X-ray crystallography. One of the ligand (L2) contains a methionine ester conjugated to a bis-pyrazole carboxylate through an amide linkage. The binding constant for complexes 1-3 with CT DNA are of the order of 10(4) M(-1). The crystal structure suggests that the axial Cu-O bonds (ca. 2.31(4) Å) are relatively labile and hence during the redox cycle with ascorbic acid and oxygen one or both the axial Cu-O bonds might open to promote copper oxygen reaction and generate ROS. The chemical nuclease activity of complexes 1-3 in dark, show complete relaxation of supercoiled DNA at 100 μM concentration in presence of ascorbic acid (H2A). The mechanistic investigation suggests that the complexes 1 and 2 show involvement of peroxo species whereas 3 shows involvement of both singlet oxygen and peroxo species in DNA cleavage. The singlet oxygen formation in dark is otherwise unfavourable but the presence of methionine as pendant arm in L2 might activate the generation of singlet oxygen from the metal generated peroxo species. The results of DNA cleavage studies suggest that methionine based copper(II) complexes can promote dual pathway for DNA cleavage. Probing the cytotoxic activity of these complexes on MCF-7, human breast cancer cell line shows that 3 is the most effective one with an IC50 of 70(2) μM.

Singlet Oxygen Production by Organic Matter and Disintegration of Pathogens and Pollutants during Wastewater Treatment: How Important?

Copyright: © 2013 Sarma SJ, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Electronically excited, highly reactive state of molecular oxygen is known as singlet oxygen. Apart from different other methods; singlet oxygen is mainly produced by irradiation of molecular oxygen in presence of photosensitizer pigments such as rose Bengal or methylene blue. Because of its potential applications in many fields including wastewater treatment, singlet oxygen remains to be one of the mostly explored research subjects of recent years. Singlet oxygen can be used as treatment mean against both pathogens and toxic organic pollutants present in wastewater [1]. For example, numbers of reports are available on oxidation of phenol and its derivatives, either in organic solvents or in aqueous solution, by the action of photosensitizer induced singlet oxygen [2]. Similarly, Schafer et al. [3] have investigated the inactivation of bacteria, such as Escherichia coli or Deinococcusradiodurans using photosensitizer technology involving singlet oxygen [3]. In addition to commonly used photosensitizer pigments, aromatic hydrocarbons (napthalenes, anthracenes, biphenyls) have also been evaluated for possible application as photosensitizer [2]. Similarly, a range of quinones can also work as sensitizers for singlet oxygen [2,4]. Even, the organic matter of an aquatic system has the potential to work as the inherent photosensitizer to support the formation of singlet oxygen as well as other reactive oxygen species [1]. Similarly, Dalrymple et al. [5] also have reported singlet oxygen production by aquatic dissolved organic matter [5]. Wastewater contains all these different types of photosensitizers; hence, degradation of different pollutants and elimination of pathogens by singlet oxygen produced during wastewater treatment process is a likely phenomenon. However, singlet oxygen has very short lifetime and they may also be involved in other intermolecular interactions, which are not relevant in pollutant degradation or pathogen inactivation [6]. Likewise, yield of singlet oxygen depends on the oxygen concentration [7]. However, the oxygen demand of wastewater treatment process is already very high. Therefore, whether the oxygen left after microbial utilization will be sufficient to generate the required amount of singlet oxygen for a significant response or not, is a question. Likewise, due to irradiation, chromophoric dissolved organic matter may be degraded to be more available for microbial utilization and it may further enhance the bacterial growth [8], including pathogens. Thus, considering additional cost involved, in the case of artificially irradiated wastewater treatment process, the purpose of pathogen inactivation and pollutant degradation using singlet oxygen may not be very effective. In this context, Mostafa & Rosario-Ortiz [1] have indicated that the concept of inherent photosensitizer (organic matter) mediated singlet oxygen generation and wastewater treatment may have more practical implication in the case of relatively cost effective sunlight-mediated nonconventional wastewater treatment processes, such as constructed wetlands [1]. Thus, in order to have a better understanding of the role of singlet oxygen in wastewater treatment, actual contribution of naturally produced singlet oxygen, in pathogen inactivation and contaminant degradation during wastewater treatment, should be precisely estimated. Further, possible enhancement of the efficiency of singlet oxygen, by the technique such as artificial irradiation and additional cost involved in such operation, should be determined. Likewise, alternative wastewater treatment processes should be designed, where maximum utilization of natural photosensitization is possible. Finally, based on the techno-economic feasibility of using artificial irradiation, the possibility of using it (in a cost effective way) to complement natural photosensitization, should also be explored.

