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The identification of unknown chemicals has emerged as a significant issue in untargeted metabolome analysis owing to the limited availability of purified standards for identification; this is a major bottleneck for the accumulation of reusable metabolome data in systems biology. Public resources for discovering and prioritizing the unknowns that should be subject to practical identification, as well as further detailed study of spending costs and the risks of misprediction, are lacking. As such a resource, we released databases, Food-, Plant- and Thing-Metabolome Repository (http://metabolites.in/foods, http://metabolites.in/plants, and http://metabolites.in/things, referred to as XMRs) in which the sample-specific localization of unknowns detected by liquid chromatography-mass spectrometry in a wide variety of samples can be examined, helping to discover and prioritize the unknowns. A set of application programming interfaces for the XMRs facilitates the use of metabolome data for large-scale analysis and data mining. Several applications of XMRs, including integrated metabolome and genome analyses, are presented. Expanding the concept of XMRs will accelerate the identification of unknowns and increase the discovery of new knowledge.
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Bases de Dados Factuais , Metaboloma , Metabolômica , Cromatografia Líquida/métodos , Espectrometria de Massas/métodos , Metabolômica/métodosRESUMO
TAFRO syndrome is a rare systemic inflammatory disorder of unknown etiology characterized by thrombocytopenia, anasarca, fever, reticulin myelofibrosis, renal dysfunction, and organomegaly. The diagnosis of TAFRO syndrome can be challenging; however, prompt diagnosis is vital because TAFRO syndrome is a progressive and life-threatening disease. We have showcased five patients with TAFRO syndrome who had similar bone marrow (BM) findings that could be considered the findings that characterize TAFRO syndrome. All patients were treated with corticosteroids and tocilizumab; three of the five patients (60 %) responded positively to the treatment. The unique BM findings observed in this study were megakaryocytes with distinct multinuclei and three-dimensional and indistinct bizarre nuclei ("dysmorphic megakaryocyte"), similar to the megakaryocyte morphology observed in myeloproliferative neoplasms (MPNs). Notably, dysmorphic megakaryocytes were observed in all five cases, whereas only two of the five patients tested positive for reticulin myelofibrosis, and three of the five patients had megakaryocytic hyperplasia, which are considered typical findings of TAFRO syndrome. Thus, the BM findings of dysmorphic megakaryocytes could help in the correct and immediate diagnosis of TAFRO syndrome.
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Megacariócitos , Humanos , Megacariócitos/patologia , Masculino , Feminino , Pessoa de Meia-Idade , Adulto , Medula Óssea/patologia , Hiperplasia do Linfonodo Gigante/patologia , Hiperplasia do Linfonodo Gigante/diagnóstico , Idoso , Trombocitopenia/patologia , Trombocitopenia/diagnóstico , Mielofibrose Primária/patologia , Mielofibrose Primária/diagnósticoRESUMO
Plant specialized metabolites (PSMs) are often stored as glycosides within cells and released from the roots with some chemical modifications. While isoflavones are known to function as symbiotic signals with rhizobia and to modulate the soybean rhizosphere microbiome, the underlying mechanisms of root-to-soil delivery are poorly understood. In addition to transporter-mediated secretion, the hydrolysis of isoflavone glycosides in the apoplast by an isoflavone conjugate-hydrolyzing ß-glucosidase (ICHG) has been proposed but not yet verified. To clarify the role of ICHG in isoflavone supply to the rhizosphere, we have isolated two independent mutants defective in ICHG activity from a soybean high-density mutant library. In the root apoplastic fraction of ichg mutants, the isoflavone glycoside contents were significantly increased, while isoflavone aglycone contents were decreased, indicating that ICHG hydrolyzes isoflavone glycosides into aglycones in the root apoplast. When grown in a field, the lack of ICHG activity considerably reduced isoflavone aglycone contents in roots and the rhizosphere soil, although the transcriptomes showed no distinct differences between the ichg mutants and wild-types (WTs). Despite the change in isoflavone contents and composition of the root and rhizosphere of the mutants, root and rhizosphere bacterial communities were not distinctive from those of the WTs. Root bacterial communities and nodulation capacities of the ichg mutants did not differ from the WTs under nitrogen-deficient conditions either. Taken together, these results indicate that ICHG elevates the accumulation of isoflavones in the soybean rhizosphere but is not essential for isoflavone-mediated plant-microbe interactions.
