The Cyanoketenyl Anion [NC3O]. Angew Chem Int Ed Engl 2024;63:e202403766. [PMID: 38470943 DOI: 10.1002/anie.202403766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Cumulenes and heterocumulenes with three or more cumulative multiple bonds are usually reactive species that serve as valuable building blocks for more complex molecules but tend to isomerize or cyclize and therefore are difficult to isolate. Using a mild ligand exchange reaction at the carbon in α-metalated ylides, we have now succeeded in the synthesis and gram-scale isolation of the elusive cyanoketenyl anion [NC3O]-. Despite its assumed cumulene-like structure and the delocalization of the negative charge across the whole 5-atom molecule, it features a bent geometry with a nucleophilic central carbon atom. Computational studies reveal an ambiguous bonding situation in the anion, which can be illustrated only by a combination of different resonance structures. Nonetheless, the anion features remarkable stability, thus allowing the storage of its potassium-crown ether salt and its application as a highly functional synthetic building block. The cyanoketenyl anion readily reacts with a series of small molecules to form more complex organic compounds, including industrially valuable compounds such as cyanoacetate. This work demonstrated that reactive species can be generated by novel synthesis methods and open up atom-economic pathways to complex compounds from small abundant molecules.

Folate-conjugated organic CO prodrugs: Synthesis and CO release kinetic studies

Carbon monoxide (CO) is an endogenous produced molecule and has shown efficacy in animal models of inflammation, organ injury, colitis and cancer metastasis. Because of its gaseous nature, there is a need for developing efficient CO delivery approaches, especially those capable of targeted delivery. In this study, we aim to take advantage of a previously reported approach of enrichment-triggered prodrug activation to achieve targeted delivery by targeting the folate receptor. The general idea is to exploit folate receptor-mediated enrichment as a way to accelerate a biomolecular Diels-Alder reaction for prodrug activation. In doing so, we first need to find ways to tune the reaction kinetics in order to ensure minimal rection without enrichment and optimal activation upon enrichment. In this feasibility study, we synthesized two diene-dienophile pairs and studied their reaction kinetics and ability to target the folate receptor. We found that folate conjugation significantly affects the reaction kinetics of the original diene-dienophile pairs. Such information will be very useful in future designs of similar targeted approaches of CO delivery.

Deoxygenative Coupling of CO with a Tetrametallic Magnesium Hydride Complex

Addition of CO to a tetrametallic magnesium hydride cluster results in both carbon-carbon bond formation and deoxygenation to generate an acetaldehyde enolate [C2OH3]- which remains coordinated to the cluster. To the best of our knowledge, this is the first example of formation of an isolable complex containing an [C2OH3]- fragment from reaction of CO with a metal hydride, and the first example of CO homologation and deoxygenation at a main group metal. DFT studies suggest that key steps in the mechanism involve nucleophilic attack of an oxymethylene on a formyl ligand to generate an unstable [C2O2H3]3- fragment, which undergoes subsequent deoxygenation.

Association Between Maternal Prenatal Exposure to Household Air Pollution and Child Respiratory Health: A Systematic Review and Meta-analysis

Maternal prenatal exposure to household air pollution (HAP) is a critical public health concern with potential long-term implications for child respiratory health. The objective of this study is to assess the level of association between prenatal household air pollution and child respiratory health, and to identify which HAP pollutants are associated with specific respiratory illnesses or symptoms and to what degree. Relevant studies were retrieved from PubMed databases up to April 27, 2010, and their reference lists were reviewed. Random effects models were applied to estimate summarized relative risks (RRs) and 95% confidence intervals (CIs). The analysis involved 11 studies comprising 387 767 mother-child pairs in total, assessing various respiratory health outcomes in children exposed to maternal prenatal HAP. Children with prenatal exposure to HAP pollutants exhibited a summary RR of 1.26 (95% CI=1.08-1.33) with moderate between-study heterogeneity (I²=49.22%) for developing respiratory illnesses. Specific associations were found between prenatal exposure to carbon monoxide (CO) (RR=1.11, 95% CI: 1.09-1.13), Nitrogen Oxides (NOx) (RR=1.46, 95% CI: 1.09-1.60), and particulate matter (PM) (RR=1.26, 95% CI: 1.2186-1.3152) and child respiratory illnesses (all had I² close to 0%, indicating no heterogeneity). Positive associations with child respiratory illnesses were also found with ultrafine particles (UFP), polycyclic aromatic hydrocarbons (PAH), and ozone (O3). However, no significant association was observed for prenatal exposure to sulfur dioxide (SO2). In summary, maternal prenatal exposure to HAP may contribute to a higher risk of child respiratory health issues, emphasizing the need for interventions to reduce this exposure during pregnancy. Targeted public health strategies such as improved ventilation, cleaner cooking technologies, and awareness campaigns should be implemented to minimize adverse respiratory effects on children.

Pediatric Polytrauma Fire Victim Simulation

Introduction

Pediatric trauma has long been one of the primary contributors to pediatric mortality. There are multiple cases in the literature involving cyanide (CN) toxicity, carbon monoxide (CO) toxicity, and smoke inhalation with thermal injury, but none in combination with mechanical trauma.

Methods

In this 45-minute simulation case, emergency medicine residents and fellows were asked to manage a pediatric patient with multiple life-threatening traumatic and metabolic concerns after being extracted from a van accident with a resulting fire. Providers were expected to identify and manage the patient's airway, burns, hemoperitoneum, and CO and CN toxicities.

Results

Forty learners participated in this simulation, the majority of whom had little prior clinical experience managing the concepts highlighted in it. All agreed or strongly agreed that the case was relevant to their work. After participation, learner confidence in the ability to manage each of the learning objectives was high. One hundred percent of learners felt confident or very confident in managing CO toxicity and completing primary and secondary surveys, while 97% were similarly confident in identifying smoke inhalation injury, preparing for a difficult airway, and managing CN toxicity.

Discussion

This case was a well-received teaching tool for the management of pediatric trauma and metabolic derangements related to fire injuries. While this specific case represents a rare clinical experience, it is within the scope of expected knowledge for emergency medicine providers and offers the opportunity to practice managing multisystem trauma.