Intense photooxidative degradation of planktonic and bacterial lipids in sinking particles collected with sediment traps across the Canadian Beaufort Shelf (Arctic Ocean)

Abstract. The lipid content of seven samples of sinking particles collected with sediment traps moored at ~ 100 m depth in summer and fall across the Canadian Beaufort Shelf (Arctic Ocean) was investigated. Our main goal was to quantify and characterize the biotic and abiotic degradation processes that acted on sinking material during these periods. Diatoms, which dominated the phytoplanktonic assemblage in every trap sample, appeared to be remarkably sensitive to Type II (i.e. involving singlet oxygen) photodegradation processes in summer, but seemed to be relatively unaffected by biotic degradation at the same time. Hence, the relative recalcitrance of phytodetritus towards biodegradation processes during the Arctic midnight sun period was attributed to the strong photodegradation state of heterotrophic bacteria, which likely resulted from the efficient transfer of singlet oxygen from photodegraded phytoplanktonic cells to attached bacteria. In addition, the detection in trap samples of photoproducts specific to wax ester components found in herbivorous copepods demonstrated that zooplanktonic faecal material exported out of the euphotic zone in summer were affected by Type II photodegradation processes as well. By contrast, sinking particles collected during the autumn were not influenced by any light-driven stress. Further chemical analyses showed that photodegraded sinking particles contained an important amount of intact hydroperoxides, which could then induce a strong oxidative stress in underlying sediments.

Stiffening of Rabbit Corneas by the Bacteriochlorophyll Derivative WST11 Using Near Infrared Light

We evaluated the efficacy and safety of photochemical corneal stiffening by palladium bacteriochlorin 13'-(2-sulfoethyl)amide dipotassium salt (WST11) and near infrared (NIR) illumination, using ex vivo and in vivo rabbit eye models. Corneas of post mortem rabbits and living rabbits were pretreated topically with 2.5 mg/mL WST11 in saline or in 20% dextran T-500 (WST-D), washed and illuminated with an NIR diode laser (755 nm, 10 mW/cm(2). Studies with corneas of untreated fellow eyes served as controls. Tensile strength measurements, histopathology, electron spin resonance, and optical spectroscopy and fluorescence microscopy were used to assess treatment effects. Comparative studies were performed with standard riboflavin/ultraviolet-A light (UVA) treatment. WST11/NIR treatment significantly increased corneal stiffness following ex vivo or in vivo treatment, compared to untreated contralateral eyes. The incremental ultimate stress and Young's modulus of treated corneas increased by 45, 113, 115%, and 10, 79, and 174% following 10, 20, and 30 minutes of incubation with WST11, respectively. WST-D/NIR had a similar stiffening effect, but markedly reduced post-treatment edema and shorter time of epithelial healing. WST11/NIR and WST-D/NIR generate hydroxyl and superoxide radicals, but no singlet oxygen in the cornea. Histology demonstrated a reduction in the keratocyte population in the anterior half of the corneal stroma, without damage to the endothelium. Treatment of rabbit corneas, with either WST11/NIR or WST-D/NIR, increases their biomechanical strength through a mechanism that does not involve singlet oxygen. The WST-D/NIR treatment showed less adverse effects, demonstrating a new potential for clinical use in keratoconus and corneal ectasia after refractive surgery.

Azide Quenching of Singlet Oxygen in Suspensions of Microenvironments of Neutral and Surface Charged Liposomes and Micelles

The azide anion is often used as a physical quencher of singlet oxygen, the important active intermediate in photosensitized oxidation. An observed effect of azide on the rate of a reaction is considered an indication to the involvement of singlet oxygen. In most biological photosensitizations, the light-absorbing sensitizer is located in a membrane or in an intracellular organelle, whereas azide is water soluble. The quenching it causes relies on a physical encounter with singlet oxygen during the latter's short lifetime. This can happen either if azide penetrates into the membrane's lipid phase or if singlet oxygen is intercepted when diffusing in the aqueous phase. We demonstrate in this article the difference, in liposomes' suspension, between the effect of azide when using a water-soluble and membrane-bound chemical targets of singlet oxygen, whereas this difference does not exist when micelles are used. We explain the difference on the population of sensitizer and target in the liposome vs micelle. We also show the effect that exists on azide quenching of singlet oxygen by electrically charged lipids in liposomes. This is a result of the accumulation or dilution of azide in the debye layer near the membranes' surface, due to the surface Gouy-Chapman potential.

