Comparative studies on structure, sensitivity and mechanical properties of CL-20/DNDAP cocrystal and composite by molecular dynamics simulation

Insight into Formation, Synchronized Release and Stability of Co-Amorphous Curcumin-Piperine by Integrating Experimental-Modeling Techniques

Intermolecular interactions between drug and co-former are crucial in the formation, release and physical stability of co-amorphous system. However, the interactions remain difficult to investigate with only experimental tools. In this study, intermolecular interactions of co-amorphous curcumin-piperine (i.e., CUR-PIP CM) during formation, dissolution and storage were explored by integrating experimental and modeling techniques. The formed CUR-PIP CM exhibited the strong hydrogen bond interaction between the phenolic OH group of CUR and the CO group of PIP as confirmed by FTIR, ss 13C NMR and molecular dynamics (MD) simulation. In comparison to crystalline CUR, crystalline PIP and their physical mixture, CUR-PIP CM performed significantly increased dissolution accompanied by the synchronized release of CUR and PIP, which arose from the greater interaction energy of H2O-CUR molecules and H2O-PIP molecules than CUR-PIP molecules, breaking the hydrogen bond between CUR and PIP molecules, and then causing a pair-wise solvation of CUR-PIP CM at the molecular level. Furthermore, the stronger intermolecular interaction between CUR and PIP was revealed by higher binding energy of CUR-PIP molecules, which contributed to the excellent physical stability of CUR-PIP CM over amorphous CUR or PIP. The study provides a unique insight into the formation, release and stability of co-amorphous system from MD perspective. Meanwhile, this integrated technique can be used as a practical methodology for the future design of co-amorphous formulations.

Crystal Structure and Noncovalent Interactions of Heterocyclic Energetic Molecules

Nitrogen-rich heterocyclic compounds are important heterocyclic substances with extensive future applications for energetic materials due to their outstanding density and excellent physicochemical properties. However, the weak intermolecular interactions of these compounds are not clear, which severely limits their widespread application. Three nitrogen-rich heterocyclic compounds were chosen to detect their molecular geometry, stacking mode and intermolecular interactions by crystal structure, Hirshfeld surface, RDG and ESP. The results show that all atoms in each molecule are coplanar and that the stacking mode of the three crystals is a planar layer style. A large amount of inter- and intramolecular interaction exists in the three crystals. All principal types of intermolecular contacts in the three crystals are N···H interactions and they account for 40.9%, 38.9% and 32.9%, respectively. Hydrogen bonding, vdW interactions and steric effects in Crystal c are stronger than in Crystals a and b. The negative ESPs all concentrate on the nitrogen atoms in the three molecules. This work is expected to benefit the crystal engineering of heterocyclic energetic materials.

Noncovalent Interactions and Crystal Structure Prediction of Energetic Materials

The crystal and molecular structures, intermolecular interactions, and energy of CL-20, HATO, and FOX-7 were comparatively predicted based on molecular dynamic (MD) simulations. By comparison, the 2D fingerprint plot, Hirshfeld surface, reduced density gradient isosurface, and electrostatic potential surface were studied to detect the intermolecular interactions. Meanwhile, the effects of vacuum and different solvents on the crystal habit of CL-20, HATO, and FOX-7 were studied by AE and MAE model, respectively. The energy calculation was also analysed based on the equilibrium structures of these crystal models by MD simulations. Our results would provide fundamental insights for the crystal engineering of energetic materials.

Molecular dynamics simulations of a cyclotetramethylene tetra-nitramine/hydrazine 5,5'-bitetrazole-1,1'-diolate cocrystal

An energetic ionic salt (EIS)-based cocrystal formation, cyclotetramethylene tetra-nitramine (HMX)/hydrazine 5,5′-bitetrazole-1,1′-diolate (HA·BTO), is predicted based on molecular dynamics simulations. HA·BTO is a newly-synthesized environmentally friendly energetic ionic salt with good detonation performance and low sensitivity. Calculated powder X-ray diffraction patterns and intermolecular interactions deduce the formation of the new cocrystal structure. Radial distribution function analysis suggests that hydrogen bonds and van der Waals (vdW) forces exist between the H⋯O pairs of HMX and HA·BTO, while the hydrogen bonds between the H of HA·BTO and the O of HMX play a prominent role. The cohesive energy density and mechanical properties are also analyzed. The cohesive energy density of the HMX/HA·BTO cocrystal is larger than that of the composite of HMX and HA·BTO, indicating an improvement in crystal stability by cocrystalization. Compared to both HMX and HA·BTO, HMX/HA·BTO has smaller Young modulus, bulk modulus and shear modulus values, but larger K/G values and a positive Cauchy pressure, suggesting decreased stiffness and improved ductibility. Moreover, the calculated formation energy is −405.79 kJ mol⁻¹ at 298 K, which implies that the proposed cocrystal structure is likely to be synthesized at ambient temperature. In summary, we have predicted an EIS-based cocrystal formation in which the safety and mechanical properties of HMX have been improved via cocrystalization with HA·BTO, and this provides deep insight into the formation mechanism of the EIS-based cocrystal.

An energetic ionic salt-based cocrystal formation, HMX/HA·BTO, is predicted based on molecular dynamics simulations.

Preparation of CL-20/TFAZ cocrystals under aqueous conditions: balancing high performance and low sensitivity

CL-20/TFAZ cocrystal explosives were prepared by a self-assembly method under aqueous conditions with both low sensitivity and high detonation performances.