For Submission to the Journal of Community Health: Carbon Monoxide Awareness and Detector Use in the State of Wisconsin

Carbon monoxide (CO) is a leading cause of poisoning. CO detectors are a known-effective prevention strategy, however, little is known about use of detectors or knowledge of risk. This study assessed awareness of CO poisoning risk, detector laws, and detector use among a statewide sample. Data collected from the Survey of the Health of Wisconsin (SHOW) included a CO Monitoring module added to the in-home interview for 466 participants representing unique households across Wisconsin in 2018-2019. Univariate and multivariable logistic regression models examined associations between demographic characteristics, awareness of CO laws and detector use. Less than half of households had a verified CO detector. Under 46% were aware of the detector law. Those aware had 2.82 greater odds of having a detector in the home compared to those unaware of the law. Lack of CO law awareness may lead to less frequent detector use and result in higher risk of CO poisoning. This highlights the need for CO risk and detector education to decrease poisonings.

A Class of Activatable NIR-II Photoacoustic Dyes for High-Contrast Bioimaging

Photoacoustic (PA) imaging is emerging as one of the important non-invasive imaging techniques in biomedical research. Small molecule- second near-infrared window (NIR-II) PA dyes combined with imaging data can provide comprehensive and in-depth in vivo physiological and pathological information. However, the NIR-II PA dyes usually exhibit "always-on" properties due to the lack of a readily optically tunable group, which hinders the further applications in vivo. Herein, a novel class of dyes GX have been designed and synthesized as an activatable NIR-II PA platform, in which the absorption/emission wavelength of GX-5 extends up to 1082/1360 nm. Importantly, the GX dyes have a strong tissue penetration depth and high-resolution for the mouse vasculature structures in NIR-II PA 3D imaging and high signal-to-noise ratio in NIR-II fluorescence (FL) imaging. Furthermore, to demonstrate the applicability of GX dyes, the first NIR-II PA probe GX-5-CO activated by carbon monoxide (CO) was engineered and employed to reveal the enhancement of the CO levels in the hypertensive mice by high-contrast NIR-II PA and FL imaging. We expect that many derivatives of GX dyes will be developed to afford versatile NIR-II PA platforms for designing a wide variety activatable NIR-II PA probes as biomedical tools.

A Single-Component Dual Donor Enables Ultrasound-Triggered Co-release of Carbon Monoxide and Hydrogen Sulfide

The development of dual gasotransmitter donors can not only provide robust tools to investigate their subtle interplay under pathophysiological conditions but also optimize therapeutic efficacy. While conventional strategies are heavily dependent on multicomponent donors, we herein report an ultrasound-responsive water-soluble copolymer (PSHF) capable of releasing carbon monoxide (CO) and hydrogen sulfide (H2 S) based on single-component sulfur-substituted 3-hydroxyflavone (SHF) derivatives. Interestingly, sulfur substitution can not only greatly improve the ultrasound sensitivity but also enable the co-release of CO/H2 S under mild ultrasound irradiation. The co-release of CO/H2 S gasotransmitters exerts a bactericidal effect against Staphylococcus aureus and demonstrates anti-inflammatory activity in lipopolysaccharide-challenged macrophages. Moreover, the excellent tissue penetration of ultrasound irradiation enables the local release of CO/H2 S in the joints of septic arthritis rats, exhibiting superior therapeutic efficacy without the need for any antibiotics.

Circadian dependency of microglial heme oxygenase-1 expression and inflammation determine neuronal injury in hemorrhagic stroke

BACKGROUND

The heme oxygenase-1 (HO-1) enzyme pathway is of crucial importance in the removal of toxic blood components and regulation of neuroinflammation following hemorrhagic stroke. Although a circadian pattern dependency in the incidence and severity of hemorrhagic stroke exists, it is unknown whether the activity of the HO-1 system in the context of hemorrhagic injury also exhibits circadian dependency. We hypothesized that the circadian regulation of microglial HO-1 would determine the extent of neuroinflammation and neuronal injury in a murine model of subarachnoid hemorrhage (SAH).

METHODS

In vitro expression patterns of HO-1 and circadian rhythm genes were analyzed in the microglial BV-2 cell line and primary microglia (PMG) using Western blot and qPCR. PMG isolated from Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice were used to evaluate the role of microglial HO-1. We further investigated the in vivo relevance in a murine subarachnoid hemorrhage (SAH) model using Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice with myeloid cell HO-1 deficiency, inducing SAH at different zeitgeber (ZT) times and analyzing the expression of HO-1 and the circadian control gene Period-2 (Per-2), respectively. Furthermore, we measured the inflammatory cytokine Monocyte Chemoattractant Protein-1 (MCP-1) in the cerebrospinal fluid of SAH patients in correlation with clinical outcome.

RESULTS

HO-1 baseline expression and response to CO with blood exposure depended on ZT. In vitro expression of circadian control genes was de-synchronized in LyzM-Cre-Hmox1fl/fl PMG and did not respond to exogenous CO exposure. We found that circadian rhythm plays a crucial role in brain damage after SAH. At ZT2, we observed less phagocytic function, more vasospasm and increased microglial activation. CO reduced mortality at ZT12 in HO-1 deficient mice and reduced the difference between ZT2 and ZT12 in the inflammatory response. Induction of MCP-1 in the CSF from SAH patients was time-dependent and correlated with the expression of circadian control genes, SAH severity, functional impairment and delirium.

CONCLUSIONS

Our data point towards a crucial role for the HO-1 enzyme system and circadian control in neuronal injury after a hemorrhagic stroke.

Carbon Monoxide Exposure Does Not Improve The In Vitro Fertilization Rate of Oocytes Obtained from Heterozygous Hmox1 Knockout Mice

In our experimental study we explored the impact of maternal reduced heme oxygenase-1 (HO-1) gene (Hmox1) expression on the in vitro fertilization (IVF) rate through the use of heterozygous Hmox1 knockout mice models (HET/Hmox1+/ -). Also, we hypothesized a beneficial role of gametes exposure during fertilization to carbon monoxide (CO), one of HO-1 by-products, that might be relevant for the improvement of IVF rates. IVF technique was performed by using oocytes obtained from wild-type (WT) or Hmox1+/ - dams fertilized with WT, Hmox1+/ - or Hmox1-/ - mice-derived sperm. The fertilization step occurred either in a conventional incubator (37°C, 5% CO2) or in an incubator implemented with CO (500 ppm). The superovulation yield of WT and Hmox1+/ - mice and the number of fertilized oocytes was assessed using an optical microscope. The dams' Hmox1 heterozygous knockout neither impact the superovulation yield, nor did influence the fertilization success rate. Moreover, CO exposure during fertilization could not significantly improve the outcome. Our study showed that the maternal Hmox1+/ -condition is not affecting the IVF rate in mice. Furthermore, we discovered that CO exposure cannot be exploited to ameliorate this critical step of the IVF protocol.

