Electrocatalytic characteristics of a 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone modified carbon-paste electrode in the oxidation of ascorbic acid.

A carbon-paste electrode spiked with 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone was constructed by the incorporation of 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone in a graphite powder silicon oil matrix. It shown by cyclic voltammetry and double potential-step chronoamperometry, which this ferrocene derivative modified a carbon-paste electrode, can catalyze the ascorbic acid oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 7.00), the oxidation of ascorbic acid at the surface of this carbon paste modified electrode occurs at a potential of about 260 mV less positive than that of an unmodified carbon-paste electrode. The catalytic oxidation peak current was linearly dependent on the ascorbic acid concentration, and a linear calibration curve was obtained in the range of 6 x 10(-5) M-7 x 10(-3) M of ascorbic acid with a correlation coefficient of 0.9997. The detection limit (2sigma) was determined to be 6.3 x 10(-5) M. This method was also used for the determination of ascorbic acid in some pharmaceutical samples, such as effervescent tablets, ampoules and multivitamin syrup, by using a standard addition method. The reliability of the method was established by a parallel determination against the official method.     

Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid–peroxydisulfate system

The polymerization of acrylamide initiated by an ascorbic acid–peroxydisulfate redox system was studied in aqueous solution at 35 ± 0.2°C in the presence of air. The concentrations studied were [monomer] = (2.0–15.0) × 10^?2 mole/liter; [peroxydisulfate] = (1.5–10.0) × 10^?3 mole/liter; and [ascorbic acid] = (2.84–28.4) × 10^?4 mole/liter; temperatures were between 25–50°C. Within these ranges the initial rate showed a half-order dependence on peroxydisulfate, a first-order dependence on an initial monomer concentration, and a first-order dependence on a low concentration of ascorbic acid [(2.84–8.54) × 10^?4 mole/liter]. At higher concentrations of ascorbic acid the rate remained constant in the concentration range (8.54–22.72) × 10^?4 mole/liter, then varied as an inverse halfpower at still higher concentrations of ascorbic acid [(22.72–28.4) × 10^?4 mole/liter]. The initial rate increased with an increase in polymerization temperature. The overall energy of activation was 12.203 kcal/mole in a temperature range of 25–50°C. Water-miscible organic solvents depressed the initial rate and the limiting conversion. The viscometric average molecular weight increased with an increase in temperature and initial monomer concentration but decreased with increasing concentration of peroxydisulfate and an additive, dimethyl formamide (DMF).     

Reduction of [VO2(ma)2]- and [VO2(ema)2]- by ascorbic acid and glutathione: kinetic studies of pro-drugs for the enhancement of insulin action

To shed light on the role of V(V) complexes as pro-drugs for their V(IV) analogues, the kinetics of the reduction reactions of [VO2(ma)2]- or [VO2(ema)2]- (Hma = maltol, Hema = ethylmaltol), with ascorbic acid or glutathione, have been studied in aqueous solution by spectrophotometric and magnetic resonance methods. EPR and 51V NMR studies suggested that the vanadium(V) in each complex was reduced to vanadium(IV) during the reactions. All the reactions studied showed first-order kinetics when the concentration of ascorbic acid or glutathione was in large excess and the observed first-order rate constants have a linear relationship with the concentrations of reductant (ascorbic acid or glutathione). Potentiometric results revealed that the most important species in the neutral pH range is [VO2(L)2]- for the V(V) system where L is either ma- or ema-. An acid dependence mechanism was proposed from kinetic studies with varying pH and varying maltol concentration. The good fits of the second order rate constant versus pH or the total concentration of maltol, and the good agreement of the constants obtained between fittings, strongly supported the mechanism. Under the same conditions, the reaction rate of [VO2(ma)2]- with glutathione is about 2000 times slower than that of [VO2(ma)2]- with ascorbic acid, but an acid dependence mechanism can also be used to explain the results for the reduction with glutathione. Replacing the methyl group in maltol with an ethyl group has little influence on the reduction rate with ascorbic acid, and the kinetics are the same no matter whether [VO2(ma)2]- or [VO2(ema)2]- is reduced.     

