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The present study experimentally demonstrated that solid H2O is formed through the surface reaction OH + H2 at 10 K. This is the first experimental evidence of solid H2O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H2O formation through the reaction OH + H2 is about one order of magnitude more effective than HDO formation through the reaction OH + D2. This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling. [ABSTRACT FROM AUTHOR]

We focus on the unique aspects of biuret and biguanide, which form six-membered ring structures via intramolecular hydrogen bonds. The proton donor and acceptor atoms differ between biuret and biguanide, leading to varying energy barrier heights for proton transfer. We performed path integral molecular dynamics (PIMD) simulations for biuret and biguanide to investigate the correlation between proton transfer and the degree of the delocalization of π-electrons in the six-membered ring framework structure. The results indicate that the π-electrons in the framework structure are delocalized regardless of the ease of intramolecular proton transfer.

Aromaticity is an important concept in organic chemistry, and thus, many theoretical and experimental studies have been conducted so far. However, the majority of theoretical studies have concentrated on the aromaticity of the stationary point structures. Herein, the influence of nuclear quantum fluctuation (nuclear quantum effects: NQEs) and thermal fluctuation on the aromaticity of benzene have been analyzed by path integral molecular dynamics (PIMD) simulation. The PIMD simulations revealed that the NQEs affected not only the C-H bonds but also the C-C bonds. The HOMA and NICS calculations demonstrated that the aromaticity decreased due to the NQEs of carbon atoms, attributed to an increase in the contribution from specific vibrational modes strongly correlated with benzene's aromaticity.

The theoretical modeling of high-pressure ice remains challenging owing to the complexity in accurately reflecting its properties attributable to nuclear quantum effects. To explore the nuclear quantum effects of the phase transition between Ice VII and Ice X, we introduce an approach based on ab initio path-integral molecular dynamics. The results indicate that quantum effects facilitate the phase transition, with the observed isotope effects consistent with the experimental outcomes. We demonstrate that quantum effects manifest differently across ice phases: In Ice VII, quantum effects reduce the pressure through the centralization of protons. In contrast, in Ice X, quantum effects increase the pressure owing to the increased kinetic energy of zero-point vibration., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

The structure of the proton-bound dimer compound of hydrogen sulfate and formate has been studied by considering nuclear quantum effects (NQEs) using the path integral molecular dynamics method. This study unveiled the location of the shared proton and answered the following question: "Is the shared proton localized on either an anion or located around the center of two anions?" We have elucidated that the shared proton is distributed in the region beyond the transition state due to the NQEs, even though the shared proton did not completely overcome the transition state for the proton shuttle.

A positive Mu is a useful tool for investigating the spin density of radical species. The theoretical estimation of its behavior in a molecule requires the inclusion of a quantum effect due to the small mass of muonium. Herein, we performed ab initio a path integral molecular dynamics (PIMD) simulation, which accurately included a multi-dimensional quantum effect, for muoniated 9H-xanthene-9-thione (μXT). Our results showed that the quantum effect significantly increased the hyperfine coupling constant (HFCC) value of μXT, which qualitatively improved the calculated HFCC value, compared to the experimental one. In the PIMD simulation, the bond length between muonium and sulfur in μXT is longer than that between hydrogen and sulfur in a hydrogenated 9H-xanthene-9-thione (HXT), leading to a spin density transfer from XT (9H-xanthene-9-thione) to muonium due to neutral dissociations. Additionally, we found that the S-Mu bond in μXT prefers a structure perpendicular to the molecular plane, where the interaction between Mu and the singly occupied molecular orbital of μXT is the strongest. These structural changes resulted in a larger HFCC value in the PIMD simulation of μXT., (© 2023 Author(s). Published under an exclusive license by AIP Publishing.)

Curcumin and its derivatives possess intramolecular low-barrier hydrogen bonds for intramolecular proton transfer. The π-delocalization in the OCCCO framework of the hydrogen bond in these compounds is reorganized concomitantly with the proton transfer. To characterize the hydrogen bond and π-delocalization, we performed path integral molecular dynamics simulations, revealing that although the proton migration and reorganization of the π-delocalized structure showed a positive correlation, the correlation was weak.

Path integral molecular dynamics (PIMD) simulations for C 6 H 6 , C 6 D 6 , and C 6 T 6 have been carried out to directly estimate the distribution of projected C-H(D,T) bond lengths onto the principal axis plane. The average values of raw C-H(D,T) bond lengths obtained from PIMD simulations are in the order of ⟨ R C-H ⟩ > ⟨ R C-D ⟩ > ⟨ R C-T ⟩ due to the anharmonicity of the potential energy curve. However, the projected C-H(D,T) bond lengths are almost the same as those reported by Hirano et al. [ J. Mol. Struct. 2021 , 1243 , 130537]. Our PIMD simulations directly and strongly support the explanation by Hirano et al. for the experimental observations that almost the same projected C-H(D) bond lengths are found for C 6 H 6 and C 6 D 6 . The PIMD simulations also predicted the same projected bond lengths for C 6 T 6 as those of C 6 H(D) 6 . In addition to the previous local mode analysis, the present PIMD simulations predicted, for benzene isotopologues, that the vibrationally averaged structure is planar but non-flat.

