A bibliometric and visualization analysis of global research status and frontiers on autophagy in cardiomyopathies from 2004 to 2023.

BACKGROUND: Autophagy is intimately associated with the development of cardiomyopathy, and has received widespread attention in recent years. However, no relevant bibliometric analysis is reported at present. In order to summarize the research status of autophagy in cardiomyopathy and provide direction for future research, we conducted a comprehensive, detailed, and multidimensional bibliometric analysis of the literature published in this field from 2004 to 2023. METHODS: All literatures related autophagy in cardiomyopathy from 2004 to 2023 were collected from the Web of Science Core Collection (WOSCC), and annual papers, global publication trends and proportion charts were analyzed and plotted using Graphpad price v8.0.2. In addition, CtieSpace (6.2.4R (64 bit) Advanced Edition) and VOSviewer (1.6.18 Edition) were used to analyze and visualize these data. RESULTS: 2279 papers about autophagy in cardiomyopathy were accessed in the WoSCC over the last 20 years, comprising literatures from 70 countries and regions, 2208 institutions, and 10,810 authors. China contributes 56.32% of the total publications, substantially surpassing other countries, while the U.S. is ranked first in frequency of citations. Among the top 10 authors, 6 are from China and 4 are from the United States. Air Force Military Medical University was the institution with the highest number of publications; while journal of molecular and cellular cardiology (62 articles, 2.71% of the total) was the journal with the highest number of papers published in the field. Clustering of co-cited references and temporal clustering analysis showed that ferroptosis, hydrogen sulfide mitophagy, lipid peroxidation, oxidative stress, and SIRT-1 are hot topics and trends in the field. The principal keywords are oxidative stress, heart and heart-failure. CONCLUSION: The research on autophagy in cardiomyopathy is in the developmental stage. This represents the first bibliometric analysis of autophagy in cardiomyopathy , revealing the current research hotspots and future research directions in this field.

Effect of Physical Activity on the Association Between Diet and Constipation: Evidence From the National Health and Nutrition Examination Survey 2007-2010.

Background/Aims: Previous studies have shown that diet and physical activity can influence constipation. However, the combined effect of diet and physical activity on constipation remains unclear. Methods: Constipation was defined based on stool consistency and frequency, while overall diet quality was assessed using Healthy Eating Index (HEI)-2015 scores. Participants were categorized into low (metabolic equivalent [MET]-min/wk < 500) and high physical activity groups (MET-min/wk ≥ 500). The association between diet and constipation across physical activity groups was analyzed using survey logistic regression and restricted cubic splines. Results: Higher HEI-2015 scores were associated with reduced constipation risk in the high physical activity group when constipation was defined by stool consistency (odds ratio [OR], 0.98; 95% confidence interval [CI], 0.97-0.99). However, in the low physical activity group, increased HEI-2015 scores did not significantly affect constipation risk (OR, 1.01; 95% CI, 0.97-1.05). Similar results were found when constipation was defined based on stool frequency. In the high physical activity group, increased HEI-2015 scores were significantly associated with a reduced constipation risk (OR, 0.96; 95% CI, 0.94-0.98). Conversely, in the low physical activity group, increased HEI-2015 scores did not affect the risk of constipation (OR, 0.96; 95% CI, 0.90-1.03). Conclusions: Our findings suggest that a higher HEI-2015 score is negatively associated with constipation among individuals with high physical activity levels but not among those with low physical activity levels. This association was consistent when different definitions of constipation were used. These results highlight the importance of combining healthy diet with regular physical activity to alleviate constipation.

High serum copper as a risk factor of all-cause and cause-specific mortality among US adults, NHANES 2011-2014.