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Isoflavonas , Isoflavonas/química , Glycine max/genética , Glycine max/metabolismo , beta-Glucosidase/genética , beta-Glucosidase/química , Rizosfera , Glicosídeos/metabolismo , Bactérias/metabolismo , SoloRESUMO
The oxygen reduction reaction (ORR) activity of Pt catalysts in polymer electrolyte fuel cells (PEFCs) should be enhanced to reduce Pt usage. The adsorption of heteroaromatic ring compounds such as melamine on the Pt surface can enhance its catalytic activity. However, melamine adsorption on Pt and the consequent ORR enhancement mechanism remain unclear. In this study, we performed density functional theory calculations to determine the adsorption structures of melamine/Pt(111). Melamine was coordinated to Pt via two N lone pairs on NH2 and N- in the triazine ring, resulting in a chemisorption structure with slight electron transfer. Four types of adsorption structures were identified: three-point adsorption (two amino groups and a triazine ring: Type A), two-point adsorption (one amino group and a triazine ring: Type B), two-point adsorption (two amino groups: Type C), and one-point adsorption (one amino group: Type D). The most stable structure was Type B. However, multiple intermediate structures were formed owing to the conformational changes from the most stable to other stable adsorption structures. The resonance structures of the adsorbed melamine stabilise the adsorption, as increased resonance allows for more electron delocalisation. In addition, the lone-pair orbital of the amino group in the adsorbed melamine acquires the characteristics of an sp3 hybrid orbital, which prevents horizontal adsorption on the Pt surface. We believe that understanding these adsorption mechanisms will help in the molecular design of organic molecule-decorated Pt catalysts and will lead to the reduction of Pt usage in PEFCs.
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Saponins are the group of plant specialized metabolites which are widely distributed in angiosperm plants and have various biological activities. The present study focused on α-tomatine, a major saponin present in tissues of tomato (Solanum lycopersicum) plants. α-Tomatine is responsible for defense against plant pathogens and herbivores, but its biological function in the rhizosphere remains unknown. Secretion of tomatine was higher at the early growth than the green-fruit stage in hydroponically grown plants, and the concentration of tomatine in the rhizosphere of field-grown plants was higher than that of the bulk soil at all growth stages. The effects of tomatine and its aglycone tomatidine on the bacterial communities in the soil were evaluated in vitro, revealing that both compounds influenced the microbiome in a concentration-dependent manner. Numerous bacterial families were influenced in tomatine/tomatidine-treated soil as well as in the tomato rhizosphere. Sphingomonadaceae species, which are commonly observed and enriched in tomato rhizospheres in the fields, were also enriched in tomatine- and tomatidine-treated soils. Moreover, a jasmonate-responsive ETHYLENE RESPONSE FACTOR 4 mutant associated with low tomatine production caused the root-associated bacterial communities to change with a reduced abundance of Sphingomonadaceae. Taken together, our results highlight the role of tomatine in shaping the bacterial communities of the rhizosphere and suggest additional functions of tomatine in belowground biological communication.