Heterogeneous Diffusion Metrics Patterns in Delayed Encephalopathy After Acute Carbon Monoxide Poisoning: A Case Report

Delayed encephalopathy (DE) following acute carbon monoxide (CO) poisoning is characterized by a wide range of neurological symptoms, including akinetic mutism, cognitive impairment, and gait disturbances. Herein, we reported the case of a 61-year-old patient with DE after acute CO poisoning, who displayed heterogeneous patterns of cortical and subcortical structural integrity on diffusion tensor imaging (DTI). Four distinct patterns of diffusion tensor metrics (fractional anisotropy [FA] and mean diffusivity [MD]) were observed in the patient compared to age-matched controls (a decrease in FA and an increase in MD, a decrease in FA only, an increase in MD only, and an increase in FA and MD). This study revealed heterogeneous patterns of cortical and subcortical damage associated with DE after CO poisoning, contributing to a deeper understanding of the diverse clinical symptoms observed in this patient.

Photoinduced Five-Component Radical Relay Aminocarbonylation of Alkenes

Radical single carbonylation reactions with CO constitute a direct and robust strategy toward various carbonyl compounds from readily available chemicals, and have been extensively studied over the past decades. However, realizing highly selective catalytic systems for controlled radical double carbonylation reactions has remained a substantial challenge, particularly for the more advanced multicomponent variants, despite their great potential value. Herein, we report a visible-light-driven radical relay five-component radical double aminocarbonylation reaction of unactivated alkenes using CO under metal-free conditions. This protocol provides direct access to valuable γ-trifluoromethyl α-ketoamides with good yields and high chemoselectivity. Crucial was the identification of distinct dual roles of amine coupling partners, sequentially acting as electron donors for the formation of photoactive electron donor-acceptor (EDA) complexes with radical precursors and then as a CO acceptor via nitrogen radical cations to form carbamoyl radicals. Cross-coupling of carbamoyl radicals with the acyl radicals that are formed in an alkene-based relay process affords double aminocarbonylation products.

An Experimental and Computational Investigation Rules Out Direct Nucleophilic Addition on the N2 Ligand in Manganese Dinitrogen Complex [Cp(CO)2 Mn(N2 )]

We have re-examined the reactivity of the manganese dinitrogen complex [Cp(CO)2 Mn(N2 )] (1, Cp=η5 -cyclopentadienyl, C5 H5 ) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N2 )MnCOPh]Li (3) that is stable only below -40 °C. Full characterization of 3 (including single crystal X-ray diffraction) was performed. This complex decomposes quickly above -20 °C with N2 loss to give a phenylate complex [Cp(CO)2 MnPh]Li (2). The latter compound was erroneously formulated as an anionic diazenido compound [Cp(CO)2 MnN(Ph)=N]Li in earlier reports, ruling out the claimed and so-far unique behavior of the N2 ligand in 1. DFT calculations were run to explore both the hypothesized and the experimentally verified reactivity of 1 with PhLi and are fully consistent with our results. Direct attack of a nucleophile on metal-coordinated N2 remains to be demonstrated.

Palladium-Catalyzed Carbonylative Difunctionalization of Unactivated Alkenes Initiated by Unstabilized Enolates

This report describes the first example of palladium-catalyzed carbonylative difunctionalization of unactivated alkenes initiated by enolate nucleophiles. The approach involves initiation by an unstabilized enolate nucleophile under an atmospheric pressure of CO and termination with a carbon electrophile. This process is compatible with a diverse range of electrophiles, including aryl, heteroaryl, and vinyl iodides to yield synthetically useful 1,5-diketone products, which were demonstrated to be precursors for multi-substituted pyridines. A PdI -dimer complex with two bridging CO units was observed although its role in catalysis is not yet understood.

Influence of Air Pollutants on the Disease Activity and Quality of Life in Rheumatoid Arthritis, an Iranian Observational Longitudinal Study

Background

Environmental exposures and genetic predisposition interactions may result in autoimmune rheumatic diseases. This study aimed to determine the effect of outdoor air pollutants on the activity of rheumatoid arthritis (RA) in a longitudinal follow-up.

Methods

We longitudinally studied 50 patients with RA bimonthly over 6 months in Mashhad, one of the most polluted cities in Iran. Disease activity and health-related quality of life (HRQoL) were examined according to the disease activity score (DAS28ESR), health assessment questionnaires (HAQ), physical health component summary (PCS), and visual analogue scale (VAS) criteria. The outdoor air pollutant was measured by monitoring the average concentration of nitrogen oxide (NO), carbon monoxide (CO), O2 level, Sulfur dioxide (SO2), and some particles less than 10 and 2.5 micrometers in diameter (PM <10 µm, PM <2.5 µm). The temperature and humidity levels were also measured. The univariate and multivariate statistical analyses were used for data analysis and the role of confounding factors was determined using the generalized estimation equation method.

Results

Statistical analysis indicated a significant increase of the DAS28ESR (B = 0.04 [0.08]; P = 0.01) and VAS (B = 4.48 [1.73]; P = 0.01) by CO concentration. Moreover, a number of polluted days increased the VAS in patients. In addition, other air pollutants, temperature, and humidity were not affected significantly by the DAS28ESR and quality of life indexes by considering confounders such as medications, age, and job.

Conclusion

Based on our findings, CO concentration was the only effective outdoor air pollutant that could increase RA disease activity. In addition, CO concentration and the number of polluted days make patients feel more ill. As the role of indoor air pollutants is highly important, further research on this critical topic is required to establish the role of air pollution on RA disease activity.

Carbon-Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates

Current examples of carbon chain production from metal formyl intermediates with homogeneous metal complexes are described in this Minireview. Mechanistic aspects of these reactions as well as the challenges and opportunities in using this understanding to develop new reactions of CO and H2 are also discussed.

Prevalence of Carbon Monoxide Poisoning and Hyperbaric Oxygen Therapy in Korea: Analysis of National Claims Data in 2010-2019

This study aimed to investigate the prevalence of carbon monoxide (CO) poisoning and the provision of hyperbaric oxygen therapy (HBOT) in South Korea. We used data from the Korea Health Insurance Review and Assessment service. In total, 44,361 patients with CO poisoning were identified across 10 years (2010-2019). The prevalence of CO poisoning was found to be 8.64/10,000 people, with a gradual annual increment. The highest prevalence was 11.01/10,000 individuals, among those aged 30-39 years. In 2010, HBOT was claimed from 15 hospitals, and increased to 30 hospitals in 2019. A total of 4,473 patients received HBOT in 10 years and 2,684 (60%) were treated for more than 2 hours. This study suggested that the prevalence of both CO poisoning and HBOT in Korea gradually increased over the past 10 years, and disparities in prevalence were observed by region.

