Synthesis, characterization, catalytic, electrochemical and thermal properties of tetradentate Schiff base complexes

In this study, the Schiff base ligands H₂L¹–H₂L³ and their Cu^II, Co^II, Ni^II, Fe^III Ru^III and VO^IV complexes have been prepared and characterized by spectroscopic and analytical techniques. All the complexes are mononuclear. Keto-enol tautomeric forms of the ligands have been investigated in polar and apolar solvents. The ligands favor the keto-form in the C₇H₈ and C₆H₁₄. The C–C coupling reaction of the 2,6-di-t-butylphenol has been investigated by the Co^II and Cu^II complexes. Thermal properties of the complexes have been assessed using thermal techniques and similar properties were found. In the Fe^III and Ru^III complexes, firstly, the coordinated water molecule is lost from the complex; in the second step, the chloride ion leaves the molecule in the 300–350 °C temperature range. Finally, the complexes decompose to the appropriate metal oxide at the higher temperature ranges. The electrochemical properties of the complexes have been studied in the two different solvents (DMF and CH₃CN).     

On the structure and activity of a Pt/C catalyst subjected to repeated deactivation and regeneration cycles

Electron microscopic studies reveal that repeated air/hydrogen regeneration cycles cause irreversible structural changes of a Pt/C catalyst involving sintering and migration of the platinum over the support. This is reflected by a serious decrease of the catalytic activity. With hydrogen treatment only, these effects are less significant.

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, / Pt/C, . . .

     

Interaction of tetraphenyl-porphyrin derivatives with DPPC-liposomes: an EPR study

The effect of the symmetry and polarity of the porphyrin molecules on their membrane localization and interaction with membrane lipids were investigated by electron paramagnetic resonance (EPR). For this purpose, two glycoconjugated tetraphenyl porphyrin derivatives were selected, respectively, symmetrically and asymmetrically substituted. Small unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and spin labeled stearic acids were prepared. The spin probe was located at the 5th or 7th or 12th or 16th position of the hydrocarbon chain in order to monitor various regions of the lipid bilayer. EPR spectra of porphyrin-free and porphyrin-bound liposomes were recorded at various temperatures below and above the phase transition temperature of DPPC. The effect on membrane fluidity proved to be stronger with the asymmetrical porphyrin derivative than with the symmetrical one. The rigidity increased when the spin label was near lipid head groups. The difference observed between control and porphyrin-treated samples when measured below the main lipid transition temperature disappeared at higher temperature. When the spin label was near the end of the hydrophobic tails, the symmetrical porphyrin derivative caused increase in fluidity, while the asymmetrical one slightly decreased it. To explain this phenomenon we propose that the asymmetrical derivative exerts a stronger ordering effect caused by its fluorophenyl group located at the level of the lipid heads, which is attenuated to the hydrophobic tails. The perturbing effect of the symmetric derivative could not lead to similar extent of ordering at the head groups and looses the hydrocarbon chains deeper in the membrane.     

Cyclic sulfonium salts with S ... O interactions 2. Molecular structures with six-membered rings

1-[2-(N-methylcarbamoyl)phenyl]-3H-2,1-naphto-(1,8-d,e)-oxathiin-1-ium chloride (2), 1-[2-(N-methylcarbamoyl)-phenyl]-2-methyl-3-oxo-3H-1, 2-naphto-(1,8-d,e)-thiazin-1-ium chloride (3), 1-[8-(N-methylcarbamoyl)naphtyl]-2-methyl-3-oxo-3H-1, 2-naphto-(1,8-d,e)-thiazin-1-ium chloride (4) and 1-(8-carboxylatonaphtyl)-2-methyl-3-oxo-3H-1,2-naphto-(1,8-d,e)-thiazin-1-ium dipolar ion (5) cyclic sulfonium salts were prepared and their chemical properties investigated (spirosulfurane-formation, hydrolysis). The molecular structures obtained from x-ray diffraction can be described with a considerably distorted trigonal bipyramidal arrangement of the ligands about the sulfonium center, with O/N—S ... O=apical angles of 173.9, 164.9, 156.6, and 159.0°, as well as with S—O/N apical bond lengths of 1.648, 1.671, 1.664, and 1.682 Å. The structures exhibit relatively short S ... O close contacts with interatomic distances of 2.253, 2.448, 2.795, and 2.619 Å.     

Study of the cis-trans isomerization of enalapril by reversed-phase liquid chromatography

Enalapril is a dipeptidic angiotensin converting enzyme inhibitor. It exists as a mixture of two conformers in solution with respect to the peptide bond involving the proline amino group. The RPLC of such products may yield peak splitting or multiple peaks as a result of the slow kinetics of the conformation change. In this study, the influence of the flow-rate, pH, temperature, organic modifier and counter ion on the peak shape and the separation of the cis and trans conformers are examined qualitatively by HPLC. It appears that decrease of relaxation time for isomerization with concomitant improvement in peak shape is favoured by a decrease in pH and flow-rate, increase of temperature, choice of organic solvent (nature, amount) and cationic counter ion concentration in the mobile phase. The elution order of the isomers was dependent on the nature of the organic modifier whereas the separation selectivity was improved by an increase of pH or the addition of a negatively charged counter ion. In addition, an NMR investigation on enalapril is described.     

Synthesis of novel tryptamine and β-carboline derivatives via palladium-catalyzed reaction of bromotryptamine with organic boronic acids

New tryptamine 5, 7 and β-carboline derivatives 3 were preparated by palladium-catalyzed coupling reaction of 5-bromotryptamine 1 with aryl boronic acids. Dedicated to Professor András Lipták on his 70^th birthday.     

Regioselectivity of Birch reductive alkylation of biaryls

[reaction: see text] The regioselectivity of the Birch reductive alkylation of polysubstituted biaryls has been investigated. Results indicate that regioselectivity is affected by the electronic nature of substituents on both aromatic rings. The electron-rich 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, while phenols and aniline are not dearomatized under these conditions. Biaryls possessing a phenol moiety are alkylated on the second ring, providing that the acidic proton has been removed prior to the Li/NH3 reduction.     

Assessment of the Fe-Sn-Zn phase diagram at 450°C

The Fe-Sn-Zn system is of interest because Sn is one element added to the Zn galvanizing bath to overcome the drawbacks due to the presence of Si in semi-killed steels. This work has been undertaken with the aim to understand the tin effect on the microstructure and the layers growth in batch galvanized coatings on low alloyed steels. Various experimental techniques such as metallography, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDX) are used in order to characterize the microstructure and the properties of such coatings elaborated in a zinc bath enriched with tin. Solidification phenomena and layers growth mechanisms during galvanization are explained by means of the ternary phase diagram Fe-Sn-Zn at 450°C. The Calphad method allows to obtain this phase diagram from the three optimized binary phase diagrams Fe-Sn, Fe-Zn and Sn-Zn and some experimental data inside the ternary Fe-Sn-Zn system.     

Synthesis of 2′,3′-dihydrosolanesyl analogues of β-d-arabinofuranosyl-1-monophosphoryldecaprenol with promising antimycobacterial activity

Two new hydrolytically stable analogues of β-d-arabinofuranosyl-1-monophosphoryldecaprenol, the donor substrate for mycobacterial arabinosyltransferase, have been prepared. Biological evaluation of these compounds in vitro against Mycobacterium tuberculosis H₃₇Rv strain revealed a promising activity.