UV initiated oxidation and chemiluminescence from aromatic–aliphatic co-polyesters and polylactic acid

The chemiluminescence of UV irradiated aromatic–aliphatic polyesters (Ecoflex and PBAT) and polylactic acid (PLA) was examined in nitrogen and oxygen atmospheres during the non-isothermal temperature runs in the interval from 40 to 250 °C and isothermally from 150 to 190 °C. The non-isothermal thermogravimetry and FTIR spectroscopy have been used for the characterization of differences in original samples. The temperature maxima of peroxidic peaks in nitrogen scaling their stability were compared and found to be in the order PBAT < Ecoflex < PLA. Their positions on the temperature scale that correlate well with the melting temperature of the respective polymer have been discussed. With prolongation of the UV irradiation period, the intensity of peroxidic peaks increased. On the other hand, the effect of pre-irradiation on non-isothermal runs of chemiluminescence measured in oxygen was not as distinct as for measurements in nitrogen. The deconvolution of the non-isothermal chemiluminescence runs in nitrogen revealed two kinds of peroxides in irradiated samples.     

Crystallisation behaviour of high density polyethylene blends with bimodal molar mass distribution: 2. Non-isothermal crystallisation

Crystallisation of high density polyethylene (HDPE) blends with broad bimodal molar mass distribution was investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. The blends were prepared by blending a high molar mass PE (M_w=330 kg/mol, M_w/M_n=4.8) and a low molar mass linear PE (M_w=34 kg/mol, M_w/M_n=10) in different ratios in xylene solution. The samples were analysed by the normal DSC at different crystallisation rates and by a thermal fractionation technique.The blends and their parent polymers behaved according to general expectations i.e., crystallinity and density decreased when the molar mass of the samples increased. Additionally, non-linear relationships between MM and different analysed parameters were found. Small addition of the high molar mass parent polymer to the low molar mass parent polymer increased crystallisation temperature, although the general trend was decreasing. Furthermore, a complicated relationship between the reciprocal of crystallisation half-time and sample composition was found. The value increased first with increasing molar mass, reached a maximum when the average molar mass of the blend was between 150 and 200 kg/mol and then decreased. The detected maximum correlated with the broadest molar mass distribution of the blends. The crystallinities and densities of the blends with the broadest molar mass distribution also deviated from the linear correlation between them and molar mass. The Avrami index under non-isothermal conditions was analysed with a method developed by Harnisch and Muschik. The results indicated that thermal nucleation and spherical growth regimes are present in all studied materials.     

Assessing the progress of degradation in polyurethanes by chemiluminescence and thermal analysis. II. Flexible polyether- and polyester-type polyurethane foams

The thermooxidative and thermal stability of polyether- and polyester-type polyurethane foams were investigated by non-isothermal chemiluminescence (CL), differential scanning calorimetry (DSC) and thermogravimetry (TG). In the presence of air and humidity, the effect of various routes and conditions of polyurethane ageing (induced thermally or by light) on the chemiluminescence, DSC and thermogravimetry patterns was assessed. The rate constants determined from non-isothermal thermogravimetry and chemiluminescence measurements at 250 °C and their not very pronounced dependence on the atmosphere of degradation indicated that depolymerisation of the polyurethane containing the aliphatic polyester and aromatic polyisocyanate moieties preceded or occurred in parallel with thermal oxidation. Under conditions of 50% relative humidity, samples of the polyester-type polyurethane, aged either by light or thermally, as well as specimens of the polyether-type polyurethane, aged by light, gave increased amounts of carbonaceous residue when heated in nitrogen to 550 °C.     