The nuclear quantum effects (NQEs) in dihydrogen bond (DHB) complexes, i.e. , NH 4 + ⋯BeH 2 and NH 4 + ⋯MgH 2 , have been investigated using multicomponent quantum mechanics (MC_QM) calculations and path integral molecular dynamics (PIMD) simulation. The MC_QM method considers the NQEs, whereas PIMD considers both the NQEs and the thermal effects. The linear C 3v structure is maintained in the optimized structures obtained by the static MP2 and MC_MP2 calculations, whereas the average structures obtained by the PIMD simulation are nonlinear. The strong DHB interaction in NH 4 + ⋯MgH 2 suppresses the fluctuation in the H δ+ NMg and H δ- MgN angles, and hence, the NH 4 + rotation did not occur in the simulation of NH 4 + ⋯MgH 2 . The analysis of the radius of gyration revealed that the nuclear quantum fluctuation in the perpendicular direction is suppressed by the formation of the DHB complex, whereas that in the parallel direction is slightly enhanced in both the H δ+ and H δ- nuclei.

The compounds Fujikurin A, B, and D, recently isolated from Fusarium fujikuroi , possess intramolecular low-barrier hydrogen bonds (LBHBs), which are hydrogen bonds with a very low-energy barrier for proton transfer. The isolated compounds have a hydrogen-bonded proton that appears to rapidly switch between two equilibrium states via a transition state (TS). To understand the characteristics of these intramolecular LBHBs in detail, we performed path integral molecular dynamics (PIMD) simulations, which can consider nuclear quantum effects (NQEs) under a finite temperature. The PIMD simulations predicted that the NQE completely washed out the energy barrier for the proton transfer reaction. Consequently, a single-well shape emerged in the results, along with the effective free-energy potential surface for the hydrogen-bonded proton distribution. Thus, we conclude that the hydrogen-bonded proton in Fujikurin does not in fact transfer between two equilibrium structures but widely delocalizes around the global minimum structure involving the TS region., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

We have performed density functional calculations to investigate the carbon monoxide hydrogenation reaction (H+CO→HCO), which is important in interstellar clouds. We found that the activation energy of the reaction on amorphous ice is lower than that on crystalline ice. In the course of this study, we demonstrated that it is roughly possible to use the excitation energy of the reactant molecule (CO) in place of the activation energy. This relationship holds also for small water clusters at the CCSD level of calculation and the two-layer-level ONIOM (CCSD : X3LYP) calculation. Generally, since it is computationally demanding to estimate activation energies of chemical reactions in a circumstance of many water molecules, this relationship enables one to determine the activation energy of this reaction on ice surfaces from the knowledge of the excitation energy of CO only. Incorporating quantum-tunneling effects, we discuss the reaction rate on ice surfaces. Our estimate that the reaction rate on amorphous ice is almost twice as large as that on crystalline ice is qualitatively consistent with the experimental evidence reported by Hidaka et al. [Chem. Phys. Lett., 2008, 456, 36.]., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reported here is the first observation of the tunneling surface diffusion of a hydrogen (H) atom on water ice. Photostimulated desorption and resonance-enhanced multiphoton ionization methods were used to determine the diffusion rates at 10 K on amorphous solid water and polycrystalline ice. H-atom diffusion on polycrystalline ice was 2 orders of magnitude faster than that of deuterium atoms, indicating the occurrence of tunneling diffusion. Whether diffusion is by tunneling or thermal hopping also depends on the diffusion length of the atoms and the morphology of the surface. Our findings contribute to a better understanding of elementary physicochemical processes of hydrogen on cosmic ice dust.

We used dibasic acid esters as the absorbent for a volatile organic compounds (VOC) recovery and reuse system geared mainly toward VOCs from painting and presswork. The system consists of three elements: absorption using dibasic acid esters, separation by vacuum spray flash method, and recovery by condensation. The concentration of both ethyl acetate (EtAc) and isopropyl alcohol (IPA) decreased around 90% at room temperature. Vacuum spray flash was found as a useful process for cost-effective and energy-effective VOC removal system. The difference in the dissolubility parameters (Hansen constant) between dibasic acid esters and VOCs and the boiling point of VOCs was the main contributor to the separation behavior.

Background: Food hypersensitivity, from the standpoint of pathogenesis as well as clinical management, remains controversial. During the food allergen-induced immediate hypersensitivity reaction, various chemical mediators are released., Objective: The purpose of our study was to determine whether thromboxane A2 participates in food antigen-induced responses in children with food hypersensitivity., Methods: Nine open food challenges were performed in nine patients with suspected food hypersensitivity. Plasma thromboxane B2 and histamine levels were measured during a 24-hour period following the challenge., Results: All the patients demonstrated immediate reactions after food challenge. The mean plasma thromboxane B2 level (a marker of thromboxane A2 activity) rose significantly at two hours and three hours after the challenge. Simultaneously, the mean plasma histamine level rose significantly at two hours and three hours after the challenge., Conclusions: The results suggest that thromboxane A2 may play a pathogenic role in part in the immediate reaction after food challenge and that thromboxane A2 is probably released from a common cellular source (eg, mast cell) with histamine and/or by a common mechanism (eg, IgE-dependent platelet activation).