Mapping burn severity and monitoring CO content in Türkiye's 2021 Wildfires, using Sentinel-2 and Sentinel-5P satellite data on the GEE platform

This study investigated forest fires in the Mediterranean of Türkiye between July 28, 2021, and August 11, 2021. Burn severity maps were produced with the difference normalised burned ratio index (dNBR) and difference normalised difference vegetation index (dNDVI) using Sentinel-2 images on the Google Earth Engine (GEE) cloud platform. The burned areas were estimated based on the determined burning severity degrees. Vegetation density losses in burned areas were analysed using the normalised difference vegetation index (NDVI) time series. At the same time, the post-fire Carbon Monoxide (CO) column number densities were determined using the Sentinel-5P satellite data. According to the burn severity maps obtained with dNBR, the sum of high and moderate severity areas constitutes 34.64%, 20.57%, 46.43%, 51.50% and 18.88% of the entire area in Manavgat, Gündoğmuş, Marmaris, Bodrum and Köyceğiz districts, respectively. Likewise, according to the burn severity maps obtained with dNDVI, the sum of the areas of very high severity and high severity constitutes 41.17%, 30.16%, 30.50%, 42.35%, and 10.40% of the entire region, respectively. In post-fire NDVI time series analyses, sharp decreases were observed in NDVI values from 0.8 to 0.1 in all burned areas. While the Tropospheric CO column number density was 0.03 mol/m² in all regions burned before the fire, it was observed that this value increased to 0.14 mol/m² after the fire. Moreover, when the area was examined more broadly with Sentinel 5P data, it was observed that the amount of CO increased up to a maximum value of 0.333 mol/m². The results of this study present significant information in terms of determining the severity of forest fires in the Mediterranean region in 2021 and the determination of the CO column number density after the fire. In addition, monitoring polluting gases with RS techniques after forest fires is essential in understanding the extent of the damage they can cause to the environment.

Anionic Magnesium and Calcium Hydrides: Transforming CO into Unsaturated Disilyl Ethers

The synthesis, characterisation and reactivity of two isostructural anionic magnesium and calcium complexes is reported. By X-ray and neutron diffraction techniques, the anionic hydrides are shown to exist as dimers, held together by a range of interactions between the two anions and two bridging potassium cations. Unlike the vast proportion of previously reported dimeric group 2 hydrides, which have hydrides that bridge two group 2 centres, here the hydrides are shown to be "terminal", but stabilised by interactions with the potassium cations. Both anionic hydrides were found to insert and couple CO under mild reaction conditions to give the corresponding group 2 cis-ethenediolate complexes. These cis-ethenediolate complexes were found to undergo salt elimination reactions with silyl chlorides, allowing access to small unsaturated disilyl ethers with a high percentage of their mass originating from the C₁ source CO.

Facile Synthesis of Uranium Complexes with a Pendant Borane Lewis Acid and 1,2-Insertion of CO into a U-N Bond

In this contribution, we illustrate uranium complexes bearing a pendant borate (i.e. 1 and 2) or a pendant borane (i.e. 3 and 4) moiety via reaction of the highly strained uranacycle I with various 3-coordinate boranes. Complexes 3 and 4 represent the first examples of uranium complexes with a pendant borane Lewis acid. Moreover, complex 3 was capable of activation of CO, delivering a new CO activation mode, and an abnormal CO 1,2-insertion pathway into a U-N bond. The importance of the pendant borane moiety was confirmed by the controlled experiments.

Chemiexcitation-Triggered Prodrug Activation for Targeted Carbon Monoxide Delivery

Photolysis-based prodrug strategy can address some critical drug delivery issues, which otherwise are very challenging to tackle with traditional prodrug strategy. However, the need for external light irradiation significantly hampers its in vivo application due to the poor light accessibility of deep tissue. Herein, we propose a new strategy of chemiexcitation-triggered prodrug activation, wherein a photoresponsive prodrug is excited for drug payload release by chemiexcitation instead of photoirradiation. As such, the bond-cleavage power of photolysis can be employed to address some critical drug delivery issues while obviating the need for external light irradiation. We have established the proof of concept by the successful development of a chemiexcitation responsive carbon monoxide delivery platform, which exhibited specific CO release at the tumor site and pronounced tumor suppression effects. We anticipate that such a concept of chemiexcitation-triggered prodrug activation can be leveraged for the targeted delivery of other small molecule-based drug payloads.

Activation of CO Using a 1,2-Disilylene: Facile Synthesis of an Abnormal N-Heterocyclic Silylene

Reaction of the 1,2-disilylene, [{ArC(NDip)₂ }Si]₂ 1 (Dip=2,6-diisopropylphenyl, Ar=4-C₆ H₄ Bu^t ), with CO proceeds via insertion of CO into one Si-N bond, and Si-Si bond cleavage, to cleanly give the bis(silylene), {ArC(NDip)₂ }Si(:)O C S i ( : ) ( N D i p )​ 2 C ‾ Ar 2, under ambient conditions. The reaction can be partially reversed when solutions of 2 are subjected to UV irradiation. The five-membered heterocyclic fragment of 2 represents the first silicon analogue of an "abnormal" N-heterocyclic carbene (aNHC), a view which is substantiated by a computational analysis of the compound. Reaction of 2 with [Mo(CO)₆ ] under UV light affords the chelate complex, [Mo(CO)₄ (κ² -Si,Si-2)] 3, while reaction with [Fe(CO)₅ ] gives the unusual silyleneyl bridged complex, [{Fe₂ (CO)₆ }{μ-Si[(NDip)₂ CAr]}₂ ] 4. The same coordination complexes can be accessed by reaction of 1 with [Mo(CO)₆ ] or [Fe(CO)₅ ] under UV light. As is the case for aNHCs, d-block metal complexes of bis(silylene) 2 could prove useful as bespoke catalysts for organic transformations.

