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Reactive oxygen species (ROS) are important modulators of physiological signaling and play important roles in bone tissue regulation. Both reactive sulfur species (RSS) and reactive selenium species (RSeS) are involved in ROS signaling, and recent work suggests RSS and RSeS involvement in the regulation of bone homeostasis. For example, RSS can promote osteogenic differentiation and decrease osteoclast activity and differentiation, and the antioxidant activity of RSeS play crucial roles in balancing bone remodeling. Here, we outline current research progress on the application of RSS and RSeS in bone disease and regeneration. Focusing on these investigations, we highlight different methods, tools, and sources of RSS and RSeS, and we also highlight future opportunities for delivery of RSS and RSeS in biological environments relating to bone.

The short C–H(…)S contacts found in available structural data for both small molecules and larger biomolecular systems suggest that such contacts are an often overlooked yet important stabilizing interaction. Moreover, many of these short C–H(…)S contacts meet the definition of a hydrogen bonding interaction. Using available structural data from the Cambridge Structural Database (CSD), as well as selected examples from the literature in which important C–H(…)S contacts may have been overlooked, we highlight the generality of C–H(…)S hydrogen bonding as an important stabilizing interaction. To uncover and establish the generality of these interactions, we compare C–H(…)S contacts with other traditional hydrogen bond donors and acceptors as well as investigate how oxidation state, coordination number, and metal bonding affect the preferred geometry of interactions in the solid state. This work establishes that the C–H(…)S bond meets the definition of a hydrogen bond and serves as a guide to identify C–H(…)S hydrogen bonds in diverse systems.

Reactions of the electron rich PhB(tBuIm)3ZnCl complex with n-BuLi and [K.18-C-6]2[S4] lead to the formation of the carbon-rich coordination complex PhB(tBuIm)3ZnBu and the tetrahedral tetrasulfido complex PhB(tBuIm)2(tBuImH)Zn(κ2-S4), respectively.

Surfactants solubilize S8 in water and promote thiol-mediated reduction to form H2S. Anionic and cationic surfactants have different impacts on the resultant reactive sulfur species distribution.

Hydrogen selenide (H2Se) is a central metabolite in the biological processing of selenium for incorporation into selenoproteins, which play crucial antioxidant roles in biological systems. Despite being integral to proper physiological function, this reactive selenium species (RSeS) has received limited attention. We recently reported an early example of a H2Se donor (TDN1042) that exhibited slow, sustained release through hydrolysis. Here we expand that technology based on the P═Se motif to develop cyclic-PSe compounds with increased rates of hydrolysis and function through well-defined mechanisms as monitored by 31P and 77Se NMR spectroscopy. In addition, we report a colorimetric method based on the reaction of H2Se with NBD-Cl to generate NBD-SeH (λmax = 551 nm), which can be used to detect free H2Se. Furthermore, we use TOF-SIMS (time of flight secondary ion mass spectroscopy) to demonstrate that these H2Se donors are cell permeable and use this technique for spatial mapping of the intracellular Se content after H2Se delivery. Moreover, these H2Se donors reduce endogenous intracellular reactive oxygen species (ROS) levels. Taken together, this work expands the toolbox of H2Se donor technology and sets the stage for future work focused on the biological activity and beneficial applications of H2Se and related bioinorganic RSeS.

Hydrogen sulfide (H(2)S) is an endogenously produced gaseous signaling molecule with important roles in regulating organelle function and stress. Because of its high reactivity, targeted delivery of H(2)S using small molecule H(2)S donors has garnered significant interest to minimize off-target effects. Although mitochondrially-targeted H(2)S donors, such as AP39, have been reported previously and exhibit significantly higher potency than non-targeted donors, the expansion of targeted H(2)S delivery to other subcellular organelles remains largely absent. To fill this key unmet need, we report a library of organelle-targeted H(2)S donors that localize H(2)S delivery to specific subcellular organelles, including the Golgi apparatus, lysosome, endoplasmic reticulum, and mitochondria. We measured H(2)S production in vitro from each donor, confirmed the localization of H(2)S delivery using organelle-specific H(2)S responsive fluorescent probes, and demonstrated enhanced potency of these targeted H(2)S donors in providing protection against organelle-specific stress. We anticipate this class of targeted H(2)S donors will enable future studies of subcellular roles of H(2)S and the pathways by which H(2)S alleviates subcellular organelle stress.

