Study on the generation mechanism of reactive oxygen species on calcium peroxide by chemiluminescence and UV-visible spectra.

In the present work, the generation mechanism of reactive oxygen species (ROS) on calcium peroxide (CaO(2)) was studied. A very intense chemiluminescence (CL) signal was observed when adding an aqueous solution of luminol or 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo[1,2alpha]-pyrazin-3-one hydrochloride (MCLA) to a suspension of CaO(2). The ROS released on CaO(2) were thought to be oxidizing agents leading to CL, and were characterized by CL, UV-visible (UV-vis) spectra and the effective scavengers of the special ROS. From experimental results, the hydroxyl (.OH) and superoxide (.O(2) (-)) radicals were suggested to exist on the surface of CaO(2). A reaction scheme for the formation of the ROS on CaO(2) was also proposed and discussed. Of more interest was the finding that the CaO(2) which released the .OH and .O(2) (-) on the surface exhibited good transition properties compared with alkaline-earth metal peroxides of the same group (MgO(2), BaO(2)).     

Determination of phenformin hydrochloride using molecular imprinting technology coupled with flow-injection chemiluminescence

A novel method was developed using molecular imprinting technology (MIT) coupled with flow‐injection chemiluminescence (FI‐CL) for highly sensitive detection of phenformin hydrochloride (PH). The phenformin imprinted polymer was synthesized with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross‐linker. Newly synthesized molecularly imprinted polymer (MIP) particles were packed into a column as a selective recognition element for determination of PH. A CL method for the determination of PH was developed based on the CL reaction of PH with N‐bromosuccinimide sensitized by eosin Y in basic media. The optimization of detection conditions was investigated. The CL intensity responded linearly to the concentration of PH in the range 0.09–2.0 µg/mL, with a correlation coefficient of 0.9920. The detection limit was 0.031 µg/mL. The relative standard deviation for the determination of 1.0 µg/mL PH solution was 1.0% (n = 11). The method was applied to the determination of PH in urine samples, with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.     

Near-infrared chemiluminescence from the oxidation of ammonia in aqueous alkaline solution.

The chemiluminescent oxidation of ammonia with hypobromite in aqueous alkaline solution evokes a broadly distributed emission in the near-infrared region, with intensity maxima at 1055 nm and 1270 nm.     

Flow‐injection chemiluminescence determination of diazepam by oxidation with N‐bromosuccinimide

A rapid and sensitive flow‐injection chemiluminescence (FI–CL) method is described for the determination of diazepam based on its reaction with N‐bromosuccinimide (NBS) in alkaline medium in the presence of dichlorofluorescein (DCF) as an effective energy‐transfer agent. Under optimum conditions, the proposed method allowed the measurement of diazepam over the range of 2.0 × 10^?6 to 2.0 × 10^?4 mol/L with a detection limit of 5.0 × 10^?7 mol/L. The relative standard deviation for 11 parallel measurements of 2.0 × 10^?5 mol/L diazepam was 2.1%. The method was applied satisfactorily for the determination of diazepam in pharmaceutical preparations, and the results agree well with those obtained by spectrophotometry. The use of the proposed system for the determination of diazepam in urine and plasma samples was also tested. The possible mechanism of the chemiluminescence reaction is discussed briefly. Copyright © 2012 John Wiley & Sons, Ltd.     

Time-resolved chemiluminescence study of the TiO2 photocatalytic reaction and its induced active oxygen species.

The time-resolved chemiluminescence (CL) method has been applied to study the TiO(2) photocatalytic reaction on a micros-ms timescale. The experimental set-up for time-resolved CL was improved for confirmation of the unique luminol CL induced by the photocatalytic reaction. The third harmonic light (355 nm) from an Nd:YAG laser was used for the light source of the TiO(2) photocatalytic reaction. Luminol CL induced by this reaction was detected by a photomultiplier tube (PMT) and a preamplifier was used for amplifying the CL signal. Experimental conditions affecting the photocatalytically induced CL were discussed in detail. The involvement of active oxygen species such as .OH, O(2) (.-) and H(2)O(2) in the CL was examined by adding their scavengers. It is concluded that .OH was greatly involved in the CL on a micros-ms timescale, especially in time periods <100 micros after illumination of the pulse laser. On the other hand, CL generated by O(2) (.-) began to increase after 100 micros and became dominant after 2.5 ms. A small part of the CL might be generated by H(2)O(2) on the whole micros-ms timescale. A CL reaction mechanism related with .OH and dissolved oxygen was proposed to explain the photocatalytically induced luminol CL on a micros-ms timescale, especially in periods <100 micros.     

