Sur une cause d'erreur dans le dosage par voie humide de l'azote dans les aciers speciaux

The estimation of nitrogen in normal or special steels by the Kjeldahl method can give results that are too high if the acid used to dissolve the steel (even “pro analysi” acid) contains impurities such as nitrates, and if the metal itself contains even negligible amounts of molybdenum (e g a few ten-thousandths). In this case the blank test can nevertheless give a very weak or negative result.In order to ascertain from this point of view the quality of the acid used, it is necessary to compare the nitrogen contents obtained on a sample with a very low nitrogen content, e g electrolytic iron, in the absence or in the presence, respectively, of a minute addition (about 0.1%) of molybdenum. The difference between these determinations should be negligible. If it is not, then the acid tested should be rejected, or distilled before use.     

Quasi-algebraic treatment of bound states of simple one-electron systems

We present a straightforward, quasi-algebraic treatment of simple one-particle quantum-mechanical systems. The method consists primarily of a canonical transformation that changes the Schrödinger equation into a first-order differential equation, thus allowing an easier derivation of the eigenvalues and eigenfunctions. We express the latter in a way which is not commonly encountered in the standard literature on quantum mechanics and quantum chemistry. The derivation of generating functions for the eigenfunctions offers no difficulty because the method is formulated in the coordinate representation. As illustrative examples, we consider the harmonic oscillator and a particle in a Kratzer potential.     

Preparation and reactivity of penta- and tetracoordinate platinum(II) hydride complexes with P(OEt)3 and PPh(OEt)2 phosphite ligands

The pentacoordinate [PtH{P(OEt)3}4]BF4 (1) hydride complex was prepared by allowing the tetrakis(phosphite) Pt{P(OEt)3}4 to react with HBF4.Et2O at -80 degrees C. Depending on the nature of the acid used, however, the protonation of the related Pt{PPh(OEt)2}4 complex yielded the pentacoordinate [PtH{PPh(OEt)2}4]BF4 (3) or the tetracoordinate [PtH{PPh(OEt)2}3]Y (4) [Y = BF4- (a), CF3SO3- (b), Cl- (c)] derivatives. Neutral PtHClP2 (7,8) [P = P(OEt)3, PPh(OEt)2] hydride complexes were prepared by allowing PtCl2P2 to react with NaBH4 in CH3CN. The tetrakis(phosphite)[Pt{P(OEt)3}4](BF4)2 (2) derivative was also synthesised and then characterised spectroscopically and by an X-ray crystal structure determination. Reactivity with aryldiazonium cations of all the hydrides was investigated and found to proceed only with the PtHClP2 complex to yield the aryldiazene [PtCl(ArN=NH)P2]BF4[P = PPh(OEt)2] derivative. The hydrazine [PtCl(NH2NH2){PPh(OEt)2}2]BPh4 complex was also prepared by allowing PtHClP2 to react first with AgCF3SO3 and then with hydrazine.     

Surfactant/nonionic copolymer interaction: a SLS, DLS, ITC, and NMR investigation

The interactions between an oxyphenylethylene-oxyethylene nonionic diblock copolymer with the anionic surfactant sodium dodecyl sulfate (SDS) have been studied in dilute aqueous solutions by static and dynamic light scattering (SLS and DLS, respectively), isothermal titration calorimetry (ITC), and 13C and self-diffusion nuclear magnetic resonance techniques. The studied copolymer, S20E67, where S denotes the hydrophobic styrene oxide unit and E the hydrophilic oxyethylene unit, forms micelles of 15.6 nm at 25 degrees C, whose core is formed by the styrene oxide chains surrounded by a water swollen polyoxyethylene corona. The S20E67/SDS system has been investigated at a copolymer concentration of 2.5 g dm(-3), for which the copolymer is fully micellized, and with varying surfactant concentration up to approximately 0.15 M. When SDS is added to the solution, two different types of complexes are observed at various surfactant concentrations. From SLS and DLS it can be seen that, at low SDS concentrations, a copolymer-rich surfactant mixed micelle or complex is formed after association of SDS molecules to block copolymer micelles. These interactions give rise to a strong decrease in both light scattering intensity and hydrodynamic radius of the mixed micelles, which has been ascribed to an effective reduction of the complex size, and also an effect arising from the increasing electrostatic repulsion of charged surfactant-copolymer micelles. At higher surfactant concentrations, the copolymer-rich surfactant micelles progressively are destroyed to give surfactant-rich-copolymer micelles, which would be formed by a surfactant micelle bound to one or very few copolymer unimers. ITC data seem to confirm the results of light scattering, showing the dehydration and rehydration processes accompanying the formation and subsequent destruction of the copolymer-rich surfactant mixed micelles. The extent of interaction between the copolymer and the surfactant is seen to involve as much as carbon 3 (C3) of the SDS molecule. Self-diffusion coefficients corroborated light scattering data.     

