Synthesis, crystal and solution structures and antimicrobial screening of palladium(II) complexes with 2-(phenylselanylmethyl)oxolane and 2-(phenylselanylmethyl)oxane as ligands

Organoselenium transition metal complexes as promising candidates in medicine area

The medicinal properties of transition metal complexes are greatly influenced by the nature and physico-chemical features of the ligand present in the complex structure. Due to the unique biological properties of the organoselenium compounds reflected in the variety of pharmacological activities (such as antioxidative, antiviral, antimicrobial and anticancer), the last years have brought increased interest for their use as a ligands compounds in the design and syntheses of range of transition metal-based coordination compounds that have been explored as antitumor and antimicrobial agents. Our aim in this review is to provide the overview of an recent development of the transition metal complexes bearing organoselenium ligands in the structure that could be promising choice for the treatment of various diseases, particularly cancer and infective diseases. For this purpose, the complexes of Co, Ni, Cu, Zn, Ru, Pd, Pt, Au and Sn as the most explored examples will be included and discussed.

Solvents and Ligands Matter: Structurally Variable Palladium and Nickel Clusters Assembled by Tridentate Selenium- and Tellurium-Containing Schiff Bases

Structurally variable organochalcogen clusters containing palladium(II) and nickel(II) ions were assembled starting from the salicylidene-substituted dichalcogenides (Y-C₆H₄-N═CH-C₆H₄-OH)₂ ({HL^Y}₂, where Y = Se or Te), and palladium or nickel acetate. The tetrameric palladium clusters contain reduced chalcogenolato ligands {Y-C₆H₄-N═CH-C₆H₄-O)}^2- ({L'^Y}^2-, where Y = Se or Te), while the initially formed trimeric nickel clusters contain the intact, coordinated dichalcogenides. The palladium clusters have a general formula of [Pd₄(L'^Y)₄] and represent the first examples of palladium complexes where both a gyrobifastigial and a pseudocubane arrangement of the central Pd₄Y₄ unit could be established with the same ligand, only depending on the solvents used for crystallization. Reduced density gradient (RDG) considerations based on density functional theory calculations suggest that the commonly referred to stabilizing chalcogen-palladium or palladium-palladium interactions for the two geometric arrangements are weak van der Waals contacts resulting from the contact of two nonbinding lone pairs. In the case of the pseudocubane arrangement, a repulsive steric effect, which is indicated by RDG analysis, is clearly supported by the cuplike distortions detected in the solid-state structure of the compound. In contrast to the reactions with palladium acetate, where the dichalcogenides were cleaved, during similar reactions with nickel acetate, the dichalcogenides remained intact and trimeric clusters of the composition [Ni-μ²-κ²-(Ni{κ⁵-L^Y}₂)₂-μ²-(OAc)₂] (Y = Se, Te) were formed. Air oxidation and hydrolysis of [Ni-μ²-κ²-(Ni{κ⁵-L^Te}₂)₂-μ²-(OAc)₂] gave a rare example of a hexanuclear nickel cluster of the composition [Ni₂-κ⁵-(Ni₄-κ⁶-μ⁶-{(L'^Te₂O₃)(L'^TeO₂)₂}₂)-μ²-(H₂O)₂], which is composed of a well-defined framework consisting of tellurinic anhydride and tellurinate units, which proves the comparably higher oxidation sensitivity of the trinickel dichalcogenide complexes. Electron spray ionization mass spectrometry spectra of both the palladium and nickel clusters indicate that they show fluctional behavior with varying nuclearity in solution and can adopt multiple charge states especially because of the noninnocence of the chalcogen-based ligands. The complexes were fully characterized by spectroscopic methods, elemental analyses, and X-ray diffraction.

Newly synthesized palladium(II) complexes with aminothiazole derivatives: in vitro study of antimicrobial activity and antitumor activity on the human prostate cancer cell line

Five new complexes of the palladium(II) ion (C1-C5) having the general formula [(PdL₂)]Cl₂ with some 2-aminothiazoles (L1-L5), where L1 = 2-amino-4-(3,4-difluorophenyl)thiazole, L2 = 2-amino-5-methyl-4-phenylthiazole, L3 = 2-amino-4-phenylthiazole, L4 = 2-amino-4-(4-chlorophenyl)thiazole, and L5 = 2-amino-4-(2,4-difluorophenyl)thiazole, have been synthesized and characterized by elemental microanalysis and infrared, ¹H NMR and ¹³C NMR spectroscopy. The in vitro antimicrobial activity of the five ligands and the corresponding Pd(II) complexes is investigated. Testing is performed by the microdilution method and the minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) have been determined. Testing is conducted against 11 microorganisms (nine strains of pathogenic bacteria and two yeast species). The tested ligands and palladium(II) complexes show selective, high and moderate activity. There is a difference in antimicrobial activity between the ligands and the corresponding palladium(II) complexes. The complexes have significant anti-staphylococcal activity and activity on Pseudomonas aeruginosa which is better than the positive control. The interactions of newly synthesized palladium(II) complexes with calf thymus DNA (CT-DNA) were investigated using UV-Vis absorption and fluorescence spectroscopy. Analysis of UV-absorption and fluorescence spectra indicates the formation of a complex between the palladium(II) complexes and DNA. The high values of intrinsic binding constants, K_b, of the order 10⁴ M^-1 and Stern-Volmer quenching constants, K_SV, of the order 10⁵ M^-1 indicated very good binding of all complexes to CT-DNA. Also, the new Pd(II) complexes show high cytotoxic activity towards the human prostate cancer cell line and insignificant activity towards non-cancerous human fibroblasts. Future research could additionally explore the biological activity of Pd(II) complexes presented in this paper and investigate the possibility of their implementation in clinical practice.

Nuclearity growth of new PdII complexes induced by the electronic effect of selenium-containing ligands

This work provides a systematic study of how the electronic effect of EDG or EWG in selenium-containing ligands influences the nuclearity of PdII complexes. The solid-state, solution and gas phase behaviors were evaluated for the complexes.

Recent Studies on the Antimicrobial Activity of Transition Metal Complexes of Groups 6–12

Antimicrobial resistance is an increasingly serious threat to global public health that requires innovative solutions to counteract new resistance mechanisms emerging and spreading globally in infectious pathogens. Classic organic antibiotics are rapidly exhausting the structural variations available for an effective antimicrobial drug and new compounds emerging from the industrial pharmaceutical pipeline will likely have a short-term and limited impact before the pathogens can adapt. Inorganic and organometallic complexes offer the opportunity to discover and develop new active antimicrobial agents by exploiting their wide range of three-dimensional geometries and virtually infinite design possibilities that can affect their substitution kinetics, charge, lipophilicity, biological targets and modes of action. This review describes recent studies on the antimicrobial activity of transition metal complexes of groups 6–12. It focuses on the effectiveness of the metal complexes in relation to the rich structural chemical variations of the same. The aim is to provide a short vade mecum for the readers interested in the subject that can complement other reviews.