Anisotropic structure deformation of ß-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine under high pressure: vibration spectra calculation and resolution based on AIMD simulation.

The phase transition of the ß-HMX crystal has been widely studied under high pressure, but the microscopic transition mechanism is not sufficiently understood. In this article, we perform a series of ab initio molecular dynamics simulations focusing on structure deformation and the corresponding vibration spectra resolution of ß-HMX at 0-40 GPa. Several typical pressure-induced phase transition processes are confirmed by analyzing the chemical bond, dihedral angle, charge transfer, and IR and Raman spectra. The corresponding relationship between molecular structure and spectral signal is constructed through the partial spectra calculations of special functional groups within the HMX molecule. The anisotropic effects of different groups on the initial structural phase transition are uncovered. The equatorial C-N and axial N-N bonds have the largest compression ratio as pressure increases, which is the intrinsic factor for the initiation of structure transformation. The C-N molecular ring plays an important role in the entire phase transition process. In addition, the phase transition of ß â†’ ζ is also closely related to the deformation of NO2, while that of ζ → ε is induced by the axial N-NO2 group. Regarding the higher-pressure phase transition, the synergetic effect of N-NO2, CH2 groups, and molecular rings becomes more considerable.

The Structure Properties of Carbon Materials Formed in 2,4,6-Triamino-1,3,5-Trinitrobenzene Detonation: A Theoretical Insight for Nucleation of Diamond-like Carbon.

The structure and properties of nano-carbon materials formed in explosives detonation are always a challenge, not only for the designing and manufacturing of these materials but also for clearly understanding the detonation performance of explosives. Herein, we study the dynamic evolution process of condensed-phase carbon involved in 2,4,6-Triamino-1,3,5-trinitrobenzene (TATB) detonation using the quantum-based molecular dynamics method. Various carbon structures such as, graphene-like, diamond-like, and "diaphite", are obtained under different pressures. The transition from a C sp2- to a sp3-hybrid, driven by the conversion of a hexatomic to a non-hexatomic ring, is detected under high pressure. A tightly bound nucleation mechanism for diamond-like carbon dominated by a graphene-like carbon layer is uncovered. The graphene-like layer is readily constructed at the early stage, which would connect with surrounding carbon atoms or fragments to form the tetrahedral structure, with a high fraction of sp3-hybridized carbon. After that, the deformed carbon layers further coalesce with each other by bonding between carbon atoms within the five-member ring, to form the diamond-like nucleus. The complex "diaphite" configuration is detected during the diamond-like carbon nucleation, which illustrates that the nucleation and growth of detonation nano-diamond would accompany the intergrowth of graphene-like layers.

Anisotropic Reaction Properties for Different HMX/HTPB Composites: A Theoretical Study of Shock Decomposition.

Plastic-bonded explosives (PBXs) consisting of explosive grains and a polymer binder are commonly synthesized to improve mechanical properties and reduce sensitivity, but their intrinsic chemical behaviors while subjected to stress are not sufficiently understood yet. Here, we construct three composites of ß-HMX bonded with the HTPB binder to investigate the reaction characteristics under shock loading using the quantum-based molecular dynamics method. Six typical interactions between HMX and HTPB molecules are detected when the system is subjected to pressure. Although the initial electron structure is modified by the impurity states from HTPB, the metallization process for HMX does not significantly change. The shock decompositions of HMX/HTPB along the (100) and (010) surface are initiated by molecular ring dissociation and hydrogen transfer. The initial oxidations of C and H within HTPB possess advantages. As for the (001) surface, the dissociation is started with alkyl dehydrogenation oxidation, and a stronger hydrogen transfer from HTPB to HMX is detected during the following process. Furthermore, considerable fragment aggregation is observed, which mainly derives from the formation of new C-C and C-N bonds under high pressure. The effect of cluster evolution on the progression of the following reaction is further studied by analyzing the bonded structure and displacement rate.

Enhanced Effect of an External Electric Field on NH3BH3 Dehydrogenation: an AIMD Study for Thermolysis.

How to improve the dehydrogenation properties of ammonia borane (AB, NH3BH3) is always a challenge for its practical application in hydrogen storage. In this study, we reveal the enhanced effect of an external electric field (E ext) on AB dehydrogenation by means of the ab initio molecular dynamics method. The molecular rotation induced by an electrostatic force can facilitate the formation of the H-N···B-H framework, which would aggregate into poly-BN species and further suppress the generation of the volatile byproducts. Meanwhile, the dihydrogen bond (N-Hδ+···Î´-H-B) is favorably formed under E ext, and the interaction between relevant H atoms is enhanced, leading to a faster H2 liberation. Correspondingly, the apparent activation energy for AB dissociation is greatly reduced from 18.42 to around 15 kcal·mol-1 with the application of an electric field, while that for H2 formation decreases from 20.4 to about 16 kcal·mol-1. In the whole process, the cleavage of the B-H bond is more favorable than that of the N-H bond, no matter whether the application of E ext. Our results give a deep insight into a positive effect of an electric field on AB dehydrogenation, which would provide an important inspiration for hydrogen storage in industry applications.

Quasi-Static Two-Dimensional Infrared Spectra of the Carboxyhemoglobin Subsystem under Electric Fields: A Theoretical Study.

