Nitrosodisulfide [S2NO]- (perthionitrite) is a true intermediate during the "cross-talk" of nitrosyl and sulfide

Inorganic Polysulfides in Solution: Structural Properties and Conformational Isomerism

We present a comprehensive theoretical examination of the structural properties of dianionic polysulfides [Sn]2- (n = 2-6), their conjugated monoacids [HSn]- (n = 2-6), and a selection of 1e--oxidized radical anions [Sn]•- (n = 2-4), in aqueous and dimethyl sulfoxide (DMSO) solutions. We investigated the structures and stabilities of various conformational isomers within these families of compounds by employing Quantum Mechanics-Molecular Mechanics (QM-MM) Molecular Dynamics (MD) simulations. The explicit inclusion of solvent molecules in the calculations revealed stable conformational structures that were previously unreported and might have appreciable concentrations in real systems. The interconversions between the isomeric structures proceed on the order of hundreds of picoseconds and are energetically similar to the isomerization processes in substituted cyclohexanes. We also conducted a detailed analysis of the stability of different isomers of the radical anion [S4]•- in solution. Our findings highlight the significant influence of the solvent on the isomerizations, a result that could be particularly relevant for enhancing the performance of metal-sulfur batteries.

Nonheme binuclear transition metal complexes with hydrosulfide and polychalcogenides

The intriguing chemistry of chalcogen (S, Se)-containing ligands and their capability to bridge multiple metal centres have resulted in a plethora of reports on transition metal complexes featuring hydrosulfide (HS-) and polychalcogenides (En2-, E = S, Se). While a large number of such molecules are strictly organometallic complexes, examples of non-organometallic complexes featuring HS- and En2- with N-/O-donor ligands are relatively rare. The general synthetic procedure for the transition metal-hydrosulfido complexes involves the reaction of the corresponding metal salts with HS-/H2S and this is prone to generate sulfido bridged oligomers in the absence of sterically demanding ligands. On the other hand, the synthetic methods for the preparation of transition metal-polychalcogenido complexes include the reaction of the corresponding metal salts with En2- or the two electron oxidation of low-valent metals with elemental chalcogen, often at an elevated temperature and/or for a long time. Recently, we have developed new synthetic methods for the preparation of two new classes of binuclear transition metal complexes featuring either HS-, or Sn2- and Sen2- ligands. The new method for the synthesis of transition metal-hydrosulfido complexes involved transition metal-mediated hydrolysis of thiolates at room temperature (RT), while the method for the synthesis of transition metal-polychalcogenido complexes involved redox reaction of coordinated thiolates and exogenous elemental chalcogens at RT. An overview of the synthetic aspects, structural properties and intriguing reactivity of these two new classes of transition metal complexes is presented.

The Reactive Species Interactome in Red Blood Cells: Oxidants, Antioxidants, and Molecular Targets

Beyond their established role as oxygen carriers, red blood cells have recently been found to contribute to systemic NO and sulfide metabolism and act as potent circulating antioxidant cells. Emerging evidence indicates that reactive species derived from the metabolism of O2, NO, and H2S can interact with each other, potentially influencing common biological targets. These interactions have been encompassed in the concept of the reactive species interactome. This review explores the potential application of the concept of reactive species interactome to understand the redox physiology of RBCs. It specifically examines how reactive species are generated and detoxified, their interactions with each other, and their targets. Hemoglobin is a key player in the reactive species interactome within RBCs, given its abundance and fundamental role in O2/CO2 exchange, NO transport/metabolism, and sulfur species binding/production. Future research should focus on understanding how modulation of the reactive species interactome may regulate RBC biology, physiology, and their systemic effects.

