Jaromir Kira

Molecular structures and stability constants of gossypol and its aza-derivative complexes with silver(I) cations studied by potentiometric, ESI MS, NMR, and AM1d semiempirical methods.

Stability constants of complexes formed by gossypol and by ten of its Schiff bases with Ag (+) cations were determined by the potentiometric method. The potentiometric and ESI MS experiments indicate the formation of AgL (+) and Ag 2L (2+) complexes between the Schiff bases G1-G7 and Ag (+) cations as well as the formation of AgL (+), Ag 2L (2+), AgL 2 (+) and Ag 3L 2 (3+) complexes between the Schiff bases G8-G10 and Ag (+) cations. The highest stability constant was found for the AgL (+) complex of G8 Schiff base and the lowest one for the AgL (+) complex of G molecule. The (13)C NMR spectra of mixtures between G and AgClO 4 as well as G1-G10 and AgClO 4 indicate that the complexation of the Ag (+) cations is exclusively realized by the aldehyde-aldehyde tautomer of gossypol and by the enamine-enamine form of gossypol Schiff bases, respectively. We show that the main coordination sites for the Ag (+) metal cations are either the oxygen or the nitrogen atoms of the amine parts of the Schiff bases of gossypol. The energetically most favorable structures of the Ag (+) complexes with gossypol (G) or with the gossypol Schiff bases (G1-G10) were calculated and visualized by the AM1d method at an semiempirical level of theory.

Potentiometric and AM1d studies of a new class of Tr-podands–silver(I) complexes

Formation of complexes of structurally comparable six silicon, boron and phosphorous Triton X podands (Tr-podands) and silver(I) cations in propylene carbonate has been studied by the potentiometric and AM1d semi-empirical methods. Three types of these podands (2–7) form stable complexes with Ag+ cations. The stability constants of the complexes including different number of silver(I) cations are determined. It has been shown that the number of Ag+ cations complexed by the podands depends strongly on the number of oxaalkyl chains and on the type of central podands atom (Si, B or P). The (7) podand (with six polyoxaalkyl chains) can complex as many as six silver(I) cations. The structures of these complexes are visualised by the AM1d semi-empirical method.

Potentiometric and spectrophotometric studies of the equilibria between silver(I) ion and crown ethers containing chromophore substituents in propylene carbonate

Potentiometric and UV-spectrophotometric methods have been used to study the coordination properties of crown ethers and their derivatives containing 9,10-dioxo-1-anthryl, 8-hydroxy-9,10-dioxo-1-anthryl and 8-tosyloxy-9,10-dioxo-1-anthryl substituents with respect to the silver(I) ion in propylene carbonate. It was found that unsubstituted crown ligands were capable of forming two types of complex ion. The silver(I) ion can enter the macrocycle cavity forming 1∶1 complexes or can coordinate externally to the nitrogen atom of a ligand as occurs for typical complexes of silver(I) with nitrogen ligands. This results in Ag(crown)2+ complexes. Introduction of chromophore groups allows investigation of the mechanism of AgL+ and AgL2+ complex formation by spectrophotometric methods. Attaching a bulky chromophore to the nitrogen atom of the aza-crown makes the formation of the AgL2+ complexes for monoaza-crown-15 strongly restricted or impossible. For 13-(9,10-dioxo-1-anthryl)-1,4,7,10-tetraoxa-13-azacyclopentadecane (A215C5AQN) the presence of only one substituent leads to an increase in the stability of the external complex (AgL2) and the formation of other complex structures Ag2L32+ and Ag3L23+.

Potentiometric, spectrophotometric, and AM1d studies of the equilibria between silver(I) ion and monoaza-crown ethers with anthraquinone in various solvents

Complex formation and stability constants between silver(I) and monoaza-12-crown, monoaza-15-crown, and monoaza-18-crown ethers with anthraquinone were determined in acetonitrile, methanol, and propylene carbonate by potentiometric and UV-spectrophotometric methods. Complexes of 1 : 1 and 1 : 2 metal-to-ligand stoichiometry were formed. The solvent composition and the size of the macrocyclic ring affect the stability constants of the complexes. The energetically most favorable structures of the 1 : 1 metal-to-ligand complexes were calculated and visualized by the AM1d method at a semiempirical level of theory.

Potentiometric and AM1d studies of the equilibria between silver(I) and monoaza, diaza, triaza and tetraaza-12-crown ethers in acetonitrile and propylene carbonate

Complex formation and stability constants between monoaza, diaza, triaza and tetraaza-12-crown ethers with silver(I) were determined in acetonitrile and propylene carbonate by the potentiometric method. Complexes of 1 : 1 and 1 : 2 metal-to-ligand stoichiometry were formed. The solvent composition and number of nitrogens significantly influence the stability constants of the complexes formed. The energetically most favorable structures of the 1 : 1 metal-to-ligand complexes were calculated and visualized by the AM1d method at the semi-empirical level of theory.

Potentiometric and AM1d studies of the equilibria between silver(I) and diaza-15-crown and diaza-18-crown ethers with nitrogen in different positions in various solvents

Abstract Complex formation and stability constants between typical and atypical diaza-15-crown and diaza-18-crown ethers with silver(I) were determined in methanol, acetonitrile and propylene carbonate by the potentiometric method. In two of the diaza crown ethers, AA-diaza-15 and AA-diaza-18-crown, two nitrogens in the macrocyclic ring replaced two consecutive oxygens instead of two opposite ones in the two other diaza crown ethers. It was found that complexes of 1:1 and 1:2 metal-to-ligand stoichiometry were formed. The solvent composition and cavity size of crown ethers significantly influences the stability constants of complexes. AA-diaza-15 and AA-diaza-18-crown ethers were examined for comparison with diaza-15-crown and diaza-18-crown ethers. AA-diaza crown ethers formed less stable 1:1 metal-to-ligand complexes with silver(I) than typical diaza crown ethers but their ability to form 1:2 metal-to-ligand complexes was stronger. The energetically most favorable structures of the 1:1 metal-to-ligand complexes were calculated and visualized by the AM1d method at the semiempirical level of theory.

Spectrophotometric and AM1d studies of the equilibria between oxidovanadium(IV) and four isomers of n-propyl-3-azido-2,3-dideoxy-d-hexopyranosides in aqueous solution

Abstract Complex formation and stability constants for complexes between isomers of n-propyl-3-azido-2,3-dideoxy-d-hexopyranosides and oxidovanadium(IV) were determined in aqueous solution by the spectrophotometric method. Complexes of 1 : 2 metal-to-ligand stoichiometry were formed. The impact of the structures of the ligands on the complex formation was discussed. The energetically most favorable structures of the complexes were calculated and visualized by the AM1d method at the semi-empirical level of theory.