Kinetics and mechanism of the reaction of hydrogen sulfide with diaquacobinamide in aqueous solution

High Reactivity of Supermolecular Nanoentities of a Vitamin B12 Derivative in Langmuir-Schaefer Films Toward Gaseous Toxins

Recently, we have described the first supermolecular nanoentities (SMEs) of a vitamin B12 derivative, viz., a monocyano form of heptabutyl cobyrinate ((CN-)BuCby), unique nanoparticles with strong noncovalent intermolecular interactions, and emerging optical and redox properties. In this work, the fast response of thin films based on the SMEs of the B12 derivative to gaseous toxins (viz., hydrogen cyanide, ammonia, sulfur dioxide, and hydrogen sulfide) particularly dangerous for humans was demonstrated. The reaction between SMEs of (CN-)BuCby in Langmuir-Schaefer (LS) films and HCN generates dicyano species and proceeds ca. 5-fold more rapidly than the process involving drop-coated films that contain (CN-)BuCby in molecular form. The highest sensitivity toward HCN was achieved by using thicker LS films. The reaction proceeds reversibly: upon exposure to air, the dicyano complex undergoes partial decyanation. The decyanated complex retains reactivity toward HCN for at least four subsequent cycles. The processes involving SMEs of (CN-)BuCby and NH3, SO2, and H2S are irreversible, and the sensitivity of the films toward these gases is lower in comparison with HCN. Presented data provides mechanistic information on the reactions involving solid vitamin B12 derivatives and gaseous toxins. In the case of NH3, deprotonation of the coordinated Co(III)-ion water molecule occurs, and the generated hydroxocyano species exhibit high air stability. After binding of SO2, a mixture of sulfito and dicyano species is produced, and the regenerated film contains aquacyano and diaqua or aquahydroxo species, which possess high reactivity toward gaseous toxins. Reaction with H2S produces a mixture of the Co(III)-dicyano form and Co(II)-species containing sulfide oxidation products, which are resistant to aerobic oxidation. Our findings can be used for the development of naked-eye, electronic optic, and chemiresistive sensors toward gaseous toxins with improved reactivity for prompt cyanide detection in air, blood, and plant samples and for analysis of exhaled gases for the diagnosis of diseases.

The inorganic chemistry of the cobalt corrinoids - an update

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B₁₂, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B₁₂-dependent enzymes is also given for the reader's convenience.

The vitamin B12 analog cobinamide ameliorates azide toxicity in cells, Drosophila melanogaster, and mice

CONTEXT

The azide anion (N3-) is highly toxic. It exists most commonly as sodium azide, which is used widely and is readily available, raising the potential for occupational incidents and use as a weapon of mass destruction. Azide-poisoned patients present with vomiting, seizures, hypotension, metabolic acidosis, and coma; death can occur. No specific azide antidote exists, with treatment being solely supportive. Azide inhibits mitochondrial cytochrome c oxidase and is likely oxidized to nitric oxide in vivo. Cytochrome c oxidase inhibition depletes intracellular adenosine triphosphate and increases oxidative stress, while increased nitric oxide causes hypotension and exacerbates oxidative damage. Here, we tested whether the cobalamin (vitamin B12) analog cobinamide, a strong and versatile antioxidant that also neutralizes nitric oxide, can reverse azide toxicity in mammalian cells, Drosophila melanogaster, and mice.

RESULTS

We found cobinamide bound azide with a moderate affinity (Ka 2.87 × 105 M-1). Yet, cobinamide improved growth, increased intracellular adenosine triphosphate, and reduced apoptosis and malondialdehyde, a marker of oxidative stress, in azide-exposed cells. Cobinamide rescued Drosophila melanogaster and mice from lethal exposure to azide and was more effective than hydroxocobalamin. Azide likely generated nitric oxide in the mice, as evidenced by increased serum nitrite and nitrate, and reduced blood pressure and peripheral body temperature in the animals; the reduced temperature was likely due to reflex vasoconstriction in response to the hypotension. Cobinamide improved recovery of both blood pressure and body temperature.

CONCLUSION

We conclude cobinamide likely acted by neutralizing both oxidative stress and nitric oxide, and that it should be given further consideration as an azide antidote.