Thermal chemiluminescence of fibrous proteins

Thermal chemiluminescence (TCL) from the fibrous proteins wool and feather keratin, silk fibroin and Type I collagen is reported for the first time. The proteins all emit TCL when heated in the atmosphere of O₂ or N₂ in the range 40-220 °C. Plotting non-isothermal CL data in O₂ in Arrhenius format showed an increase in the activation energy at temperatures in the range 129-161 °C for each protein. This may indicate that a different free radical oxidation process operates when the mobility of the amorphous phase of the protein is increased above its T_g. Wool, silk and collagen exhibited a luminescence peak at 130 °C (with feather keratin at 145 °C) during non-isothermal CL experiments in N₂, similar to that observed in many synthetic polymers and characteristic of polymer hydroperoxides.     

A lanthanide sensitized chemiluminescence method of flow-injection for the determination of ulifloxacin and prulifloxacin

A lanthanide sensitized chemiluminescence method of flow-injection was developed for the determination of a new fluoroquinolone, ulifloxacin (UFX), and its prodrug prulifloxacin (PUFX). The proposed method was based on the remarkable chemiluminescence enhancement effect of UFX (PUFX) on KMnO₄−Na₂S₂O₄−Ln(III). Tb(III) ion was chosen from lanthanides because it showed the best sensitizing effect. Under optimized experimental conditions, the relative chemiluminescence intensity was in linear relationship with UFX and PUFX concentrations in the ranges of 1.0 × 10⁻⁸ − 5.0 × 10⁻⁶ M and 9.0 × 10⁻⁹ − 5.0 × 10⁻⁶ M, respectively. The minimum detectable value and relative standard deviation were 5.5 × 10⁻⁹ M, 1.5% for UFX and 7.0 × 10⁻⁹ M, 2.9% for PUFX, respectively. The proposed method was applied to the determination of UFX in spiked human serum and urine, and of PUFX in tablets with satisfactory results. The possible mechanism of chemiluminescence was also proposed. The text was submitted by the authors in English.     

The effects of annealing in inert atmospheres and of oxygen concentration on chemiluminescence from polypropylene

It has been shown that heating polypropylene powder under a nitrogen atmosphere leads to the significant prolongation of the oxidation induction time measured by chemiluminescence in oxygen at 130 and 140 °C. While heating in nitrogen from 0 to 4 h at 140 °C leads to the linear increase of oxidation induction time, the maximum chemiluminescence intensity I_stat increases with the time of sample annealing until 2 h; then it starts to decay. The different and sometime unknown thermal history of the sample may thus explain the scatter of induction times of oxidation observed with different PPs whether they be pure or stabilised. Maximum chemiluminescence intensity plotted vs. concentration of oxygen in the surrounding atmosphere at 130 and 140 °C also increases linearly; however, this does not correspond with very small reduction of oxidation induction time. The four-parametric “master equations” used in our earlier papers were applied to fit the chemiluminescence runs both in oxygen and in nitrogen. The equation operates with the rate constants of hydroperoxide decomposition and oxidation spreading but at the same time, it takes into account the possible effect of oxidation products on decomposition of hydroperoxides.     

Mechanism of the oscillating chemiluminescence reaction in the luminol-H2O2-KSCN-CuSO4-NaOH system

We conducted a simultaneous measurement of the potential of Cu²⁺, oxidation-reduction potential (ORP), and the chemiluminescence intensity in the luminol-H₂O₂-KSCN-CuSO₄-NaOH system. Two types of chemiluminescence were identified: a very faint continuous chemiluminescence and a strong oscillating chemiluminescence. The correlation between the potential of Cu²⁺ and ORP was measured experimentally for the first time. The effect of the initial concentrations of Cu²⁺ and H₂O₂ on the overall chemiluminescence intensity and the oscillation frequency was investigated in detail. Time-dependent concentration variation of the chemical species existing in the reaction system was calculated using a Runge-Kutta method. Two elementary chemical reactions not considered previously were taken into consideration. The overall experimental behavior was well explainable with our simulation. Based upon the comparison of our simulation with the experiment, we proposed that the strong oscillating chemiluminescence was induced by the reaction of luminol with ·OS(O)CN.     