The role of nitric oxide and hydrogen sulfide in regulation of redox homeostasis at extreme temperatures in plants

Nitric oxide and hydrogen sulfide, as important signaling molecules (gasotransmitters), are involved in many functions of plant organism, including adaptation to stress factors of various natures. As redox-active molecules, NO and H₂S are involved in redox regulation of functional activity of many proteins. They are also involved in maintaining cell redox homeostasis due to their ability to interact directly and indirectly (functionally) with ROS, thiols, and other molecules. The review considers the involvement of nitric oxide and hydrogen sulfide in plant responses to low and high temperatures. Particular attention is paid to the role of gasotransmitters interaction with other signaling mediators (in particular, with Ca²⁺ ions and ROS) in the formation of adaptive responses to extreme temperatures. Pathways of stress-induced enhancement of NO and H₂S synthesis in plants are considered. Mechanisms of the NO and H₂S effect on the activity of some proteins of the signaling system, as well as on the state of antioxidant and osmoprotective systems during adaptation to stress temperatures, were analyzed. Possibilities of practical use of nitric oxide and hydrogen sulfide donors as inductors of plant adaptive responses are discussed.

Hydropersulfides (RSSH) and Nitric Oxide (NO) Signaling: Possible Effects on S-Nitrosothiols (RS-NO)

S-Nitrosothiol (RS-NO) formation in proteins and peptides have been implicated as factors in the etiology of many diseases and as possible regulators of thiol protein function. They have also been proposed as possible storage forms of nitric oxide (NO). However, despite their proposed functions/roles, there appears to be little consensus regarding the physiological mechanisms of RS-NO formation and degradation. Hydropersulfides (RSSH) have recently been discovered as endogenously generated species with unique reactivity. One important reaction of RSSH is with RS-NO, which leads to the degradation of RS-NO as well as the release of NO. Thus, it can be speculated that RSSH can be a factor in the regulation of steady-state RS-NO levels, and therefore may be important in RS-NO (patho)physiology. Moreover, RSSH-mediated NO release from RS-NO may be a possible mechanism allowing RS-NO to serve as a storage form of NO.

Nitrosopersulfide (SSNO-) Is a Unique Cysteine Polysulfidating Agent with Reduction-Resistant Bioactivity

Aims: The aim of the present study was to investigate the biochemical properties of nitrosopersulfide (SSNO^-), a key intermediate of the nitric oxide (NO)/sulfide cross talk. Results: We obtained corroborating evidence that SSNO^- is indeed a major product of the reaction of S-nitrosothiols with hydrogen sulfide (H₂S). It was found to be relatively stable (t_1/2 ∼1 h at room temperature) in aqueous solution of physiological pH, stabilized by the presence of excess sulfide and resistant toward reduction by other thiols. Furthermore, we here show that SSNO^- escapes the reducing power of the NADPH-driven biological reducing machineries, the thioredoxin and glutathione reductase systems. The slow decomposition of SSNO^- produces inorganic polysulfide species, which effectively induce per/polysulfidation on glutathione or protein cysteine (Cys) residues. Our data also demonstrate that, in contrast to the transient activation by inorganic polysulfides, SSNO^- induces long-term potentiation of TRPA1 (transient receptor potential ankyrin 1) channels, which may be due to its propensity to generate a slow flux of polysulfide in situ. Innovation: The characterized properties of SSNO^- would seem to represent unique features in cell signaling by enabling sulfur and nitrogen trafficking within the reducing environment of the cytosol, with targeted release of both NO and polysulfide equivalents. Conclusion: SSNO^- is a surprisingly stable bioactive product of the chemical interaction of S-nitrosothiol species and H₂S that is resistant to reduction by the thioredoxin and glutathione systems. As well as generating NO, it releases inorganic polysulfides, enabling transfer of sulfane sulfur species to peptide/protein Cys residues. The sustained activation of TRPA1 channels by SSNO^- is most likely linked to all these properties.

