40 research outputs found

    Kinetic Studies on Nucleophilic Substitution Reactions of <i>O</i>-Aryl Thionobenzoates with Azide, Cyanide, and Hydroxide: Contrasting Reactivity and Mechanism

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    A kinetic study is reported for nucleophilic substitution reactions of O-Y-substituted phenyl thionobenzoates (1a−h) and O-4-nitrophenyl X-substituted thionobenzoates (2a−f) with N3− and CN− in 80 mol % H2O−20 mol % DMSO at 25.0 ± 0.1 °C. The Brønsted-type plot for the reactions of 1a−h with N3− exhibits a downward curvature, i.e., the slope (βlg) changes from −1.10 to −0.33 as the leaving group basicity decreases, indicating that the reactions proceed through a stepwise mechanism with a change in rate-determining step (RDS). In contrast, the Brønsted-type plot for the corresponding reactions with CN− is linear with a βlg value of −0.33. This value is similar to that found previously for the reactions of 1a−h with OH− (−0.35). Besides, σo constants result in much better Hammett correlation than σ− constants. Thus, the reactions with CN− and OH− have been concluded to proceed through a stepwise mechanism in which departure of the leaving group occurs after RDS. Reactions of 2a−f with N3− and CN− result in nonlinear Hammett plots. However, the Yukawa−Tsuno plots for the same reactions exhibit excellent linearity with r = 0.5 ± 0.1, indicating that the nonlinear Hammett plots are not due to a change in RDS but are caused by ground state stabilization through resonance interactions between the electron-donating substituent and the thio carbonyl functionality. Calculation of the k1 values (nucleophile attack as RDS) for the reactions of 1a−h with N3− indicates that azide ion is more reactive than OH− toward the thione esters, although the former is over 11 pKa units less basic than the latter. The high polarizability of N3− has been suggested to be responsible for its great affinity for the polarizable thione esters 1a−h and 2a−f

    Genomic and Metabolomic Analyses of <i>Nocardiopsis maritima</i> YSL2 as the Mycorrhizosphere Bacterium of <i>Suaeda maritima</i> (L.) Dumort

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    Nine bacteria were isolated from the episphere of Suaeda maritima (L.) Dumort. Among them, the bacterial strain YSL2 displayed the highest antimicrobial activity on agar plates and exhibited significant novelty compared with other bacteria based on 16S rRNA analysis. Consequently, Nocardiopsis maritima YSL2T was subjected to phenotypic characterization and whole-genome sequencing. Phylogenetic analysis revealed its close association with Nocardiopsis aegyptia SNG49T. Furthermore, genomic analysis of strain YSL2T revealed the presence of various gene clusters, indicating its potential for producing antimicrobial secondary metabolites. Upon cultivation on a large scale, maritiamides A and B (1 and 2) were isolated and characterized as cyclic hexapeptides based on nuclear magnetic resonance, ultraviolet, infrared, and mass spectrometric data. The absolute configurations of the amino acid residues in the maritiamides were determined through chiral derivatization, utilizing FDAA and GITC. Maritiamides 1 and 2 exhibited promising antibacterial activities against Staphylococcus epidermidis and weakly inhibited the growth of Escherichia coli and Pseudomonas fluorescens

    Encapsulation of Anionic guests in a New Hydantoinylamido Molecular Capsule

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    Resorcin[4]arene-based tetrakis(N-hydantoinylamido)cavitand 1 forms a stable molecular capsule in the presence of suitable anionic guests such as CH3OSO3– or BF4– in C2D2Cl4. Molecular capsule G2@12 is stabilized by the eight intermolecular imide N-H···OC hydrogen bondings, two from each four paired hydantoinyl units, and the eight intramolecular amide N-H···O–CH2-O hydrogen bondings, four on each two cavitands. The formations of molecular capsules were confirmed by 1H, 2D NOESY, and 2D-DOSY NMR

    Baseline characteristics in the dataset.

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    BackgroundReducing the duration of intraoperative hypoxemia in pediatric patients by means of rapid detection and early intervention is considered crucial by clinicians. We aimed to develop and validate a machine learning model that can predict intraoperative hypoxemia events 1 min ahead in children undergoing general anesthesia.MethodsThis retrospective study used prospectively collected intraoperative vital signs and parameters from the anesthesia ventilator machine extracted every 2 s in pediatric patients undergoing surgery under general anesthesia between January 2019 and October 2020 in a tertiary academic hospital. Intraoperative hypoxemia was defined as oxygen saturation ResultsIn total, 1,540 (11.73%) patients with intraoperative hypoxemia out of 13,130 patients’ records with 2,367 episodes were included for developing the model dataset. After model development, 200 (13.25%) of the 1,510 patients’ records with 289 episodes were used for holdout validation. Among the models developed, the GBM had the highest AUROC of 0.904 (95% confidence interval [CI] 0.902 to 0.906), which was significantly higher than that of the LSTM (0.843, 95% CI 0.840 to 0.846 P P P P ConclusionsMachine learning models can be used to predict upcoming intraoperative hypoxemia in real-time based on the biosignals acquired by patient monitors, which can be useful for clinicians for prediction and proactive treatment of hypoxemia in an intraoperative setting.</div
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