Synthesis, characterization, electrical conductivity and luminescence properties of two copper(II) complexes with tridentate N 2 O chelating ligands containing imine bond

Enantiomeric pairs of copper(II) complexes with tridentate Schiff bases derived from R- and S-methionine: the role of decorating organic groups of the ligand in crystal packing and biological activity

Three enantiomeric pairs consisting of copper(II) complexes with tridentate Schiff bases have been synthesized for employing in biological assessments: 1∞[Cu₂(R/S-salmet)₂(H₂O)] (1-R/S·H2O), 1∞[Cu(R/S-3-HOMe-5-Me-salmet)] (2-R/S), and 1∞[Cu(R/S-3-MeO-salmet)] (3-R/S) (where R/S-salmetH₂, R/S-3-HOMe-5-Me-salmetH₂, and R/S-3-MeO-salmetH₂ result from the condensation of R/S-methionine with salicylaldehyde, 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde, and 3-methoxy-salicylaldehyde, respectively, in a 1 : 1 molar ratio). The crystal structures of 1-R·H2O and 2-R/S are reported. Moreover, the 1-R/S·H2O enantiomers have been subjected to a single-crystal-to-single-crystal (SC-SC) transformation by heating at 160 °C to afford their dehydrated forms, 1∞[Cu₂(R/S-salmet)₂] (1-R/S), whose structures have also been crystallographically determined. The coordination polyhedra of the metal centers, the binding modes of the ligands, and the 1-D double chain assemblies generated by the chiral mononuclear units are comparatively described. The diffuse reflectance UV-Vis and circular dichroism (CD) spectra of compounds 1-R/S·H2O, 1-R/S, and 2-R/S are analysed with respect to their structural peculiarities and compared to those of 3-R/S. The UV-Vis and CD spectra of solutions of 1-R/S, 2-R/S, and 3-R/S point to the collapse of the double chains via dissolution. Biological tests performed on the model eukaryote Saccharomyces cerevisiae indicated low toxicity for 1-R/S, 2-R/S, and 3-R, and moderate toxicity for 3-S. The S-type complexes were accumulated by cells in higher quantity compared to their R-type counterparts due to selective transport via the high-affinity S-methionine transporter, Mup1. A chemogenomic analysis of 3-S toxicity performed on a collection of yeast knockout mutants revealed that most of the deleted genes identified in the screen were involved in the cell response to oxidative stress, calcium-mediated response, or metal homeostasis. Altogether, it was concluded that 3-S accumulation may perturb the redox state of the cell, also interfering with the calcium-mediated response to oxidative stress or metal-related oxidative stress.

Differential Immunomodulatory Activities of Schiff Base Complexes Depending on their Metal Conjugation

Immunomodulatory compounds have become crucial with advances in immunotherapy. Using our own immune system cells, we can direct the immune cell function and develop desired response against a certain threat. Immunotherapy applications have been suggested against tumors, autoimmune disorders, and infectious diseases. Vaccination can be considered as one of the best known example of immunotherapy. Infectious agent's signature molecular structures are introduced to the immune cells together with the adjuvants that further activate the immune cells to mount a proper immune response and memory. Immunotherapy and vaccine formulations are in constant need of a library of immunomodulatory reagents that can be applied depending on the target. In order to expand the number of immunomodulatory reagents that can find medicinal applications, our group has been testing unique chemical structures on the immune system cells, especially macrophages. Schiff base complexes are known for their anti-inflammatory and antimicrobial activities. In this study, we used previously characterized Schiff base complexes with different metal conjugations. These molecules had differential immunostimulatory and immunomodulatory potentials on macrophages in vitro depending on the type of the conjugated metal. After light exposure, these complexes changed their characteristics and became powerful anti-inflammatory complexes. Due to their possible antimicrobial potentials, we also tested their activities against gram negative and gram positive bacteria. All of the complexes exerted antimicrobial activities which were not light responsive. Here, we present Schiff base complexes with differential immunostimulatory and immunomodulatory activities that can also efficiently eliminate gram positive and gram negative bacteria. Upon photo activation, they block the production of inflammatory TNFα cytokine. Therefore, together with the light, they can be used to treat bacterial infections associated with damaging inflammation. Graphical Abstract.

Novel Copper Bearing Schiff Bases with Photodynamic Anti-Inflammatory and Anti-Microbial Activities

Schiff bases and their copper complexes have been previously studied for their anti-inflammatory, anti-tumor as well as anti-microbial activities. Schiff bases can be derivatized to gain photoluminiscence capacity. This property of the schiff bases enables the transfer of the electrons upon absorption of the light at a specific wavelength. In this study, we exploited this attribute of novel copper bearing schiff bases and tested their photodynamic biological activities. These compounds exerted photodynamic anti-inflammatory activities on the in vitro activated mammalian macrophages. Compared with salicylic acid control groups, these novel schiff bases had stronger activity which became more prominent with photo-induction. Moreover, they also had anti-microbial activity on gram negative bacteria E.coli and gram positive bacteria S.aureus.This anti-microbial activity was stronger than that of Neomycin on both bacterial strains. Our results suggest their potential use as anti-inflammatory and anti-microbial agents both in the dark as well as after photo-induction.

The crystal and molecular structures of three copper-containing complexes and their activities in mimicking galactose oxidase

The structures of three copper-containing complexes, namely (benzoato-κ²O,O')[(E)-2-({[2-(diethylamino)ethyl]imino}methyl)phenolato-κ³N,N',O]copper(II) dihydrate, [Cu(C₇H₅O₂)(C₁₃H₁₉N₂O)]·2H₂O, 1, [(E)-2-({[2-(diethylamino)ethyl]imino}methyl)phenolato-κ³N,N',O](2-phenylacetato-κ²O,O')copper(II), [Cu(C₈H₇O₂)(C₁₃H₁₉N₂O)], 2, and bis[μ-(E)-2-({[3-(diethylamino)propyl]imino}methyl)phenolato]-κ⁴N,N',O:O;κ⁴O:N,N',O-(μ-2-methylbenzoato-κ²O:O')copper(II) perchlorate, [Cu₂(C₈H₇O₂)(C₁₂H₁₇N₂O)₂]ClO₄, 3, have been reported and all have been tested for their activity in the oxidation of D-galactose. The results suggest that, unlike the enzyme galactose oxidase, due to the precipitation of Cu₂O, this reaction is not catalytic as would have been expected. The structures of 1 and 2 are monomeric, while 3 consists of a dimeric cation and a perchlorate anion [which is disordered over two orientations, with occupancies of 0.64 (4) and 0.36 (4)]. In all three structures, the central Cu atom is five-coordinated in a distorted square-pyramidal arrangment (τ parameter of 0.0932 for 1, 0.0888 for 2, and 0.142 and 0.248 for the two Cu centers in 3). In each species, the environment about the Cu atom is such that the vacant sixth position is open, with very little steric crowding.