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Microbiota/fisiologia , Raízes de Plantas/metabolismo , Rizosfera , Solanum lycopersicum/metabolismo , Tomatina/metabolismo , Bactérias/metabolismo , Fenômenos Fisiológicos Bacterianos , Solanum lycopersicum/microbiologia , Raízes de Plantas/microbiologiaRESUMO
BACKGROUND: This longitudinal study aimed to determine chronological changes in the seroprevalence of prior SARS-CoV-2 infection, including asymptomatic infections in Hiroshima Prefecture, Japan. METHODS: A stratified random sample of 7,500 residents from five cities of Hiroshima Prefecture was selected to participate in a three-round survey from late 2020 to early 2021, before the introduction of the COVID-19 vaccine. The seroprevalence of anti-SARS-CoV-2 antibodies was calculated if at least two of four commercially available immunoassays were positive. Then, the ratio between seroprevalence and the prevalence of confirmed COVID-19 cases in Hiroshima was calculated and compared to the results from other prefectures where the Ministry of Health, Labour and Welfare conducted a survey by using the same reagents at almost the same period. RESULTS: The numbers of participants in the first, second, and third rounds of the survey were 3025, 2396, and 2351, respectively and their anti-SARS-CoV-2 antibodies seroprevalences were 0.03% (95% confidence interval: 0.00-0.10%), 0.08% (0.00-0.20%), and 0.30% (0.08-0.52%), respectively. The ratio between the seroprevalence and the prevalence of confirmed COVID-19 cases in Hiroshima was 1.2, which was smaller than that in similar studies in other prefectures. CONCLUSIONS: The seroprevalence of anti-SARS-CoV-2 antibodies in Hiroshima increased tenfold in a half year. The difference between seroprevalence and the prevalence of confirmed COVID-19 cases in Hiroshima was smaller than that in other prefectures, suggesting that asymptomatic patients were more actively detected in Hiroshima.
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Vacinas contra COVID-19 , COVID-19 , Anticorpos Antivirais , COVID-19/epidemiologia , Humanos , Estudos Longitudinais , SARS-CoV-2 , Estudos SoroepidemiológicosRESUMO
Collective cell migration is a key process during the development of multicellular organisms, in which the migrations of individual cells are coordinated through chemical guidance and physical contact between cells. Talin has been implicated in mechanical linkage between actin-based motile machinery and adhesion molecules, but how talin contributes to collective cell migration is unclear. Here we show that talin B is involved in chemical coordination between cells for collective cell migration at the multicellular mound stage in the development of Dictyostelium discoideum. From early aggregation to the mound formation, talB-null cells exhibited collective migration normally with cAMP relay. Subsequently, talB-null cells showed developmental arrest at the mound stage, and at the same time, they had impaired collective migration and cAMP relay, while wild-type cells exhibited rotational cell migration continuously in concert with cAMP relay during the mound stage. Genetic suppression of PI3K activity partially restored talB-null phenotypes in collective cell migration and cAMP relay. Overall, our observations suggest that talin B regulates chemical coordination via PI3K-mediated signaling in a stage-specific manner for the multicellular development of Dictyostelium cells.
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Movimento Celular , Dictyostelium/citologia , Fosfatidilinositol 3-Quinases/metabolismo , Talina/fisiologia , Agregação Celular , AMP Cíclico/metabolismo , Dictyostelium/metabolismo , Proteínas de ProtozoáriosRESUMO
Using density functional theory based calculations and atomic-force-microscopy observations, we investigated the interaction between [RhIII(OEP)(Cl)] (OEP = octaethylporphyrin) and a graphite basal surface, and the electronic structure of [RhIII(OEP)(Cl)]/graphite. The [RhIII(OEP)(Cl)] complex has an electronic structure effective for CO activation, possessing a closed singlet structure as its ground state; hence, both σ-donation from the CO molecule (anode-reaction reactant) to RhIII, and π-back-donation from RhIII to CO, occur, because the [RhIII(OEP)(Cl)] complex does not have a singlet occupied molecular orbital on the porphyrin ring, the π-π stacking interaction between porphyrin and graphite is not present and their interaction is dominated by dispersion forces. The [RhIII(OEP)(Cl)] complex easily diffused on the graphite basal surface, and an aggregated structure of [RhIII(OEP)(Cl)] was observed by atomic force microscopy. The difference of the electronic structures of [RhIII(OEP)(Cl)] before and after its adsorption is very small, the dispersion force being the dominant force for the adsorption. However, the lowest unoccupied molecular orbital of [RhIII(OEP)(Cl)]/graphite is a σ bonding orbital between RhIII and graphite that will cause fast electron transfer from [RhIII(OEP)(Cl)] to graphite during the CO electro-oxidation; this would be a reason why the carbon-supported [RhIII(OEP)(Cl)] has high catalytic activity for CO electro-oxidation.
