SÍNTESE, CARACTERIZAÇÃO E ESTUDO FOTOFÍSICO DE DOIS NOVOS COMPLEXOS DE OURO (I) COM PROMISSORA ATIVIDADE BIOLÓGICA FRENTE A BACTÉRIAS RESISTENTES E CÉLULAS TUMORAIS

Abstract

Pyrazoline ligands, as well as their substituted derivatives, has been widely studied due to their photophysical and biological properties. Recent publication, carried out by our research group, shows that the ligand studied has a luminescent property when excited in 300 nm in solution and when complexed with an AgI metallic center, this property was intensified. Gold complexes, may have biological activities such as anti-tumor, antibacterial and anti-biofilm action for Staphylococcus aureus. This study shows the synthesis, characterization and antibacterial, cytotoxic and luminescent assays of two AuI complexes. The new complexes [Au(L1)Cl]∙1/2 DMF (1a) and [Au(L2)Cl] (2) have two synthesis routes, obtaining colorless crystals by slow evaporation of the solvent, or powder, by precipitation, being that, in the powder form, the compound (1a) does not have the dimethylformamide molecule as solvate, assuming the formula [Au(L1)Cl] (1b) (L1 = 5- (4-methoxyphenyl)-3-phenyl-1-thiocarbamoyl4,5-dihydro-1H-pyrazole; L2 = 3,5-diphenyl-1-thiocarbamoyl-4,5-dihydro-1H-pyrazole). The crystals are of great interest because it allows the characterization by X-ray diffractometry in monocrystal. The ligand of each of the respective complexes was coordinated to the metal center of AuI through the sulfur atom of the thiocarbamoyl group in a monodentate manner. A chlorine atom, from the precursor [THTAuCl] (THT = tetrahydrothiophene), complements the coordination site of the AuI atom. The analysis of the connection angles for the complex (1a) S(1)-Au(1)-Cl(1) of 174,29(3)º and S(2)-Au(2)-Cl(2) of 172,73(3)º and for the complex (2) S(1)-Au(1)-Cl(1) of 172,10(8)º demonstrates an approximately linear geometry for the prepared compounds. Spectroscopic analyzes showed that the complexes were luminescent when excited in the 300 nm. The evaluation of the electronic molecular absorption spectra in the solid state and in solution for the ligands shows two absorption bands, at the wavelengths of 240 and 325 nm, these bands are attributed to the electronic transitions π → π*, n → π*, respectively. When complexed, there is a slight hypochromic effect (decrease in the intensity of the absorption band). TD-DFT (Time Dependent Density Functional Theory) calculations support the assignments of the two absorption bands in the complex (2), the band at 324 nm refers to the transfer of charge from the metal, chloride and sulfur to the pyrazoline ligand (M + X + S)LCT, and the band between 246-236 nm is attributed to the transfer of charge from the chloride to the pyrazolinic ligand and between the pyrazolinic ligand LLCT + IL. Antibacterial tests showed that both compound (1b) and compound (2) are bactericidal or bacteriostatic for Gram-positive strains: S. aureus standard, S. aureus resistant to various types of antibiotics and S. intermedius, and (2) is bacteriostatic for 3 Gram-negative strains. Cytotoxic evaluations demonstrate that complexes are more active than their respective ligands, showing that complexation increases antitumor activity. The complete characterization of the synthesized complexes involved, in addition to X-ray diffraction, vibrational spectroscopy in the infrared region and 1H and 13C nuclear magnetic resonance. In view of the data in the literature, these new complexes are promising within the theme of bioinorganic and luminescent chemistry.