Highly Enhanced Aromatics Selectivity by Coupling of Chloromethane and Carbon Monoxide over H-ZSM-5

The transformation of methane into high value-added chemicals such as aromatics provides a more desired approach towards sustainable chemistry but remains a critical challenge due to the low selectivity of aromatics and poor stability. Herein, we first report a coupling reaction of CH₃ Cl and CO (CCTA) based on methane conversion, which achieves extremely high aromatics selectivity (82.2 %) with the selectivity of BTX up to ca. 60 % over HZSM-5. The promoting effects have been demonstrated on other zeolites especially 10-membered rings (10 MR) zeolites. Multiple characterizations show that 2,3-dimethyl-2-cyclopentene-1-one (DMCPO) is generated from acetyl groups and olefins. Furthermore, isotopic labeling analysis confirms that CO is inserted into the DMCPO and aromatics rings. A new aromatization mechanism is proposed, including the formation of the above intermediates, which conspicuously weakens the hydrogen transfer reaction, leading to a considerable increase of aromatics selectivity and a dramatic drop in alkanes.

Synthesis of CuO by Electrospinning Method for Sensing of Hydrogen and Carbon Monoxide Gases

The pure CuO nanofibers were synthesized via the electrospinning method successfully. The calcinated CuO nanofibers were investigated for sensing hydrogen and carbon monoxide gases. Structural properties of the synthesized calcinated nanofibers were studied using Fourier -transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), and particle morphology by scanning electron microscopy (SEM). SEM images confirmed string-like structures, nanofibers. The sensor based on the calcinated CuO nanofibers exhibited excellent gas sensing performance at the low operating temperature of 175 °C and the fast response and recovery characteristics at a low concentration. Moreover, good stability, prominent reproducibility, and excellent selectivity are also observed based on the calcinated nanofibers. These results demonstrate the potential application of calcinated CuO nanofibers for sensing hydrogen (10-200 ppm) and carbon monoxide (400-700 ppm) gases.

A MOF Multifunctional Cargo Vehicle for Reactive Gas Delivery and Catalysis

Efficient delivery of reactive and toxic gaseous reagents to organic reactions was studied using metal-organic frameworks (MOFs). Simultaneous cargo vehicle and catalytic capabilities of several MOFs were probed for the first time using the examples of  aromatization, aminocarbonylation, and carbonylative Suzuki-Miyaura coupling reactions. These reactions highlight that MOFs can serve a dual role as a gas cargo vehicle and a catalyst,  leading to product formation with yields similar to reactions employing pure gases. Furthermore, the MOFs can be recycled without sacrificing product yield, while simultaneously maintaining crystallinity. The reported findings were supported crystallographically and spectroscopically (e.g.,  diffuse reflectance infrared Fourier transform spectroscopy), foreshadowing a pathway for the development of multifunctional MOF-based reagent-catalyst cargo vessels for reactive reagents, as an attractive alternative to the use of toxic pure gases or gas generators.

Structural and Electronic Properties of Iron(0) PNP Pincer Complexes

In the present work we have prepared and fully characterized several Fe(0) complexes of the type [Fe(PNP)(CO)2] treating Fe(II) complexes [Fe(PNP)(Cl)2] with KC8 in the presence of carbon monoxide. While complexes [Fe(PNPNMe-iPr)(CO)2], [Fe(PNPNEt-iPr)(CO)2] adopt a trigonal bipyramidal geometry, the bulkier and more electron rich [Fe(PNPNH-tBu)(CO)2] is closer to a square pyramidal geometry. Mössbauer spectra showed isomer shifts very close to 0 and similar to those reported for Fe(I) systems. Quadrupole splitting values range between 2.2 and 2.7 mm s-1 both in experiments and DFT calculations, while those of Fe(I) complexes are much smaller (∼0.6 mm s-1).

Assessing adolescent tobacco use in a substance use treatment program with self-report and biological measures

Tobacco use in adolescents can alter their lifetime health outcomes. Despite the importance of early identification and treatment, adolescent tobacco use, including that of electronic vapor products (e.g., e-cigarettes), is often missed. In a state-funded substance use treatment program, we added biological measures, including urinary cotinine and exhaled carbon monoxide to self-report measures to assess recent and lifetime tobacco use. We conducted a retrospective review of the de-identified charts to examine the feasibility of screening for self-report and biological measures of tobacco use. Self-report, urinary cotinine, and exhaled carbon monoxide samples were obtained at every visit, including intake and follow-up. There were 52 adolescents with a total of 400 clinic visits to the program. Of those 400 visits, 258 included self-reported tobacco use and 142 included a denial of using any form of tobacco. However, of those 142 visits with a negative self-report of tobacco, 31 tested positive for cotinine and 6 had positive exhaled carbon monoxide. Although 111 of the 142 had negative cotinine, 5 had positive carbon monoxide, but all of those self-reported recent cannabis use. Despite using a sensitive measure of self-report of tobacco use, almost 22% of visits had a discordant self-report with a biological measure that indicated tobacco use. Considering the lifelong impact of adolescent tobacco use, clinicians should consider augmenting self-report with biological measures of tobacco use. Identification of tobacco use in adolescents with substance use can assist clinicians in providing education about tobacco use, such as electronic vapor products, and individualizing treatments.

Acute and delayed toxicity from co-ingestion of methylene chloride and methanol

Methylene chloride is a volatile, chlorinated hydrocarbon and colorless solvent found in multiple industrial products including paint strippers, metal cleaners, automotive products, pesticides and aerosol containers. Occupational exposure to methylene chloride is reported in automotive technicians, painters, and other industrial workers with adverse health effects including gastrointestinal, neurological, as well as hepato-renal injuries. International Agency for Research on Cancer (IARC) classifies methylene chloride as a 2 A carcinogen. Through a series of reactions catalyzed by cytochrome P450 2E1 (CYP2E1), metabolism of methylene chloride leads to the formation of formyl chloride, and ultimately carbon monoxide (CO). Most reports of methylene chloride toxicity are due to dermal and inhalational exposure in occupational settings. Ingestion of methylene chloride is uncommon, yet can lead to significant toxicity and prolonged CO toxicity. Methylene chloride is frequently formulated with methanol; individuals who intentionally ingest methylene chloride can experience concomitant methanol toxicity. We present a case of acute ingestion of paint stripper containing methanol and methylene chloride. We discuss the clinical presentation, key management decisions, relevant pathophysiology and biochemistry, as well as the clinical course and management.

