Theoretical Kinetics studies of isoprene peroxy radical chemistry: The fate of Z-δ-(4-OH, 1-OO)-ISOPOO radical.

The OH radical recycling mechanism in isoprene oxidation is one of the most exciting topics in atmospheric chemistry, and the corresponding studies expand our understanding of oxidation mechanisms of volatile organic compounds in the troposphere and provide reliable evidence to improve and develop conventional atmospheric models. In this work, we performed a detailed theoretical kinetics study on the Z-δ-(4-OH, 1-OO)-ISOPOO radical chemistry, which is proposed as the heart of OH recycling in isoprene oxidation. With the full consideration of its accumulation and consumption channels, we studied and discussed the fate of Z-δ-(4-OH, 1-OO)-ISOPOO radical by solving the energy-resolved master equation over a broad range of conditions, including not only room temperatures but also high temperatures of a forest fire or low temperatures and pressures of the upper troposphere. We found non-negligible pressure dependence of its fate at combustion temperatures (up to two orders of magnitude) and demonstrated the significance of both the multi-structural torsional anharmonicity and tunneling for accurately calculating kinetics of the studied system. More interestingly, the tunneling effect on the phenomenological rate constants of the H-shift reaction channel is also found to be pressure-dependent due to the competition with the O2 loss reaction. In addition, our time evolution calculations revealed a two-stage behavior of critical species in this reaction system and estimated the shortest half-lives for the Z-δ-(4-OH, 1-OO)-ISOPOO radical at various temperatures, pressures and altitudes. This detailed kinetics study of Z-δ-(4-OH, 1-OO)-ISOPOO radical chemistry offers a typical example to deeply understand the core mechanism of OH recycling pathways in isoprene oxidation, and provides valuable insights for promoting the development of relevant atmospheric models.

Master equation study of hydrogen abstraction from HCHO by OH via a chemically activated intermediate.

The abstraction reaction of hydrogen from formaldehyde by OH radical plays an important role in formaldehyde oxidation. The reaction involves a bimolecular association to form a chemically activated hydrogen-bonded reaction complex followed by a unimolecular reaction of the complex to generate the products. The reaction rate is usually considered to be pressure-independent by assuming equilibrium between the reactants and the complex. However, our nonequilibrium calculations based on the chemically significant eigenmode of the master equation, carried out with our recently developed TUMME program, indicate that the reaction complex makes the rate constant dependent on pressure at low temperatures (T < 200 K). The calculations include anharmonicity, variational effects, and multi-dimensional tunneling. We find that the reaction rate constant reaches a low-pressure limit at pressures below 10 Torr over the whole investigated temperature range (20-1800 K), which explains why the available low-temperature experiments, which are for pressures below 2 Torr, did not observe the pressure dependence. A new extension of the TUMME master-equation program is used to explore the time evolutions of the concentrations of the OH radical and the complex under pseudo-first-order conditions. The time-dependent evolution of the concentrations of the complex at a low temperature provide direct evidence for the stabilization of the reaction complex at high pressures, and it shows the negligible role of the stabilized reaction complex at low pressures. The picture that emerges is qualitatively consistent with our previous study of the reaction of methanol with OH in that the tunneling in the unimolecular step from the complex to the products affects the phenomenological reaction rate constants differently at high and low pressures and leads to a significant pressure effect.

Pressure-dependent kinetics of the o-xylene reaction with OH radicals.

