Fluctuation dynamics of chemiluminescence in the maillard reaction

The general problems of information deriving from the oscillation kinetics of Belousov-Zhabotinsky reactions were discussed. The discussion was organized around a particular example of the complex fluctuation dynamics of the Maillard reaction, i.e., a multistage reaction between a carbonylcontaining compound and the nucleophilic amino group of an amino-containing compound at different temperatures, as visualized by chemiluminescence. Flicker-noise spectroscopy served as methodological background of the fluctuation analysis comprising the two main steps: separation of low-frequency components attributed to resonances and their interference, from the source signals and analysis of the remaining chaotic components. Possibility of modeling the chaotic dynamics of fluctuations of the measured dynamic variables in terms of anomalous diffusion was shown.     

对硝基甲苯与多硫化钠反应的机理研究

对硝基甲苯与多硫化钠在乙醇-水溶液中加热,可以生成对氨基苯甲醛,这是目前工业上合成对氨基苯甲醛的最佳途径。本文用紫外-可见光谱仪监测反应过程吸收光谱的变化,并测定了反应物的电子自旋共振谱,以探索这一反应的正确机理。     

Oxalate/hydrogen peroxide chemiluminescence reaction. A 19F NMR probe of the reaction mechanism

The mechanism of the oxalate/hydrogen peroxide chemiluminescence reaction has been examined by magnetic resonance techniques. Investigation of the reactive intermediates involved in chemiluminescence was carried out with bis(2,6-difluorophenyl)oxalate (DFPO) using 19F NMR to probe its reactions with aqueous hydrogen peroxide. Formation and reactions of the intermediate hydroperoxy oxalate ester B along with the formation of the half ester product C and difluorophenol D were monitored by 19F NMR. When the reaction of DFPO and aqueous hydrogen peroxide was carried out in the presence of dansylphenylalanine, a typical fluorescent analyte, the intensity of the resonance due to the intermediate B was diminished in direct proportion to the concentration of the analyte. Comparison of the time/intensity profile of the chemiluminescence emission with that of the 19F NMR transient suggests that the hydroperoxy oxalate ester B is the likely 'reactive' intermediate, capable of participating in a chemically initiated electron exchange luminescence mechanism.     

Computational study on the reaction mechanism of atmospheric oxidation of ethanol with ozone

The reaction of C₂H₅OH and O₃ on the singlet potential energy surface is carried out using the MP2 and CCSD(T)//MP2 theoretical approaches in connection with the 6-311++G(d,p) basis set. Three pre-reactive complexes C1, C2, and C3 are formed between ethanol and ozone at atmospheric pressure and 298.15 K temperature. With variety of the complexes, seven types of product are obtained which four types of them have enough thermodynamic stability. In thermodynamic approach, the most favor product begins with the formation of pre-reactive C2 complex and produces the CH₃CH(OH)₂ + O₂ as final adduct in a process that is computed to be exothermic by ?53.759 kcal/mol and spontaneous reaction by ?51.833 kcal/mol in Gibbs free energy. In kinetic viewpoint, the formation of CH₃COH + cis-H₂O₃ as a final adducts is the most favor path.     

The NO+O3 reaction: a triple oxygen isotope perspective on the reaction dynamics and atmospheric implications for the transfer of the ozone isotope anomaly