Quenching effect of some heavy metal ions on the fast peroxyoxalate-chemiluminescence of 1-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane as a novel fluorophore

The fast chemiluminescence (CL) arising from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of 1-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane (L) as a novel fluorophore, and imidazole as catalyst, has been studied in ethyl acetate solution. The relationships between the chemiluminescence intensity and concentrations of TCPO, imidazole, hydrogen peroxide and L are reported. In the presence of imidazole as catalyst, the entire CL signal was completed in less than 3 s. The quenching effect of Cu²⁺, Pb²⁺, Cd²⁺, Hg²⁺ and Ag⁺ ions on the chemiluminescent system was investigated, the resulting Stern–Volmer plots were obtained and the K_Q values were calculated. It was found that the quenching effect of metal ions on the chemiluminescence of L decreases in the order Cu²⁺ > Pb²⁺ > Cd²⁺ > Hg²⁺ > Ag⁺.     

Thermal decomposition kinetics of potassium iodate

The thermal decomposition of potassium iodate (KIO₃) has been studied by both non-isothermal and isothermal thermogravimetry (TG). The non-isothermal simultaneous TG–differential thermal analysis (DTA) of the thermal decomposition of KIO₃ was carried out in nitrogen atmosphere at different heating rates. The isothermal decomposition of KIO₃ was studied using TG at different temperatures in the range 790–805 K in nitrogen atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of KIO₃. The non-isothermal decomposition of KIO₃ was subjected to kinetic analyses by model-free approach, which is based on the isoconversional principle. The isothermal decomposition of KIO₃ was subjected to both conventional (model fitting) and model-free (isoconversional) methods. It has been observed that the activation energy values obtained from all these methods agree well. Isothermal model fitting analysis shows that the thermal decomposition kinetics of KIO₃ can be best described by the contracting cube equation.     

The Effect of Cyclodextrins on the Luminol-Hydrogen Peroxide Chemiluminescence

The action of different molar ratios of α, β, γ-cyclodextrin upon the chemiluminescence of the luminol-H₂O₂ in alkaline buffer Tris-HCl, pH=8.5 has been evidenced. It was found out that α, β, γ- cyclodextrin have an antioxidant capacity, probably due to the free radicals (that are generate in the system) encapsulation in the their cavity. This behaviour depends on α, β, γ-cyclodextrin molar ratio; α-cyclodextrin and γ-cyclodextrin protects more efficiently against free radicals than β-cyclodextrin. These findings could be very important regarding the oxidative stress process.     

Thermal degradation of aliphatic hyperbranched polyesters and their derivatives

In this study results of thermal degradation of aliphatic hyperbranched polyesters, AHBP, and their derivatives, determined by non-isothermal thermogravimetric analysis in inert atmosphere (N₂) are presented. The thermal stability of linear polyester PHPA (polyhydroxypivalic acid), additionally synthesized from hydroxypivalic acid, was also studied. AHBP samples, from second to tenth pseudo-generation, were synthesized starting from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylolpropane. Modification of some selected AHBP samples was accomplished with the propionyl and benzoyl chloride, as well as with stearic acid. Thermal degradation of AHBP samples starts in the region between 250 °C and 275 °C and it ends around 430 °C. The thermal stability of AHBP samples increases with the number of end groups in the macromolecule, as well as with the modification of end groups with stearic acid and propionyl chloride. An AHBP sample of the fourth pseudo-generation, where all -OH end groups are modified with benzoyl chloride, shows lower thermal stability than the corresponding unmodified sample. The thermal stability of the linear polyester PHPA is lower than the thermal stability of the AHBP samples of the similar molar mass. The activation energies of thermal degradation for all synthesized AHBP samples were also calculated.     