OH-initiated oxidation reactions of o-xylene are widely concerned both in combustion and atmospheric chemistry. In this work, the kinetics of the o-xylene reaction with OH radicals has been studied systematically in a wide temperature range of 220-3000 K for the high-pressure limit and several selected pressures from 1 torr to 500 atm using multi-structural variational transition state theory with the small-curvature tunneling approximation (MS-CVT/SCT) and the system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) method. The calculations fully considered various factors which could affect the accuracy of the calculated rate constants including anharmonicity of both low- and high-frequency modes and multiple low-energy conformers, variational effect, and tunneling. The results are in good agreement with the available experimental data. The obtained overall rate constants exhibit a nonmonotonic temperature dependence due to the competition between the hydrogen abstraction and addition reactions. At low temperatures, the addition channels are dominant reactions, but the abstraction reactions are also non-ignorable with a ∼12% contribution to the overall rate constants at 298 K and 1 atm. Above 800 K, the abstraction reactions become dominant under all the pressure conditions. In addition, we observed a more significant pressure dependence of o-xylene plus OH reaction as compared to the similar toluene plus OH reaction, which is the effect of the additional methyl group. At T = 500-1000 K, the pressure can influence the total rate constants of the o-xylene reaction by a factor of up to 2.5. These kinetics data provide us with a comprehensive understanding of the mechanism and pressure-dependence of kinetics for the o-xylene + OH reaction, which is also beneficial for the study of other similar aromatic hydrocarbon reactions.

Observing Intramolecular Vibrational Energy Redistribution via the Short-Time Fourier Transform.

Intramolecular vibrational energy relaxation (IVR) is important in many problems in chemical physics. Here, we apply the short-time Fourier transform method for analyzing IVR with classical dynamics. Calculating time-dependent Fourier transforms to perform such an analysis requires extending the usual Fourier transform method, and we do that here. The guiding concept behind the generalization is that if there is a shift of vibrational energy from one frequency range to another, we see a difference between the spectrum before the shift and the spectrum after the shift. We use time-window functions to transform the power spectrum of a trajectory into a time-dependent density spectrum of the average kinetic energy. The time-dependent average kinetic energy for each interval of the spectrum becomes an indicator to monitor the extent and nature of the energy transfer into and out of the corresponding modes. We illustrate this method for the H2O molecule. By analyzing cases with different initial conditions, we show that the short-time Fourier transform method can distinguish trends in IVR that depend on the initial distribution of energy and not just on the total energy.

Phonon lasing with an atomic thin membrane resonator at room temperature.

Graphene has been considered as one of the best materials to implement mechanical resonators due to their excellent properties such as low mass, high quality factors and tunable resonant frequencies. Here we report the observation of phonon lasing induced by the photonthermal pressure in a few-layer graphene resonator at room temperature, where the graphene resonator and the silicon substrate form an optical cavity. A marked threshold in the oscillation amplitude and a narrowing linewidth of the vibration mode are observed, which confirms a phonon lasing process in the graphene resonator. Our findings will stimulate the studies on phononic phenomena, help to establish new functional devices based on graphene mechanical resonators, and might find potential applications in classical and quantum sensing fields, as well as in information processing.

Energy Dependence of Ensemble-Averaged Energy Transfer Moments and Its Effect on Competing Decomposition Reactions.

We carried out a direct dynamics study on the internal-energy dependence of the ensemble-averaged energy transfer moments of the isobutyl radical in collisions with N2 bath gas. We find a linear dependence of the downward moment ⟨ΔEd⟩ and the root-mean-square moment ⟨ΔE2⟩ on the initial internal energy, but the upward moment ⟨ΔEu⟩ is found to be independent of the molecule's internal energy. We improved the exponential-down relaxation model by including a linear dependence of ⟨ΔEd⟩ on the initial energy, and we used the improved treatment in the 1D master equation for isobutyl radical decomposition reactions and for a model of competitive reactions with a larger difference in barrier heights. We calculated phenomenological rate constants and branching ratios from chemically significant eigenmodes of the master equation and showed that the energy dependence of ⟨ΔEd⟩ has a greater influence on channels with higher barriers in competitive reactions. Rate constants and branching ratios from master equation calculations indicate that for a given temperature and pressure, there is a constant ⟨ΔEd⟩ that can reproduce results obtained with an E-dependent ⟨ΔEd⟩. But a constant ⟨ΔEd⟩ cannot do this for all temperatures and pressures, with larger differences when the barriers for the competing channels differ more. We conclude that when the branching ratio of competitive reactions is sensitive to pressure, including the energy dependence of ⟨ΔEd⟩ in master equation simulations can make a significant difference in the results.

Low-Pressure Limit of Competitive Unimolecular Reactions.