Atmospheric nitrate shows a large oxygen isotope anomaly (Delta 17 O), characterized by an excess enrichment of 17 O over 18 O, similar to the ozone molecule. Modeling and observations assign this specific isotopic composition mainly to the photochemical steady state that exists in the atmosphere between ozone and nitrate precursors, namely, the nitrogen oxides (NOx=NO+NO2). However, this transfer is poorly quantified and is built on unverified assumptions about which oxygen atoms of ozone are transferred to NO(x), greatly weakening any interpretation of the nitrate oxygen isotopic composition in terms of chemical reaction pathways and the oxidation state of the atmosphere. With the aim to improve our understanding and quantify how nitrate inherits this unusual isotopic composition, we have carried out a triple isotope study of the reaction NO+O3. Using ozone intramolecular isotope distributions available in the literature, we have found that the central atom of the ozone is abstracted by NO with a probability of (8+/-5)%(+/-2 sigma) at room temperature. This result is at least qualitatively supported by dynamical reaction experiments, the non-Arrhenius behavior of the kinetic rate of this reaction, and the kinetic isotope fractionation factor. Finally, we have established the transfer function of the isotope anomaly of O3 to NO2, which is described by the linear relationship Delta 17 O(NO2)=A x Delta 17 O(O3)+B, with A=1.18+/-0.07(+/-1 sigma) and B=(6.6+/-1.5)[per thousand](+/-1 sigma). Such a relationship can be easily incorporated into models dealing with the propagation of the ozone isotope anomaly among oxygen-bearing species in the atmosphere and should help to better interpret the oxygen isotope anomaly of atmospheric nitrate in terms of its formation reaction pathways.     

Flow injection chemiluminescence detection and solvent extraction for human skin ointment dexamethasone acetate absorption analysis and the reaction mechanism study

A flow-injection chemiluminescence (CL) method coupled with solvent extraction for the determination of dexamethasone acetate (DA) in ointment was presented in this paper. It was based on the enhancing effect of the studied drug on CL emission of luminol–K₃Fe(CN)₆ system. This method has the advantages of simple sample treatment, cheap instrumentation and rapid detection. Under the optimum conditions, relative CL intensities were proportional to DA concentrations in the 0.044–4.4 μg ml⁻¹ range. The limit of detection was 0.01 μg ml⁻¹ (3σ) for DA. The method was applied to DA quantification in commercial DA ointment pharmaceutical and to human skin DA absorption analysis. Experiments were performed to evaluate the nature of DA enhanced luminol–K₃Fe(CN)₆ CL reaction. Based on the experimental results, it was suggested that in this CL system, DA was oxidized by K₃Fe(CN)₆ to form a medium product (DAox), DAox oxidized luminol with a faster kinetic step comparing with K₃Fe(CN)₆ oxidized luminol to an active form. As a result, DA speed the luminol CL reaction, and finally intensified the CL signal.     

Investigation on sensitized chemiluminescence systems and their mechanism for five fluoroquinolones

The novel chemiluminescence (CL) reaction systems were established for lomefloxacin (LMFX), ofloxacin(OFLX), norfloxacin (NFLX), gatifloxacin (GAFX) and enoxacin (ENX). The sensitized CL emission mechanism was investigated for the five systems by comparing the fluorescence emission with CL spectra. For LMFX-Ce(IV)-S₂O₃²⁻-H₂SO₄ and OFLX-Ce(IV)-S₂O₄²⁻-H₂SO₄ systems, the CL intensity is enhanced through intermolecular energy transfer from the excited SO₂^* to LMFX and OFLX. For NFLX-Ce(IV)-S₂O₄²⁻-HNO₃ system, the sensitized CL is based on intermolecular energy transfer from the excited SO₂^* to NFLX oxide. For Eu³⁺-GAFX-Ce(IV)-S₂O₄²⁻-HCl and Dy³⁺-ENX-Ce(IV)-S₂O₃²⁻-H₂SO₄ systems, the CL spectra are from the narrow characteristic emission at 590, 619 and 649 nm of Eu^3+* (⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃) and at 482 and 578 nm of Dy³⁺ (⁴F₉ → ⁶H_15/2, ⁴F₉ → ⁶H_13/2) through intermolecular energy transfer from the excited SO₂^* to GAFX and ENX, followed by intramolecular energy transfer from GAFX^* to Eu³⁺ and ENX^* to Dy³⁺. The conditions of CL emission were investigated and optimized. The proposed five enhanced CL systems have good linearity, higher sensitivity, precision and potential capability for residue analysis of studied analytes in foods and biological samples.     

The reaction of sodium arsenite with sodium chlorite

Existing procedures for the standardisation of sodium chlorite solutions are critically examined and a suitable method detailed. The reaction between sodium chlorite and sodium arsenite solutions is discussed; reaction is quantitative in the presence of sodium bicarbonate and osmic acid as catalyst.     

