Computational study of energetic nitrogen-rich derivatives of 1,4-bis(1-azo-2,4-dinitrobenzene)-iminotetrazole

The heats of formation (HOFs), electronic structure, energetic properties, and thermal stabilities for a series of 1,4-bis(1-azo-2,4-dinitrobenzene)-iminotetrazole derivatives with different substituents and substitution positions and numbers of nitrogen atoms in the nitrobenzene rings were studied using the DFT-B3LYP method. All the substituted compounds have higher HOFs than their parent compounds. As the number of nitrogen atoms in the nitrobenzene ring increases, the HOFs of the derivatives with the same substituent rise gradually. Replacing carbon atoms in the nitrobenzene with nitrogen atoms to form N–N bonds is very helpful in improving their HOFs. Most of the substituted compounds have higher HOMO–LUMO gaps than the corresponding unsubstituted compounds. Substitution of the –NO₂, –NF₂, or –ONO₂ group and an increase in the number of nitrogen atoms in the nitrobenzene rings are useful for enhancing their detonation performance. The substituents’ substitution is not favorable for improving thermal stability. Considering detonation performance and thermal stability, five compounds may be considered potential candidates for high energy density compounds (HEDCs).     

A theoretical study on 1,5-diazido-3-nitrazapentane (DANP) and 1,7-diazido-2,4,6-trinitrazaheptane (DATNH): molecular and crystal structures, thermodynamic and detonation properties, and pyrolysis mechanism

1,5-Diazido-3-nitrazapentane (DANP) and 1,7-diazido-2,4,6-trinitrazaheptane (DATNH) are two energetic plasticizers. To better understand them, a detailed theoretical investigation was carried out using density functional theory and molecular mechanics methods. The crystal structures, spectra, thermodynamic properties, heats of formation, detonation velocity, detonation pressure, specific impulse and thermal stability were estimated. Possible initiation steps of pyrolysis were discussed by considering the bond breaking of N–NO₂, C–N₃, and N–N₂ (via hydrogen transfer) for both compounds and the cyclization of the adjacent nitro and azido groups for DATNH. Results show that the rupture of N–NO₂ and N–N₂ (via hydrogen transfer) may happen simultaneously as the initial step of pyrolysis. Both crystals have P-1 symmetry as was observed experimentally. DANP has higher stability than DATNH, while DATNH has better detonation performance than DANP. In addition, DANP has a lower while DATNH has a higher specific impulse than RDX, which shows their prospects as propellant components.     

Theoretical design of energetic nitrogen-rich derivatives of 1,7-diamino-1,7-dinitrimino-2,4,6-trinitro-2,4,6-triazaheptane

The heats of formation (HOFs), energetic properties, and thermal stability of a series of 1,7-diamino-1,7-dinitrimino-2,4,6-trinitro-2,4,6-triazaheptane derivatives with different substituents, different numbers of substituents, and different original chains are found by using the DFT-B3LYP method. The results show that -NO₂ or -NH₂ is an effective substituent for increasing the gas-phase HOFs of the title compounds, especially -NO₂ group. As the numbers of substitutents increase, their HOFs enhance obviously. Increasing the length of original chain is helpful for improving their HOFs. The substitution of -NO₂ is useful for enhancing their detonation performances and the effects of the length of original chains on detonation properties are coupled with those of the substituents. An analysis of the BDE of the weakest bonds indicates that the substitution of the -NH₂ groups and replacing the -NO₂ groups of N-NO₂ by the -NH₂ groups are favorable for improving their thermal stability, while the substitution of -NO₂ and increasing the length of original chain decrease their thermal stability. Considering the detonation performance and thermal stability, seven compounds may be considered as the potential candidates of high energy density compounds.     

