Titanium(IV) complexes of disulfide-linked Schiff bases

The Synthesis and Biological Activity of Organotin Complexes with Thio-Schiff Bases Bearing Phenol Fragments

A number of novel di- and triorganotin(IV) complexes 1-5 (Ph₂SnL¹, Ph₂SnL², Et₂SnL², Ph₃SnL³, Ph₃SnL⁴) with mono- or dianionic forms of thio-Schiff bases containing antioxidant sterically hindered phenol or catechol fragments were synthesized. Compounds 1-5 were characterized by ¹H, ¹³C NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes 1 and 2 in the crystal state were established by single-crystal X-ray analysis. The antioxidant activity of new complexes as radical scavengers was estimated in DPPH and ABTS assays. It was found that compounds 4 and 5 with free phenol or catechol fragments are more active in these tests than complexes 1-3 with tridentate O,N,S-coordinated ligands. The effect of compounds 1-5 on the promoted oxidative damage of the DNA by 2,2'-azobis(2-amidinopropane) dihydrochloride and in the process of rat liver (Wistar) homogenate lipid peroxidation in vitro was determined. Complexes 4 and 5 were characterized by more pronounced antioxidant activity in the reaction of lipid peroxidation in vitro than compounds 1-3. The antiproliferative activity of compounds 1-5 was investigated against MCF-7, HTC-116, and A-549 cell lines by an MTT test. The values of IC₅₀ are significantly affected by the presence of free antioxidant fragments and the coordination site for binding.

Different Schiff Bases-Structure, Importance and Classification

Schiff bases are a vast group of compounds characterized by the presence of a double bond linking carbon and nitrogen atoms, the versatility of which is generated in the many ways to combine a variety of alkyl or aryl substituents. Compounds of this type are both found in nature and synthesized in the laboratory. For years, Schiff bases have been greatly inspiring to many chemists and biochemists. In this article, we attempt to present a new take on this group of compounds, underlining of the importance of various types of Schiff bases. Among the different types of compounds that can be classified as Schiff bases, we chose hydrazides, dihydrazides, hydrazones and mixed derivatives such as hydrazide-hydrazones. For these compounds, we presented the elements of their structure that allow them to be classified as Schiff bases. While hydrazones are typical examples of Schiff bases, including hydrazides among them may be surprising for some. In their case, this is possible due to the amide-iminol tautomerism. The carbon-nitrogen double bond present in the iminol tautomer is a typical element found in Schiff bases. In addition to the characteristics of the structure of these selected derivatives, and sometimes their classification, we presented selected literature items which, in our opinion, represent their importance in various fields well.

An experimental and DFT study of a disulfide-linked Schiff base: synthesis, characterization and crystal structure of bis (3-methoxy-salicylidene-2-aminophenyl) disulfide in its anhydrous and monohydrate forms

A detailed structural and spectroscopic study of the disulfide Schiff base obtained from condensation of 2-aminothiophenol and o-vanillin is reported. It includes the analyses of the anhydrous and monohydrate forms of the title compound. Structures of both solids were resolved by X-ray diffraction methods. A comparison between experimental and theoretical results is presented. The conformational space was searched and geometries were optimized both in gas phase and including solvent effects. Vibrational (IR and Raman) and electronic spectra were measured and assigned with the help of computational methods based on the Density Functional Theory. Calculated MEP-derived atomic charges were calculated to predict coordination sites for metal complexes formation.

Dioximate- and Bis(salicylaldiminate)-Bridged Titanium and Zirconium Alkoxides: Structure Elucidation by Mass Spectrometry

The treatment of titanium alkoxides with 1,5-pentanedioxime or 2,5-hexanedioxime resulted in the formation of complexes [{TiL(OR)₂}₂] in which the dioximate ligands (L) bridge a dimeric Ti₂(μ₂-OR)₂ unit. The structures of the complexes were determined by single-crystal structure analysis, ESI mass spectrometry, and 1D and 2D solution NMR spectroscopy. In contrast, the treatment of titanium alkoxides with dioximes bearing cyclic linkers, such as cyclohexyl or aryl groups, resulted in insoluble polymeric compounds. The treatment of various bis(salicylaldiminates) with titanium and zirconium alkoxides resulted in compounds with the same composition [{TiL(OR)₂}₂], in which, however, two monomeric Ti(OR)₂ units are bridged by the ligands L. The two structural possibilities can be distinguished by low-energy collision-induced dissociation owing to their different fragmentation patterns.