Accelerated discovery of thermostable high-energy materials with intramolecular donor-acceptor building blocks.

A domain-related data search promoted triazolotriazine-fused energetic scaffold filtration with combinatorial design to alleviate the lack of thermostable high-energy materials; 16 candidates were discovered that may show promising energy and safety performance, as well as excellent thermal stability. Novel fused triazolo-1,2,4-triazine energetic material 7-nitro-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c][1,2,4]triazin-4-amine-2-oxide (Candidate No. 4) with excellent thermal stability, high energy performance and low sensitivity was developed successfully by using a facile N-oxide synthetic method. Our findings may be applicable to a wider range of materials and prove equally powerful for searching for other high-performing energetic materials.

Molecular polarizabilities of some energetic compounds.

The dependence of sensitivity of an explosive on its molecular structure may be mainly attributed to the molecular deformability, which can be expressed by some characteristic parameters, resonance energy for aromatic an explosive, strain energy for a strained-ring or strained-cage explosive, large π-π separation energy for a large π-π linked-explosive, bond rotational energy barriers of C-NO2, N-NO2, O-NO2 for C-NO2, N-NO2, O-NO2 bond-based explosives, and so on. Molecular polarizability of an explosive is also an important molecular deformability index, which can be effectively used to compare impact sensitivities of explosive's isomers, isoelectronic species, and similar structures. Interestingly, comparing the molecular polarizabilities under external electric fields with different energy levels of isomeric N20(Ih) and N20(D3d) clusters and the Mo2N20 and Re2N20 complex compounds, it is found that there are different energy thresholds of significant molecular expansion.

Comparative Study of the Decomposition Mechanism and Kinetics of Biimidazole-Based Energetic Explosives.

It is well known that imidazoles, possessing two or more nitro substituents, are potential candidates for highly energetic explosives with detonation parameters comparable to those of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane. 4,4',5,5'-Tetranitro-2,2'-bi-imidazole (TNBI) is a typical imidazole explosive with energy equivalent to that of RDX but suffers from low sensitivity (impact sensitivity 7 J). 1,1'-Diamino-4,4',5,5'-tetranitro-2,2'-biimidazole (DATNBI), a derivative of TNBI, possesses two -NH2 groups and has a higher detonation velocity (9063 m s-1) and lower impact sensitivity of 15 J, which indicates great potential for future applications. Examination of the thermal decomposition mechanism and kinetics of TNBI and DATNBI gives a more comprehensive view of the influence that the -NH2 group has on the sensitivity and storage safety of the energetic explosive-based TNBI molecular skeleton. Herein, the thermal decomposition mechanism is studied, showing that detachment of -NH2 groups from DATNBI generates 1-diamino-4,4',5,5'-tetranitro-2,2'-biimidazole (ATNBI) and TNBI and induces self-decomposition. Although the decomposition peak temperature of DATNBI is significantly lower than that of TNBI at the same heating rate; its self-accelerating decomposition temperature (50 kg) is only 4 K lower. Therefore, the -NH2 group displays good ability of reducing sensitivity but has no influence on storage safety of DATNBI.

Kinetics and mechanism of decomposition induced by solvent evolution in ICM-101 solvates: solvent-evolution-induced low-temperature decomposition.

[2,2'-Bi(1,3,4-oxadiazole)]-5,5'-dinitramide (ICM-101), a high-energy-density material, was reported in recent years. ICM-101 is the first energetic material with the 2,2'-bi(1,3,4-oxadiazole) structure as the main ring structure. The molecular structure of ICM-101 shows excellent planar characteristics, providing a new option for the design of high-energy-density materials. However, during crystal preparation, ICM-101 easily interacts with solvents and forms the corresponding solvates. Interestingly, during thermal decomposition, when the solvent escapes from ICM-101 solvates, it induces the decomposition of ICM-101. In this study, the decomposition of ICM-101 induced by solvent evolution was evaluated in detail, and the decomposition kinetic equation was established. The mechanism of solvent-evolution-induced decomposition in ICM-101 solvates was further studied, and it was found that solvent evolution might produce defects in the crystals of ICM-101 solvates, and induce the decomposition of ICM-101 on the defects.

The effects of H+, NH3OH+ and NH4+ on the thermal decomposition of bistetrazole N-oxide anion.

