Syntheses,crystal structures,and antibacterial activities of manganese(III), nickel(II), and copper(II) complexes containing a tetradentate Schiff base

Three new mononuclear Schiff-base complexes, namely [Mn(L)Cl] (1), [Ni(L)] (2), and [Cu(L)] (3), where L?=?anion of [N,N′-bis(2-hydroxybenzophenylidene)]propane-1,2-diamine, have been synthesized by reacting equimolar amounts of the respective metal chloride and the tetradentate Schiff base, H₂L, in methanol. The complexes have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction, and other physicochemical studies. Structural studies reveal that 1 adopts a distorted square-pyramidal geometry whereas 2 and 3 are isotypic with distorted square-planar geometries. The antibacterial activities of 1–3 along with their Schiff base have been tested against some Gram(+) and Gram(?) bacteria.     

Ruthenium(III) tetradentate Schiff-base complexes: spectral,catalytic, and its biocidal efficacy

New six-coordinate ruthenium(III) Schiff-base complexes of general formula [Ru(X)(PPh₃)(L)] (where X = Cl/Br and L = mononucleating bibasic tetradentate ligand derived by condensing actetoacetanilide/acetoacetotoludide with o-aminophenol/o-aminothiophenol/o-aminobenzoic acid in 1 : 2 molar ratio in ethanol) have been synthesized and characterized by physico-chemical and spectroscopic methods. The new ruthenium(III) complexes possess 2NO/2NS metal binding sites and are catalysts for the oxidation of alcohols using molecular oxygen as co-oxidant and in C–C coupling reactions. These complexes possess good biocidal (antibacterial and antifungal) activity.     

Synthesis and NMR Characterization of Cobalt(III) Complexes with 1,8-diamino-3,6-dithiaoctane, 2,2-Bipyridine,and 1,10-phenanthroline

The complexes [Co(eee)(bipy)]Cl₃ and [Co(eee)(phen)]Cl₃ (eee, 1,8-diamino-3,6-dithiaoctane) were synthesized and characterized by two-dimensional NMR spectroscopy. The presence of the bidentate aromatic ligands 2,2-bipyridine and 1,10-phenanthroline caused the ¹H resonances to be spread into a wider spectral width than previously observed for [Co(eee)(NO₂)₂]Cl and [Co(eee)Cl₂]Cl. Separate multiplets were observed for the four protons in the terminal ethylene linkage. It was possible to positively assign each multiplet and to determine the relative spatial orientations of the corresponding protons.     

Imidazole containing ligands for the modulation of physical properties of metal complexes upon (de)protonation

The synthetic route towards a novel tetradentate ligand bearing two amido and imidazole rings is reported. This ligand has been designed to study the relationship between the protonic state of the ligand through the imidazole moieties towards the electronic behaviour of metal complexes.     

A simple and efficient tetradentate Schiff base derived palladium complex for Suzuki–Miyaura reaction in water

A simple and efficient catalytic system based on Pd complex of tetradentate Schiff base ligands is found to be highly active (up to 99% isolated yield) for Suzuki–Miyaura reaction of aryl bromides with arylboronic acids in water at room temperature. Further the scope of this protocol has been extended to the Suzuki–Miyaura cross-coupling reaction of aryl chlorides with arylbronic acids in isopropanol.     

Complete investigation on the synthesis of [Ru(bpydip)Cl2]: the nonformation of cis isomer

Complexation between the Schiff base N₄-tetradentate N,N′-bis(7-methyl-2-pyridylmethylene)-1,3-diiminopropane (bpydip) and ion Ru(II) occurs only in trans geometry. However, it is known that the most complex of these ligands with ruthenium present predominantly cis geometry. In order to clarify the effects that drive the formation of the complex [Ru(bpydip)Cl₂], we performed a new experimental study of the reaction and a complete theoretical investigation of their transition states. The results showed that nonformation of the cis isomer could be explained by the difference in relative stability of the reaction products and the transition states proposed.     

Convenient synthesis of tridentate 2,6-di(pyrazol-1-yl)-4-carboxypyridine and tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′-bipyridine ligands

Citrazinic acid is used as a convenient starting material for both tridentate 2,6-di(pyrazol-1-yl)-pyridine and tetradentate 6,6′-di(pyrazol-1-yl)-2,2′-bipyridine ligands containing carboxylic groups useful for further anchoring of sensitizer on TiO₂ for dye-sensitized solar cells (DSCs). Using 2,6-dichloro-4-carboxypyridine, the synthesis of the terdentate ligands was improved compared to previously used 2,6-dibromo-4-carboxypyridine or 2,6-dichloro-4-ethylcarboxylate pyridine. Controlling the reaction conditions, it is possible to efficiently obtain the monosubstituted 2-chloro-6-pyrazol-1-yl-4-carboxypyridine, a key intermediate for the preparation of tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′-bipyridine ligand.     