Supermolecular Nanoentities of Vitamin B12 Derivative as a Link in the Evolution of the Parent Molecules During Self-Assembly at the Air-Water Interface

Nanoarchitectures with promising properties have now been formed from many important biomolecules. However, the preparation of nanoparticles of vitamin B₁₂ and its derivatives remains an ongoing research challenge. This paper describes the formation of supermolecular nanoentities (SMEs) of vitamin B₁₂ derivatives, unique nanoparticles with strong noncovalent intermolecular interactions, emerging properties, and activity. These were created by a nanoarchitectonic approach using directed assembly of layers at the air-water interface as a link in the chain of evolution of the parent molecules under specially created conditions. Such layers can be represented as a nanocosm, where, at a critical density, the assemblies act as nanoreactors in which the transformation of the original material occurs. The discovered SMEs not only replicate the functioning of vitamin B₁₂ assemblies with proteins in living organisms and act as vitamin B₁₂-depended enzymes but also demonstrate important advantages over vitamin B₁₂. They are more efficient in oxygen reduction/evolution reactions and in transformation into other forms. These SMEs, in performing advanced tasks, are an alternative to widely used materials based on noble metals for catalysis, medicine, and environment protection. Our findings open new perspectives both for the fabrication of novel SMEs of biomolecules and for a better understanding of the evolution of biomolecules in nature.

Differences in the Formation of Reactive Oxygen Species and Their Cytotoxicity between Thiols Combined with Aqua- and Cyanocobalamins

Cobalamin is an essential nutrient required for the normal functioning of cells. Its deficiency can lead to various pathological states. Hydroxocobalamin (HOCbl) and cyanocobalamin (CNCbl) are the forms of vitamin B12 that are most commonly used for supplementation. There is substantial evidence indicating that cobalamins can both suppress and promote oxidative stress; however, the mechanisms underlying these effects are poorly understood. Here, it was shown that the oxidation of thiols catalyzed by HOCbl and CNCbl is accompanied by reactive oxygen species (ROS) production and induces, under certain conditions, oxidative stress and cell death. The form of vitamin B12 and the structure of thiol play a decisive role in these processes. It was found that the mechanisms and kinetics of thiol oxidation catalyzed by HOCbl and CNCbl differ substantially. HOCbl increased the rate of oxidation of thiols to a greater extent than CNCbl, but quenched ROS in combination with certain thiols. Oxidation catalyzed by CNCbl was generally slower. Yet, the absence of ROS quenching resulted in their higher accumulation. The aforementioned results might explain a more pronounced cytotoxicity induced by combinations of thiols with CNCbl. On the whole, the data obtained provide a new insight into the redox processes in which cobalamins are involved. Our results might also be helpful in developing new approaches to the treatment of some cobalamin-responsive disorders in which oxidative stress is an important component.

Versatile Enzymology and Heterogeneous Phenotypes in Cobalamin Complementation Type C Disease

Nutritional deficiency and genetic errors that impair the transport, absorption, and utilization of vitamin B₁₂ (B₁₂) lead to hematological and neurological manifestations. The cblC disease (cobalamin complementation type C) is an autosomal recessive disorder caused by mutations and epi-mutations in the MMACHC gene and the most common inborn error of B₁₂ metabolism. Pathogenic mutations in MMACHC disrupt enzymatic processing of B₁₂, an indispensable step before micronutrient utilization by the two B₁₂-dependent enzymes methionine synthase (MS) and methylmalonyl-CoA mutase (MUT). As a result, patients with cblC disease exhibit plasma elevation of homocysteine (Hcy, substrate of MS) and methylmalonic acid (MMA, degradation product of methylmalonyl-CoA, substrate of MUT). The cblC disorder manifests early in childhood or in late adulthood with heterogeneous multi-organ involvement. This review covers current knowledge on the cblC disease, structure–function relationships of the MMACHC protein, the genotypic and phenotypic spectra in humans, experimental disease models, and promising therapies.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Methyl mercaptan gas: mechanisms of toxicity and demonstration of the effectiveness of cobinamide as an antidote in mice and rabbits

CONTEXT

Methyl mercaptan (CH₃SH) is a colorless, toxic gas with potential for occupational exposure and used as a weapon of mass destruction. Inhalation at high concentrations can result in dyspnea, hypoventilation, seizures, and death. No specific methyl mercaptan antidote exists, highlighting a critical need for such an agent. Here, we investigated the mechanism of CH₃SH toxicity, and rescue from CH₃SH poisoning by the vitamin B₁₂ analog cobinamide, in mammalian cells. We also developed lethal CH₃SH inhalation models in mice and rabbits, and tested the efficacy of intramuscular injection of cobinamide as a CH₃SH antidote.

