Edward R. Dockal

Preparation, characterization and thermogravimetric studies of [N,N′-cis-1,2-cyclohexylene bis(salicylideneaminato)]cobalt(II) and [N,N′-(±)-trans-1,2-cyclo-hexylene bis(salicylideneaminato)]cobalt(II)

Abstract The synthesis, characterization and thermogravimetric studies of [ N , N ′ -cis -1,2-cyclohexylene bis(salicylideneaminato)]cobalt(II), [Co(II)( c -Salcn)], and [ N , N’ -( ± )- trans -1,2-cyclohexylene bis(salicylideneaminato)]cobalt(II), [Co(II)( t -Salcn)] are reported. The free ligands were characterized by elemental analyses, melting points, IR, electronic, and 1 H and 13 C NMR spectra. The cobalt(II) complexes were characterized by elemental analyses, melting points, IR and electronic spectra. The IR and electronic spectra of the free ligands and the complexes are compared and discussed. The thermogravimetric data for both isomers showed two-step decomposition, but the trans isomer was less stable than the cis . Different cobalt oxides are formed as the final decomposition product depending on the atmosphere used, nitrogen or air.

Caracterização de quitosanas comerciais de diferentes origens

Chitosan is a linear polysaccharide obtained from the deacetylation of chitin. The physico-chemical properties of chitosan dependent on the average degree of acetylation () and of the average molar mass (). Several applications of chitosan have been proposed in the literature, mainly in water treatment, cosmetic and drug manufacturing, food additives, semipermeable membranes and development of biomaterials. In this work, three commercial chitosan samples were characterized by proton nuclear magnetic resonance (1H NMR), infrared spectroscopy (IR), conductimetric titration and thermal analysis (TG and DSC) in order to compare commercial chitosans from different supplies. The average viscosimetric molecular weight Mv was estimated from the intrinsic viscosity. The results confirmed remarkable differences in relation to the mean degree of acetylation () (or desacetylation, ). The thermal analysis data permitted to follow the dehydration, decomposition, and glass transition temperature (Tg).

Synthesis and characterization of aquo[N,N′-ethylenebis(3-ethoxysalicylideneaminato)]dioxouranium(VI)

Abstract The synthesis, spectra and structure of [UO2(3-EtOsalen)(H2O) · H2O [where (3-EtOsalen) is the Schiff base N,N′-ethylenebis(3-ethoxysalicylidieniminato)] are reported. The IR spectra and 1H and 13C NMR spectra of the free ligand and the uranyl complex were recorded. Assignment of the IR bands and NMR chemical shifts are given. Four bands were observed for the complex, 455, 396, 341 and 267 nm in acetonitrile and 472, 396, 345 and 269 nm in dimethyl sulphoxide. The weak bands at 455 and 472 nm are assigned to the 1 E ∗ → 2 π u transition. The UO22+ ion is coordinated to two nitrogen and two oxygen atoms of the ligand, with a water molecule completing the characteristic seven-coordinate, pentagonal-bipyramidal geometry. Another water molecule completes the crystal structure and is involved in several intra- and intermolecular hydrogen bonds.

Tetradentate schiff base copper(II) complexes

Abstract Ten copper(II) complexes of tetradentate Schiff bases obtained by condensing two moles of an o-hydroxyphenylcarbonyl compound with a diamine have been prepared and characterized by elemental analyses, melting points, IR and electronic spectra. The IR and electronic spectra of the free ligand and the complexes are compared and discussed. The deconvolution of the visible spectra of the complexes in CHCl3, approximately C2V or C1, yielded four peaks at ca. 15000, 17000, 18000-19000, and 20000-22000 cm−l, assigned to the four d-d transitions.

TETRADENTATE SCHIFF BASE OXOVANADIUM(IV) COMPLEXES

SummaryEleven oxovanadium(IV) complexes of tetradentate Schiff bases, obtained by condensating two moles of an o-hydroxycarbonyl compound with a diamine, have been prepared and characterized by elemental analysis, m.p., and i.r. and electronic spectra. The i.r. and electronic spectra of the free ligand and the complexes are compared and discussed. The Gaussian analysis of the vis. spectra of the complexes, normally C1 or Cs, in MeCN yielded four peaks at ca. 12000, 15000, 17700 and 20000–23000cm−1, assigned to the four d-d transitions.

