T. J. Janjić

Salting-out thin-layer chromatography of transition metal complexes: II. Mixed aminocarboxylatocobalt(III) complexes on a polyacrylonitrile sorbent

Abstract Fourteen mixed aminocarboxylatocobalt(III) complexes, belonging to three homologous series, were investigated by salting-out thin-layer chromatography on a polyacrylonitrile sorbent using six aqueous ammonium sulphate solutions. An increase in the salt concentration of the solvent system was found to result in a decrease in the R F values of the complexes, giving rise to a reversed-phase order. It was established that the members of a homologous series containing aminocarboxylato ligands with a straight carbon chain exhibit lower R F values than the isomeric members with branched chains. A linear dependence was found between the R M values of the complexes belonging to the same homologous series and the number of carbon atoms in their hydrophobic parts. An increase in the salt content of the solvent system causes an increase in the separation factor (α) between two adjacent members of a homologous series, and a linear dependence between log α and the concentration of ammonium sulphate was established. The separation processes described are consistent with a mechanism of non-specific hydrophobic interactions.

Study of heterogeneous equilibria in saturated aqueous solutions of some 7-chloro-1,4-benzodiazepines

Acid-base equilibria in heterogeneous and homogeneous systems of some sparingly soluble benzodiazepines (diazepam, prazepam, chlordiazepoxide and medazepam) were investigated in aqueous solution and the corresponding equilibrium constants were determined by the application of pH-metric, spectrophotometric and solubility methods. The sites of protonation were predicted on the basis of the analysis of the corresponding carbon-13 nuclear magnetic resonance spectra. In addition, buffer characteristics of saturated aqueous solutions of these drugs in the presence of the solid phase were investigated and it was established that they possess a very high buffer capacity over a specific pH range.

Salting-out thin-layer chromatography of transition metal complexes: I. Investigation of the behaviour of mixed aminocar☐ylato cobalt(III) complexes on silica gel

Twenty-four mixed aminocar☐ylato cobalt(III) complexes of anionic and neutral types, containing nitro ligands with or without ammonia ligands and belonging to six homologous series, were investigated by salting-out thin-layer chromatography on silica gel, using seven ammonium sulphate solutions in water. In most cases it was established that a decrease in theRF values of the complexes accompanied increasing salt concentration of the solvent systems used. A positive linear dependence between theRM [log (1/RF - 1)] values of the complexes and the mol percent (mol fraction × 100) of ammonium sulphate in the solvent systems used was found. Finally, a positive linear dependence between theRM values of the complexes of a homologous series and the number of carbon atoms in the hydrophobic part of a complex was also established. To explain these results, a mechanism based on hydrophobic interaction between the sorbate and the sorbent is proposed.

Effect of the geometrical configuration of facial and meridional isomers of cobalt(III) and chromium(III) complexes on their RF values

Abstract The RF values of eight pairs of facial and meridional of cobalt(III) and chromium(III) complexes have been determined by thin-layer chromatography with 21 solvent systems and by paper chromatography with 26 solvent systems. In the thin-layer chromatographic separations on silica gel the meridional isomers always exhibited higher RF values when single component solvent systems were used. On the contrary, with multicomponent solvent systems, in 30% of cases the elution order of the isomers was reversed. In paper chromatographic separations with solvent systems not containing strong acids the meridional isomers were found to exhibit higher RF values. However, when solvent systems containing strong acids were used in some cases the elution order was reversed. Possible mechanisms for the separation of those isomers are considered.

Salting-out thin-layer chromatography of transition metal complexes. III: Investigation of the behaviour of mixed aminocarboxylato cobalt(III) complexes on cellulose

SummarySalting-out thin-layer chromatography of fourteen mixed aminocarboxylato cobalt(III) complexes (three homologous series) on cellulose has been investigated with eight aqueous ammonium sulphate solutions. A pronounced salting-out effect, with reversed-phase order, was observed with bis(aminocarboxylato) complexes, whereas with mono(aminocarboxylato) complexes such a behaviour was noticeable only at higher salt concentrations. In both cases a positive linear dependence between the RM values of the complexes and mol % of the salt in the solvent system, and between the RM values and the number of carbon atoms in the hydrocarbon part of the complexes belonging to the same homologous series, were found. These phenomena were explained by the mechanism of non-specific hydrophobic interactions.