RESULTS

We found that cobinamide binds to CH₃SH (K_d = 84 µM), and improved growth of cells exposed to CH₃SH. CH₃SH reduced cellular oxygen consumption and intracellular ATP content and activated the stress protein c-Jun N-terminal kinase (JNK); cobinamide reversed these changes. A single intramuscular injection of cobinamide (20 mg/kg) rescued 6 of 6 mice exposed to a lethal dose of CH₃SH gas, while all six saline-treated mice died (p = 0.0013). In rabbits exposed to CH₃SH gas, 11 of 12 animals (92%) treated with two intramuscular injections of cobinamide (50 mg/kg each) survived, while only 2 of 12 animals (17%) treated with saline survived (p = 0.001).

CONCLUSION

We conclude that cobinamide could potentially serve as a CH₃SH antidote.

Bioinformatic and chemoneurocytological analysis of the pharmacological properties of vitamin B12 and some of its derivatives

More than three thousand five hundred biological properties of vitamin B[Formula: see text] and four of its derivatives (aquacobalamin, cyanoaquacobyrinic acid heptamethyl ester, dicyanocobyrinic acid heptamethyl ester and stable yellow corrinoid) have been assessed by bioinformation analysis. Based on the data obtained (including the assessments of the interaction of molecules with the proteins of rat proteome), conclusions were drawn about the potential effects and safety of the investigated substances. In particular, it has been shown that heptamethyl esters of cyanoaquacobyrinic and dicyanocobyrinic acids, as well as a stable yellow corrinoid (antivitamin), can be recommended for further study as analgesics, anti-inflammatory drugs and, also, antitumor agents aimed at the therapy of glioblastoma, hepatoblastoma and T-cell leukemia. Estimates of the LD50 constants for rats and the TD50 and IC50 constants for rat muscle cells in culture, along with the results of assessments of the interaction of molecules with the rat proteome, showed that all the compounds studied were of low toxicity. At the same time, cyanocobalamin and aquacobalamin are distinguished by the least cumulative properties in comparison with other studied compounds. Chemoneurocytological analysis of compounds showed that cyanocobalamin and aquacobalamin may have the greatest neuroprotective effects: increase in the concentration of the substances by 1 mmol/l causes the estimate of neuronal survival to increase by 25%.

Intramuscular cobinamide as an antidote to methyl mercaptan poisoning

BACKGROUND

Methyl mercaptan occurs naturally in the environment and is found in a variety of occupational settings, including the oil, paper, plastics, and pesticides industries. It is a toxic gas and deaths from methyl mercaptan exposure have occurred. The Department of Homeland Security considers it a high threat chemical agent that could be used by terrorists. Unfortunately, no specific treatment exists for methyl mercaptan poisoning.

METHODS

We conducted a randomized trial in 12 swine comparing no treatment to intramuscular injection of the vitamin B₁₂ analog cobinamide (2.0 mL, 12.5 mg/kg) following acute inhalation of methyl mercaptan gas. Physiological and laboratory parameters were similar in the control and cobinamide-treated groups at baseline and at the time of treatment.

RESULTS

All six cobinamide-treated animals survived, whereas only one of six control animals lived (17% survival) (p = 0.0043). The cobinamide-treated animals returned to a normal breathing pattern by 3.8 ± 1.1 min after treatment (mean ± SD), while all but one animal in the control group had intermittent gasping, never regaining a normal breathing pattern. Blood pressure and arterial oxygen saturation returned to baseline values within 15 minutes of cobinamide-treatment. Plasma lactate concentration increased progressively until death (10.93 ± 6.02 mmol [mean ± SD]) in control animals, and decreased toward baseline (3.79 ± 2.93 mmol [mean ± SD]) by the end of the experiment in cobinamide-treated animals.

CONCLUSION

We conclude that intramuscular administration of cobinamide improves survival and clinical outcomes in a large animal model of acute, high dose methyl mercaptan poisoning.

