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

Abstract

The structural differences between the aerobic reaction products of Rh 2 (AcO) 4 (1; AcO À = CH 3 COO À ) 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 Rh 2 (AcO) 4 with Rh-SH bonds of 2.5-2.6 Å keeps the Rh II -Rh II bond intact (2.41 AE 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 Rh 2 (AcO) 4 framework in the presence of O 2 to form an oligomeric chain of triply S-bridged Rh(III) ions, each with six Rh-S (2.36 AE 0.02 Å ) bonds. The Rh III Á Á ÁRh III distance, 3.18 AE 0.02 Å , in the chain is similar to that previously found for the aerobic reaction product from aqueous solutions of Rh 2 (AcO) 4 and glutathione (H 3 A), {Na 2 [Rh 2 III -(HA) 4 ]Á7H 2 O} n , in which each Rh(III) ion is surrounded by about four Rh-S (2.33 AE 0.02 Å ) and about two Rh-O (2.08 AE 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.

Search for new biologically active compounds: in vitro studies of antitumor and antimicrobial activity of dirhodium(ii,ii) paddlewheel complexes

“…The complex showed significant antitumor activity against Ehrlich-Lettre ascites carcinoma, [32][33][34] sarcoma 180 35 and lymphocytic leukemia L1210 36 and P388. 35 Further studies on the mechanism of action showed that the probable biomolecular targets of dinuclear rhodium(II,II) complexes are single-and double-stranded DNA, 35 proteins, [37][38][39][40][41][42][43][44][45][46] peptides 47,48 and amino acids, 31,[49][50][51] although the mode of binding to proteins has not yet been fully elucidated.…”

Kinetics of Reactions of Dirhodium and Diruthenium Paddlewheel Tetraacetate Complexes with Nucleophilic Protein Sites: Computational Insights

“…The dirhodium tetraacetate complex [Rh 2 (μ-O 2 CCH 3 ) 4 ] includes a Rh­(II)–Rh­(II) bond with four carboxylates playing the role of bridging ligands arranged in a lantern-like form around the central bimetal unit, whereas neutral solvent molecules (L) occupy the axial coordination sites. Although causing toxic side effects, this complex has a proven activity against several cancer types, such as sarcoma 180, P388 leukemia, L1210 tumors, and Ehrlich-Lettre ascites carcinoma. − Nevertheless, its mode of action is not yet disentangled despite several studies on its interaction with various proteins, − although it is hypothesized that its biomolecular targets are single- and double-stranded DNA, proteins, − peptides, , and amino acids. − Moreover, interaction of dirhodium compounds with peptides and proteins was investigated in the framework of protein modification with the aim of designing artificial metalloenzymes. , Usually, Rh-based complexes are coordinated to proteins either via the covalent linkage, involving direct binding of these metal complexes to proteins, , or via the dative anchoring which is based on the formation of noncovalent interactions between protein atoms and Rh ligands as well as coordinative bonds between protein side chains and Rh centers . There are experimental pieces of evidence of the Rh-complex selectivity toward side chains of Asn, Asp, His, Lys, and the C-terminal carboxylate. ,, …”