Structure and electronic properties of hydrated mesityl oxide: a sequential quantum mechanics/molecular mechanics approach

Novel Approach for Predicting Vertical Electron Attachment Energies in Bulk-Solvated Molecules

When low-energy electrons interact with molecules, they can give rise to transient anion states commonly known as resonances. These states are formed through vertical electron attachment processes and have the potential to induce various forms of DNA lesions, including base damage, single- and double-strand breaks, cross-links, and clustered lesions that are challenging to repair. So far, most experimental and theoretical studies have investigated the formation of resonances of (bio)molecules in the gas phase or in microsolvated environments. Since cellular environments are mainly composed of water molecules, it is crucial to understand how bulk water affects the resonances of (bio)molecules. Given the existing gap in studies on resonances of bulk-solvated molecules, we propose a novel theoretical-computational approach to address this void. Our approach combines the multibasis-set (time-dependent-)density functional theory and self-consistent sequential quantum mechanics/molecular mechanics polarizable electrostatic embedding methods. We apply this combined methodology to predict the vertical electron attachment energies of 1-methyl-5-nitroimidazole (1M5NI), a well-known radiosensitizer model, in bulk water. In addition, we analyze the rapid mutual polarization between the resonances (both shape- and core-excited) of 1M5NI and the surrounding bulk water environment. For comparison, we also studied the isolated and microsolvated 1M5NI. Overall, while the polarization of the environment is clearly sensitive to the solute charge, causing a significant impact on the vertical electron affinity and consequently on the attachment electron energies, it does not have a significant impact on the excitation energies of the anion.

Spectrophotometric studies of charge-transfer complexes formed with ions N,N'-alkyldiyl-bis(pyridinium) derivatives and iodide

The charge-transfer complexes (CTC) between electron donor iodide and pyridinium dimers and monomers as acceptors have been studied spectrophotometrically in acetonitrile, DMSO and water. The dimers were: N,N'-alkyldiyl-bis(4-cyanopyridinium) and N,N'-alkyldiyl-bis(2-bromopyridinium), and the monomers were: N-alkyl-4-cyanopyridinium and N-alkyl-2-bromopyridinium, bridged by n methylene spacers. The formation constant (K_CTC), molar absorptivity (ε_CTC), fluorescence-quenching constant (K_SV) were determined. The results indicate that the stoichiometry of the CTC for dimers and monomers is 1:1 (equimolar ratio), and its formation is favored for dimers more than for monomers, especially dimers with short methylene spacers forming a "sandwiched type-complex" in which the iodide is close to the two pyridinium rings. Solvents with low polarity favored the complex, which was destroyed by the presence of water. The experimental studies were complemented with theoretical studies with quantum mechanics (QM) calculations using density functional theory (DFT) and molecular mechanics (MM) simulations with Molecular Dynamics for identify the most stable conformers in acetonitrile solution. The electronic excitations were calculated with sequential QM/MM hybrid method, showing a charge-transfer wavelength in agreement with the UV-Vis absorption spectra obtained experimentally. It confirms the "sandwiched type-complex" conformers favoring the interaction of the iodide with one pyridinium rings and simultaneously forming one, or two, hydrogen bonds with the alkyl chain and additionally, for the case of dimers, with the other pyridinium ring.