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

Éva A. Enyedy, János P. Mészáros, Orsolya Dömötör, Carmen M. Hackl, Alexander Roller, Bernhard K. Keppler, Wolfgang Kandioller

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11 Citations (Scopus)

Abstract

Complex formation equilibrium processes of the (N,N) donor containing 2,2'-bipyridine (bpy) and ethylenediamine (en) with (5-pentamethylcyclopentadienyl)rhodium(III) were investigated in aqueous solution via pH-potentiometry, 1H NMR spectroscopy, and UVvis spectrophotometry in the absence and presence of chloride ions. The structure of [RhCp∗(en)Cl]ClO4 (Cp∗, pentamethylcyclopentadienyl) was also studied by single-crystal X-ray diffraction. pKa values of 8.56 and 9.58 were determined for [RhCp∗(bpy)(H2O)]2+ and [RhCp∗(en)(H2O)]2+, respectively resulting in the formation of negligibleamount of mixed hydroxido complexes at pH 7.4. Stability and the H2O/Cl- co-ligand exchange constants of bpy and en complexes considerably exceed those of the bidentate O-donor deferiprone. The strong affinity of the bpy and en complexes to chloride ionsmost probably contributes to their low antiproliferative effect. Interactions between human serum albumin (HSA) and [RhCp∗(H2O)3]2+, its complexes formedwith deferiprone, bpy and n were also monitored by 1H NMRspectroscopy, ultrafiltration/UVvis and spectrofluorometry. Numerous binding sites (=8) are available for [RhCp∗(H2O)3]2+; and the interaction takes place most probably via covalent bonds through the imidazole nitrogen of His. According to the various fluorescence studies [RhCp∗(H2O)3]2+ binds on sites I and II, and coordination of surface side chain donor atoms of the protein is also feasible. The binding of the bpy and en complex is weaker and slower compared to that of [RhCp∗(H2O)3]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.

Original languageEnglish
Pages (from-to)93-103
Number of pages11
JournalJournal of Inorganic Biochemistry
Volume152
DOIs
Publication statusPublished - Nov 15 2015

Keywords

  • Albumin
  • Deferiprone
  • Half-sandwich complexes
  • Rhodium
  • Stability constants
  • X-ray crystal structure

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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