Photodissociation Dynamics of the Highly Stable ortho-Nitroaniline Cation

0rtho-Nitroaniline (ONA) is a model for the insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) that shares strong hydrogen bonding character between adjacent nitro and amino groups. This work reports femtosecond time-resolved mass spectrometry (FTRMS) measurements and theoretical calculations that explain the high stability of the ONA cation compared with related nitroaromatic molecules. Ab initio calculations found that the lowest-lying electronic excited state of the ONA cation, D1, lies more than 2 eV above the ground state, and the energetic barriers to rearrangement and dissociation reactions exceed this D1 energy. These theoretical results were confirmed by FTRMS pump-probe measurements showing that (1) fragment ions represented less than 30% of the total ion yield when a 1014 W cm-2, 1300 nm, 20 fs pump pulse was used to ionize ONA; and (2) 3.1 eV (400 nm) photons were required to induce dissociation of the ONA cation. Stronger coupling between the ground D0 and excited D4 states of the ONA cation at the geometry of neutral ONA resulted in a transient enhancement of fragment ion yields at <300 fs pump-probe delay times, prior to relaxation of the ONA cation to its optimal geometry.

Vibrational, spectroscopic, chemical reactivity, molecular docking and in vitro anticancer activity studies against A549 lung cancer cell lines of 5-Bromo-indole-3-carboxaldehyde

Spectroscopic investigations are performed for 5-Bromo-1H-indole-carboxaldehyde by using experimental (FT-IR, FT-Raman) and theoretical (DFT) calculations. Vibrational assignments of the fundamental modes were assigned on the basis of Potential energy distribution (PED) calculations. Electron Localization Function (ELF) and Local Orbital Localizer (LOL) studies were performed to visualize the electron delocalization in the molecule. Frontier molecular orbitals (FMOs) and related molecular properties were computed. The electron-hole distribution of the molecule was also computed using Multiwfn 3.3.9 software to predict the charge transfer within the molecule. The total and partial density of states (TDOS and PDOS) and also the overlap population density of states (OPDOS) spectra were simulated. UV-Vis spectrum of the compound was also recorded. The reactive sites of the compound were studied from the MEP and Fukui function analysis. The charge delocalization and stability of the title molecule were investigated using natural bond orbital (NBO) analysis. The lung cancer activity of the title compound against p53 tumor suppressor proteins was studied using molecular docking analysis. The in-vitro cytotoxic activity of the molecule against human pulmonary lung cancer cell lines (A549) was determined by MTT assay.

A Photophysical Deactivation Channel of Laser-Excited TATB Based on Semiclassical Dynamics Simulation and TD-DFT Calculation

A deactivation channel for laser-excited 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) was studied by semiclassical dynamics. Results indicate that the excited state resulting from an electronic transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular mrbital (LUMO) is deactivated via pyramidalization of the activated N atom in a nitro group, with a lifetime of 2.4 ps. An approximately 0.5-electron transfer from the aromatic ring to the activated nitro group led to a significant increase of the C–NO₂ bond length, which suggests that C–NO₂ bond breaking could be a trigger for an explosive reaction. The time-dependent density functional theory (TD-DFT) method was used to calculate the energies of the ground and S₁ excited states for each configuration in the simulated trajectory. The S₁←S₀ energy gap at the instance of non-adiabatic decay was found to be 0.096 eV, suggesting that the decay geometry is close to the conical intersection.