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Boluses used in electron radiotherapy need to have radiation field visibility and water equivalence. In this report, we have examined field visibility and water equivalence of a new colorless transparent bolus. We examined field visibility, water equivalence, and dose profile. Field visibility was evaluated by comparison to conventional bolus. Water equivalence was investigated by a measured fluence scaling factor. The dose profile was measured by using radiochromic film with the bolus and an ionization chamber in water. We confirmed that the irradiation field could clearly be seen through the transparent colorless bolus. The bolus did not cast a field edge as compared with the conventional bolus. The fluence scaling factor was less than 0.8% as compared to water. We confirmed that the colorless transparent bolus was treated as a water equivalent material. The percentage depth dose (PDD) measured by using radiochromic film with the bolus matched the PDD measured with an ionization chamber in water. R50 was less than 1 mm as compared to PDD measured with an ionization chamber. It was confirmed that the colorless transparent bolus can use to set up patient without losing visibility on flat ground planes. The fluence scaling factor and dose profile measured by using the bolus matched the results measured in water. Therefore, the new colorless transparent bolus has feasibility to improve patient setup efficiency and can improve calculation accuracy by using the fluence scaling factor.
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Planejamento da Radioterapia Assistida por Computador , Radioterapia/métodos , Tecnologia Radiológica , Água , Cor , Elétrons , Desenho de Equipamento , Humanos , Radioterapia/instrumentação , Dosagem Radioterapêutica , Pele , Tecnologia Radiológica/instrumentação , Visão OcularRESUMO
Correction for 'Effects of p-substituents on electrochemical CO oxidation by Rh porphyrin-based catalysts' by Shin-ichi Yamazaki et al., Phys. Chem. Chem. Phys., 2010, 12, 8968-8976.
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IMPORTANCE: Saponins are a group of plant specialized metabolites with various bioactive properties, both for human health and soil microorganisms. Our previous works demonstrated that Sphingobium is enriched in both soils treated with a steroid-type saponin, such as tomatine, and in the tomato rhizosphere. Despite the importance of saponins in plant-microbe interactions in the rhizosphere, the genes involved in the catabolism of saponins and their aglycones (sapogenins) remain largely unknown. Here we identified several enzymes that catalyzed the degradation of steroid-type saponins in a Sphingobium isolate from tomato roots, RC1. A comparative genomic analysis of Sphingobium revealed the limited distribution of genes for saponin degradation in our saponin-degrading isolates and several other isolates, suggesting the possible involvement of the saponin degradation pathway in the root colonization of Sphingobium spp. The genes that participate in the catabolism of sapogenins could be applied to the development of new industrially valuable sapogenin molecules.
