Exploring the thermal decomposition and detonation mechanisms of 2,4-dinitroanisole by TG-FTIR-MS and molecular simulations.

2,4-dinitroanisole (DNAN), an insensitive explosive, has replaced trinitrotoluene (TNT) in many melt-cast explosives to improve the safety of ammunition and becomes a promising material to desensitize novel explosives of high sensitivity. Here, we combine thermogravimetric-Fourier transform infrared spectrometry-Mass spectrometry (TG-FTIR-MS), density functional theory (DFT), and ReaxFF molecular dynamics (MD) to investigate its thermal decomposition and detonation mechanisms. As revealed by TG-FTIR-MS, the thermal decomposition of DNAN starts at ca. 453 K when highly active NO2 is produced and quickly converted to NO resulting in the formation of a large amount of Ph(OH)(OH2)OCH3+. DFT calculations show that the activation energy of DNAN is higher than that of TNT due to the lack of α-H. Further steps in both thermal decomposition and detonation reactions of the DNAN are dominated by bimolecular O-transfers. ReaxFF MD indicates that DNAN has a lower heat of explosion than TNT, in accordance with the observation that the activation energies of polynitroaromatic explosives are inversely proportional to their heat of explosion. The inactive -OCH3 group and less nitro groups also render DNAN higher thermal stability than TNT.

How are N-methylcarbamates encapsulated by ß-cyclodextrin: insight into the binding mechanism.

Guest molecules containing chromophore groups encapsulated by ß-cyclodextrin (ß-CD) generate circular dichroism (CD) signals, which enables a preliminary prediction of their binding modes. However, the accurate determination of the representative binding conformation (RC) remains a challenging task due to the complex conformational space of these host-guest systems. Here, we combine a molecular dynamics/quantum mechanics/continuum solvent model (MD/QM/CSM) with induced circular dichroism (ICD) data (N. L. Pacioni, A. B. Pierini and A. V. Veglia, Spectrochim. Acta A Mol. Biomol. Spectrosc., 2013, 103, 319-324.) to explore the binding mechanism of ß-CD with four N-methylcarbamate molecules: promecarb (PC), bendiocarb (BC), carbaryl (CY) and carbofuran (CF). In aqueous solution, their stability decreases as: PC > BC > CY > CF. Comparing the ECD spectra computed from TD-DFT with the ICD data can help eliminate many common binding configurations and identify the RC. The host-guest binding affinities (BAs) estimated using a ONIOM2(B971:PM6)/SMD model reproduce the measured binding trend, reveal the competition between the non-covalent interaction and solvent effect and explain the large difference in their binding modes. We also examine the fluctuations in the computed BA using similar structures.

Antibacterial and antibiofilm mechanisms of carbon dots: a review.

Due to the increasing bacterial resistance to conventional antibiotics, developing safe and effective approaches to combat infections caused by bacteria and biofilms has become an urgent clinical problem. Recently, carbon dots (CDs) have received great attention as a promising alternative to conventional antimicrobial agents due to their excellent antimicrobial efficacy and biocompatibility. Although CDs have been widely used in the field of antibacterial applications, their antibacterial and antibiofilm mechanisms have not been systematically discussed. This review provides a systematic overview on the complicated mechanisms of antibacterial and antibiofilm CDs based on recent development.

Cytocompatible Amphipathic Carbon Quantum Dots as Potent Membrane-Active Antibacterial Agents with Low Drug Resistance and Effective Inhibition of Biofilm Formation.

It is very challenging to design nanomaterials with both excellent antibacterial activity and cytocompatibility when facing bacterial infection. Here, inspired by antimicrobial peptides (AMPs), we fabricate carbon quantum dots (CQDs) derived from hydrophobic tryptophan and hydrophilic lysine or arginine (Lys/Trp-CQDs and Arg/Trp-CQDs), which possess amphipathic properties. These CQDs could effectively destroy bacterial membranes without developing resistance, inhibit biofilms formed by Staphylococcus aureus, and exhibit good in vitro biocompatibility. The antibacterial activities are caused by not only surface cationic structures and excess intracellular reactive oxygen species (ROS) generated by the CQDs but also the effects of the surface hydrophobic groups. These combined mechanisms of actions lead to bacterial membrane disruption, which raises the hope for combating bacterial infection without concern about drug resistance. What's more, the effect of amphiphilicity on balancing sterilization with biocompatibility expands the research ideas for developing available antibacterial nanomaterials.