Comparative theoretical studies of differently bridged nitramino-substituted ditetrazole 2-<Emphasis Type="Italic">N</Emphasis>-oxides with high detonation performance and an oxygen balance of around zero

In this work, six (A–F) nitramino (–NHNO₂)-substituted ditetrazole 2-N-oxides with different bridging groups (–CH₂–, –CH₂–CH₂–, –NH–, –N=N–, and –NH–NH–) were designed. The six compounds were based on the parent compound tetrazole 2-N-oxide, which possesses a high oxygen balance and high density. The structure, heat of formation, density, detonation properties (detonation velocity D and detonation pressure P), and the sensitivity of each compound was investigated systematically via density functional theory, by studying the electrostatic potential, and using molecular mechanics. The results showed that compounds A–F all have outstanding energetic properties (D: 9.1–10.0 km/s; P: 38.0–46.7 GPa) and acceptable sensitivities (h ₅₀: 28–37 cm). The bridging group present was found to greatly affect the detonation performance of each ditetrazole 2-N-oxide, and the compound with the –NH–NH– bridging group yielded the best results. Indeed, this compound (F) was calculated to have comparable sensitivity to the famous and widely used high explosive 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), but with values of D and P that were about 8.7% and 19.4% higher than those for HMX, respectively. The present study shows that tetrazole 2-N-oxide is a useful parent compound which could potentially be used in the design of new and improved high-energy compounds to replace existing energetic compounds such as HMX.     

Is 1-nitro-1-triazene a high energy density material?

An azo bridge (–N?=?N–) can not only desensitize explosives but also dramatically increase their heats of formation and explosive properties. Amino and nitro are two important high energy density functional groups. Here, we present calculations on 1-nitro-1-triazene (NH₂–N?=?N–NO₂). Thermal stability and detonation parameters were predicted theoretically at CCSD(T)/6-311G* level, based on the geometries optimized at MP2/6-311G* level. It was found that the p?→?π conjugation interaction and the intramolecular hydrogen bonding that exist in the system together increase the thermal stability of the molecule. Moreover, the detonation parameters were evaluated to be better than those of the famous HMX and RDX. Finally, the compound was demonstrated to be a high energy density material.     

Theoretical studies on the thermodynamic properties, densities, detonation properties, and pyrolysis mechanisms of trinitromethyl-substituted aminotetrazole compounds

Trinitromethyl-substituted aminotetrazoles with –NH₂, –NO₂, –N₃, and –NHC(NO₂)₃ groups were investigated at the B3LYP/6-31G(d) level of density functional theory. Their sublimation enthalpies, thermodynamic properties, and heats of formation were calculated. The thermodynamic properties of these compounds increase with temperature as well as with the number of nitro groups attached to the tetrazole ring. In addition, the detonation velocities and detonation pressures of these compounds were successfully predicted using the Kamlet–Jacobs equations. It was found that these compounds exhibit good detonation properties, and that compound G (D = 9.2 km/s, P = 38.8 GPa) has the most powerful detonation properties, which are similar to those of the well-known explosive HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Finally, the electronic structures and bond dissociation energies of these compounds were calculated. The BDEs of their C–NO₂ bonds were found to range from 101.9 to 125.8 kJ/mol^-1. All of these results should provide useful fundamental information for the design of novel HEDMs.     

Thermal Stability Investigation and the Kinetic Study of Folnak<Superscript>®</Superscript> Degradation Process Under Nonisothermal Conditions

The nonisothermal degradation process of Folnak^® drug samples was investigated by simultaneous thermogravimetric and differential thermal analysis in the temperature range from an ambient one up to 810°C. It was established that the degradation proceeds through the five degradation stages (designated as I, II, III, IV, and V), which include: the dehydration (I), the melting process of excipients (II), as well as the decomposition of folic acid (III), corn starch (IV), and saccharose (V), respectively. It was established that the presented excipients show a different behavior from that of the pure materials. During degradation, all excipients increase their thermal stability, and some kind of solid–solid and/or solid–gas interaction occurs. The kinetic parameters and reaction mechanism for the folic acid decomposition were established using different calculation procedures. It was concluded that the folic acid decomposition mechanism cannot be explained by the simple reaction order (ROn) model (n?=?1) but with the complex reaction mechanism which includes the higher reaction orders (RO, n?>?1), with average value of <n?>?=?1.91. The isothermal predictions of the third (III) degradation stage of Folnak^® sample, at four different temperatures (T _iso?=?180°C, 200°C, 220°C, and 260°C), were established. It was concluded that the shapes of the isothermal conversion curves at lower temperatures (180–200°C) were similar, whereas became more complex with further temperature increase due to the pterin and p-amino benzoic acid decomposition behavior, which brings the additional complexity in the overall folic acid decomposition process.     

