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Methionine Binding to Dirhodium(II) Tetraacetate.

ABSTRACT: The reaction between antitumor active dirhodium(II) tetraacetate and dl-methionine (HMet) was followed in aqueous solution and showed initially mixtures of 1:1 and 1:2 adducts [Rh2(AcO)4(HMet)(H2O)] (AcO- = CH3COO-) and [Rh2(AcO)4(HMet)2] formed at room temperature (RT), as evidenced by UV-vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Rh K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy confirmed methionine thioether binding to the axial positions of the Rh2(AcO)4 cage structure. With excess HMet at RT, stepwise displacement of the acetate groups was observed after some time using ESI-MS. Heating the solution to 40° for 24 h accelerated the substitution reaction leading to stable dirhodium(II) species with two acetate ligands displaced by two methionine groups. The crystal structure of the purple [RhII2(AcO)2(d-Met)(l-Met)]·6H2O compound obtained from the solution revealed tridentate coordination of the methionine ligands to the Rh(II) ions, with the thioether S atoms in equatorial positions. A minor amount of a light orange monomeric [RhIII(Met)2](AcO) complex also formed in the solution was isolated by size exclusion chromatography and identified by ESI-MS. Crystals of [RhIII(d-Met)(l-Met)]Cl·3H2O were prepared by reacting RhCl3 and dl-HMet. The crystal structure showed tridentate binding of the methionine ligands to the Rh(III) ion in a trans-S, N, O arrangement.

SUBMITTER: Enriquez Garcia A

PROVIDER: S-EPMC6311416 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Methionine Binding to Dirhodium(II) Tetraacetate.

Enriquez Garcia Alejandra A Jalilehvand Farideh F Niksirat Pantea P Gelfand Benjamin S BS

Inorganic chemistry 20180924 20

The reaction between antitumor active dirhodium(II) tetraacetate and dl-methionine (HMet) was followed in aqueous solution and showed initially mixtures of 1:1 and 1:2 adducts [Rh2(AcO)4(HMet)(H2O)] (AcO- = CH3COO-) and [Rh2(AcO)4(HMet)2] formed at room temperature (RT), as evidenced by UV-vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Rh K-edge extended X-ray absorption f ...[more]

PMID: 30247895

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Project description:We have combined results from several spectroscopic techniques to investigate the aerobic reactions of Rh2(AcO)4 (AcO- = CH3COO-) with l-cysteine (H2Cys) and its derivatives d-penicillamine (3,3'-dimethylcysteine, H2Pen), with steric hindrance at the thiol group, and N-acetyl-l-cysteine (H2NAC), with its amino group blocked. Previous investigations have shown that antitumor active dirhodium(II) carboxylates may irreversibly inhibit enzymes containing a thiol group at or near their active sites. Also, cysteine, the only thiol-containing proteinogenic amino acid, interacts in vivo with this class of antitumor compounds, but structural information on the products of such reactions is lacking. In the present study, the reactions of Rh2(AcO)4 and H2L were carried out in aqueous solutions at the pH of mixing (acidic) and at physiological pH, using the different mole ratios 1:2, 1:4, and 1:6, which resulted in the same products in increasing yields. Electrospray ionization mass spectrometry (ESI-MS) indicates formation of dimeric [RhIII 2Pen4]2- or oligomeric {RhIII 2L4} n (L = Cys, NAC) complexes with bridging thiolate groups. Analyses of Rh K edge extended X-ray absorption fine structure (EXAFS) data reveal 3-4 Rh-S and 2-3 Rh-(N/O) bonds around six-coordinated Rh(III) ions at mean distances of 2.33 ± 0.02 and 2.09 ± 0.02 Å, respectively. In the N-acetyl-l-cysteine compound, the RhIII···RhIII distance 3.10 ± 0.02 Å obtained from the EXAFS spectrum supports trithiolate bridges between the Rh(III) ions, as was also found when using glutathione as ligand. In the cysteine and penicillamine complexes, double thiolate bridges join the Rh(III) ions, with the nonbridging Cys2- and Pen2- ligands in tridentate chelating (S,N,O) mode, which is consistent with the ΔδC = 7.3-8.4 ppm shift of the COO- signal in their carbon-13 cross polarization magic angle spinning (CPMAS) NMR spectra. For the penicillamine complex, the 2475.6 eV peak in its S K edge X-ray absorption near edge structure (XANES) spectrum shows partial oxidation, probably caused by peroxide generated from reduction of dissolved O2, of thiolato to sulfenato (S=O) groups, which were also identified by ESI-MS for all three {RhIII 2L4} n compounds.

Dataset Information

Methionine Binding to Dirhodium(II) Tetraacetate.

Publications

Methionine Binding to Dirhodium(II) Tetraacetate.

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