Design and exploration of 5-nitro-3-trinitromethyl-1H-1,2,4-triazole and its derivatives as energetic materials.

According to the fact that 5-nitro-3-trinitromethyl-1H-1,2,4 triazole (NTNMT) is a successful, good explosive, energetic groups such as -CH3, -NH2, -NHNO2, -NO2, -ONO2, -NF2, -CN, -NC, -N3 groups were introduced into NTNMT and their oxygen balance was at about zero. The energetic properties, detonation performance, and sensitivity were studied at the B3LYP/6-31G** level of density functional theory to seek for possible high energy density compounds. The effects of substituent groups on heat of formation (HOF), density ρ, detonation velocity D, detonation pressure P, detonation energy Q, and sensitivity (evaluated using oxygen balance OB, the nitro group charges -QNO2, and bond dissociation energies BDE were studied and discussed. The order of contribution of the substituent groups to ρ, D, and P was -NF2 > -ONO2 > -NO2 > -NHNO2 > -N3 > -NH2 > -NC > -CN > -CH3; while to HOF is -N3 > -NC > -CN > -NO2 > -NF2 > -ONO2 > -NH2 > -NHNO2 > -CH3. The trigger bonds in the pyrolysis process for NTNMT derivatives may be N-NO2, N-NH2, N-NHNO2, C-NO2, or O-NO2 varying with the attachment of different substituents. Results show that NTNMT-NHNO2, -NH2, -CN, and -NC derivatives have high detonation performance and good stability. In a word, the oxygen balance at about zero strategy in this work offers new routes for the improvement in properties and stabilities of energetic materials. In the present paper, several 5-nitro-3-trinitromethyl-1H-1,2,4 triazole (NTNMT) derivatives were designed. Their energetic properties, detonation performance, and sensitivity were studied at the B3LYP/6-31G** level of density functional theory (DFT) to seek for possible high energy density compounds (HEDCs). The different substituents have some changes in the influence on heat of formation (HOF), density ρ, detonation velocity D, detonation pressure P, detonation energy Q, and sensitivity. In a word, the oxygen balance at about zero strategy in this work offers new routes for the improvement in properties and stabilities of energetic materials.

Theoretical study on the gas-phase reaction mechanism of ammonia with nitrous oxide.

Applications of nitrous oxide (N2O) as an oxidant in green propellants and propulsion systems have attracted a lot of attention. In this study, the reaction pathways for the oxidation of ammonia (NH3) with N2O were studied using the B3LYP/6-31++G** method of density functional theory (DFT). The results reveal that the reaction between N2O and NH3 proceeds through a chain reaction mechanism. N2O reacts with NH3 to form N2 and NH3O first and then NH3O decomposes into NH3 and O. This process corresponds to the apparent reaction N2O+M=N2+O+M (M=NH3), but the energy barrier of the process (183.49 kJ/mol) is much lower than the direct decomposition reaction of N2O=N2+O (279.05 kJ/mol). The O radical produced in this process reacts subsequently with NH3 and N2O to produce more radicals such as NH2, OH, and NO, which will take part in further reactions like NH3+OH=NH2+H2O and NH2+NO=N2+H2O until the reactants are consumed.

Low-toxicity carbon quantum dots derived from gentamicin sulfate to combat antibiotic resistance and eradicate mature biofilms.

Carbon quantum dots derived from gentamicin sulfate are directly developed by facile calcination at different temperatures. A promising nanomaterial, CQD180, even shows a much superior antibacterial activity compared with the antibiotic counterpart and low drug resistance, by preserving the active structure of the starting materials and providing an additional antibacterial mode arising from the positive charge surface and induced reactive oxygen species simultaneously. Moreover, CQD180 can effectively disrupt mature Staphylococcus aureus biofilm and selectively eliminate bacteria over mammalian cells.