Chemical Studies on Ambergris

So called ambreinolal (IV),* a component of ambergris, was first synthesized by CrO₃ oxidation of ambreinolol (III)* which was obtained from ambreinolide (II) by reduction with LiAlH₄. Ambreinolol (III) was converted to the C₁₇-saturated oxide (VII) in a good yield through the monotosylate (VIII) by treatment with p-toluenesulfonyl chloride in pyridine.

Ambrein (I), a major constituent of ambergris, was easily converted to ambrein-tetrahydropyranylether (II), of which thermal decomposition gave back ambrein (I). The tetrahydropyranylether (II) was oxidized to ambreinolal-tetrahydropyranylether (V) in two steps. Ambreinolal-tetrahydropyranylether (V) was synthesized from ambreinolol (VII) in four steps and converted to the C₁₇-unsaturated oxide (VI) on heating.     

Chromosomal localizations by in situ hybridization of the repetitious human DNA families and evidence of their satellite DNA equivalents

Four of the five major repetitious human DNA families, have been mapped by the in situ hybridization technique at their T_OPT values. Two of the lighter density DNA families have autoradiographic grain patterns over heterochromatic chromosomal regions that resemble those of known satellite DNAs. The two heaviest density DNA families have autoradiographic grain patterns of middle repetitious DNAs, with all chromosomes showing labelling. Some evidence suggests that one of these DNA families is concentrated in certain chromosomal regions. Both DNA families exhibit biphasic T_OPT curves. The presence of two thermal stability classes of hybrids suggests sequence interspersion. By co-enrichment studies in Ag⁺-Cs₂SO₄ gradients, evidence suggests the origin of the three lightest density renaturated human DNA families to be satellites I, II and III.     

Assay and subcellular localization of the arylsulphatases in rat brain

—The properties and subcellular localization of type I (nitrophenyl) and type II (nitrocatechol) arylsulphatases were investigated in brain tissue of the rat, and optimal assay conditions were established. Sulphate, phosphate and sulphite ions inhibited the nitrocatechol sulphatases; nitrophenyl sulphatase was inhibited only by sulphite. The presence of latent enzyme activity was demonstrated for the nitrocatechol sulphatases, beta-glucuronidase, and beta-glycerophosphatase in rat and mouse brain homogenates. These hydrolases were highly sensitive to mechanical and osmotic damage; and Triton X-100 was very effective in releasing their latent (bound) activities, a finding suggestive of a lysosomal localization. Activity of nitrophenyl sulphatase was unaffected by osmotic changes or Triton X-100, characteristics suggesting a membranous association for this enzyme. Total activity of nitrophenyl sulphatase was approximately twice as great in canine gray matter as in canine white matter; the converse obtained for beta-glucuronidase activity. Values for total enzymic activity of the nitrocatechol sulphatases in canine white and gray matter were similar. Fractionation of homogenates from rat brain by differential centrifugations and separation of crude mitochondrial fractions by sucrose density gradient centrifugations revealed the following: (1) most of the nitrocatechol sulphatase activity (93 per cent) and all of the nitrophenyl sulphatase activity were sedimentable; (2) crude mitochondrial fractions exhibited the highest relative specific activity (RSA = 1·38) for the nitrocatechol sulphatases, whereas microsomal fractions displayed the highest RSA for nitrophenyl sulphatase (1·89); (3) the lightest fraction (A + B) and the densest fraction (E) from the sucrose density gradient contained most of the activity for both the type I and type II arylsulphatases, whereas the RSA of cytochrome oxidase was greatest in the intermediate density regions (fractions C and D); (4) the highest RSA for beta-glucuronidase and beta-glycerophosphatase occurred in gradient fraction C; (5) appreciable activity of beta-glycerophosphatase was found in a nerve ending fraction (M₃). It is suggested that the hydrolases in heterogeneous tissue like brain might be associated with lysosomal particles of differing enzyme compositions and varying populations, and that the data on distribution lend credence to the concept of bimodal and possible trimodal particle affinity for the hydrolases of brain tissues.     