The bistetrazole N-oxide energetic ionic salt dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) has attracted great interest as it breaks through the limitations of the traditional nitro group, high detonation velocity and moderate impact sensitivity. Reports show that TKX-50 transforms into the 5,5'-bis(2-hydroxytetrazole) (BTO) precursor, which is further decomposed and partly converted to diamino 5,5'-bistetrazole-1,1'-diolate (ABTOX). Studying the effects of H+, NH3OH+ and NH4+ on the thermal decomposition mechanism of bistetrazole N-oxide anion would provide a more comprehensive understanding of the TKX-50 decomposition mechanism. Herein, TKX-50, BTO and ABTOX decomposition rates, on-line analysis of the gas products, as well as quantitative analysis, are presented. It was found that the presence of two H+ decreases the decomposition temperature, whereas NH3OH+ greatly increases the decomposition rate. In the presence of NH3OH+, the bistetrazole N-oxide anion completely decomposes without producing C2N2; however, NH4+ promotes the polymerization of C2N2 generated by the bistetrazole N-oxide anion, and the amount of NO produced is greater than that of N2O. Therefore, in the TKX-50 decomposition process, the bistetrazole N-oxide anion does not receive two H+ simultaneously and converts into BTO. Furthermore, the competition between cations and their decomposition products for the H+ affects the degree of decomposition, which is important in understanding the energy release mechanism.

A study on the comprehension of differences in specific kinetic energy of TKX-50 and HMX from the perspective of gas products.

5,5'-Bitetrazole-1,1'-dioxydihydroxylamine salt (TKX-50), a high-energy energetic material, possesses good safety and energy properties. The energy characteristic data of TKX-50 are commonly generated via theoretical simulation and experimental measurements. Interestingly, the detonation velocity of TKX-50 is higher than HMX, but the specific kinetic energy of TKX-50 is the opposite. Thus, a systematic study on the decomposition mechanism of TKX-50 is important to establish the reasons for this variation in specific kinetic energy. Although the thermal decomposition mechanism of TKX-50 has been reported, the specific compositional changes of its gas products under different heating conditions remain unknown, hindering a comprehensive understanding of the mechanism from the perspective of gas products. Herein, the gas products of TKX-50 and HMX in thermal decomposition and thermal explosion are investigated and compared. It was found that more TKX-50 is converted to ABTOX for further decomposition when the heating rate increases. ABTOX can decompose to C2N2, which is prone to polymerization, generating a solid residue under high temperature and pressure. Although polymerized C2N2 decomposes and burns during the explosion, it delays the time of TKX-50 reaching its maximum amount of outgassing, thereby affecting its specific kinetic energy. Furthermore, in the thermal explosion, compared with HMX, TKX-50 generates less H2 and CO. Since the combustion heat of hydrogen is much higher than that of carbon, the more hydrogen generated, the higher the detonation heat obtained. Therefore, TKX-50 has a lower detonation heat, which also affects its specific kinetic energy.

Hyper-branched structure-an active carrier for copolymer with surface activity, anti-polyelectrolyte effect and hydrophobic association in enhanced oil recovery.

Herein, a hyper-branched polymer h-PMAD with, simultaneously, surface activity, an anti-polyelectrolyte effect and a hydrophobic association was prepared via aqueous solution free radical polymerization, and characterized by IR, NMR, TG-DTG and SEM. The polymer h-PMAD provided excellent comprehensive properties in terms of surface activity, thickening, water solubility, rheology and aging, which were compared with studies of HPAM and the homologous linear polymer PMAD. Specifically, the IFT value was 55.40 mN m-1, 789.24 mPa s apparent viscosity with a dissolution time of 72 min, 97.72, 90.77 and 105.81 mPa s with Na+, Ca2+ and Mg2+ of 20 000, 2000 and 2000 mg L-1, respectively. Meanwhile, the non-Newtonian shear thinning behavior had a 96.33% viscosity retention while the shear rate went from 170 s-1 to 510 s-1 and then returned to 170 s-1 again and 0.12 Hz curve, with an intersection frequency of G' and G''. Also, it had 33.51% and 50.96% viscosity retention in formation and deionized water at 100 °C and a low viscosity loss in formation water at 80 °C over 4 weeks. Moreover, the h-PMAD had an EOR of 11.61%, was obviously higher than PMAD with 8.19% and HPAM with 5.88%. Most importantly, the better EOR of h-PMAD over that of PMAD testified that the hyper-branched structure provided an active carrier for copolymers with functionalized monomers to exert greater effects in displacement systems, which is of an extraordinary meaning.

The Chemistry and Properties of Energetic Materials Bearing [1,2,4]Triazolo[4,3-b][1,2,4,5]tetrazine Fused Rings.