Design of pH-Responsive Dissociable Nanosystem Based on Carbon Dots with Enhanced Anti-biofilm Property and Excellent Biocompatibility.

Bacterial biofilm poses a serious threat to human health, leading to increased and prolonged bacterial infections. How to solve the problem of eliminating biofilms effectively and rapidly while being nontoxic to normal cells is still a challenge. Here, we design a pH-sensitive anti-biofilm nanosystem formed by self-assembly between negatively charged carboxyl groups of poly(ethylene glycol_-COOH-polyethylenimine-2,3-dimethylmaleic anhydride (PPD) and positively charged amines on the surface of carbon dots derived from the ashes of calcined l-lysine powder (CDLys) (PPD@CDLys for short). The outmost copolymer could make PPD@CDLys facilely diffuse into the dense biofilm and reverse to be positively charged via hydrolysis, which lead to the acid-triggered disassembly of the nanosystem. After hydrolyzation, PPD would turn into a biocidal cationic polymer, which is prone to attaching on bacteria inside the biofilm and efficiently killing them. In addition, the released CDLys could induce intracellular reactive oxygen species (ROS) across the whole biofilm to degrade the matrix of extracellular polymer substances and kill resident bacteria deep into the biofilm. Finally, the prepared nanosystem effectively inhibits the formation of Staphylococcus aureus biofilm and rapidly destroys the mature biofilm by the synergy antibacterial effects of the cation and ROS. We also evaluate the biocompatibility of the nanocomposites. The results show that PPD@CQDLys has no toxicity to L929 and 3T3 cells and exhibits a zero hemolytic rate even when the concentration is up to 2000 µg/mL. The outstanding biocompatibility coupled with rapid anti-biofilm ability of the nanosystem presents an opportunity for it to be utilized as an effective pH-responsive and targetable anti-biofilm agent for controlling bacterial infections.

UPLC-Q-TOF/MS-based untargeted metabolomics coupled with chemometrics approach for Tieguanyin tea with seasonal and year variations.

The taste and aroma quality of Tieguanyin tea fluctuate seasonally and yearly. However, the compounds responsible for the seasonal and year variations of metabolic pattern and its sensory quality are far from clear. 60 Tieguanyin tea samples harvested in different years and seasons were analyzed by ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) and chemometrics. Principal component analysis (PCA) explained 33.2% of the total variance, while orthogonal projection to latent structures discriminate analysis (OPLS-DA) can obtain potential metabolites with better discrimination, and with R2X and Q2 of cross-validation as 0.974 and 0.937, respectively. Subsequently, heat map analysis (HCA) visualized relationships between Tieguanyin teas with these significantly different potential metabolites by Mann-Whitney U test (p < 0.05). Furthermore, the best discriminate metabolites contributing to different sensory qualities were revealed by stepwise liner discrimination analysis (SLDA) with 100% accuracy rate. The present strategy also exhibited great potential for untargeted metabolomics of other foods.

Theoretical studies on a new series of 1,2,3,4-tetrazine 1,3-dioxide annulation with an imidazole ring or oxazole ring.

To continue our previous work, the structure and some properties of a new series of 1,2,3,4-tetrazine 1,3-dioxides annulated with an imidazole ring or oxazole ring were studied in this paper. Four imidazolo-v-tetrazine 1,3-dioxides (ITDOs) I1-I4 and eight oxazolo-v-tetrazine 1,3-dioxides (OTDOs) O1-O8 were designed. We employed the density functional theory (DFT) in B3LYP/6-311++G(d,p) to study their geometrical structures and the homodesmotic reaction method to calculate the enthalpies of formation. Detonation properties and stabilities were also studied. Generally speaking, ITDOs and OTDOs have more preferable stabilities than TTDOs or pyrazolo-TDOs. I3, I4, O1, and O2 were found to be comparable to the energy level of RDX; O5 and O6 are even as powerful as HMX. The stabilities analysis in this paper can also prove that the five-membered ring deformation and the steric hindrance change caused by the different substituents will affect the stabilities of the structures of 1,2,3,4-tetrazine 1,3-dioxides annulated with a five-membered nitrogen-rich heterocycle. Other factors, such as the position of the electron-withdrawing substituents or the position of coordinated oxygen atom, are worthwhile to investigate in future work.

