Comparative solution equilibrium studies on pentamethylcyclopentadienyl rhodium complexes of 2,2ʹ-bipyridine and ethylenediamine and their interaction with human serum albumin

Abstract

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.

Comparative equilibrium and structural studies of new pentamethylcyclopentadienyl rhodium complexes bearing (O,N) donor bidentate ligands

“…A dependence of cytotoxic efficacy on chloride ion affinity has been observed for several [Ru(II)(η 6 -arene)] complexes [49][50][51]. In the case of the studied RhCp* complexes of the form [Rh(Cp*)(L)(H 2 O)] + (similarly to previously characterized complexes [27,28,32]) the chloride-water exchange process was found to be fast and takes place within a few minutes. Figure S8 shows the spectral changes of 1 upon the increase in chloride ion concentration.…”

“…This assumption was confirmed both in chloride free and 0.2 M KCl containing aqueous solution, using the RhCp* -3-iQA system in a 1:1 ratio: a dilution series (from 2 mM down to 4 µM) was prepared at pH 7.40 and the recorded UV-Vis spectra, after normalization, were identical under the applied conditions, which indicates that there is no complex decomposition in the studied concentration range (see Figure S7). coordination mode (4.99 [28]), but more than two orders of magnitude lower than the pM 7.4 value of the 2,2´-bipyridine complex (7.82 [32]). …”

“…Ethylenediamine was chosen as competitor since the stability constants for the RhCp* -ethylenediamine complex were acquired under the same conditions as applied in this study [32]. sample.…”

“…While complexes of deferiprone, picolinic acid, ethylenediamine, bpy and 8-hydroxyquinoline are sufficiently to outstandingly stable, no direct relationship can be established between their activity and their stability in aqueous solution [28,32,33]. It is a reasonable hypothesis that the increased chloride ion affinity of RhCp* complexes, just like in case of analogous Ir(III)-Cp* and some Ru(II)-arene compounds [34][35][36], may correlate with the poor in vitro anticancer activity.…”

“…Calculations were performed with the computer program PSEQUAD [46] in the same way as in our previous works [27,28,32,33].…”