Red Blood Cells as a "Central Hub" for Sulfide Bioactivity: Scavenging, Metabolism, Transport, and Cross-Talk with Nitric Oxide

Significance: Sulfide was revealed to be an endogenous signaling molecule regulating a plethora of cellular functions. It is involved in the regulation of fundamental processes, including blood pressure regulation, suspended animation, and metabolic activity of mitochondria, pain, and inflammation. The underlying biochemical pathways and pharmacological targets are still largely unidentified. Recent Advances: Red blood cells (RBCs) are known as oxygen transporters and were proposed to contribute to cardiovascular homeostasis by regulating nitric oxide (NO) metabolism, also via interaction of hemoglobin with nitrite and NO itself. Interestingly, recent evidence indicates that RBCs may also play a central role in systemic sulfide metabolism and homeostasis, and, potentially, in the crosstalk with NO. Heme-containing proteins such as hemoglobin were shown to be targeted by both NO and sulfide. In this article, we aim at revising and discussing the potential impact of RBCs on systemic sulfide metabolism in the cardiovascular system. Critical Issues: Although the synthetic pathways and the reactivity of hemoglobin and other heme proteins with sulfide and NO are known, the in vivo role of RBCs in sulfide metabolism, physiology, pharmacology, and its pathophysiological implications have not been characterized so far. Future Directions: To allow a better understanding of the role of RBCs in systemic sulfide metabolism and its cross-talk with NO, basic and translational science studies should be focused on dissecting the enzymatic and nonenzymatic sulfur metabolic pathways in RBCs in vivo and their impact on the cardiovascular system in animal models and clinical settings.

Hydrogen Sulfide: From a Toxic Molecule to a Key Molecule of Cell Life

Hydrogen sulfide (H2S) has always been considered toxic, but a huge number of articles published more recently showed the beneficial biochemical properties of its endogenous production throughout all regna. In this review, the participation of H2S in many physiological and pathological processes in animals is described, and its importance as a signaling molecule in plant systems is underlined from an evolutionary point of view. H2S quantification methods are summarized and persulfidation is described as the underlying mechanism of action in plants, animals and bacteria. This review aims to highlight the importance of its crosstalk with other signaling molecules and its fine regulation for the proper function of the cell and its survival.

17O NMR spectroscopy-assisted in vitro bioactivity studies of the intermediates formed via Na2S and RSNO cross-linking reactions

The cross-linking reaction between sulfide and S-nitrosothiol moieties has been intensively investigated and thionitrite/thionitrous acid (SNO⁻/HSNO) as well as nitrosopersulfide (SSNO⁻) were reported to be the intermediates that could serve as reservoirs for nitric oxide (NO). However, debate still exists regarding the stability and biological activity of SNO⁻/HSNO and SSNO⁻. In order to investigate the chemical properties and biological activity of SNO⁻ and SSNO⁻, we set out to re-characterize the reaction intermediates using UV-Vis and ¹⁵N NMR spectroscopy techniques, as well as a new ¹⁷O NMR approach. The effects of SNO⁻ and SSNO⁻ on cellular NO and cGMP levels were assessed via cell culture experiments, and also the effects of SNO⁻ and SSNO⁻ on cell proliferation, migration, and capillary-like structure formation were evaluated with human umbilical vein endothelial cells (HUVEC). Through this work, the characteristic peaks and half-lives of SNO⁻ and SSNO⁻ were elucidated under various preparation conditions. The biological assays demonstrated that SSNO⁻ increased the cellular NO and cGMP levels and also facilitated cell proliferation, migration and stimulated angiogenesis, while in contrast SNO⁻ did not exhibit these effects.

By using UV-Vis, ¹⁵N NMR and ¹⁷O NMR spectroscopy techniques, we characterized the intermediates (SSNO⁻ and SNO⁻) obtained from RSNO and Na₂S cross-linking reaction. We found that SSNO⁻ could serve as NO reservoir in cell culture experiments.

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.

Emerging Roles of Carbonyl Sulfide in Chemical Biology: Sulfide Transporter or Gasotransmitter?