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Sapogeninas , Saponinas , Solanum lycopersicum , Humanos , Sapogeninas/metabolismo , Esteroides , Saponinas/metabolismo , Plantas/metabolismoRESUMO
α-Tomatine is a major saponin that accumulates in tomatoes (Solanum lycopersicum). We previously reported that α-tomatine secreted from tomato roots modulates root-associated bacterial communities, particularly by enriching the abundance of Sphingobium belonging to the family Sphingomonadaceae. To further characterize the α-tomatine-mediated interactions between tomato plants and soil bacterial microbiota, we first cultivated tomato plants in pots containing different microbial inoculants originating from three field soils. Four bacterial genera, namely, Sphingobium, Bradyrhizobium, Cupriavidus, and Rhizobacter, were found to be commonly enriched in tomato root-associated bacterial communities. We constructed a pseudo-rhizosphere system using a mullite ceramic tube as an artificial root to investigate the influence of α-tomatine in modifying bacterial communities. The addition of α-tomatine from the artificial root resulted in the formation of a concentration gradient of α-tomatine that mimicked the tomato rhizosphere, and distinctive bacterial communities were observed in the soil close to the artificial root. Sphingobium was enriched according to the α-tomatine concentration gradient, whereas Bradyrhizobium, Cupriavidus, and Rhizobacter were not enriched in α-tomatine-treated soil. The tomato root-associated bacterial communities were similar to the soil bacterial communities in the vicinity of artificial root-secreting exudates; however, hierarchical cluster analysis revealed a distinction between root-associated and pseudo-rhizosphere bacterial communities. These results suggest that the pseudo-rhizosphere device at least partially creates a rhizosphere environment in which α-tomatine enhances the abundance of Sphingobium in the vicinity of the root. Enrichment of Sphingobium in the tomato rhizosphere was also apparent in publicly available microbiota data, further supporting the tight association between tomato roots and Sphingobium mediated by α-tomatine.
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Partial water exchange is one of the most common conventional methods used to maintain water quality and aesthetic beauty in recirculating aquarium systems (RASs). However, this method uses substantial amount of water. The ozone-down-flow hanging sponge-up-flow sludge blanket (ozone-DHS-USB) system attempts to be a more responsible method for aquarium maintenance. It eliminates the necessity for water exchange in aquarium by maintaining nitrogen concentrations at a safe level and by reducing yellow substances. Also, the impact of O3 on the DHS-USB system was investigated. The system was assayed using an on-site freshwater aquarium influenced by ambient temperature ranging from 23°C to 34°C. During ozonation Phases 1 and 3, the colour of the water in the aquarium was successfully maintained below 10 colour units. The 16S rRNA gene analysis of microorganisms in the DHS revealed that constant application of O3 has caused a decrease in nitrite-oxidizing bacteria (NOB). Nevertheless, NH3 and NO2- were maintained within 0.1â mg N L-1, and NO3- was maintained at 14.6 ± 9.20â mg N L-1 throughout the study. Carps survived for 425 days without any water exchange performed. Our study supports that the ozone-DHS-USB system has a high potential towards creating low-maintenance aquaria.
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Ozônio , Reatores Biológicos , Água Doce , RNA Ribossômico 16S , EsgotosRESUMO
Cell migration plays an important role in multicellular organism development. The cellular slime mold Dictyostelium discoideum is a useful model organism for the study of cell migration during development. Although cellular ATP levels are known to determine cell fate during development, the underlying mechanism remains unclear. Here, we report that ATP-rich cells efficiently move to the central tip region of the mound against rotational movement during the mound phase. A simulation analysis based on an agent-based model reproduces the movement of ATP-rich cells observed in the experiments. These findings indicate that ATP-rich cells have the ability to move against the bulk flow of cells, suggesting a mechanism by which high ATP levels determine the cell fate of differentiation.
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Dictyostelium , Movimento Celular , Diferenciação Celular , Trifosfato de AdenosinaRESUMO
Several factors related to anti-spike(S) IgG antibody titers after mRNA COVID-19 vaccination have been elucidated, but the magnitude of the effects of each factor has not been fully understood. This cross-sectional study assessed anti-S and anti-nucleocapsid (N) antibody titers on 3744 healthy volunteers (median age, 36 years; IQR, 24-49 years; females, 59.0%) who received two doses of mRNA-1273 or BNT162b2 vaccine and completed a survey questionnaire. Multiple regression was conducted to identify factors associated with antibody titers. All but one participant tested positive for anti-S antibodies (99.97%). The following factors were independently and significantly associated with high antibody titer: < 3 months from vaccination (ratio of means 4.41); mRNA-1273 vaccine (1.90, vs BNT162b2); anti-N antibody positivity (1.62); age (10's: 1.50, 20's: 1.37, 30's: 1.26, 40's: 1.16, 50's: 1.15, vs â§60's); female (1.07); immunosuppressive therapy (0.54); current smoking (0.85); and current drinking (0.96). The largest impact on anti-S IgG antibody titers was found in elapsed time after vaccination, followed by vaccine brand, immunosuppressants, previous SARS-CoV-2 infection (anti-N antibody positive), and age. Although the influence of adverse reactions after the vaccine, gender, smoking, and drinking was relatively small, they were independently related factors.
