Saturated heterocycles. 251 . Determination of σ+ values of heteroaryl-substituted phenyl groups via ring-chain tautomerism

The Hammett-Brown electrophilic substituent constants σ⁺ for five heteroaryl-substituted phenyl groups were estimated via the ring-chain tautomeric equilibria of three sets of oxazolidines and 1,3-oxazines in deuteriochloroform solution. For oxazolidines derived from norephedrine and norpseudoephedrine, the σ⁺ values were also determined via the gas-phase ring-chain equilibria, by means of mass spectrometry. The results show that the heteroaromatic substituents studied have a slight electron-withdrawing character, with σ⁺ in the range -0.03 to 0.59. The gas-phase σ⁺ values are significantly higher than the solution values.     

Pt coated Cr2O3 thin films for resistive gas sensors

The resistive response of atomic layer deposited thin epitaxial α-Cr₂O₃(0 0 1) films, to H₂ and CO in air, was studied. The films were covered with Pt nanoislands formed by electron-beam evaporation of a sub-monolayer amount of the material. The gas measurements were performed at 250°C and 450°C. These temperatures led to different proportion of chemical states, Pt²⁺ and Pt⁴⁺, to which the Pt oxidized. The modification was ascertained by the X-ray photoelectron spectroscopy method. As a result of the modification, the response was fast at 250°C, but slowed at 450°C. A disadvantageous abundance of Pt⁴⁺ arising at 450°C in air could be diminished by high-vacuum annealing thus restoring the response properties of the system at 250°C.      

Quality control and evaluation of mass spectra

Over 1400 electron ionization mass spectra of selected organic compounds have been measured under carefully defined conditions. In this paper, the variables such as sample purity and spectrometer calibration that are controlled are described. The quality of the resulting spectra as well as the cost of the measurements is reported.     

Diagnostic performance of low field MRI in acute knee injuries

The diagnostic performance of low field (0.1 T) magnetic resonance imaging (MRI) was studied prospectively and double-blindly among 33 patients with acute knee injuries. The subsequent arthroscopy was the golden standard. For lesions of the medial meniscus low field MR had a sensitivity of 88% and a specificity of 80%; for lesions of the lateral meniscus the sensitivity was 25% and the specificity 97%. For anterior cruciate ligament tears, low field MRI had a sensitivity of 83% and a specificity of 85%. The specificity for posterior cruciate ligament tears was 97%. The performance of low field MRI equalled that reported earlier for high field MRI, the only exception being the sensitivity for lateral meniscus lesions.     

Carboxymethyl cellulose on a fiber substrate: the interactions with cationic polyelectrolytes

High and low molecular weight (M_w) carboxymethyl celluloses (CMC) were adsorbed on a well-characterized fiber substrate (long fibers of a commercial bleached birch kraft pulp with the carboxylic acid groups in Na-form) to increase the charge of the fibers in a controlled fashion. The M_w played a role in the utilization of CMCs as a strength additive in paper sheets nearly doubling the tensile strength with the high M_w CMC. Swelling properties of the CMC treated fibers were measured with water retention value (WRV). The WRV increased more with the high M_w CMC. The swelling was further tuned by two highly cationic polyelectrolytes; high M_w poly(diallyldimethyl ammonium chloride) (PDADMAC) and low M_w polybrene (hexadimethrine bromide, [3,6]-ionene). They were chosen because of their known ability to neutralize the anionic charge either exclusively on the surface or in the whole fiber, respectively. Adsorption of PDADMAC could reduce WRV of the CMC pre-treated fibers to the level of the untreated reference, while polybrene adsorbed pulps with 3–10 times more cationic polyelectrolyte deswelled the fibers only slightly more than the surface neutralized fibers. These results indicated surface conformation differences with low and high M_w CMCs. While the conformation did play a role after physical alteration (drying and rewetting) of the fibers, the paper sheets produced from these fibers showed remarkable differences. In extreme cases, the strength of the paper could be retained after drying (low M_w CMC + PDADMAC) or paper, resistant to disintegration, could be achieved (CMC + polybrene).     