SIGNIFICANCE

Carbonyl sulfide (COS) is the most prevalent sulfur-containing gas in the Earth's atmosphere, and it plays important roles in the global sulfur cycle. COS has been implicated in origin of life peptide ligation, is the primary energy source for certain bacteria, and has been detected in mammalian systems. Despite this long and intertwined history with terrestrial biology, limited attention has focused on potential roles of COS as a biological mediator. Recent Advances: Although bacterial COS production is well documented, definitive sources of mammalian COS production have not been confirmed. Enzymatic COS consumption in mammals, however, is well documented and occurs primarily by carbonic anhydrase (CA)-mediated conversion to hydrogen sulfide (H2S). COS has been detected in ex vivo mammalian tissue culture, as well as in exhaled breath as a potential biomarker for different disease pathologies, including cystic fibrosis and organ rejection. Recently, chemical tools for COS delivery have emerged and are poised to advance future investigations into the role of COS in different biological contexts.

CRITICAL ISSUES

Possible roles of COS as an important biomolecule, gasotransmitter, or sulfide transport intermediate remain to be determined. Key advances in both biological and chemical tools for COS research are needed to further investigate these questions.

FUTURE DIRECTIONS

Further evaluation of the biological roles of COS and disentangling the chemical biology of COS from that of H2S are needed to further elucidate these interactions. Chemical tools for COS delivery and modulation may provide a first avenue of investigative tools to answer many of these questions. Antioxid. Redox Signal. 28, 1516-1532.

Chemical Reactivity and Spectroscopy Explored From QM/MM Molecular Dynamics Simulations Using the LIO Code

In this work we present the current advances in the development and the applications of LIO, a lab-made code designed for density functional theory calculations in graphical processing units (GPU), that can be coupled with different classical molecular dynamics engines. This code has been thoroughly optimized to perform efficient molecular dynamics simulations at the QM/MM DFT level, allowing for an exhaustive sampling of the configurational space. Selected examples are presented for the description of chemical reactivity in terms of free energy profiles, and also for the computation of optical properties, such as vibrational and electronic spectra in solvent and protein environments.

Natural Products Containing a Nitrogen-Sulfur Bond

Only about 100 natural products are known to contain a nitrogen-sulfur (N-S) bond. This review thoroughly categorizes N-S bond-containing compounds by structural class. Information on biological source, biological activity, and biosynthesis is included, if known. We also review the role of N-S bond functional groups as post-translational modifications of amino acids in proteins and peptides, emphasizing their role in the metabolism of the cell.

Chemical Biology of Hydropersulfides and Related Species: Possible Roles in Cellular Protection and Redox Signaling

SIGNIFICANCE

For >20 years, physiological signaling associated with the endogenous generation of hydrogen sulfide (H₂S) has been of significant interest. Despite its presumed importance, the biochemical mechanisms associated with its actions have not been elucidated. Recent Advances: Recently it has been found that H₂S-related or derived species are highly prevalent in mammalian systems and that these species may be responsible for some, if not the majority, of the biological actions attributed to H₂S. One of the most prevalent and intriguing species are hydropersulfides (RSSH), which can be present at significant levels. Indeed, it appears that H₂S and RSSH are intimately linked in biological systems and likely to be mutually inclusive.

CRITICAL ISSUES

The fact that H₂S and polysulfides such as RSSH are present simultaneously means that the biological actions previously assigned to H₂S can be instead because of the presence of RSSH (or other polysulfides). Thus, it remains possible that hydropersulfides are the biological effectors, and H₂S serves, to a certain extent, as a marker for persulfides and polysulfides. Addressing this possibility will to a large extent be based on the chemistry of these species.

FUTURE DIRECTIONS

Currently, it is known that persulfides possess unique and novel chemical properties that may explain their biological prevalence. However, significantly more work will be required to establish the possible physiological roles of these species. Moreover, an understanding of the regulation of their biosynthesis and degradation will become important topics in piecing together their biology. Antioxid. Redox Signal. 00, 000-000.

