title: Comparative solution equilibrium studies on pentamethylcyclopentadienyl rhodium complexes of 2,2'-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. 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 negligible amount 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 ions most probably contributes to their low antiproliferative effect. Interactions between human serum albumin (HSA) and [RhCp*(H2O)3](2+), its complexes formed with deferiprone, bpy and en were also monitored by (1)H NMR spectroscopy, ultrafiltration/UV-vis 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.
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary. Electronic address: enyedy@chem.u-szeged.hu.
authors.forename: Éva A
authors.initials: ÉA
authors.lastname: Enyedy
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary.
authors.forename: János P
authors.initials: JP
authors.lastname: Mészáros
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary; MTA-SZTE Bioinorganic Chemistry Research Group, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary.
authors.forename: Orsolya
authors.initials: O
authors.lastname: Dömötör
authors.affiliation: Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria.
authors.forename: Carmen M
authors.initials: CM
authors.lastname: Hackl
authors.affiliation: Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria.
authors.forename: Alexander
authors.initials: A
authors.lastname: Roller
authors.affiliation: Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria; University of Vienna, Research Platform Translational Cancer Therapy Research, Waehringer Str. 42, A-1090 Vienna, Austria.
authors.forename: Bernhard K
authors.initials: BK
authors.lastname: Keppler
authors.affiliation: Institute of Inorganic Chemistry, Faculty of Chemistry, University of Vienna, Waehringer Str. 42, A-1090 Vienna, Austria; University of Vienna, Research Platform Translational Cancer Therapy Research, Waehringer Str. 42, A-1090 Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kandioller
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D000418:Albumins / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D012238:Rhodium / Q000737:chemistry*
chemical_list: D000418:Albumins; D056831:Coordination Complexes; D005029:Ethylenediamines; D009942:Organometallic Compounds; D015082:2,2'-Dipyridyl; C031234:ethylenediamine; D012238:Rhodium
keywords: Albumin; Deferiprone; Half-sandwich complexes; Rhodium; Stability constants; X-ray crystal structure