1O2 Concentration Research Articles

Comparison of noninvasive photodynamic therapy dosimetry methods using a dynamic model of ALA-PDT of human skin

A numerical model of ALA photodynamic therapy of human skin was used to calculate photosensitizer fluorescence and singlet-oxygen luminescence (SOL) observable at the skin surface during treatment. From the emissions, three practical dose metrics were calculated: the fractional fluorescence bleaching metric (FFBM) given by , where F is photosensitizer protoporphyrin IX (PpIX) fluorescence and F0 is its initial value, the absolute fluorescence bleaching metric (AFBM) given by F0−F, and the cumulative SOL (CSOL). These three metrics can be measured during clinical PDT treatment, but their relation to actual singlet-oxygen distribution in the skin is complex and may depend on treatment parameters such as irradiance. Using the model, the three metrics were compared to the average singlet-oxygen dose in the dermis. Despite the complex dependence of 1O2 concentration on depth, a roughly linear correlation was found for all three dose metrics. The correlation for the FFBM was not robust when treatment parameters were varied and this metric was especially sensitive to the initial PpIX concentration and its depth dependence. The AFBM was less sensitive to treatment conditions but CSOL demonstrated the best overall performance.

半胱氨酸化学键合金纳米颗粒用于氧化性小分子可视化测定的载体研究

Gold nanoparticles (AuNPs) have the unique property of plasmon resonance absorption (PRA). In this contribution, universal colorimetric detection of oxidants was achieved using cysteine induced AuNPs aggregation, which leads to a red-shift of in the PRA. The SH group of a cysteine molecule can be oxidized into a –S–S– bond in the presence of oxidants such as H2O2 or 1O2, which leads to reduced aggregation in the AuNPs. These blue-shifts of the PRA from 740 nm to 531 nm, and results in a blue-to-red color change. It was found that the ratio of absorbance at 740 nm to that at 531 nm ( A 740/ A 531) was in proportion to the concentrations of H2O2 and 1O2. Also, this colorimetric method can be successfully applied to detecting H2O2 in rat brains, which offers performance similar to flow injection-chemiluminescence.

Visible Light Sensitized Inactivation of MS-2 Bacteriophage by a Cationic Amine-Functionalized C60 Derivative

Recently, we reported the successful synthesis of various hexakis C60 derivatives (i.e., C60 with six functional groups containing NH3+-, CO2H-, or OH-terminals) with enhanced stability in water for aqueous phase application (Lee et al., Environ. Sci. Technol. 2009, 43, pp 6604-6610). Among these newly synthesized C60 derivatives, the cationic hexakis C60 derivative with amine functionality, C60(CR2)6 (R=CO2(CH2)2NH3+CF3CO2-), was found to exhibit remarkable efficiency to inactivate Escherichia coli and MS-2 bacteriophage under UVA irradiation. Herein, we report that this amine-functionalized C60 derivative is also photoactive in response to visible light from both commercial fluorescence lamps and sunlight. Efficient production of 1O2, facile reaction of 1O2 with proteins in MS-2 phage capsid and electrostatic attraction between positively charged C60 derivative and negatively charged MS-2 phage collectively contributed to high efficiency of MS-2 phage inactivation in this photocatalytic disinfection system. The rate of 1O2 production was evaluated using a probe compound, furfuryl alcohol, and 1O2 CT (the product of 1O2 concentration and exposure time) required to achieve a target level of virus inactivation was quantitatively analyzed. The unique visible-light sensitized virucidal property makes this C60 derivative highly desirable for the development of sustainable disinfection strategies that do not require continuous chemical addition nor an external energy source other than ambient light.

A heterogeneous optimization algorithm for reacted singlet oxygen for interstitial PDT.

