The extra-weak chemiluminescence generated during oxidation of some tetracycline antibiotics. 1. Autoxidation.

Chemiluminescence (CL) appearing during autoxidation of tetracycline (TC) antibiotics has been studied. The CL spectrum consists of four emission bands with maxima at 520, 585, 640 and 700 nm. The bands at 585, 640 and 700 nm are similar to those observed for singlet molecular oxygen (1O2). The effect of 1O2 quenchers and free radical reaction inhibitors on the light emission is also reported. The data support the concept that, during the autoxidation of TCs, cytotoxic oxygen species such as HO., O2.-, H2O2 and 1O2 are formed.     

Feasibility of Fluorescence Detection of Tetracycline in Media Mixtures Employing A Fiber Optic Probe

Abstract

This work assesses the feasibility of fluorescence detection of tetracycline in very optically dense mixtures of highly fluorescent media ingredients used in tetracycline production by fermentation. The fluorescence measurements are accomplished with a fiber optic probe. Seven different mixtures were examined in this study. Each one contained a nonfluorescent base of nutrients and salts along with one of the following media ingredients at 5 g/100 mL: cottonseed flour, corn gluten meal, soybean flour, distiller 's grains and solubles, corn steep liquor, brewer's yeast, and molasses. The concentration of tetracycline was varied in each mixture and fluorescence measurements were made at every concentration step. Excitation light of 390 nm was used to probe the samples, and emission spectra were obtained over the wavelength range from 400 to 600 nm. In most of the samples studied, the fluorescence intensity in the wavelength range corresponding to background media fluorescence (420–480 nm) decreased as the tetracycline concentration increased. The decreases in the short wavelength range might be explained by the absorption by tetracycline of 390 nm excitation light (in competition with absorption by the media) and/or by absorption of background media fluorescence by tetracycline. Frequently, the maximum emission of the mixtures shifted to longer wavelengths. The maximum approached that of tetracycline (approximately 520 nm). Plots of integrated fluorescence intensity, in the emission wavelength regions of 420-480 nm and 500-560 nm, versus tetracycline hydrochloride concentration reflect these shifts. We have found that the changes in fluorescence intensity in these two wavelength regions during tetracycline addition depend on the identity of the media component in the mixture. For corn meal, soybean, brewer's, and molasses media, the fluorescence in the short emission wavelength range decreases while that in the long region increases. In the case of distiller's and corn steep media, the fluorescence changes very little during tetracycline addition. Finally, in cottonseed medium, the fluorescence increases in both wavelength ranges. The data show that fluorescence can be used to detect tetracycline, at least qualitatively, in the presence of the highly fluorescent media ingredients.     

The extra-weak chemiluminescence generated during oxidation of some tetracycline antibiotics. II. Peroxidation.

This study was undertaken to establish the mechanism of chemiluminescence during the oxidation reaction of tetracycline antibiotics in the presence of molecular oxygen and H2O2. The spectral distribution of chemiluminescence and fluorescence and the quantum yields of chemiluminescence were measured. The chemiluminescence spectrum measured with cut-off filters revealed one broad blue-green band and bands with maxima at 580, 640 and 700 nm. The bands at 580, 640 and 700 nm were similar to those observed for singlet molecular oxygen. The effect of superoxide radical, hydroxyl radical inhibitors, singlet oxygen quenchers and D2O as solvent on the light emission was also studied. The formation of singlet oxygen during the oxidation of the investigated tetracyclines was also checked using the spectrophotometric method based on the bleaching of p-nitrosodimethylaniline. A mechanism for the reactions generating electronically excited compounds is proposed.     

镝荧光探针的构建及对牛奶中四环素残留的检测

在乙醇体系中构建三元配合物的镝荧光探针,并利用盐酸四环素(TC)对镝荧光探针具有荧光猝灭作用,提出了一种检测牛奶中四环素残留的新方法.首先确定体系的激发波长为305 nm,发射波长为574 nm.在配比、加料顺序、时间等方面对镝荧光探针进行了条件优化,确定了镝离子(Dy³⁺)、磺基水杨酸(SSA)、三正辛基氧化磷(TOPO)的最佳配比为1:2:0.1和30 min最佳检测时间.其次建立了检测盐酸四环素的线性曲线,并获得检测范围为10^-6~2×10^-5 mol/L.最后,利用此荧光探针对处理的牛奶样品进行加样回收检测,回收率在96.9 %~104.4 %.实验证明建立的方法科学可行,对盐酸四环素具有高选择性.     

Electrochemical oxidation of tetracycline on a boron doped diamond electrode within the stability potentials of water

Electrochemical oxidation of tetracycline on a boron doped diamond electrode within the stability potentials of water was studied in order to develop an approach for the purification of waste water containing medicinal agents. Cyclic voltammetry, HPLC, and high resolution mass spectrometry were used to establish that in the electrochemical oxidation process, tetracycline adds one oxygen atom to further form organic compounds with molecular weights higher than that of tetracycline. It was found that tetracycline in this region of potentials can be almost completely deactivated without its mineralization.     

