Characterization of chemiluminescence from singlet oxygen under laminar flow conditions in a micro-channel and its quenching with beverages

Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by a syringe pump, providing a laminar flow liquid-liquid interface. The chemiluminescence from the singlet oxygen was emitted in the collapse of the interface due to molecular diffusion under laminar flow conditions. The chemiluminescence intensity was observed continuously and stably for each combination of reagents fed into the micro-channel; while, in the normal batch-type reactor the chemiluminescence peaks from singlet oxygen were observed within ca. 5 s. The features of the chemiluminescence emitted under laminar flow conditions were examined by changing the concentrations of sodium hypochlorite and hydrogen peroxide; the concentrations of 2.5 mM sodium hypochlorite and 7.5 mM hydrogen peroxide provided highest chemiluminescence intensities without bubble formation. Also, the effects of beverages, such as green tea, coffee, white wine, red wine, and sake (rice wine), on the chemiluminescence intensity as well as the concentrations of sodium hypochlorite and hydrogen peroxide were examined. The chemiluminescence intensities observed with addition of the beverages to the reagents decreased in the following orders; green tea > coffee > red wine > rice wine > white wine (being added to sodium hypochlorite); coffee > white wine > green tea > red wine > rice wine (being added to hydrogen peroxide). It was found that coffee decreased the chemiluminescence intensity (ca. 33% chemiluminescence decrease) without altering the concentrations of sodium hypochlorite or hydrogen peroxide. The cause of the decrease in chemiluminescence with coffee is discussed.     

Determination of free chlorine in water by chemiluminescence reaction with hydrogen peroxide

The analytical utility of the hydrogen peroxide—hypochlorite singlet oxygen chemiluminescence reaction for the determination of hypochlorite in water is investigated. Effects of pH and hydrogen peroxide concentration are discussed and interference data for over 35 species in the absence and presence of hypochlorite are provided. The limit of detection is 4 μg l^-1 with a usable non-linear calibration curve up to about 200 μg l^-1. The new method is shown to be relatively free from interferences and to give results for tap water comparable to a standard colorimetric method based on a reaction with N, N-diethyl-p-phenylenediamine.     

Direct evidence of singlet molecular oxygen [O2(1Deltag)] production in the reaction of linoleic acid hydroperoxide with peroxynitrite

Peroxynitrite (ONOO-), a biologically active species, can induce lipid peroxidation in biological membranes, thereby leading to the formation of various hydroperoxides. We report herein on the formation of singlet molecular oxygen [O(2) ((1)Delta(g))] in the reaction of peroxynitrite with linoleic acid hydroperoxide (LAOOH) or (18)O-labeled LAOOH. The formation of O(2) ((1)Delta(g)) was characterized by (i) dimol light emission in the red spectral region (lambda > 570 nm) using a red-sensitive photomultiplier; (ii) monomol light emission in the near-infrared region (lambda = 1270 nm) with a liquid nitrogen-cooled germanium diode or a photomultiplier coupled to a monochromator; (iii) the enhacing effect of deuterium oxide on chemiluminescence intensity, as well as the quenching effect of sodium azide; and (iv) chemical trapping of O(2) ((1)Delta(g)) or (18)O-labeled O(2) ((1)Delta(g)) with the 9,10-diphenylanthracene (DPA) and detection of the corresponding DPAO(2) or (18)O-labeled DPA endoperoxide by HPLC coupled to tandem mass spectrometry. Moreover, the presence of O(2) ((1)Delta(g)) was unequivocally demonstrated by a direct spectral characterization of the near-infrared light emission attributed to the transition of O(2) ((1)Delta(g)) to the triplet ground state. For the sake of comparison, O(2) ((1)Delta(g)) deriving from the thermolysis of the endoperoxide of 1,4-dimethylnaphthalene or from the H(2)O(2)/hypochlorite and H(2)O(2)/molybdate systems were also monitored. These novel observations identified the generation of O(2) ((1)Delta(g)) in the reaction of LAOOH with peroxynitrite, suggesting a potential O(2) ((1)Delta(g))-dependent mechanism that contributes to cytotoxicity mediated by lipid hydroperoxides and peroxynitrite reactions in biological systems.     