Singlet oxygen (1O2) is the major cytotoxic agent for type II photodynamic therapy (PDT). The production of 1O2 involves the complex reactions among light, oxygen molecule, and photosensitizer. From universal macroscopic kinetic equations which describe the photochemical processes of PDT, the reacted 1O2 concentration, [1O2]rx, with cell target can be expressed in a form related to time integration of the product of 1O2 quantum yield and the PDT dose rate. The object of this study is to develop optimization procedures that account for the optical heterogeneity of the patient prostate, the tissue photosensitizer concentrations, and tissue oxygenation, thereby enable delivery of uniform reacted singlet oxygen to the gland. We use the heterogeneous optical properties measured for a patient prostate to calculate a light fluence kernel. Several methods are used to optimize the positions and intensities of CDFs. The Cimmino feasibility algorithm, which is fast, linear, and always converges reliably, is applied as a search tool to optimize the weights of the light sources at each step of the iterative selection. Maximum and minimum dose limits chosen for sample points in the prostate constrain the solution for the intensities of the linear light sources. The study shows that optimization of individual light source positions and intensities is feasible for the heterogeneous prostate during PDT. To study how different photosensitizer distributions as well as tissue oxygenation in the prostate affect optimization, comparisons of light fluence rate were made with measured distribution of photosensitizer in prostate under different tissue oxygenation conditions.

The Proteasome Is an Integral Part of Solar Ultraviolet A Radiation-induced Gene Expression

Solar ultraviolet (UV) A radiation is a well known trigger of signaling responses in human skin fibroblasts. One important consequence of this stress response is the increased expression of matrix metalloproteinase-1 (MMP-1), which causes extracellular protein degradation and thereby contributes to photoaging of human skin. In the present study we identify the proteasome as an integral part of the UVA-induced, intracellular signaling cascade in human dermal fibroblasts. UVA-induced singlet oxygen formation was accompanied by protein oxidation, the cross-linking of oxidized proteins, and an inhibition of the proteasomal system. This proteasomal inhibition subsequently led to an accumulation of c-Jun and phosphorylated c-Jun and activation of activator protein-1, i.e. transcription factors known to control MMP-1 expression. Increased transcription factor activation was also observed if the proteasome was inhibited by cross-linked proteins or lactacystin, indicating a general mechanism. Most importantly, inhibition of the proteasome was of functional relevance for UVA-induced MMP-1 expression, because overexpression of the proteasome or the protein repair enzyme methionine sulfoxide reductase prevented the UVA-induced induction of MMP-1. These studies show that an environmentally relevant stimulus can trigger a signaling pathway, which links intracellular and extracellular protein degradation. They also identify the proteasome as an integral part of the UVA stress response.

Photochemistry of Aqueous C60 Clusters: Evidence of 1O2 Formation and its Role in Mediating C60 Phototransformation

The expected rapid expansion of nanotechnology industries has raised concern over the environmental fate and effects of materials created by these industries, including carbon-based fullerenes. In this study, the reaction mechanism responsible for the photochemical transformation of aqueous C60 clusters (nC60) in sunlight has been examined. Evidence is presented that under lamps that emit light only within the solar spectrum, 1O2 is produced via aqueous nC60 suspensions, using furfuryl alcohol (FFA) as an indicator. In air-equilibrated suspensions, the losses of 0.2 mM FFA and 0.8 mg/L C60 were >90% and 70% after 15 h, while removing oxygen, the precursor of 1O2, stopped both reactions, indicating that 1O2 was produced and mediated nC60 phototransformation. Similar reactions performed in deuterium oxide and with added azide ion resulted in accelerated and slowed loss of FFA, respectively, as expected if 1O2 is a reaction intermediate. 1O2 production (as measured by FFA loss) increased with time as more water-soluble intermediate products accumulated in solution. In summer sunlight (West Lafayette, IN, 86 degrees 55' W, 40 degrees 26' N), suspensions of 5 mg/L nC60 produced 1O2 concentrations 1 order of magnitude higher thanthe average value typically found in natural waters containing the same mass of natural organic carbon.