Treatment of heterocyclic amines featuring fused rings of [1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine with fuming HNO3 /P2 O5 leads to six fully characterized explosives through multiple nitration and reduction or oxidation mechanism. Thus, 4-nitro-N-(3-nitro[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl)-1,2,5-oxadiazol-3-amine (3 b, TTDNF) showed high performance (D=9180 m s-1 , P=36.7 GPa) and low impact sensitivity (IS>40 J) while N-([1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl)-3-nitro-1,2,4-oxadiazol-5-amine (4 a, TTNOA) exhibited a potential cast explosive component with low melting point at 88.2 °C and high onset decomposition temperature at 226.2 °C.

5-Amino-1H-1,2,4-triazole-3-carbohydrazide and its applications in the synthesis of energetic salts: a new strategy for constructing the nitrogen-rich cation based on the energetic moiety combination.

Nitrogen-rich cation 5-amino-1H-1,2,4-triazole-3-carbohydrazide and its derivatives were synthesized by a new molecular design strategy based on the energetic moiety combination. All derivatives were fully characterized by vibrational spectroscopy (IR), multinuclear (1H, 13C) NMR spectroscopy, elemental analysis, differential scanning calorimetry (DSC), and impact and friction-sensitivity tests. The structures of compounds 1-4, 7 and 8 were further confirmed by single-crystal X-ray diffraction and six different types of crystal packing were surprisingly discovered. The results show that the extensive hydrogen bonding interactions between the cations and anions lead to a complex 3D network, which contribute greatly to the high density, insensitivity and thermal stability of the 5-amino-1H-1,2,4-triazole-3-carbohydrazide salts. It is also found that the cationic form of 5-amino-1H-1,2,4-triazole-3-carbohydrazide can decrease the sensitivity and elevate the nitrogen content of the target salts effectively. Some of these salts exhibit reasonable physical properties, such as good thermal stability (up to 407 °C) and reasonable impact sensitivities (IS = 5-80 J). In addition, theoretical detonation properties of the energetic salts obtained with EXPLO 5 (version 6.02) confirm them as competitively energetic compounds comparable to those of RDX or HMX.

Gem-dinitromethyl-substituted Energetic Metal-Organic Framework based on 1,2,3-Triazole from in situ Controllable Synthesis.

Synthesizing energetic metal-organic frameworks at ambient temperature and pressure has been always a challenge in the research area of energetic materials. In this work, through in situ controllable synthesis, energetic metal-organic framework gem-dinitromethyl-substituted dipotassium 4,5-bis(dinitromethyl)-1,2,3-triazole with a "cage-like" crystal packing was obtained and characterized. Most importantly, for the first time, we found that it could be successfully afforded with a catalytic effect of trifluoroacetic acid. This new compound exhibited its high density (2.04 g cm-3 ) at ambient temperature, superior detonation velocity (8715 m s-1 ) to that of lead azide (5877 m s-1 ) and comparable to that of RDX (8748 m s-1 ). Its detonation products are mainly N2 (48.1 %), suggesting it is also a green energetic material. The above-mentioned performance indicates its potential applications in detonator devices as lead-free primary explosive.

ROS-driven and preferential killing of HepG2 over L-02 cells by a short-term cooperation of Cu(II) and a catechol-type resveratrol analog.

This study was aimed at understanding why dietary polyphenols with a catechol skeleton tend to exhibit cancer chemopreventive activity by using a catechol-type stilbene (3,4-DHS) as a model molecule. Only a short-term cooperation of 3,4-DHS and exogenous Cu(II) exhibited a strong preferential ability to kill HepG2 cells over normal L02 cells. Mechanism studies reveal that this 3,4-DHS/Cu(II) system could produce extracellularly reactive oxygen species (ROS) and o-quinone through two sequential proton loss electron transfer followed by diffusion of ROS into cells, leading to higher intracellular accumulation of ROS, preferential disruption of redox homeostasis and more effective mitochondria-dependent apoptosis as well as necrosis of HepG2 cells than L-02 cells. This work provides further evidence that dietary catechol-type molecules show chemopreventive activity by virtue of their copper-dependent prooxidant action.

Synthesis, and single crystal structure of fully-substituted polynitrobenzene derivatives for high-energy materials.

New energetic fully-substituted polynitrobenzene derivatives were synthesized via the reaction of 1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) with 1,2,4-triazole followed by the nucleophilic substitution of the halo groups by aqueous ammonia or sodium azide. These compounds were charactered by 1H NMR, 13C NMR and HRMS. Additionally, the structures of amino derivatives 6, 8 and azido derivative 7 were further confirmed by single crystal X-ray diffraction analysis. Their decomposition temperatures and impact sensitivities were also determined. The derivative 1,2-di-1H-triazol-4,6-diamino-3,5-dinitrobenzene (8) exhibits good thermal stability (T d = 314 °C) and low impact sensitivity (IS = 30 J), which are both superior to that of TNT (T d = 295 °C, IS = 15 J). These synthesized compounds showed high heat of formation ranging from 31.77 to 1014.68 kJ mol-1, and reasonable detonation velocities and pressures.

