Mingzhu Xia

A study of the solvent effect on the morphology of RDX crystal by molecular modeling method

Abstract Molecular dynamics simulations have been performed to investigate the effect of acetone solvent on the crystal morphology of RDX. The results show that the growth morphology of RDX crystal in vacuum is dominated by the (111), (020), (200), (002), and (210) faces using the BFDH laws, and (111) face is morphologically the most important. The analysis of surface structures of RDX crystal indicates that (020) face is non-polar, while (210), (111), (002), and (200) faces are polar among which (210) face has the strongest polarity. The interaction between acetone solvent and each RDX crystal face is different, and the order of binding energy on these surfaces is (210) > (111) > (002) > (200) > (020). The analysis of interactions among RDX and acetone molecules reveal that the system nonbond interactions are primary strong van der Waals and electrostatic interactions containing π-hole interactions, the weak hydrogen bond interactions are also existent. The effect of acetone on the growth of RDX crystal can be evaluated by comparing the binding energies of RDX crystalline faces. It can be predicted that compared to that in vacuum, in the process of RDX crystallization from acetone, the morphological importance of (210) face is increased more and (111) face is not the most important among RDX polar surfaces, while the non-polar (020) face probably disappears. The experimentally obtained RDX morphology grown from acetone is in agreement with the theoretical prediction.

Solvent effect on the crystal morphology of 2,6-diamino-3,5-dinitropyridine-1-oxide: a molecular dynamics simulation study.

The attachment energy (AE) calculations were performed to predict the growth morphology of 2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO) in vacuum. The molecular dynamics (MD) method was applied to simulate the interaction of trifluoroacetic acid solvent with the habit faces and the corrected AE model was adopted to predict the growth habit of ANPyO in the solvent. The results indicate that the growth morphology of ANPyO in vacuum is dominated by (110), (100), (10-1) and (11-2) faces. The corrected AE energies change in the order of (110)>(10-1)>(11-2)>(100), which causes the crystal morphology to become very close to a flake in trifluoroacetic acid solvent and accords well with the results obtained from experiments. The radial distribution function analysis shows that the solvent molecules adsorb on the ANPyO faces mainly via the solvent-crystal face interactions of hydrogen bonds, Coulomb and Van der Waals forces. In addition to the above results, the analysis of diffusion coefficient of trifluoroacetic acid molecules on the crystal growth faces shows that the growth habit is also affected by the diffusion capacity of trifluoroacetic acid molecules. These suggestions may be useful for the formulation design of ANPyO.

A study of the solvent effect on the crystal morphology of hexogen by means of molecular dynamics simulations

In this work, molecular dynamics simulations have been performed to study the solvent effect on the crystal morphology of hexogen. The hexogen growth habits in a vacuum predicted by the AE model are dominated by the (111), (020), (200), (002), and (210) faces. Hexogen surfaces–acetone solvent micro interface models are constructed to study the adsorption behavior of acetone on these habit planes. The modified attachment energy model considering both the solvent–surface adsorption interactions and surface structures is proposed to predict the crystal morphology of hexogen in the acetone solvent. The calculations of the modified attachment energies suggest that via the effect of acetone solvent, the (210) face has the largest morphology importance and the morphological importance of the (111), (002) and (200) faces reduces, whereas the (020) face disappears. The predicted result is in reasonable agreement with the observed experiment shape. Furthermore, the diffusion coefficients of acetone solvent toward the different RDX surfaces suggests that the (210) and (111) faces are the dominate growth faces on the final RDX crystal habits, whereas the (020) face probably disappears, which validates the reliability of the modified attachment energy model.

Prediction of crystal morphology of cyclotrimethylene trinitramine in the solvent medium by computer simulation: a case of cyclohexanone solvent.

The crystal morphology of the energetic material cyclotrimethylene trinitramine (also known as RDX) influenced by the solvent effect was investigated via molecular dynamics simulation. The modified attachment energy (MAE) model was established by incorporating the growth parameter-solvent term. The adsorption interface models were used to study the adsorption interactions between solvent and RDX surfaces. The RDX crystal morphology grown from the cyclohexanone (CYC) solvent as a case investigation was calculated by the MAE model. The calculation results indicated that, due to the effect of CYC solvent, (210) and (111) faces had the greatest morphological importance on the final RDX crystal, while the morphological importance of (020), (002), and (200) faces were reduced. The predicted RDX morphology was in reasonable agreement with the observed experiment result.

Modeling the interaction of seven bisphosphonates with the hydroxyapatite(100) face

The interaction of seven pamidronate bisphosphonate (Pami-BPs) and its analogs with the hydroxyapatite (HAP) (100) surface was studied using density functional theory (DFT) and molecular dynamic (MD) methods. Partial Mulliken oxygen atomic charges in protonated structures were calculated at the level of B3LYP/6-31G*. The MD simulation was performed using the Discover module of Material Studio by compass force field. The results indicate the abilities of donating electrons of the oxygen atoms of the phosphate groups that are closely associated with the antiresorptive potency. The binding energies, including vdw and electrostatic, are used to discuss the mechanism of antiresorption. The results of calculations show that the strength of interaction of the HAP (100) face with the bisphosphonates is N4 > N6 > N7 > N5 > N3 > N2 > N1 according to their experimental pIC50 values.

