Carotenoid radical cations as a probe for the molecular mechanism of nonphotochemical quenching in oxygenic photosynthesis

Nonphotochemical quenching (NPQ) is a fundamental mechanism in photosynthesis which protects plants against excess excitation energy and is of crucial importance for their survival and fitness. Recently, carotenoid radical cation (Car*+) formation has been discovered to be a key step for the feedback deexcitation quenching mechanism (qE), a component of NPQ, of which the molecular mechanism and location is still unknown. We have generated and characterized carotenoid radical cations by means of resonant two color, two photon ionization (R2C2PI) spectroscopy. The Car*+ bands have maxima located at 830 nm (violaxanthin), 880 nm (lutein), 900 nm (zeaxanthin), and 920 nm (beta-carotene). The positions of these maxima depend strongly on solution conditions, the number of conjugated C=C bonds, and molecular structure. Furthermore, R2C2PI measurements on the light-harvesting complex of photosystem II (LHC II) samples with or without zeaxanthin (Zea) reveal the violaxanthin (Vio) radical cation (Vio*+) band at 909 nm and the Zea*+ band at 983 nm. The replacement of Vio by Zea in the light-harvesting complex II (LHC II) has no influence on the Chl excitation lifetime, and by exciting the Chls lowest excited state, no additional rise and decay corresponding to the Car*+ signal observed previously during qE was detected in the spectral range investigated (800-1050 nm). On the basis of our findings, the mechanism of qE involving the simple replacement of Vio with Zea in LHC II needs to be reconsidered.     

非镉柱还原-流动注射分光光度法检测硝酸盐

阐述了一种基于碱性条件下,采用还原液将硝酸盐还原为亚硝酸盐,从而实现淡水中硝酸盐的还原液-流动注射分光光度检测方法,通过优化实验确定了最优分析条件。硝酸盐浓度在50～2000μg/L范围内与峰高呈良好的线性关系,方法检出限3.5μg/L,相对标准偏差0.90%(n=15,500μg/L)。方法应用于环境水样中硝酸盐的检测,加标回收率为95.0%～100.2%。该方法避免了镉还原柱再生处理,简化了操作,易于实现无人值守式的在线自动监测。     

Fluorescent quenching method for determination of trace hydrogen peroxide in rain water

A simple and sensitive fluorescent quenching method for the determination of trace hydrogen peroxide (H(2)O(2)) has been proposed to determine hydrogen peroxide in rain water sample. The method is based on the reaction of H(2)O(2) with 3,3'-diethyloxadicarbocyanine iodide (DI) to form a compound which has no fluorescence in acetate buffer solution (pH 3.09). The maximum emission wavelength of the system is located at 604 nm with excitation at 570 nm. Under the optimal conditions, the calibration graph was obtained between the quenched fluorescence intensity and hydrogen peroxide concentration in the range of 5.0 x 10(-7) to 9.0 x 10(-4) mol L(-1). The proposed method was applied to determine H(2)O(2) in rain water samples, and the result was satisfactory. The mechanism involved in the reaction was also studied.     

A meta effect in nonphotochemical processes: the homolytic chemistry of m-methoxyphenol

The m-methoxy group is normally electron-withdrawing (EW), sigma(m) = +0.12, sigma(m+) = +0.05. The strong EW activity of a phenoxyl radical's O* atom causes the m-methoxy group to become electron-donating (ED), sigma(m)(+) = -0.14. In valence bond terms, this can be ascribed to the nonclassical resonance structures 1c-e. Although it has long been known that m-methoxy is ED in photoexcited states, it has now been found to be ED for homolytic O-H bond breaking in ground-state 3-methoxyphenol.     

Fluorimetric determination of aluminium in water by sequential injection through column extraction

A fluorimetric procedure for the determination of aluminium with matrix removal in drinking water is proposed. The system is based both on the solid phase extraction of aluminium on a new chelating resin (XAD-4 modified by grafting salicylic acid) and the fluorimetric detection of a complex formed between 8-hydroxyquinoline-5-sulfonic acid (HQS) and Al(III), after elution of the resin by hydrochloric acid. The sorption and elution of aluminium were studied in both competitive and non-competitive conditions, varying pH, flow-rates, volume and concentration of reagents, as well as time contact. The optimised procedure allows determination of Al³⁺ at the sub-ppb level (LOD: 0.2 g L^–1 for 1 ml of sample) within a working range of 0.2–500 g L^–1. The analytical procedure was successfully employed for the determination of aluminium in drinking water during and after flocculation/coagulation treatment processes.     