Enhancement of carbon monoxide concentration in atmosphere due to large scale forest fire of Uttarakhand

The richly forested Indian state of Uttarakhand experienced widespread forest fires in April to May 2016. The current study examines dispersion of carbon monoxide (CO) from the source regions of forest fire to distant places, using the Lagrangian particle dispersion model, FLEXPART. Atmospheric Infrared Sounder (AIRS) observations revealed that CO columnar concentrations had increased by almost 28 percentage during 24 April to 02 May 2016 with respect to the previous non-burning period of April 2016 at Uttarakhand. It is also seen that there is considerable enhancement of 45 percentage in average columnar concentration of CO during the burning period, compared to that in the previous 5 years as observed by AIRS. In the present study, concentrations of CO at different pressure levels and columnar CO over Uttarakhand during the forest fire event have been simulated using FLEXPART. The area averaged profile of model derived CO has been compared with the profile from AIRS onboard Aqua. Comparison between model derived columnar CO and satellite observations shows good agreement with coefficient of correlation (r) approximately 0.91 over the burnt areas. Further analysis using FLEXPART reveals that the transport of pollutants is towards north-eastern and eastern regions from the locations of forest fire events. Model derived vertical distribution of CO over Tibet, which is situated at the north-east of Uttarakhand, shows significant increase of CO concentration at higher altitudes around 3 km from the mean sea level during the fire event. FLEXPART results show that the emissions from the Uttarakhand fires were transported to Tibet during the study period.

Influence of Air Pollution on Hospital Admissions in Adult Asthma in Northeast China

Background:

Asthma is a common chronic respiratory disease and is related to air pollution exposure. However, only a few studies have concentrated on the association between air pollution and adult asthma. Moreover, the results of these studies are controversial. Therefore, the present study aimed to analyze the influence of various pollutants on hospitalization due to asthma in adults.

Methods:

A total of 1019 unrelated hospitalized adult asthma patients from Northeast China were recruited from 2014 to 2016. Daily average concentrations of air pollutants (particulate matter <2.5 μm [PM_2.5], particulate matter <10 μm [PM₁₀], sulfur dioxide [SO₂], nitrogen dioxide [NO₂], and carbon monoxide [CO]) were obtained from the China National Environmental Monitoring Centre website from 2014 to 2016. Cox logistic regression analysis was used to analyze the relationship between air pollutants and hospital admissions in adult asthma.

Results:

The maximum odds ratio (OR) value for most air pollutants occurred on lag day 1. Lag day 1 was chosen as the exposure period, and 8 days before onset was chosen as the control period. Three pollutants (PM_2.5, CO, and SO₂) were entered into the regression equation, and the corresponding OR (95% confidence interval) was 0.995 (0.991–0.999), 3.107 (1.607–6.010), and 0.979 (0.968–0.990), respectively.

Conclusions:

A positive association between hospital admissions and the daily average concentration of CO was observed. CO is likely to be a risk factor for hospital admissions in adults with asthma.

Development of Prediction Equation of Diffusing Capacity of Lung for Koreans

Background

The diffusing capacity of the lung is influenced by multiple factors such as age, sex, height, weight, ethnicity and smoking status. Although a prediction equation for the diffusing capacity of Korea was proposed in the mid-1980s, this equation is not used currently. The aim of this study was to develop a new prediction equation for the diffusing capacity for Koreans.

Methods

Using the data of the Korean National Health and Nutrition Examination Survey, a total of 140 nonsmokers with normal chest X-rays were enrolled in this study.

Results

Using linear regression analysis, a new predicting equation for diffusing capacity was developed. For men, the following new equations were developed: carbon monoxide diffusing capacity (DLco)=−10.4433−0.1434×age (year)+0.2482×heights (cm); DLco/alveolar volume (VA)=6.01507−0.02374×age (year)−0.00233×heights (cm). For women the prediction equations were described as followed: DLco=−12.8895−0.0532×age (year)+0.2145×heights (cm) and DLco/VA=7.69516−0.02219×age (year)−0.01377×heights (cm). All equations were internally validated by k-fold cross validation method.

Conclusion

In this study, we developed new prediction equations for the diffusing capacity of the lungs of Koreans. A further study is needed to validate the new predicting equation for diffusing capacity.

Characteristics of Children with Acute Carbon Monoxide Poisoning in Ankara: A Single Centre Experience

The purpose of the study was to define characteristics of children with acute carbon monoxide poisoning. Eighty children hospitalized with acute carbon monoxide poisoning were recruited prospectively over a period of 12 months. Sociodemographic features, complaints and laboratory data were recorded. When the patient was discharged, necessary preventive measures to be taken were explained to parents. One month later, the parents were questioned during a control examination regarding the precautions that they took. The ages of the cases were between one month and 16 yr. Education levels were low in 86.2% of mothers and 52.6% of fathers. All families had low income and 48.8% did not have formal housing. The source of the acute carbon monoxide poisoning was stoves in 71.2% of cases and hot-water heaters in 28.8% of cases. Three or more people were poisoned at home in 85.1% of the cases. The most frequent symptoms of poisoning were headache and vertigo (58.8%). Median carboxyhemoglobin levels at admission to the hospital and discharge were measured as 19.5% and 1.1% (P < 0.001). When families were called for re-evaluation, it was determined that most of them had taken the necessary precautions after the poisoning incident (86.3%). This study determined that children with acute childhood carbon monoxide poisoning are usually from families with low socioeconomic and education levels. Education about prevention should be provided to all people who are at risk of carbon monoxide poisoning before a poisoning incident occurs.

Carbon monoxide (CO) is a novel inhibitor of connexin hemichannels

Hemichannels (HCs) are hexamers of connexins that can form gap-junction channels at points of cell contacts or "free HCs" at non-contacting regions. HCs are involved in paracrine and autocrine cell signaling, and under pathological conditions may induce and/or accelerate cell death. Therefore, studies of HC regulation are of great significance. Nitric oxide affects the activity of Cx43 and Cx46 HCs, whereas carbon monoxide (CO), another gaseous transmitter, modulates the activity of several ion channels, but its effect on HCs has not been explored. We studied the effect of CO donors (CORMs) on Cx46 HCs expressed in Xenopus laevis oocytes using two-electrode voltage clamp and on Cx43 and Cx46 expressed in HeLa cells using a dye-uptake technique. CORM-2 inhibited Cx46 HC currents in a concentration-dependent manner. The C-terminal domain and intracellular Cys were not necessary for the inhibition. The effect of CORM-2 was not prevented by guanylyl-cyclase, protein kinase G, or thioredoxin inhibitors, and was not due to endocytosis of HCs. However, the effect of CORM-2 was reversed by reducing agents that act extracellularly. Additionally, CO inhibited dye uptake of HeLa cells expressing Cx43 or Cx46, and MCF-7 cells, which endogenously express Cx43 and Cx46. Because CORM-2 carbonylates Cx46 in vitro and induces conformational changes, a direct effect of that CO on Cx46 is possible. The inhibition of HCs could help to understand some of the biological actions of CO in physiological and pathological conditions.

