Quantification of 2-hydroxyfluorene in human urine by column-switching high performance liquid chromatography with fluorescence detection

A high performance liquid chromatographic (HPLC) method for the quantification of 2-hydroxyfluorene (2-OHF) in normal human urine was established using deuterated 2-hydroxyfluorene (2-OHF-d9) as an internal standard with column-switching and fluorescence detection. The 2-OHF-d9 was synthesized by the metabolism of deuterated fluorene with cytochrome P450. The analytes were cleaned up on an ODS pre-column, via column-switching, and separated on an alkylamide-type reversed phase column. The internal standard eluted immediately prior to non-deuterated 2-OHF on the HPLC system and had nearly the same fluorescence characteristics as the non-deuterated 2-OHF. The detection limit was 0.03 nmol l(-1) (S/N = 3) and the calibration range of urine sample was from 0.2 to 50 nmol l(-1). The urine sample treatment involved enzymatic hydrolysis followed by solid phase extraction using a Sep-Pak C18 cartridge. 2-OHF was observed in the form of conjugates such as glucuronide and/or sulfate in human urine, and urinary metabolites were completely hydrolyzed for 2 h with beta-glucuronidase/aryl sulfatase. The proposed method was used to determine urinary 2-OHF in smokers and non-smokers, and showed that the urinary concentrations of 2-OHF in smokers were significantly higher than those in non-smokers (P < 0.01). Thus, the data suggest that urinary 2-OHF might be a sensitive and specific biological marker for the assessment of the exposure to polycyclic aromatic hydrocarbons.     

Development of a novel potentiometric titration method for determination of polypropylene degradation

In this study, a novel potentiometric titration of hydroperoxide in degraded polypropylene (PP) is proposed. This titration is quite sensitive compared with the conventional ones such as UV and manual titrations, and its detection limit was about 2 meq/kg. The sensitivity was equal to that of molecular weight measurement by GPC for the degraded PP and, in addition, the volatilization behavior of the hydroperoxide could be detected. This titration was found to be very effective for the determination of PP degradation.     

Improvement of an automatic HPLC system for nitropolycyclic aromatic hydrocarbons: removal of an interfering peak and increase in the number of analytes.

An automatic HPLC system for analyzing nitropolycyclic aromatic hydrocarbons (NPAHs, nitroarenes) in airborne particulates was previously described (Anal. Chim. Acta, 2001, 445, 20). Some problems with this system were that it generated a peak originating from an ascorbic acid solution that elutes at a retention time close to that of 1,6-dinitropyrene (DNP), and that it was able to analyze only 1,3-, 1,6-, 1,8-DNPs and 1-nitropyrene (I-NP). Here, we describe an improved system that effectively removes the interfering peak by introducing an ODS column just after the pump for the ascorbic acid solution, and which is capable of analyzing several additional compounds (2-, 4-NPs, 2-nitrofluorene. 6-nitrochrysene, 7-nitrobenz[a]anthracene, 3-nitroperylene and 6-nitrobenzo[a]pyrene etc.). The improved sensitivities were achieved by concentrating the compounds in a benzene-ethanol extract from airborne particulates, by increasing the loading time of the sample solution from 20 to 38 min, and by increasing the flow rate of an ascorbic acid solution from 1.3 to 1.8 mL/min.     

Excitation-energy migration in self-assembled cyclic zinc(II)-porphyrin arrays: a close mimicry of a natural light-harvesting system

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(II)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization as well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N = 5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.     

Induction of a remarkable conformational change in a human telomeric sequence by the binding of naphthyridine dimer: inhibition of the elongation of a telomeric repeat by telomerase

The binding of a dimeric form of the 2-amino-1,8-naphthyridine derivative (naphthyridine dimer) to a human telomeric sequence, TTAGGG, was investigated by UV melting, CD spectra, and CSI-MS measurements. Both the 9-mer d(TTAGGGTTA) and the 15-mer d(TTAGGGTTAGGGTTA) showed apparent melting temperatures (T(m)) of 45.6 and 63.6 degrees C, respectively, in the presence of naphthyridine dimer (30 microM) in sodium cacodylate buffer (50 mM, pH 7.0) containing 100 mM NaCl. The CD spectra at 235 and 255 nm of the 9-mer increased in intensity accompanied with strong induced CDs at 285 and 340 nm upon complex formation with naphthyridine dimer. UV titration of the binding of naphthyridine dimer to the 9-mer at 320 nm showed a hypochromism of the spectra. A Scatchard plot of the data showed the presence of multiple binding sites with different association constants. Cold spray ionization mass spectrometry of the complex between naphthyridine dimer and the 9-mer clearly showed that one to three molecules of the ligand bound to the dimer duplex of the 9-mer. Telomeric repeat elongation assay showed that the binding of naphthyridine dimer to the telomeric sequence inhibits the elongation of the sequence by telomerase.     

