Theoretical investigation on action mechanism and mollifying efficacy of propellant stabilizers.

CONTEXT: This project performed quantum chemical computation, through kinetic and thermodynamic analyses to compare relative reactivity, reaction rate, and equilibrium composition from the possible pathways in connection with stabilizer-nitrodioxide reactions to determine the stability of the materials for practical application. Corresponding achievements have promoted the use of N-methyl-p-nitroaniline (MNA) and dinitrophenyl malonamide series (M3, M4, and M5) stabilizers as high priorities for selection. METHODS: The Gaussian 09 program (G09) (Frisch et al 2009) and density functional theory (DFT) calculations with the B3LYP/6-31G(d,p) function were performed to obtain related geometric and thermodynamic energy data for the molecular systems in this study. The synchronous transit-guided quasi-Newton method (STQN) (Peng and Schlegel Isr J Chem 33:49, 1993) was applied through the QST3 procedure to identify single imaginary frequency-valued transition-state species. The related reaction rate constant (k) and pre-exponential factor (A) were obtained, based on transition state theory (Su 2008), using Eqs. 11 and 12.

Comparative modeling of improved synthesis of energetic dinitrobenzofuroxan (DNBF) derivatives.

Quantum chemical theoretical computation was performed on gaseous molecular reaction systems to simulate parallel synthesis of energetic primary explosive precursor 4,6-dinitrobenzofuroxan (4,6-DNBF) and its isomeric derivatives. Related polarized continuum model (PCM) and Materials Studio (MS/forcite) energies were collected via kinetic rate and thermodynamic equilibrium analyses, enabling comparison of and suggestions as to suitable reaction conditions (reaction temperature, reagent concentration, mixed acid ratio) together with feasible pathways to obtain a high production yield of the research target. In summary, at a low reaction temperature of 278 K, 1.0 M 4-nitrobenzofuroxan (or 5,6-nitrobenzofuroxan) could be nitrated using concentrated nitric acid/sulfuric acid at a 1 to 2 volume ratio to efficiently and rapidly produce 4,6-dinitro-benzofuroxan (or 5,6-dinitrobenzofuroxan), in agreement with the experimental results reported in the literature. Graphical abstract.

Graphene Wrinkles affect electronic transport in nanocomposites: Insight from molecular dynamics simulations.

Molecular dynamics (MD) simulations were carried out to study the physical properties of graphene-oxide (GO) and polydimethylsiloxane (PDMS) interfacial systems. Simulations were performed for GO molecules dispersed into short-chain, long-chain, and long-chain and cross-linked PDMS polymers. Various structural properties, dipole moments and dielectric constants of the graphene-oxide molecules were calculated, which were correlated with the electron transport properties of the GO/PDMS system. The effects of polymer length and type of linkage on transport properties were also examined.

Computer simulation for the study of the liquid chromatographic separation of explosive molecules.

The application of high performance liquid chromatography (HPLC) to separate explosive chemicals was investigated by molecular dynamics (MD) simulations. The explosive ingredients including NG, RDX, HMX and TNT were assigned as solutes, while methanol (CH3OH) and acetonitrile (CH3CN) were assigned as solvents in the solution system. The polymeric-molecular siloxanes (SiC8) and poly-1,2-methylenedioxy-4-propenyl benzene (PISAF) compounds were treated as stationary phase in the simulation. The simulation results showed that the different species of explosive ingredients were separated successfully in the solutions by each of the constructed stationary phase of SiC8 and PISAF after a total simulation time of 12.0 ps approximately, which were consistent with the experimental analysis of HPLC spectra. The origin for the separation was found due to the electrostatic interactions between polymer and explosives.

Computational study of Simultaneous synthesis of optically active (RS)-1,2,4-butanetriol trinitrate (BTTN).

In respective water or ethanol polarizable continuum cavity environments, simultaneous aldol condensation was performed using density functional theory (DFT) computational method to model the synthesis of optically active (RS)-1,2,4-butanetriol trinitrate (BTTN). The results of reaction energy barrier analysis suggested feasible routes with lower activation energies to obtain either the (R)- or (S)-configuration product in ethanolic solution. In addition, local analysis of average inter-particulate distances of reaction species revealed that a stronger inter-particulate interaction accompanied a shorter average distance in the ethanol system. The stabilization effect also indicated that related syntheses would be able to proceed in ethanol. Furthermore, relative to the production of (R)-BTTN, a lower overall energy of 425.3 kJ/mol was required for the synthesis of (S)-BTTN. Through analysis of the effects of temperature on the reaction rates of individual parallel stages of (R)- and (S)-species synthesis, it was simple to adjust the reaction temperature accordingly to differentiate between relative rates in order to obtain a product of a specific configuration. Graphical abstract ᅟ.

Comparative simulation study of chemical synthesis of functional DADNE material.