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Vacinas contra COVID-19 , COVID-19 , Imunoglobulina G , Vacina de mRNA-1273 contra 2019-nCoV/administração & dosagem , Vacina de mRNA-1273 contra 2019-nCoV/efeitos adversos , Vacina de mRNA-1273 contra 2019-nCoV/imunologia , Adulto , Vacina BNT162/administração & dosagem , Vacina BNT162/efeitos adversos , Vacina BNT162/imunologia , COVID-19/epidemiologia , COVID-19/prevenção & controle , Vacinas contra COVID-19/administração & dosagem , Vacinas contra COVID-19/efeitos adversos , Vacinas contra COVID-19/imunologia , Estudos Transversais , Feminino , Voluntários Saudáveis , Humanos , Esquemas de Imunização , Imunoglobulina G/sangue , Imunossupressores , Japão/epidemiologia , Masculino , Pessoa de Meia-Idade , Estudos Soroepidemiológicos , Vacinação , Adulto JovemRESUMO
Plant specialized metabolites (PSMs) are secreted into the rhizosphere, i.e., the soil zone surrounding the roots of plants. They are often involved in root-associated microbiome assembly, but the association between PSMs and microbiota is not well characterized. Saponins are a group of PSMs widely distributed in angiosperms. In this study, we compared the bacterial communities in field soils treated with the pure compounds of four different saponins. All saponin treatments decreased bacterial α-diversity and caused significant differences in ß-diversity when compared with the control. The bacterial taxa depleted by saponin treatments were higher than the ones enriched; two families, Burkholderiaceae and Methylophilaceae, were enriched, while eighteen families were depleted with all saponin treatments. Sphingomonadaceae, which is abundant in the rhizosphere of saponin-producing plants (tomato and soybean), was enriched in soil treated with α-solanine, dioscin, and soyasaponins. α-Solanine and dioscin had a steroid-type aglycone that was found to specifically enrich Geobacteraceae, Lachnospiraceae, and Moraxellaceae, while soyasaponins and glycyrrhizin with an oleanane-type aglycone did not specifically enrich any of the bacterial families. At the bacterial genus level, the steroidal-type and oleanane-type saponins differentially influenced the soil bacterial taxa. Together, these results indicate that there is a relationship between the identities of saponins and their effects on soil bacterial communities.
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The plant root-associated environments such as the rhizosphere, rhizoplane, and endosphere are different from the outer soil region (bulk soil). They establish characteristic conditions including microbiota, metabolites, and minerals, and they can directly affect plant growth and development. However, comprehensive insights into those characteristic environments, especially the rhizosphere, and molecular mechanisms of their formation are not well understood. In the present study, we investigated the spatiotemporal dynamics of the root-associated environment in actual field conditions by multi-omics analyses (mineral, microbiome, and transcriptome) of soybean plants. Mineral and microbiome analyses demonstrated a characteristic rhizosphere environment in which most of the minerals were highly accumulated and bacterial communities were distinct from those in the bulk soil. Mantel's test and co-abundance network analysis revealed that characteristic community structures and dominant bacterial taxa in the rhizosphere significantly interact with mineral contents in the rhizosphere, but not in the bulk soil. Our field multi-omics analysis suggests a rhizosphere-specific close association between the microbiota and mineral environment.