大气漂尘中苯并[a]芘的简单同步荧光测定

通过选择合适的能量差(Δ-υ=1 400 cm-1),建立了大气漂尘中苯并[a]芘的恒能量同步荧光分析法。苯并[a]芘在甲醇与十二烷基磺酸钠(SDS)溶液中均有良好的线性关系(R>0.999),检出限分别达到1.34 nmol/L与0.40 nmol/L。该法亦可应用于18种多环芳烃混合物中苯并[a]芘的鉴别。     

Determination of tributyltin in toluene extract from sea water by graphite furnace atomic absorption spectrometry with a new matrix modifier

A new matrix modifier composed of calcium and chromium[VI] was proposed for the determination of tributyltin (TBT) in toluene extract from sea water containing sediment by graphite furnace atomic absorption spectrometry (GFAAS). Fourteen inorganic and organic compounds (barium, calcium, chromium[VI], lanthanum, magnesium, nickel, palladium, strontium, calcium-chromium[VI], calcium-strontium, nickel isocaprylate, 5%-, 10%-aqueous solution of ascorbic acid and toluene-saturated solution of ascorbic acid) as a matrix modifier were comparatively studied and a matrix modifier composed from 5 microg of calcium and 1 microg of chromium[VI] was found to give the best performance. The interference effects of co-existing elements in sea water containing sediment (aluminium, iron, magnesium, sodium and strontium) were studied. TBT in eight toluene extracts was determined by GFAAS with the proposed matrix modifier. The relative standard deviation was 3.0% for 63 ng ml(-1) of TBT (n = 11). The recoveries were 88-104%. The characteristic mass was 7 pg. The linearity range was 0-250 ng mg(-1).     

Reaction of 3,4-dioxohexane-1,6-dioic acid esters with 2,4-dinitrophenylhydrazine

Reaction was studied of 3,4-dihydroxyhexa-2,4-diene-1,6-dioic acid esters with 2,4-dinitrophenylhydrazine that led to the formation of esters of (3E)-3-[2-(2,4-dinitrophenyl)-hydrazinylidene]-4-oxohexane-1,6-dioic and (3E,4E)-3,4-bis[2-(2,4-dinitrophenyl)hydrazinylidene]-hexane-1,6-dioic acids. The structural features of compounds synthesized were established from the data of IR and NMR spectra and X-ray diffraction (XRD) analysis.     

Synthese der enantiomeren 1,6-Spiro[4.4]nonadiene

Two new syntheses of spiro[4.4]nonane-1, 6-dione (I) are described: one by rearrangement of 1,6-epoxy-bicyclo[4.3.0]-nonane-2-one (IV) with boron trifluoride, the other by an acid catalyzed, intramolecular Claisen condensation of 4-(2-oxocyclopentyl)-butyric acid. Spiro[4.4]-nonane-1,6-dione is converted into trans, trans-spiro[4.4]nonane-1,6-diol which is resolved into enantiomers via the diastereomeric esters with (?)-camphanic acid. (+)-(5S)-Spiro[4.4]nona-1,6-diene (III) is prepared from (1R, 6R)-trans,trans-spiro[4.4]nonane-1,6-diol (II) by pyrolysis of the corresponding bis-4-methylphenyl-thionocarbonate. This modification of the Chugaev reaction is particularly useful with sterically hindered alcohols which cannot be converted into S-me-thylxanthates. The circular dichroism, UV.- and NMR.-spectrum of optically active spiro[4.4]-nonane-1,6-diene are discussed.     

Determination of dissolved organic phosphorus in soil solutions by an improved automated photo-oxidation procedure

An improved automated photo-oxidation procedure to determine dissolved organic phosphorus in soil solutions is described. Organically combined phosphorus is converted quantitatively to orthophosphate under UV radiation and an excess of dissolved oxygen. The orthophosphate is determined spectrophotometrically using the Murphy and Riley procedure, modified by increasing the concentration of ascorbic acid. Fluoride was added to the system to overcome potential interference when working with soil solution. The limit of detection was 0.64 mug/l. PO(4)(-3) -P and calibration was linear over the range studied (5-1000 mug/l. PO(4)(-3) -P).     

Determination of atmospheric nitrobenzanthrones by high-performance liquid chromatography with chemiluminescence detection.