Determination of superoxide dismutase and SOD-mimetic activities by a chemical system: Co2/H2O2/lucigenin

The bright chemiluminescence has been observed in the system: Co²⁺/hydrogen peroxide/lucigenin. The chemiluminescence intensity was directly proportional to either cobalt, hydrogen peroxide, or lucigenin concentrations. A procedure of determination of superoxide dismutase (SOD) activity by the chemiluminescence method in the cobalt–hydrogen peroxide–lucigenin system at pH 8.5 is suggested. A linear dependence was established between a relative chemiluminescence intensity and SOD concentration in the range of SOD concentrations between 0 and 4.5 nM, c _1/2 = 0.8 nM. The determination of SOD activity was performed in several tissue samples (rat plasma, erythrocyte hemolysate, and liver mitochondria). A technique of tissue sample preparation with the use of thermal inactivation of interfering proteins at 60 °C was used. The method was successfully applied for comparison of the efficiency of SOD mimetics.     

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.     

Flow injection chemiluminescence determination of isoniazid using luminol and silver nanoparticles

The effect of silver colloidal nanoparticles (AgNPs) on the luminol–isoniazid system was investigated. It was found that AgNPs could act as a nanocatalyst on the luminol–isoniazid system to generate chemiluminescence (CL). The CL emission spectrum of the luminol–isoniazid–AgNPs system showed a peak with a maximum at 425 nm. It was suggested that the luminophor species was the excited state 3-aminophthalate. The reduction of dissolved O₂ to H₂O₂ by isoniazid and decomposition of H₂O₂ to the oxygen-related radicals were attributed to the catalytic effect of AgNPs. Under optimized conditions, the CL signal intensity was linear with the isoniazid concentration in the range of 10–1000 ng mL^{− 1}, with the correlation coefficient of 0.9996. The limit of detection was 2.7 ng mL^{− 1} isoniazid. The relative standard deviations for seven repeated measurements of 60 and 200 ng mL^{− 1} isoniazid were 1.4 and 2.4%, respectively. The effect of potent interfering compounds on the CL signal intensity of the proposed luminol–isoniazid–AgNPs system was investigated. The proposed method was successfully applied to the determination of isoniazid in a pharmaceutical sample.     

Determination of traces of boron in semiconductor amorphous silicon film by filament-vaporization inductively-coupled plasma/atomic emission spectrometry

Silicon is dissolved from the platinum substrate by nitric/hydrofluoric acids. The recovery of boron on direct analysis was poor, but was increased to >95% by the addition of 500–5000 μg ml^?1 phosphorus as phosphoric acid. The results compared well with the molar ratio of the gases (B₂H₆/(Ar + H₂) used to form the film and the intensity ratio of ¹¹B⁺ and ³⁰Si⁺ obtained by secondary-ion mass spectrometry.     

Determination of the Molar Mass and the Radius of Gyration, Together with their Distributions for Methylhydroxyethylcelluloses

Three molar mass series were produced by different methods of degradation (namely ultrasonic (seven samples), oxidation (seven samples) and autoclaving (eight samples)) from a methylhydroxyethylcellulose (MHEC) sample with an average degree of substitution (DS) of 1.3, a molar degree of substitution (MS) of 0.46, a radius of gyration of 67 nm and a weight-average molar mass, M _w, of 318,000 g/mol. The degraded samples were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated apparatus consisting of size exclusion chromatography and multi-angle laser light scattering and concentration detector (SEC/MALLS/DRI) at 25 °C in 0.1 M NaNO₃ solution (with 200 ppm NaN₃ as antibactericide). The refractive index increment was determined as dn/dc = 0.135 cm³/g. It was possible to reduce the weight-average molar mass down to approximately 10% of the initial molar mass using all the methods. In a comparison of the three degradation methods it was shown that only ultrasonic degradation retains the monomodal distribution, whereas the other two degradation methods yield a bimodal molar mass distribution. Consequently, only ultrasonic degradation represents a suitable method for producing homologous molar mass series. An R _G–M relationship of R _G = 0.0511 × M ^0.56 was established for the sample used in this case, and from this it was possible to calculate an []–M relationship of [] = 0.3587 × M ^0.68.     