Temperature effect on peak width and column efficiency in subcritical water chromatography

Subcritical water has been recently employed as the mobile phase to eliminate the use of organic solvents in reversed-phase liquid chromatography. Although the influence of temperature on retention in subcritical water chromatography has been reported, the temperature effect on peak width and column efficiency has not yet been quantitatively studied. In this work, several polar and chlorinated compounds are separated using pure subcritical water on Zorbax RX-C8, PRP-1 (polystyrene-divinylbenzene), Hypersil ODS, and ZirChrom-polybutadiene columns. Isothermal separations are performed at temperatures ranging from 60 degrees C to 160 degrees C. The retention time and peak width of analytes are reduced with increasing temperature. However, the column efficiency is either improved or almost unchanged with the increasing temperature in the low-temperature range (lower than the 100 degrees C to 120 degrees C range), but it is decreased when temperature is further raised in the high-temperature range (higher than the 100 degrees C to 120 degrees C range). Therefore, a maximum in column efficiency is obtained at temperatures within the 100 degrees C to 120 degrees C range in most cases.     

Fast determination of anions on a short coated column

In this paper, a simple method for the separation and determination of common inorganic anions by fast ion-exchange chromatography, using a modified short (25 mm x 4.6 mm) monolithic column, is reported. Coating the column with a cationic surfactant, cetylpyridinium chloride (CPC), the isocratic separation of some inorganic anions in minutes was possible, by direct or indirect UV detection. The coated column demonstrated excellent stability over time, even at a high flow-rate, giving retention times with an average relative standard deviation of 1.3% for over 10 consecutive runs. The developed column exhibited unusual selectivity for common anions, was successfully applied to the rapid analysis of inorganic anions of food samples, river water and factory waste water samples.     

On the determination of the column dead volume from homologous series

Summary The calculation of the column dead volume from high precision gross retention times of the n-alkanes pentane to heptadecane in an ODS/MeOH system yields values showing an apparently linear decrease with increasing carbon number. This effect is thought to be related to the partial exclusion from pores. If retention data are corrected for exclusion, one uniform dead volume is obtained.     

Simultaneous determination of tungsten and molybdenum in sea water by catalytic current polarography after preconcentration on a resin column

The simultaneous determination of tungsten and molybdenum in sea water is based on preconcentration by column extraction with 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (Kelex- 100) resin, and measurement of the polarographic catalytic currents obtained in a solution of chlorate, benzilic acid and 2-methyl-8-quinolinol. When the concentration factor is 50, the detection limits are 2.4 pM for tungsten and 17 pM for molybdenum (for a signal-to-noise ratio of 3). The precision of the determination is ca. 10% for 67 pM tungsten and ca. 5% for 106 nM molybdenum in sea water (n=4). Results for sea water and other natural waters are presented.     

On-line column preconcentration for the determination of cobalt in sea water by flow-injection chemiluminescence detection

A flow-injection method for the determination of dissolved cobalt(II) in sea water has been studied based on a combination of column preconcentration using 8-quinolinol immobilized on silica gel, fluoride containing metal alkoxide glass (8HQ-MAF) and chemiluminescence detection with a gallic acid-hydrogen peroxide system. Co(II) is selectively recovered from an acidified sample with 8-quinolinol immobilized on silica gel. After elution with dilute hydrochloric acid the resultant eluent is mixed with the reagent solutions, heated to 60^°C and then introduced into the CL cell. The analysis time including the 2-min sample load was 8 min per sea water sample with a corresponding detection limit of 0.62 ngl^-1 (3). The average standard deviation calculated for 10 replicate measurements of artificial sea water samples with a concentration of 10 ngl^-1 cobalt was ±2.1%. The method has been tested with the standard reference sea waters NASS and CASS.     

On-line column preconcentration for the determination of cobalt in sea water by flow-injection chemiluminescence detection

A flow-injection method for the determination of dissolved cobalt(II) in sea water has been studied based on a combination of column preconcentration using 8-quinolinol immobilized on silica gel, fluoride containing metal alkoxide glass (8HQ-MAF) and chemiluminescence detection with a gallic acid-hydrogen peroxide system. Co(II) is selectively recovered from an acidified sample with 8-quinolinol immobilized on silica gel. After elution with dilute hydrochloric acid the resultant eluent is mixed with the reagent solutions, heated to 60 ( degrees )C and then introduced into the CL cell. The analysis time including the 2-min sample load was 8 min per sea water sample with a corresponding detection limit of 0.62 ng l(-1) (3sigma). The average standard deviation calculated for 10 replicate measurements of artificial sea water samples with a concentration of 10 ng l(-1) cobalt was +/-2.1%. The method has been tested with the standard reference sea waters NASS and CASS.     