A method using high-performance liquid chromatography with chemiluminescence detection was developed for analyzing mutagenic nitrobenzanthrone (NBA) isomers in airborne particulates. The method was a modification of our previously described method for analyzing nitropolycyclic aromatic hydrocarbons (NPAHs). The pretreatment and reducing conditions for 1-, 2-, 3- and 10-NBAs were the same as those for NPAHs. In order to separate these NBA isomers, we used a polymeric-type ODS column (Cosmosil 5C-18MS); a mixture of 40% acetonitrile and 60% 10 mM imidazole-HClO4 buffer was employed as the mobile phase at a flow rate of 1 mL/min. The isomers of 1-, 2-, 3- and 10-NBA were determined in chemiluminescence with linear calibration graphs from 0.1 to 4 pmol, from 200 to 4000 pmol, from 1 to 50 pmol and from 10 to 400 pmol, respectively. The detection limits (S/N = 3) of 1-, 2-, 3- and 10-NBA isomers were 0.02 pmol, 35 pmol, 0.3 pmol and 3 pmol, respectively. The method was used to analyze airborne particulates at a heavy traffic site in Kanazawa. 2- and 3-NBAs were detected in the extracts of the particulates, while 1-NBA and 10-NBA were not detected. The atmospheric concentrations of 2- and 3-NBAs were 1.83 pmol/m3 and 24.7 fmol/m3, respectively.     

Ascorbic acid for homogenous redox buffering in electrospray ionization–mass spectrometry

Electrospray ionization (ESI) involves the dispersion of a liquid containing analytes of interest into a fine aerosol by applying a high potential difference to the sample solution with respect to a counter electrode. Thus, from the electrochemical point of view, the ESI source represents a two-electrode controlled-current electrochemical flow cell. The electroactive compounds part of the solvent sprayed may be altered by occurring electrolysis (oxidation in positive ion mode and reduction in negative ion mode). These reactions can be troublesome in the context of unknown identification and quantification. In the search for a simple, inexpensive, and efficient way to suppress electrochemical oxidation in positive ESI, the usability of ascorbic acid, hydroquinone, and glutathione for homogenous redox buffering was tested. Performance of the antioxidants was assessed by analyzing pharmaceutical compounds covering a broad range of functional groups prone to oxidation. Different emitter setups were applied for continuous infusion, flow injection, and liquid chromatography/mass spectrometry experiments. Best performance was obtained with ascorbic acid. In comparison to hydroquinone and glutathione, ascorbic acid offered superior antioxidant activity, a relatively inert oxidation product, and hardly any negative effect on the ionization efficiency of analytes. Furthermore, ascorbic acid suppressed the formation of sodiated forms and was able to induce charge state reduction. Only in the very special case of analyzing a compound isobaric to ascorbic acid, interference with the low-abundant [ascorbic acid+H](+) signal may become a point of attention.     

Studies of the Photochemical Degradation Kinetics of BaP on Different Substrates: Formation of Oxygenated Compounds

Abstract

The rate constant for BaP decomposition induced by exposure to UV rays and rate constants for BaP1,6; 3,6; 6,12 diones formation were determined. Experiments were conducted by depositing the BaP on clean glass fiber-filter and on airborne paniculate collected by filter. The BaP half-life appears to be positively correlated with filter loading and airborne particulates protect BaP from UV degradation. Our results suggest that BaP1,6dione, BaP3,6dione, BaP6,12dione are not the main by-products of BaP photodegradation induced by UV.     

Optimization of iodine determination according to Schöniger Analytical chemistry with 1,3-dibromo-5,5-dimethylhydantoin (DBH)a Part 1, Oxygen flask combustion Part 7 [1, 2]

The method of iodine determination in organic compounds according to Schöniger [3, 4] was improved by using an alkaline absorption solution of DBH. In contrast to elemental bromine DBH is a stable and easy to handle crystalline compound. For the removal of the excess of DBH 5-sulfosalicylic acid (C₇H₆O₆S × 2H₂O [5965-83-3]) [5] is more suitable than formic acid [64-18-6]. Assays for the determination of 2-iodobenzoic acid in the range from 1 to 25 mg iodine are described. 32 organic iodine compounds, mostly x-ray contrast media, could be analyzed with a percentage relative standard deviation of about 0.2%.     