Quantification of singlet oxygen and hydroxyl radicals upon UV irradiation of surface water

We measured the formation rate and the steady-state concentration of hydroxyl radicals and of singlet oxygen upon irradiation of lake water. There is controversy about the importance of singlet oxygen in the environmental photochemistry, but here we show that the steady-state concentration of 1O2 under irradiation can be higher by about two orders of magnitude compared to the hydroxyl radical. The higher occurrence of singlet oxygen in surface waters is mainly due to a higher rate of formation, because the transformation rate constants of 1O2 (collision with the solvent) and of ·OH (reaction with dissolved compounds) are comparable.

Optimization of physiological parameter for macroscopic modeling of reacted singlet oxygen concentration in an in-vivo model.

Singlet oxygen (1O2) is generally believed to be the major cytotoxic agent during photodynamic therapy (PDT), and the reaction between 1O2 and tumor cells define the treatment efficacy. From a complete set of the macroscopic kinetic equations which describe the photochemical processes of PDT, we can express the reacted 1O2 concentration, [1O2]rx, in a form related to time integration of the product of 1O2 quantum yield and the PDT dose rate. The production of [1O2]rx involves physiological and photophysical parameters which need to be determined explicitly for the photosensitizer of interest. Once these parameters are determined, we expect the computed [1O2]rx to be an explicit dosimetric indicator for clinical PDT. Incorporating the diffusion equation governing the light transport in turbid medium, the spatially and temporally-resolved [1O2]rx described by the macroscopic kinetic equations can be numerically calculated. A sudden drop of the calculated [1O2]rx along with the distance following the decrease of light fluence rate is observed. This suggests that a possible correlation between [1O2]rx and necrosis boundary may occur in the tumor subject to PDT irradiation. In this study, we have theoretically examined the sensitivity of the physiological parameter from two clinical related conditions: (1) collimated light source on semi-infinite turbid medium and (2) linear light source in turbid medium. In order to accurately determine the parameter in a clinical relevant environment, the results of the computed [1O2]rx are expected to be used to fit the experimentally-measured necrosis data obtained from an in vivo animal model.

Indirect Photodegradation of Dissolved Free Amino Acids: The Contribution of Singlet Oxygen and the Differential Reactivity of DOM from Various Sources

The role of photochemically generated singlet oxygen (1O2) in the DOM-sensitized degradation of eighteen dissolved free amino acids was investigated. The fraction of total sensitized degradation due to reaction with 1O2 was determined through a kinetic analysis based on a measured reaction rate constant for each amino acid coupled with measured 1O2 concentrations and was confirmed through quenching experiments. Only four of the eighteen free amino acid residues examined were found to be photolabile under environmentally relevant conditions: histidine, methionine, tyrosine, and tryptophan. The fraction of Suwannee River Humic Acid (SRHA)-sensitized degradation due to reaction with 1O2 ranged from an upper value of 110 +/- 10% for histidine to 8 +/- 1% for tryptophan, with 26 +/- 3% contribution for methionine and 33 +/- 4% for tyrosine. In addition to degradation through reaction with 1O2, other reactive intermediates involved in the SRHA-photosensitized degradation of these amino acids were identified. Methionine was thought to be additionally degraded through reaction with H2O2 and triplet excited-state DOM, and 67% of tyrosine's indirect photodegradation was assigned to an oxygen-dependent type I photooxidation reaction. The majority of tryptophan indirect degradation was due to reaction with 3DOM. Photodegradation experiments with various DOM sources including Pony Lake (Antarctica) fulvic acid and a synthetic estuarine sample, as well as Minnesota freshwater samples (lakes Itasca, Superior, Josephine, and the St Louis River), demonstrated distinct reactivity patterns, indicating that DOM's 1O2-generation efficiency is not strongly coupled to its ability to promote other photooxidation pathways. These four amino acids highlightthe differential photoreactivity of DOM from various sources.

