Cellular Effects of Cationic Copper(II) Schiff Base Complexes: Anti-Inflammatory and Antiproliferative Properties.

A series of potassium isothiocyanato-(N-salicylidene-aminoacidato) cuprates (1-5) with the general formula of the monomeric unit K[Cu(sal-aa)(NCS)] ⋅ xH2O (x=0 or 2), containing a Schiff-base ligand (H2sal-aa) derived from natural amino acids such as glycine, DL-α-alanine, DL-valine, DL-phenylalanine and ß-alanine, and salicylaldehyde, was screened for in vitro antiradical and major cellular effects against selected cancerous and normal cells. The complexes exhibited strong antioxidant properties against superoxide in vitro and a protective effect on DNA under Fenton-like reaction conditions. Screening of their cellular effects revealed moderate in vitro cytotoxicity against human cancer cell lines (A2780, A2780R and MCF-7), with IC50 values of 25-35 µM, and relatively low toxicity to normal fibroblast MRC-5 cells (with IC50 values>50 µM). Additional experiments performed on A2780 cells revealed that the most potent complex 5 significantly increased the number of A2780 cells arrested in the G2/M phase of the cell cycle and triggered intracellular oxidative stress. The selected flow cytometry experiments (detection of apoptosis/autophagy and activation of caspases 3/7 and depletion of mitochondrial membrane potential) did not reveal the dominant mechanism underlying the cytotoxicity of the complexes but clearly differentiated their molecular effects from those of the reference drug cisplatin. All the complexes exerted anti-inflammatory effects by modulating the levels of the proinflammatory cytokines TNF-α and IL-1ß in LPS-activated THP-1 macrophage-like cells. Complex 5 also slightly influenced the activity of the upstream NF-κB transcription factor, while no effect on PPARγ activation was detected.

Efficient two-step excitation energy transfer in artificial light-harvesting antenna based on bacteriochlorophyll aggregates.

Chlorosomes of green photosynthetic bacteria are large light-harvesting complexes enabling these organisms to survive at extremely low-light conditions. Bacteriochlorophylls found in chlorosomes self-organize and are ideal candidates for use in biomimetic light-harvesting in artificial photosynthesis and other applications for solar energy utilization. Here we report on the construction and characterization of an artificial antenna consisting of bacteriochlorophyll c co-aggregated with ß-carotene, which is used to extend the light-harvesting spectral range, and bacteriochlorophyll a, which acts as a final acceptor for excitation energy. Efficient energy transfer between all three components was observed by means of fluorescence spectroscopy. The efficiency varies with the ß-carotene content, which increases the average distance between the donor and acceptor in both energy transfer steps. The efficiency ranges from 89 to 37% for the transfer from ß-carotene to bacteriochlorophyll c, and from 93 to 69% for the bacteriochlorophyll c to bacteriochlorophyll a step. A significant part of this study was dedicated to a development of methods for determination of energy transfer efficiency. These methods may be applied also for study of chlorosomes and other pigment complexes.