Barker and Ortiz found unusual falloff effects in the flux coefficients of the competitive unimolecular reactions of 2-methylhexyl radicals, and they concluded that this might have important effects on the rate constants of reactions with higher thresholds. To study this effect, we carried out master equation calculations of the same reaction system to learn whether this effect shows up in measurable rate constants, and the answer is yes. We also studied specially designed mechanisms to reveal that the various reactive pathways connecting the reagents can have a large effect on the rate constants, causing them to be quite different than if the reactions proceeded independently, and that reactions with significantly higher barriers may nevertheless have larger rate constants. This provides a new perspective for interpreting and predicting the kinetics of competitive unimolecular reactions.

Quantum Effects on H2 Diffusion in Zeolite RHO: Inverse Kinetic Isotope Effect for Sieving.

We use canonical variational theory (CVT) with small-curvature tunneling (SCT) contributions to investigate quantum effects on the H2 diffusion process in the pure-silica zeolite RHO. At low temperature we find an inverse kinetic isotopic sieving effect in that the heavier isotopic species diffuses faster than the lighter one. Three quantum effects contribute to this kinetic isotope effect (KIE). The first one is quantum mechanical tunneling; this-on its own-would lead to a normal kinetic isotopic sieving effect, in which lighter diprotium diffuses faster than dideuterium. The second factor, which we find to dominate in the present case, is zero-point energy (ZPE). Deuterium has a lower ZPE, which leads to a smaller effective barrier for tunneling because the transition state has a larger ZPE than the precursor stable state; this results in an inverse KIE. The third factor, the thermal vibrational energy (computed from the quantized vibrational partition function), also favors a normal KIE, but it is outweighed by the ZPE effect. The vibrations of the zeolite host framework are found to play an important role at low temperatures, and our calculations consider up to 7296 degrees of freedom at the equilibrium structure and the saddle point and up to 221 degrees of freedom along the reaction path. The importance of quantum considerations on the dynamics is elucidated by comparison to a purely classical treatment.

Computational kinetics of the hydrogen abstraction reactions of n-propanol and iso-propanol by OH radical.

Propanol (n-propanol or iso-propanol (i-propanol)) is a promising clean-burning oxygenated fuel component and fuel additive. Understanding its reactions with OH radical is of great significance in both combustion and atmospheric chemistry. In this work, we calculate the rate constants and branching ratios of the hydrogen abstraction reactions of n-propanol and i-propanol by OH radical in a broad temperature range of 63-2000 K using the competitive canonical unified statistical (CCUS) model. For both n-propanol and i-propanol, in both the high-pressure and low-pressure limits, the total reaction rate constants show a significant negative dependence on temperature in the low temperature regime and approach the capture rate for the formation of the pre-reactive complex when temperature is down to the ultracold regime. Several factors, tunneling, remarkable anharmonicity of high-frequency modes of transition states, and the presence of reaction channels with a negative free energy barrier, contribute to this phenomenon. We observe pressure-dependent branching fractions at T < ∼400 K for n-propanol or T < 200 K for i-propanol, and at higher temperatures, the branching fractions are independent of the pressure. The alpha-hydrogen (Hα) abstraction with a lower barrier is not always dominant as traditionally expected. The H-abstraction from the terminal carbon (Ht) of i-propanol, with a higher barrier, is dominant above 1000 K because of the remarkably larger effect of multi-structural and torsional (MS-T) anharmonicity. In the pressure-dependent ultra-low temperature regime and high-pressure limit, the beta-hydrogen (Hß) abstraction and the hydrogen abstraction from the hydroxyl group (HO) become dominant for n-propanol and i-propanol, respectively, mainly due to the tunneling effect.

Invasion Genetics of Woolly Apple Aphid (Hemiptera: Aphididae) in China.