Carbon monoxide-releasing molecule-3 (CORM-3; Ru(CO)3Cl(glycinate)) as a tool to study the concerted effects of carbon monoxide and nitric oxide on bacterial flavohemoglobin Hmp: applications and pitfalls

CO and NO are small toxic gaseous molecules that play pivotal roles in biology as gasotransmitters. During bacterial infection, NO, produced by the host via the inducible NO synthase, exerts critical antibacterial effects while CO, generated by heme oxygenases, enhances phagocytosis of macrophages. In Escherichia coli, other bacteria and fungi, the flavohemoglobin Hmp is the most important detoxification mechanism converting NO and O2 to the ion nitrate (NO3(-)). The protoheme of Hmp binds not only O2 and NO, but also CO so that this ligand is expected to be an inhibitor of NO detoxification in vivo and in vitro. CORM-3 (Ru(CO)(3)Cl(glycinate)) is a metal carbonyl compound extensively used and recently shown to have potent antibacterial properties. In this study, attenuation of the NO resistance of E. coli by CORM-3 is demonstrated in vivo. However, polarographic measurements showed that CO gas, but not CORM-3, produced inhibition of the NO detoxification activity of Hmp in vitro. Nevertheless, CO release from CORM-3 in the presence of soluble cellular compounds is demonstrated by formation of carboxy-Hmp. We show that the inability of CORM-3 to inhibit the activity of purified Hmp is due to slow release of CO in protein solutions alone i.e. when sodium dithionite, widely used in previous studies of CO release from CORM-3, is excluded. Finally, we measure intracellular CO released from CORM-3 by following the formation of carboxy-Hmp in respiring cells. CORM-3 is a tool to explore the concerted effects of CO and NO in vivo.

Dynamics of the heme-binding bacterial gas-sensing dissimilative nitrate respiration regulator (DNR) and activation barriers for ligand binding and escape

DNR (dissimilative nitrate respiration regulator) is a heme-binding transcription factor that is involved in the regulation of denitrification in Pseudomonas aeruginosa. In the ferrous deoxy state, the heme is 6-coordinate; external NO and CO can replace an internal ligand. Using fluorescence anisotropy, we show that high-affinity sequence-specific DNA binding occurs only when the heme is nitrosylated, consistent with the proposed function of DNR as NO sensor and transcriptional activator. This role is moreover supported by the NO "trapping" properties revealed by ultrafast spectroscopy that are similar to those of other heme-based NO sensor proteins. Dissociated CO-heme pairs rebind in an essentially barrierless way. This process competes with migration out of the heme pocket. The latter process is thermally activated (Ea ∼ 7 kJ/mol). This result is compared with other heme proteins, including the homologous CO sensor/transcription factor CooA, variants of the 5-coordinate mycobacterial sensor DosT and the electron transfer protein cytochrome c. This comparison indicates that thermal activation of ligand escape from the heme pocket is specific for systems where an external ligand replaces an internal one. The origin of this finding and possible implications are discussed.

Inhibition of the cardiac Na⁺ channel Nav1.5 by carbon monoxide

Sublethal carbon monoxide (CO) exposure is frequently associated with myocardial arrhythmias, and our recent studies have demonstrated that these may be attributable to modulation of cardiac Na(+) channels, causing an increase in the late current and an inhibition of the peak current. Using a recombinant expression system, we demonstrate that CO inhibits peak human Nav1.5 current amplitude without activation of the late Na(+) current observed in native tissue. Inhibition was associated with a hyperpolarizing shift in the steady-state inactivation properties of the channels and was unaffected by modification of channel gating induced by anemone toxin (rATX-II). Systematic pharmacological assessment indicated that no recognized CO-sensitive intracellular signaling pathways appeared to mediate CO inhibition of Nav1.5. Inhibition was, however, markedly suppressed by inhibition of NO formation, but NO donors did not mimic or occlude channel inhibition by CO, indicating that NO alone did not account for the actions of CO. Exposure of cells to DTT immediately before CO exposure also dramatically reduced the magnitude of current inhibition. Similarly, l-cysteine and N-ethylmaleimide significantly attenuated the inhibition caused by CO. In the presence of DTT and the NO inhibitor N(ω)-nitro-L-arginine methyl ester hydrochloride, the ability of CO to inhibit Nav1.5 was almost fully prevented. Our data indicate that inhibition of peak Na(+) current (which can lead to Brugada syndrome-like arrhythmias) occurs via a mechanism distinct from induction of the late current, requires NO formation, and is dependent on channel redox state.

Experimental study on the nitrogen dioxide and particulate matter emissions from diesel engine retrofitted with particulate oxidation catalyst

A particulate oxidation catalyst (POC) was employed to perform experiments on the engine test bench to evaluate the effects on the nitrogen dioxide (NO2) and particulate matter (PM) emissions from diesel engine. The engine exhaust was sampled from both upstream and downstream of the POC. The results showed that the POC increased the ratios of NO2/NOx significantly in the middle and high loads, the ratio of NO2/nitrogen oxides (NOx) increased 4.5 times on average under all experiment modes with the POC. An engine exhaust particle sizer (EEPS) was used to study the particle number-weighted size distributions and the abnormal particle emissions with the POC. The results indicated that the average reduction rate of particle number (PN) was 61% in the operating range of the diesel engine. At the engine speed of 1,400 r/min, the reduction rates of PN tended to decrease with the larger particle size. In the long time run under the steady mode (520 Nm, 1,200 r/min), abnormal particle emissions after the POC happened seven times in the first hour, and the average PN concentration of these abnormal emission peaks was much higher than that in normal state. The particle emissions of peaks 1-5 equaled the particles emitted downstream of the POC in normal state for 1.9h in number concentration, and for 3.6h in mass concentration. The PN concentrations tended to increase over time in 5h under the steady engine mode and the increase of the PN in the size range of 6.04-14.3 nm was more evident.