The second chemiluminescence emission of luminol-periodate-menadione sodium bisulfite system and its analytical application

In this paper, a new chemiluminescence phenomenon described as the second chemiluminescence emission was observed when menadione sodium bisulfite was injected into a reaction mixture of luminol and potassium periodate, in which luminol was oxidized by excess amount of potassium periodate for about 24 h. The mechanism of the second chemiluminescence emission was proposed based a series of experiments. Moreover, our experiment discovered that the second chemiluminescence intensity was a linear function of the concentration of menadione sodium bisulfite in the range of 2 × 10⁻⁹ to 4 × 10⁻⁵ g L⁻¹. Based on this phenomenon, a new flow-injection method for the determination of menadione sodium bisulfite has been established.     

The inhibition by amines and amino acids of bleach-induced luminol chemiluminescence during forensic screening for blood

Sprays containing alkaline solutions of peroxide and luminol are used as presumptive screens for bloodstains at crime scenes. These sprays can be subject to interference from hypochlorite-based cleaning agents (bleaches), leading to false positive results. This paper reports the screening of amines for their ability to decrease the interference by bleach while not greatly affecting the reaction with blood. The addition of glycine (0.05 mol L⁻¹) to the Grodsky formulation of luminol spray, together with an adjustment of the pH to 12, gave good discrimination between blood and bleach, and has the advantage that glycine is non-toxic compared to many other amines. The modified spray gave similar chemiluminescence intensity and duration as the unmodified Grodsky spray. However, it is recommended that this modification only be used when there is evidence that hypochlorite bleach may have been used at a scene. The amines triethylamine and sulfamate led to enhanced chemiluminescence in the presence of hypochlorite.     

Peroxide-related chemiluminescence of cellulose and its self-absorption

In chemiluminometry, we measure the very faint light as a consequence of chemical reactions. During oxidation of cellulose, several reaction pathways lead to light production and in the present work we investigated chemiluminescence as a consequence of peroxide formation.With ¹³C-1 labelled glucose we studied oxidation of the end groups by following the emission of ¹³CO₂ using gas chromatography-mass spectrometry. A mechanism of peroxyacyl radical formation is suggested. Its proposed decomposition is a first-order reaction, which is reflected in chemiluminometric experiments. From these, we calculated the activation energy of the process, which depends on the temperature and is approximately 75 kJ mol⁻¹ at T > 100 °C and ∼55 kJ mol⁻¹ at T < 100 °C.Evidence is also presented on self-absorption of chemiluminescence in cellulose, suggesting that the phenomenon may account for up to 50% intensity loss.     

INVESTIGATIONS ON THE LIGHT-EMITTING SPECIES IN THE REACTION OF METMYOGLOBIN AND METHEMOGLOBIN WITH HYDROGEN PEROXIDE

Abstract The formation of a compound I type ferryl complex in the reaction of methemoglobin (MetHb) and metmyoglobin (MetMyo) with hydrogen peroxide is accompanied by strong chemiluminescence. An approach to identify the nature of the light-emitting species was made by the use of quenchers and sensitizers reacting with singlet oxygen and compounds interfering in the formation and reactivity of other reactive oxygen species. Singlet oxygen is not the source of light emission. This could be concluded from the results obtained using the specific singlet oxygen trap 9,10-anthracenedipropionic acid (ADPA) in combination with high-performance liquid chromatography (HPLC) analysis. The singlet oxygen adduct of ADPA was not formed in the incubation systems (MetHb or MetMyo/H₂O₂). Instead, ADPA was oxidized by the ferryl ion to a different oxidation product, which was characterized by HPLC and IR spectroscopy. In the case of MetHb-related chemiluminescence, light emission does not result from a single source. Both, SH-groups and O₂^.¯ radicals are involved because blocking of thiol-groups with N-ethylmaleimide (NEM) and scavenging of O₂^.¯(by superoxide dismutase) suppressed chemiluminescence by 50% and 30%, respectively. Development of MetMyo-related chemiluminescence is not dependent on thiol groups (which are not present in the globin moiety) and also 0₂^.¯is not involved. Although generation of chemiluminescence in MetHb and MetMyo seems to follow different mechanisms, both types of light-emitting species are sensitive to antioxidants, such as uric acid and ascorbate. The detection of the respective free radicals by means of ESR demonstrates that both MetHb- and MetMyo-mediated chemiluminescence is associated with a strong one-electron oxidizing species, which seems to be identical with the light-emitting source itself. Also desferal, which was originally used to exclude the involvement of a Fenton-type reaction, was readily oxidized to the nitroxide free radical associated with a strong decrease of chemiluminescence. This quenching effect was not dependent on iron complexation because the addition of iron was ineffective. In summary, chemiluminescence is not restricted to a single chemical process but is related to different one-electron transfer reactions from globin residues to the oxo-heme center.     