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Bactérias , Glycine max/microbiologia , Microbiota/fisiologia , Rizosfera , Filogenia , Raízes de Plantas/microbiologia , Microbiologia do SoloRESUMO
L-Canavanine, a conditionally essential non-proteinogenic amino acid analog to L-arginine, plays important roles in cell division, wound healing, immune function, the release of hormones, and a precursor for the synthesis of nitric oxide (NO). In this report, we found that the L-canavanine is released into the soil from the roots of hairy vetch (Vicia villosa) and declines several weeks after growth, while it was absent in bulk proxy. Hairy vetch root was able to exudate L-canavanine in both pots and in vitro conditions in an agar-based medium. The content of the L-canavanine in pots and agar conditions was higher than the field condition. It was also observed that the addition of L-canavanine significantly altered the microbial community composition and diversity in soil. Firmicutes and Actinobacteria became more abundant in the soil after the application of L-canavanine. In contrast, Proteobacteria and Acidobacteria populations were decreased by higher L-canavanine concentration (500 nmol/g soil). Prediction of the soil metabolic pathways using PICRUSt2 estimated that the L-arginine degradation pathway was enriched 1.3-fold when L-canavanine was added to the soil. Results indicated that carbon metabolism-related pathways were altered and the degradation of nitrogen-rich compounds (i.e., amino acids) enriched. The findings of this research showed that secretion of the allelochemical L-canavanine from the root of hairy vetch may alter the soil microbial community and soil metabolite pathways to increase the survival chance of hairy vetch seedlings. This is the first report that L-canavanine acts as an allelochemical that affects the biodiversity of soil microbial community.
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Carbon monoxide (CO) poisoning of platinum (Pt)-based electrocatalysts is a huge obstacle in the development of proton-exchange membrane fuel cells. Fuel cell performance can be improved by removing CO through electrolytic oxidation. Yamazaki et al. synthesized several rhodium (Rh) tetraphenylporphyrin complexes as electrocatalysts to reduce CO poisoning. Experimental results showed that these complexes display higher electrochemical CO oxidation activity than previously synthesized Rh octaethylporphyrin complex and that the differences in the structures of p-substituted groups influence their activity. To confirm the formation of these Rh tetraphenylporphyrin complexes, analyses were performed using electrospray ionization mass spectrometry (ESI-MS), electrospray ionization tandem mass spectrometry (ESI-MS/MS), and capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI-MS). In ESI-MS, peaks other than that of the Rh tetraphenylporphyrin complex were occasionally detected at different m/z values. The ESI-MS/MS and CE-ESI-MS results suggest that these peaks correspond to the complexes coordinating CO or other ions, or to remaining uncoordinated tetraphenylporphyrins. Coordination of CO is supported by the ESI-MS/MS results for the Rh octaethylporphyrin complex. Separation of the uncoordinated tetraphenylporphyrin from Rh tetraphenylporphyrin complex was achieved by CE-ESI-MS.
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Electrochemical CO oxidation by several carbon-supported rhodium tetraphenylporphyrins with systematically varied meso-substituents was investigated. A quantitative analysis revealed that the p-substituents on the meso-phenyl groups significantly affected CO oxidation activity. The electrocatalytic reaction was characterized in detail based on the spectroscopic and X-ray structural results as well as electrochemical analyses. The difference in the activity among Rh porphyrins is discussed in terms of the properties of p-substituents along with a proposed reaction mechanism. Rhodium tetrakis(4-carboxyphenyl)porphyrin (Rh(TCPP)), which exhibited the highest activity among the porphyrins tested, oxidized CO at a high rate at much lower potentials (<0.1 V vs. a reversible hydrogen electrode, at 60 degrees C) than the present PtRu catalysts. This means that CO is electrochemically oxidized by this catalyst when a slight overpotential is applied during the operation of a proton exchange membrane fuel cell. This catalyst exhibited little H(2) oxidation activity, in contrast to Pt-based catalysts.