Two new dicopper(II) complexes with oxamido-bridged ligand: Synthesis, crystal structures, DNA binding/cleavage and BSA binding activity

New oxamido-bridged copper(II) complexes, [Cu2(oxbp)(H2O)2(NCS)2] (1) and [Cu2(oxbp)(μ-DMSO)2(NCS)2][Cu2(oxbp)(DMSO)2(NCS)2] (2) (H2oxbp=N,N′-bis(2-(diethylamino)ethyl)oxalamide), were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR, and electronic spectra. X-ray analysis revealed that complex 1 consists of neutral binuclear [Cu2(oxbp)(H2O)2(NCS)2] units which forms a two-dimensional network through intermolecular hydrogen bonds and complex 2 is constructed by neutral [Cu2(oxbp)(μ-DMSO)2(NCS)2] (2a) and [Cu2(oxbp)(DMSO)2(NCS)2] (2b) entities which alternately distribute to form a two-dimensional network by means of quasi μ-DMSO bridge and intermolecular hydrogen bonds. In both 1 and 2, bicopper centers are linked by the “trans-form” oxamido bridges with the distances of 5.272Å for 1 and av. 5.296Å for 2, respectively. The interaction of Cu(II) complexes with DNA was investigated by UV-visible, fluorescence emission spectrometry and agarose gel electrophoresis. The apparent binding constant (Kapp) values of 3.16×105M−1 for 1 and 4.9×105M−1 for 2 suggest moderate intercalative binding modes between the complexes and DNA. Complex 1 displayed efficient oxidative cleavage of supercoiled DNA, which might indicate that the underlying mechanism involves singlet oxygen (1O2) as reactive oxygen species. Complex 2 is characteristic of the involvement of a singlet oxygen-like entity and hydrogen peroxide in the cleavage process. In addition, our present work showed, by fluorescence spectrometry of BSA with complexes, both 1 and 2 bind to BSA with a medium affinity through a static mode which is tentatively assigned binding to Trp134 in BSA.

Reactivity of cycloxydim toward singlet oxygen in solution and on wax film

The reactivity of the herbicide cycloxydim (CD) toward singlet oxygen was studied in organic solution and on wax films to mimic the leaf surface. Experiments in solution were conducted in acetonitrile using phenalenone as a sensitizer. For the experiments in the solid state, phenalenone was included in paraffinic wax films and CD deposited at the film surface. By laser flash photolysis we observed that the triplet of phenalenone reacts with CD with a bimolecular rate constant of (9.6±1)×106M−1s−1. However, scavenging experiments using β-carotene as a singlet oxygen quencher showed that the observed CD degradation in aerated acetonitrile involves singlet oxygen essentially. The bimolecular rate constant of reaction of CD with singlet oxygen was evaluated to (1.0±0.2)×107M−1s−1. Phenalenone included in the wax films also significantly increased the rate of CD photodegradation, the involvement of singlet oxygen being very likely. The photoproducts formed via the singlet oxygen pathway resulted from the oxidation of the thiol group and/or the cyclohexene ring. This study should help to better understand the fate of CD after its spraying on crops.

Generation of an Isolable, Monomeric Manganese(V)–Oxo Complex from O2 and Visible Light

The direct conversion of a Mn(III) complex [(TBP(8)Cz)Mn(III) (1)] to a Mn(V)-oxo complex [(TBP(8)Cz)Mn(V)(O) (2)] with O(2) and visible light is reported. Complex 1 is also shown to function as an active photocatalyst for the oxidation of PPh(3) to OPPh(3). Mechanistic studies indicate that the photogeneration of 2 does not involve singlet oxygen but rather likely occurs via a free-radical mechanism upon photoactivation of 1.

