Synthesis and characterisation of thermomesogenic polysiloxanes with 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione units in the main chain

The synthesis of the first two liquid crystalline polysiloxanes bearing 3,6-diaryl-2,5-dihydropyrrolo-[3,4-c]pyrrole-1,4-dione units in their main chain are described. Investigations on their thermotropic phase behaviour by polarising microscopy reveal nematic or smectic enantiotropic phases, respectively.     

Biplanes with flag-transitive automorphism groups of almost simple type,with exceptional socle of Lie type

In this paper we prove that there is no biplane admitting a flag-transitive automorphism group of almost simple type, with exceptional socle of Lie type. A biplane is a (v,k,2)-symmetric design, and a flag is an incident point-block pair. A group G is almost simple with socle X if X is the product of all the minimal normal subgroups of G, and X⊴G≤Aut (G). Throughout this work we use the classification of finite simple groups, as well as results from P.B. Kleidman’s Ph.D. thesis which have not been published elsewhere.     

Electrostatic interactions in dissipative particle dynamics using the Ewald sums

The electrostatic interactions in dissipative particle dynamics (DPD) simulations are calculated using the standard Ewald [Ann. Phys. 64, 253 (1921)] sum method. Charge distributions on DPD particles are included to prevent artificial ionic pair formation. This proposal is an alternative method to that introduced recently by Groot [J. Chem. Phys. 118, 11265 (2003)] where the electrostatic field was solved locally on a lattice. The Ewald method is applied to study a bulk electrolyte and polyelectrolyte-surfactant solutions. The structure of the fluid is analyzed through the radial distribution function between charged particles. The results are in good agreement with those reported by Groot for the same systems. We also calculated the radius of gyration of a polyelectrolyte in salt solution as a function of solution pH and degree of ionization of the chain. The radius of gyration increases with the net charge of the polymer in agreement with the trend found in static light scattering experiments of polystyrene sulfonate solutions.     

(13)C NMR spectral assignment of 1,4-diarylpiperazinones

The piperazinone derivatives have potential application in the pharmaceutical, polymer and textile fields. The present work describes the preparation of a series of new 1,4-diarylsubstituted-2-piperazinones by condensation of substituted N,N'-bis-(2-hydroxyphenyl)-ethylenediamines with glyoxal and the complete (13)C NMR spectral assignment accomplished using APT, HMQC and HMBC techniques. Substituent chemical-shift effects (SCS) were calculated, which showed different values for the lactam- and amine-substituted aromatic rings. The results show that predictions based on SCS effects are not simple for these molecules due to electronic and steric effects. Moreover, in the case of the ortho-substituted derivative 2 g, the NMR spectra reveal a dynamic behavior related to restricted rotation of the phenyl groups (atropisomerism).     

Determination of cyclosporine A in whole blood: comparison of a chromatographic method with three different immunological methods

Cyclosporine A is potent immunosuppressive agent characterized by a narrow therapeutic range, inter- and intra-individual variability and a lack of correlation between drug dosage and blood levels. In view of these facts, blood levels of CyA should be routinely monitored to assess organ rejection and toxicity.

We evaluated CyA as well as its metabolites (AM9, AM19, AMl, and AM4N) in whole blood samples from 117 patients using commercially available immunological assays (AxSYM, EMIT, Dimension) and HPLC.

Cross-reactivity of the immunological assays was evaluated using different concentrations of the CyA metabolites (in vitro cross-reactivity) and by statistical analysis of patient data (in vivo cross-reactivity). Cross-reactivity was seen in all immunological assays, with differences in in vitro and in vivo cross-reactivity.

The statistical analysis showed a classical correlation between HPLC and AxSYM of r² = 0.89, HPLC versus EMIT of r² = 0.93, and HPLC versus Dimension of r² = 0.93.

The percentage metabolite cross-reactivity (%) by immunological assays for four metabolites at two concentrations each (250 and 1000 ng ml⁻¹) was lowest with the Dimension assay.

Of the immunological methods examined, the new Dimension for CyA determination can be relied on to produce results comparable to HPLC; other advantages are its simplicity, practicability and ease of handling.     