The visible chemiluminescence of the reaction F + CH3F

By using molecular beam apparatus the visible (450–900 nm) chemiluminescence of the reaction F + CH₃F was investigated. Seven vibronic bands of HCF (Ã₁A-XA') and four vibrational bands of HF ground state overtone transitions were obtained. The relative vibrational state distributions of HF (V'=4,5,6) states and the rotational temperature of HF (V'=3) state were obtained. The analyses show that the two kinds of spectra were caused by the secondary reaction F+CH₃F. The results may be helpful to explain the contradictory results of the experiments in F+CH₃F system.     

Investigation and analytical application of the sulphide-hypobromite chemiluminescence reaction

The results of an investigation of the sensitized and non-sensitized chemiluminescence reaction between sulphide and hypobromite in alkaline solution are presented. The reaction can be used for the determination of traces of sulphide at concentrations above 5 x 10(-8)M. For this purpose a special flow system is employed which includes coulometric generation of reagent, and photon-counting. The flow system can also be combined with a special microdistillation apparatus, making it possible to analyse impregnated filters such as are used for the collection of hydrogen sulphide from ambient air.     

Direct dynamics study on mechanism and kinetics of the biradical self‐reaction of HOO

A theoretical study of the mechanism and the kinetics for the hydrogen abstraction reaction of the biradical hydroperoxy radical has been presented at the CCSD(T)/6‐311++G(3d,2p)//CCSD/6‐31+G(d,p) level of theory. Our theoretical calculations suppose a stepwise mechanism involving the formation of a postreactant complex in the triplet and singlet entrance channels. Four transition states of the six‐membered chain complexes (³TS1 and ¹TS1) and six‐membered ring complexes (³TS2 and ¹TS2) are located at the high dual level CCSD(T)/6‐311++G(3d,2p)//CCSD/6‐31+G(d,p) method. The rate constants of Path 1 ～ Path 4 at the CCSD(T)/6‐311++G(3d,2p)//CCSD/6‐31+G (d,p) level are calculated by means of the conventional transition state theory (TST) and canonical variational TST without and with small‐curvature tunneling (SCT) correction within the temperature range of 200–2,500 K. The calculated results show that the triplet channel is the dominating reaction channel and Path 2 is found to be the most favorable pathway. The rate constants of Path 2 are in good agreement with the experimental values at the experimentally measured temperatures. Moreover, the variational effect is not obvious in the low temperature range but is not neglectable in the high temperature range. The SCT plays an important role particularly in the low temperature range. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

MnO_2纳米溶胶-抗坏血酸化学发光反应的研究

在中性条件下利用Na2S2O3还原KMnO4制备出平均粒径约40 nmMnO2溶胶。研究发现,该溶胶在酸性条件下可氧化抗坏血酸产生化学发光。基于此,结合流动注射技术,对影响化学发光反应的各种因素进行了考察,建立了测定抗坏血酸的流动注射化学发光新方法。该方法测定抗坏血酸的线性范围为2.0×10-6~1.0×10-4g/mL,检出限为4×10-7g/mL,相对标准偏差为2.1%(1.0×10-5g/mL抗坏血酸溶液,n=11)。该方法已用于片剂中抗坏血酸的测定,结果与药典方法一致。     

芳香族硝基化合物与苯硫酚钠盐的亲核取代反应: 自由基IPSO取代机理

作者通过苯硫酚钠盐与对硝基苯甲酸甲酯(1), 对硝基苯甲酸苯酯(2), 间硝基苯甲酸甲酯(3), 3,5-二硝基苯甲酸甲酯(4)和对二硝基苯(5)反应研究, 用自旋捕获技术检测到苯硫基自由基; 同时, 从产物混合物中分离到二苯基二硫化物PhSSPh。提出苯硫基自由基与芳香族硝基化合物1,2,3,4和5反应的自由基IPSO亲核取代机理。     