Salting-out thin layer chromatography of transition metal complexes : a comparative study of the effect of increased number of CH2 groups in chelate rings

SummaryThe regularities previously established in salting-out thin-layer chromatography on silica gel of Co(III) complexes, in which the side chains of a specific chelate ring were successively increased in length, were also found to be valid for two series of Co(III) complexes of the EDTA type, in which different chelate rings were enlarged by one CH2 group. It was found that in the case of complexes of the EDTA type the salting-out efficiencies were practically the same for all members of a series, while the values of the separation factors were paractically independent of the ammonium sulphate concentration in the solvent system used. The results obtained were consistent with the mechanism of nonspecific hydrophobic interactions. The method used can be applied to the separation of the members of the series of complexes that we investigated.

Salting-out thin-layer chromatography of transition metal complexes. IV: Effect of sorbent on the behaviour of mixed aminocarboxylato cobalt (III) complexes

SummaryFrom literature data for 14 mixed aminocarboxylato cobalt(III) complexes, the effect of the sorbent on RM values, salting-out efficiency (m) and separation factors (α) of adjacent members of homologous series was investigated in salting-out, thin-layer chromatography on silica gel, polyacrylonitrile and cellulose sorbents, using ammonium sulphate solutions as developers. For complexes belonging to the same homologous series, linear dependence was found between RM,m and log α values, respectively, on two different sorbents. Polyacrylonitrile was shown to be the most suitable sorbent for the separation of the complexes since it gave the highest values for RM,m and α.

Effect of the substituents of β-diketonato ligands on RF values of tris(chelate) transition metal complexes obtained by normal- and reversed-phase thin-layer chromatography on unmodified silica gel

Abstract Three series of tris(β-diketonato) complexes of cobalt(III), chromium(III) and ruthenium(III), in which acetylacetonato ligands were successively replaced with dibenzoylmethanato ligands, were chromatographed on silica gel thin layers and the corresponding mechanisms were considered. The RF values increased with non-aqueous and decreased with aqueous solvent systems. It was established that unmodified silica gel can be used as a sorbent for both normal- and reversed-phase chromatography of metal complexes. The earlier rule of a linear dependence between the RM values of tris(chelate) transition metal complexes and the number of substituted chelate ligands by others was extended.

Linear relation between RM values obtained in salting-out planar chromatography and Mol% ammonium sulphate in aqueous solvent systems

SummaryExistence of a linear relation between RM and mol % ammonium sulphate in an aqueous solvent system, established earlier for mixed aminocarboxylato cobalt(III) complexes in salting-out, thin-layer chromatography on silica gel, polyacrylonitrile and cellulose, was verified by linear regression analysis of the corresponding data reported in the literature for 108 organic compounds separated on cellulose. The same regularity was also found for seven inorganic anions.

Effect of electronegativity of donor atoms on RF values of tris(β-diketonato) complexes of cobalt(III), chromium(III) and ruthenium(III) by thin-layer chromatography on silica gel

SummaryThe effect of the electronegativity of donor atoms on RF values obtained by TLC on silica gel was investigated with two series of complexes of the type [M(acac)3−n(phacphac)n] and [M(acac)3−n(phacphSac)n], where M is Co(III), Cr(III) or Ru(III), acac=2,4-pentandionato ion, phacphac=1,3-diphenyl-1,3-propanedionato ion and phacphSac=3-mercapto-1,3-diphenyl-prop-2-en-1-on ion (n=0–3). Development was with nine single and six two-component solvent systems. The RF values of the complexes increase by replacing one oxygen atom of a β-diketonato ligand with a less electronegative sulphur atom. A positive linear dependence between the RM values of the complexes and the numbers of acac substituted by phacphSac ligands was established. The separation mechanisms and separation factors are discussed.