Synthesis and crystal structure of ammonium (picrate) (dibenzo-18-crown-6)

NH₄(Pic)(DB18C6) (Pic=picrate and DB18C6=dibenzo-18-crown-6), (C₂₆H₃₀N₄O₁₃) FW 606.56, arthorhombic,Pmn2₁,a=26.045(5),b=12.055(3),c=8.982(3) Å,V=2820(1) ų,Z=4,D _c =1.429 g/cm³, CuK, =1.54184 Å, (CuK)=9.5 cm^–1,F(000)=1272,T=298 K. The structure has been refined toR=0.0475 for 2617 unique observed reflections. In the lattice the 1:1 complex exists as a 2:2 dimer in which the crown are coupled through the Pic anions and NH₄ ⁺ cations. The asymmetric unit consists of two independent half crown ethers of which two opposite O atoms are on the mirror plane, two half ammonium cations of which the N and two H atoms are also on the mirror plane while the Pic anion is in a general position. Relative to each other, the corwn ethers are shifted by about 7.3 Å alongb and 1 Å alongc. The 1:1 sandwich of NH₄ with DB18C6 and Pic on dimerisation becomes a club pseudo-sandwich with three phenyl rings on either side of the mirror plane, thus forming a nearly parallel stack with a 3.6 Å inter-ring distance. The NH₄ ions hold the structure; two H atoms on the mirror plane are hydrogen-bonded to the opposite oxygens of the crown located on the purely aliphatic part of the ring (2.10(1), 2.06(3) and 2.26(3), 2.05(1) Å) for the two independent crowns, respectively, while the other two H atoms form mirror-related bifurcated hydrogen bonds with the phenoxide oxygen (1.99(1) and 2.01(1) Å) and theo-nitrogen oxygen (2.44(2) and 2.34(1) Å) of the picrates. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82037 (29 pages)     

PHOTOCHEMICAL DAMAGE TO DNA TREATED WITH CHLORPROMAZINE AND NEAR UV RADIATION UNDER AEROBIC AND ANAEROBIC CONDITIONS

Double stranded salmon sperm DNA in a chlorpromazine (CPZ) solution is damaged when irradiated with near UV light. The damage of irradiated DNA can be estimated by measuring the increase in extinction at 260 nm following incubation at 60°C of the DNA with formaldehyde. Moreover, DNA irradiated in the presence of CPZ or kept in the dark separate quite differently in an aqueous polymer two-phase system. DNA irradiated in the presence of CPZ seemed to be susceptible to digestion by endonuclease S1, while the endonuclease of Neurospora crassa could not digest this DNA. Irradiation under aerobic conditions seemed to be less disastrous for DNA than under anaerobic conditions.     

Determination of preservatives in cosmetic products. I. Thin-layer chromatographic procedure for the identification of preservatives in cosmetic products

A thin-layer chromatographic procedure is presented for the separation and identification of preservatives that are listed in the current EEC Council Directive on cosmetic products or have been permitted in the past. The method consists of an extraction of acidified cosmetics with methanol, separation of the extracts by thin-layer chromatography on aluminium oxide and silica gel-coated plates using one developing solvent, and visualization of the preservatives on the plates using short-wavelength UV light and six detection reagents. The retention behaviour and the detectability of 88 preservatives were investigated, of which 74 were characterized by this method. The preservatives in fourteen commercial cosmetic products were tentatively identified by the procedure described. In general this method will permit the routine detection of preservatives in cosmetics in an approximate concentration of 0.1% (w/w).     

Applicability of the polyphenylene oxide film dosimeter to high UV exposures in aquatic environments

Previous research has proven that the Poly (2,6-dimethyl-1, 4-phenylene oxide) (PPO) dosimeter is capable of receiving both in-air and underwater UV exposures that are significantly greater than those of the more commonly used polysulphone dosimeter, within a range of accuracy close to what would be expected of dosimetric measurements made in-air provided that the necessary calibrations are completed correctly by factoring in different atmospheric column ozone levels, SZA ranges, varying water turbidity and DOM levels. However, there is yet to be an investigation detailing the performance of the PPO dosimeter and its ability to measure UV in an actual field environment over an extended period of time. This research aims to bridge this gap in the knowledge by presenting a measurement campaign carried out in two real world aquatic environments and a simulated sea water environment using a batch of PPO dosimeters set at different depths and aligned to a range of different angles and geographical directions by means of attachment to a custom built dosimeter submersible float (DSF) unit over the space of a year at a sub-tropical location. Results obtained from this measurement campaign were used to compute a K_d value for the sea water in each particular season. These K_d values where found to be in close agreement to standalone K_d values derived from results taken using a standard calibrated spectrometer in the same sea water.     

Group testing procedures with incomplete identification and unreliable testing results

We consider multistage group testing with incomplete identification and unreliability features. The objective is to find a cost‐efficient group testing policy to select a prespecified number of non‐defective items from some population in the presence of false‐positive and false‐negative test results, subject to reliability and other constraints. To confirm the status of tested groups, various sequential retesting procedures are suggested. We also extend the model to include the possibility of inconclusive test results. We derive all relevant cost functionals in analytically closed form. Numerical examples are also given. Copyright © 2006 John Wiley & Sons, Ltd.     

On the radiation pattern of a paraboloid of revolution

Summary The radiation pattern of a paraboloid of revolution is determined by using the mathematical form of Huygens' principle where the field intensities in a given domain are expressed in their tangential components on the boundary. These tangential components are supposed to have the values which follow from the reflection of a plane wave at an infinite metal plate, coinciding with the tangent plane to the surface of the paraboloid. Expressions involving infinite series of Bessel functions are obtained which give the intensities of the distant field when an electric dipole is placed at the focus. Approximations are made for the main lobe in the planes perpendicular to and through the dipole. Finally Zuhrt's method leads to the same results as the approximations given in the present paper.     

Copper(0) in the Ullmann heterocycle-aryl ether synthesis of 4-phenoxypyridine using multimode microwave heating

The action of nanoparticulate copper catalysts with a mean particle size of 10 nm in the Ullmann ether synthesis is reported using multimode microwave heating and employing stable chloropyridine salts and unactivated phenol, with stabilized copper nanoparticles outperforming other copper catalysts in terms of stability and reusability.