Simultaneous determination of ampicillin and tetracycline in milk by using a stopped-flow/T-format spectrofluorimeter

A fast and simple fluorimetric method is described for the simultaneous determination of ampicillin and tetracycline in milk by combining the stopped-flow mixing technique with a T-format spectrofluorimeter. Ampicillin determination is based on its hydrolysis with penicillinase and reaction with mercuric chloride, while the intramolecular energy transfer from tetracycline to europium ions in the presence of thenoyltrifluoracetone is used for tetracycline determination. The similar excitation wavelengths of both systems and the separation between the corresponding emission wavelengths allow the direct determination of both analytes by measuring simultaneously the initial rate of the ampicillin system and the equilibrium signal of the tetracycline system. The relative standard deviations were lower than 2%. The proposed method was applied to the determination of these antibiotics in different milk samples with a recovery of 95.0-103.3% for ampicillin and 93.3-103.3% for tetracycline.     

RED CHEMILUMINESCENCE FROM RAM SEMINAL VESICLE MICROSOMES: PITFALLS IN THE USE OF SPECTRALLY RESOLVED RED CHEMILUMINESCENCE AS A TEST FOR SINGLET OXYGEN IN BIOLOGICAL SYSTEMS

Abstract— The assignment of the red chemiluminescence bands in the ram seminal microsome system to singlet oxygen as previously reported by Cadenas and Sies (1983) Hoppe-Seyler's Z. Physiol. Chem. 364, 519-528 was re-evaluated. Measurements of 1268 nm emission demonstrated that ram seminal vesicle microsomes produced very small quantities of singlet oxygen (0.41 2 0.05 p.M) when they metabolized high concentrations of 15-hydroperoxyarachidonic acid (1 mM). The red chemilumi- nescence, however, was not due to singlet oxygen, since it failed to increase in deuterium oxide and it was five orders of magnitude larger than the predicted emission from singlet oxygen produced in this system. Quantitative measurements of the time integral of the square root of the red chemiluminescence intensity may be a useful test to confirm the assignment of red emission to singlet oxygen in other biochemical systems.     

CUTANEOUS PHOTOTOXICITY OF TETRACYCLINE ANTIBIOTICS: GENERATION OF FREE RADICALS and SINGLET OXYGEN DURING PHOTOLYSIS AS MEASURED BY SPIN-TRAPPING and THE PHOSPHORESCENCE OF SINGLET MOLECULAR OXYGEN

Chlortetracycline (CTC) generated an aryl radical in aqueous buffer (pH 7.4) during near UV irradiation, as evidenced by the formation of 2-methyl-2-nitrosopropane spin adducts. The radical was produced via dechlorination, a photoprocess not previously reported for tetracyclines. Demeclocyc-line (DEM), another chlorinated tetracycline, did not produce detectable aryl radicals. Relative ¹O₂ yields obtained by direct luminescence measurements at 1268 nm for five tetracyclines in alkaline ethanol (demeclocycline · tetracycline · chlortetracycline · doxycycline · minocycline) showed that DEM produced approximately three times as much singlet oxygen as CTC. This constitutes direct evidence that tetracyclines sensitize both Type I and Type II photoreactions.     

SPECTRAL ANALYSES OF LOW LEVEL CHEMILUMINESCENCE OF A SHORT LIFETIME USING A HIGHLY SENSITIVE POLYCHROMATIC SPECTROMETER INCORPORATING A TWO DIMENSIONAL PHOTON-COUNTING TYPE DETECTOR

Abstract— Spectral analyses of low level chemiluminescence were carried out by using a newly developed polychromatic spectrometer in which a diffracted photon emission was detected simultaneously using a two dimensional photon-counting device. The spectrometer was sensitive in the 400–800 nm wavelength range. Low level chemiluminescence generated in a 1 nM luminol solution could be detected as a spectrum, showing a peak at 430 nm. Short lifetime photon emission from singlet oxygen showed only two peaks at around 630 and 700 nm in this highly time-resolved spectroscopy. Lipid peroxidation of linoleic acid by the lipoxygenase emitted a low intensity peak centered at 440 nm, but singlet oxygen emission arising from the decomposition of lipid peroxide was not observed. An injured cotyledon of a soybean seedling gave a broad emission centered at 725 nm in the absence of hydrogen peroxide, while in its presence a different emission peak appeared at a shorter wavelength (515 nm). Oxygenated, fluorescent components in the soybean seedling may be the emitting species. Singlet oxygen and triplet carbonyl groups were shown to be unlikely sources of the emission.     