The hydrogenase activity of the molybdenum/copper-containing carbon monoxide dehydrogenase of Oligotropha carboxidovorans

The reaction of the air-tolerant CO dehydrogenase from Oligotropha carboxidovorans with H2 has been examined. Like the Ni-Fe CO dehydrogenase, the enzyme can be reduced by H2 with a limiting rate constant of 5.3 s(-1) and a dissociation constant Kd of 525 μM; both kred and kred/Kd, reflecting the breakdown of the Michaelis complex and the reaction of free enzyme with free substrate in the low [S] regime, respectively, are largely pH-independent. During the reaction with H2, a new EPR signal arising from the Mo/Cu-containing active site of the enzyme is observed which is distinct from the signal seen when the enzyme is reduced by CO, with greater g anisotropy and larger hyperfine coupling to the active site (63,65)Cu. The signal also exhibits hyperfine coupling to at least two solvent-exchangeable protons of bound substrate that are rapidly exchanged with solvent. Proton coupling is also evident in the EPR signal seen with the dithionite-reduced native enzyme, and this coupling is lost in the presence of bicarbonate. We attribute the coupled protons in the dithionite-reduced enzyme to coordinated water at the copper site in the native enzyme and conclude that bicarbonate is able to displace this water from the copper coordination sphere. On the basis of our results, a mechanism for H2 oxidation is proposed which involves initial binding of H2 to the copper of the binuclear center, displacing the bound water, followed by sequential deprotonation through a copper-hydride intermediate to reduce the binuclear center.

Effects of brief smoking cessation education with expiratory carbon monoxide measurement on level of motivation to quit smoking

Background

Smoking rates among Korean adult males is still high despite multifaceted efforts to reduce it. In Korea, there have been several studies on the effectiveness of smoking cessation education for inpatients, health check-ups, and smoking cessation clinics. However, there haven't been any studies on the effectiveness of smoking cessation education conducted outside the hospital. This study investigated effectiveness of brief education on smoking cessation with an expiratory carbon monoxide (CO) measurement outside the hospital among adult male office-workers in Korea.

Methods

From April 1st to May 10th, 2012, we conducted a controlled trial among 95 adult male office workers over the age of 19 who smoke outside, in a public place in Seoul by cluster sampling. For the education group, we provided smoking cessation education for about 5 to 10 minutes, measured the expiratory CO level, and made the subjects complete questionnaires, while only self-help materials on quitting smoking were given to the control group. After 4 weeks, we evaluated the change in the level of motivation or success to quit smoking in both groups via e-mail or mobile phone.

Results

In the education group, the level of motivation to quit smoking was improved significantly. A multiple logistic regression analysis showed that the odds ratio of improved motivation to quit smoking in the education group was 28.10 times higher than that of the control group.

Conclusion

Brief education on smoking cessation with expiratory CO measurement conducted outside the hospital could enhance the level of motivation to quit smoking.

Heme sensor proteins

Heme is a prosthetic group best known for roles in oxygen transport, oxidative catalysis, and respiratory electron transport. Recent years have seen the roles of heme extended to sensors of gases such as O2 and NO and cell redox state, and as mediators of cellular responses to changes in intracellular levels of these gases. The importance of heme is further evident from identification of proteins that bind heme reversibly, using it as a signal, e.g. to regulate gene expression in circadian rhythm pathways and control heme synthesis itself. In this minireview, we explore the current knowledge of the diverse roles of heme sensor proteins.

Impacts of earthquake aftermath on indoor carbon monoxide levels in Turkish coffeehouses environment in duzce, Turkey

BACKGROUND

In 1999, Duzce suffered two consecutive devastating earthquakes above magnitude 7 in August and November. In the present study, we aimed to evaluate the indoor air quality of coffeehouses by determining carbon monoxide (CO) levels and their contributing factors in coffeehouses built before and after the earthquake.

METHODS

We conducted our study in 76 Turkish coffeehouses in Duzce in winter (November 2007-March 2008) during rush hours (18:00-23:00). The Turkish coffeehouses included in the study were evaluated under four categories based on smoking status and construction date. The characteristics of the coffeehouses, such as their CO levels and temperatures both indoors and outdoors, were all measured. These analyses were carried out with the SPSS 15.0 program.

RESULTS

The CO levels in Turkish coffeehouses were above the values indicated as being safe by the WHO. While stoves and cooking equipment were determined to contribute to indoor CO levels, cigarettes were found to be the main source. Indoor CO levels at second hour were very strongly correlated (r: 0.84, P<0.001) (r: 0.91, P<0.001) with indoor CO levels at initial and first hour as well as with smoking status (r: 0.69, P<0.001); they were also moderately correlated with the room volume (r: 0.34, P<0.001) and construction materials (r: 0.31, P<0.001) of the coffeehouse.

CONCLUSION

Elevated CO levels in Turkish coffeehouses indicate the possible presence of other pollutants, particularly when the main source is smoking. In such cases, both individuals and the whole of society are affected negatively in many ways. Therefore, smoking should be prohibited by law in Turkish coffeehouses and national awareness programs should be developed based on peoples' lifestyles. Moreover, the standards for construction and management of Turkish coffeehouses should be improved as well.

Inhibition of hypoxic pulmonary vasoconstriction of rats by carbon monoxide

Hypoxic pulmonary vasoconstriction (HPV), a unique response of pulmonary circulation, is critical to prevent hypoxemia under local hypoventilation. Hypoxic inhibition of K(+) channel is known as an important O(2)-sensing mechanism in HPV. Carbon monoxide (CO) is suggested as a positive regulator of Ca(2+)-activated K(+) channel (BK(Ca)), a stimulator of guanylate cyclase, and an O(2)-mimetic agent in heme moiety-dependent O(2) sensing mechanisms. Here we compared the effects of CO on the HPV (P(O(2)), 3%) in isolated pulmonary artery (HPV(PA)) and in blood-perfused/ventilated lungs (HPV(lung)) of rats. A pretreatment with CO (3%) abolished the HPV(PA) in a reversible manner. The inhibition of HPV(PA) was completely reversed by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor. In contrast, the HPV(lung) was only partly decreased by CO. Moreover, the partial inhibition of HPV(lung) by CO was affected neither by the pretreatment with ODQ nor by NO synthase inhibitor (L-NAME). The CO-induced inhibitions of HPV(PA) and HPV(lung) were commonly unaffected by tetraethylammonium (TEA, 2 mM), a blocker of BK(Ca). As a whole, CO inhibits HPV(PA) via activating guanylate cyclase. The inconsistent effects of ODQ on HPV(PA) and HPV(lung) suggest that ODQ may lose its sGC inhibitory action when applied to the blood-containing perfusate.