Electrochemical modified electrodes based on metal-salen complexes

Abstract A general view of the electroanalytical applications of metal‐salen complexes is discussed in this review. The family of Schiff bases derived from ethylenediamine and ortho‐phenolic aldehydes (N,N′‐ethylenebis(salicylideneiminato)—salen) and their complexes of various transition metals, such as Al, Ce, Co, Cu, Cr, Fe, Ga, Hg, Mn, Mo, Ni, and V have been used in many fields of chemical research for a wide range of applications such as catalysts for the oxygenation of organic molecules, epoxidation of alkenes, oxidation of hydrocarbons and many other catalyzed reactions; as electrocatalyst for novel sensors development; and mimicking the catalytic functions of enzymes. A brief history of the synthesis and reactivity of metal‐salen complexes will be presented. The potentialities and possibilities of metal‐Salen complexes modified electrodes in the development of electrochemical sensors as well as other types of sensors, their construction and methods of fabrication, and the potential application of these modified electrodes will be illustrated and discussed.

The thermal behaviour of nickel, copper and zinc complexes with the Schiff bases cis- and trans-N, N'-bis(salicylidene)-1,2-ciclohexadiamine (Salcn)

Abstract The Schiff base complexes were prepared and characterised by UV, IR and NMR ( 1 H and 13 C ) spectroscopy, elemental analysis and X-ray powder diffractometry. Free ligands and some new complexes were submitted to thermal analysis (TG and DSC) under dynamic air atmosphere. The differences in the decomposition profiles were related to the structure of isomers and decomposition intermediates were characterised according to their X-ray diffraction pattern.

A Simple and Efficient Synthesis of Thymoquinone and Methyl P-Benzoquinone

Abstract The Co(II) (salen) catalysed oxidations of thymol (1), carvacrol (2), o- and m-cresol, with molecular oxygen give high yields of the corresponding p-benzoquinones.

Electrochemistry of organometallic compounds. Part III. Oxidations of methyl derivatives of organocobalt(III) complexes with delocalized electronic structure in dimethylformamide

The influence of the equatorial ligand on the electrochemical oxidation of the compounds [H3CCo(chel)B], where chel is bis (dimethylglyoximato), (DH)2; bis(salicylaldehyde)ethylenediimine, salen; bis(salicylaldehyde) o-phenylenediimine, salophen; bis(salicylaldehyde)cyclohexylenediimine, salcn; bis(acetylacetone) ethylenediimine, bae; and where B is pyridine when chel is (DH2), and dimethylformamide (DMF) when chel represents a Schiff base (salen, salcn, salophen and bae), was studied by means of cyclic voltammetry in DMF, 0.2 M in tetraethylammonium perchlorate, between 25 and −25°C, with a platinum disk working electrode. Absorption spectra in the visible and near ultraviolet regions for these compounds in DMF at 25°C were obtained. The complexes exhibit a reversible one-electron oxidation, at −20°C with scan rates >0.5 V s−; chemical reactions following electron transfer are not detected under these conditions. At slower potential or higher temperatures, the oxidized product decomposes chemically in a solvent-assisted (or nucleophile-assisted) reaction, yielding products which are electroactive in the applied potential range. The behavior of the [H3CCo (DH2)py] derivative is better described as a quasi-reversible charge transfer followed by an irreversible chemical reaction. Experimental evidence suggests that in the case of the [H3CCo(bae)] derivative at −20°C, the reactive -species is pentacoordinated and weakly adsorbed at the electrode surface. The value of E12 and the energies of the first two absorption bands in the visible spectra reveal the ability of the studied complexes to donate and to delocalize electronic charge.

Electrochemical sensor for ranitidine determination based on carbon paste electrode modified with oxovanadium (IV) salen complex

The preparation and electrochemical characterization of a carbon paste electrode modified with the N,N-ethylene-bis(salicyllideneiminato)oxovanadium (IV) complex ([VO(salen)]) as well as its application for ranitidine determination are described. The electrochemical behavior of the modified electrode for the electroreduction of ranitidine was investigated using cyclic voltammetry, and analytical curves were obtained for ranitidine using linear sweep voltammetry (LSV) under optimized conditions. The best voltammetric response was obtained for an electrode composition of 20% (m/m) [VO(salen)] in the paste, 0.10 mol L(-1) of KCl solution (pH 5.5 adjusted with HCl) as supporting electrolyte and scan rate of 25 mV s(-1). A sensitive linear voltammetric response for ranitidine was obtained in the concentration range from 9.9×10(-5) to 1.0×10(-3) mol L(-1), with a detection limit of 6.6×10(-5) mol L(-1) using linear sweep voltammetry. These results demonstrated the viability of this modified electrode as a sensor for determination, quality control and routine analysis of ranitidine in pharmaceutical formulations.