Determination of total bilirubin in human serum by chemiluminescence from the reaction of bilirubin and peroxynitrite

Peroxynitrous acid (ONOOH) was produced by the on-line reaction of acidified hydrogen peroxide with nitrite in a flow system, and peroxynitrite (ONOO⁻) was generated from ONOOH in NaOH solution. A weak chemiluminescent (CL) emission was observed due to the production of singlet oxygen ( ) during the decomposition of ONOO⁻. Bilirubin and its conjugate were found to enhance the CL emission of in a suitable micellar medium. For the first time, the feasibility of employing the present CL system for the sensitive and selective determination of total bilirubin contents in human serum was demonstrated and the results were compared with certified values. The present method showed a great improvement on overcoming bis(2,4,6-trichlorophenyl)oxalate CL highly insolubility in aqueous solution and exhibiting higher tolerance towards interferences than redox reaction of bilirubin with various oxidizing agents such as sodium hypochlorite and iodine. The recoveries of bilirubin were found to fall in the range between 95 and 108%. The detection limits (S/N=3) for bilirubin and its conjugate were determined to be 10 and 8 ng ml⁻¹, respectively. The relative standard deviations (R.S.D.) for the consecutive CL detection of a series of bilirubin (30 μg l⁻¹) and bilirubin ditaurite (25 μg l⁻¹) were 3.2 and 2.9% (n=11), respectively.     

Generation of Singlet Molecular Oxygen by Lipid Hydroperoxides and Nitronium Ion†

Singlet molecular oxygen is a reactive species involved in biological oxidative processes. The major cellular targets of singlet molecular oxygen are unsaturated fatty acids in the membrane, as well as nucleic acids and proteins. The aim of this study was to investigate whether lipids and commercial hydroperoxides generate singlet molecular oxygen, in presence of nitronium and activated nitronium ion. For this purpose, monomol light emitted in the near-infrared region (λ = 1270 nm) was used to monitor singlet molecular oxygen decay in different solvents, with different hydroperoxides and in the presence of azide. Direct measurements of the singlet molecular oxygen spectrum at 1270 nm recorded during the reaction between lipids and commercial hydroperoxides and nitronium ions unequivocally demonstrated the formation of this excited species.     

Light Emission Resulting from Hydroxylamine-Induced Singlet Oxygen Formation of Oxidizing LDL Particles

Abstract— Oxidation of low-density lipoprotein (LDL) by low amounts of cupric ions resulted in the formation of singlet oxygen (₁O₂, ₁DL_g) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed to the dimol decay of singlet oxygen. Additional evidence for the existence of singlet oxygen came from the enhancing effect of deuterium oxide buffer (D20) on chemiluminescence intensity and the quenching effect of sodium azide. A linear correlation between NH2OH-de-pendent chemiluminescence intensity and the amount of diene conjugates (DC) formed in this reaction was observed. Removal of adventitious transition metals by adequate chelators prevented chemiluminescence in this system; NH2OH was also found to efficiently decrease metabolites of lipid peroxidation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced state, thereby stimulating the formation of alkoxy- and peroxy-radicals. Peroxyradicals decompose in a bimolecular Russel reaction to hydroxyl compounds and singlet oxygen while the majority of alkoxy radicals are eliminated by a secondary reaction with NH2OH. Identical effects were observed when reducing antioxidants such as ascorbic acid or trolox C were used instead of hydroxylamine.     

Photodegradation mechanisms in poly(2,6-butylenenaphthalate-co-tetramethyleneglycol) (PBN-PTMG), Part III: Photodegradation induced by the carbonyl group in n, π excited states

In order to identify the initiation step in the photodegradation of poly(2,6-butylenenaphthalate)-block-poly(tetramethyleneglycol) (PBN-PTMG), we undertook its photolysis with monochromatic irradiation. We discuss the initiation reaction on the basis of the analytical results for the PBN-PTMG in the presence or absence of 2,2′-dihydroxy-4-methoxybenzophenone as a UV absorber, 2-hydroxy-4-methoxybenzophenone as a UV absorber, β-carotene as a quencher of singlet oxygen or methylene blue as a photosensitiser, respectively.The PBN-PTMG containing 2,2′-dihydroxy-4-methoxybenzophenone exhibits better resistance to the incident light of ca. 370 nm corresponding to the absorption of the n, π^* transition of the carbonyl group in the PBN block than the PBN-PTMG containing 2-hydroxy-4-methoxybenzophenone. The PBN-PTMG containing β-carotene shows similar photodegradation tendencies as that of the PBN-PTMG without β-carotene. In contrast, the PBN-PTMG with methylene blue is not degraded by monochromatic radiation in the range λ = 600-690 nm. These facts indicate that singlet oxygen does not participate in the initiation reaction of the photodegradation of the PBN-PTMG. Therefore, we concluded that the photodegradation of the PBN-PTMG is induced through the hydrogen abstraction by carbonyl groups in n, π^* excited states.     

