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A-234 (ethyl N-[1-(diethylamino)ethylidene]phosphoramidofluoridate) is one of the highly toxic Novichok nerve agents, and its efficient degradation is of significant importance. The possible degradation mechanisms of A-234 by H2O, H2O2, NH3, and their combinations have been extensively investigated by using density functional theory (DFT) calculations. According to the initial intermolecular interaction and the proton transfer patterns between the detergent and the substrate A-234, the A-234 degradation reaction is classified into three categories, denoted as A, B, and C. In modes A and B, the degradation of A-234 by H2O2, H2O, and NH3 is initiated by the nucleophilic attack of the O or N atom of the detergent on the P atom of A-234, coupled with the proton transfer from the detergent to the O or N atom of A-234, whereas in mode C, the direct interaction of H2N–H with the F–P bond of A-234 triggers ammonolysis through a one-step mechanism with the formation of H–F and N–P bonds. Perhydrolysis and hydrolysis of A-234 can be remarkably promoted by introducing the auxiliary NH3, and the timely formed hydrogen bond network among detergent, auxiliary, and substrate molecules is responsible for the enhancement of degradation efficiency. [ABSTRACT FROM AUTHOR]

Triphenylamine derivatives with narrowband emission have attracted growing attention in purely organic thermally-activated fluorescence (TADF) materials owing to their enhanced color purity and flexible molecular design strategy. Combined time-dependent density functional theory (TD-DFT) and ONIOM (QM/MM) calculations indicate that the excellent planarity of the experimentally developed DQAO could result in gradually decreased intermolecular interactions in the aggregated state at ambient pressure and upon compression, which is unfavorable for suppressing structural relaxation and achieving narrowband emission in its non-doped practical application. Therefore, three structure-modified derivatives, DQAO-Cb, DQAO-Ph, and DQAO-PhCb, were theoretically designed by introducing the spherical o-carborane and dangling phenyl units positioned para to the N atom of the DQAO to provide additional geometrical distortion and steric hindrance. The explorations on the reported DQAO, OQAO, and SQAO found that small structural relaxations, suppressed low-frequency vibrations, and noticeable short-range charge-transfer (SR-CT) natures of DQAO and OQAO are responsible for their much narrower emission spectral full-width at half-maxima (FWHMs) compared to that of SQAO. Introducing the o-carborane unit directly at the para position of the N atom could result in additional scissoring and stretching vibrations of the corresponding DQAO-Cb while the presence of the phenyl unit in DQAO-Ph is beneficial for suppressing the high-frequency vibrations of the pristine DQAO. More importantly, the bridged phenyl unit incorporated in DQAO-PhCb is of particular importance to inhibit the undesired low-frequency scissoring and high-frequency stretching vibrations of the o-carborane unit, which is crucial to reduce the reorganization energy of DQAO-PhCb and achieve narrowband emission. Also, the phenyl unit in DQAO-Ph and DQAO-PhCb helps to shorten charge transfer distances and improve ISC and RISC processes. Since the o-carborane unit is an adopted building block to achieve piezochromic behaviors, the theoretically structure-modified DQAO-PhCb is expected to exhibit narrowband emission, TADF, and piezochromic features all together. Our findings will hopefully provide ideas for designing triphenylamine-based TADF emitters with narrowband emission and piezochromic behaviors. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) and time‐dependent DFT methods were used to investigate the electronic and optoelectronic properties of several main group atom‐doped polycyclic aromatic hydrocarbons, such as oxygen‐substituted PHO1 and PHO2, and sulfur‐substituted PHS1 and PHS2. The ground‐state structures of these molecules generally have an open‐shell singlet configuration with a certain diradical character. In comparison with PHO1 and PHO2, PHS1 and PHS2 own larger diradical character indices due to their increased anti‐aromaticity. Although the substitution of sulfur for the peripheral oxygen has a significant effect on the molecular geometry, the adiabatic excitation energy levels of the corresponding low‐lying excited states of these molecules are less changed. Calculations reveal that here the intersystem crossing (ISC) and reverse intersystem crossing processes in CH2Cl2 mainly occur between the S1 and T2 states, and the cis molecules PHO2 and PHS2 have better charge transportation performance. Furthermore, the electronic and photophysical properties of these B‐containing molecules are predicted to be tuned by the peripheral atom substitution and the structural and aggregation changes. [ABSTRACT FROM AUTHOR]

The spike glycoprotein on the surface of the SARS-CoV-2 envelope plays an important role in its invasion into host cells. The binding of the spike glycoprotein RBD to the angiotensin-converting enzyme 2 (ACE2) receptor as a critical step in the spread of the virus has been explored intensively since the outbreak of COVID-19, but the high transmissibility of the virus such as the Delta variant is still not fully understood. Here, molecular simulations on the binding interactions of the wild-type spike protein and its four variants (Beta, Kappa, Delta, and Mu) with ACE2 and the antibody were performed, and the present results reveal that the residue mutations will not strengthen the binding affinity of the variant for ACE2, but remarkably influences the spatial orientation of the spike protein. Only the up-right conformational receptor binding domain (RBD) can bind ACE2, which is stabilized by the nearby RBDs in the down state, revealing that the RBD bears dual functional characteristics. The present results provide new insights into plausible mechanisms for high infectivity of the virus variants and their immune escape. [ABSTRACT FROM AUTHOR]