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.

Intermolecular Vibration Energy Transfer Process in Two CL-20-Based Cocrystals Theoretically Revealed by Two-Dimensional Infrared Spectra.

Inspired by the recent cocrystallization and theory of energetic materials, we theoretically investigated the intermolecular vibrational energy transfer process and the non-covalent intermolecular interactions between explosive compounds. The intermolecular interactions between 2,4,6-trinitrotoluene (TNT) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and between 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and CL-20 were studied using calculated two-dimensional infrared (2D IR) spectra and the independent gradient model based on the Hirshfeld partition (IGMH) method, respectively. Based on the comparison of the theoretical infrared spectra and optimized geometries with experimental results, the theoretical models can effectively reproduce the experimental geometries. By analyzing cross-peaks in the 2D IR spectra of TNT/CL-20, the intermolecular vibrational energy transfer process between TNT and CL-20 was calculated, and the conclusion was made that the vibrational energy transfer process between CL-20 and TNTII (TNTIII) is relatively slower than between CL-20 and TNTI. As the vibration energy transfer is the bridge of the intermolecular interactions, the weak intermolecular interactions were visualized using the IGMH method, and the results demonstrate that the intermolecular non-covalent interactions of TNT/CL-20 include van der Waals (vdW) interactions and hydrogen bonds, while the intermolecular non-covalent interactions of HMX/CL-20 are mainly comprised of vdW interactions. Further, we determined that the intermolecular interaction can stabilize the trigger bond in TNT/CL-20 and HMX/CL-20 based on Mayer bond order density, and stronger intermolecular interactions generally indicate lower impact sensitivity of energetic materials. We believe that the results obtained in this work are important for a better understanding of the cocrystal mechanism and its application in the field of energetic materials.

Revealing the Relationship between Electric Fields and the Conformation of Oxytocin Using Quasi-Static Amide-I Two-Dimensional Infrared Spectra.

It is reported that the cis/trans conformation change of the peptide hormone oxytocin plays an important role in its receptors and activation and the cis conformation does not lead to antagonistic activity. Motivated by recent experiments and theories, the quasi-static amide-I 2D IR spectra of oxytocin are investigated using DFT/B3LYP (D3)/6-31G (d, p) in combination with the isotope labeling method under different electric fields. The theoretical amide-I IR spectra and bond length of the disulfide bond are consistent with the experimental values, which indicates that the theoretical modes are reasonable. Our theoretical results demonstrate that the oxytocin conformation is transformed from the cis conformation to the trans conformation with the change of the direction of the electric field, which is confirmed by the distance of the backbone carbonyl oxygen of Cys6 and Pro7, the Ramachandran plot of Cys6 and Pro7, the dihedral angle of Cß-S-S-Cß, and the rmsd of the oxytocin backbone. Moreover, the trans conformation as the result of the turn in the vicinity of Pro7 has a tighter secondary spatial structure than the cis conformation, including stronger hydrogen bonds, longer γ-turn geometry involving five amino acids, and a more stable disulfide bond. Our work provides new insights into the relationship between the conformation, the activation of the peptide hormone oxytocin, and the electric fields.

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.

[Clinical analysis of 438 patients with essential thrombocythemia].

OBJECTIVE: To analyse the clinical feature and natural course of essential thrombocythemia (ET). METHODS: A retrospective analysis was conducted in ET patients treated in our hospital during May 1980 to December 2006. RESULTS: Four hundred and thirty eight patients (201 males and 237 females with a median age of 48 years) were diagnosed. Hemorrhage occurred in 101 cases (23.1%), thrombosis in 86 cases (19.6%), and both hemorrhage and thrombosis in 13 cases (3.0%). Splenomegaly occurred in 150 cases and hepatomegaly occurred in 60 cases. One hundred and forty-nine cases (34%) had no symptoms at diagnosis and 145 cases (33.1%) confirmed by routine blood tests due to other diseases. The median platelet count at diagnosis was 1000 x 10(9)/L [(533 -3740) x 10(9)/L]. Bone marrow biopsy was performed in 255 cases which showed mainly increase of enlarged mature megakaryocytes with hyper-lobulated nuclei and local proliferation of reticular fiber was revealed in 51 cases. JAK2V617F mutation was detected in 90(78.9%) of 114 patients studied. Karyotype analysis was performed in 180 cases and 6 (3.3%) had clonal chromosomal aberrations. Two hundred and sixty-one patients were followed up over 12 months with a median of 60 months (range from 12 to 300 months). Seventeen cases (6.5%) evolved into marrow fibrosis (MF) and one case into polycythemia vera (PV). One case evolved into PV 6 years and then MF 20 years after diagnosis of ET. Three cases developed acute monocyte leukemia (M5), myelodysplastic syndrome (MDS) and multiple myeloma (MM), respectively. CONCLUSIONS: ET is a chronic myeloproliferative disorder characterized predominantly by thrombocytosis and hemorrhage. The percentage of asymptomatic cases is high. The prognoses for most cases were good with a few cases may evolve into MF.

Chronic idiopathic thrombocytopenic purpura in adult Chinese patients: a retrospective single-centered analysis of 1791 cases.

BACKGROUND: Adult chronic idiopathic thrombocytopenic purpura (ITP) is a common hematologic disease characterized by persistent thrombocytopenia. So far, there were only a few reports on adult Chinese patients with chronic ITP. This study aimed at defining the treatment outcome and prognostic factors for chronic ITP based on a large cohort of Chinese patients followed up for over 25 years at a single center. METHODS: The medical records of 1791 patients aged 14 years or older who were diagnosed as having chronic ITP at our hospital from 1974 to 1999 were retrospectively analyzed. RESULTS: The female-to-male ratio was 2:1, with a median age of 34 years (ranging from 14 to 80 years), median platelet count of 38 x 10(9)/L [range (1-99) x 10(9)/L], and median follow-up of 36 months (range 1-220 months). Steroids were used in 689 patients, among them 209 (30.3%) achieved complete remission (CR). A splenectomy was performed in 124 patients, and response to steroid pre-splenectomy was not available in 14 patients. The CR rate after a splenectomy was lower in steroid nonresponders (29 of 90, 32.2%) than in those who relapsed after successful steroid treatment (12 of 20, 60.0%) (P < 0.05). In comparison with patients negative for antinuclear antibody (ANA), those who were ANA positive had similar responses to steroids, but a significantly shorter remission period after a splenectomy (P < 0.01). CONCLUSIONS: Adult Chinese chronic ITP patients can have long-term remission after steroid therapy and splenectomies. Primary steroid refractoriness is a prognostic factor predicting poor subsequent response to a splenectomy.