Recent studies have highlighted how reactive sulfur species (RSS) can be regulated and transported by metal-sulfur coordination compounds. We report herein the reactivity of PhB(tBuIm)3NiCl (1) with RSS, including the hydrosulfide anion ([Bu4N][SH]) and a reduced tetrasulfide ([K18-C-6]2[S4]). The strongly donating tris(carbene) ligand in 1 is geometrically constrained to a tetrahedral geometry, and the energetically preferable square planar geometry is not achievable with the [PhB(tBuIm)3]- ligand. Upon reaction of 1 with [Bu4N][SH] and [K18-C-6]2[S4], the square planar complexes PhB(tBuIm)2(tBuImH)Ni(SH)2 (2) and PhB(tBuIm)2(tBuImH)Ni(η2-S2) (3) are formed, respectively, via the protonation of one carbene ligand donor atom. Mechanistic investigation suggest that protonation occurs either from decomposition of 1 during the reaction progress, reactions with advantageous [Bu4N]+/[K18-C-6]+ countercations or from the generation of transient unidentified RSS that facilitate proton transfer reactions.

Hydrogen sulfide (H(2)S) is an important biomolecule, and self-immolative thiocarbamates have shown great promise as triggerable H(2)S donors with suitable analogous control compounds, however thiocarbamates with electron-deficient payloads are less efficient H(2)S donors. We report here the synthesis and study of a series of N-methylated esterase-triggered thiocarbamates that block the postulated unproductive deprotonation-based pathway for these compounds. The relative reaction profiles for H(2)S release across a series of electron-rich and electron-poor N-Me aniline payloads are examined experimentally and computationally. We show that thiocarbamate N-methylation does block some side reactivity and increases the H(2)S release profiles for electron-poor donors. Additionally, we show that isothiocyanate release is not a competitive pathway, and rather that the reduced efficiency of electron-poor donors is likely due to other side reactions.

Hydrogen sulfide is a biologically important molecule and developing chemical tools that enable further investigations into the functions of H

Hydrogen sulfide (H2S) is an important biological signaling molecule and one of three established gasotransmitters. Upon oxidation, H2S can form reactive sulfur species (RSS) that play a central role in protein persulfidation. Here we report that a molybdenum tetrasulfide can react directly with hydrosulfide to form polysulfides and oxidize the Mo center. Specifically, [NBu4][TpMoS(S4)] reacts with 2 equiv of [NBu4][SH] to form [NBu4][TpMoS3]. Trapping experiments with BnBr confirm the formation of polysulfides, as evidenced by the direct trapping of Bn2S2. This work demonstrates new reaction pathways for H2S oxidation and RSS generation from metal-bound polysulfides that will increase our understanding of the potential roles that metals play in signaling processes.

Supramolecular chemistry provides an effective strategy for the molecular recognition of diverse molecules. Significant efforts to design synthetic hosts have enabled the successful binding of many types of guests; however, less is known about how host-guest environments influence binding. Herein, we present a comprehensive study in which we measure the host-guest binding of a bis(arylethynyl phenylurea) host with a chloride guest in eight solvents spanning

H2S is a well-known toxic gas and also a gaseous signaling molecule involved in many biological processes. Advanced chemical tools that can regulate H2S levels in vivo are useful for understanding H2S biology as well as its potential therapeutic effects. To this end, we have developed a series of 7-nitro-1,2,3-benzoxadiazole (NBD) amines as potential H2S scavengers. The kinetic studies of thiolysis reactions revealed that incorporation of positively-charged groups onto the NBD amines greatly increased the rate of the H2S-specific thiolysis reaction. We demonstrate that these reactions proceed effectively, with second order rate constants (k2) of >116 M−1 s−1 at 37 °C for NBD-S8. Additionally, we demonstrate that NBD-S8 can effectively scavenge enzymatically-produced and endogenous H2S in live cells. Furthering the biological significance, we demonstrate NBD-S8 mediates scavenging of H2S in mice., We demonstrate that positively-charged NBD amines can effectively scavenge biological H2S in live cells and in mice.