Intramuscular aminotetrazole cobinamide as a treatment for inhaled hydrogen sulfide poisoning in a large swine model

Hydrogen sulfide (H₂ S), a high-threat chemical agent, occurs naturally in a variety of settings. Despite multiple incidents of exposures and deaths, no FDA-approved antidote exists. A rapid-acting, easy to administer antidote is needed. We conducted a randomized control trial in swine comparing intramuscular administration of aminotetrazole cobinamide (2.9 mL, 18 mg/kg) to no treatment following inhalation of H₂ S gas. We found that aminotetrazole cobinamide administered 2 min after the onset of respiratory depression-defined as a tidal volume of less than 3 mL/kg for 2 consecutive minutes-yielded 100% survival, while all control animals died. Respiratory depression resolved in the treatment group within 3.6 ± 1.5 min (mean ± SD) of cobinamide administration, whereas control animals had intermittent gasping until death. Blood pressure and arterial oxygen saturation (SO₂ ) returned to baseline values within 5 and 10 min, respectively, of cobinamide treatment, and plasma lactate concentration decreased to less than 50% of the highest value by the end of the experiment. In control animals, plasma lactate rose continuously until death. We conclude that intramuscular aminotetrazole cobinamide is effective in a large animal, inhalational model of acute, severe H₂ S poisoning.

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.

Reactivity of Small Oxoacids of Sulfur

Oxidation of sulfide to sulfate is known to consist of several steps. Key intermediates in this process are the so-called small oxoacids of sulfur (SOS)—sulfenic HSOH (hydrogen thioperoxide, oxadisulfane, or sulfur hydride hydroxide) and sulfoxylic S(OH)₂ acids. Sulfur monoxide can be considered as a dehydrated form of sulfoxylic acid. Although all of these species play an important role in atmospheric chemistry and in organic synthesis, and are also invoked in biochemical processes, they are quite unstable compounds so much so that their physical and chemical properties are still subject to intense studies. It is well-established that sulfoxylic acid has very strong reducing properties, while sulfenic acid is capable of both oxidizing and reducing various substrates. Here, in this review, the mechanisms of sulfide oxidation as well as data on the structure and reactivity of small sulfur-containing oxoacids, sulfur monoxide, and its precursors are discussed.

Hydrogen Sulfide Toxicity: Mechanism of Action, Clinical Presentation, and Countermeasure Development

INTRODUCTION

Hydrogen sulfide (H₂S) is found in various settings. Reports of chemical suicide, where individuals have combined readily available household chemicals to produce lethal concentrations of H₂S, have demonstrated that H₂S is easily produced. Governmental agencies have warned of potential threats of use of H₂S for a chemical attack, but currently there are no FDA-approved antidotes for H₂S. An ideal antidote would be one that is effective in small volume, readily available, safe, and chemically stable. In this paper we performed a review of the available literature on the mechanism of toxicity, clinical presentation, and development of countermeasures for H₂S toxicity.

DISCUSSION

In vivo, H₂S undergoes an incomplete oxidation after an exposure. The remaining non-oxidized H₂S is found in dissolved and combined forms. Dissolved forms such as H₂S gas and sulfhydryl anion can diffuse between blood and tissue. The combined non-soluble forms are found as acid-labile sulfides and sulfhydrated proteins, which play a role in toxicity. Recent countermeasure development takes into account the toxicokinetics of H₂S. Some countermeasures focus on binding free hydrogen sulfide (hydroxocobalamin, cobinamide); some have direct effects on the mitochondria (methylene blue), while others work by mitigating end organ damage by generating other substances such as nitric oxide (NaNO2).

CONCLUSION

H₂S exists in two main pools in vivo after exposure. While several countermeasures are being studied for H₂S intoxication, a need exists for a small-volume, safe, highly effective antidote with a long shelf life to treat acute toxicity as well as prevent long-term effects of exposure.

Synthesis of vitamin B12 derivatives with sodium hydroxymethanesulfinate

The reaction of cyanocobalamin (CNCbl) with sodium hydroxymethanesulfinate (HMS) was studied over a wide range of pH (4–11) under aerobic conditions. CNCbl is destroyed in the presence of HMS in aqueous solution to form uncolored substances. The accumulation of stable yellow corrinoids (SYCs) preceded these changes at pH [Formula: see text] 8. The major stable yellow corrinoid is (15R)-Co[Formula: see text], Coß — dicyano-13-dehydro-15-hydro-l5-hydroxycob(III)alamin. The yield of this SYC is 25%, and the stability of this compound decreases significantly with increasing concentrations of HMS, pH and temperature.