Background: Several studies have shown that serum copper levels are related to coronary heart disease, diabetes, and cancer. However, the association of serum copper levels with all-cause, cause-specific [including cardiovascular disease (CVD) and cancer] mortality remains unclear. Objectives: This study aimed to prospectively examine the association of copper exposure with all-cause, CVD, and cancer mortality among US adults. Methods: The data for this analysis was obtained from the National Health and Nutrition Examination Survey (NHANES) between 2011 and 2014. Mortality from all-causes, CVD, and cancer mortality was linked to US National Death Index mortality data. Cox regression models were used to estimate the association between serum copper levels and all-cause, CVD, and cancer mortality. Results: A total of 2,863 adults were included in the main study. During the mean follow-up time of 81.2 months, 236 deaths were documented, including 68 deaths from cardiovascular disease and 57 deaths from cancer. The weighted mean overall serum copper levels was 117.2 ug/L. After adjusting for all of the covariates, compared with participants with low (1st tertile, <103 µg/L)/medium (2st tertile, 103-124 µg/L) serum copper levels, participants with high serum copper levels (3rd tertile, ≥124 µg/L) had a 1.75-fold (95% CI, 1.05-2.92)/1.78-fold (1.19,2.69) increase in all-cause mortality, a 2.35-fold (95% CI, 1.04-5.31)/3.84-fold (2.09,7.05) increase in CVD mortality and a 0.97-fold (95% CI, 0.28-3.29)/0.86-fold (0.34,2.13) increase in cancer mortality. In addition, there was a linear dose-response association between serum copper concentration with all-cause and CVD mortality (P for nonlinear > 0.05). Conclusions: This prospective study found that serum copper concentrations were linearly associated with all-cause and CVD mortality in US adults. High serum copper levels is a risk factor for all-cause and CVD mortality.

Prevalence of Chronic Kidney Disease Among US Adults With Hypertension, 1999 to 2018.

BACKGROUND: Hypertension is a major cause of end-stage renal disease. Assessing temporal trends in the prevalence of chronic kidney disease (CKD) in hypertension could provide information for public health policies and plans. METHODS: From the National Health and Nutrition Examination Survey from 1999 to 2018, a probability sample of adults aged ≥20 years was collected. The primary outcomes were classified according to the estimated glomerular filtration rate and urinary albumin. Trend tests were performed to assess age-standardized prevalence trends of CKD, albuminuria, and macroalbuminuria in US adults with hypertension. RESULTS: A total of 23 120 US adults with hypertension were included in this study. The prevalence of any CKD, albuminuria, or macroalbuminuria in hypertension remained relatively stable. However, the age-standardized prevalence of stage 1 CKD in hypertension increased from 4.9% in 2003 to 2006 to 7.0% in 2015 to 2018 (P=0.0077 for trend). The age-standardized prevalence of stage 3b CKD in hypertension decreased from 2.9% in 2011 to 2014 to 2.1% in 2015 to 2018 (P=0.0350 for trend). A similar trend was observed for the age-standardized prevalence of stages 3 to 5 CKD in hypertension, which declined from 10.9% in 2011 to 2014 to 8.9% in 2015 to 2018 (P=0.0160 for trend). CONCLUSIONS: Among US adults with hypertension, the prevalence of any CKD, albuminuria, and macroalbuminuria remained relatively stable from 1999 to 2018, whereas the hypertensive population showed an increasing trend in stage 1 CKD from 2003 to 2006 to 2015 to 2018 and a decreasing trend in the prevalence of stages 3 to 5 and 3b CKD from 2011 to 2014 to 2015 to 2018.

Xiaotangzhike Pill Attenuates the Progression of Diabetes In Vivo through the Mediation of the Akt/GSK-3ß Axis.

Background: Diabetes seriously threatens the health of people. Traditional Chinese medicine has been proven to inhibit the progression of diabetes. Meanwhile, the Xiaotangzhike pill (XTZK) was known to alleviate the symptom of diabetes. Thus, this research decided to investigate the mechanism underlying the impact of XTZK in diabetes remains unexplored. Methods: To assess the impact of XTZK in diabetes, in vivo model of diabetes was constructed. The contents of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) in the rats were tested by the commercial kits. In addition, Masson and hematoxylin and eosin (H&E) staining were applied for assessing the histological changes and fibrosis in the rats, respectively. Furthermore, a western blot was applied to assess the protein levels. Results: Streptozotocin (STZ) significantly increased the levels of area under the curve (AUC), TG, TC, LDL-C, and decreased the contents of HDL-C in rats, while these phenomena were partially reversed by XTZK. In addition, STZ notably induced inflammatory infiltration and fibrosis in the liver tissues of rats, which was greatly restored by XTZK. The levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and malondialdehyde (MDA) in the serum of rats were notably upregulated by STZ, while the effect of STZ was markedly abolished by XTZK. Meanwhile, STZ-caused the upregulation of p-Smad2 and α-SMA in rats was restored by XTZK. Furthermore, XTZK notably inhibited the progression of Qi and Yin deficiency syndrome in diabetes through the mediation of the Akt/GSK-3ß axis. Conclusion: The Xiaotangzhike pill attenuates the progression of diabetes through the mediation of the Akt/GSK-3ß axis. Hence, our study might supply a novel insight into discovering new strategies against diabetes.