Sodium azide and metal chelator effects on 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging compounds from methylene blue photosensitized lard

AbstractThermal oxidation of edible oils can generate 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging compounds from oxidized lipids (RSOLs). However, effects of photosensitization on the formation of RSOLs have not been reported yet. Methylene blue (MB) photosensitization and involvement of singlet oxygen and transition metals on the RSOL formations were determined in stripped lard oils. RSOLs were formed in lard containing MB and visible light irradiation only. Addition of sodium azide decreased RSOLs with concentration dependent manner, which implies singlet oxygen was involved on the RSOL formation. Ethylenediammetetraacetic acid (EDTA), a well known metal chelator, accelerated the formation of RSOLs through protecting the decomposition of MB photosensitizer. Results from p‐anisidine values showed that RSOLs from photosensitization may not be formed from the same pathways compared to thermal oxidation.Practical application: Understanding mechanisms of lipid oxidation can help extend the shelf‐life of foods. Photosensitization plays important roles in accelerating the rates of lipid oxidation. The results of this study showed that foods containing photosensitizers can generate radical scavenging compounds from oxidized lipids (RSOLs) under visible light irradiation and singlet oxygen is involved in the formations of these compounds. However, these compounds may not share the same pathways with thermally oxidized lipids. Metal chelating agents accelerated the rates of lipid oxidation and formation of RSOLs which implies that metal chelators can act as prooxidant. Careful considerations are necessary on the addition of metal chelators because non‐polar photosensitizers can act a prooxidant.

Generation of reactive oxygen species in water under exposure to visible or infrared irradiation at absorption bands of molecular oxygen

It is found that in bidistilled water saturated with oxygen hydrogen peroxide and hydroxyl radicals are formed under the influence of visible and infrared radiation in the absorption bands of molecular oxygen. Formation of reactive oxygen species (ROS) occurs under the influence of both solar and artificial light sourses, including the coherent laser irradiation. The oxygen effect, i.e. the impact of dissolved oxygen concentration on production of hydrogen peroxide induced by light, is detected. It is shown that the visible and infrared radiation in the absorption bands of molecular oxygen leads to the formation of 8-oxoguanine in DNA in vitro. Physicochemical mechanisms of ROS formation in water when exposed to visible and infrared light are studied, and the involvement of singlet oxygen and superoxide anion radicals in this process is shown.

Mutagenicity induced by UVC in Escherichia coli cells: Reactive oxygen species involvement

We previously demonstrated that reactive oxygen species (ROS) could be involved in the DNA damage induced by ultraviolet-C (UVC). In this study, we evaluated singlet oxygen (1O2) involvement in UVC-induced mutagenesis in Escherichia coli cells. First, we found that treatment with sodium azide, an 1O2 chelator, protected cells against UVC-induced lethality. The survival assay showed that the fpg mutant was more resistant to UVC lethality than the wild-type strain. The rifampicin mutagenesis assay showed that UVC mutagenesis was inhibited five times more in cells treated with sodium azide, and stimulated 20% more fpg mutant. These results suggest that 1O2 plays a predominant role in UVC-induced mutagenesis. 1O2 generates a specific mutagenic lesion, 8-oxoG, which is repaired by Fpg protein. This lesion was measured by GC–TA reversion in the CC104 strain, its fpg mutant (BH540), and both CC104 and BH540 transformed with the plasmid pFPG (overexpression of Fpg protein). This assay showed that mutagenesis was induced 2.5-fold in the GC–TA strain and 7-fold in the fpg mutant, while the fpg mutant transformed with pFPG was similar to GC–TA strain. This suggests that UVC can also cause ROS-mediated mutagenesis and that the Fpg protein may be involved in this repair.

The spectral and catalytic studies of chlorophylls and pheophytins in mimetic biotransformation of α-pinene

Natural porphyrin pigments isolated from spinach in the form of a crude extract, chlorophyll a, chlorophyll b, pheophytin a and pheophytin b were studied as potential catalysts for the biomimetic transformation of α-pinene to trans-pinocarveol, pinocarvone and myrtenal. The reaction of monoterpene oxidation was performed in an organic solution under visible light irradiation. Significant changes in the distribution of the products were achieved using β-pinene as the substrate. The pheophytins showed the highest catalytic efficiency among the photocatalysts examined. The photographic visualization of α-pinene oxidation course at the beginning of the reaction, after 4 and 24 h exposure to light showed a distinct shift in the colour excited catalysts. This may indicate a change in their structure leading to their degradation. The absorbance and fluorescence spectra revealed that pheophytins are significantly stable photocatalysts in comparison to both chlorophylls. Pheophytin b displayed the highest stability in the biotransformation, whereas the highest rate of photodecomposition was proved for chlorophyll b under the reaction condition. Differences were noticed in the behaviour of the chlorophylls in the photodegradation process. From the changes in the intensity of the singlet oxygen band on infrared fluorescence spectra of pigments upon pinene addition, and from the reactivity experiments with radicals scavengers, it can be deduced that the biotransformation of pinene by chlorophylls and pheophytins proceeds by common oxygenation mechanism involving singlet oxygen and free radicals.