The Reactive Species Interactome: Evolutionary Emergence, Biological Significance, and Opportunities for Redox Metabolomics and Personalized Medicine

SIGNIFICANCE

Oxidative stress is thought to account for aberrant redox homeostasis and contribute to aging and disease. However, more often than not, administration of antioxidants is ineffective, suggesting that our current understanding of the underlying regulatory processes is incomplete. Recent Advances: Similar to reactive oxygen species and reactive nitrogen species, reactive sulfur species are now emerging as important signaling molecules, targeting regulatory cysteine redox switches in proteins, affecting gene regulation, ion transport, intermediary metabolism, and mitochondrial function. To rationalize the complexity of chemical interactions of reactive species with themselves and their targets and help define their role in systemic metabolic control, we here introduce a novel integrative concept defined as the reactive species interactome (RSI). The RSI is a primeval multilevel redox regulatory system whose architecture, together with the physicochemical characteristics of its constituents, allows efficient sensing and rapid adaptation to environmental changes and various other stressors to enhance fitness and resilience at the local and whole-organism level.

CRITICAL ISSUES

To better characterize the RSI-related processes that determine fluxes through specific pathways and enable integration, it is necessary to disentangle the chemical biology and activity of reactive species (including precursors and reaction products), their targets, communication systems, and effects on cellular, organ, and whole-organism bioenergetics using system-level/network analyses.

FUTURE DIRECTIONS

Understanding the mechanisms through which the RSI operates will enable a better appreciation of the possibilities to modulate the entire biological system; moreover, unveiling molecular signatures that characterize specific environmental challenges or other forms of stress will provide new prevention/intervention opportunities for personalized medicine. Antioxid. Redox Signal. 00, 000-000.

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.

Characterization of the electronic states of the biological relevant SSNO molecule

Using configuration interaction ab initio methods, we investigate the lowest electronic states of doublet and quartet spin multiplicities of SSNO where the one-dimensional cuts of the six-dimensional potential energy surfaces of these electronic states along the stretching and bending coordinates are computed. Mainly, these electronic states are found to be repulsive along the central SN distance. A high density of electronic states is computed even at low excitation energies that may favor their couplings. Therefore, the dynamics of the SSNO electronic states is expected to be very complex. We also characterized the bound electronic states spectroscopically where we derived their equilibrium structures and vibrational frequencies. Our calculations show the importance of taking into account of dynamical correlation, in addition to static correlation, for the accurate description of SSNO electronic excited states and more generally for those of R-NO molecular species. Finally, we highlighted the potential role of SSNO in light-induced NO delivery from SSNO related species in biological media.

Inorganic Reactive Sulfur-Nitrogen Species: Intricate Release Mechanisms or Cacophony in Yellow, Blue and Red?

Since the heydays of Reactive Sulfur Species (RSS) research during the first decade of the Millennium, numerous sulfur species involved in cellular regulation and signalling have been discovered. Yet despite the general predominance of organic species in organisms, recent years have also seen the emergence of inorganic reactive sulfur species, ranging from inorganic polysulfides (HS_x^-/S_x^2-) to thionitrous acid (HSNO) and nitrosopersulfide (SSNO^-). These inorganic species engage in a complex interplay of reactions in vitro and possibly also in vivo. Employing a combination of spectrophotometry and sulfide assays, we have investigated the role of polysulfanes from garlic during the release of nitric oxide (^•NO) from S-nitrosoglutathione (GSNO) in the absence and presence of thiol reducing agents. Our studies reveal a distinct enhancement of GSNO decomposition by compounds such as diallyltrisulfane, which is most pronounced in the presence of cysteine and glutathione and presumably proceeds via the initial release of an inorganic mono- or polysulfides, i.e., hydrogen sulfide (H₂S) or HS_x^-, from the organic polysulfane. Albeit being of a preliminary nature, our spectrophotometric data also reveals a complicated underlying mechanism which appears to involve transient species such as SSNO^-. Eventually, more in depth studies are required to further explore the underlying chemistry and wider biological and nutritional implications of this interplay between edible garlic compounds, reductive activation, inorganic polysulfides and their interplay with ^•NO storage and release.

Advances in spectroscopy and dynamics of small and medium sized molecules and clusters

Investigations of the spectroscopy and dynamics of small- and medium-sized molecules and clusters represent a hot topic in atmospheric chemistry, biology, physics, atto- and femto-chemistry and astrophysics.