Fabrication and application of biocompatible nanogenerators.

As a new sustainable energy source, ubiquitous mechanical energy has received great attention and was successfully harvested by different types of nanogenerators. Among them, biocompatible nanogenerators are of particular interests due to their potential for biomedical applications. In this review, we provide an overview of the recent achievements in the fabrication and application of biocompatible nanogenerators. The development process and working mechanism of nanogenerators are introduced. Different biocompatible materials for energy harvesting, such as amino acids, peptide, silk protein, and cellulose, are discussed and compared. We then discuss different applications of biocompatible nanogenerators. We conclude with the challenges and potential research directions in this emerging field.

Influence of Vacuum Debinding Temperature on Microstructure and Mechanical Properties of Three-Dimensional-Printed Alumina via Stereolithography.

Herein, the influence of vacuum debinding temperature on microstructure and mechanical properties of three-dimensional-printed alumina is systematically investigated by employing a variety of characterization techniques. The results reveal that the debinding temperature >400°C resulted in negligible weight loss. Moreover, the crystallite size of the sintered alumina decreased with increasing debinding temperature. The lower debinding temperature of 300-350°C did not remove the photosensitive resin, which resulted in a loose lamellar structure. However, the higher debinding temperature (450-600°C) resulted in several irregular small-sized particles. Moreover, the size of alumina particles increased after the sintering process. The Raman analysis revealed that the debinded samples contain C, Al, and O; however, the C has not been detected after sintering. In general, the physical properties, such as shrinkage, open porosity, and relative density, exhibited a close relationship with the flexural strength, which is influenced by the debinding temperature. Based on the physical properties and processing requirements, the optimal vacuum debinding temperature should be in the range of 400-500°C.

Network topological model of reconstructive solid-state transformations.

Reconstructive solid-state transformations are followed by significant changes in the system of chemical bonds, i.e. in the topology of the substance. Understanding these mechanisms at the atomic level is crucial for proper explanation and prediction of chemical reactions and phase transitions in solids and, ultimately, for the design of new materials. Modeling of solid-state transitions by geometrical, molecular dynamics or quantum-mechanical methods does not account for topological transformations. As a result, the chemical nature of the transformation processes are overlooked, which limits the predictive power of the models. We propose a universal model based on network representation of extended structures, which treats any reorganization in the solid state as a network transformation. We demonstrate this approach rationalizes the configuration space of the solid system and enables prediction of new phases that are closely related to already known phases. Some new phases and unclear transition pathways are discovered in example systems including elementary substances, ionic compounds and molecular crystals.

Multiscale modelling for the heterogeneous strength of biodegradable polyesters.

A heterogeneous method of coupled multiscale strength model is presented in this paper for calculating the strength of medical polyesters such as polylactide (PLA), polyglycolide (PGA) and their copolymers during degradation by bulk erosion. The macroscopic device is discretized into an array of mesoscopic cells. A polymer chain is assumed to stay in one cell. With the polymer chain scission, it is found that the molecular weight, chain recrystallization induced by polymer chain scissions, and the cavities formation due to polymer cell collapse play different roles in the composition of mechanical strength of the polymer. Therefore, three types of strength phases were proposed to display the heterogeneous strength structures and to represent different strength contribution to polymers, which are amorphous phase, crystallinity phase and strength vacancy phase, respectively. The strength of the amorphous phase is related to the molecular weight; strength of the crystallinity phase is related to molecular weight and degree of crystallization; and the strength vacancy phase has negligible strength. The vacancy strength phase includes not only the cells with cavity status but also those with an amorphous status, but a molecular weight value below a threshold molecular weight. This heterogeneous strength model is coupled with micro chain scission, chain recrystallization and a macro oligomer diffusion equation to form a multiscale strength model which can simulate the strength phase evolution, cells status evolution, molecular weight, degree of crystallinity, weight loss and device strength during degradation. Different example cases are used to verify this model. The results demonstrate a good fit to experimental data.

Emergence of novel hydrogen chlorides under high pressure.