Design and selection of nitrogen-rich bridged di-1,3,5-triazine derivatives with high energy and reduced sensitivity

The heats of formation (HOFs), electronic structures, energetic properties, and thermal stabilities of a series of energetic bridged di-1,3,5-triazine derivatives with different substituents and linkages were studied using density functional theory. It was found that the groups -N(3) and -N=N- are effective structural units for improving the HOF values of the di-1,3,5-triazine derivatives. The effects of the substituents on the HOMO-LUMO gap combine with those of the bridge groups. The calculated detonation velocities and detonation pressures indicate that substituting the -ONO(2), -NF(2), or -N=N- group is very useful for enhancing the detonation performance of these derivatives. Analysis of the bond dissociation energies for several relatively weak bonds suggests that most of the derivatives have good thermal stability. On the whole, the -NH(2), -N(3), -NH-, and -CH=CH- groups are effective structural units for increasing the thermal stabilities of the derivatives. Based on detonation performance and thermal stability, nine of the compounds can be considered potential candidates for high energy density materials with reduced sensitivity.     

Screening for potential energetic C–N cages with high energy and good stability: a theoretical comparative study

This paper presents a theoretical study on carbon-nitrogen cages as potentially high energy density materials (HEDMs) using density functional theory. The energetic properties, detonation performance, and stability of two C₆N₆H₁₂ cages were researched comparison with two similar common cage compounds hexaazaisowurtzitane and cubane. Results indicate that both of two C₆N₆H₁₂ cages have high positive heat of formation and good stability. Their densities and detonation characteristics are equivalent or slightly superior to those of hexaazaisowurtzitane and cubane, indicating that they have good detonation performance.     

Characterization of nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrazole-based polyheterocyclic compounds: heats of formation, thermal stability, and detonation properties

The heats of formation (HOFs), thermal stability, and detonation properties for a series of nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrazole-based polyheterocyclic compounds (3,6-bis(1H-1,2,3,4-tetrazole-5-ylamino)-1,2,4,5- tetrazine (TST), 3,6-bis(furazan-5-ylamino)-1,2,4,5-tetrazine (FSF), 3,4-bis(1,2,4,5- tetrazine-3-ylamino)-furazan (SFS), 3,4-bis(1H-1,2,3,4-tetrazole-5-ylamino)-furazan (TFT), 1,5-bis(1,2,4,5-tetrazine-3-ylamino)-1H-1,2,3,4-tetrazole (STS), and 1,5-bis(furazan-3-ylamino)-1H-1,2,3,4-tetrazole (FTF) derivatives) were systematically studied by using density functional theory. The results show that the -N(3) or -NHNH(2) group plays a very important role in increasing the HOF values of the derivatives. Among these series, the SFS derivatives have lower energy gaps, while the TFT derivatives have higher ones. Incorporation of the -NH(2) group into the FSF, SFS, STS, or FTF ring is favorable for enhancing its thermal stability, whereas the substitution of the -NHNH(2) group could increase the thermal stability of the TST, SFS, STS, or FTF ring. The calculated detonation properties indicate that the -NO(2) or -NF(2) is very helpful for enhancing the detonation performance for these derivatives. Considering the detonation performance and thermal stability, six derivatives may be regarded as promising candidates of high-energy density materials (HEDMs). These results provide basic information for the molecular design of novel HEDMs.     