Theoretical studies on vicinal-tetrazine compounds: furoxano-1,2,3,4-tetrazine-1,3,5-trioxide (FTTO-α) and furoxano-1,2,3,4-tetrazine-1,3,7-trioxide (FTTO-β)

The derivatives of 1,2,3,4-tetrazine may be promising candidates of high-energy density compounds and are receiving more and more attention. In this study, two 1,2,3,4-tetrazines, furoxano-1,2,3,4-tetrazine-1,3,5-trioxide (FTTO-α) and furoxano-1,2,3,4-tetrazine-1,3,7-trioxide (FTTO-β), were theoretically studied. The geometrical structures in gas phase were studied at the B3LYP/6-311++G(d,p) level of density functional theory (DFT). The gas phase enthalpies of formation were calculated by the homodesmotic reaction method. The enthalpies of sublimation and solid phase enthalpies of formation were predicted with corrections of electrostatic potential method at the B3PW91/6-31G(d,p) level. The detonation properties were estimated with the Kamlet-Jacobs equations based on the predicted densities and enthalpies of formation in solid state. The available free space in the lattice was calculated to evaluate their stability. Calculations of potential energy surface and structure interconversion thermodynamics under different temperatures were carried out to further confirm their stability. FTTOs have better performance than HMX and FTDO but are easy to decompose to 5,6-dinitroso-v-tetrazine 1,3-dioxide. A synthesis route for FTTO-β was proposed to provide a consideration for the further study. We believe FTTOs could be the key compounds to synthesize other v-tetrazines such as TTTO.

Efficient and stable ZrO2/Fe modified hollow-C3N4 for photodegradation of the herbicide MTSM

Hollow graphitic carbon nitride (HCN) ZrO2/g-C3N4 hybrid composites (HCN–ZR) and the target catalyst Fe/ZrO2/g-C3N4 (HCN–FZR) were prepared successfully by a solvo-thermal method and evaluated for photo-degradation of organic pollutants, i.e. MO, and herbicides, metsulfuron methyl (MTSM). These materials were characterized by a variety of techniques, including Fourier transform infrared spectroscopy, UV-vis spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, HPLC-MS and scanning electron microscopy. The characterization and degradation results showed that FZR particles are well distributed on the surface of HCN to give a photo-catalytically active material. Photodegradation split MTSM completely into a lot of intermediate products, as depicted in the HPLC-MS results. Mooring of FZR on HCN increased the surface-area and light absorption capability of HCN–FZR, due to heterojunction formation between the semiconductors, which retarded electron–hole recombination and enhanced the photo-activity.

Crystal morphology prediction of 1,3,3-trinitroazetidine in ethanol solvent by molecular dynamics simulation.

In order to understand the mechanism of the effect of solvent on the crystal morphology of explosives, and be convenient for the choice of crystallization solvent, the attachment energy (AE) model was performed to predict the growth morphology and the main crystal faces of 1,3,3-trinitroazetidine (TNAZ) in vacuum. The molecular dynamics simulation was applied to investigate the interactions of TNAZ crystal faces and ethanol solvent, and the growth habit of TNAZ in ethanol solvent was predicted using the modified AE model. The results indicate that the morphology of TNAZ crystal in vacuum is dominated by the six faces of [021], [112], [002], [102], [111] and [020], and the crystal shape is similar to polyhedron. In ethanol solvent, The binding strength of ethanol with TNAZ faces changes in the order of [021]>[112]>[002]>[102]>[111]>[020], which causes that [111] and [020] faces disappear and the crystal morphology becomes more regular. The radial distribution function analysis shows that the interactions between solvent and crystal faces mainly consist of coulomb interaction, van der Waals force and hydrogen bonds.

Encapsulating nano rods of copper–biphenylamines framework on g-C3N4 photocatalysts for visible-light-driven organic dyes degradation: promoting charge separation efficiency

For the first time we have successfully constructed semi conductive copper–biphenylamines framework hybrid photocatalysts to degrade organic pollutants. Cu complexes sensitized photocatalysts of g-C3N4, i.e. CN-Cu(BN), CN-Cu(PD) and CN-Cu(BA), have been successfully tested for photocatalytic degradation of organic pollutants under visible light illumination, and a significant enhancement in catalytic activity was observed for CN-Cu(BA) in comparison to pristine g-C3N4. The modified material creates a charge separation with the electrons populating the higher CB and the holes the lower VB, thus enhancing the redox reaction power of the charge carriers. CN-Cu (BA) can easily degrade 99% of RhB in 1.5 hours and 60% of phenol in 2 hours. While the degradation efficiency of CN-Cu(BN), CN-Cu(PD) and g-C3N4 is lower than that of CN-Cu(BA). The kobs for CN-Cu(BN) is 0.01985 min−1, 5.2 times higher than that of g-C3N4, and that of CN-Cu(BA) is 0.0292 min−1 which is 7.55 times greater than that of pristine g-C3N4. These degradation outcomes are favourable for developing a modified catalyst in bulk amount and its application. The strong holes can directly degrade RhB and phenol. Promoting the injection of electrons from g-C3N4 into the copper unit as well as strengthening the electronic interactions between the two units enhanced its activity.

Preparation and Evaluation of a C18-Sulfonic Group Dual Modification Chromatographic Stationary Phase

Abstract A C18-sulfonic group dual modification chromatographic stationary phase was prepared by one-pot reaction to modify the surface of silica with two modifier of octadecyltrichlorosilane (OTS) and trimethoxysilylpropanethiol (MPS), and then oxidize the thiol group. Under the optimized reaction conditions, the stationary phase with a mole ratio of 3:7 between C18 and sulfonic group was obtained. The morphology and feature of the stationary phase were characterized by scanning electronic microscopy, elemental analysis and infrared spectra. The chromatographic properties of the prepared stationary phase were systematically investigated in different separation modes. Five alkyl benzenes and three nucleosides were separated successfully by reversed phase chromatography and hydrophilic interaction chromatography, respectively. The bovine serum albumin digest was also well separated on the stationary phase. The results indicated that the prepared mixed-mode stationary phase could provide multiple separation mechanism and had potential advantages in separating complex samples and adjusting the selectivity.