INHIBITION AND ENHANCEMENT OF SINGLET OXYGEN ('Ag) DIMOL CHEMILUMINESCENCE

Abstract— Various nitrogen containing compounds have previously been shown to quench singlet oxygen (10z). When measuring the dimol ¹O₂ light emission arising from the H ₂O₂ /OCI- reaction, we found that certain cyclic diamines increase the emission of light, while other amines were inhibitory. This increase of light emission was seen with both 1, 4diazabicyclo[2.2.2]octane and N, N'-dimethylpi-perazine but not with acyclic analogues. Sodium azide inhibited both the normal and enhanced light emission. The enhanced light emission shows spectral properties characteristic of ^lO₂ dimol emission.     

A portable and low cost equipment for flow injection chemiluminescence measurements

A compact, reliable and low cost flow injection chemiluminescence system is described. The flow system consists of a set of solenoid micro-pumps that can dispense reproductive micro-volumes of solutions. The luminometer was based on a coiled cell constructed from polyethylene tubing that was sandwiched between two large area photodiodes. The whole equipment costs about US$ 750 and weights ca. 3 kg. Equipment performance was evaluated by measuring low concentrations of hydrogen peroxide by oxidation of luminol and for the determination of ammonium, based on its inhibition of the luminescence provided by the reaction of luminol and sodium hypochlorite. Linear responses were achieved within 1.0-80 μmol L⁻¹ H₂O₂ and 0.6-60 μmol L⁻¹ NH₄⁺ with detection limits estimated as 400 nmol L⁻¹ H₂O₂ and 60 nmol L⁻¹ NH₄⁺ at the 99.7% confidence level. Coefficients of variation were 1.0 and 1.8%, estimated for 20 μmol L⁻¹ H₂O₂ and 15 μmol L⁻¹ NH₄⁺ (n = 20), respectively. Reagent consumption of 55 μg luminol, effluent volume of 950 μL per determination and sampling rate of 120 samples per hour were also achieved.     

Chemiluminescence from singlet oxygen under laminar flow condition in a micro-channel

Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by syringe pumps, providing a laminar flow. Such a laminar flow forms a liquid–liquid interface instantly in a micro-channel, and then the interface collapses gradually through molecular diffusion with the residence times. The chemiluminescence from the singlet oxygen was emitted in the course of the collapse of the interface under laminar flow condition. The chemiluminescence intensity was observed continuously and stably in the micro-channel as long as the reagents were fed into the channel. We examined the features of the chemiluminescence emitted in the micro-channel by changing the flow rates of reagents and the detection points in the micro-channel. The data obtained were considered along with the residence times and diffusion lengths. We also examined the effects of antioxidants, such as sodium azide, histidine, nitroblue tetrazolium, and 2-propanol on the chemiluminescence intensity.     

Determination of Melatonin in Rat Pineal Gland and Drug with Flow-Injection Chemiluminescence

A flow-injection chemiluminescence （CL） method for the determination of melatonin based on the CL reaction of melatonin with hydrogen peroxide and sodium hypochlorite （NaOCl） in a basic alkaline solution was developed. The possible CL mechanism has been discussed, and a proposal for the reaction pathway was given that singlet oxygen was clarified to be produced in this reaction system and was responsible for the CL emission. Under the optimized conditions, the linear concentration range of application was 1.0×10^-7-2.5 × 10^-4 moloL-I with a de- tection limit of 5.0 ×10^-8 moloL-1 （S/N= 3）. The relative standard deviation for eight repeated measurements of 1.0×10^-6 mol·L^-1 melatonin was 2.8%. The interferences of several important biological substances, some indole compound, cations and anions were studied. No interference was found for the anions, glucose, starch, most of cations and low concentration （less than 3.0 × 10^-6 mol·L^-1） of some biological substances and indole compound. The method was applied to the determination of melatonin in rat pineal gland and drug with satisfactory results. The sample throughput was 90 injections per hour.     