HCl is a textbook example of a polar covalent molecule, and has a wide range of industrial applications. Inspired by the discovery of unexpected stable sodium and potassium chlorides, we performed systematic ab initio evolutionary searches for all stable compounds in the H-Cl system at pressures up to 400 GPa. Besides HCl, four new stoichiometries (H2Cl, H3Cl, H5Cl and H4Cl7) are found to be stable under pressure. Our predictions substantially differ from previous theoretical studies. We evidence a high significance of zero-point energy in determining phase stability. The newly discovered compounds display a rich variety of chemical bonding characteristics. At ambient pressure, H2, Cl2 and HCl molecular crystals are formed by weak intermolecular van der Waals interactions, and adjacent HCl molecules connect with each other to form asymmetric zigzag chains, which become symmetric under high pressure. In H5Cl, triangular H3+ cations are stabilized by electrostatic interactions with the anionic chloride network. Further increase of pressure drives H2 dimers to combine with H3+ cations to form H5+ units. We also found chlorine-based Kagomé layers which are intercalated with zigzag HCl chains in H4Cl7. These findings could help to understand how varied bonding features can co-exist and evolve in one compound under extreme conditions.

Diverse Chemistry of Stable Hydronitrogens, and Implications for Planetary and Materials Sciences.

Nitrogen hydrides, e.g., ammonia (NH3), hydrazine (N2H4) and hydrazoic acid (HN3), are compounds of great fundamental and applied importance. Their high-pressure behavior is important because of their abundance in giant planets and because of the hopes of discovering high-energy-density materials. Here, we have performed a systematic investigation on the structural stability of N-H system in a pressure range up to 800 GPa through evolutionary structure prediction. Surprisingly, we found that high pressure stabilizes a series of previously unreported compounds with peculiar structural and electronic properties, such as the N4H, N3H, N2H and NH phases composed of nitrogen backbones, the N9H4 phase containing two-dimensional metallic nitrogen planes and novel N8H, NH2, N3H7, NH4 and NH5 molecular phases. Another surprise is that NH3 becomes thermodynamically unstable above ~460 GPa. We found that high-pressure chemistry of hydronitrogens is much more diverse than hydrocarbon chemistry at normal conditions, leading to expectations that N-H-O and N-H-O-S systems under pressure are likely to possess richer chemistry than the known organic chemistry. This, in turn, opens a possibility of nitrogen-based life at high pressure. The predicted phase diagram of the N-H system also provides a reference for synthesis of high-energy-density materials.

Effects of carbon vacancies on the structures, mechanical properties, and chemical bonding of zirconium carbides: a first-principles study.

Interstitial carbides are able to maintain structural stability even with a high concentration of carbon vacancies. This feature provides them with tunable properties through the design of carbon vacancies, and thus making it important to reveal how carbon vacancies affect their properties. In the present study, using first-principles, we have calculated the properties of a number of stable and metastable zirconium carbides ZrC1-x (x = 0 and 1/n, n = 2-8) which were predicted by the evolutionary algorithm USPEX. Effects of carbon vacancies on the structures, mechanical properties, and chemical bonding of these zirconium carbides were systematically investigated. The distribution of carbon vacancies has significant influence on mechanical properties, especially Pugh's ratio. Nonadjacent carbon vacancies enhance Pugh's ratio, while grouped carbon vacancies decrease Pugh's ratio. This is explained by the changes in strength of Zr-C and Zr-Zr bonding around differently distributed carbon vacancies. We further explored the mechanical properties of zirconium carbides with impurities (N and O) by inserting N and O atoms into the sites of carbon vacancies. The enhanced mechanical properties of zirconium carbides were found.

Pressure-driven formation and stabilization of superconductive chromium hydrides.

Chromium hydride is a prototype stoichiometric transition metal hydride. The phase diagram of Cr-H system at high pressures remains largely unexplored due to the challenges in dealing with the high activation barriers and complications in handing hydrogen under pressure. We have performed an extensive structural study on Cr-H system at pressure range 0 ∼ 300 GPa using an unbiased structure prediction method based on evolutionary algorithm. Upon compression, a number of hydrides are predicted to become stable in the excess hydrogen environment and these have compositions of Cr2Hn (n = 2-4, 6, 8, 16). Cr2H3, CrH2 and Cr2H5 structures are versions of the perfect anti-NiAs-type CrH with ordered tetrahedral interstitial sites filled by H atoms. CrH3 and CrH4 exhibit host-guest structural characteristics. In CrH8, H2 units are also identified. Our study unravels that CrH is a superconductor at atmospheric pressure with an estimated transition temperature (T c) of 10.6 K, and superconductivity in CrH3 is enhanced by the metallic hydrogen sublattice with T c of 37.1 K at 81 GPa, very similar to the extensively studied MgB2.

Novel compounds in the Zr-O system, their crystal structures and mechanical properties.