In China, the woolly apple aphid, Eriosoma lanigerum (Hausmann), was first detected as an invasive species during the 1910s to 1930s, restricted to Shandong, Liaoning, and Yunnan Provinces. However, since the 1990s, the pest has spread into many other areas of China. To determine the possible spread routes of the recently established populations, the genetic diversity and genetic structure of 24 populations in 10 provinces were analyzed using eight microsatellite loci. Analyses using STRUCTURE software identified two genetic clusters overall. Three populations from Yunnan and Xinjiang consisted of individuals originating from a single cluster. Nineteen populations from eight northern provinces consisted only of individuals from another cluster, which formed a single large and panmictic population, resembling a distinct "supercolony" in Northern China. The other two populations from Yunnan consisted of individuals from both clusters. The possible routes of spread of the recently established populations of E. lanigerum in China were revealed as follows: 1) the populations in Northern China (including these from Henan, Hebei, Shanxi, Shannxi, Jiangsu, and Gansu) may have been introduced from Shandong or Liaoning Provinces; 2) the populations in Yunnan consisted of an early-established population and a population introduced secondarily from Shandong or neighboring areas, indicating that the population in Yunnan has at least two sources; and 3) the recently established populations of E. lanigerum in Xinjiang might not have been introduced from the "supercolony" in Northern China. Knowledge of these routes of spread is useful for avoiding further dissemination and/or additional introductions.

Population structure of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), an invasive species from the Americas, 60 years after invading China.

Though the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) was introduced into China more than 60 years ago, the genetic diversity and structure of this exotic insect pest and virus vector have not been studied. To investigate the population genetic characteristics of this invasive species and to identify potential invasion routes, the genetic diversity and population structure of 17 collections of T. vaporariorum from nine provinces in China were analyzed using seven microsatellite loci. The results of the analyses indicated that the genetic diversity for the populations examined from the four provinces: Jilin, Ningxia, Guizhou and Qinghai, was lower than the genetic diversity of populations from the five provinces: Yunnan, Shandong, Shanxi, Liaoning, and Gansu. The T. vaporariorum populations analyzed in this study grouped as two distinct genetic clusters based on the analysis using STRUCTURE, whereas, 8 clusters were identified based on the BAPS analysis. Of the 136 genetic distance (Fst) values, 128 (94%) were associated with a significant exact test. However, there was no significant relationship between Fst and geographical distance. These results demonstrate that populations of T. vaporariorum in China exhibit significant genetic differentiation, indicating the likelihood that multiple introductions of T. vaporariorum into China have occurred. Also, the populations collected from the provinces of Jilin, Ningxia, Guizhou and Qinghai appear to represent secondary introductions originating from other Chinese provinces.

[Transurethral plasmakinetic enucleation of prostate and suprapubic small cut in the treatment of high risk and senior patient with benign prostatic hyperplasia and bladder stones].

OBJECTIVE: To explore the safety and efficiency of transurethral plasmakinetic enucleation of prostate (TUPKEP) and suprapubic small cut in the treatment of high-risk and senior patients with benign prostatic hyperplasia and bladder stones. METHODS: A retrospective review was conducted for 68 high-risk and senior patients with benign prostatic hyperplasia and bladder stones. All of them were treated by TUPKEP and suprapubic small cut. RESULTS: Operation was successfully performed in all 68 cases. And there was no instance of transurethral resection syndrome, shock, myocardial infarct, cerebral infarction, cerebral hemorrhage, permanent urinary incontinence or surgical site infection. Seven patients with temporal urinary incontinence recovered at a mean time of (9.48 ± 1.52) days post-operation. The mean operative duration was (48.63 ± 4.14) min and the mean volume of blood loss (50.97 ± 5.33) ml. The changes of maximum flow rate (Qmax), international prostatic symptom score (I-PSS) and quality-of-life (QOL) were statistically significant before and after operation. Qmax increased from (4.56 ± 0.35) to (18.82 ± 1.65) ml/s (P < 0.001), I-PSS decreased form (21.96 ± 1.89) to (11.23 ± 0.86) (P = 0.018) and QOL decreased from (4.94 ± 0.35) to (1.95 ± 0.32) (P = 0.011). CONCLUSION: The approach of TUPKEP and suprapubic small cut is both safe and effective in the treatment of high-risk and senior patient with benign prostatic hyperplasia and bladder stones and should be widely applied.

Comprehensive Theoretical Study on Four Typical Intramolecular Hydrogen Shift Reactions of Peroxy Radicals: Multireference Character, Recommended Model Chemistry, and Kinetics.