Short and long term stability of the elemental composition of human body fluid reference materials and their use as master lots

Summary Studies have been made of both short and long term stability of trace elements in lyophilized human body fluid reference materials, as well as the stability of mercury in reconstituted urine solutions. No detectable concentration changes for mercury, lead and aluminium occurred during the 5-year period. There are large differences in the amounts of mercury loss among different reconstituted materials. Addition of traces of gold to the solutions minimized the mercury loss and increased the useable time of the reconstituted material from hours to 8 days. A certification process based on direct determinations by reference laboratories and by comparison against master lots of the same material and against similar certified reference materials is presented. Values for calcium, copper and mercury obtained from reference laboratories and using the data transfer principle have been assigned in new batches of urine and serum.     

Metallic Conductivity and Magnetic Interactions in Nickel and Copper Phthalocyanine Iodides

We discuss the charge transport and magnetic properties of the titled molecular metals. Replacement of the diamagnetic Ni(+2) by paramagnetic Cu(+2) introduces a novel coupling between local Cu(+2) spins the mobile charge carriers, and produces a coupled transition at 8 K.     

{2,2′‐[(R,R)‐Cyclo­hexane‐1,2‐diyl­bis(nitrilo­methyl­idyne)]­bis[6‐tert‐butyl‐4‐(tri­phenyl­phosphonio­methyl)­phenol­ato]‐O,N,N′,O′}copper(II) dichloride hexakis­(deutero­chloro­form) solvate

The title compound, [Cu(C₆₆H₆₈N₂O₂P₂)]Cl₂·6CDCl₃, consists of complex cations, chloride ions and deutero­chloro­form solvate mol­ecules. The complex cation crystallizes in two different conformations. In both cases, Cu^II ions lie on twofold axes and the geometry around them is slightly distorted square planar. The dihedral angles between the N/Cu/N and O/Cu/O planes are 5.6 (9) and 3.9 (10)° for mol­ecules A and B, respectively.     

Some observations on sulfuric acid reactions in electrothermal atomic absorption spectroscopy with graphite furnaces

Interferences were found when mixtures of sulfuric acid with either nitric or perchloric acid were atomized in the graphite furnace of an atomic absorption spectrometer. The mixtures apparently formed thermally stable compounds with the graphite, which were not removed by pyrolysis at temperatures up to 1100°C. During the subsequent atomization, volatile species were released and their absorption could not be compensated by the conventional deuterium lamp system. The absorption and emission spectra of the species formed in the furnace showed the presence of CS and probably COS, as well as bands appropriate to S₂, SO₂ and NS. The uncorrectable absorptions detected at the 303.8-nm nickel line, the 303.94-nm indium line, and the 304.40-nm cobalt line are thought to be caused by the fine-structure of an unknown molecular compound.     

Recombination luminescence of CaSO4:Tb3+ and CaSO4:Gd3+phosphors

A comparative study of the excitation of luminescence by VUV radiation as well as of thermally and photostimulated luminescence has been carried out for CaSO₄:Tb³⁺ and CaSO₄:Gd³⁺ phosphors, where Na⁺ or F⁻ ions are used for charge compensation. The distinction in hole processes for the phosphors with Na⁺ or F⁻ compensators is determined by the differing thermal stability of the holes localized at/near Tb³⁺Na⁺ and Gd³⁺Na⁺ (up to 100–160 K) or at/near Tb³⁺F⁻ V _Ca and Gd³⁺F⁻ V _Ca centers involving also a cation vacancy (up to 400–550 K). Tunnel luminescence in the pairs of localized electrons and holes nearby Tb³⁺ or Gd³⁺ has been detected. The mechanisms of electron-hole, hole-electron and tunnel recombination luminescence as well as a subsequent released energy transfer to RE³⁺ ions are considered.