Construction and Preparation of the Novel ADN/CL-20 Cocrystal via Directional Hydrogen Bonding Design for Turning Hygroscopicity

Ammonium dinitramide (ADN), as a novel and environmentally friendly oxidizer, has strong hygroscopicity when exposed to high-humidity air, which seriously hinders its application in solid propellants. Modification of oxidizers by cocrystallization is an effective strategy to improve the hygroscopicity of energetic components. In this paper, the theoretical simulation of ADN/CL-20 cocrystals was developed via a directional hydrogen bonding design to establish a cocrystal with improved hygroscopicity. Intermolecular interaction analyses reveal that hydrogen bonds and van der Waals interactions synergistically lead to the formation of cocrystals. The ADN/CL-20 cocrystal was prepared experimentally by the spray drying self-assembly technique, and the corresponding thermal analysis and sensitivity properties were conducted to illustrate the thermal stability and high safety. Furthermore, the critical relative humidity (CRH) measurement was carried out to evaluate the hygroscopicity of the cocrystal, exhibiting a certain degree of antihygroscopic effect with a CRH of 65%. The hydrogen bonds formed between ADN and CL-20 saturate the ammonium ions of ADN, further preventing ADN from absorbing water molecules in the air. The ADN/CL-20 cocrystal has high specific impulse characteristics (Isp: 272.6 s). Accordingly, this work clearly demonstrates that the ADN/CL-20 cocrystal is expected to be used in a solid propellant to make up for the deficiency of the ADN oxidizer.

Prediction of Ethanol-Mediated Growth Morphology of Ammonium Dinitramide/Pyrazine-1,4-Dioxide Cocrystal at Different Temperatures

The crystal morphology of high energetic materials plays a crucial role in aspects of their safety performance such as impact sensitivity. In order to reveal the crystal morphology of ammonium dinitramide/pyrazine-1,4-dioxide (ADN/PDO) cocrystal at different temperatures, the modified attachment energy model (MAE) was used at 298, 303, 308, and 313 K to predict the morphology of the ADN/PDO cocrystal under vacuum and ethanol. The results showed that under vacuum conditions, five growth planes of the ADN/PDO cocrystal were given, which were (1 0 0), (0 1 1), (1 1 0), (1 1 -1), and (2 0 -2). Among them, the ratios of the (1 0 0) and (0 1 1) planes were 40.744% and 26.208%, respectively. In the (0 1 1) crystal plane, the value of S was 1.513. The (0 1 1) crystal plane was more conducive to the adsorption of ethanol molecules. The order of binding energy between the ADN/PDO cocrystal and ethanol solvent was (0 1 1) > (1 1 -1) > (2 0 -2) > (1 1 0) > (1 0 0). The radial distribution function analysis revealed that there were hydrogen bonds between the ethanol and the ADN cations, van der Waals interactions with the ADN anions. As the temperature increased, the aspect ratio of the ADN/PDO cocrystal was reduced, making the crystal more spherical, which helped to further reduce the sensitivity of this explosive.

A novel cocrystal of metformin hydrochloride with citric acid: Systematic synthesis and computational simulation

Pharmaceutical cocrystals have matured into an effective technique for tuning the physicochemical and mechanical properties of drugs in solid form simultaneously. Herein, in order to provide a novel cocrystal form of oral medicine metformin hydrochloride (MH), citric acid (CA) was selected as an efficient ligand after screening a variety of inorganic and organic acids. Thus, based on the principle of crystal engineering, we report a novel cocrystal: metformin hydrochloride - citric acid (MHCA) after the systematic screening, which was experimentally proved to be constituted with 1:1 stoichiometry. Compared with pure MH, MHCA has been proved higher solubility in water, methanol, and ethanol from 283.15 to 313.15 K. Through single-crystal X-ray diffraction (SC-XRD), the particular molecular structure of MHCA has been determined as the orthorhombic system and Pbca space group. Besides, the binding model of MH-CA was built for investigating the binding energy and stability between two components at 278, 298, and 318 K, which were found to be essential for the prediction and analysis of cocrystals. The contribution of different intermolecular interactions and the strength of molecular packing in the cocrystal also have been investigated by Hirshfeld surface analysis. It was found that the cocrystal structure was mainly stabilized by intermolecular hydrogen bonds existing as N-H···O between components, which indicated that the diffusion-combination trend of molecules enhanced the regular array of cocrystal. The results revealed that the molecules of MH and CA formed supramolecular cocrystals mainly induced by hydrogen bonds after passive contacts, such as co-crystallization or grind.

Theoretical simulation study on crystal property and hygroscopicity of ADN doping with nitramine explosives (RDX, HMX, and CL-20)

To effectively modify the strong hygroscopicity of ammonium dinitramide (ADN) crystal, the modification of ADN crystal in the 298 K under vacuum environment was studied through theoretical calculation. Three kinds of energetic nitramine molecules (X = RDX, HMX, and CL-20) were inserted into ADN crystal in different proportions (the molecular ratios of ADN to X are 6/1, 12/1, 18/1, and 24/1), to form a total of 12 kinds of designed ADN crystals. The results show that with the modification of ADN crystal with RDX, HMX, and CL-20, the crystal space group, cell parameters, crystal density, and growth morphology will be changed under vacuum conditions. According to the analyses of adsorption heat data, four proportional modification systems all reduced the hygroscopicity of ADN crystal to varying degrees. It is worth noting that the hygroscopicity of modified ADN crystal tends to decrease with the increase of the proportion of doping molecules, but the stability gradually deteriorates, especially 18ADN/1CL-20 and 24ADN/1CL-20. Although they have an excellent anti-moisture effect, from the perspective of crystal energy stability, the actual syntheses of these two kinds of crystal cells are the most difficult. Combined with the energy stability and hygroscopicity analysis, 1HMX/24ADN crystal is a more suitable anti-hygroscopicity modification scheme among the doped ADN crystals. In this case, the isothermal adsorption heat of ADN crystal decreases from 0.692 kcal/mol to 0.573 kcal/mol. The theoretical simulation study of ADN doping modification in a vacuum will provide significant references for ADN modification in the actual situation.

Study on the solubilization of telmisartan by forming cocrystals with aromatic carboxylic acids

The solubility of insoluble telmisartan could be greatly improved by forming cocrystals with aromatic carboxylic acids.