With the motivation of exploring new high-strength ceramics, ab initio evolutionary simulations are performed to search for all the stable compounds in the Zr-O system. We have found that not only the traditional compound ZrO2, but also the ordered suboxides R3̅-Zr6O, R3̅c-Zr3O, P3̅1m-Zr2O and P6̅2m-ZrO are stable at zero pressure. The crystal structure of semimetallic P6̅2m-ZrO consists of Zr-graphene layers and can be described as an intercalated version of the ω-Zr structure. An interesting massive Dirac cone is found in the three-dimensional (3D) band structure of P6̅2m-ZrO at the Γ-point. The elastic properties, the hardness and the correlation between the mechanical properties of Zr-O compounds and the oxygen content have been systematically investigated. Surprisingly, the hardest zirconium oxide is not ZrO2, but ZrO. Both P6̅2m-ZrO and P3̅1m-Zr2O exhibit relatively high hardness values of 14 GPa and 10 GPa, respectively. The anisotropic Young's modulus E, torsion shear modulus Gt and linear compressibility ß have been derived for P6̅2m-ZrO and P3̅1m-Zr2O. Further analyses of the density of states, the band structure and the crystal orbital Hamilton population indicate that the electronic structure of Zr-O compounds is directly related to their mechanical properties. The simultaneous occurrence of the 3D-framework of Zr-O and the strong Zr-Zr bonds in P6̅2m-ZrO explains its high hardness.

Phase stability, chemical bonding and mechanical properties of titanium nitrides: a first-principles study.

We have performed first-principles evolutionary searches for stable Ti-N compounds and have found, in addition to the well-known rock-salt TiN, new ground states Ti3N2, Ti4N3, Ti6N5 at atmospheric pressure, and Ti2N and TiN2 at higher pressures. The latter nitrogen-rich structure contains encapsulated N2 dumbbells with a N-N distance of 1.348 Å at 60 GPa. TiN2 is predicted to be mechanically stable and quenchable. Our calculations on the mechanical properties (bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and hardness) are in excellent agreement with the available experimental data. Further analyses of the electronic density of states, crystal orbital Hamilton population and the electron localization function reveal that the hardness is enhanced by strengthening directional covalent bonds and disappearance of Ti-Ti metallic bonding.

Formation of stoichiometric CsFn compounds.

Alkali halides MX, have been viewed as typical ionic compounds, characterized by 1:1 ratio necessary for charge balance between M(+) and X(-). It was proposed that group I elements like Cs can be oxidized further under high pressure. Here we perform a comprehensive study for the CsF-F system at pressures up to 100 GPa, and find extremely versatile chemistry. A series of CsFn (n ≥ 1) compounds are predicted to be stable already at ambient pressure. Under pressure, 5p electrons of Cs atoms become active, with growing tendency to form Cs (III) and (V) valence states at fluorine-rich conditions. Although Cs (II) and (IV) are not energetically favoured, the interplay between two mechanisms (polyfluoride anions and polyvalent Cs cations) allows CsF2 and CsF4 compounds to be stable under pressure. The estimated defluorination temperatures of CsFn (n = 2,3,5) compounds at atmospheric pressure (218°C, 150°C, -15°C, respectively), are attractive for fluorine storage applications.

Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides.

High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as a fitness function in conjunction with first-principles calculations and the global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some of which are new. The results allow us to propose characteristics (genes) common to high-fitness structures--these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue for discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery.

Transition metal atoms pathways on rutile TiO2 (110) surface: distribution of Ti3+ states and evidence of enhanced peripheral charge accumulation.

Charge transfer between metal nanoparticles and the supported TiO2 surface is primarily important for catalytic applications as it greatly affects the catalytic activity and the thermal stability of the deposited nanoparticles on the surface. Herein, systematic spin-polarized density functional and HSE06 calculations are performed to evaluate the adsorption, diffusion, and charge state of several transition metal monomers on both stoichiometric and reduced rutile TiO2 (110) surface. Although the presence of oxygen vacancy (Ov) increases the binding of Au, Pt and Pd on the surface, it weakens the interaction thus enhancing the diffusion for Fe, Co, Ni, Ag, and Cu adatoms on the surface. For pristine reduced surface, only a small portion (around 5%) of the excess electrons occupy the topmost surface, which are mainly delocalized at the second nearest and third nearest fivefold coordinated Ti (Ti5c) atoms. Excess electrons populating at the Ti5c atoms on the basal plane can be transferred to strongly electronegative adsorbates like Au and Pt thus enabling a moderate adsorption at this site, whereas no stable adsorption is found for other less electronegative transition metal adatoms (Ag, Cu, Fe, Co, Ni, and Pd) on the reduced surface and for all the adatoms on stoichiometric surface. This result clarifies the origin of the experimental observation of the adsorption of O2 and CO molecules at Ti5c sites in connection with charge transfer. In addition, the spatial redistribution of the excess electrons around the Ov upon the adsorption of the monomers is thoroughly examined. Our finding of an accumulation of excess electrons at the Ti5c sites around the monomers explains the critical role of the perimeter interface of the deposited nanoparticles in promoting the adsorption and activation of reactants observed in experiments.