Mechanisms of inhibition of chemiluminescence in the oxidation of luminol by sodium hypochlorite

Two different mechanisms of inhibition of chemiluminescence in the oxidation of luminol by sodium hypochlorite were found. Most substances investigated in these experiments acted by scavenging NaOCI. This mechanism was independent of the concentration of hydrogen peroxide and the incubation time between luminol and inhibitors. The most potent inhibitors were substances containing SH groups. Compounds with amino groups as a target for HOCI/OCI^? to yield chloramines were much less effective inhibitors. Another mechanism of inhibition was found for catalase. It depended on the presence of hydrogen peroxide in the incubation medium and the incubation time between luminol and catalase. The enzyme inhibited the luminescence by removing H₂O₂ at molar concentrations much smaller than those found for all other inhibitors. Our results confirm the present models of the mechanism of generation of luminescence in luminol oxidation.     

5种石斛及其组织培养物对活性氧的清除作用

采用化学发光法,以3种活性氧R0S(02、     

Chemiluminescence intensities and spectra of luminol oxidation by sodium hypochlorite in the presence of hydrogen peroxide

Hydrogen peroxide amplifies the chemiluminescence in the oxidation of luminol by sodium hypochlorite. A linear relationship between concentration of hydrogen peroxide and light intensity was found in the concentration range 5 × 10^?8?7.5 × 10^?6 mol/l. At 7.5 × 10^?6 mol/l H₂O₂ the chemiluminescence is amplified 550—fold. The chemiluminescence spectra of these reactions have a wavelength maximum at 431 nm independent of the concentration of hydrogen peroxide. The results indicate that hydrogen peroxide is a necessary component in the chemiluminescent oxidation of the luminol by sodium hypochlorite.     

Urate attenuates oxidation of native low-density lipoprotein by hypochlorite and the subsequent lipoprotein-induced respiratory burst activities of polymorphonuclear leukocytes

Oxidation converts native low-density lipoprotein (LDL) into a signal molecule promoting inflammatory processes during atherogenesis. The exact contribution of different antioxidants in prevention of LDL oxidation is not known. Uric acid efficiently scavenges oxidants including hypochlorite. We investigated the effect of different urate concentrations (25-500 mol/l) on the oxidation of isolated native LDL by sodium hypochlorite (1000 mol/l). While relative electrophoretic mobility declined continuously with increasing urate concentrations in the oxidation medium, lipid peroxidation as measured by TBARS was blunted only at high molar urate/NaOCl ratios. By decreasing oxidative modifications, urate dose-dependently (beginning with a urate/NaOCl ratio of 1:40) diminished stimulatory effects of oxidized LDL on the respiratory burst of resting polymorphonuclear leukocytes (PMNL). Protecting effects of urate against the proinflammatory action of oxidized LDL on activated cells were evident only at a molar urate/NaOCl ratio of 1:2 suggesting different sensitivities of PMNL to LDL oxidation state in dependence on their activity state.     

Scavenging of reactive oxygen species by the plant phenols genistein and oleuropein.

The plant-derived phenolic compounds genistein and oleuropein are known to exhibit several biological properties, many of which may result from their antioxidant and free radical scavenger activity. In this paper we report the results of a complex study of antioxidant activity of genistein and oleuropein, using electron spin resonance (ESR), chemiluminescence, fluorescence and spectrophotometric techniques. Different reaction systems were applied to study the inhibitory effect of the phenolic compounds studied: (a) the potassium superoxide/18-crown-6 dissolved in DMSO system, which generates superoxide radical (O(2).(-)) and hydrogen peroxide (H(2)O(2)); (b) the Co(II)-EDTA-H(2)O(2) system (the Fenton-like reaction), which generates hydroxyl radical (HO.); (c) 2,2'-azobis(2-amidino-propane)dichloride (AAPH) as the peroxyl radical (ROO.) generator, and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical test. Results showed that genistein and oleuropein decreased the chemiluminescence sum from the O(2).(-) generating system, an inhibitory effect that was dependent on their concentration. These compounds also reacted with ROO radicals and they showed activity about two-fold greater than the standard Trolox. The antioxidant effects were studied at different concentrations and reflected in protection against the fluorescence decay of beta-phycoerythrin (beta-PE), due to ROO. attack on this protein. Using the Fenton-like reaction and the spin trap agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the phenolic compounds examined were found to inhibit DMPO-.OH radical formation in the range 10-90% at concentrations of 0.1 mmol/L to 2 mmol/L. Furthermore, these compounds also inhibited HO.-dependent deoxyribose degradation; about 20% and 60% inhibitions were observed in the presence of 0.5 mmol/L genistein and oleuropein, respectively. It was also demonstrated that genistein had a weaker DPPH radical scavenging activity than oleuropein. Our results confirm good scavenging activity towards O(2).(-), HO. and ROO. and the antioxidant effect of genistein and oleuropein.     