Significance: Hydrogen sulfide (H(2)S) is an important biological signaling molecule involved in many physiological processes. These diverse roles have led researchers to develop contemporary methods to deliver H(2)S under physiologically relevant conditions and in response to various stimuli. Recent Advances: Different small-molecule donors have been developed that release H(2)S under various conditions. Key examples include donors activated in response to hydrolysis, to endogenous species, such as thiols, reactive oxygen species, and enzymes, and to external stimuli, such as photoactivation and bio-orthogonal chemistry. In addition, an alternative approach to release H(2)S has utilized the catalyzed hydrolysis of carbonyl sulfide (COS) by carbonic anhydrase to generate libraries of activatable COS-based H(2)S donors. Critical Issues: Small-molecule H(2)S donors provide important research and pharmacological tools to perturb H(2)S levels. Key needs, both in the development and in the use of such donors, include access to new donors that respond to specific stimuli as well as donors with well-defined control compounds that allow for clear delineation of the impact of H(2)S delivery from other donor byproducts. Future Directions: The abundance of reported small-molecule H(2)S donors provides biologists and physiologists with a chemical toolbox to ask key biological questions and to develop H(2)S-related therapeutic interventions. Further investigation into different releasing efficiencies in biological contexts and a clear understanding of biological responses to donors that release H(2)S gradually (e.g., hours to days) versus donors that generate H(2)S quickly (e.g., seconds to minutes) is needed.

We report here that a fluorescent benzobisimidazolium salt (TBBI) can be used for the fluorescent and colorimetric detection of carbonyl sulfide (COS) over related heterocumulenes including CO(2) and CS(2) in wet MeCN. The reaction between TBBI and COS in the presence of fluoride yields a highly fluorescent (λ(em) = 354 nm) and colored product (λ(max) = 321, 621 nm), that is readily observed by the naked eye. We view these results as a first step toward developing activity-based probes for COS detection.

S/N crosstalk species derived from the interconnected reactivity of H

Hydrogen sulfide (H

Hydrogen sulfide (H2S) is an important biomolecule and significant efforts have focused on developing chemical tools to aid different biological investigations. Of such tools, there are relatively few chemiluminescent or bioluminescent methods for H2S detection. Here we report two dioxetane-based chemiluminescent probes for H2S detection. With these probes, we directly compare the probe response to H2S-mediated azide reduction and nucleophilic displacement of 2,4-dinitrophenyl (DNP) motifs and demonstrate that the SNAr cleavage of the DNP group results in a larger response and greater stability in water.

Persulfides (RSSH) are important reactive sulfur species (RSS) that are intertwined with the biological functions of hydrogen sulfide (H

Hydrogen selenide (H

Fluorophores are powerful tools for interrogating biological systems. Carbon nanotubes (CNTs) have long been attractive materials for biological imaging due to their near-infrared excitation and bright, tunable optical properties. The difficulty in synthesizing and functionalizing these materials with precision, however, has hampered progress in this area. Carbon nanohoops, which are macrocyclic CNT substructures, are carbon nanostructures that possess ideal photophysical characteristics of nanomaterials, while maintaining the precise synthesis of small molecules. However, much work remains to advance the nanohoop class of fluorophores as biological imaging agents. Herein, we report an intracellular targeted nanohoop. This fluorescent nanostructure is noncytotoxic at concentrations up to 50 μM, and cellular uptake investigations indicate internalization through endocytic pathways. Additionally, we employ this nanohoop for two-photon fluorescence imaging, demonstrating a high two-photon absorption cross-section (65 GM) and photostability comparable to a commercial probe. This work further motivates continued investigations into carbon nanohoop photophysics and their biological imaging applications.