No single way to understand singlet oxygen signalling in plants

When plant cells are under environmental stress, several chemically distinct reactive oxygen species (ROS) are generated simultaneously in various intracellular compartments and these can cause oxidative damage or act as signals. The conditional flu mutant of Arabidopsis, which generates singlet oxygen in plastids during a dark-to-light transition, has allowed the biological activity of singlet oxygen to be determined, and the criteria to distinguish between cytotoxicity and signalling of this particular ROS to be defined. The genetic basis of singlet-oxygen-mediated signalling has been revealed by the mutation of two nuclear genes encoding the plastid proteins EXECUTER (EX)1 and EX2, which are sufficient to abrogate singlet-oxygen-dependent stress responses. Conversely, responses due to higher cytotoxic levels of singlet oxygen are not suppressed in the ex1/ex2 background. Whether singlet oxygen levels lower than those that trigger genetically controlled cell death activate acclimation is now under investigation.

Association with Natural Organic Matter Enhances the Sunlight-Mediated Inactivation of MS2 Coliphage by Singlet Oxygen

MS2 coliphage, a surrogate for human enteric viruses, is inactivated by singlet oxygen (1O2) produced via sunlight-mediated excitation of natural organic matter (NOM) in surface waters. The 1O2 concentration within a NOM macromolecule or supramolecular assembly ([1O2]internal) is orders of magnitude higher than in the bulk solution ([1O2]bulk). In close proximity of NOM, MS2 is thus exposed to an elevated 1O2 concentration ([1O2]NOM), and inactivation is likely to be enhanced as compared to the bulk solution. In experiments using a solar simulator, we determined [1O2]bulk, [1O2]internal, as well as the association of MS2 with four NOMs (Fluka humic acid, FHA; Suwannee river humic acid, SRHA; Aldrich humic acid, AHA; Pony lake fulvic acid, PLFA), and studied their effect on the MS2 inactivation rate constant, k(obs), over a range of 1-25 mg NOM/L. The k(obs) values were modeled as the sum of the inactivation rate constants in close proximity to the NOM and in the bulk solution, assuming Langmuir-type adsorption of NOM onto MS2. FHA and SRHA exhibited 13-22 fold greater adsorption equilibrium constants than AHA and PLFA. Inactivation in the bulk solution contributed between 2% (20 mg/L FHA) and 39% (5 mg/L AHA) toward the overall k(obs). Thus, even for the less adsorbing NOM, inactivation was dominated by [1O2]NOM rather than [1O2]bulk. Changes in solution chemistry to promote closer interactions between MS2 and NOM also enhanced k(obs). Addition of Mg2+ to neutralize the negative surface charge of MS2 and NOM increased k(obs) up to 4.1-fold. Similarly, lowering the solution pH closer to the isoelectric point of MS2 (pl = 3.9) enhanced k(ob), 51-fold in 5 mg/L AHA.

Sunlight-Mediated Inactivation of MS2 Coliphage via Exogenous Singlet Oxygen Produced by Sensitizers in Natural Waters

Pathogens in sunlit surface waters can be damaged directly by UVB light. Indirect inactivation by reactive oxygen species (ROS) generated by sunlight interacting with external sensitizer molecules may also be important, but this mechanism has not been conclusively demonstrated. To better understand the role of ROS, we investigated the inactivation of MS2 coliphage, a commonly used surrogate for human enteric viruses, in water samples irradiated with a solar simulator and containing different types of sensitizers: waste stabilization pond (WSP) constituents, Fluka humic acid (FHA), and Suwannee River humic acid (SRHA). Inactivation of MS2 by the indirect mechanism was significant for all three sensitizers, and the efficiency of the sensitizers at inactivating MS2 was FHA > SRHA > WSP. Both dissolved and particulate fractions in the WSP water contributed to inactivation. In the WSP water, the indirect process was quantitatively more importantthan direct damage by UVB light, due to the rapid attenuation of UVB compared to the longer wavelengths that may initiate the indirect mechanism. Singlet oxygen (1O2) was the most important ROS involved in the inactivation of MS2. The addition of histidine, a 1O2 quencher, decreased inactivation, whereas inactivation rate constants increased in solutions of D20. Selective quenchers for other ROS showed little or no protective effect. Inactivation in WSP water was a function of the steady-state 102 concentration and could be described by a second-order rate expression.

