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.

[Response of radial growth of Pinus koraiensis in broad-leaved Korean pine forests with different latitudes to climatical factors.] / ä¸åŒçº¬åº¦é˜”å¶çº¢æ¾æž—çº¢æ¾å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å› å­çš„å“åº”.

To reveal the radial growth trends of Pinus koraiensis and the differences in their responses to climate factors among different latitudes, and to assess the dynamic characteristics, adaptabi-lity and sensitivity of P. koraiensis under the influence of climate change, dendrochronological techniques were used to study the relationships between the climatic variables and the radial growth of P. koraiensis in broad-leaved Korean pine forests with different latitudes. The results showed that there were differences in the responses of the radial growth of P. koraiensis in four different latitudes to local climatic factors. In Baishilazi Nature Reserve, the southernmost sample plot, the radial growth of P. koraiensis was significantly positively correlated to the average relative humidity but significantly negatively correlated to the average maximum temperature of growing season. In low altitude of Changbai Mountain Nature Reserve, the intermediate sample plot, it was significantly positively correlated with precipitation, average relative humidity and PDSI, and significantly negatively correlated with the average maximum temperature in growing season. In Liangshui Nature Reserve, the intermediate sample plot, significantly positive correlations occurred for average relative humidity and PDSI in growing season, while significantly negative correlations occurred for the average temperature and the average maximum temperature in growing season. Nevertheless, in Shengshan Nature Reserve, the northernmost sample plot, it was positively correlated to the tempe-rature factors of most months. The climatic variables in June of current year were the main factors limiting the radial growth of P. koraiensis in all latitudes, and the average maximum temperature in June of current year was highly negatively correlated with radial growth for P. koraiensis measured at all sites. In recent four decades, with the rising of temperature, the radial growth of P. koraiensis decreased significantly in the southernmost point, increased significantly in the northernmost point, and did not change significantly in middle latitudes. The distribution area of P. koraiensis would be reduced if the temperature increased and precipitation remained unchanged in the future.

[Climatic effects on radial growth of Korean pines with different bark forms in Liangshui Natural Reserve, Northeast China].

Dendrochronological techniques including correlation functions and single-years analysis were used to study the relationship between the two kinds of Korean pine radial growth in Liangshui Natural Reserve and climatic variables, and to assess the similarities and differences between Korean pine with coarse bark (Pinus koraiensis forma pachidermis) and fine bark (Pinus koraiensis forma leptodermis) in response to climate factors, the main affecting factors and whether the response relationship could be of long-term stability. The results showed that the Korean pine with fine bark was more suitable for dendrochronological study. The radial growth of the two kinds of Korean pine was very sensitive to environmental variables and their climate responses had no significant differ- ences. From 1902 to 2009, meteorological factors in the growing season, especially in June were the primary factors affecting the radial growth of the two kinds of Korean pine in the study area. The temperature showed a significant negative correlation and the precipitation showed a significant positive correlation. The Korean pine growing in different periods had a significantly different iresponse to meteorological factors. With the rapid rise of temperature and drought after 1970, the radial growth of the two kinds of Korean pine was more sensitive to the meteorological factors than before, which was especially more sensitive to temperature in growing season and PDSI in many seasons.