Correction: Synthesis, and single crystal structure of fully-substituted polynitrobenzene derivatives for high-energy materials.

[This corrects the article DOI: 10.1039/C7RA13346D.].

Energetic π-conjugated vinyl bridged triazoles: a thermally stable and insensitive heterocyclic cation.

A new family of vinyl bridge 1,1'-(ethane-5-yl)-bis(3,4-diamino-1,2,4-triazolium) salts were explored as novel structural energetic materials. These new salts were further characterized by elemental analysis, infrared and multinuclear NMR spectra. Structural confirmation of nine salts such as 4-11 and 14 was supported by single-crystal X-ray diffraction. Theoretical investigations associated with heats of formation and detonation performance were carried out by employing the Gaussian 09 program and the EXPLO5 V6.02 code, respectively. The sensitivities towards impact and friction were studied using BAM standards. According to the experimental and computational data, these salts show densities ranging from 1.61 to 1.82 g cm-3 at 298 K, good thermal stabilities (Td: 217 °C-322 °C), excellent detonation performance (P: 7809 m s-1 to 9640 m s-1, D: 24.6 GPa-33.9 GPa) and rational impact and friction sensitivities (IS: 4 J to 60 J, FS: 120 N to 360 N).

Thermally Stable Energetic Salts Composed of Heterocyclic Anions and Cations Based on 3,6,7-Triamino-7 H-s-triazolo[5,1-c]-s-triazole: Synthesis and Intermolecular Interaction Study.

To create intermolecular N-H⋅⋅⋅O and N-H⋅⋅⋅N hydrogen-bond (HB) interactions, a series of energetic N-heterocyclic anions including polynitro- and multi-nitrogen anions were introduced into the 3,6,7-triamino-7 H-s-triazolo[5,1-c]-s-triazole (TATT) cation to get numerous novel energetic salts. Single-crystal X-ray diffraction was employed to confirm the crystal structure and crystal packing properties of compounds 2⋅H2 O, 6, and 9. Additionally, Hirshfeld surface analysis and atoms-in-molecules topology analysis provided insights into the intermolecular hydrogen-bond interaction of these new salts. With the assistance of the EXPLO5 program, the detonation velocities, detonation pressures, and specific impulses of the salts were found to fall in the ranges 8113-9477 m s-1 , 24.1-31.4 GPa, and 203.2-224.2 s, respectively. The predicted detonation performance indicate that all the energetic salts based on TATT are similar to those of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) or even overtake octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), which reveal that they can be candidates for the future insensitive high-performance energetic materials (IHPEMs).

Computational assessment of several hydrogen-free high energy compounds.

Tetrazino-tetrazine-tetraoxide (TTTO) is an attractive high energy compound, but unfortunately, it is not yet experimentally synthesized so far. Isomerization of TTTO leads to its five isomers, bond-separation energies were empolyed to compare the global stability of six compounds, it is found that isomer 1 has the highest bond-separation energy (1204.6kJ/mol), compared with TTTO (1151.2kJ/mol); thermodynamic properties of six compounds were theoretically calculated, including standard formation enthalpies (solid and gaseous), standard fusion enthalpies, standard vaporation enthalpies, standard sublimation enthalpies, lattice energies and normal melting points, normal boiling points; their detonation performances were also computed, including detonation heat (Q, cal/g), detonation velocity (D, km/s), detonation pressure (P, GPa) and impact sensitivity (h50, cm), compared with TTTO (Q=1311.01J/g, D=9.228km/s, P=40.556GPa, h50=12.7cm), isomer 5 exhibites better detonation performances (Q=1523.74J/g, D=9.389km/s, P=41.329GPa, h50= 28.4cm).

Hypohalous acid-mediated halogenation of resveratrol and its role in antioxidant and antimicrobial activities.

The reactions of resveratrol with proinflammatory oxidants including hypochlorous and hypobromous acids in phosphate-buffered saline/methanol solution were carried out and eight halogenated resveratrol derivatives differing in the number and position of halogen atoms, and the configuration of double bond were obtained. Halogenation of resveratrol took place only at the aromatic A ring, and interestingly, the halogenation increased antioxidant activity of this parent molecule in the 2,2'-azobis(2-amidinopropane) hydrochloride-induced RBC haemolysis model. Additionally, antimicrobial activity of the derivatives against Gram-positive bacteria, Gram-negative bacteria and fungi were tested, and toward Candida albicans, 2-chloro-resveratrol and 2-bromo-resveratrol were more active than the unmodified form and the reference compound fluconazole.