Stable Dioxetane Precursors as Selective Trap-and-Trigger Chemiluminescent Probes for Singlet Oxygen

A set of highly selective chemiluminescent probes has been developed for the detection and quantitation of singlet oxygen (1O2), a reactive oxygen species that is known to transform organic pollutants in the aquatic environment and elicits cytotoxic effects in biological systems. In this study, a trap-and-trigger detection method is employed, based on the reaction of 1O2 with a spiroadamantyl-substituted vinyl ether probe to form the corresponding thermally stable dioxetane, which undergoes chemiluminescent decomposition upon addition of a chemical trigger. The detection method is highly selective for 1O2 relative to superoxide anion and hydrogen peroxide. The sensitivity of this method allows for the accurate measurement of environmentally relevant (picomolar) steady-state 1O2 concentrations in relatively short exposure times. The detection method was used to detect and quantify 1O2 production in the reaction of dibenzoyl peroxide with superoxide anion.

Endogenous isoprene protects Phragmites australis leaves against singlet oxygen

The possible protective role of endogenous isoprene against oxidative stress caused by singlet oxygen (1O2) was studied in the isoprene‐emitting plant Phragmites australis. Leaves emitting isoprene and leaves in which isoprene synthesis was inhibited by fosmidomycin were exposed to increasing concentrations of 1O2 generated by Rose Bengal (RB) sensitizer at different light intensities. In isoprene‐emitting leaves, photosynthesis and H2O2 and malonyldialdehyde (MDA) contents were not affected by low to moderate 1O2 concentrations generated at light intensities of 800 and 1240 µmol m−2 s−1, but symptoms of damage and reactive oxygen accumulation started to be observed when high levels of 1O2 were generated by very high light intensity (1810 µmol m−2 s−1). A dramatic decrease in photosynthetic performance and an increase in H2O2 and MDA levels were measured in isoprene‐inhibited RB‐fed leaves, but photosynthesis was not significantly inhibited in leaves in which the isoprene leaf pool was reconstituted by fumigating exogenous isoprene. The inhibition of photosynthesis in isoprene‐inhibited leaves was linearly associated with the light intensity and with the consequently formed 1O2. Hence, physiological levels of endogenous isoprene may supply protection against 1O2. The protection mechanisms may involve a direct reaction of isoprene with 1O2. Moreover, as it is a small lipophilic molecule, it may assist hydrophobic interactions in membranes, resulting in their stabilization. The isoprene‐conjugated double bond structure may also quench 1O2 by facilitating energy transfer and heat dissipation. This action is typical of other isoprenoids, but we speculate that isoprene may provide a more dynamic protection mechanism as it is synthesized promptly when high light intensity produces 1O2.

Photochemical fate of pharmaceuticals in the environment: cimetidine and ranitidine.