Cobinamide is effective for treatment of hydrogen sulfide-induced neurological sequelae in a mouse model

Hydrogen sulfide (H₂ S) is a highly neurotoxic gas. Acute exposure can lead to neurological sequelae among survivors. A drug for treating neurological sequelae in survivors of acute H₂ S intoxication is needed. Using a novel mouse model we evaluated the efficacy of cobinamide (Cob) for increasing survival of, and reducing neurological sequalae in, mice exposed to sublethal doses of H₂ S. There were two objectives: (1) to determine the dose-response efficacy of Cob and (2) to determine the effective therapeutic time window of Cob. To explore objective 1, mice were injected intramuscularly with Cob at 0, 50, or 100 mg/kg at 2 min after H₂ S exposure. For objective 2, mice were injected intramuscularly with 100 mg/kg Cob at 2, 15, and 30 min after H₂ S exposure. For both objectives, mice were exposed to 765 ppm of H₂ S gas. Cob significantly reduced H₂ S-induced lethality in a dose-dependent manner (P < 0.05). Cob-treated mice exhibited significantly fewer seizures and knockdowns compared with the H₂ S-exposed group. Cob also reversed H₂ S-induced weight loss, behavioral deficits, neurochemical changes, cytochrome c oxidase enzyme inhibition, and neurodegeneration in a dose- and time-dependent manner (P < 0.01). Overall, these findings show that Cob increases survival and is neuroprotective in a mouse model of H₂ S-induced neurological sequelae.

Efficacy of Intravenous Cobinamide Versus Hydroxocobalamin or Saline for Treatment of Severe Hydrogen Sulfide Toxicity in a Swine (Sus scrofa) Model

BACKGROUND

Hydrogen sulfide (H₂ S) is a potentially deadly gas that naturally occurs in petroleum and natural gas. The Occupational Health and Safety Administration cites H₂ S as a leading cause of workplace gas inhalation deaths. Mass casualties of H₂ S toxicity may be caused by exposure from industrial accidents or release from oil field sites. H₂ S is also an attractive terrorism tool because of its high toxicity and ease with which it can be produced. Several potential antidotes have been proposed for hydrogen sulfide poisoning but none have been completely successful.

OBJECTIVE

The objective was to compare treatment response assessed by the time to spontaneous ventilation among groups of swine with acute H₂ S-induced apnea treated with intravenous (IV) cobinamide (4 mg/kg in 0.8 mL of 225 mmol/L solution), IV hydroxocobalamin (4 mg/kg in 5 mL of saline), or saline alone.

METHODS

Twenty-four swine (45-55 kg) were anesthetized, intubated, and instrumented with continuous femoral and pulmonary artery pressure monitoring. After stabilization, anesthesia was adjusted such that animals would spontaneously ventilate with an FiO₂ of 0.21. Sodium hydrosulfide (NaHS; concentration of 8 mg/mL) was begun at 1 mg/kg/min until apnea was confirmed for 20 seconds by capnography. This infusion rate was sustained for 1.5 minutes postapnea and then decreased to a maintenance rate for the remainder of the study to replicate sustained clinical exposure. Animals were randomly assigned to receive cobinamide (4 mg/kg), hydroxocobalamin (4 mg/kg), or saline and monitored for 60 minutes beginning 1 minute postapnea. G* power analysis using the Z-test determined that equal group sizes of eight animals were needed to achieve a power of 80% in detecting a 50% difference in return to spontaneous ventilations at α = 0.05.

RESULTS

There were no significant differences in baseline variables. Moreover, there were no significant differences in the mg/kg dose of NaHS (5.6 mg/kg; p = 0.45) required to produce apnea. Whereas all of the cobinamide-treated animals survived (8/8), none of the control (0/8) or hydroxocobalamin (0/8)-treated animals survived. Mean (±SD) time to spontaneous ventilation in the cobinamide-treated animals was 3.2 (±1.1) minutes.

CONCLUSIONS

Cobinamide successfully rescued the severely NaHS-poisoned swine from apnea in the absence of assisted ventilation.

Comparative studies of reaction of cobalamin (II) and cobinamide (II) with sulfur dioxide

The kinetics of reactions of cobalamin (II) and cobinamide (II) with sulfur dioxide was studied by UV-visible (UV-vis) spectroscopy. Reaction results in oxidation of Co(II) center and involves two aquated SO₂ moieties. The final product is suggested to be complex Co(III)-S₂O ₄^•- . The absence of corrin ring modifications during the reactions was proved.

