Theoretical analysis of photosensitization of DNA by thionine.

Context: In this work, we are the first to perform a theoretical analysis of photoinduced charge transfer in the intercalation complex of thionine (TH) with double-stranded DNA, which was observed in experiments. Efficient DNA binding and long-wave absorption maximum make TH an attractive photosensitizer. d(CpG) tetranucleotide was used as a minimal model DNA fragment.

TD-DFT analysis of excitation of the closed-form spironaphthopyran in methanol solution: The contribution of vibronic transitions and intermolecular hydrogen bonds.

A set of forty hybrid functionals, combined with a 6-31++G(d,p) basis set and an IEFPCM solvent description, was applied to calculate the S→S excitation of the spironaphthopyran (SNP) photochromic compound. None of the hybrid functionals resulted in C-O bond cleavage upon optimization of the S excited state of the SNP, in contrast to the spiropyran BIPS which we studied earlier. At the same time, the deformations of the SNP during excitation turned out to be very small (in contrast to those for BIPS) which made it possible to calculate its vibronic absorption spectrum.

Intramolecular excimers of open forms of 2-benzopyran, 2- and 3-naphthopyrans in solution: TD-DFT/DFT analysis.

We hypothesized that in the open forms of diphenyl-substituted photochromic compounds, immediately after the photoinduced cleavage of the C-O bond, one of the phenyl rings forms a stack with an aromatic system at the other end of the alkyl linker. The formation of these intramolecular stacking excimers is made possible by a known increase in the rotational mobility of the linker double bonds in the excited state. The flexibilities of linkers are analyzed in terms of changes in their dihedral angles.

4a,4b-Dihydrophenanthrene → cis-stilbene photoconversion: TD-DFT/DFT study.

Context: DHP → CS photoconversion was analyzed in terms of electron density redistribution for the first time. The following explanation for the non-recovery of the C4a-C4b bond upon CS relaxation is proposed: during this process, the Coulomb repulsion energy between these pairs of atoms increases by almost one and a half times, and their bonding by an electron at LUMO is insufficient to recover the C4a-C4b bond. According to calculations, upon CS relaxation, the linker connecting the benzene rings undergoes significant structural changes.

TD-DFT study of BIPS spiropyran: Effects of functionals and high-polarity solvent on C O bond dissociation and recovery.

We performed a theoretical analysis of the BIPS photochemical cycle using an extensive set of forty hybrid functionals and taking into account a highly polar solvent (methanol). The functionals with a small fraction of the exact Hartree-Fock exchange (%HF) showed the predominant S  → S transition with the strengthening of the C O bond. At the same time, functionals with medium and high %HF (including those with long-range correction) gave a dominant S  → S transition with weakening or breaking of the C O bond, which corresponds to the experimental results.

Theoretical study of the excitation of proflavine H-dimers in an aqueous solution: the effect of functionals and dispersion corrections.

Analysis of the ground and excited states of the H-dimer of the proflavine dye cation (PF) in an aqueous solution was performed using the DFT/TD-DFT method with an implicit specification of the aqueous environment and using various hybrid functionals (APFD, B2PLYP, B3LYP, B3PW91, BMK, CAM-B3LYP, M05, M052X, M06, M062X, M06HF, mPW2PLYP, PBE0, PW6B95, and ωB97XD), Grimme dispersion corrections, and Becke-Johnson damping. To our knowledge, this is the first theoretical study on the dimerization of charged monomers. The use of the B2PLYP, B3LYP, B3PW91, BMK, CAM-B3LYP, PBE0, M05, mPW2LYP, and PW6B95 functionals without additional dispersion corrections led to dimer dissociation due to Coulombic repulsion between PF cations.

Acriflavine in aqueous solution: excitation and hydration.

Using TD-DFT/DFT, the ground and excited states of the acriflavine dye were studied in an aqueous medium. The mutual influence of photoexcitation and strong hydrogen bonds with the solvent was studied by comparing the purely implicit and combined modeling of the aqueous environment of the dye. The excitation of acriflavine was calculated considering the vibronic coupling.

Coumarin 343 in aqueous solution: theoretical analysis of absorption.

Vibronic coupling and hydration were taken into account when describing the absorption of coumarin C343 (both neutral and anionic forms) in an aqueous media. It was shown that the B3LYP functional with the 6-31 +  + G(d,p) basis set and the IEFPCM solvent continuum model give theoretical vibronic absorption spectra, which are coincide with the experimental ones. Of the structural differences between C343 and C343, there is a different twisting of the carboxyl group additionally changing due to excitation.

Excitation of neutral red dye in aqueous media: comparative theoretical analysis of neutral and cationic forms.

The main goal of this work was the theoretical interpretation of the absorption spectra of neutral red in an aqueous solution (both neutral NR and protonated NR forms). To achieve this problem, TD-DFT/DFT calculations with different hybrid functionals, the IEFPCM solvent model, and the 6-31 +  + G(d,p) basis set were used. MN12SX functional provided the best agreement with the experiment for both dye forms.

Excitation of rhodamine 800 in aqueous media: a theoretical investigation.

The main goal of this work was to obtain a calculated absorption spectrum of rhodamine 800 in an aqueous solution, which most accurately reproduces the experimental one. To achieve this result, I used the hybrid functionals supported by Gaussian 16 software package. In this case, the basis set (6-31++G(d,p)) and the solvent model (IEFPCM) were not varied.

Photoexcitation of oxazine 170 dye in aqueous solution: TD-DFT study.

The vibronic absorption spectra of OX170 dye in an aqueous solution using 40 hybrid functionals, the 6-31 +  + G(d,p) basis set, and the SMD solvent model were calculated. It turned out that the long-range corrected ωB97XD functional provided the best agreement with the experiment in the positions of the main maximum and the short-wavelength shoulder. Calculations showed that this shoulder is vibronic and is not caused by a separate electronic transition.

The vibronic absorption spectrum and electronic properties of Azure B in aqueous solution: TD-DFT/DFT study.

The vibronic absorption spectrum of Azure B (AB) in an aqueous solution is calculated using the time-dependent density functional theory (TD-DFT). The results of calculations are analyzed using all hybrid functionals supported by Gaussian16, the 6-31++G(d,p) basis set, and the IEFPCM and SMD solvent models. The solvent model IEFPCM gave significantly underestimated values of λ in comparison with the experiment.

The vibronic absorption spectra and electronic states of acridine orange in aqueous solution.

The time-dependent density functional theory (TD-DFT) was used to obtain vibronic absorption spectra of acridine orange dye (AO) in an aqueous solution that were in good agreement with the experiment. The protonated and neutral forms of the dye have been investigated. The results of calculations using various functionals and basis sets have been analyzed.

Interaction of pseudoephedrine and azithromycin with losartan: Spectroscopic, dissolution and permeation studies.

This study aims at investigating the potential effect of selected cationic drugs (azithromycin (AZN) and pseudoephedrine sulfate (PSD) on the dissolution profile and intestinal permeation of losartan potassium (LOS) that might occur due to ion pair salt formation. DSC, FT-IR and H NMR indicated the formation of ion pair salts between LOS and each of AZN and PSD. Based on NMR chemical shifts calculations, utilizing specialized software, the most likely structures of the salt were proposed and revealed interesting structural features.