Comparative study of antioxidants as quenchers or scavengers of reactive oxygen species based on quenching of MCLA-dependent chemiluminescence.

The quenching or scavenging effect of non-enzymatic antioxidants against reactive oxygen species (ROS) was studied by comparing the degree of suppression of chemiluminescence (CL) caused by the oxidation of MCLA (methoxylated Cypridina luciferin analogue) by ROS. MCLA-dependent CL caused by O2- was effectively quenched by ascorbic acid, beta-carotene, lycopene and astaxanthin, while it was enhanced by alpha-tocopherol. The CL by 1O2 was quenched effectively by beta-carotene, lycopene and astaxanthin, moderately by ascorbic acid, and slightly by alpha-tocopherol. beta-Carotene and alpha-tocopherol remarkably suppressed the CL when ROS was HO*. The present study revealed that MCLA-dependent CL assay provides a simple and rapid method for the evaluation of antioxidants as a quencher or scavenger against any kind of ROS.     

Understanding the disrupting mechanism of the Tau aggregation motif “306VQIVYK311” by phenylthiazolyl‐hydrazides inhibitors

Alzheimer's disease is a progressive neurodegenerative disorder characterized by the abnormal processing of the Tau and the amyloid precursor proteins. The unusual aggregation of Tau is based on the formation of intermolecular β‐sheets through two motifs: ²⁷⁵VQIINK²⁸⁰ and ³⁰⁶VQIVYK³¹¹. Phenylthiazolyl‐hydrazides (PTHs) are capable of inhibiting/disassembling Tau aggregates. However, the disaggregation mechanism of Tau oligomers by PTHs is still unknown. In this work, we studied the disruption of the oligomeric form of the Tau motif ³⁰⁶VQIVYK³¹¹ by PTHs through molecular docking, molecular dynamics, and free energy calculations. We predicted hydrophobic interactions as the major driving forces for the stabilization of Tau oligomer, with V306 and I308 being the major contributors. Nonpolar component of the binding free energy is essential to stabilize Tau‐PTH complexes. PTHs disrupted mainly the van der Waals interactions between the monomers, leading to oligomer destabilization. Destabilization of full Tau filament by PTHs and emodin was not observed in the sampled 20 ns; however, in all cases, the nonpolar component of the binding free energy is essential for the formation of Tau filament‐PTH and Tau filament‐emodin. These results provide useful clues for the design of more effective Tau‐aggregation inhibitors.     

A kinetic study of the enhancement of solution chemiluminescence of glyoxylic acid oxidation by manganese species

In order to study the mechanism of the enhancement of solution chemiluminescence, the kinetics of the decay of the oxidant and the chemiluminescence emission were followed for oxidations by permanganate, manganese dioxide sol and Mn³⁺_(aq) of glyoxylic acid, using stopped‐flow spectrophotometry. Results are reported for the glyoxylic acid oxidized under pseudo first‐order conditions and in an acidic medium at 25 °C. For permanganate under these conditions, the decay is sigmoidal, consistent with autocatalysis, and for manganese dioxide sol and Mn³⁺ it is pseudo first order. The effects of the presence of aqueous formaldehyde and Mn²⁺ were observed and a fit to a simple mechanism is discussed. It is concluded that chemiluminescent enhancement in these systems is best explained by reaction kinetics. Copyright © 2014 John Wiley & Sons, Ltd.     