Possible Involvement of Hydrosulfide in B12-Dependent Methyl Group Transfer

Evidence from several fields of investigation lead to the hypothesis that the sulfur atom is involved in vitamin B₁₂-dependent methyl group transfer. To compile the evidence, it is necessary to briefly review the following fields: methylation, the new field of sulfane sulfur/hydrogen sulfide (S°/H₂S), hydrosulfide derivatives of cobalamins, autoxidation of hydrosulfide radical, radical S-adenosylmethionine methyl transfer (RSMT), and methionine synthase (MS). Then, new reaction mechanisms for B₁₂-dependent methyl group transfer are proposed; the mechanisms are facile and overcome difficulties that existed in previously-accepted mechanisms. Finally, the theory is applied to the effect of S°/H₂S in nerve tissue involving the “hypomethylation theory” that was proposed 50 years ago to explain the neuropathology resulting from deficiency of vitamin B₁₂ or folic acid. The conclusions are consistent with emerging evidence that sulfane sulfur/hydrogen sulfide may be beneficial in treating Alzheimer’s disease.

Development of a Hydrogen Sulfide End-of-Service-Life Indicator for Respirator Cartridges Using Cobinamide

An inexpensive paper-based sensor was developed for detecting low ppm concentrations of hydrogen sulfide gas. A piece of filter paper containing aquohydroxocobinamide [OH(H2O)Cbi] was placed on the end of a bifurcated optical fiber, and the reflectance spectrum of the OH(H2O)Cbi was monitored during exposure to 10.0 ppm hydrogen sulfide gas (NIOSH recommended exposure limit). Reaction of sulfide (HS-) yielded an increase in reflectance from 400-450 nm, and decrease from 470-550 nm. Spectral changes were monitored as a function of time at 25, 50, and 85% relative humidity. Spectral shifts at high-er humidity suggested reduction of the Cbi(III) compound. The sensor was used to detect hydrogen sulfide breakthrough from respirator carbon beds and results correlated well with a standard electrochemical detector. The simple paper-based sensor could provide a real-time end-of-service-life alert for hydrogen sulfide gas.

Hydrogen Sulfide--Mechanisms of Toxicity and Development of an Antidote

Hydrogen sulfide is a highly toxic gas—second only to carbon monoxide as a cause of inhalational deaths. Its mechanism of toxicity is only partially known, and no specific therapy exists for sulfide poisoning. We show in several cell types, including human inducible pluripotent stem cell (hiPSC)-derived neurons, that sulfide inhibited complex IV of the mitochondrial respiratory chain and induced apoptosis. Sulfide increased hydroxyl radical production in isolated mouse heart mitochondria and F₂-isoprostanes in brains and hearts of mice. The vitamin B₁₂ analog cobinamide reversed the cellular toxicity of sulfide, and rescued Drosophila melanogaster and mice from lethal exposures of hydrogen sulfide gas. Cobinamide worked through two distinct mechanisms: direct reversal of complex IV inhibition and neutralization of sulfide-generated reactive oxygen species. We conclude that sulfide produces a high degree of oxidative stress in cells and tissues, and that cobinamide has promise as a first specific treatment for sulfide poisoning.

Development of a cobinamide-based end-of-service-life indicator for detection of hydrogen cyanide gas

We describe an inexpensive paper-based sensor for rapid detection of low concentrations (ppm) of hydrogen cyanide gas. A piece of filter paper pre-spotted with a dilute monocyanocobinamide [CN(H₂O)Cbi] solution was placed on the end of a bifurcated optical fiber and the reflectance spectrum of the CN(H₂O)Cbi was monitored during exposure to 1.0-10.0 ppm hydrogen cyanide gas. Formation of dicyanocobinamide yielded a peak at 583 nm with a simultaneous decrease in reflectance from 450-500 nm. Spectral changes were monitored as a function of time at several relative humidity values: 25, 50, and 85% relative humidity. With either cellulose or glass fiber papers, spectral changes occurred within 10 s of exposure to 5.0 ppm hydrogen cyanide gas (NIOSH recommended short-term exposure limit). We conclude that this sensor could provide a real-time end-of-service-life alert to a respirator user.