Synthetic conditions were evaluated to intercalate norbixin into layered double hydroxides (LDH). Norbixin was isolated from a hydrosoluble commercial annatto extract. LDH samples comprising M2+/Al3+ (M = Mg, Zn) were synthesized by coprecipitation and characterized by X-ray diffraction, thermal analysis coupled to mass spectrometry, vibrational spectroscopies, and solid-state 13C nuclear magnetic resonance. Radical scavenging activity of LDH hybrids was monitored by electron paramagnetic resonance towards the stable radical DPPH (1,1-diphenyl-2-picrylhydrazyl). LDH hosts presented more than 50 wt.% of norbixin and d-spacing (003) values of about 2.5 or 3.0 nm depending of the cation LDH composition. Vibrational spectra assignment (supported by density functional theory calculations) confirmed the chemical integrity of norbixin after intercalation into LDH. The inorganic layers were found to enhance the thermal stability of norbixin upon intercalation. The free radical scavenging capacity of norbixin was retained when immobilized into LDH. Considering that zinc and magnesium-LDH matrices are biocompatible and that norbixin presents biological activity, the hybrid materials appear as promising systems for biomedical assessment.

Herein, the immobilization of some Schiff base-copper(II) complexes in smectite clays is described as a strategy for the heterogenization of homogeneous catalysts. The obtained materials were characterized by spectroscopic techniques, mostly UV/Vis, EPR, XANES and luminescence spectroscopy. SWy-2 and synthetic Laponite clays were used for the immobilization of two different complexes that have previously shown catalytic activity in the dismutation of superoxide radicals, and disproportionation of hydrogen peroxide. The obtained results indicated the occurrence of an intriguing intramolecular redox process involving copper and the imine ligand at the surface of the clays. These studies are supported by computational calculations.

Interações de alguns compostos di-imínicos de cobre(II) com albumina de soro bovino (BSA) foram investigadas por técnicas espectroscópicas, visando comparar a estabilidade dos complexos e verificar a sua capacidade de causar danos oxidativos à proteína. Os ligantes imínicos tri- e tetradentados utilizados neste trabalho contêm grupamentos piridina, pirazina ou imidazol, frequentemente encontrados no meio biológico. A estabilidade termodinâmica relativa de cada um dos complexos foi determinada através de dicroísmo circular (CD), usando a própria BSA como ligante competitivo. Os valores estimados das constantes de equilíbrio aparentes foram muito semelhantes entre si e ao da espécie Cu(BSA), para a qual log K Cu(BSA) = 12.9 já foi relatado na literatura, mostrando que os complexos estudados são bastante estáveis em condições fisiológicas. Dois diferentes sítios de coordenação do íon cobre foram verificados nestes estudos, evidenciados por medidas espectroscópicas (UV-Vis, CD e EPR), dependendo do ligante e da proporção estequiométrica [CuL]/[BSA] utilizada. Entretanto, a inserção do íon cobre em qualquer dos sítios ligantes ocasionou danos oxidativos significativos à proteína, especialmente em presença de peróxido de hidrogênio, indicando um processo oxidativo com formação de espécies reativas de oxigênio (EROs). Um tripeptídeo amidado, Asp-Thr-His-NH2, mimético do sítio N-terminal da BSA, foi sintetizado e a investigação de sua interação com os complexos de cobre permitiu uma compreensão melhor do sistema cobre-BSA. Cálculos de estrutura eletrônica empregando a teoria do funcional de densidade (DFT) foram efetuados para determinar as energias de ligação do cobre em cada complexo e no sítio N-terminal da proteína, buscando correlacioná-las com os dados de estabilidade termodinâmica.

Interactions of some diimine copper(II) complexes with bovine serum albumin (BSA) were investigated by spectroscopic techniques in order to compare the stability of the complexes and their capability of causing oxidative damage to the protein. The tri- and tetradentate imine ligands employed in this work contain pyridine, pyrazine or imidazole moieties, which are ubiquitous in biological systems. The relative thermodynamic stabilities of the copper(II) complexes were estimated by circular dichroism (CD) using BSA as the competitive ligand. The apparent stability constants determined for the complexes are very similar to one another and to that of the Cu(BSA) complex itself, for which log K Cu(BSA) = 12.9 has already been described in the literature, indicating that the complexes are quite stable under physiological conditions. Two different copper binding sites were evidenced on BSA by spectroscopic measurements (CD, UV-Vis and EPR), depending on the ligand and on the [CuL]:[protein] stoichiometric ratio. Metal binding to any of the sites gives rise to significant protein oxidative damage, especially in the presence of hydrogen peroxide, indicating an oxidative process based on reactive oxygen species (ROS). A small amidated peptide, Asp-Thr-His-NH2, corresponding to the N-terminal region of BSA was synthesized, and its interaction with all the diimine-copper(II) complexes was also investigated in order to clarify the copper imine complex-albumin interactions. Electronic structure calculations at the density functional theory (DFT) level were made to compare the copper-ligand binding energies for each complex with that of the metal coordinated at the N-terminal site of the protein.