The signal vs. concentration relationships in fluorimetry

Formulae for the fluorescence signal are derived which take into account some factors hitherto neglected. From these formulae conditions are deduced, for which a linear relationship exists between the concentration of the fluorescent components and the intensity of the fluorescence. In some cases of practical interest the fulfilment of these conditions cause too low a sensitivity. For such cases a method of optimization is outlined, by means of which the conditions are found which lead to the least deviation from linearity at the required sensitivity.     

The luminescence of uranime-activated yttrium tungstate (Y2WO6)

The luminescence of uranium in Y₂WO₆ can be excited with long wavelength ultraviolet radiation at temperatures below room temperature. The emission consists of a fairly narrow band in the orange part of the spectrum. Its characteristics are comparable with the luminescence of uranium in MgWO₄ and the scheelites MWO₄ (M = Ca, Sr, Ba). It is possible to relate the thermal quenching temperature of the luminescence to spectral data. Energy transfer from the tungstate group to the uranate group is observed, but its efficiency is not very high compared with other systems.     

Expert system for precision testing in validation of liquid chromatographic methods

After a liquid chromatographic method has been developed, it must be validated to establish its limitations in daily use. Method validation is becoming increasingly important as stricter rules are applied by regulatory authorities. Precision testing is a vital step in this validation; both intralaboratory testing and interlaboratory testing are needed. In an intralaboratory test, repeatability and ruggedness tests are usually done. Expert systems are available for both tests. Here they are integrated to form an intralaboratory precision-testing expert system; special integration architecture is described. Important features of the integrated system are a supervisor containing planning knowledge about the tests and a common data structure containing all the objects necessary for an expert system in this area.     

Solvatochromism and piezochromism of dicyano-, tricyano-, and tetracyano-diimine-iron(II) complexes

The solvatochromism of several dicyano-bis-diimine-iron(II) complexes in various binary aqueous solvent mixtures has been established, at 25 °C. A solvent sensitivity scale has been developed for these complexes. The solvatochromic properties of two tricyano-terdentate ligand iron(II) complexes in several solvents have also been determined, as have those of a series of tetracyano-diimine complexes in DMSO–water media. These results have been analysed and systematic but varied trends of solvation were demonstrated. Piezochromic parameters for two complexes have been obtained and are discussed in the context of a solvatochromism/piezochromism correlation.     

Synthesis and Catalytic Properties of Di- and Trinuclear Palladium Complexes with PCP-Pincer Ligands

Linear and branched conjugated pincer ligands having Ph₂P groups were synthesized: 3,3',5,5'- tetrakis(diphenylphosphinomethyl)diphenylacetylene, 3,3',5,5'-tetrakis(diphenylphosphinomethyl)diphenyldi- acetylene, 1,3,5-tris[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene, and hexakis[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene. Palladation of these ligands by heating with Pd(BF₄)₂(MeCN)₄ in boiling acetonitrile gave the corresponding di- and trinuclear ionic pincer palladium complexes. No individual complex was obtained from hexakis[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene. The ionic com- plexes were converted into the corresponding chloride complexes by treatment with sodium chloride in a mixture of water with methylene chloride. The structure of the ionic palladium complex with 3,3',5,5'-tetrakis(diphenylphosphinomethyl)diphenylacetylene was established by X-ray analysis. The obtained palladium complexes exhibited a considerable catalytic activity in the Heck reaction of iodobenzene with ethyl acrylate and in the Michael addition of ethyl cyanoacetate with methyl vinyl ketone. The catalytic activity per palladium atom decreases as the number of palladium atoms in the complex increases.     

Mass spectrometry of nitroazoles: 2—the mass spectra of methyl substituted nitroimidazoles

The mass spectra of six isomers of methylnitroimidazoles are reported and discussed. All compounds exhibit strong molecular ions, along with the characteristic fragmentations of aromatic nitro compounds. In some cases ortho effects—losses of OH^., H₂O, CHO^., CH₂O—are observed, due to interactions of adjacent substituents.     

The effect of preparation conditions on the activity and stability of copreciptitated Ni/Al2O3 catalysts for the methanation of carbon monoxide

The activities and stabilities of coprecipitated Ni/Al₂O₃ methanation catalysts depend markedly on their preparation and pretreatment. The results are discussed in relation to the structure of the precipitate and to changes which occur during calcination and reduction.

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Ni/Al₂O₃ . , .

     

On non-analytic thermodynamic behaviour of the classical linear chain

The free energy ? per particle and the two-particle distribution function g have been expressed as functionals of the nearest-neighbour interaction Φ(x) for a variety of boundary conditions. For some boundary conditions and potentials Φ(x), ? and g behave singularly at a critical density

$\text{ρ}{}_{\mathrm{<mtext>c</mtext>}}\text{=}\text{lim}\text{s→0}{}^{\mathrm{+}}\text{∫}\text{0}\text{∞}\text{e}{}^{\mathrm{?sx?\beta \Phi (x)}}\text{d}\text{x?}\text{∫}\text{0}\text{∞}\text{x}\text{e}{}^{\mathrm{?sx?\beta \Phi (x)}}\text{d}\text{x.}$

     

A hard sphere model for order-disorder transitions in colloidal dispersions

Use of a hard sphere model and the concept of an effective hard sphere diameter of a colloidal particle with its associated double layer is reported. This method allows rapid determination of the order-disorder transition in colloidal dispersions and yields reasonable estimates of the osmotic pressures compared with “exact” Monte Carlo calculations.