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Reactions of Rh₂(CH₃COO)₄ with thiols and thiolates: a structural study.

ABSTRACT: The structural differences between the aerobic reaction products of Rh₂(AcO)₄ (1; AcO^- = CH₃COO^-) with thiols and thiolates in non-aqueous media are probed by X-ray absorption spectroscopy. For this study, ethanethiol, dihydrolipoic acid (DHLA; a dithiol) and their sodium thiolate salts were used. Coordination of simple thiols to the axial positions of Rh₂(AcO)₄ with Rh-SH bonds of 2.5-2.6?Å keeps the Rh^II-Rh^II bond intact (2.41 ± 0.02?Å) but leads to a colour change from emerald green to burgundy. Time-dependent density functional theory (TD-DFT) calculations were performed to explain the observed shifts in the electronic (UV-vis) absorption spectra. The corresponding sodium thiolates, however, break up the Rh₂(AcO)₄ framework in the presence of O₂ to form an oligomeric chain of triply S-bridged Rh(III) ions, each with six Rh-S (2.36 ± 0.02?Å) bonds. The Rh^III...Rh^III distance, 3.18 ± 0.02?Å, in the chain is similar to that previously found for the aerobic reaction product from aqueous solutions of Rh₂(AcO)₄ and glutathione (H₃A), {Na₂[Rh₂^III(HA)₄]·7H₂O}_n, in which each Rh(III) ion is surrounded by about four Rh-S (2.33 ± 0.02?Å) and about two Rh-O (2.08 ± 0.02?Å). The reaction products obtained in this study can be used to predict how dirhodium(II) tetracarboxylates would react with cysteine-rich proteins and peptides, such as metallothioneins.

SUBMITTER: Enriquez Garcia A

PROVIDER: S-EPMC6412178 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Reactions of Rh2(CH3COO)4 with thiols and thiolates: a structural study.

Enriquez Garcia Alejandra A Jalilehvand Farideh F Niksirat Pantea P

Journal of synchrotron radiation 20190213 Pt 2

The structural differences between the aerobic reaction products of Rh2(AcO)4 (1; AcO- = CH3COO-) with thiols and thiolates in non-aqueous media are probed by X-ray absorption spectroscopy. For this study, ethanethiol, dihydrolipoic acid (DHLA; a dithiol) and their sodium thiolate salts were used. Coordination of simple thiols to the axial positions of Rh2(AcO)4 with Rh-SH bonds of 2.5-2.6 Å keeps the RhII-Rh ...[more]

PMID: 30855255

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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

Reactions of Rh₂(CH₃COO)₄ with thiols and thiolates: a structural study.

Publications

Reactions of Rh<sub>2</sub>(CH<sub>3</sub>COO)<sub>4</sub> with thiols and thiolates: a structural study.

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