Formation of [RuIII(edta)(SNO)]2– in RuIII(edta)-Mediated S-Nitrosylation of Bisulfide Ion

Reaction mechanisms relevant to the formation and utilization of [Ru(edta)(NO)] complexes in aqueous media

The advancement of Ru(edta) complexes (edta^4- = ethylenediamineteraacetate) mediated reactions, including NO generation and its utilization, has not been systematically reviewed to date. This review aims to report the research progress that has been made in exploring the application of Ru(edta) complexes in trapping and generation of NO. Furthermore, utilization of the potential of Ru(edta) complexes to mimic NO synthase and nitrite reductase activity, including thermodynamics and kinetics of NO binding to Ru(edta) complexes, their NO scavenging (in vitro), and antitumor activity will be discussed. Also, the role of [Ru(edta)(NO)] in mediating electrochemical reduction of nitrite, S-nitrosylation of biological thiols, and cross-talk between NO and H₂S, will be covered. Reports on the NO-related chemistry of Fe(edta) complexes showing similar behavior are contextualized in this review for comparison purposes. The research contributions compiled herein will provide in-depth mechanistic knowledge for understanding the diverse routes pertaining to the formation of the [Ru(edta)(NO)] species, and its role in effecting the aforementioned reactions of biochemical significance.

Thionitrite and Perthionitrite in NO Signaling at Zinc

NO and H₂ S serve as signaling molecules in biology with intertwined reactivity. HSNO and HSSNO with their conjugate bases ^- SNO and ^- SSNO form in the reaction of H₂ S with NO as well as S-nitrosothiols (RSNO) and nitrite (NO₂ ^- ) that serve as NO reservoirs. While HSNO and HSSNO are elusive, their conjugate bases form isolable zinc complexes ^Ph,Me TpZn(SNO) and ^Ph,Me TpZn(SSNO) supported by tris(pyrazolyl)borate ligands. Reaction of Na(15-C-5)SSNO with ^Ph,Me TpZn(ClO₄ ) provides ^Ph,Me TpZn(SSNO) that undergoes S-atom removal by PEt₃ to give ^Ph,Me TpZn(SNO) and S=PEt₃ . Unexpectedly stable at room temperature, these Zn-SNO and Zn-SSNO complexes release NO upon heating. ^Ph,Me TpZn(SNO) and ^Ph,Me TpZn(SSNO) quickly react with acidic thiols such as C₆ F₅ SH to form N₂ O and NO, respectively. Increasing the thiol basicity in p-substituted aromatic thiols ^4-X ArSH in the reaction with ^Ph,Me TpZn(SNO) turns on competing S-nitrosation to form ^Ph,Me TpZn-SH and RSNO, the latter a known precursor for NO.

Inorganic reaction mechanisms. A personal journey

This review covers highlights of the work performed in the van Eldik group on inorganic reaction mechanisms over the past two decades in the form of a personal journey. Topics that are covered include, from NO to HNO chemistry, peroxide activation in model porphyrin and enzymatic systems, the wonder-world of Ru^III(edta) chemistry, redox chemistry of Ru(iii) complexes, Ru(ii) polypyridyl complexes and their application, relevant physicochemical properties and reaction mechanisms in ionic liquids, and mechanistic insight from computational chemistry. In each of these sections, typical examples of mechanistic studies are presented in reference to related work reported in the literature.

Chemistry of Ru(edta) complexes relevant to oxidoreductase mimicking: a personal perspective

This article chronicles the enzyme mimicking chemistry of Ru(edta) complexes (edta⁴⁻ = ethylenediaminetetraacetate) in regard to small molecule activation.

Saying NO to H2S: A Story of HNO, HSNO, and SSNO. Inorg Chem 2019;58:4039-4051. [PMID: 30883105 DOI: 10.1021/acs.inorgchem.8b02592]

Interactions between small inorganic molecules are fundamental to the understanding of basic reaction mechanisms and some of the initial processes of chemical evolution that preceded organic molecules and led to the origin of life. The kinetics of these processes are suitable for the fast generation of a variety of new chemical entities and the propagation of a cascade of chemical reactions, a property that is ideal for signaling purposes even in biological systems. NO and H₂S are such molecules that are nowadays recognized as biological gasotransmitters involved in the regulation of physiological functions through protein modifications such as S-nitrosothiol, disulfide, and persulfide formations. In this Viewpoint, we review the current understanding of interactions of NO (and organic and metal nitrosyl species) with H₂S, in both chemical and biochemical contexts. Through the formation of HNO, (H)SNO (and its isomers), (H)SSNO, and polysulfides, these two gasotransmitters initiate reaction networks with significant roles in cell signaling. The chemical reactivities and biological effects of these nitrogen and sulfur species are still unresolved, and, thus, a cross-talk between all of them represents a challenging interdisciplinary field that awaits exciting new findings. We tackle some of the intriguing and open questions and provide perspectives for future research directions.

RuIII(edta)-mediated interaction of nitrite and sulphide: formation of an N-bonded thionitrous acid (HSNO) complex of RuIII(edta) in aqueous solution

It is reported for the first time that [Ru^III(edta)(NO⁺)] (edta⁴⁻ = ethylenediaminetetraacetate) generated from [Ru^III(edta)(NO₂)]²⁻ at lower pH (∼3.5) can react with NaHS to form the thionitrous acid bound Ru(edta) complex in aqueous solution.

Chemical Biology of H2S Signaling through Persulfidation

Signaling by H2S is proposed to occur via persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH). Persulfidation provides a framework for understanding the physiological and pharmacological effects of H2S. Due to the inherent instability of persulfides, their chemistry is understudied. In this review, we discuss the biologically relevant chemistry of H2S and the enzymatic routes for its production and oxidation. We cover the chemical biology of persulfides and the chemical probes for detecting them. We conclude by discussing the roles ascribed to protein persulfidation in cell signaling pathways.

Nitrosopersulfide (SSNO-) decomposes in the presence of sulfide, cyanide or glutathione to give HSNO/SNO-: consequences for the assumed role in cell signalling

The emergence of hydrogen sulfide (H₂S) as a new signalling molecule able to control vasodilation, neurotransmission and immune response, prompted questions about its possible cross-talk with the other gasontransmitter, nitric oxide (NO). It has been shown that H₂S reacts with NO and its metabolites and several potentially biologically active species have been identified. Thionitrous acid (HSNO) was proposed to be an intermediate product of the reaction of S-nitrosothiols with H₂S capable of crossing the membranes and causing further trans-nitrosation of proteins. Alternatively, formation of nitrosopersulfide (SSNO^-) has been proposed in this reaction. SSNO^- was claimed to be particularly stable and inert to H₂S, thiols and cyanides. It is suggested that this putative SSNO^- slowly decomposes to give NO, HNO and polysulfides. However, the chemical studies with pure SSNO^- salts showed some conflicting observations. In this study, we work with pure PNP⁺SSNO^- to show that contrary to everything that is claimed for the yellow reaction product of GSNO with H₂S, pure SSNO^- decomposes readily in the presence of cyanide, H₂S and glutathione to form SNO^-. Based on literature overview and chemical data about the structures of HSNO/SNO^- and SSNO^- we discuss the biological role these two species could have.