Modified sampling and analysis method for large volatility range airborne polycyclic aromatic hydrocarbons (PAH) using gas chromatography-mass spectrometry

A sampling method has been developed for the measurement for polycyclic aromatic hydrocarbons in ambient air by gas chromatography isotope dilution mass spectrometry. The method has been designed to measure the largest possible volatility range of PAHs including the abundant naphthalenes. Sample volumes were approx. 500 m³ in size at a sampling rate of approx. 18 m³/h. The sampler contained three sorption stages for the simultaneous capturing of particle bound and low and high volatile gaseous PAH, respectivley. Recoveries of sampling spikes were on average 90%. The detection limit was approx. 5 pg/m³ for the high boiling range PAH. Results obtained showed a quite steady profile for most PAH in background air in The Netherlands. Comparison of abundance ratios with literature data indicate that traffic exhausts are the major source for the PAH in the area.     

Optimization of performance and minimization of silicate interference in continuous flow phosphate analysis

Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH>0.5. At final pH of 0.78 there is maximum interference from silicate in the sample. We recommend therefore as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction and a [H(+)]/[Mo] ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.     

A heterocyclic peptide nanotube

An open-ended hollow tubular structure is designed based on hydrogen-bond-directed self-assembly of a chimeric cyclic peptide subunit comprised of alternating alpha- and epsilon-amino acids. The design features a novel 1,4-disubstituted-1,2,3-triazole epsilon-amino acid and its utility as a peptide backbone substitute. The N-Fmoc-protected epsilon-amino acid was synthesized in high yield and optical purity in three steps from readily available starting materials and was employed in solid-phase peptide synthesis to afford the desired cyclic peptide structure. The cyclic peptide self-assembly has been studied in solution by (1)H NMR and mass spectrometry and the resulting tubular ensemble characterized in the solid state by X-ray crystallography.     

OXIDATION-REDUCTION REACTIONS OF P700 AND CYTOCHROME f IN FRACTION 1 PARTICLES PREPARED FROM SPINACH CHLOROPLASTS BY FRENCH PRESS TREATMENT

Abstract— –Fraction-1 particles were prepared by passing spinach chloroplasts three times through the French pressure cell and centrifuging in a sucrose gradient. With the electron donor DAD (diaminodurol or 2,3,5,6-tetramethyl-p-phenylenediamine) and ascorbate, a light-induced difference spectrum revealed the oxidation of both cytochrome f and P700 upon illumination of these particles. The oxidation of cytochrome f was completed in less than 0.5 msec. P700 and cytochrome f thus seem to be tightly bound to each other in these particles. Addition of Triton X-100 abolished the fast oxidation of cytochrome f but not that of P700. Artificial electron donors such as DAD, DCIP (2,6-dichlorophenol indophenol), and PMS (N-methylphenazonium methosulfate) were good electron donors for photoreaction 1 in these particles, while neither plastocyanin, Porphyra cytochrome 553, nor Euglena cytochrome-552 reduced P700 efficiently. However, after treatment of fraction 1 particles with Triton X-100 reduced DAD, DCIP and PMS were no longer efficient electron donors, while plastocyanin and the algal cytochromes were highly active in reducing P700. Mammalian cytochrome c was not a good electron donor either before or after Triton treatment. Measurements of the effectiveness of P700 reduction as a function of concentration in Triton-treated particles showed plastocyanin to be about four times more active than Porphyra or Euglena cytochromes which in turn were about fourteen times more active than mammalian cytochrome c. Recent studies by Murata and Brown have shown that plastocyanin is not required for the reduction of NADP in these particles with DCIP and isoascorbate as electron donors. The present investigation and that of Murata and Brown indicate that disintegration of chloroplasts with the French pressure cell and centrifugation in a sucrose gradient is the best method to separate system-1 particles having an electron-transport system in almost the native state as in chloroplasts.     

S-4-methylphenyl-o,o-bis[1-benzotriazolyl] phosphorothioate: a versatile phosphorylating agent

The phosphorylating agent obtained by treatment of S-4-methylphenyl phosphorodichloridothioate with 1-hydroxybenzotriazole can not only be applied for the introduction of polyphosphate functions at the terminal ends of nucleic acids, but also for the formation of 3′-5′-phosphotriester linkages.     

PROFLAVINE MEDIATED PHOTOINACTIVATION OFBACTERIOPHAGE φX174 AND ITS ISOLATED DNA: EFFECTS OF AGENTS MODIFYING VARIOUS PHOTOCHEMICAL PATHWAYS

Abstract. Thiols and disulfides protect both φX174 phage and its isolated DNA from the lethal action of proflavine plus light. The protective ability of these compounds appears to be attributed to the -SH or the -S-S- group and the property to interact with the proflavine-phage DNA complex. The phage inactivation efficiency per proflavine bound to DNA is reduced by 50 to 30% upon addition of cysteine or cystamine. Substances that affect the lifetime of singlet oxygen modify the rate of phage photoinactivation in the presence of proflavine; the inactivation rate is decreased by N^-₃ and increased by D₂O. Irradiation under N₂ atmosphere markedly decreases the phage photosensitization by proflavine. Irradiation with monochromatic light of 440 nm is less efficient than irradiation with light of 440 nm plus 360 nm, and the difference is more pronounced in N₂ than in air. These results are discussed in relation to various possible photochemical pathways.     

Photoelectron spectra of substituted benzenes

Photoelectron spectra of several substituted dimethylanilines, nitrobenzenes, acetophenones and nitrosobenzenes have been studied with a view to examine the electronic effects of substituents on the various φ and n levels. The results are discussed in the light of molecular orbital calculations and electronic absorption spectra. Correlation of substituent effects on the IE's with π-electron densities and Hammett substituent constants has enabled rationalization of all available data on mono- and disubstituted benzenes. The IE's generally increase with the electron-withdrawing power of the substituents.     

Automated chemical separations in routine activation analysis

In recent years increased information is required about the distribution of elements at low concentration levels in the biosphere. Neutron activation analysis can play an important role if it can supply many data at relatively low cost. As some of the concentrations are too low for determination by non-destructive techniques, equipment for chemical separations on a routine basis is necessary. For environmental studies a separation scheme has been developed successfully for arsenic, antimony, cadmium, copper, mercury, selenium and zinc. It is based on a combination of distillation and ion-exchange. Special attention is paid to the prevention of interference from bromine and sodium. Additional information about chromium, cobalt, nickel and tungsten can easily be obtained. Experience gathered with an automated instrument for fifty samples a week is described.     

Rapid analysis of small glass fragments by atomic-absorption spectroscopy

A rapid method is described for the determination of magnesium, iron and manganese in small glass fragments (250-500 mug). The speed of the analytical procedure is made possible by the use of a convenient cold digestion stage allied to a discrete sampling method which permits the three elements of interest to be determined by flame atomic-absorption spectrophotometry.     

A photometric detector based on a blue light-emitting diode

The suitability of blue light-emitting diodes as radiation sources in molecular absorption spectroscopy was evaluated. Electronic as well as spectral considerations are discussed. A transducer based on a blue light-emitting diode and a photodiode is described which yields direct absorbance readings by passing the photocurrent to an integrated circuit logarithmic converter. The performance of this device was tested for commonly used spectrophotometric procedures for Cr, Mn, Zn, Fe and Cl and compared with conventional molecular absorption spectroscopy. Also investigated was the application of the transducer as a detector in flow-injection analysis.