Decomposition reaction rate of BCl3-C3H6(propene)-H2 in the gas phase.

The decomposition reaction rate in the BCl(3)-C(3)H(6)-H(2) gas phase reaction system in preparing boron carbides was investigated based on the most favorable reaction pathways proposed by Jiang et al. [Theor. Chem. Accs. 2010, 127, 519] and Yang et al. [J. Theor. Comput. Chem. 2012, 11, 53]. The rate constants of all the elementary reactions were evaluated with the variational transition state theory. The vibrational frequencies for the stationary points as well as the selected points along the minimum energy paths (MEPs) were calculated with density functional theory at the B3PW91/6-311G(d,p) level and the energies were refined with the accurate model chemistry method G3(MP2). For the elementary reaction associated with a transition state, the MEP was obtained with the intrinsic reaction coordinates, while for the elementary reaction without transition state, the relaxed potential energy surface scan was employed to obtain the MEP. The rate constants were calculated for temperatures within 200-2000 K and fitted into three-parameter Arrhenius expressions. The reaction rates were investigated by using the COMSOL software to solve numerically the coupled differential rate equations. The results show that the reactions are, consistent with the experiments, appropriate at 1100-1500 K with the reaction time of 30 s for 1100 K, 1.5 s for 1200 K, 0.12 s for 1300 K, 0.011 s for 1400 K, or 0.001 s for 1500 K, for propene being almost completely consumed. The completely dissociated species, boron carbides C(3)B, C(2)B, and CB, have very low concentrations, and C(3)B is the main product at higher temperatures, while C(2)B is the main product at lower temperatures. For the reaction time 1 s, all these concentrations approach into a nearly constant. The maximum value (in mol/m(3)) is for the highest temperature 1500 K with the orders of -13, -17, and -23 for C(3)B, C(2)B, and CB, respectively. It was also found that the logarithm of the overall reaction rate and reciprocal temperature have an excellent linear relationship within 700-2000 K with a correlation coefficient of 0.99996. This corresponds to an apparent activation energy 337.0 kJ/mol, which is comparable with the energy barrier 362.6 kJ/mol of the rate control reaction at 0 K but is higher than either of the experiments 208.7 kJ/mol or the Gibbs free energy barrier 226.2 kJ/mol at 1200 K.

Reaction rate of propene pyrolysis.

The reaction rate of propene pyrolysis was investigated based on the elementary reactions proposed in Qu et al., J Comput Chem 2009, 31, 1421. The overall reaction rate was developed with the steady-state approximation and the rate constants of the elementary reactions were determined with the variational transition state theory. For the elementary reaction having transition state, the vibrational frequencies of the selected points along the minimum energy path were calculated with density functional theory at B3PW91/6-311G(d,p) level and the energies were improved with the accurate model chemistry method G3(MP2). For the elementary reaction without transition state, the frequencies were calculated with CASSCF/6-311G(d,p) and the energies were refined with the multireference configuration interaction method MRCISD/6-311G(d,p). The rate constants were evaluated within 200-2000 K and the fitted three-parameter expressions were obtained. The results are consistent with those in the literatures in most cases. For the overall rate, it was found that the logarithm of the rate and the reciprocal temperature have excellent linear relationship above 400 K, predicting that the rate follows a typical first-order law at high temperatures of 800-2000 K, which is also consistent with the experiments. The apparent activation energy in 800-2000 K is 317.3 kJ/mol from the potential energy surface of zero Kelvin. This value is comparable with the energy barriers, 365.4 and 403.7 kJ/mol, of the rate control steps. However, the apparent activation energy, 215.7 kJ/mol, developed with the Gibbs free energy surface at 1200 K is consistent with the most recent experimental result 201.9 ± 0.6 kJ/mol.