Effect of the chelate ring size of diamine-Co(III) complexes on their hR(F) values obtained under salting-out thin-layer chromatography conditions

The effect of the chelate ring size of diamine Co(III) complexes under salting-out thin-layer chromatography (TLC) conditions was investigated. For that purpose, 16 neutral and cationic complexes containing from five- to seven-membered diamine chelate rings were chromatographed on the thin layers of silica gel, cellulose and polyacrylonitrile sorbents. Six aqueous solutions of ammonium sulphate at various concentrations were used as solvent systems. In all of the instances studied, it was established that hR(F) values decrease with increasing ring size. It was also found that the R-M Values obtained were a linear function; on the one side, salt concentrations in the chromatographic solvent systems used, and on the other side the diamine chelate ring size. To explain these results, a mechanism based on hydrophobic interaction between the sorbend and sorbent is proposed. (C) 1999 Elsevier Science B.V. All rights reserved

Mixed cobalt(III) complexes with S-tyrosine and 1,3-diaminopropane

Four out of six theoretically possible isomers of the (1,3-diaminopropane)bis(S-tyrosinato)cobalt(III) complex, having the cis(O) configuration, were isolated, and the trans(O) isomer was only defined in the eluate. The isomers were separated on an optically active Sephadex QAE column. Geometrical and absolute configurations of the isomers were determined by electronic absorption, circular dichroic and H-1 NMR spectra. The effect of the aromatic side group of the coordinated S-tyrosinato ligand on the stereoselective formation of the obtained isomers was examined

NH...pi interactions stabilize the most-hindered rotamer of the (S)-tyrosinato side group in bis[(S)-tyrosinato](diamine)cobalt(III) complexes: An NMR spectroscopic and DFT study

Conformational analysis based on an analysis of the vicinal alpha- and beta-proton coupling constants of (S)-tyrosinato ligands in diastereomers of a bis[(S)-tyrosinato](1,3-diaminopropane)cobalt(III) complex is used to calculate the mol fractions of the three most stable rotamers (t, g, h) of the (S)-tyrosinato ligand's side groups in D2O solution. The results of this conformational analysis indicate a population increase in the sterically least favorable rotamer h in diastereomers of Cl-molecular symmetry (complexes 5 and 6). The TOCSY spectrum of complex 6 in aqueous solution shows an exceptionally small chemical shift of one NH2 proton from the coordinated diamine, which is explained by an interligand NH center dot center dot center dot pi interaction. These findings demonstrate the persistence of this weak, noncovalent interaction in water solution. DFT calculations for complex 6, whose diamine ring is in a chair conformation, indicate that the complex with an h conformation in both its (S)-tyrosinato ligand side-residues, which yields the most frequent NH center dot center dot center dot pi interactions, represents an energy minimum. The fact that coordinated 1,3-diaminopropane in the examined complex 6 is in a chair conformation in aqueous solution is proved by the NMR analysis. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005

Synthesis and absolute configuration of novel mono- and dinuclear cobalt(III) complexes containing S-phenylalanine

Two diastereomers of bis(1,3-diaminopropane)(S-phenylalaninato)cobalt(III) were prepared by reaction of S-phenylalanine with carbonatobis(1,3-diaminopropane)cobalt(III). The diastereomers were separated on an optically active Sephadex QAE column and their absolute configurations assigned by means of circular dichroism. In addition, H-1 NMR spectra of the diastereomers were analyzed in terms of the population of the three predominant rotamers of the coordinated S-phenylalaninato ligand. One out of 24 theoretically possible diastereomers of the dinuclear species di-mu-hydroxo-tetrakis(S-phenylalaninato)dicobalt(III) was obtained by direct synthesis and its absolute configuration deduced from CD spectra

Mixed cobalt(III) complexes with aromatic amino acids and diamine. Part IV. Influence of noncovalent intraand interligand interactions on rotamer population of the S-phenylalaninato and S-tyrosinato side groups in (1,2-diaminoethane)bis(S-aminocarboxylato

Rotamer population of S-tyrosinato and S-phenylalaninato ligands side groups in diastereomers of (1,2-diaminoethane)bis(S-aminocarboxylato)cobalt(III) complexes is calculated by vicinal alpha and beta proton coupling constant analysis. The effect of noncovalent intra- and interligand interactions on the population of rotamers in D2O solution is discussed. It has been established that in all the complexes investigated the most abundant is rotamer t, in which aromatic voluminous moiety and carboxylic group are in an anti position. In almost all complexes the lowest content is of rotamer g, in which these two groups are in the nearest position. Relatively high population of rotamer b in complex 5 tyr, in spite of high steric hindrances, is due to intra- and interligand NH... pi interactions

Mixed cobalt(III) complexes with aromatic amino acids and diamine - Part V. Thermal investigation of (1,2-diaminoethane)bis(S-tyrosinato)cobalt(III) complex diastereomers

Thermal properties of (1,2-diaminoethane)bis(S-tyrosinato)cobalt(III) complex diastereomers are investigated by means of TG technique in 293-873 K temperature range. This is a first thermal study of [Co(S-aa)(2)en](+) (S-aa = anion of S-amino acid; en = 1,2-diaminoethane) complex diastereomers. It is shown that thermal decompositions of these complexes are multi-step degradation processes, which in some cases can be satisfactory separated into individual steps, depending on the molecular symmetry. It is proposed that the degradation processes occur with cleavage of the side chain of one S-tyrosinato ligand, followed by the cleavage of the second side chain by further heating. The proposed pathways of decomposition are in accordance with results of thermal degradation of noncoordinated S-tyrosine [F. Rodante, G. Marrosu, G. Catalani, Thermochim. Acta 194 (1992) 197-213]. In the case of diastereomers which crystallize with water molecules, the departure of both hygroscopic and crystal water occurs before. The corresponding kinetic and thermodynamic parameters of some processes were determined. (c) 2004 Elsevier B.V. All rights reserved