Removal of Ammonia Interference in the Redox Chemiluminescence Assay of Nitric Oxide

Abstract

Nitric oxide (NO) is now recognized as an important mediator that regulates a number of physiological functions. The most sensitive chemical method for its quantitation is via a redox-chemiluminescence detector (RCD), which can detect sub-picomole quantities of NO. In a microsomal metabolism study involving nitroglycerin, we observed that NH₃ could produce a chemiluminescence signal that interfered with the assay of NO, although the RCD sensitivity toward NH₃ was, on a molar basis, approximately 2700× less than that toward NO. Incorporation of a Porapak® T column either completely removed NH₃ RCD signal (< 40 nmole), or caused a chromatographic separation between NH₃ and NO (> 40 nmole of NH₃). The presence of the polymer packing did not affect the sensitivity of detector response toward NO. The applicability of this separation method was validated in a biochemical study in which microsomes from bovine coronary artery smooth muscle cells were incubated under conditions that would produce NO as well as NH₃ the latter probably through protein degradation. The separation method described appears to be useful in safeguarding artifactual contamination from NH₃ in the redox chemiluminescence assay of NO.     

Thermal Oxidation and Its Relation to Chemiluminescence from Polyolefins and Polyamides

Chemiluminescence (CL) from oxidation of polypropylene, polyethylene and polyamide has been compared and kinetic parameters based on the simplified kinetic scheme involving both bimolecular decomposition of hydroperoxides as an initiating event and correction for the oxidation spreading were determined. Induction times of oxidation determined from the autocatalytic shape of chemiluminescence intensity-time runs increase with an increasing initial molar mass of polypropylene within low molar masses up to 180 kDa regardless of the route of the polypropylene synthesis. The more complex chemiluminescence patterns in case of polyamides may be related with an increase of initially present defect structures including the terminal amino groups.     

CdTe nanocrystals sensitized chemiluminescence and the analytical application

It was found that the mixing of CdTe semiconductor nanocrystals (NCs) with luminol in the presence of KMnO₄ can induce a great sensitized effect on chemiluminescence (CL) emission. When the concentration of luminol, KMnO₄ and NaOH were fixed at 1 μM, 1 μM and 0.05 M, respectively, the most excellent performance can be obtained for the CdTe NCs sensitized CL. By means of CL and photoluminescence spectra, we suppose the enhanced CL signals resulted from the accelerated luminol CL induced by the oxidized species of CdTe NCs. Based on the finding, using thioglycolic acid-capped CdTe NCs as label and immunoglobulin G (IgG) as a model analyte, a CL immunoassay protocol for IgG content detection was developed. The strong inhibition effect of phenol compounds on luminol-KMnO₄-CdTe NCs CL system was also observed. All these findings demonstrated the possibility of semiconductor nanocrystals induced chemiluminescence to be utilized for more practical applications.     

On the relation between positron annihilation lifetime spectroscopy and lattice‐hole‐theory free volume

A coincidence between the temperature‐dependent hole (free volume) fraction h above the glass transition temperature, derived from lattice‐hole theory, and the corresponding function h_Ps obtained from positronium lifetime spectroscopy has been previously observed for four polystyrene fractions ranging from 4000 to 400,000 in molar mass. This result was based on the assumed proportionality of h_Ps and the product of the orthopositronium intensity I₃ and the mean cavity volume, the proportionality constant C being molar mass dependent. However, a recent analysis of the data based on volume arguments by Olson and Jamieson revealed systematic departures between the two sets of free volume functions. We reexamine the situation by departing from the customary assumption of spherical cavities, and allowing for nonspherical geometries represented by prismatic or cylindrical disks. Agreement between spectroscopic and thermodynamic functions ensues with fixed, temperature‐independent asymmetry factors decreasing with increasing molar mass. These tentative findings suggest that systematic studies of melts with varying chain flexibility and molar mass should be attempted. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2225–2229, 2005