Intramolecular hydrogen shift reactions in peroxy radicals (RO2• → •QOOH) play key roles in the low-temperature combustion and in the atmospheric chemistry. In the present study, we found that a mild-to-moderate multireference character of a potential energy surface (PES) is widely present in four typical hydrogen shift reactions of peroxy radicals (RO2•, R = ethyl, vinyl, formyl methyl, and acetyl) by a systematic assessment based on the T1 diagnostic, %TAE diagnostic, M diagnostic, and contribution of the dominant configuration of the reference CASSCF wavefunction (C02). To assess the effects of these inherent multireference characters on electronic structure calculations, we compared the PESs of the four reactions calculated by the multireference method CASPT2 in the complete basis set (CBS) limit, single-reference method CCSD(T)-F12, and single-reference-based composite method WMS. The results showed that ignoring the multireference character will introduce a mean unsigned deviation (MUD) of 0.46-1.72 kcal/mol from CASPT2/CBS results by using the CCSD(T)-F12 method or a MUD of 0.49-1.37 kcal/mol by WMS for three RO2• reactions (R = vinyl, formyl methyl, and acetyl) with a stronger multireference character. Further tests by single-reference Kohn-Sham (KS) density functional theory methods showed even larger deviations. Therefore, we specifically developed a new hybrid meta-generalized gradient approximation (GGA) functional M06-HS for the four typical H-shift reactions of peroxy radicals based on the WMS results for the ethyl peroxy radical reaction and on the CASPT2/CBS results for the others. The M06-HS method has an averaged MUD of 0.34 kcal/mol over five tested basis sets against the benchmark PESs, performing best in the tested 38 KS functionals. Last, in a temperature range of 200-3000 K, with the new functional, we calculated the high-pressure-limit rate coefficients of these H-shift reactions by the multi-structural variational transition-state theory with the small-curvature tunneling approximation (MS-CVT/SCT) and the thermochemical properties of all of the involved key radicals by the multi-structural torsional (MS-T) anharmonicity approximation method.

Treatment of common cold patients with the shi-cha capsule: a multicenter, double-blind, randomized, placebo-controlled, dose-escalation trial.

This study was designed to determine the therapeutic efficacy and safety of the Shi-cha capsule, a Chinese herbal formula, in the treatment of patients with wind-cold type common cold. In our multi-center, prospective, double-blind, randomized, placebo-controlled, dose-escalation trial, patients with wind-cold type common cold received 0.6 g of Shi-cha capsule plus 0.6 g placebo (group A), 1.2 g of Shi-cha capsule (group B), or 1.2 g placebo (group C), three times daily for 3 days and followed up to 10 days. The primary end point was all symptom duration. The secondary end points were main symptom duration, minor symptom duration, the changes in cumulative symptom score, main symptom score, and minor symptom score 4 days after the treatment, as well as adverse events. A total of 377 patients were recruited and 360 met the inclusive criteria; 120 patients constituted each treatment group. Compared with patients in group C, patients in groups A and B had significant improvement in the all symptom duration, main symptom duration, minor symptom duration, as well as change from baseline of cumulative symptom score, main symptom score, and minor symptom score at day 4. The symptom durations and scores showed slight superiority of group B over group A, although these differences were not statistically significant. There were no differences in adverse events. The Shi-cha capsule is efficacious and safe for the treatment of patients with wind-cold type common cold. Larger trials are required to fully assess the benefits and safety of this treatment for common cold.

Evaluation of digestibility differences for apple polyphenolics using in vitro elderly and adult digestion models.

We evaluated the in vitro digestibility of apple polyphenols mimicking elderly and adult digestion models (dynamic and static systems). The digestibility of total apple polyphenols in small intestine was much higher in the adult dynamic system (62 µg/100 g fresh apple) compared to the static system (20 µg/100 g fresh apple) and elderly dynamic digestion conditions (33 µg/100 g fresh apple). Elderly in vitro static digestion showed better antioxidant activity than the adult system (OH and ABTS+ methods). Thus, the in vitro dynamic digestion system can more truly reflect the digestion of apple polyphenols than static digestion system. Moreover, elderly digestion conditions negatively influenced the digestibility of apple polyphenols including chlorogenic acid, epicatechin, phlorizin, rutin, phloretin, hyperoside, proanthocyanidin B2, and quercetin. Hence, appropriate selection of in vitro digestion models for elderly is a prerequisite to exploring the digestibility of phytochemicals for the development of functional food products for elderly.