Theoretical study on benzoheterocycle based energetic materials,effect of heterocyclic-fused,conjugation, hydrogen bond,and substitutional group on the detonation performance

In this paper, four series of benzoheterocycle based energetic materials (EMs) have been designed to plan out a strategy to improve the density and safety of EMs, such as combining the insensitive group with aminobenzene ring and the high energetic nitramine explosives, benzo-heterocycle mother ring, designing multi-nitrogen heterocycles with a conjugated system containing N-N and C-N high energy bonds, and hydrogen bonding. Their optimized structure and detonation properties were first calculated and discussed using DFT methods. After calculation, these designed explosives all showed good detonation from 7352 m/s to 8788 m/s. Among them, the compounds with six nitro groups, 1c, 2c, 3c, and 4c, exhibit better performance and rather poor impact sensitivity. However, we found that the compounds with five nitro groups and one amino group have a limited performance reduction and a rapid stability improvement. These four compounds, 1b, 2b, 3b, and 4b, have good detonation performance and better stability. Moreover, the synthesis routes for these four compounds were also designed. The precursor 4–0 and mononitro product 4–1 were successfully synthesized. Their 1H NMR, single crystal, and elemental analysis were also done to verify the structures.     

β-Galactosidases of Lilium pollen

Lily (Lilium auratum) pollen contains very high levels of β-galactosidase. There are three forms: β-galactosidase I and II differ in M_r, while β-galactosidase III is firmly bound in the pollen wall. The two cytoplasmic forms were separated and partially purified using a combination of chromatography on DEAE-cellulose, Sephadex G-200 and Sepharose 6B. Forms I and II appear to be glycoprotein in nature as shown by binding to Con A-Sepharose. The three enzymes were optimally active near pH 4, and all were inhibited by galactose and galactonolactone. The wall-bound enzyme, β-galactosidase III effectively hydrolysed nitrophenyl β-galactosidase but not lactose, and could not be released from the wall polysaccharide matrix by high salt concentrations or detergents. The total β-galactosidase activity of lily pollen remained constant during in vitro germination. A possible role for this enzyme may be in degradation of stylar arabinogalactans providing a carbon source for pollen tube nutrition.     

Theoretical investigations of a high density cage compound 10-(1-nitro-1, 2, 3, 4-tetraazol-5-yl)) methyl-2, 4, 6, 8, 12-hexanitrohexaazaisowurtzitane

A new polynitro cage compound with the framework of HNIW and a tetrazole unit, i.e., 10-(1-nitro-1, 2, 3, 4-tetraazol-5-yl)) methyl-2, 4, 6, 8, 12-hexanitrohexaazaisowurtzitane (NTz-HNIW) has been proposed and studied by density functional theory (DFT) and molecular mechanics methods. Properties such as IR spectrum, heat of formation, thermodynamic properties, and crystal structure were predicted. The compound belongs to the Pbca space group, with the lattice parameters a = 15.07 ?, b = 12.56 ?, c = 18.34 ?, Z = 8, and ρ = 1.990 g·cm^-3. The stability of the compound was evaluated by the bond dissociation energies and results showed that the first step of pyrolysis is the rupture of the N–NO₂ bond in the side chain. The detonation properties were estimated by the Kamlet-Jacobs equations based on the calculated crystal density and heat of formation, and the results were 9.240 km·s^-1 for detonation velocity and 40.136 GPa for detonation pressure. The designed compound has high thermal stability and good detonation properties and is probably a promising high energy density compound (HEDC).     