The photochemical fates of the histamine H2-receptor antagonists cimetidine and ranitidine were studied. Each of the two environmentally relevant pharmaceuticals displayed high rates of reaction with both singlet oxygen (1O2, O2(1delta(g))) and hydroxyl radical (*OH), two transient oxidants formed in sunlit natural waters. For cimetidine, the bimolecular rate constant for reaction with *OH in water is 6.5 +/- 0.5 x 10(9) M(-1) s(-1). Over the pH range 4-10, cimetidine reacts with 1O2 with bimolecular rate constants ranging from 3.3 +/- 0.3 x 10(6) M(-1) s(-1) at low pH to 2.5 +/- 0.2 x 10(8) M(-1) s(-1) in alkaline solutions. The bimolecular rate constants for ranitidine reacting with 1O2 in water ranges from 1.6 +/- 0.2 x 10(7) M(-1) s(-1) at pH 6-6.4 +/- 0.2 x 10(7) M(-1) s(-1) at pH 10. Reaction of ranitidine hydrochloride with *OH proceeds with a rate constant of 1.5 +/- 0.2 x 10(10) M(-1) s(-1). Ranitidine was also degraded in direct photolysis experiments with a half-life of 35 min under noon summertime sunlight at 45 degrees latitude, while cimetidine was shown to be resistant to direct photolysis. The results of these experiments, combined with the expected steady-state near surface concentrations of 1O2 and *OH, indicate that photooxidation mediated by 1O2 is the likely degradation pathway for cimetidine in most natural waters, and photodegradation by direct photolysis is expected to be the major pathway for ranitidine, with some degradation caused by 1O2. These predictions were verified in studies using Mississippi River water. Model compounds were analyzed by laser flash photolysis experiments to assess which functionalities within ranitidine and cimetidine are most susceptible to singlet-oxygenation and direct photolysis. The heterocyclic moieties of the pharmaceuticals were clearly implicated as the sites of reaction with 1O2, as evidenced by the high relative rate constants of the furan and imidazole models. The nitroacetamidine portion of ranitidine has been shown to be the moiety active in direct photolysis.

Quantum efficiency of the laser-excited singlet-oxygen-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine

An investigation was made of the ratios of the intensity Idf of the singlet-oxygen(1O2)-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine (ZnTBPc), with the maximum at λ = 685 nm, to the intensity I1270 of the photosensitised phosphorescence of 1O2 with the maximum at λ = 1270 nm in deuterated benzene when excited with λ = 337 nm nitrogen-laser pulses. Depending on the energy density of the laser radiation (0.25 — 0.7 mJ cm-2) and on the concentration of ZnTBPc (0.06 — 3.4 μM), the ratio of the zero-time intensities of the delayed fluorescence of ZnTBPc and of the singlet-oxygen phosphorescence Idf0/I12700 varied from 0.01 to 0.2 in air-saturated solutions of ZnTBPc. The intensity Idf0 decreased fivefold as a result of saturation with oxygen of air-saturated solutions. The quantum efficiency of the delayed fluorescence was represented by the coefficient α =(Idf0/I12700)kr/(γf[1O2]0[ZnTBPc]), where [1O2]0 is the zero-time concentration of 1O2 after a laser shot; kr is the rate constant of radiative deactivation of 1O2 in the investigated solvent; γf is the quantum yield of the ZnTBPc fluorescence. It was established that in the case of air-saturated solutions of ZnTBPc this coefficient was approximately 200 times less than for metal-free tetra(4-tert-butyl)phthalocyanine and its absolute value was ~2 × 1011 M-2 s-1.

Mechanism of singlet-oxygen induced delayed fluorescence of bacteriopheophytin in laser excitation

The relative intensity of photosensitized phosphorescence of singlet oxygen (1O2) at 1270 nm (L1270) and1O2-induced delayed fluorescence (Ldf) of bacteriopheophytin a (BPh) (770 nm) in air-saturated solutions of BPh in hexafluorobenzene in excitation by 337-nm pulses of a nitrogen laso is investigated. It is established that Ldf≪L1270. The ratio of the initial intensity of delayed fluorescence and phosphorescence of1O2(Ldf)0/(L1270)0 changed from 0.02 to 0.30 as a function of the energies of laser pulses (2.5–5.0 mJ/cm1) and the BPh concentration (6–18 μM). As the index of quantum efficiency of the delayed fluorescence, the authors used the coefficient $$\alpha = [(L_{df} )_0 /(L_{1{\text{270}}} )_0 ]k_r /(\gamma f[^1 O_{\text{2}} ]_0 [Bpn),$$ where [1O2]0 is the initial concentration of1O2 after the laser burst; [Bpn] is the concentration of BPh; kr is the constant of the rate of1O2 radiative deactivation in the solvent under study; γf is the quantum yield of BPh fluorescence. It is established that this coefficient is smaller by a factor of ∼2000 than in phthalocyanine, while its absolute value is ∼2·1010M−2sec−1. The saturation of BPh solutions with oxygen at atmospheric pressure is shown to lead to a fivefold attenuation of the delayed fluorescence as compared to air-saturated solutions. The possibility of BPh triplet molecules being involved in the radiation of delayed fluorescence of the pigment is discussed.