Scavenging of reactive oxygen species by N‐substituted indole‐2 and 3‐carboxamides

Indole‐2 and 3‐carboxamides (IDs) are proposed to be selective cyclooxygenase inhibitors. Since cyclooxygenase‐1 may be involved in reactive oxygen species (ROS) production, we hypothesize that these indole derivatives have antioxidative properties. We have employed chemiluminescence (CL) and electron spin resonance (ESR) spin trapping to examine this hypothesis. We report here the results of a study of reactivity of 10 selected indole derivatives towards ROS. The following generators of ROS were applied: potassium superoxide (KO₂) as a source of superoxide radicals (O₂^·?), the Fenton reaction (Co‐EDTA/H₂O₂) for hydroxyl radicals (HO^·), and a mixture of alkaline aqueous H₂O₂ and acetonitrile for singlet oxygen (¹O₂). Hydroxyl radicals were detected as 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) spin adduct, whereas 2,2,6,6‐tetramethyl‐piperidine (TEMP) was used as a detector of ¹O₂. Using the Fenton reaction, 0.5 mmol/L IDs were found to inhibit DMPO‐?H radical formation in the range 7–37%. Furthermore the tested compounds containing the thiazolyl group also inhibited the ¹O₂‐dependent TEMPO radical, generated in the acetonitrile + H₂O₂ system. About 20% inhibition was obtained in the presence of 0.5 mmol/L IDs. 1 mmol/L IDs caused an approximately 13–70% decrease in the CL sum from the O₂^·? generating system (1 mmol/L). The aim of this paper is to evaluate these indole derivatives as antioxidants and their abilities to scavenge ROS. Copyright © 2004 John Wiley & Sons, Ltd.     

The determination of glutamine with flow‐injection chemiluminescence detection and mechanism study

The main purpose of this study was to develop an inexpensive, simple, rapid and sensitive chemiluminescence (CL) method for the determination of glutamine (Gln) using a flow‐injection (FI) system. Gln was found to strongly inhibit the CL signal of the luminol–H₂O₂–CuSO₄ system in Na₂B₄O₇ solution. A new FI‐CL method was developed for the determination of Gln. Parameters affecting the reproducibility and CL detection were optimized systematically. Under the optimized conditions, the corresponding linear regression equation was established over the range of 5.0 × 10^?7 to 2.5 × 10^?6 mol/L with the detection limit of 1.8 × 10^?8 mol/L. The relative standard deviation was found to be 1.8% for 11 replicate determinations of 1.5 × 10^?6 mol/L Gln. The proposed method has been satisfactorily applied for the determination of Gln in real samples (Marzulene‐s granules) with recoveries in the range of 98.7–108.6%. The minimum sampling rate was about 100 samples/h. The possible mechanism of this inhibitory CL was studied by fluorescence spectrophotometer and UV–vis spectrophotometer. Copyright © 2009 John Wiley & Sons, Ltd.     

Sensitive determination of epinephrine in pharmaceutical preparation by flow injection coupled with chemiluminescence detection and mechanism study

A novel, rapid and sensitive method was described for the determination of epinephrine (EP) using flow injection analysis coupled with chemiluminescence (CL) detection, which based on EP enhanced the weak CL emission of luminol–KIO₄ system in NaOH solution. Parameters affecting the CL intensity and reproducibility were optimized systematically. Under the optimized experiment conditions, the net CL intensity was proportional to the concentration of EP in the range of 5.0 × 10^?8 to 1.5 × 10^?6 mol/L with a detection limit of 1.9 × 10^?9 mol/L. The relative standard deviation (RSD) was found to be 0.7% for 13 replicate determinations of 3.0 × 10^?7 mol/L EP. The applicability of the proposed method was illustrated in the determination of EP in pharmaceutical preparation. The recoveries of EP at different levels in EP hydrochloride injection were between 95.4 and 104.7%. One assay procedure takes only 27 s, and the sampling rate was calculated about to be 130 samples/h. The possible mechanism of the enhanced CL intensity was studied by examining CL spectra and UV–vis spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Extreme stability of helices formed by water-soluble poly-N-substituted glycines (polypeptoids) with alpha-chiral side chains.

Poly-N-substituted glycines or "peptoids" are protease-stable peptide mimics. Although the peptoid backbone is achiral and lacks hydrogen-bond donors, substitution with alpha-chiral side chains can drive the formation of stable helices that give rise to intense CD spectra. To systematically study the solution properties and stability of water-soluble peptoid helices with alpha-chiral side chains, we have synthesized and characterized an amphipathic, 36-residue N-substituted glycine oligomer. CD was used to investigate effects of concentration and solvent environment on this helical peptoid. We saw no significant dependence of helical structure on concentration. Intense, "alpha-helix-like" CD spectra were observed for the 36-mer in aqueous, 2,2,2-trifluorethanol (TFE), and methanol solution, proving a relative insensitivity of peptoid helical structure to solvent environment. While CD spectra taken in these different solvents were fundamentally similar in shape, we did observe some interesting differences in the intensities of particular CD bands in the various solvents. For example, the addition of TFE to an aqueous solvent increases the degree of peptoid helicity, as is observed for polypeptide alpha-helices. Moreover, the helical structure of peptoids appears to be virtually unaffected by heat, even in an aqueous buffer containing 8 M urea. The extraordinary resistance of these peptoid helices to denaturation is consistent with a dominant role of steric forces in their structural stabilization. The structured polypeptoids studied here may have potential as robust mimics of helical polypeptides of therapeutic interest.     