We highlight a convenient synthesis to selectively deuterate an aryl C–H hydrogen bond donor in an arylethynyl bisurea supramolecular anion receptor and use the Perrin method of competitive titrations to study the deuterium equilibrium isotope effects (DEIE) of anion binding for HS−, Cl−, and Br−. This work highlights the utility and also challenges in using this method to determine EIE with highly reactive and/or weakly binding anions.

Hydrogen sulfide (H2S) is a biologically relevant molecule, and recent efforts have focused on developing small molecular donors that deliver H2S on demand. Acid-activated donors have garnered significant interest due to the potential application of such systems in myocardial ischemia injury or for suppressing tumor growth. In this work, we report a new strategy for tuning H2S delivery to a specific pH window. Specifically, we utilize self-immolative thiocarbamates with an imine-derived triggering group. After imine hydrolysis, the self-immolative decomposition releases carbonyl sulfide (COS), which is quickly hydrolyzed to H2S by carbonic anhydrase. Although acid-mediated hydrolysis results in imine cleavage, environments that are too acidic result in protonation of the aniline intermediate and results in inhibition of COS/H2S release. Taken together, this mechanism enables access to donor motifs that are only activated within specific pH windows. Here, we demonstrate the design, preparation, and pH eval...

We report here the first chiral barbiturate to act as a single-component LMOG capable of gelating a variety of chlorinated and aromatic solvents. Solution-based DOSY NMR experiments, solid-state VP-SEM, and X-ray crystallography techniques were used to characterize chloroform-based gels at a variety of size domains. This scaffold provides a simple system to study the dynamics of gelation and self-assembly.

Investigations into hydrogen sulfide (H2S) signaling pathways have demonstrated both the generation and importance of persulfides, which are reactive sulfur species that contain both reduced and oxidized sulfur. These observations have led researchers to suggest that oxidized sulfur species, including sulfane sulfur (S0), are responsible for many of the physiological phenomena initially attributed to H2S. A common method of introducing S0 to biological systems is the administration of organic polysulfides, such as diallyl trisulfide (DATS). However, prior reports have demonstrated that commercially-available DATS often contains a mixture of polysulfides, and furthermore a lack of structure-activity relationships for organic polysulfides has limited our overall understanding of different polysulfides and their function in biological systems. Advancing our interests in the chemical biology of reactive sulfur species including H2S and S0, we report here our investigations into the rates and quantities of H2S release from a series of synthetic, pure benzyl polysulfides, ranging from monosulfide to tetrasulfide. We demonstrate that H2S is only released from the trisulfide and tetrasulfide, and that this release requires thiol-mediated reduction in the presence of cysteine or reduced glutathione. Additionally, we demonstrate the different effects of trisulfides and tetrasulfides on cell proliferation in murine epithelial bEnd.3 cells.

Hydrogen sulfide (H(2)S) is an important gasotransmitter and biomolecule, and many synthetic small-molecule H(2)S donors have been developed for H(2)S-related research. One important class of triggerable H(2)S donors are self-immolative thiocarbamates, which function by releasing carbonyl sulfide (COS), which is rapidly converted to H(2)S by the ubiquitous enzyme carbonic anhydrase (CA). Prior studies of esterase-triggered thiocarbamate donors reported significant inhibition of mitochondrial bioenergetics and toxicity when compared to direct sulfide donors, suggesting that COS may function differently than H(2)S. Here, we report a suite of modular esterase-triggered self-immolative COS donors and include the synthesis, H(2)S release profiles, and cytotoxicity of the developed donors. We demonstrate that the rate of ester hydrolysis correlates directly with the observed cytotoxicity in cell culture, which further supports the hypothesis that COS functions as more than a simple H(2)S shuttle in certain biological systems.

Dithioesters have a rich history in polymer chemistry for RAFT polymerizations and are readily accessible through different synthetic methods. Here we demonstrate that the dithioester functional group is a tunable motif that releases H2S upon reaction with cysteine and that structural and electronic modifications enable the rate of cysteine-mediated H2S release to be modified. In addition, we use (bis)phenyl dithioester to carry out kinetic and mechanistic investigations, which demonstrate that the initial attack by cysteine is the rate-limiting step of the reaction. These insights are further supported by complementary DFT calculations. We anticipate that the results from these investigations will allow for the further development of dithioesters as important chemical motifs for studying H2S chemical biology.