Design of Zero Oxygen Balance Energetic Materials on the Basis of Diels-Alder Chemistry.

Herein, a novel zero oxygen balance polycyclic energetic compound trans-3,3,4,4,7,7,8,8-octanitro-9,10-dioxatricyclo[4.2.1.12,5]-decane ( trans-BIT) was designed and expected to exhibit high crystal density (ρ = 2.06 g/cm3), outstanding detonation performance ( D = 9.473 km/s, P = 42.2 GPa), and promising thermostability and sensitivity. We proposed that the synthesis of this compound could be achieved via a facile Diels-Alder reaction, using tetranitroethylene and oxadiazole as starting materials. We also predicted that the crystal structure of trans-BIT would have P21/ C space group symmetry.

High-Energy Nitramine Explosives: A Design Strategy from Linear to Cyclic to Caged Molecules.

After carefully analyzing the Kamlet-Jacobs (K-J) equations and the structural traits of well-known explosives, hexahydro-1,3,5-trinitro-1,3,5-triazin (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and hexanitrohexaazaisowurtizitane (CL-20), diverse nitramine explosives including linear (Models IAn, IBn, and ICn), cyclic (Model IIn), and caged (Models IIIAn and IIIBn) molecules were designed by incorporating various number (n) of -CH2NNO2- structural unit and studied using the B3LYP/6-31G* and B3PW91/6-31G** methods of the density functional theory. Computational results show that all of the energetic parameters, that is, density (ρ), detonation velocity (D), and detonation pressure (P), follow the order of IIIBn > IIIAn > IIn > IAn > IBn > ICn. With the increasing n, the D and P of linear nitramines eventually keep stable. This clearly indicates that elongating the chain length (e.g., polymerization) brings little or even negative benefit in boosting the explosive properties. The oxygen balance and the K-J equation parameter ϕ both have a significant influence on the detonation properties. Caged compound IIIA2 has not only comparable energetic properties but also better sensitivity and thermal stability than CL-20.

QSPR modeling of detonation parameters and sensitivity of some energetic materials: DFT vs. PM3 calculations.

The quantitative structure-property relationship (QSPR) methodology was applied to describe and seek the relationship between the structures and energetic properties (and sensitivity) for some common energy compounds. An extended series of structural and energetic descriptors was obtained with density functional theory (DFT) B3LYP and semi-empirical PM3 approaches. Results indicate that QSPR model constructed using quantum descriptors can be applied to verify the confidence of calculation results compared with experimental data. It can be extended to predict the properties of similar compounds.

Theoretical studies on a new furazan compound bis[4-nitramino-furazanyl-3-azoxy]azofurazan (ADNAAF).

Bis[4-nitraminofurazanyl-3-azoxy]azofurazan (ADNAAF), synthesized in our previous work [1], contains four furazan units connected to the linkage of the azo-group and azoxy-group. For further research, some theoretical characters were studied by the density functional theoretical (DFT) method. The optimized structures and the energy gaps between the HOMO and LUMO were studied at the B3LYP/6-311++G** level. The isodesmic reaction method was used for estimating the enthalpy of formation. The detonation performances were estimated with Kamlet-Jacobs equations based on the predicted density and enthalpy of formation in the solid state. ADAAF was also calculated by the same method for comparison. It was found that the nitramino group of ADNAAF can elongate the length of adjacent C-N bonds than the amino group of ADAAF. The gas-phase and solid-phase enthalpies of formation of ADNAAF are larger than those of ADAAF. The detonation performances of ADNAAF are better than ADAAF and RDX, and similar to HMX. The trigger bond of ADNAAF is the N-N bonds in the nitramino groups, and the nitramino group is more active than the amino group (-NH2).

