Intelligent Molecular Identification for High Performance Organosulfide Capture Using Active Machine Learning Algorithm

Machine learning and computer-aided approaches significantly accelerate molecular design and discovery in scientific and industrial fields increasingly relying on data science for efficiency. The typical method used is supervised learning which needs huge datasets. Semi-supervised machine learning approaches are effective to train unlabeled data with improved modeling performance, whereas they are limited by the accumulation of prediction errors. Here, to screen solvents for removal of methyl mercaptan, a type of organosulfur impurities in natural gas, we constructed a computational framework by integrating molecular similarity search and active learning methods, namely, molecular active selection machine learning (MASML). This new model framework identifies the optimal molecules set by molecular similarity search and iterative addition to the training dataset. Among all 126,068 compounds in the initial dataset, 3 molecules were identified to be promising for methyl mercaptan (MeSH) capture, including benzylamine (BZA), p-methoxybenzylamine (PZM), and N,N-diethyltrimethylenediamine (DEAPA). Further experiments confirmed the effectiveness of our modeling framework in efficient molecular design and identification for capturing methyl mercaptan, in which DEAPA presents a Henry's law constant 89.4% lower than that of methyl diethanolamine (MDEA).

Synthesis of Methyl Mercaptan on Mesoporous Alumina Prepared with Hydroxysafflor Yellow A as Template: The Synergistic Effect of Potassium and Molybdenum

K-promoted Mo-based catalysts showed great promise for the hydrogenation of CS2 to methyl mercaptan (CH3SH). However, the research on the synergistic effect of K and Mo, and the active site of CS2 hydrogenation to CH3SH were unexplored widely. To solve this problem, the synergistic effect of K and Mo in the K-promoted Mo-based catalysts for CS2 hydrogenation to prepare CH3SH was investigated. The mesoporous alumina was the support and loaded the active components potassium and molybdenum to prepare the catalyst. The results suggested that the active components K and Mo can not only cooperatively regulate the acid-base sites on the catalyst surface, but also stabilize the molybdate species at +5 valence during the reduction process and increase the Mo unsaturated coordination sites. Combined with the results of the catalytic activity evaluation, indicating that the main active site of the catalysts is the weak Lewis acid-base site, and the strong acidic site and strong alkaline site are not conducive to the formation of CH3SH. Moreover, the possible catalytic mechanism of CS2 hydrogenation to CH3SH on the weak Lewis acid-base sites of the catalysts was proposed. The research results of this paper can provide an experimental basis and theoretical guidance for the design of high-performance CH3SH synthesis catalyst and further mechanism research.

The tongue biofilm metatranscriptome identifies metabolic pathways associated with halitosis and its prevention

Halitosis is an oral condition caused by an increase in the concentration of volatile sulfur compounds (VSCs), such as methyl mercaptan and hydrogen sulfide, generated as a consequence of bacterial metabolism on the tongue biofilm. Microbial communities on the tongue of halitosis patients have been studied by bacterial culture, 16S rRNA taxonomic studies and metagenomics. However, there are currently no reports on the microbial gene-expression profiles. In this study, we performed RNAseq of tongue coating samples from control individuals and halitosis patients with different levels and composition of VSCs, as determined by gas chromatography. In this metatranscriptomic study, the activity of Streptococcus, Veillonella and Rothia species was associated with halitosis-free individuals while Prevotella, Fusobacterium and Leptotrichia species were associated with halitosis. Although methyl mercaptan is considered an indicator of halitosis, the metatranscriptome of patients in which only this VSC was present in elevated levels was similar to that of halitosis-free individuals. Veillonella dispar, Streptococcus parasanguinis and Rothia mucilaginosa were over-represented in halitosis-free communities in comparison to the rest of the groups, suggesting that these species could be used as a halitosis-free biomarkers. In contrast, the abundance of Prevotella shahi and Fusobacterium nucleatum were significantly higher when hydrogen sulfide concentration was over the established halitosis-threshold, making these species putative halitosis biomarkers. Finally, gene expression profiles showed a significant over-expression of genes involved in L-cysteine and L-homocysteine synthesis in halitosis-free individuals and an over-expression of genes responsible for cysteine degradation into hydrogen sulfide in halitosis patients. In addition, nitrate reduction into nitrite was also over-expressed in halitosis-free patients. In conclusion, halitosis was associated with communities that degrade amino acids and reduce sulfide, whereas tongue communities that produce L-cysteine from hydrogen sulfide and that reduce nitrate were associated with the absence of halitosis. The latter could provide new strategies to treat this condition.

CH3SH and H2S Sensing Properties of V2O5/WO3/TiO2 Gas Sensor

Resistive-type semiconductor-based gas sensors were fabricated for the detection of methyl mercaptan and hydrogen sulfide. To fabricate these sensors, V2O5/WO3/TiO2 (VWT) particles were deposited on interdigitated Pt electrodes. The vanadium oxide content of the utilized VWT was 1.5, 3, or 10 wt.%. The structural properties of the VWT particles were investigated by X-ray diffraction and scanning electron microscopy analyses. The resistance of the VWT gas sensor decreased with increasing methyl mercaptan and hydrogen sulfide gas concentrations in the range of 50 to 500 ppb. The VWT gas sensor with 3 wt.% vanadium oxide showed high methyl mercaptan and hydrogen sulfide responses and good gas selectivity against hydrogen at 300 °C.

Inhibitory effect of black cumin (Nigella sativa) seed essential oil on Fusobacterium nucleatum L-methionine-γ-lyase (L-methioninase) activity

The enzyme L-methionine-γ-lyase is commonly found in a wide range of bacteria and catalyzes the α-elimination and γ-elimination of L-methionine to produce methyl mercaptan, α-ketobutyrate, and ammonia. Black cumin seed essential oil (BC oil) reportedly exhibits deodorizing activity against methyl mercaptan. Therefore, we hypothesized that BC oil may also suppress methyl mercaptan production. In this study, we aimed to evaluate the inhibitory effect of BC oil on L-methionine-γ-lyase activity in Fusobacterium nucleatum. Recombinant L-methionine-γ-lyase was incubated under appropriate conditions with BC oil and its constituent thymoquinone. To analyze L-methionine-γ-lyase activity, α-ketobutyric acid and ammonia concentrations were determined. The concentrations of α-ketobutyric acid and ammonia were significantly decreased by 10 µg mL−1 of BC oil (P < 0.01) and 16.4 µg mL−1 of thymoquinone (P < 0.05). An enzyme kinetic assay showed a mixed inhibition pattern between L-methionine-γ-lyase and thymoquinone. In conclusion, BC oil not only had a deodorizing effect against methyl mercaptan but also an inhibitory effect on methyl mercaptan production through the suppression of L-methionine-γ-lyase activity. Thymoquinone may be mainly responsible for these effects of BC oil. Thus, application of natural BC oil may be adapted not only for medical use but also in other areas of life.