Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.     

Regioselective palladium-catalyzed phenylation of ethyl 4-oxazolecarboxylate

The efficient and regioselective palladium-catalyzed C-2 arylation of ethyl 4-oxazolecarboxylate 1 with phenyliodide is described. The different parameters (solvent, base, ligand and catalyst) for the optimal conditions of this arylation process have been screened.     

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.     

Magnetostriction measurement by means of strain modulated ferromagnetic resonance (SMFMR)

A novel method for measuring magnetostriction constants is presented. A strain, periodic in time, applied to the sample, causes a modulation of the ferromagnetic resonance line position. The height of the signal obtained after phase-sensitive detection is proportional to the strain modulation depth. The appropriate magnetostriction constant λ is obtained by comparing the height of the SMFMR signal with that of the FMR line, as recorded by means of magnetic field modulation. Features of the new technique are:

1. high sensitivity: λ_min? 10_?9 forM=100 Oe and linewidth ΔH _d=1 Oe;
2. λ's belonging to distinct precession modes are separately determined;
3. applicable to thin layers for which strain gauge techniques cannot be used;
4. wide temperature range: 1.2 K<T<300 K;
5. uniform stress.

An illustrative example (YIG layer on GGG substrate) is given.     

Optimization of a GFAAS method for determination of total inorganic arsenic in drinking water

The new 10 μg l⁻¹ arsenic standard in drinking water has been a spur to the search for reliable routine analytical methods with a limit of detection at the μg l⁻¹ level. These methods also need to be easy to handle due to the routine analyses that are required in drinking water monitoring. Graphite furnace atomic absorption spectrometry (GFAAS) meets these requirements, but the limit of detection is generally too high except for methods using a pre-concentration or separation step. The use of a high-intensity boosted discharge hollow-cathode lamp decreases the baseline noise level and therefore allows a lower limit of detection. The temperature program, chemical matrix modifier and thermal stabilizer additives were optimized for total inorganic arsenic determination with GFAAS, without preliminary treatment. The optimal furnace program was validated with a proprietary software. The limit of detection was 0.26 μg As l⁻¹ for a sample volume of 16 μl corresponding to 4.2 pg As. This attractive technique is rapid as 20 samples can be analysed per hour. This method was validated with arsenic reference solutions. Its applicability was verified with artificial and natural groundwaters. Recoveries from 91 to 105% with relative standard deviation <5% can be easily achieved. The effect of interfering anions and cations commonly found in groundwater was studied. Only phosphates and silicates (respectively at 4 and 20 mg l⁻¹) lead to significant interferences in the determination of total inorganic arsenic at 4 μg l⁻¹.     

Free-energy calculations of protein-ligand cation-pi and amino-pi interactions: from vacuum to proteinlike environments

To probe the role of cation-pi and amino-pi interactions in the context of protein-ligand interactions, the stability of 55 X-ray cation/amino-pi motifs involving the Ade moieties of cofactor molecules and Arg, Lys, Asn, or Gln side chains of their host protein was evaluated using quantum chemistry calculations. The conjunction of vacuum interaction energies, vibrational entropy, and solvation contributions led to identify Arg-Ade as the most favorable cation/amino-pi complex in the solvents considered, followed by Asn/Gln-Ade and Lys-Ade: their minimum interaction free energies are approximately equal to -7, -4, and -2 kcal/mol, respectively, in the solvents of dielectric constant similar to that estimated for proteins (i.e., acetone, THF, and CCl(4)). Remarkably, these free-energy values of cation/amino-pi interactions correlate well with their frequency of occurrences in protein-ligand structures, which corroborates our approach in the absence of experimental data.     

Use of electrospray mass spectrometry (ESI-MS) for the study of europium(III) complexation with bis(dialkyltriazinyl)pyridines and its implications in the design of new extracting agents

ESI mass spectrometry was used to investigate the europium complexation by tridentate ligands L identical with 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridines (DATP) that have shown unique separation properties of actinides(III) from lanthanides(III) in nitric acid solutions. Complexes of three ligands, namely methyl (DMTP), n-propyl (DnPTP), and iso-propyl (DiPTP), have been investigated in acidic solutions to check the aqueous-phase stability of Eu(L)(3)(3+) ions identified previously in the solid state. The data obtained show, first, the presence of stable Eu(L)(3)(3+) ions with DnPTP (log beta(3)(app) = 12.0 +/- 0.5) and DiPTP (log beta(3)(app) = 14.0 +/- 0.6) in methanol/water (1:1 v/v) solutions under pH range 2.8-4.6 and, second, a mechanism whereby alkyl moieties contribute to a self-assembling process leading to the formation of Eu(L)(3)(3+) ions. Other complexes such as Eu(L)(2)(3+) ions are only observed for DnPTP (log beta(2)(app) = 6.7 +/- 0.5) and DMTP (log beta(2)(app) = 6.3 +/- 0.1) and Eu(L)(3+) only for DMTP (log beta(1)(app) = 2.9 +/- 0.2). The log beta(n)(app) values for the Eu(L)(n)(3+) (n = 1-3) complexes were determined at pH 2.8. Better insight was given in this study concerning the role of the hydrophobic exterior of the ligands for the design of a new range of extracting agents.     

Design and characterization of libraries of molecular fragments for use in NMR screening against protein targets

We have designed four generations of a low molecular weight fragment library for use in NMR-based screening against protein targets. The library initially contained 723 fragments which were selected manually from the Available Chemicals Directory. A series of in silico filters and property calculations were developed to automate the selection process, allowing a larger database of 1.79 M available compounds to be searched for a further 357 compounds that were added to the library. A kinase binding pharmacophore was then derived to select 174 kinase-focused fragments. Finally, an additional 61 fragments were selected to increase the number of different pharmacophores represented within the library. All of the fragments added to the library passed quality checks to ensure they were suitable for the screening protocol, with appropriate solubility, purity, chemical stability, and unambiguous NMR spectrum. The successive generations of libraries have been characterized through analysis of structural properties (molecular weight, lipophilicity, polar surface area, number of rotatable bonds, and hydrogen-bonding potential) and by analyzing their pharmacophoric complexity. These calculations have been used to compare the fragment libraries with a drug-like reference set of compounds and a set of molecules that bind to protein active sites. In addition, an analysis of the overall results of screening the library against the ATP binding site of two protein targets (HSP90 and CDK2) reveals different patterns of fragment binding, demonstrating that the approach can find selective compounds that discriminate between related binding sites.     

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.     

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

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