Studies of iron-uptake mechanisms in two bacterial species of the shewanella genus adapted to middle-range (Shewanella putrefaciens) or antarctic (Shewanella gelidimarina) temperatures

Iron(III)-uptake mechanisms in bacteria indigenous to the Antarctic, which is the most Fe-deficient continent on Earth, have not been extensively studied. The cold-adapted, Antarctic bacterium, Shewanella gelidimarina, does not produce detectable levels of the siderophore, putrebactin, in the supernatant of Fe(III)-deprived cultures. This is distinct from the putrebactin-producing bacterium from the same genus, Shewanella putrefaciens, which is adapted to middle-range temperatures. The production of putrebactin by S. putrefaciens is optimal, when the pH value of the medium is 7.0. According to the strong positive response from whole cells in the Chrome Azurol S (CAS) agar diffusion assay, Shewanella gelidimarina appears to produce cell-associated siderophores. In the RP-HPLC trace of an Fe(III)-loaded extract from the cell-associated components of S. gelidimarina cultured in media with [Fe(III)] ca. 0 microM, a peak appears at [MeCN] ca. 77%, which decreases in intensity in a parallel experiment in which [Fe(III)] ca. 5 microM, and is barely detectable in Fe(III)-replete media ([Fe(III)] ca. 20 microM). The Fe(III)-dependence of this peak suggests that the attendant species, which is significantly more hydrophobic than putrebactin (RP-HPLC elution: [MeCN] ca. 14%), is associated with Fe(III)-management in S. gelidimarina. This study highlights the diversity in Fe(III)-uptake mechanisms in Shewanella species adapted to different environmental and thermal niches.     

Unprecedented chemiluminescence behaviour during peroxyoxalate chemiluminescence of oxalates with fluorescent or electron-donating aryloxy groups.

A series of diaryl and bis(4-styrylphenyl) oxalates with electron-donating substituents or fluorescent moieties were subjected to the peroxyoxalate chemiluminescence (PO-CL) reaction, some of which were found to behave in a unprecedented manner. The reaction of bis(p-methyoxyphenyl) oxalate, as a representative example, emits light due not only to the emission from the externally added excited fluorophore, but also from the presumable excimer of p-methoxyphenol. Also, during the reaction of the bis(4-styrylphenyl) oxalates, the emission based on the fluorescence as well as the excimer of the eliminating group were observed. These experimental results suggest that such emitting species would be formed by an intra- and intermolecular electronic interaction with a high-energy intermediate, such as a dioxetanone.     

Determination of aromatic compounds by high-performance liquid chromatography with on-line photoreactor and peroxyoxalate chemiluminescence detection.

This paper describes a novel high-performance liquid chromatographic (HPLC) method for the determination of aromatic compounds with peroxyoxalate chemiluminescence (PO-CL ) detection following on-line UV irradiation. Aromatic compounds were UV irradiated (254 nm, 15 W) to generate hydrogen peroxide, which was determined via PO-CL detection using a mixture of bis(2,4,6-trichlorophenyl)oxalate (aryloxalate) and 2,4,6,8-tetrathiomorpholinopyrimido[5,4-d]pyrimidine (fluorophore) as a post-column CL reagent. Generation of hydrogen peroxide from aromatic compounds was confirmed using a flow injection analysis (FIA) system incorporating an enzyme column reactor immobilized with catalase. The conditions for UV irradiation were optimized using benzene and monosubstituted benzenes (phenol, benzaldehyde, nitrobenzene and N,N-dimethylaniline) by an HPLC system to evaluate the analytical performance of the proposed system. The detection limits for benzene and monosubstituted benzenes were in the range 2.1-124 pmol/injection at signal:noise (S:N) ratio = 3. Monocyclic and polycyclic hydrocarbons were also employed to investigate their CL properties. The possibility of PO-CL detection for a wide variety of aromatic compounds was shown for the first time.