The interaction of half-sandwich (η5-Cp*)Rh(III) cation with histidine containing peptides and their ternary species with (N,N) bidentate ligands.

Our goal was to explore the possible interactions of the potential metallodrug (η5-Cp*)Rh(III) complexes with histidine containing biomolecules (peptides/proteins) in order to understand the most important thermodynamic factors influencing the biospeciation and biotransformation of (η5-Cp*)Rh(III) complexes. To this end, here we report systematic solution thermodynamic and solution structural study on the interaction of (η5-Cp*)Rh(III) cation with histidine containing peptides and their constituents ((N-methyl)imidazole, GGA-OH, GGH-OH, histidine-amide, HGG-OH, GHG-NH2), based on extensive 1H NMR, ESI-MS and potentiometric investigations. The comparative evaluation of our data indicated that (η5-Cp*)Rh(III) cation is able to induce the deprotonation of amide nitrogen well below pH 7. Consequently, at physiological pH the peptides are coordinated to Rh(III) by tridentate manner, with the participation of amide nitrogen. At pH 7.4 the (η5-Cp*)Rh(III) binding affinity of peptides follow the order GGA-OH < < GGH-OH < < histidine-amide < HGG-OH < GHG-NH2, i.e. the observed binding strength essentially depends on the presence and position of histidine within the peptide sequence. We also performed computational study on the possible solution structures of complexes present at near physiological pH. At pH 7.4 all histidine containing peptides form ternary complexes with strongly coordinating (N,N) bidentate ligands (ethylenediamine or bipyridyl), in which the peptides are monodentately coordinated to Rh(III) through their imidazole N1­nitrogens. In addition, the strongest chelators histidine-amide, HGG-OH and GHG-NH2 are also able to displace these powerful bidentate ligands from the coordination sphere of Rh(III).

Toxicity and uptake of nanoparticulate and bulk ZnO in nematodes with different life strategies.

Despite the increasing number and quantity of nanomaterials released in the environment, our knowledge on their bioavailability and possible toxicity to organisms is rather limited. Thus, we know quite little about sensitivity of various nematode feeding types and life strategies to treatments with nano metal oxides. The toxicity of zinc oxide nanoparticles (nano-ZnO) (with a particle size of 25 nm) and the bulk counterpart was investigated in two free-living nematode species of different life strategies: Xiphinema vuittenezi, a K-strategist plant-feeder nematode and Panagrellus redivivus, an r-strategist bacterivor nematode. The internal zinc concentration and the concentration of minor and trace elements were determined by total reflection X-ray fluorescence spectrometry. Concentration-dependent mortality in both nematode species was observed following a 24-h exposure both to nano-ZnO and bulk ZnO. The zinc concentration of the treating suspension had a significant effect on the internal zinc content of the animals in both cases. Particle size did not influence the internal zinc content. Our results show that nano and bulk ZnO have a similar dose-response effect on mortality of the bacterivor P. redivivus. In contrast, the nano-ZnO has stronger toxic effect on the mortality of X. vuittenezi. In general, X. vuittenezi did not react more sensitively to the treatments than P. redivivus, but appeared sensitive to the nano-ZnO treatment compared to bulk ZnO.