On the Hydrolysis of the Tetravalent Uranium Ion U4+

The formation of the hydrolytic complexes of U(IV) has been investigated at 25.00°C by measuring the Emf of a cell containing inert metal sponge and glass electrodes, in 3 mol·dm^?3 aqueous NaClO₄ solutions containing both U(VI) and U(IV) at acidities ranging between 10^?0.5 and 10^?1.8 mol·dm^?3. The lower limit of acidity is imposed by the precipitation of the sparingly soluble oxides of U(IV) whereas the upper limit has been chosen in order to avoid large corrections for the liquid junction potential. The experimental data have been treated using classical graphical methods (Rossotti, F.J.C., Rossotti, H.: The Determination of Stability Constants. McGraw Hill Book Company, Inc. New York (1961)) and by the computerized least-squares program LETAGROP-ETITR (Sillen, L.G., Warnqvist, B.: Arkiv för Kemi. 31, 315–39 (1969)). The results can be explained by assuming the formation of two mononuclear complexes, U(OH)³⁺ and $\mathop {{\rm U(OH)}}\nolimits_4^0The formation of the hydrolytic complexes of U(IV) has been investigated at 25.00°C by measuring the Emf of a cell containing inert metal sponge and glass electrodes, in 3 mol·dm⁻³ aqueous NaClO₄ solutions containing both U(VI) and U(IV) at acidities ranging between 10^−0.5 and 10^−1.8 mol·dm⁻³. The lower limit of acidity is imposed by the precipitation of the sparingly soluble oxides of U(IV) whereas the upper limit has been chosen in order to avoid large corrections for the liquid junction potential. The experimental data have been treated using classical graphical methods (Rossotti, F.J.C., Rossotti, H.: The Determination of Stability Constants. McGraw Hill Book Company, Inc. New York (1961)) and by the computerized least-squares program LETAGROP-ETITR (Sillen, L.G., Warnqvist, B.: Arkiv f?r Kemi. 31, 315–39 (1969)). The results can be explained by assuming the formation of two mononuclear complexes, U(OH)³⁺ and . The obtained formation constants in the 3 mol·dm⁻³ NaClO₄ ionic medium are: and . The formal standard potential ^* E _6,4 for the couple UO₂ ^{2 +}/U^{4 +} at the same conditions is 335.7± 0.5 mV.     

Testing green coffee for ochratoxin A, part III: performance of ochratoxin A sampling plan

Green coffee shipments are often inspected for ochratoxin A (OTA) and classified into good or bad categories depending on whether the OTA estimates are above or below a defined regulatory limit. Because of the uncertainty associated with the sampling, sample preparation, and analytical steps of an OTA test procedure, some shipments of green coffee will be misclassified. The misclassification of lots leads to some good lots being rejected (sellers' risk) and some bad lots being accepted (buyers' risk) by an OTA sampling plan. Reducing the uncertainty of an OTA test procedure and using an accept/reject limit less than the regulatory limit can reduce the magnitude of one or both risks. The uncertainty of the OTA test procedure is most effectively reduced by increasing sample size (or increasing the number of samples analyzed), because the sampling step is the largest source of uncertainty in the OTA test procedure. The effects of increasing sample size and changing the sample accept/reject limit relative to the regulatory limit on the performance of OTA sampling plans for green coffee were investigated. For a given accept/reject limit of 5 microg/kg, increasing sample size increased the percentage of lots accepted at concentrations below the regulatory limit and increased the percentage of lots rejected at concentrations above the regulatory limit. As a result, increasing sample size reduced both the number of good lots rejected (sellers' risk) and the number of bad lots accepted (buyers' risk). For a given sample size (1 kg), decreasing the sample accept/reject limit from 5 to 2 microg/kg relative to a fixed regulatory limit of 5 microg/kg decreased the percentage of lots accepted and increased the percentage of lots rejected at all OTA concentrations. As a result, decreasing the accept/reject limit below the regulatory limit increased the number of good lots rejected (sellers' risk), but decreased the number of bad lots accepted (buyers' risk).     

Chemistry of Bridging Phosphanes: A Comparative Study within CuI‐AgI‐AuI Triad‐Based Homonuclear Dimers

Bridging ligands in Ag^I and Au^I bimetallic complexes: The P moiety of bis(2‐pyridyl)phosphole acts as a symmetrically, semi‐, or non‐bridging donor in Ag^I dimers (see figure). In related Au^I complexes, only the non‐bridging mode is observed. An unsaturated Ag^I dimer is used as an adaptive molecular clip for the synthesis of π‐stacked metallocyclophanes.