Synthesis, structure and spectroscopic properties of cobalt(III) complexes with 1-benzoyl-(3,3-disubstituted)thiourea

Potentiometric Studies on Binary and Ternary Complexes of Ni(II) and Cu(II) Ions with L-Valine and Paracetamol

The protonation constants of the free ligands and the stability constants of binary and ternary complexes of bivalent metal ions of Ni(II) and Cu(II) with a biologically important amino acid of L-valine, Val, and paracetamol, Para, were studied potentiometrically in aqueous solutions at 313.15 ± 0.1 K and a fixed ionic strength of I = 0.10 M NaCl. The complexation model for each system was established using the Irving-Rossotti equation. The formation of the 1:2 or 1:1 binary complexes and 1:1:1 ternary complexes in which the amino acid Val was used as the primary ligand and Para as the secondary ligand, as inferred from the corresponding potentiometric pH-metric titration curves, and their relative stabilities compared to the corresponding ML and ML2 binary complexes are expressed in terms of statistical parameters ∆logK, logK1 and logK2. The complex stability was found to follow the order of Cu(II) > Ni(II). Through these diagnostic studies, it was possible to give the general formula of compounds prepared from amino acids and paracetamol. Amino acid binds to the central ion through oxygen in the hydroxyl group and nitrogen atom in the amine group (-NH2), whereas paracetamol forms a unipolar bond by binding to the concentrated ion through the oxygen atom in the hydroxyl group. Most of the nickel complexes had octahedral symmetry with valine and paracetamol ligands, while the copper complexes had square or hierarchical to square base symmetry.

Cobalt(III) Metallacryptates and Their Guest Cation-Exchange in Solution Monitored by 59Co NMR

One-pot reactions of the catechol-scaffolding aroylbis(N,N-diethylthiourea) H₂L^cat with mixtures of CoCl₂ and MCl (M⁺ = Cs⁺, Rb⁺, K⁺, Tl⁺, or NH₄⁺) or with a Co(NO₃)₂/TlNO₃ mixture lead to the self-assembly of a series of cationic Co(III) metallacryptates of the general formula [M ⊂ {Co₂(L^cat)₃}]⁺ (M⁺ = Cs⁺, Rb⁺, K⁺, Tl⁺, or NH₄⁺). Crystalline PF₆^- salts were obtained after workup with (n-Bu₄N)(PF₆), and the single-crystal structures of all five metallacryptates have been determined. Depending on the nature of the guest cations, the directional interactions between guest cations and the metallacryptand {Co₂(L^cat)₃} are either weak coordination contacts or hydrogen bonds. The bonding mode and the size of the guest ions slightly influence the molecular skeleton of the host molecule. These small structural variations also exist in solution and could be detected by means of ⁵⁹Co NMR spectroscopy, which is shown to be a unique tool for an easy characterization of such compounds. ⁵⁹Co NMR chemical shifts are extraordinarily sensitive to the guest cation in the metallacryptates, and time-arrayed ⁵⁹Co NMR experiments show that cation-exchange processes in biphasic organic/aqueous systems can be studied in detail. This leads to insights into the relative rates of cation exchange, as well as the relative conditional distribution coefficients of such Co(III) metallacryptates between the aqueous and organic phases. Thus, the extent and the relative rate of the NH₄⁺ ion exchange in [NH₄ ⊂ {Co₂(L^cat)₃}](PF₆) by Cs⁺ and K⁺ ions across the organic/aqueous phase boundary at room temperature have been studied by in situ ⁵⁹Co NMR experiments. Preliminary ⁵⁹Co NMR experiments show that the K⁺ ion in [K ⊂ {Co₂(L^cat)₃}](PF₆) can be removed by its competitive complexation with the highly potassium-selective [2.2.2]cryptand, to give a transient ⁵⁹Co NMR signal of the relatively unstable "empty" {Co₂(L^cat)₃} complex, which slowly decomposes in solution.

Experimental and computational studies on ruthenium(ii) bis-diimine complexes of N,N′-chelate ligands: the origin of changes in absorption spectra upon oxidation and reduction

The first report seeking to determine the origin of the observed spectral changes by investigating the frontier MOs and electronic structures of the ligands.

Synthesis, characterization and biological studies of a cobalt(III) complex of sulfathiazole

The emergence of old and new antibiotic resistance created in the last decades revealed a substantial medical need for new classes of antimicrobial agents. The antimicrobial activity of sulfa drugs is often enhanced by complexation with metal ions, which is in concordance with the well-known importance of metal ions in biological systems. Besides, sulfonamides and its derivatives constitute an important class of drugs, with several types of pharmacological agents possessing antibacterial, anti-carbonic anhydrase, diuretic, hypoglycemic, antithyroid, antiviral and anticancer activities, among others. The purpose of this work has been the obtainment, characterization and determination of biological properties (antibacterial, antifungal, mutagenicity and phytotoxicity) of a new Co(III)-sulfathiazole complex: Costz, besides of its interaction with bovine serum albumin (BSA). The reaction between sodium sulfathiazole (Nastz) and cobalt(II) chloride in the presence of H₂O₂ leads to a brown solid, [Co^III(stz)₂OH(H₂O)₃], (Costz). The structure of this compound has been examined by means of elemental analyses, FT-IR, ¹H NMR, UV-Visible spectrometric methods and thermal studies. The Co(III) ion, which exhibits a distorted octahedral environment, could coordinate with the N thiazolic atom of sulfathiazolate. The complex quenched partially the native fluorescence of bovine serum albumin (BSA), suggesting a specific interaction with the protein. The Costz complex showed, in vitro, a moderate antifungal activity against Aspergillus fumigatus and A. flavus. As antibacterial, Costz displayed, in vitro, enhanced activity respective to the ligand against Pseudomonas aeruginosa. Costz did not show mutagenic properties with the Ames test. In the Allium cepa test the complex showed cytotoxic properties but not genotoxic ones. These results may be auspicious, however, further biological studies are needed to consider the complex Costz as a possible drug in the future.

Crystal structure of 4-meth-oxy-N-(piperidine-1-carbono-thio-yl)benzamide

In the title compound, C14H18N2O2S, the piperidine ring has a chair conformation. Its mean plane is twisted with respect to the 4-meth-oxy-benzoyl ring, with a dihedral angle of 63.0 (3)°. The central N-C(=S)-N(H)-C(=O) bridge is twisted with an N-C-N-C torsion angle of 74.8 (6)°. In the crystal, mol-ecules are linked by N-H⋯O and C-H⋯O hydrogen bonds, forming chains along the c-axis direction. Adjacent chains are linked by C-H⋯π inter-actions, forming layers parallel to the ac plane. The layers are linked by offset π-π inter-actions [inter-centroid distance = 3.927 (3) Å], forming a supra-molecular three-dimensional structure.

Crystal structure of 4-meth-oxy-N-[(pyrrolidin-1-yl)carbo-thio-yl]benzamide

In the title compound, C₁₃H₁₆N₂O₂S, the pyrrolidine ring has a twisted conformation on the central –CH₂–CH₂– bond. Its mean plane is inclined to the 4-meth­oxy­benzoyl ring by 72.79 (15)°. In the crystal, mol­ecules are linked by N—H⋯O and C—H⋯O hydrogen bonds to the same O-atom acceptor, forming chains along [001]. The chains are linked via slipped parallel π–π inter­actions [inter-centroid distance = 3.7578 (13) Å], forming undulating slabs parallel to (100).