Synthesis of the penta-glutamyl derivative of N-[4-[N-[3-(2,4-diamino-1,6-dihydro-6-oxo-5-pyrimidinyl)-propyl]amino]benzoyl]-L-glutamic acid (5-DACTHF). An acyclic analogue of tetrahydrofolic acid

The penta-glutamyl derivative of N-[4-[N-[3-(2,4-diamino-1,6-dihydro-6-oxo-5-pyrimidinyl)propyl]amino]-benzoyl)-L-glutamic acid (1, 5-DACTHF, 543U76) was synthesized by a convergent route. L-γ-Glutamyl-L-γ-glutamyl-L-γ-glutamyl-L-γ-glutamyl-L-γ-glutamyl-L-glutamic acid heptakis t-butyl ester ( 20 ) was prepared in ten steps from L-glutamic acid di-t-butyl ester and N-(benzyloxycarbonyl)-L-glutamic acid α-t-butyl ester. 4-[N-[3-(2,4-Diamino-1,6-dihydro-6-oxo-5-pyrimidinyl)propyl]trifluoroacetamido]benzoic acid ( 6 ), which was synthesized from pyrimidinylpropionaldehyde 3 in three steps, was condensed with 20 , followed by deprotection to provide N-[4-[N-[3-(2,4-diamino-1,6-dihydro-6-oxo-5-pyrimidinyl)propyl]amino]benzoyl]-L-γ-glutamyl-L-γ-glutamyl-L-γ-glutamyl-L-γ-glutamyl-L-γ-glutamyl-L-glutamic acid ( 2 ). Hexaglutamate 2 is a potent inhibitor of glycinamide ribonucleotide transformylase.     

Macropolyhedral boron-containing cluster chemistry. A synthetic approach via the auto-fusion of [6,9-(SMe2)2-arachno-B10H12

In an attempt to build up borane-based multicluster assemblies, thermolysis of [6,9-(SMe2)2-arachno-B10H12] 1 in inert hydrocarbon solution, followed by chromatographic separation, has resulted in the isolation not only of the previously established single-cluster product from this reaction, [5-(SMe2)-nido-B10H12] 2 (30%), but also the two two-cluster species [6,9-(SMe2)2-arachno-B10H11-1-(6-nido-B10H13)] 3 (20%) and [1,6-(nido-B10H13)2] 6 (ca. 0.5%) and the two three-cluster species [6,9-(SMe2)2-arachno-B10H10-1,5-(6-nido-B10H13)2] 4 (5%), characterized crystallographically, and [6,9-(SMe2)2-arachno-B10H10-1,3-(6-nido-B10H13)2] 5 (<1%), identified by NMR spectroscopy. An improved crystallographic investigation of [5-(SMe2)-nido-B10H12] 2 is also presented. The feasibility of the stability of species resulting from multiple adjacent substitution of nido-decaboranyl units on the [6,9-(SMe2)2-arachno-B10H12] skeleton is tested by DFT calculations. In an extension, to attempt the use of pre--linked two-cluster compounds as starting substrates, two-cluster [5-(SMe2)-4-(2-nido-B10H13)-nido-B10H11] 7 (0.6%) has been isolated from the reaction of SMe2 with [1,5-(nido-B10H13)2], other identified products being compound 1 (39%) and compound 3 (10.5%).     

Thermodynamic and micellization studies of a cationic gemini surfactant 16-6-16: Influence of ascorbic acid and temperature

Herein, we report the study of the influence of ascorbic acid and temperature on the micellization of a cationic gemini surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide), 16-6-16. The critical micelle concentration (CMC) of 16-6-16 was measured by the conductivity method and dye solubilisation technique. A tendency of the CMC values to increase with temperature and upon the adding of ascorbic acid was found. The standard Gibbs energy, standard enthalpy, and standard entropy of micellization of 16-6-16 were evaluated. The results of calculations suggest the decrease of the stability of the 16-6-16 micellar solution in the presence of ascorbic acid.     