Mo-La2O3模拟阴极的高温XPS/AES研究Ⅰ. 表面氧状态及其性质

对稀土氧化物体系Ｌａ２Ｏ３中Ｏｌｓ的超高温原位ＸＰＳ进行研究,着重讨论了Ｍｏ－Ｌａ２Ｏ３阴级激活过程中温度变化导致表面氧状态改变的过程,并初步分析其对电子发射性能的影响。高温１３００℃以上,存在两类不同氧种的氧,低结合能端的氧是表面晶格氧,高结合能端的氧为吸附氧;     

SPECIES DIFFERENCES IN RESPONSE TO PHOTOHEMOLYTIC AGENTS

Species differences in red blood cell susceptibility to the photohemolytic agents chlorpromazine, menadione and tetracycline were examined in mouse, rat, dog, and human blood. Menadione and tetracycline (25 microM) hemolyzed mouse but not dog, rat, or human red blood cells (RBC) when irradiated with UV light but not in the dark. Chlorpromazine (25 microM) produced a photohemolytic response in all four species with mouse and rat RBC lysing fastest followed by human then dog cells. Investigations into the nature of these species differences suggested that the size of mouse RBC may contribute to its high sensitivity to photohemolytic agents. An investigation of the effect of UV light on key antioxidant enzymes revealed species differences in enzyme inactivation. These data suggest that mouse RBC may be particularly vulnerable to phototoxic agents, especially those compounds which produce active oxygen species and, therefore, may prove more useful than human RBC as a model for predicting phototoxic potential of some chemical entities.     

Monitoring the degradation of tetracycline by ozone in aqueous medium via atmospheric pressure ionization mass spectrometry

The degradation of tetracycline (1) by ozone in aqueous solution was investigated. High performance liquid chromatography (HPLC), UV-visible spectroscopy (UV-Vis), and total organic carbon (TOC) analyses revealed that although tetracycline was quickly consumed under this oxidative condition, it did not mineralize at all. Continuous monitoring by electrospray ionization mass spectrometry in the positive ion mode, ESI(+)-MS, revealed that tetracycline (1), detected in its protonated form ([1 + H]+) of m/z 445, reacted to yield almost exclusively two unprecedented oxidation products (2 and 3) via a net insertion of one and two oxygen atoms, respectively. Compound 2, suggested to be formed via an initial 1,3-dipolar cycloaddition of ozone at the C11a-C12 double-bond of 1, and Compound 3, proposed to be produced via a subsequent ozone attack at the C2-C3 double-bond of 2, were detected in their protonated forms in the ESI(+)-MS, i.e., [2 + H]+ of m/z 461 and [3 + H]+ of m/z 477, and were further characterized by ESI(+)-MS(n). LC-APCI(+)-MS (liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry in the positive ion mode) experiments corroborated the results.     

不同煤燃烧方式降低NOx排放比较及解耦燃烧应用

采用两段反应器研究了三种煤在不同燃烧方式下抑制NO_x生成的效果。结果表明,煤的热解气和部分气化生成气再燃均能较好的抑制NO_x生成,抑制效果优于空气分级燃烧,解耦燃烧方式抑制NO_x生成的效果最显著,相对于传统燃烧其NO_x排放降低了32%以上。煤种对各种燃烧方式降低NO_x的程度有明显影响,煤中单位氮含量的燃料比(固定碳/挥发分)越小,煤的热解气和部分气化生成气再燃以及解耦燃烧方式下NO_x的排放量越低。在煤部分气化生成气再燃烧方式中,部分氧化气化段通氧量不同,降低NO_x排放的效果也不同,在氧气体积分数为8%~10%时的NO_x生成量最低。基于解耦燃烧技术原理,研制了1.4 MW解耦燃烧工业锅炉,在燃烧同一煤种时,解耦燃烧锅炉和传统立式锅炉相比,烟气中NO_x排放量降低了32.9%。     

Tryptophan-to-dye fluorescence energy transfer applied to oxygen sensing by using type-3 copper proteins

A fluorescence-based system to sense oxygen in solution is described. The method exploits the sensitivity of the endogenous fluorescence of type-3 copper proteins towards the presence of oxygen by translating the near-UV emission of the protein to label fluorescence in the visible range through a FRET mechanism. The main protein in this study, a recombinant tyrosinase from the soil bacterium Streptomyces antibioticus, has been covalently labeled with a variety of fluorescent dye molecules with emission maxima spanning the whole visible wavelength range. In all cases, the emission of the label varied considerably between O2-bound and O2-free protein with a contrast exceeding that of the Trp emission for some labels. It is shown that different constructs may be simultaneously observed using a single excitation wavelength. Next to the described application in oxygen sensing, the method may be applicable to any protein showing variations in tryptophan fluorescence, for example as a function of ligand binding or catalysis.     