Purification, structural characterization, and anticoagulant activity evaluation of chondroitin sulfate from codfish (Gadus macrocephalus) bones.

Chondroitin sulfate (CCS) was purified from discarded codfish (Gadus macrocephalus) bones, and its chemical structure and anticoagulant activity were assessed. CCS was obtained via enzymatic lysis and ion-exchange column chromatography, with a yield of approximately 0.15%. High-performance gel performance chromatography revealed CCS to be a largely homogeneous polysaccharide with a relatively low molecular weight of 12.3 kDa. FT-IR spectroscopy, NMR spectroscopy, and SAX-HPLC indicated that CCS was composed of monosulfated disaccharides (ΔDi4S 73.85% and ΔDi6S 19.06%) and nonsulfated disaccharides (ΔDi0S 7.09%). In vitro anticoagulation analyses revealed that CCS was able to significantly prolong activated partial thromboplastin time (APTT) and thrombin time (TT) (p < 0.05). At a CCS concentration of 5 µg/mL and 25 µg/mL, APTT and TT were approximately 1.08 and 1.12 times higher, respectively, compared to the negative control group. The results indicated that CCS might offer value as a dietary fiber supplement with the potential to prevent the incidence of coagulation-related thrombosis.

Mechanisms underlying operational energy consumption of buildings for low carbon city construction: A review.

With rapid urbanization, the increasing building stock, building operation energy consumption and the corresponding carbon emissions have become the important factors restricting the sustainable development of cities. To reduce energy consuming, it is necessary to explore the mechanisms underlying building's operational energy consumption and carbon emission. Although previous studies have analyzed the influencing factors and driving mechanism of urban building carbon emission from different perspectives, a systematical review of the relevant studies which could provide comprehensive guidance for building energy conservation and consumption reduction is fairly scarce. Following the Social-Economic-Natural Complex Ecosystem theory, we comprehensively discussed the driving mechanisms of the building's operational energy consumption and carbon emission. We further analyzed the various single-source driving mechanisms from the perspective of socio-economic, building feature, regional climate and microclimate conditions. Finally, we tackled the weaknesses of current researches and addressed the prospect for future development. The driving mechanism summarized in this work would contribute to the development of related research and support low carbon city construction.

Treatment of functional constipation with the Yun-chang capsule: a double-blind, randomized, placebo-controlled, dose-escalation trial.

BACKGROUND AND AIM: Functional constipation is a common functional bowel disorder for which there is no reliable medical treatment. This study was designed to determine the therapeutic efficacy and safety of the Yun-chang capsule, a Chinese herbal formula, in the treatment of patients with functional constipation. METHODS: In our multi-center, prospective, double-blind, randomized, placebo-controlled, dose-escalation trial, patients with functional constipation received 70 mg of Yun-chang capsule plus 35 mg placebo (group A), 105 mg of Yun-chang capsule (group B), or 105 mg placebo (group C), three times daily for 2 weeks. The primary end-points were the changes in main symptom score and cumulative symptom score 2 weeks after the treatment. The secondary end-points were adverse events. RESULTS: A total of 140 patients were recruited and 132 met the inclusion criteria; 44 patients constituted each of the three treatment groups. Compared with patients in group C, patients in groups A and B had significant improvement in the main symptom score, cumulative symptom score, the change from baseline of the main symptom score, and the change from baseline of the cumulative symptom score at week 1 and week 2. The scores showed slight superiority of group B over group A at week 1 and week 2, although these differences were not statistically significant. There were no differences in adverse events. CONCLUSIONS: The Yun-chang capsule is efficacious and safe for the treatment of patients with functional constipation. Larger and longer-term trials are required to fully assess the benefits and safety of this treatment for functional constipation.