Hydrogen sulfide (H2S) is an important cellular signaling molecule that exhibits promising protective effects. Although a number of triggerable H2S donors have been developed, spatiotemporal feedback from H2S release in biological systems remains a key challenge in H2S donor development. Herein we report the synthesis, evaluation, and application of caged sulfenyl thiocarbonates as new fluorescent H2S donors. These molecules rely on thiol cleavage of sulfenyl thiocarbonates to release carbonyl sulfide (COS), which is quickly converted to H2S by carbonic anhydrase (CA). This approach is a new strategy in H2S release and does not release electrophilic byproducts common from COS-based H2S releasing motifs. Importantly, the release of COS/H2S is accompanied by the release of a fluorescent reporter, which enables the real-time tracking of H2S by fluorescence spectroscopy or microscopy. Dependent on the choice of fluorophore, either one or two equivalents of H2S can be released, thus allowing for the dynamic range of the fluorescent donors to be tuned. We demonstrate that the fluorescence response correlates directly with quantified H2S release and also demonstrate the live-cell compatibility of these donors. Furthermore, these fluorescent donors exhibit anti-inflammatory effects in RAW 264.7 cells, indicating their potential application as new H2S-releasing therapeutics. Taken together, sulfenyl thiocarbonates provide a new platform for H2S donation and readily enable fluorescent tracking of H2S delivery in complex environments.

Selenium is essential to human physiology and has recently shown potential in the treatment of common pathophysiological conditions ranging from arsenic poisoning to cancer. Although the precise metabolic and chemical pathways of selenium incorporation into biomolecules remain somewhat unclear, many such pathways proceed through hydrogen selenide (H2Se/HSe-) formation. Despite this importance, well-characterized chemistry that enables H2Se release under controlled conditions remains lacking. Motivated by this need, we report here the development of a hydrolysis-based H2Se donor (TDN1042). Utilizing 31P and 77Se NMR experiments, we demonstrate the pH dependence of H2Se release and characterize observed reaction intermediates during the hydrolysis mechanism. Finally, we confirm H2Se release using electrophilic trapping reagents, which not only demonstrates the fidelity of this donor platform but also provides an efficient method for investigating future H2Se donor motifs. Taken together, this work provides an early example of an H2Se donor that functions through a well-defined and characterized mechanism.

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H(2)S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H(2)S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

Mechanical interlocking of a nanohoop fluorophore and a reactive thread couples the benefits of a reaction-based probe with a sterically congested active site for enhanced selectivity. Advantageously, the thread design uses dual function stoppers that act as both a quencher and a trigger for sensing. In progress toward expanding this approach to biologically relevant analytes, this system is used to demonstrate steric differentiation and provide a selective turn-on fluorescent response with size selectivity for HS(−) rather than larger thiolates.

We have prepared and characterized hydrosulfide-selective ChemFET devices based on a nitrile butadiene rubber membrane containing tetraoctylammonium nitrate as a chemical recognition element that is applied to commercially available field-effect transistors. The sensors have fast (120 s) reversible responses, selectivity over other biologically relevant thiol-containing species, detection limits of 8 mM, and a detection range from approximately 5 to 500 mM. Sensitivities are shown to be 53 mV per decade at pH 8. Use of this compact, benchtop sensor platform requires little training - only the ability to measure DC voltage, which can be accomplished with a conventional multimeter or a simple analog data acquisition device paired with a personal computer. To the best of our knowledge, this report describes the first example of direct potentiometric measurement of the hydrosulfide ion in water.

Hydrogen sulfide (H2S) is an important biomolecule that plays key signaling and protective roles in different physiological processes. With goals of advancing both the available research tools and the associated therapeutic potential of H2S, researchers have developed different methods to deliver H2S on demand in different biological contexts. A recent approach to develop such donors has been to design compounds that release carbonyl sulfide (COS), which is quickly converted to H2S in biological systems by the ubiquitous enzyme carbonic anhydrase (CA). Although highly diversifiable, many approaches using this general platform release quinone methides or related electrophiles after donor activation. Many such electrophiles are likely scavenged by water, but recent efforts have also expanded alternative approaches that minimize the formation of electrophilic byproducts generated after COS release. This mini-review focuses specifically on recent examples of COS-based H2S donors that do no generate quinone methide byproducts after donor activation.