There is no doubt that electric fields of a specific frequency and intensity could excite certain vibrational modes of a macromolecule, which alters its mode coupling and conformation. Motivated by recent experiments and theories, we study the mode coupling between the Fe-CO mode and CO-stretch mode and vibration energy transfer among the active site and proteins in carboxyhemoglobin (HbCO) under different electric fields using the quasi-static two-dimensional infrared spectra. This study uses iron-porphyrin-imidazole-CO and two distal histidines in HbCO as the subsystem. The potential energy and dipole moment surfaces of the subsystem are calculated using an all-electron ab initio (B3LYP-D3(BJ)) method with the basis set Lanl2dz for the Fe atom and 6-31G(d,p) for C, H, O, and N atoms. Although the subsystem is reduced dimensionally, the anharmonic frequency and anharmonicity of the CO-stretch mode show excellent agreement with experimental values. We use the revealing noncovalent interaction method to confirm the hydrogen bond between the Hε atom of the His63 and the CO molecule. Our study confirms that the mode coupling between the Fe-CO mode and CO-stretch mode does not exist when the subsystem is free of electric field perturbation, which is coupled when the electric field is -0.5142 V/nm. In addition, with the increases of distance between the active site and the His92, there is no vibrational energy transfer between them when the electric field is 1.028 V/nm. We believe that our work could provide new ideas for increasing the dissociation efficiency of the Fe-CO bond and theoretical references for experimental research.

[Role of macrophage migration inhibitory factor in septic shock-induced cardiovascular dysfunction: experiment with rats].

OBJECTIVE: To investigate the role of macrophage migration inhibitory factor (MIF) in septic shock-induced cardiovascular dysfunction. METHODS: 56 SD rats were randomly divided into 7 equal groups: CLP group (undergoing cecal ligation and puncture so as to cause septic shock), CLP + ISO-1 group (ISO-1, was injected before and after CLP), CLP + MIF antibody group (MIF-Ab was injected before and after CLP), CLP + dexamethasone (DEX)-1, 5, and 20 groups [I, 5, or 20 mg/kg was injected 1 h after CLP), and sham operation group. Echocardiography was performed 6 h after CLP to measure the LVEDD, LVESD, FS%, CO, and PP. Catheters were inserted into the femoral artery and vein to measure the mean arterial pressure (MAP) and to be used as the route of drug administration. Phenylephrine (PE) of the concentrations of 0.5, 1, 2, and 2.5 microg/kg was injected intravenously and then the MAP increase percentage (DeltaMAP%) was calculated. Then the rats were euthanized with their hearts and aortas taken out. The aortas were cut into rings, and bathed in Krebs solution. PE of the concentrations of 1 mol/L to 30 micromol/L was added into the solution cumulatively to produce the dose-reaction curve of PE. The maximum energy (Emax) and median effective concentration (EC50) of PE were calculated. Western blotting was used to examine the protein expression of MIF in the myocardium and aorta. Another 70 SD rats were divided into 7 groups as mentioned above to observe the cumulative survival rates within 72 h. RESULTS: The LVEDD and LVESD of the CLP group decreased by 56% and 54% respectively 6 h after CLP, and the LVEDD and LVESD of the ISO-1, MOF-Ab, and DEX-20 groups were all significantly higher than that of the CLP group (all P < 0.05) The FS% of the CLP group was significantly lower than that of the Sham groups, and the FS% of the ISO-1, MOF-Ab, and DEX-20 groups were all significantly higher than that of the CLP group (all P < 0.05). The PP value of the ISO-1, MIF-Ab, and DEX-20 groups were all significantly higher than that of the CLP group (all P < 0.06). The CO of the CLP group was significantly lower than that of the Sham group, and those of the ISO-1, MIF-Ab, and DEX-20 groups were all significantly higher than that of the CLP group (all P < 0.001). The DeltaMAP% of different group all increased after the addition of PE dose-dependently, however, the DeltaMAP% was significantly lower in the CLP group than in the Sham group (P < 0.05), and t significantly higher in the ISO-1, MIF-Ab, and DEX-20 groups than in the CLP group (all P < 0.05). The values of PE-induced maximum aorta tension of the SO-1 and MIF-Ab groups were both significantly higher than that of the CLP group (both P < 0.05). The values of PE-induced maximum aorta tension of the DEX-20 group were all higher than those of the CLP group when the PE concentration was between 1.0 x 10(-6) - 1.0 x 10(-5) mol/L (all P < 0.05), however, were not significantly different those of the CLP group when the PE concentration was over 1.0 x 10(-5) mol/L. The values of Emax were significantly lower in the 6 experimental groups than in the Sham group (all P < 0.05), however, were all significantly higher in the ISO-1, MIF-Ab, and DEX-20 groups than in the CLP group (all P < 0.05). The values of EC50 were significantly higher in the 6 experimental groups than in the Sham group (all P < 0.05), however, were significantly lower in the ISO-1, MIF-Ab, and DEX-20 groups than in the CLP group (all P < 0.05). The protein expression levels of MIF in the heart and aorta were significantly higher in the 6 experimental groups than in the Sham group (all P < 0.05), however, the DEX-1 and DEX-5 groups showed significantly higher MIF expression than DEX-20 group (both P < 0.05). The 72 h survival rates of the ISO-1 and MIF-Ab groups were both significantly higher than that of the CLP group (0%, both P < 0.05). DEX of different dose failed to increase the survival rate. CONCLUSION: MIF plays a pivotal role in the circulation dysfunction in septic ambience. Antagonism and blockade of MIF improve corresponding hemodynamics, vascular responsiveness, and prognosis. Glycocorticoid of high and low dose are poles apart in effects on septic hemodynamics and vaso-reactivity, however, fails to improve the prognosis of sepsis no matter how high is the dose.