Theoretical investigations on the stability of alkali metal substituted phenylpentazole.

The alkali metal (M=Li, Na, and K) para-substituted (M-1), meta-substituted (M-2) or ortho-substituted (M-3) derivatives of phenylpentazole (PhN5) were studied using density functional theory. The substituted metals improve the energy barrier for decomposition of the N5 ring of PhN5 by 19.3 ∼ 65.0 kJ/mol. M-3 has the ionic N-M bond, which is not found for M-1 and M-2. M-1 and M-2 have similar electrostatic potentials and dispersion interactions between metal and N5 ring. The comparable intramolecular interactions of M-1 and M-2 lead to similar N5 ring stability. Compared to M-1 and M-2, M-3 has a more negative charge on N5 ring and stronger dispersion interaction. The stronger intramolecular interactions of M-3 result in the higher N5 ring stability. For M-1 and M-2, different metals have slight affects on N5 ring stability. For M-3, N5 ring stability decreases in the order of Li > Na > K. The substituted metal lowers E(g) of PhN5.

Theoretical investigations on stability of pyridylpentazoles, pyridazylpentazoles, triazinylpentazoles, tetrazinylpentazoles, and pentazinylpentazole searching for a replacement of phenylpentazole as N5 (-) source.

Stabilities of pyridylpentazoles, pyridazylpentazoles, triazinylpentazoles, tetrazinylpentazoles, and pentazinylpentazole were studied using density functional theory to assess their potentials as the source of pentazole anion (N5 (-)) for replacement of phenylpentazole (PhN 5 ). Replacing the aryl group of PhN 5 by six-member heterocycle weakens pentazole ring. Compared to PhN 5 , title molecules have longer N-N bonds and lower activation energy (E a,1) needed for the N5 ring breaking. E a,1 decreases with the increasing number of nitrogen atoms of heterocycle. The ortho nitrogen of heterocycle most obviously lowers the stability of pentazole. The central C-N bond dissociation energies (BDEs) of title molecules are lower than that of PhN 5 . For the molecule with 0~1 ortho-nitrogen, H rearrangement happens during the central C-N bond breaking. The energy (E a,2) required for H rearrangement is considerably smaller than the corresponding BDE. ΔE a,2 (E a,2(PhN5) - E a,2 = 7.5~35.7 kJ mol(-1)) is larger than ΔE a,1 (E a,2(PhN5) - E a,2 = 4.6~15.5 kJ mol(-1)), while ΔE a,2/E a,2(PhN5) (2~9.5 %) is smaller than ΔE a,1/E a,1(PhN5) ( 4.4~15.0 %). The larger ΔE a,1/E a,1(PhN5) suggests that title molecules can not be the better N5 (-) than PhN 5 .

Theoretical studies of the structure, stability, and detonation properties of vicinal-tetrazine 1,3-dioxide annulated with a five-membered heterocycle. 2. Annulation with a pyrazole ring.

1,2,3,4-Tetrazine (vicinal-tetrazine) high-energy-density compounds (HEDCs) are receiving increasing attention due to their promise as explosives. We have performed a series of studies of vicinal-tetrazine 1,3-dioxides annulated with a range of five-membered heterocycles, considering their potential as high-energy, low-sensitivity explosives. In the present work, 12 pyrazolo-1,2,3,4-tetrazine 1,3-dioxides (pyrazolo-TDOs), P1-P12, were studied theoretically. Their geometrical structures in the gas phase were studied at the B3LYP/6-311++G(d,p) level of density functional theory (DFT). Their gas-phase enthalpies of formation were calculated by the homodesmotic reaction method. Their enthalpies of sublimation and solid phase enthalpies of formation were also predicted. Their detonation properties were estimated with the Kamlet-Jacobs equations, based on their predicted densities and enthalpies of formation in the solid state. Their bond dissociation activation energies (BDAEs) and the available free space in the lattice of each compound were calculated to evaluate their stabilities. P1, P4, and P11 were found to achieve the energy level of RDX and have acceptable stabilities, and are therefore considered to be the three most promising pyrazolo-TDOs for use as high-energy, low-sensitivity explosives. We believe that further studies, both experimental and theoretical, of these three targets would be worthwhile.