Finding more active antioxidants and cancer chemoprevention agents by elongating the conjugated links of resveratrol.

Resveratrol is the subject of intense research as a natural antioxidant and cancer chemopreventive agent. There has been a great deal of interest and excitement in understanding its action mechanism and developing analogs with antioxidant and cancer chemoprevention activities superior to that of the parent compound in the past decade. This work delineates that elongation of the conjugated links is an important strategy to improve the antioxidant activity of resveratrol analogs, including hydrogen atom- or electron-donating ability in homogeneous solutions and antihemolysis activity in heterogeneous media. More importantly, C3, a triene bearing 4,4'-dihydroxy groups, surfaced as an important lead compound displaying remarkably increased antioxidant, cytotoxic, and apoptosis-inducing activities compared with resveratrol.

Hydroxycinnamic acids as DNA-cleaving agents in the presence of Cu(II) ions: mechanism, structure-activity relationship, and biological implications.

The effectiveness of hydroxycinnamic acids (HCAs), that is, caffeic acid (CaA), chlorogenic acid (ChA), sinapic acid (SA), ferulic acid (FA), 3-hydroxycinnamic acid (3-HCA), and 4-hydroxycinnamic acid (4-HCA), as pBR322 plasmid DNA-cleaving agents in the presence of Cu(II) ions was investigated. Compounds bearing o-hydroxy or 3,5-dimethoxy groups on phenolic rings (CaA, SA, and ChA) were remarkably more effective at causing DNA damage than the compounds bearing no such groups; furthermore, CaA was the most active among the HCAs examined. The involvement of reactive oxygen species (ROS) and Cu(I) ions in the DNA damage was affirmed by the inhibition of the DNA breakage by using specific scavengers of ROS and a Cu(I) chelator. The interaction between CaA and Cu(II) ions and the influence of ethylenediaminetetraacetic acid (EDTA), the solvent, and pH value on the interaction were also studied to help elucidate the detailed prooxidant mechanism by using UV/Vis spectroscopic analysis. On the basis of these observations, it is proposed that it is the CaA phenolate anion, instead of the parent molecule, that chelates with the Cu(II) ion as a bidentate ligand, hence facilitating the intramolecular electron transfer to form the corresponding CaA semiquinone radical intermediate. The latter undergoes a second electron transfer with oxygen to form the corresponding o-quinone and a superoxide, which play a pivotal role in the DNA damage. The intermediacy of the semiquinone radical was supported by isolation of its dimer from the Cu(II)-mediated oxidation products. Intriguingly, CaA was also the most cytotoxic compound among the HCAs toward human promyelocytic leukemia (HL-60) cell proliferation. Addition of exogenous Cu(II) ions resulted in an effect dichotomy on cell viability depending on the concentration of CaA; that is, low concentrations of CaA enhanced the cell viability and, conversely, high concentrations of CaA almost completely inhibited the cell proliferation. On the other hand, when superoxide dismutase was added before, the two stimulation effects of exogenous Cu(II) ions were significantly ameliorated, thus clearly indicating that the oxidative-stress level regulates cell proliferation and death. These findings provide direct evidence for the antioxidant/prooxidant mechanism of cancer chemoprevention.

4,4'-Dihydroxy-trans-stilbene, a resveratrol analogue, exhibited enhanced antioxidant activity and cytotoxicity.

Resveratrol (3,5,4'-trans-trihydroxystibene) is a natural phytoalexin present in grapes and red wine, which possesses a variety of biological activities including antioxidant activity. In order to find more active antioxidant with resveratrol as the lead compound we synthesized 4,4'-dihydroxy-trans-stilbene (4,4'-DHS). The antioxidant activities of resveratrol and 4,4'-DHS were evaluated by the reaction kinetics with galvinoxyl radical or Cu(II) ions, and the inhibition effects against free-radical-induced peroxidation of human erythrocyte ghosts. It was found that 4,4'-DHS exhibits remarkably higher antioxidant activity than resveratrol. The oxidative products of resveratrol and 4,4'-DHS in the presence of Cu(II) in acetonitrile were identified as the dihydrofuran dimers by spectroscopic method, and the antioxidant mechanism for 4,4'-DHS was proposed. In addition, 4,4'-DHS exhibits remarkably higher cytotoxicity against human promyelocytic leukemia (HL-60) cells than resveratrol.