10.6084/m9.figshare.9544214.v1 Valerie Brunskill Valerie Brunskill Alejandra Enriquez Garcia Alejandra Enriquez Garcia Farideh Jalilehvand Farideh Jalilehvand Benjamin S. Gelfand Benjamin S. Gelfand Mengya Wu Mengya Wu Reaction of dirhodium(II) tetraacetate with <i>S</i>-methyl-<i>L</i>-cysteine Taylor & Francis Group 2019 Dirhodium(II) tetraacetate S-methyl-L-cysteine ESI–MS UV–vis spectroscopy crystal structure 2019-08-12 13:28:40 Journal contribution https://tandf.figshare.com/articles/journal_contribution/Reaction_of_dirhodium_II_tetraacetate_with_i_S_i_-methyl-_i_L_i_-cysteine/9544214 <p>The reaction of antitumor active dirhodium(II) tetraacetate, [Rh<sub>2</sub>(AcO)<sub>4</sub>], with <i>S</i>-methyl-<i>L</i>-cysteine (HSMC) was studied at the pH of mixing (=4.8) in aqueous media at various temperatures under aerobic conditions. The results from UV–vis spectroscopy and electrospray ionization mass spectrometry (ESI–MS) showed that HSMC initially coordinates <i>via</i> its sulfur atom to the axial positions of the paddlewheel framework of the dirhodium(II) complex, and was confirmed by the crystal structure of [Rh<sub>2</sub>(AcO)<sub>4</sub>(HSMC)<sub>2</sub>]. After some time (48 h at 25 °C), or at elevated temperature (40 °C), Rh-SMC chelate formation causes breakdown of the paddlewheel structure, generating the mononuclear Rh(III) complexes [Rh(SMC)<sub>2</sub>]<sup>+</sup>, [Rh(AcO)(SMC)<sub>2</sub>] and [Rh(SMC)<sub>3</sub>], as indicated by ESI–MS. These aerobic reaction products of [Rh<sub>2</sub>(AcO)<sub>4</sub>] with HSMC have been compared with those of the two proteinogenic sulfur-containing amino acids methionine and cysteine. Comparison shows that the (<i>S,N</i>)-chelate ring size influences the stability of the [Rh<sub>2</sub>(AcO)<sub>4</sub>] paddlewheel cage structure and its Rh<sup>II</sup>–Rh<sup>II</sup> bond, when an amino acid with a thioether group coordinates to dirhodium(II) tetraacetate. </p>