Aquation and Anation Kinetics of Rhenium(I) Dicarbonyl Complexes: Relation to Cell Toxicity and Bioavailability
journal contribution
posted on 2020-10-21, 15:30 authored by Marietjie Schutte-Smith, Sierra C. Marker, Justin J. Wilson, Hendrik G. VisserThe
aquation reactions of four rhenium(I) dicarbonyl complexes,
[Re(CO)2(NN)(PR3)(Cl)], where NN = 1,10-phenanthroline
(Phen) and 2,9-dimethyl-1,10-phenanthroline (DMPhen) and PR3 = 1,3,5-triaza-7-phosphaadamantane (PTA) and 1,4-diacetyl-1,3,7-triaza-5-phosphabicylco[3.3.1]nonane
(DAPTA). Additionally, the anation reactions of the corresponding
aqua complexes with Cl– were investigated. Single
crystals of [Re(CO)2(DMPhen)(PTA)(Cl)]·DMF and [Re(CO)2(DMPhen)(DAPTA)(Cl)] were obtained, and their structures were
determined using X-ray diffraction. The Re–Cl interatomic distances
are 2.4991(13) and 2.4922(6) Å, respectively, indicating a mild
trans influence effect of the phosphine ligands. The rate constants, kaq, for the aquation reactions of these complexes
spanned a range of (3.7 ± 0.3) × 10–4 to
(15.7 ± 0.3) × 10–4 s–1 with the two Phen complexes having rate constants that are 2.5 times
greater than those of the DMPhen complexes at 298 K. Similarly, the
second-order anation rate constants (kCl) of the resulting aqua complexes, [Re(CO)2(NN)(PR3)(H2O)]+, with Cl– ions at 298 K varied between (2.99 ± 0.05) × 10–3 and (6.79 ± 0.09) × 10–3 M–1 s–1. Likewise, these rate constants for the Phen
complexes were almost 2 times faster than those of the DMPhen complexes.
The pKa values of the four aqua complexes
were determined to be greater than 9.0 for all of the complexes with
[Re(CO)2(Phen)(PTA)(H2O)]+ having
the highest pKa value of 9.28 ± 0.03.
From the pKa values and the ratios of
the aquation and anation rate contants, which give thermodynamic Cl– binding constants, the speciation of the rhenium(I)
complexes in blood plasma, the cytoplasm, and the cell nucleus were
estimated. The data suggest that the aqua complexes would be the dominant
species in all three environments. This result may have important
implications on the potential biological activity of these complexes.