Copper(II) complexes of N4 tetradentate ligands with flexible alkyl spacers: Crystal structure,DNA binding and cleavage studies

Mononuclear copper(II) complexes, [Cu L1] (ClO₄)₂ (1), [Cu L2] (ClO₄)₂ (2) and [Cu L3] (ClO₄)₂ (3) with quadridentate Schiff base ligands L1 (N,N′-bis-pyridin-2-ylmethyl-butane-1,4-diimine), L2 (N,N′-bis-pyridin-2-ylmethyl-pentane-1,5-diimine) and L3 (N,N′-bis-pyridin-2-ylmethyl-hexane-1,6-diimine) have been synthesized and characterized. The crystal structure data of 1 reveals the existence of the complex in two different geometries, namely a square pyramid and a distorted octahedron, which eventually leads to the packing of the molecule into helical and anti-parallel structures respectively. Absorption titration studies with calf thymus DNA for all three complexes are suggestive of groove binding with binding constant values for 1, 2 and 3 being 2.6 ± 0.2 × 10⁴ M⁻¹, 11.5 ± 0.2 × 10⁴ M⁻¹ and 1.83 ± 0.2 × 10⁴ M⁻¹ respectively. Control cleavage experiments using pBR 322 plasmid DNA and distamycin suggest minor groove binding for these complexes. In the presence of ascorbic acid, the complexes show efficient DNA cleavage, the order of efficiency being 1 > 2 ≅ 3.     

Hybrid Chelator-Based PSMA Radiopharmaceuticals: Translational Approach

(1) Background: Prostate-specific membrane antigen (PSMA) has been extensively studied in the last decade. It became a promising biological target in the diagnosis and therapy of PSMA-expressing cancer diseases. Although there are several radiolabeled PSMA inhibitors available, the search for new compounds with improved pharmacokinetic properties and simplified synthesis is still ongoing. In this study, we developed PSMA ligands with two different hybrid chelators and a modified linker. Both compounds have displayed a promising pharmacokinetic profile. (2) Methods: DATA^5m.SA.KuE and AAZTA⁵.SA.KuE were synthesized. DATA^5m.SA.KuE was labeled with gallium-68 and radiochemical yields of various amounts of precursor at different temperatures were determined. Complex stability in phosphate-buffered saline (PBS) and human serum (HS) was examined at 37 °C. Binding affinity and internalization ratio were determined in in vitro assays using PSMA-positive LNCaP cells. Tumor accumulation and biodistribution were evaluated in vivo and ex vivo using an LNCaP Balb/c nude mouse model. All experiments were conducted with PSMA-11 as reference. (3) Results: DATA^5m.SA.KuE was synthesized successfully. AAZTA⁵.SA.KuE was synthesized and labeled according to the literature. Radiolabeling of DATA^5m.SA.KuE with gallium-68 was performed in ammonium acetate buffer (1 M, pH 5.5). High radiochemical yields (>98%) were obtained with 5 nmol at 70 °C, 15 nmol at 50 °C, and 60 nmol (50 µg) at room temperature. [⁶⁸Ga]Ga-DATA^5m.SA.KuE was stable in human serum as well as in PBS after 120 min. PSMA binding affinities of AAZTA⁵.SA.KuE and DATA^5m.SA.KuE were in the nanomolar range. PSMA-specific internalization ratio was comparable to PSMA-11. In vivo and ex vivo studies of [¹⁷⁷Lu]Lu-AAZTA⁵.SA.KuE, [⁴⁴Sc]Sc-AAZTA⁵.SA.KuE and [⁶⁸Ga]Ga-DATA^5m.SA.KuE displayed specific accumulation in the tumor along with fast clearance and reduced off-target uptake. (4) Conclusions: Both KuE-conjugates showed promising properties especially in vivo allowing for translational theranostic use.     

Syntheses,characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL¹)₂](ClO₄)₂ (1) and [Ni(HL²)₂](ClO₄)₂ (2) and a square planar complex [Ni(HL³)]ClO₄ (3) have been prepared, where [HL¹ = 3-(2-amino-ethylimino)-butan-2-one oxime, HL² = 3-(2-amino-propylimino)butan-2-one oxime] and H₂L³ = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-butan-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography; complexes 1 and 2 are seen to be the mer isomers.