Theoretical studies of energetic nitrogen-rich ionic salts composed of substituted 5-nitroiminotetrazolate anions and various cations

We have performed density functional theory and volume-based thermodynamics calculations to study the effects of different combinations of energetic anions and cations on the crystal densities, heats of formation, energetic properties, and thermodynamics of formation for a series of 5-nitroiminotetrazolate-based ionic salts. The results show that the substitution of the -NO₂, -NF₂, -N₃, or -C(NO₂)₃ group is helpful for increasing the densities of the salts. Incorporating every substituent (-NH₂, -NO₂, -NF₂, -N₃, or -C(NO₂)₃) into the salt is favorable for improving its HOF and detonation performance. Incorporating the cation B1, B2, B10, or B11 into the salts is helpful for improving its detonation properties. Increasing negative charge for the 5-nitroiminotetrazolate-based salts is unfavorable for enhancing the density and detonation performance, but is helpful for increasing the HOFs. Many salts present comparable detonation performance with commonly used explosives RDX or HMX. Among them, 21 salts have near or better properties than HMX. The thermodynamics of formation of the salts show that the majority of the 5-nitroiminotetrazolate salts with the cation B1, B3, B9, B10, B12 could be synthesized by the proposed reactions.     

Looking for high energy density compounds among polynitraminepurines

A series of purine derivatives with nitramine groups are calculated by using density functional theory (DFT). The molecular theory density, heats of formation, bond dissociation energies and detonation performance are investigated at DFT-B3LYP/6-311G** level. The isodesmic reaction method is employed to calculate the HOFs of the energies obtained from electronic structure calculations. Results show that the position of nitramine groups can influence the values of HOFs. The bond dissociation energies and the impact sensitivity are analyzed to investigate the thermal stability of the purine derivatives. The calculated bond dissociation energies of ring-NHNO₂ and NH-NO₂ bond show that the NH-NO₂ bond should be the trigger bond in pyrolysis processes. The H₅₀ of most compounds are larger than that of CL-20 and RDX.     

Theoretical study on the thermal decomposition of model compounds for Poly (dialkyl fumarate)

The thermal decomposition of model compounds for poly (dialkyl fumarate) was studied by using ab initio and density functional theory (DFT) calculations. To determine the most favorable reaction pathway of thermal decomposition, geometries, structures, and energies were evaluated for reactants, products, and transition states of the proposed pathways at the HF/6-31G(d) and B3LYP/6-31G(d) levels. Three possible paths (I, II and III) and subsequent reaction paths (IV and V) for the model compounds of poly (dialkyl fumarate) decomposition had been postulated. It has been found that the path (I) has the lowest activation energy 193.8 kJ mol⁻¹ at B3LYP/6-31G(d) level and the path (I) is considered as the main path for the thermal decomposition of model compounds for poly (dialkyl fumarate).      

The search for new powerful energetic transition metal complexes based on 3,3′-dinitro-5,5′-bis-1,2,4-triazole-1,1′-diolate anion: a DFT study

In this study, employing a new high oxygen balance energetic 3,3′-dinitro-5,5′-bis-1,2,4-triazole-1,1′-diolate anion (DNBTDO) as the bidentate ligand, NH₃ and NH₂NO₂ as short energetic ligands, and Cu/Ni as the metal atoms, two series of novel energetic metal complexes were computationally designed. Their structures and properties were studied by density functional theory, electrostatic potential data, and molecular mechanics methods. The results showed that the designed metal complexes have high detonation performance and acceptable sensitivity: Cu/Ni(DNBTDO)(NH₂NO₂)₂ (A3/B3) have better detonation properties and lower sensitivity than the most powerful CHNO explosive hexanitrohexaazaisowurtzitane, Cu/Ni(DNBTDO)(NH₃)(NH₂NO₂) (A2/B2) have comparable energetic performance and sensitivity with 1,3,5,7-tetranitro-1,3,5,7-tetrazocane, Ni(DNBTDO)(NH₃)₂ (B1) has comparative energy level and sensitivity with 1,3,5-trinitro-1,3,5-triazinane. These five energetic metal complexes may be attractive to energetic materials researchers. Besides, both the energetic ligands and metal atoms could have a great influence on the structures, heats of formation, detonation properties, and stability of energetic metal complexes, and the effects are coupled with each other. This study may be helpful in the search for and development of new improved energetic materials.