Amorphous molecular simulation to model the reaction species in the synthesis of chemically inert and energetic 1,1-diamino-2,2-dinitroethene (DADNE) explosive material was performed in this work. Nitromethane was selected as the starting reactant to undergo halogenation, nitration, deprotonation, intermolecular condensation, and dehydration to produce the target DADNE product. The Materials Studio (MS) forcite program allowed fast energy calculations and reliable geometric optimization of all aqueous molecular reaction systems (0.1-0.5 M) at 283 K and 298 K. The MS forcite-computed and Gaussian polarizable continuum model (PCM)-computed results were analyzed and compared in order to explore feasible reaction pathways under suitable conditions for the synthesis of DADNE. Through theoretical simulation, the findings revealed that synthesis was possible, and a total energy barrier of 449.6 kJ mol-1 needed to be overcome in order to carry out the reaction according to MS calculation of the energy barriers at each stage at 283 K, as shown by the reaction profiles. Local analysis of intermolecular interaction, together with calculation of the stabilization energy of each reaction system, provided information that can be used as a reference regarding molecular integrated stability. Graphical Abstract Materials Studio software has been suggested for the computation and simulation of DADNE synthesis.

Comparative theoretical kinetics and thermodynamics study on high-energy insensitive explosive 1,1-diamino-2,2-dinitroethene synthesis.

Two synthesis methods were investigated in this study in order to explore feasible reaction pathways to obtain the target DADNE product: (1) the nitration of tetrahalogen ethene and (2) the reaction of acetamidine hydrochloride with dicarbonyl dichloride. Through theoretical simulation, the findings revealed that synthesis was possible, starting from acetamidine hydrochloride in a hydrated environment, followed by subsequent reaction routes via cyclization of the methoxy-substituted acetamidine anion intermediate with oxalyl chloride to form 2-methoxy-2-methyl-imidazolan-4,5-dione, acid-catalyzed synthesis of 2-methylene-imidazolan-4,5-dione, nitration using nitric acid to obtain 2-dinitromethylene-imidazolan-4,5-dione, and hydrolysis to produce 1,1-diamino-2,2-dinitroethene. A total energy of 1048.4 kJ mol(-1) was needed to carry out the reaction according to calculation of the energy barriers at each stage, as shown by the reaction profiles.

Computational study of decomposition mechanisms and thermodynamic properties of molecular-type cracking patterns for the highly energetic molecule GZT.

This study uses the Gaussian 03 program and density functional theory B3LYP with three basis set methods-[B3LYP/6-311+G(d,p), B3LYP/6-31+G(2d,p), and B3LYP/6-31G(d,p)]-to model the highly energetic ionic compound diguanidinium 5,5'-azotetrazolate (GZT) to research its decomposition mechanisms and thermodynamic properties. Molecular-type cracking patterns are proposed, which were initiated by heterocyclic ring opening, sequential cracking of the two five-membered rings of GZT, and simultaneous release of N2 molecules; whereas proton transfer, bond-breaking, and atomic rearrangements were performed subsequently. Finally, 15 reaction paths and five transition states were obtained. All possible decomposition species and transition states, including intermediates and products, were identified, and their corresponding enthalpy and Gibbs free energy values were obtained. The results revealed that (1) the maximum activation energy required is 187.8 kJ mol(-1), and the enthalpy change (ΔH) and Gibbs free-energy change (ΔG) of the net reaction are -525.1 kJ mol(-1) and -935.6 kJ mol(-1), respectively; (2) GZT can release large amounts of energy, the main contribution being from the disintegration of the 5,5'-azotetrazolate anion (ZT(2-)) skeleton (ΔH = -598.3 kJ mol(-1)); and (3) the final products contained major amounts of N2 gas, but remaining gas molecules such as HCN and NH3 were obtained, which are in agreement with experimental results. The detailed decomposition simulation results demonstrated the feasibility of this method to calculate the energies of the thermodynamic reactions for the highly energetic GZT and predict the most feasible pathways and the final products.

Modified calculations of hydrocarbon thermodynamic properties.

A test set of 65 hydrocarbons was examined to elucidate theoretically their thermodynamic properties by performing the density-functional theory (DFT) and ab initio calculations. All the calculated data were modified using a three-parameter calibration equation and the least-squares approach, to determine accurately enthalpies of formation (DeltaH(f)), entropies (S), and heat capacities (C(p)). Calculation results demonstrated that the atomization energies of all compounds exhibited an average absolute relative error ranging between 0.11- 0.13%, and an DeltaH(f) of formation with a mean absolute absolute error (M.|A.E.|) ranging from only 5.7-6.8 kJ/mol (1.3-1.6 kcal/mol) (i.e., those results correlated with those of Dr. Herndon's 1.1 kcal/mol). Additionally, the entropy ranged from 3.5-4.2 J/mol K (0.8-1.0 cal/mol K) M.|A.E.|; a heat capacity between 2.3-2.9 J/mol K (0.5-0.7 cal/mol K) M.|A.E.| was obtained as well.

Improved modification for the density-functional theory calculation of thermodynamic properties for C-H-O composite compounds.

A three-parametric modification equation and the least-squares approach are adopted to calibrating hybrid density-functional theory energies of C(1)-C(10) straight-chain aldehydes, alcohols, and alkoxides to accurate enthalpies of formation DeltaH(f) and Gibbs free energies of formation DeltaG(f), respectively. All calculated energies of the C-H-O composite compounds were obtained based on B3LYP6-311++G(3df,2pd) single-point energies and the related thermal corrections of B3LYP6-31G(d,p) optimized geometries. This investigation revealed that all compounds had 0.05% average absolute relative error (ARE) for the atomization energies, with mean value of absolute error (MAE) of just 2.1 kJ/mol (0.5 kcal/mol) for the DeltaH(f) and 2.4 kJ/mol (0.6 kcal/mol) for the DeltaG(f) of formation.