Complex formation equilibrium processes of the (N,N) donor containing 2,2'-bipyridine (bpy) and ethylenediamine (en) with (η 5 -pentamethylcyclopentadienyl)rhodium(III) were investigated in aqueous solution via pH-potentiometry, 1 H NMR spectroscopy, and UV-Vis spectrophotometry in the absence and presence of chloride ions. 2+ , and formation of ternary HSA-RhCp*-ligand adducts was proved. In the case of the deferiprone complex, the RhCp* fragment is cleaved off when HSA is loaded with low equivalents of the compound.

Thiomaltol, a potential S,O-coordinating molecule, has been utilized for the complexation of four different organometallic fragments, yielding the desired Ru , Os , Rh , and Ir complexes having a "piano-stool" configuration. In addition to the synthesis of these compounds with a chlorido leaving group, the analogous 1-methylimidazole derivatives have been prepared, giving rise to thiomaltol-based organometallics with enhanced stability under physiological conditions. The organometallic compounds have been characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their behavior in aqueous solution and their interactions with certain amino acids have been studied by ESI mass spectrometry. Their pH-dependent stability has been investigated by H NMR in aqueous solution, and their cytotoxicity against three different cancer cell lines has been investigated. Furthermore, their capacity as topoisomerase IIα inhibitors as well as their effect on the cell cycle distribution and reactive oxygen species (ROS) generation have been elucidated.

d/ ppm 3.5 2.2 1.6 pH N O OH N O OH Abstract Complex formation processes of rhodium(III)-η 5 -pentamethylcyclopentadienyl cation [RhCp*(H 2 O) 3 ] 2+ with 1,2-dimethyl-3-hydroxy-pyridin-4(1H)-one (deferiprone, dhp) and pyridine-2-carboxylic acid (pic) were studied with the aid of pH-potentiometry, 1 H NMR and UV-visible spectrophotometry in aqueous solution in the presence and in the absence of chloride ions. Stoichiometry and overall stability constants of the complexes formed were determined. Formation of mononuclear, mono-ligand complexes such as [RhCp*(L)Z] (where L = dhp or pic; Z = Clor H 2 O) and mixed-hydroxido species [RhCp*(L)(OH)] was found. Relatively high pK a values (9.32-11.90) were determined for the hydrolysis of the [RhCp*(L)Z] complexes. [RhCp*(L)Z] species predominate at physiological pH, and negligible decomposition is probable only at low micromolar concentrations. More favored complex formation was found in the case of pic. Stability of the studied organorhodium complexes was compared to analogous Ru(II)(h 6 -p-cymene) compounds. In addition, the aqua/chlorido ligand replacement reaction in the complexes [RhCp*(L)(H 2 O)] + of dhp and pic was monitored to provide equilibrium constants with which the extent of aquation at various chloride concentrations can be estimated. Single crystals of [RhCp*(dhp)Cl] suitable for Xray diffraction analysis were also obtained. The [RhCp*(L)Cl] complexes of dhp and pic were tested for cytotoxicity in various human cancer cell lines where they showed activity depending on the attached ligand scaffold.

dmen), N,N,N 0 ,N 0 -tetramethylethylenediamine (tmeda), 2-picolylamine (pin) and 1,10-phenanthroline (phen) were studied in aqueous solution by 1 H NMR spectroscopy, UV-vis spectrophotometry and pHpotentiometry. Formation and deprotonation of [Rh(Z 5 -C 5 Me 5 )(L)(H 2 O)] 2+ complexes and exchange process of the aqua to chlorido ligand were characterized in addition to single-crystal X-ray diffraction analysis of [Rh(Z 5 -C 5 Me 5 )(L)(Cl)] + complexes (L = dmen, tmeda and pin). Formation of complexes with significantly high stability was found except tmeda due to the sterical hindrance between the methyl groups of the chelating ligand and the arenyl ring resulting in an increased methyl group-ring plane torsion angle. [Rh(Z 5 -C 5 Me 5 )(L)(H 2 O)] 2+ complexes of dmen, pin, phen predominate at pH 7.4 without decomposition even in the micromolar concentration range. The complexes were characterized by relatively high chloride affinity and a strong correlation was obtained between the log K 0 (H 2 O/Cl À ) and pK a of [Rh(Z 5 -C 5 Me 5 )(L)(H 2 O)] 2+ constants for a series of (O,O), (O,N) and (N,N)-chelated complexes. For this set of 12 complexes a relationship between log K 0 (H 2 O/Cl À ) values and certain crystallographic parameters was found using multiple linear regression approach. DNA binding of these complexes was also monitored and compared by ultrafiltration and fluorimetry.