Preconcentration of triazine herbicides from water by an ion chromatography column and determination by gas chromatography-mass spectrometry

The efficiency of ion chromatography columns packed with styrene-divinylbenzene copolymer containing quaternary ammonium groups to preconcentrate triazine herbicides and their degradation products below μg/l levels has been established. Retention is studied for different types of water. Pure methanol was used in a one-step elution. Enrichment factors of at least 4000 are achieved. Determination was carried out by using gas chromatography-single-ion monitoring mass spectrometry. Recoveries for run-off agricultural water were between 67–100% and close to 100% for ground water. The maximum admissible concentration ion drinking water (0.1 μg/l) and the alert and alarm threshold values in surface water (1 and 3 μg/l, respectively) dictated by the European Union can be measured.     

Preconcentration and determination of cadmium in water by reversed-phase column chromatography and atomic absorption

Studies were made of the solvent extraction of cadmium(II) from hydrochloric acid into a tri-n-octylamine—cyclohexene mixture. Distribution ratios, as a function of amine and acid concentration, were determined and this information was used to establish optimum extraction conditions and the probable nature of the extracted species. This system was used as the basis for the development of a reversed-phase column chromatographic technique for preconcentrating Cd(II). The amine—cyclohexene phase was coated on an inert macroreticular resin (XAD-2) to provide a stable column. With this system, Cd(II) in acidified water samples as large as 31. may be concentrated to 10 ml and determined by conventional atomic absorption. Interferences were studied, and the method was applied to the analysis of fresh-water streams for Cd(II).     

Flow injection spectrophotometry coupled with a crushed barium sulfate reactor column for the determination of sulfate ion in water samples

A new type of a reactor column, a crushed BaSO₄ reactor column used for the flow injection spectrophotometric determination of sulfate ion using the exchange reaction of sulfate ion and barium-dimethylsulfonazo III is proposed. The column is very simple and economical. It can be continuously used for 8 h before washing with water for repeated usage of at least 1 month. The procedure is sensitive. Application to various water samples was demonstrated.     

A general chemiluminescence method for the determination of surfactants based on its quenching effect on the luminol-NaIO4-cyclodextrin reaction

Here we report that all types of surfactant could be simply and sensitively determined, by directly quenching the chemiluminescence (CL) between luminol and NaIO4 in a basic solution containing one polyhydroxyl compound such as cyclodextrin (CD), glucose or glycerol. This specific quenching effect was attributed to the change of the microenvironment of the CL reaction, caused by the addition of various surfactants. Based on this fact, the potential use of this CL reaction was exemplified by the cationic surfactant CTMAB, anionic surfactant SDS and non-ionic surfactant Triton X-100. It was found that the measurable range of CTMAB, SDS and Triton X-100 were 4.0 x 10(-6)-4.0 x 10(-4) M by using a basic CD-luminol-NaIO4 CL reaction. With our simple setup, CTMAB, SDS and Triton X-100 were detectable at a concentration as low as 2 microM. Overall, this new CL reaction is quite promising for the post-column determination of surfactant mixtures.     

A liquid chromatography method using a monolithic column for the determination of corticoids in animal feed and animal feeding water

An HPLC-DAD method for determining corticoids in calf feed and in animal feeding water samples using a monolithic column has been developed and validated. The method optimization included the study of binary mobile phases of water and acetonitrile. The optimum separation was achieved at 40 °C, with acetonitrile:H₂O 29:71 v/v used as mobile phase and a 3 ml/min flow-rate, which resulted in their separation in about 5 min. Two reported sample procedures were applied to feed and for animal feeding water samples prior to HPLC. Method validation was carried out according to the EU criteria established for quantitative screening methods. The results indicate that this method is highly specific, reproducible and accurate. The proposed method was found to be robust and unaffected by small variations in the extraction procedure and in HPLC conditions. The developed method for the determination of corticoids in feed and water samples was also found to be suitable for different kinds of feeds and waters.     

动力学荧光猝灭法测定柠檬酸的研究

在稀H2SO4介质中,柠檬酸活化钒(Ⅴ)催化溴酸钾氧化吡口罗红Y的褪色反应,使其荧光猝灭,建立了动力学荧光猝灭法测定柠檬酸的新方法。反应在沸水浴中进行10min,测定柠檬酸的线性范围为0.1～4.0μg/mL,检出限为6.0×10-8g/L。本法用于饮料中柠檬酸的测定,并进行了加标回收试验,回收率在96%～103%之间。