A novel fluorescent probe design based on the interlocking of a reactive thread in a rigid nanohoop fluorophore is reported. This rotaxane design leads to size-selective sensing of thiolates in organic solution. More broadly, the work suggests the promise of mechanical interlocking to enhance the selectivity of reaction-based probes.

The article by Fan et al. inaccurately states that ProPerDP is inadequate for protein persulfide detection., The recent report by Fan et al. alleged that the ProPerDP method is inadequate for the detection of protein persulfidation. Upon careful evaluation of their work, we conclude that the claim made by Fan et al. is not supported by their data, rather founded in methodological shortcomings. It is understood that the ProPerDP method generates a mixture of cysteine-containing and non–cysteine-containing peptides. Instead, Fan et al. suggested that the detection of non–cysteine-containing peptides indicates nonspecific alkylation at noncysteine residues. However, if true, then such peptides would not be released by reduction and therefore not appear as products in the reported workflow. Moreover, the authors’ biological assessment of ProPerDP using Escherichia coli mutants was based on assumptions that have not been confirmed by other methods. We conclude that Fan et al. did not rigorously assess the method and that ProPerDP remains a reliable approach for analyses of protein per/polysulfidation.

Sulfur-based ligands are versatile donors that play important roles in a wide array of subdisciplines of inorganic chemistry including organometallic chemistry, bioinorganic chemistry, and cluster science. Despite the breadth of compounds containing sulfur-based ligands, those containing the simplest mercapto group, hydrosulfide ion (HS-), are significantly less developed. The acceptance of H2S/HS- as important biological signaling compounds during the last decade has engendered a renewed interest in the chemistry of these species. Bioinorganic reactivity of hydrosulfide, however, is only one aspect of its fascinating chemistry, much of which revolves around its interactions with transition metal ions. The coordination of HS- to d-block elements produces a unique class of substances that differ in significant ways from more ubiquitous metal thiolates. This review examines the preparation, structure, spectroscopy, and reactivity of such compounds and the roles they play across several fields of chemistry.

Supramolecular anion receptors can be used to study the molecular recognition properties of the reactive yet biologically-critical hydrochalcogenide anions (HCh(–)). Achieving selectivity for HCh(–) over the halides is challenging but is necessary for not only developing future supramolecular probes for HCh(–) binding and detection, but also for understanding the fundamental properties that govern these binding and recognition events. Here we demonstrate that linear free energy relationships (LFERs)—including Hammett and Swain-Lupton plots—reveal a clear difference in sensitivity to the polarity of an aryl C–H hydrogen bond (HB) donor for HS(–) over other HCh(–) and halides. Analysis using electrostatic potential maps highlights that this difference in sensitivity results from a preference of the aryl C–H HB donor for HS(–) in this host scaffold. From this study, we demonstrate that LFERs are a powerful tool to gain interpretative insight into motif design for future anion-selective supramolecular receptors and highlight the importance of C–H HB donors for HS(–) recognition. From our results, we suggest that aryl C–H HB donors should be investigated in the next generation of HS(–) selective receptors based on the enhanced HS(–) selectivity over other competing anions in this system.

The enzymatic conversion of carbonyl sulfide (COS) to hydrogen sulfide (H2S) by carbonic anhydrase has been used to develop self-immolating thiocarbamates as COS-based H2S donors to further elucidate the impact of reactive sulfur species in biology. The high modularity of this approach has provided a library of COS-based H2S donors that can be activated by specific stimuli. A common limitation, however, is that many such donors result in the intermediate formation of an electrophilic quinone methide byproduct during donor activation. As a mild alternative, we demonstrate here that dithiasuccinoyl groups can function as COS/H2S donor motifs and that these groups release two equivalents of COS/H2S and uncage an amine payload under physiologically relevant conditions. Additionally, we demonstrate that COS/H2S release from this donor motif can be altered by electronic modulation and alkyl substitution. These insights are further supported by DFT investigations, which reveal that aryl and alkyl thiocarbamates release COS with significantly different activation energies.