Brush‐First ROMP of poly(ethylene oxide) macromonomers of varied length: impact of polymer architecture on thermal behavior and Li+ conductivity

The properties of polymeric materials are dictated not only by their composition but also by their molecular architecture. Here, by employing brush‐first ring‐opening metathesis polymerization (ROMP), norbornene‐terminated poly(ethylene oxide) (PEO) macromonomers ( MM‐n , linear architecture), bottlebrush polymers ( Brush‐n , comb architecture), and brush‐arm star polymers ( BASP‐n , star architecture), where n indicates the average degree of polymerization (DP) of PEO, are synthesized. The impact of architecture on the thermal properties and Li⁺ conductivities for this series of PEO architectures is investigated. Notably, in polymers bearing PEO with the highest degree of polymerization, irrespective of differences in architecture and molecular weight (~100‐fold differences), electrolytes with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as an Li⁺ source exhibit normalized ionic conductivities (σ_n) within only 4.9 times difference (σ_n = 29.8 × 10^?5 S cm^?1 for MM‐45 and σ_n = 6.07 × 10^?5 S cm^?1 for BASP‐45 ) at a concentration of Li⁺ r = [Li⁺]/[EO] = 1/12 at 50 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 448–455     

Statistics of reaction progress variable and mixture fraction gradients of a pulverised coal jet flame using Direct Numerical Simulation data

The statistical behaviour of the variances, covariance and gradients of the reaction progress variable (c), and the mixture fraction (ξ) have been analysed in a pulverised coal jet flame using a three-dimensional carrier phase direct numerical simulation (DNS) dataset. It has been observed that the Favre-probability density functions (PDFs) of c and ξ can be parametrised by the standard β function. Furthermore, the log-normal distribution has been found to accurately represent |?c| and |?ξ|. It is also found that ?c and ?ξ remain aligned throughout the flame brush. Finally the joint PDF of |?c| and |?ξ| has been compared with the product of the PDF of |?c| and PDF of |?ξ| extracted from carrier phase DNS, and it has been found that |?c| and |?ξ| are not statistically independent in the case investigated.The bivariate log-normal distributions with and without correlation have also been considered, and the former is found to be in better agreement with the carrier phase DNS data.     

Determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry using Pd/Mg chemical modifier and slurry sampling

Effectiveness of Pd/Mg chemical modifier for the accurate direct determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry (GF-AAS) using slurry samples was evaluated. A calibration curve prepared by aqueous zinc standard solution with addition of Pd/Mg chemical modifier is used to determine the zinc concentration in the sediment. The accuracy of the proposed method was confirmed using Certified Reference Materials, NMIJ CRM 7303-a (lacustrine sediment) from National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Japan, and MESS-3 (marine sediment) and PACS-2 (marine sediment) from National Research Council, Canada. The analytical results obtained by employing Pd/Mg modifier are in good agreement with the certified values of all the reference sediment materials. Although for NRC MESS-3 an accurate determination of zinc is achieved even without the chemical modifier, the use of Pd/Mg chemical modifier is recommended as it leads to establishment of a reliable and accurate direct analytical method. One quantitative analysis takes less than 15 minutes after we obtain dried sediment samples, which is several tens of times faster than conventional analytical methods using acid digested sample solutions. The detection limits are 0.13?µg?g^?1 (213.9?nm) and 16?µg?g^?1 (307.6?nm), respectively, in sediment samples, when 40?mg of dried powdered samples are suspended in 20?mL of 0.1?mol?L^?1 nitric acid and a 10?µl portion of the slurry sample is measured. The precision of the proposed method is 8–15% (RSD).     

Mn(III)-based reaction of alkenes with quinolinones. Formation of peroxyquinolinones and quinoline-related derivatives

The reactions of 1,1-disubstituted alkenes with 4-hydroxyquinolin-2(1H)-ones under both Mn(III)-catalyzed aerobic oxidation conditions at room temperature and Mn(III)-mediated oxidation conditions at reflux temperature are described. The Mn(III)-catalyzed aerobic oxidation afforded bis(hydroperoxyethyl)quinolinones and azatrioxa[4.4.3]propellanes, while the oxidation with Mn(OAc)₃·2H₂O produced furo[3,2-c]quinolin-4-one analogues. The existence of a substituent at the 3-position of the 4-hydroxyquinolin-2(1H)-ones prevented a double reaction with the alkenes, and (endoperoxy)quinolinones and/or (hydroperoxyethyl)quinolinones were obtained under the Mn(III)-catalyzed aerobic conditions, while furo[3,2-c]quinolinone hemiacetals and vinylquinolinones were selectively produced under the Mn(III)-mediated oxidation conditions depending on the reaction temperature and times. Cyclic assembly of quinolinone-related 1,3-dicarbonyl compounds such as dihydropyridinones, pyranones, and dimedone derivatives was also examined under elevated temperature conditions.