Mechanistic studies on oxidation of L-ascorbic acid by an oxo-bridged diiron complex in aqueous acidic media

[Fe2(micro-O)(phen)4(H2O)2]4+ (1) (Fig. 1, phen = 1,10-phenanthroline) equilibrates with [Fe2(micro-O)(phen)4(H2O)(OH)]3+ (2) and [Fe2(micro-O)(phen)4(OH)2]2+ (3) in aqueous solution in the presence of excess phen, where no phen-releasing equilibria from 1, 2 and 3 exist. 1 quantitatively oxidizes ascorbic acid (H2A) to dehydroascorbic acid (A) in the pH range 3.00-5.50 in the presence of excess phen, which buffers the reaction within 0.05 pH units and ensures complete formation of end iron product ferroin, [Fe(phen)3]2+. The reactive species are 1, 2 and HA- and the reaction proceeds through an initial 1 : 1 inner-sphere adduct formation between 1 and 2 with HA-, followed by a rate limiting outer-sphere one electron one proton (electroprotic) transfer from a second HA- to the ascorbate-unbound iron(III).     

Retrospective analyses of atmospheric polycyclic and nitropolycyclic aromatic hydrocarbons in an industrial area of a western site of Japan.

Thirteen polycyclic aromatic hydrocarbons (PAHs) and four nitropolycyclic aromatic hydrocarbons (NPAHs) on the surfaces of airborne particulates, which were collected at an industrial area of a western site of Japan during periods from 1976 to 1998, were retrospectively analyzed. PAHs and NPAHs were extracted from airborne particulates using hexane with ultrasonication, and then analyzed by HPLC systems with fluorescence detection and chemiluminescence detection, respectively. The total concentrations (mean +/- SD, n = 34) were 15.54 +/- 21.24 ng/m3 for PAHs and 5.85 +/- 8.16 pg/m3 for NPAHs. The concentrations of PAHs and NPAHs were found to be highest during the period between 1979 and 1982, and then reduced. The annual concentrations of PAHs and NPAHs were highly correlated with those of air pollutants from motor vehicle origin, such as carbon monoxide, suspended particulates and non-methane hydrocarbons. The results suggested that motor vehicle emissions were one of the predominant sources of atmospheric PAHs and NPAHs.     

Cu~(2+)-Catalyzed Oscillatory Oxidation of Ascorbic Acid by O_2 Flow

The most widely studied oscillatory chemical reactions are based on homogeneous systems, such as the BrO3--driven BZ type oscillations1, the IO3--driven BR type oscillations2, and the ClO2- driven oscillations performed in CSTR3. Recently, oscillations have also been found in some heterogeneous systems, such as the oscillations across the liquid membrane4, the oscillations on the electrode5, and the oscillations in catalysis6. The metal-catalyzed oscillatory oxidation of the organic subst…     

Optimization of iodine determination according to Sch?niger Analytical chemistry with 1,3-dibromo-5,5-dimethylhydantoin (DBH)a Part 1, Oxygen flask combustion Part 7 [1, 2]

The method of iodine determination in organic compounds according to Sch?niger [3, 4] was improved by using an alkaline absorption solution of DBH. In contrast to elemental bromine DBH is a stable and easy to handle crystalline compound. For the removal of the excess of DBH 5-sulfosalicylic acid (C₇H₆O₆S × 2H₂O [5965-83-3]) [5] is more suitable than formic acid [64-18-6]. Assays for the determination of 2-iodobenzoic acid in the range from 1 to 25 mg iodine are described. 32 organic iodine compounds, mostly x-ray contrast media, could be analyzed with a percentage relative standard deviation of about 0.2%. Received: 10 March 1997 / Accepted: 15 May 1997     

Application of capillary gas chromatography to environmental analysis

Routine analytical methods for benzo[a]pyrene and nitroarenes in airborne particulates are presented. Benzo[a]pyrene in airborne particulates was easily analyzed by a capillary GC/NCIMS. Analysis time was about 10 min and analytical values obtained by this method agreed well with those by HPLC/spectrofluorometry. Nineteen nitroarenes were analyzed by capillary GC/FTD following a simple clean-up procedure. Fifteen out of 19 nitroarenes analyzed were mutagenic for Salmonella typhimurium TA100 and TA98, and 4 nitroarenes were carcinogenic to experimental animals.