Triplet Excited States and Singlet Oxygen Production by Analogs of Red Wine Pyranoanthocyanins

During the maturation of red wines, the anthocyanins of grapes are transformed into pyranoanthocyanins, which possess a pyranoflavylium cation as their basic chromophore. Photophysical properties of the singlet and triplet excited states of a series of synthetic pyranoflavylium cations were determined at room temperature in acetonitrile solution acidified with 0.10 mol dm^?3 trifluoroacetic acid (TFA, to inhibit competitive excited state proton transfer) and at 77 K in a rigid TFA‐acidified isopropanol glass. In solution, the triplet states of these pyranoflavylium cations are efficiently quenched by molecular oxygen, resulting in sensitized formation of singlet oxygen, as confirmed by direct detection of the triplet‐state decay by laser flash photolysis and of singlet oxygen monomol emission in the near infrared. The strong visible light absorption, the relatively small singlet‐triplet energy differences, the excited state redox potentials and the reasonably long lifetimes of pyranoflavylium triplet states in the absence of molecular oxygen suggest that they might be useful as triplet sensitizers and/or as cationic redox initiators in polar aprotic solvents like acetonitrile.     

Determination of hypochlorite in water using a chemiluminescent test strip

We have developed a selective and reusable chemiluminescent test strip to determine hypochlorite. The hypochlorite-sensitive test strip contains a 10 mm × 9 mm piece of anionic cellulose paper in fluoresceinate cycle, glued to a 10 mm × 4 cm × 0.5 mm polyester strip. The measurement of the chemiluminescence in a luminometer when 1 ml of sample is injected into a conventional cell containing the strip makes it possible to determine hypochlorite. The composition of the membrane and reaction conditions have been adjusted to obtain adequate sensitivity and selectivity. The test strip responded linearly to hypochlorite over two linear ranges, the first 2.0-10.3 mg L⁻¹ and the second 10.3-51.4 mg L⁻¹, with a detection limit of 0.4 mg L⁻¹. The reproducibility using the same disposable test strip at a medium level of the range was 6.6%, as relative standard deviation (R.S.D.), and 12.3% using different test strips. The procedure was applied to the determination of hypochlorite in different types of waters.     

Chemiluminescence during decomposition of 1,4-dimethylnaphthalene endoperoxide on the silica gel and alumina surface

Decomposition of 1,4-dimethylnaphthalene endoperoxide supported on the silica gel and alumina surface is accompanied by chemiluminescence (CL) in the IR and visible spectral regions. The CL emitter in the IR region is singlet oxygen. The ¹O₂ dimol contributes mainly to the emission at λ_max = 630 and 700 nm. It was shown by the IR-CL method that endoperoxide decomposition on the sorbent surface follows the first-order kinetics. The activation parameters of the process were determined. On the Al₂O₃ and silica gel surfaces a substantial acceleration of the decomposition of 1,4-dimethylnaphthalene endoperoxide is observed compared to the solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 199–204, February, 2007.     

Determination of a non-ionic surfactant in aqueous environmental samples by flow-injection analysis with chemiluminescence detection

A flow-injection procedure for the determination of a commercially available fatty amine ethoxylate-based non-ionic surfactant in sea water over the range 0–50 mg l^?1 is described. The procedure is based on measurement of the chemiluminescence emission resulting from oxidation of the tertiary amine group with sodium hypochlorite at pH 10.5 in the presence of Rhodamine B, which acts as a sensitizer.     

Flow-injection investigation of the chemiluminescent reaction of bis(2,4,6-(trichlorophenyl)oxalate) with free chlorine

This work investigated the chemiluminescent reaction of free chlorine with bis(2,4,6-(trichlorophenyl)oxalate) (TCPO) in the presence of 9,10-diphenylanthracene in acetonitrile/water medium, with analytical application for free chlorine in tap water. In the absence of free chlorine, the background signal increased with the pH and the chemiluminescence emission showed strong dependence with the sample acidity. A flow injection analysis system, for free chlorine determination, was developed. The linear range for free chlorine was (0.2-3.0)×10⁻⁵ mol l⁻¹. Chloramine 1.0×10⁻⁵ mol l⁻¹ and chlorite 1.0×10⁻⁶ mol l⁻¹ also enhanced the chemiluminescence intensity.