The molecular structure of cis- and trans-1,2-difluoro-ethene: An electron diffraction study

The molecular structure of cis- and trans-1,2-difluoroethene was studied in the gas phase by electron diffraction, using the sector-microphotometer technique. The molecules are planar. For trans-difluoroethene the geometrical parameters are: C-F bond: 1.338(0.003) Å; CC bond: 1.320(0.009) Å; C-H bond: 1.088(0.004) Å, ∠CCF 119.8°(0.2°); ∠CCH: 125° (1.2°). For cis-difluoroethene: C-F bond: 1.332(0.003) Å; CC bond: 1.311(0.008) Å; C-H bond: 1.100(0.003) Å; ∠CCF: 122.5°(0.2°); ∠CCH:127.0 °(2.3°).     

Spectroscopy in separated flames-II The use of the separated air-acetylene flame in long path atomic absorption spectroscopy

The application of a separated air-acetylene flame to the determination of several elements by long-path atomic-absorption spectroscopy is described. The factors which govern the stability and reproducibility of the separated flame have been investigated. High sensitivity and stability and low background absorption are obtained in the the determination of zinc, iron, copper, mercury, magnesium and silver by the method described.     

Application of the chemiluminescence systems to evaluate the role of Fcgamma and complement receptors in stimulating the oxidative burst in neutrophils

We have established a luminol- and a lucigenin-dependent CL methods to investigate the role of the receptors for Fc portion of IgG (FcgammaR) and/or complement receptors (CR) in mediating the oxidative burst in neutrophils from systemic lupus erythematosus (SLE) patients compared with healthy controls. In the luminol-CL system, all the reactive oxygen species (ROS) are responsible for light production, whereas in the lucigenin-CL system, only the first ROS generated, converts the lucigenin into an unstable intermediate molecule, which also emits light. First, neutrophils from healthy controls and SLE patients were stimulated with different IC opsonized or not with complement from normal human serum (NHS) or SLE serum, in presence of 10(-4) M luminol. This method was able to differentiate the role of the FcgammaR, CR and FcgammaR/CR co-operation in mediating the oxidative burst, as well as show that the oxidative burst mediated by these receptors was reduced in neutrophils from SLE patients. Second, neutrophils from healthy controls and SLE patients were stimulated with different IC, opsonized or not with NHS, in presence of 10(-3) M lucigenin. In this case, the lucigenin-CL system was also able to differentiate the role of FcgammaR and FcgammaR/CR co-operation, as well as show differences among healthy controls and two different groups of SLE patients according to their clinical manifestations. In conclusion, we have established two sensitive CL systems to study the role of FcgammaR and/or CR in stimulating the oxidative burst of neutrophils, which can be applied in monitoring the involvement of these receptors in the immunopathogenesis of SLE.     

Aggregation processes of biomolecules in presence of trehalose

Among disaccharides, trehalose, a naturally-occurring glass-forming disaccharide, is particularly effective in terms of its ability to preserve several organisms under stress conditions. The present work is aimed to investigate the bioprotective action of trehalose on lysozyme as a function of temperature. In order to extract quantitative information about the dimensional changes of the proteins, we performed Small Angle Neutron Scattering measurements on lysozyme/D₂O solutions in absence and in presence of the disaccharide. The findings emphasise the capability of trehalose to stabilise the protein, activating aggregation processes.     

Oxygen adsorption on nickel surfaces: Detection of different species by x-ray photoelectron spectroscopy

Interaction of oxygen with evaporated nickel films has been studied by X-ray photoelectron spectroscopy, XPS, over the temperature range 77–500 K and pressure range 10^?9?10^?4 torr. Three oxygen species have been positively identified from O(1s) binding energy shifts (I, II and III with BE's 529.5, 531.4 and 533.2 eV). A fourth state at ca. 534.8 eV may also exist. The relative proportions of each species present depends on the temperature of the substrate. Type I is tentatively considered to represent oxygen atoms in an oxide-like electronic environment, type II is assigned as chemisorbed oxygen atoms, although the possibility of assignment at high oxygen coverages to a defect Ni₂ O₃ structure is admitted. Type III is only formed in sub-monolayer quantities on interaction at 77 K; converting irreversibly to II on warming to 300 K. I and II are always formed together between 300 and 500 K. The authors believe this implies some incorporation of oxygen atoms from the start of adsorption, which in turn has important implications for recent LEED studies.     

Mass Spectrometry of π-complexes of transition metals : IV. π-Cyclopentadienylirondicarbonyldichlorogermaniums

The mass spectra of C₅H₅(CO)₂FeGECl₂X (X = Cl, Me, Et, n-Pr or CH₂Ph) show very intensive rearrangement ions which are formed due to cyclopentadienyl ring migration from iron to the germanium atom or chlorine (subsituent) migration from germanium to atom.     

Ergebnisse der umsetzung von carbonylcobaltaten mit chlordifluoracetylchlorid

We have been able to synthesize chlorodifluomethyltetracarbonyl- cobalt (1) by the reaction of chlorodifluoroacetyl chloride and sodium tetracarbonylcobaltate(-I) at low temperatures. (1) decomposes at normal temperature to yield μ-difluoromethylene-μ-carbonyl-bis(tricarbonylcobalt) (Co-Co) (2), di-μ-difluoromethylene-bis (tricarbonylcobalt) (Co-Co) (3) and μ-difluormethylene-μ-tetrafluoroethylidene-bis (tricarbonylcobalt) (Co-Co) (4). (2) proved to be an intermediate in the formation of the cluster fluoromethinyl-enneacarbonyltricobalt (5).Na[Co(CO)₃P(C₆H₅)₃] (or Na[Co(CO)₄] in presence of triphenylphosphine) and ClCF₂COCl react to form the acetyl derivative ClCF₂ CO·Co(CO)₃P(C₆H₅)₃ (6) which cannot be decomposed to give the corresponding methyl compound.     

Action des derives du phosphore trivalent sur les composes α-cyano α-halo carbonyles : Orientation de la reaction entre un anion enolate et un cation halophosphonium

The factors responsible for the orientation in the reaction between an anion derived from an α-cyano α-haloketo compound with an halophosphonium cation are determined. Steric effects are important, but electronic effects are not negligible. This reaction is controlled more by frontier electron densities for cations derived from trialkyl or triarylphosphines than for cations derived from trialkylphosphites or trisdime´thylaminophosphine.     

The entropy of small clusters of atoms using an Einstein model

We present a generalized Einstein model for calculating thermodynamic properties of small clusters of atoms and demonstrate its validity by comparing its predictions with Burton's exact calculations. The simplicity of the method enables one to easily compute thermodynamic quantities for many systems beyond those previously considered.     

Determination of iron at ng/ml level by solid phase spectrophotometry after preconcentration on cation exchange filters

A cationic exchanger paper is used to retain analytes in solution and, after drying, to analyze directly by measuring the UV-Vis absorbance of the paper. The method was applied to determination of iron using its known 1,10-phenanthroline complex. Using 100 ml of sample the applicable concentration range was between 1.0 and 10.0 ng/ml with a detection limit of 0.2 ng/ml and a RSD around 2%. The method was applied to determination of iron total in snow, human serum and wine.