Singlet-Oxygen-Sensitized Delayed Fluorescence: Direct Detection of Triplet Phthalocyanine as an Intermediate

We have detected an intermediate in the process of singlet-oxygen-sensitized delayed fluorescence (SOSDF) using tetra-tert-butylphthalocyanine (Pc) as the fluorescer and C60 as the sensitizer. The observed intermediate is dependent on the concentrations of Pc, 1O2, and 3O2, as is SOSDF. By modeling the kinetics of the intermediate according to previously proposed mechanisms for SOSDF, we are able to rule out the singlet oxygen dimol as the intermediate. The intermediate kinetics are in agreement with either an exciplex or a triplet Pc mechanism. Since the intermediate has a spectrum identical to that of the triplet Pc, the triplet is the most likely intermediate.

Influence of solvents on the quantum efficiency of laser-excited delayed fluorescence of phthalocyanine sensitised by singlet oxygen

An investigation was made of the intensity ratios of the phosphorescence of singlet oxygen 1O2 at λ = 1270 nm (L1270) and of the 1O2-sensitised delayed fluorescence (Ldf) of tetra-(4-tert-butyl)phthalocyanine (Pc) in hexafluorobenzene, benzene, and acetone were also studied. Tetraphenylporphine and Pc were used as photosensitisers of O2 formation. Excitation was provided by a pulsed nitrogen laser emitting at λ = 337 nm. The ratio Ldf0 =L01270 of the initial intensities of the delayed fluorescence of Pc and of the 1O2 phosphorescence varied from 14 to 70, depending on the energy of the laser pulses (1 — 2 mJ cm-2), on the Pc concentration (0.25 — 1.2 μM), and on the nature of the photosensitiser and its optical density (0.1 — 0.2) in the excitation region. A criterion of the quantum efficiency of the delayed fluorescence was defined as the coefficient α = (Ldf0/L12700kr/γf) [1O2]0[Pc], where [1O2]0 is the initial concentration of 1O2 after a laser pulse; [Pc] is the concentration of Pc; kr is the rate constant of radiative deactivation of 1O2 in the investigated solvent; γf is the quantum yield of the Pc fluorescence. Within the limits of the experimental error, the coefficient α was the same for all the investigated media and amounted approximately to 4 × 1013 M-2 s-1. An analysis of the results indicated that the quantum efficiency of the delayed fluorescence of Pc excited in aprotic media remained high irrespective of the presence and number of hydrogen atoms in the solvent molecule and also independent of the solvent permittivity in the range 2.3(benzene) — 21.5(acetone).

Near‐infrared Light Emission from Nanomolar‐level Singlet Molecular Oxygen Generated with an Ultra low Concentration Mixture of Hypochlorite and Hydrogen Peroxide

Abstract— We report the detection of a weak near‐infrared light emission originating from 8 nM singlet molecular oxygen (1O2) produced in a mixture of 1 mM hypochlorite (OC1‐) and 8 nM hydrogen peroxide (H2O2). The measurements were made with a highly sensitive detection system for ultraweak light emission in the 1.0‐1.5 μm wavelength region. The emission intensity exhibited linear dependence for H2O2 concentrations in the range of 8‐670 nM. The mixture containing a lower concentration (33 μM) of OCl‐ pseudocontinuously emitted near‐infrared light for 5 s. The rate constant for 1O2 production obtained from the kinetic analysis agrees with that previously reported. Our results demonstrate the possibility of measuring very low concentrations of 1O2 in a OCi‐/H2O2 mixture as well as 1O2 production in intact living systems.