4th order derivative spectrophotometric determination of quinine in soft drinks

A method is developed for the 4rd order derivative spectrophotometric determination of down to 1–6 g/ml of quinine. This method has been applied to its determination in soft drinks. Comparison are made between this method and a spectrofluorimetric method.     

Skeletal isomerization of 1-butene on ZrO2/Al2O3 treated with sulfate ion

The catalytic activity for skeletal isomerization of 1-butene on ZrO₂ supported on Al₂O₃ and doped with sulfate ion has been found to be higher than on pure ZrO₂/Al₂O₃, Al₂O₃ containing sulfate ion and a commercial SiO₂–Al₂O₃ of H_o<–13.7. Sulfate ion was capable of transforming ZrO₂/Al₂O₃ into a solid superacid.

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1- ZrO₂, Al₂O₃ , , ZrO₂, , Al₂O₃, , SiO₂–Al₂O₃ H_o < –13,7. ZrO₂/Al₂O₃ .

     

Raman fibre optic approach to artwork dating

Raman micro-probe spectroscopy has been applied to the analysis of a non catalogued hand-crafted wallpaper during its restoration process. The analysis has been totally non-destructive without the necessity of taking any sample. The artwork showed a great chromatic palette having been detected the presence of calcium carbonate, Prussian blue, ultramarine blue, gypsum (CaSO4.2H2O), minium (Pb3O4), vermilion (HgS), chrome orange (CaCO3), chrome yellow (PbCrO4), barium sulphate and carbon black (C). From the spectroscopic analysis the date of its manufacturing has been set between 1828 and 1830, introduction of chrome yellow and orange, as well as artificial ultramarine blue, and 1840, when continuous industrial wallpapers were extensively manufactured in Europe.     

Theoretical study of the structure and antimicrobial activity of horminone

The structural and electronic parameters of the horminone molecule, an abietan diterpene quinone, were studied by means of all‐electron calculations using Hartree–Fock and density functional theory‐based methods, as implemented in the Gaussian98 program. The 6‐31G orbital basis sets were used for the C, H, O, and Mg atoms. The results allow the identification of the negative site of horminone (HM) most favorable for its binding to the Mg²⁺ ion. The HM–Mg²⁺ complex is assumed to play a significant role in the antibacterial activity. First, it penetrates the membrane cell. Then, through its interaction with rRNA, it inhibits the protein synthesis in several types of bacteria. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 411–421, 2003     

On-line ion-pair solid-phase extraction-liquid chromatography-mass spectrometry for the analysis of quaternary ammonium herbicides

An ion-pair on-line solid-phase extraction procedure using C8 extraction disks, suitable for liquid chromatography-mass spectrometry analysis is developed to determine quaternary ammonium herbicides (quats) in water samples. The separation of these compounds was performed using ion-pair chromatography with heptafluorobutyric acid (15 mM, pH 3.3) and acetonitrile gradient elution. Detection was carried out using a quadrupole mass spectrometer. Water sample volumes up to 50 ml can be preconcentrated with recoveries higher than 70%. Good precision and accuracy (day-to-day and run-to-run) were obtained and the detection limits ranged from 6 to 85 ng l(-1). The proposed on-line ion-pair solid-phase method enables compliance with European Community directives for drinking waters (100 ng l(-1)).     

On the use of carboxamidomethyl esters (cam esters) in the synthesis of model peptides. scope and limitations

The usefulness of carboxamidomethyl esters (CAM esters) as a carboxyl protecting group for peptide synthesis was demonstrated. The synthesis of the chemotactic peptide For-Met-Leu-Phe-OH as well as the synthesis of Met-enkephalin using CAM ester as carboxyl terminal protection were performed. These esters showed good stability during acidolytic removal of BOC N-protecting group, during hydrogenolysis of Z N-protecting group and during removal of FMOC N-protecting group. CAM esters were selectively and rapidly cleaved by NaOH 0.5 N or by Na₂CO₃. However, we did not succeed in removing selectively the CAM ester when β-benzyl ester of aspartic acid was present in the sequence.