Manganese porphyrins (MnPs), MnTE-2-PyP5+, MnTnHex-2-PyP5+ and MnTnBuOE-2-PyP5+, are superoxide dismutase (SOD) mimetics and form a redox cycle between O2 and reductants, including ascorbic acid, ultimately producing hydrogen peroxide (H2O2). We previously found that MnPs oxidize hydrogen sulfide (H2S) to polysulfides (PS, H2Sn, n = 2&ndash, 6) in buffer. Here, we examine the effects of MnPs for 24 h on H2S metabolism and PS production in HEK293, A549, HT29 and bone marrow derived stem cells (BMDSC) using H2S (AzMC, MeRho-AZ) and PS (SSP4) fluorophores. All MnPs decreased intracellular H2S production and increased intracellular PS. H2S metabolism and PS production were unaffected by cellular O2 (5% versus 21% O2), H2O2 or ascorbic acid. We observed with confocal microscopy that mitochondria are a major site of H2S production in HEK293 cells and that MnPs decrease mitochondrial H2S production and increase PS in what appeared to be nucleoli and cytosolic fibrillary elements. This supports a role for MnPs in the metabolism of H2S to PS, the latter serving as both short- and long-term antioxidants, and suggests that some of the biological effects of MnPs may be attributable to sulfur metabolism.

Reactive sulfur species, including hydrogen sulfide (H2S), are important biological mediators and play key roles in different pathophysiological conditions. Small molecules that release H2S on demand, often referred to as "H2S donors," constitute a key investigative tool for H2S-related research. A significant challenge, however, is correlating the rate of H2S release from such donors in complex systems with biological outcomes, because release rates are commonly perturbed by different biological environments. In this chapter, we outline an approach to use H2S donors that provide a fluorescent response upon H2S release to address this problem. These compounds leverage the intermediate release of carbonyl sulfide (COS), which is quickly converted to H2S by the endogenous enzyme carbonic anhydrase (CA), to provide activatable donors with an optical response. The described donors are activated by biological thiols and provide a fluorescence response that correlates directly with H2S delivery, which allows for delivered H2S levels to be measured in real time by fluorescence techniques.

Native chemical ligation (NCL) is a simple, widely used, and powerful synthetic tool to ligate N-terminal cysteine residues and C-terminal α-thioesters via a thermodynamically stable amide bond. Building on this well-established reactivity, as well as advancing our interests in the chemical biology of reactive sulfur species including hydrogen sulfide (H2S), we hypothesized that thionoesters, which are constitutional isomers of thioesters, would undergo a similar NCL reaction in the presence of cysteine to release H2S under physiological conditions. Herein, we report mechanistic and kinetic investigations into cysteine-mediated H2S release from thionoesters. We found that this reaction proceeds with high H2S-releasing efficiency (∼80%) and with a rate constant (9.1 ± 0.3 M–1 s–1) comparable to that for copper-catalyzed azide–alkyne cycloadditions (CuAAC). Additionally, we found that the final product of the reaction of cysteine with thionoesters results in the formation of a stable dihydrothiazole, which ...

Hydrogen sulfide (H2 S) is a biologically active molecule that exhibits protective effects in a variety of physiological and pathological processes. Although several H2 S-related biological effects have been discovered by using H2 S donors, knowing how much H2 S has been released from donors under different conditions remains challenging. Now, a series of γ-ketothiocarbamate (γ-KetoTCM) compounds that provide the first examples of colorimetric H2 S donors and enable direct quantification of H2 S release, were reported. These compounds are activated through a pH-dependent deprotonation/β-elimination sequence to release carbonyl sulfide (COS), which is quickly converted into H2 S by carbonic anhydrase. The p-nitroaniline released upon donor activation provides an optical readout that correlates directly to COS/H2 S release, thus enabling colorimetric measurement of H2 S donation.