Pharmacokinetic and clinical studies on SY5555, a new oral penem antibiotics, were performed in pediatric infections and the following results were obtained. 1. Pharmacokinetics studies Pharmacokinetics of SY5555 was studied in 5 children (5y1m-10y11m) using doses of 5 mg/kg (n = 3) and 10 mg/kg (n = 2). The average peak plasma levels were 0.65 microgram/ml at 1 or 2 hours after administration of 5 mg/kg and 2.12 micrograms/ml at 1 or 2 hours after administration of 10 mg/kg, and the plasma half-lives were 0.81 and 1.08 hours, respectively. Average cumulative urinary recovery rates at 0-6 hours were 2.97 and 3.96%, respectively. 2. Clinical studies SY5555 was administered to 45 patients with various infectious diseases (2 with acute pharyngitis, 8 with acute tonsillitis, 4 with lacunar tonsillitis, 3 each with acute bronchitis, pneumonia and pertussis, 7 with scarlet fever, 3 with impetigo contagiosa, 6 with acute urinary tract infections, 2 with balanoposthitis and 1 each with cervical lymphadenitis, S.S.S.S., vulvitis and acute colitis) at daily doses between 3.4-10 mg/kg, t.i.d., for 3-14 days. Clinical responses were excellent in 27 patients, good in 15 patients, fair in 1 patient, and poor in 2 patients, and the efficacy rate was 93.3%. Causative organisms were examined and 39 strains of 11 species were identified. The eradication rate was 78.9%. Side effects were observed in 1 patient with diarrhea. An abnormal laboratory test value was observed in 1 patient with elevation of eosinophils. The above results suggest that SY5555 may be a very useful and safe drug for the treatment of pediatric infection.

This study was undertaken to investigate the kinetics of histamine and tryptase in the circulation of patients with food allergy and to determine whether the measurements of plasma histamine and tryptase concentrations after food challenges provided additional predictive markers for the diagnosis and evaluation of food allergy. Twenty-one open food challenges were performed on 13 patients with suspected food allergy. Plasma histamine and tryptase concentrations were measured during 4 hours after challenge. In the group of patients with immediate reactions after challenges, the mean plasma histamine concentration rose significantly at 120 and 240 minutes after the challenge, and the mean plasma tryptase concentration was increased significantly at 240 minutes after challenge. Plasma histamine and tryptase concentrations were measured during 24 hours after 8 open food challenges in 7 other patients with suspected food allergy. In each patient with a nonimmediate reaction, plasma histamine concentrations were increased at the onset of symptoms after challenge, but no plasma tryptase concentrations increased. The elevation of plasma histamine and tryptase in patients with immediate reactions following food challenge indicates mast cell activation. On the other hand, the elevation of plasma histamine without elevated plasma tryptase in the patients with nonimmediate reactions following food challenge may indicate basophil activation rather than mast cell activation. Plasma histamine and tryptase measurements after food challenge may be useful in the detection and evaluation of food allergy.

Effects of weight reduction on serum levels of lipids and apolipoproteins were measured in 13 obese children (seven girls, six boys). Mean weight loss of 8.4% of the initial body weight was achieved after 4 weeks of energy intake restriction and exercise. Serum total cholesterol (5.46 +/- 1.01 mmol/L) and triglyceride (2.08 +/- 0.52 mmol/L) levels were significantly high compared with control values before treatment and were significantly reduced to 4.32 +/- 0.75 and 1.31 +/- 0.42 mmol/L, respectively, after treatment. Serum high-density lipoprotein cholesterol level (1.03 +/- 0.23 mmol/L) was significantly low and unchanged after treatment (0.94 +/- 0.25 mmol/L). Serum apolipoprotein A-I level (0.039 +/- 0.009 mmol/L or 111 +/- 0.26 g/L) was normal before treatment and significantly reduced, to 0.032 +/- 0.007 mmol/L or 0.92 +/- 0.19 g/L, after weight reduction. Serum apolipoprotein B level (0.00019 +/- 0.00007 mmol/L or 1.07 +/- 0.21 g/L) was significantly high before treatment and decreased to the normal range after treatment (0.00014 +/- 0.0009 mmol/L or 0.76 +/- 0.24 g/L). The ratio of apolipoprotein B to apolipoprotein A-I (1.09 +/- 0.29) was significantly high on admission and decreased significantly to 0.64 +/- 0.12 after treatment. Serum apolipoprotein E level (0.0014 +/- 0.0006 mmol/L or 0.05 +/- 0.02 g/L) was normal and decreased to 0.0008 +/- 0.0002 mmol/L or 0.03 +/- 0.01 g/L after treatment. In conclusion, weight reduction achieved by energy intake restriction and exercise had beneficial effects on serum lipid and apolipoprotein concentrations for the prevention of future atherosclerosis.