A detailed reaction mechanism for hexamethyldisiloxane combustion via experiments and ReaxFF molecular dynamics simulations

Hexamethyldisiloxane (HMDSO) is one of the main impurities in the syngas produced from sewage and landfill plants. In order to utilize this syngas or control the characteristics of the generated silica particles, it is crucial to understand the chemical kinetics of HMDSO combustion. This study investigated the process of HMDSO combustion using synchrotron radiation mass spectrometry (SRMS), gas chromatography (GC), and ReaxFF molecular dynamics simulations. First, the force field used for ReaxFF simulation was validated by comparing the energies of different bond lengths, bond angles, and dihedral angles with the ones from DFT calculations. Good agreements were found. Then, ReaxFF simulations of HMDSO combustion with this force field were conducted under various conditions, which include different equivalence ratios (0.67, 1.0, and 1.5) and temperatures ranging from 2000 to 3500 K. The oxidation characteristics of HMDSO were analyzed, including the evolution of gas products and particle formation. Finally, based on the results from experiments and ReaxFF simulations, the reaction pathways, reaction lists, and reaction kinetics data during HMDSO combustion were obtained. A detailed reaction mechanism was proposed and validated by applying it in modeling the H₂/HMDSO/O₂ combustion systems. The temperature and part of the gas products such as CO and CO₂ as well as SiO could be well predicted.     

NBS-荧光素-盐酸头孢吡肟化学发光体系的研究

盐酸头孢吡肟(Cefepime Hydrochloride)作为第四代头孢菌素类抗菌新药,具有高效、广谱、低毒、耐细菌β-内酰胺酶等特点。目前测定盐酸头孢吡肟的方法有液相色谱[1]、高效液相色谱法[2-7]、红外与X-射线[8]等。本文研究发现,在氢氧化钠介质中,盐酸头孢吡肟可被N-溴代琥珀酰亚胺(NBS)氧化产生微弱的化学发光,在荧光素共存时产生较强的化学发光,其发光强度与盐酸头孢吡肟的质量浓度在0·05mg·L-1~10mg·L-1范围内呈良好的线性关系。基于此,结合流动注射技术,建立了测定盐酸头孢吡肟的流动注射化学发光方法。该法的检出限(3σ)为29μg·L-…     

Experimental studies on the chemiluminescence reaction mechanism of carbonate/bicarbonate and hydrogen peroxide in the presence of cobalt(II)

Chemiluminescence (CL) phenomena of carbonates or bicarbonates of potassium, sodium, or ammonium with hydrogen peroxide in the presence of cobalt sulfate were reported. After cobalt(II) solution was injected into the mixture of carbonate/bicarbonate and hydrogen peroxide, a CL signal was given out briefly. The CL conditions of these systems were optimized. The CL reaction mechanisms were studied experimentally by examining the spectrum emitted by the CL system and the effect of various free radical scavengers on CL emission intensity. The results showed that the maximal emission wavelengths of the CO32--H2O2-Co2+ and HCO3--H2O2-Co2+ systems were 440 and 490 nm, respectively. As a result, a radical scavenger of ascorbic acid, thiourea, and superoxide dismutase exhibited different effects on these CL systems. The different CL mechanisms involving the carbon dioxide dimer and the oxygen dimer were revealed, respectively.     

An investigation of the chemiluminescence reaction in the sodium hypochlorite–folic acid–emicarbazide hydrochloride system

A chemiluminescence method for the determination of folic acid by the sodium hypochlorite–folic acid–semicarbazide hydrochloride system with a new flow injection technique has been established. The new method can perform simple, sensitive and rapid determinations of folic acid. The response to the concentration of folic acid, in the range of 1.0×10⁻⁷5.0×10⁻⁵ g/ml, is linear. The relative standard deviation of the method is 2.3% (C_s=4.0×10⁻⁶ g/ml, n=11). The detection limit is 2.7×10⁻⁸ g/ml. This method is suitable for automatic and continuous analysis, and has been successfully tested for the determination of folic acid in a folic acid tablet.