DFT, QTAIM, and NBO investigations of the ability of the Fe or Ni doped CNT to absorb and sense CO and NO.

The structures and intramolecular interactions of complexes (FeCNT-CO, FeCNT-NO, NiCNT-CO, and NiCNT-NO) formed by the Fe or Ni doped single-wall carbon nanotube (FeCNT or NiCNT) and gas CO or NO were studied using density functional theory, quantum theory of atom in molecule (QTAIM), and natural bond orbital methods. The adsorption processes of CO and NO on surfaces of FeCNT and NiCNT are chemisorption, energetically favored, exothermic, and spontaneous. High temperature is not good for adsorption. Introducing NO more obviously elongates the distances between Fe/Ni and C atoms and decreases ∠CFe(Ni)C than adding CO. QTAIM analysis shows that the covalent bonding interactions of FeCNT-NO (NiCNT-NO) are stronger than that of FeCNT-CO (NiCNT-CO). NO plays a role of electron acceptor while CO is electron donator in complexes. Electrostatic interaction of FeCNT-NO (NiCNT-NO) is stronger than that of FeCNT-CO (NiCNT-CO). The stronger intramolecular interactions of FeCNT-NO and NiCNT-NO reveal that FeCNT and NiCNT are more effective to adsorb and sense NO than CO. CO and NO considerably change the electronic properties of FeCNT and NiCNT, which is useful for designing sensors for CO and NO.

Theoretical studies of the structure, stability, and detonation properties of vicinal-tetrazine 1,3-dioxide annulated with a five-membered heterocycle. 1. Annulation with a triazole ring.

1,2,3,4-Tetrazine (vicinal-tetrazine) high-energy-density compounds (HEDCs) are receiving increasing attention due to their promise as explosives. We have performed a series of studies of vicinal-tetrazine 1,3-dioxides annulated with a range of five-membered heterocycles, considering their potential as high-energy, low-sensitivity explosives. In the present work, twelve 1,2,3-triazol-1,2,3,4-tetrazine 1,3-dioxides (TTDOs; T1-T12) were studied theoretically. Their geometric structures in the gas phase were studied at the B3LYP/6-311++G(d,p) level of density functional theory (DFT). Their gas-phase enthalpies of formation were calculated by the homodesmotic reaction method. Their enthalpies of sublimation and solid-phase enthalpies of formation were also predicted. Their detonation properties were estimated with the Kamlet-Jacobs equations, based on their predicted densities and enthalpies of formation in the solid state. Their bond dissociation activation energies (BDAEs) and the available free space in the lattice of each compound were calculated to evaluate their stabilities. T2, T5, and T11 were found to have higher energies than RDX and acceptable stabilities, and are therefore considered to be the three most promising TTDOs for use as high-energy, low-sensitivity explosives. We believe that further studies, both experimental and theoretical, of these three targets would be worthwhile.

Comparative theoretical investigation of the structures, energetics, and stabilities of C7N5H11cages.

Carbon-nitrogen cages are the focus of much research due to their potential use as high energy density materials (HEDMs). Several such cage isomers of C7N5H11, created by modifying the most stable N12 cage, were examined by performing theoretical calculations to evaluate their suitability as potential HEDMs. Calculations were carried out with density functional theory and Møller-Plesset perturbation theory (MP2) using the basis sets 6-31+G(d,p) and cc-pvdz. The relative thermodynamic stabilities of the isomers were explored in two ways: (1) the thermodynamic stability of one isomer was compared to that of another isomer based on their relative energies; (2) the kinetic stabilities of the isomers were determined by calculating the corresponding bond-breaking energies.