The effects of oxygen on the detection of mercury using laser-induced breakdown spectroscopy

A systematic study of the processes associated with mercury atomic emission in a laser-induced plasma and the interactions of mercury with oxygen species is presented. At early plasma decay times, on the order of 5–10 μs, no significant variation in mercury atomic emission was observed with the addition of oxygen-containing species. At intermediate and long decay times (10–100 μs), a significant reduction in the 253.7-nm mercury emission intensity was recorded with the introduction of oxygen-containing species. The decrease in mercury emission was temporally coincident with the recombination of atomic oxygen, as measured by the O(I) emission. The decreased mercury emission was not due to thermal effects, based on plasma temperature measurements, and was independent of the molecular source of oxygen, for similar concentrations of oxygen as air, carbon dioxide, and carbon monoxide. Analysis of additional mercury atomic emission lines revealed that the reduction in mercury emission in the presence of oxygen species is limited primarily to the 253.7-nm transition. In concert, the data lead to the conclusion that the 253.7-nm mercury emission line is selectively quenched by oxygen species, primarily O₂ and NO, that are formed during the plasma recombination process. Implications for laser-induced breakdown spectroscopy-based emissions monitoring of mercury species are discussed.     

基于碳点-铕的比率荧光探针可视化检测四环素

结合四环素对碳点(CDs)的荧光猝灭及对铕离子(Eu ³⁺)的荧光增强作用, 建立了一种肉眼可辨的比率荧光分析方法用于水样中四环素残留的便捷检测. 通过优化CDs/Eu ³⁺比例、 溶液pH值等实验条件, 使检测体系对四环素的荧光响应呈现由蓝色→粉色→红色的颜色转变过程, 易于通过肉眼进行分辨和半定量分析. 实验结果表明, 2种荧光探针响应比(I₆₁₈/I₄₄₀)的对数值与四环素的浓度在20~100 nmol/L范围内呈线性关系, 方法的检出限为1 nmol/L. 将该方法应用于江水样品中四环素的加标检测, 获得了较好结果.     

Partial least-squares analysis of time decay data for Eu(III)-tetracycline complexes: simultaneous luminescent determination of tetracycline and oxytetracycline in bovine serum

A simple and sensitive methodology to simultaneously quantify tetracycline and oxytetracycline in bovine serum samples is described. The method combines the advantages of the lanthanide-sensitized luminescence (i.e., sensitivity and selectivity) with partial least-squares (PLS) analysis, and requires no previous separation steps. Due to the strong overlapping of emission and excitation spectra of the analytes and their europium complexes, the luminescence decay curve (intensity of luminescence vs. time) of analyte-Eu complex was selected to resolve mixtures of tetracycline and oxytetracycline. Partial least-squares uses the luminescence decay as discriminatory parameter and regresses the luminescence versus time onto the concentrations of standards. Using a 16-sample aqueous calibration set, 10 validation samples, 11 spiked serum bovine samples and a blank of serum were studied. The analyte recoveries from serum samples ranged from 87 to 104% for tetracycline and from 94 to 106% for oxytetracycline. The results obtained by the developed method were statistically comparable to those obtained with high performance liquid chromatography.     

Characteristics of pine wood oxidative pyrolysis: Degradation behavior,carbon oxide production and heat properties

Oxidative pyrolysis of pine wood was studied by thermogravimetric analysis (TGA) coupled with mass spectrometer (MS) and differential scanning calorimetry (DSC) methods. The effects of oxygen concentration on pyrolysis behavior, carbon oxide production and heat properties were investigated. Several parameters were defined to evaluate the oxygen influence. It was found that oxygen dramatically promotes the oxidative degradation and char oxidation rate. The reactivity index was found to be proportional to the oxygen concentration, which suggested that oxidative degradation reactions were under increasingly kinetic control in elevated oxygen concentration environments. Carbon oxides evolution properties were investigated. There are two releasing peaks in MS curves for oxidative condition comparing with one peak under inert condition. They are related with oxidative degradation and char oxidation, respectively. Both total amounts and rates of carbon oxides emission were found to increase with oxygen concentration. The cumulative emission ratio of CO to CO₂ first decreases then increases with oxygen concentration with 10% as turning point. It may be caused by different oxygen diffusion behaviors with variable oxygen concentrations. The absolute reaction heat value of oxidative pyrolysis (−7.23 MJ kg⁻¹, 5% O₂) is much larger than that of inert condition (+0.28 MJ kg⁻¹). Increasing of oxygen concentration results in an increase of heat emission. Comparing with pine wood low heat value, the net heat emission efficiencies under different oxygen concentrations (5%, 10%, 15%, 21%) are 39.73%, 44.84%, 68.90% and 78.41%, respectively.     

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.