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In this work, the structural, electronic, topological and vibrational properties of potential antiviral to treatment of COVID-19, niclosamide (NCL) have been studied in different media together with its reactivities by combination of DFT calculations with molecular docking. Properties of two most stable conformers of niclosamide (C1 and C2) were reported in gas phase and water, ethanol and chloroform solvents. Calculations using the integral equation formalism variant polarised continuum (IEFPCM) and solvation methods in the different solutions have revealed solvation energy values for C1 and C2 in aqueous solution (GC= -78.43 and -64.53 kJ/mol, respectively) comparable with that observed for the antiviral agent zalcitabine (-78.92 kJ/mol). Probably, the high stability of C1, predicted by NBO studies, explains the experimental existence of C1 in the solid phase. Comparisons of frontier orbitals with eleven antiviral agents have evidenced the high reactivity of C2 slightly higher than brincidofovir, an antiviral agent used in the treatment to ebola disease. Possibly, the presence of deactivating groups (NO2 and Cl) in the chloro-4-nitrophenyl and hydroxybenzamide rings of both forms of NCL could explain the higher reactivities predicted in the different media. Here, the harmonic force fields and force constants for both forms are reported together with the assignments of 80 vibration modes expected in the experimental infrared spectrum of NCL. The predicted UV-Vis spectra in the different solvents suggest the presence of both forms of NCL in solution. Molecular docking results were discussed basing on the type of interaction between the ligands and several amino acid residues.

In this study, three anhydrous species of trehalose and their dihydrated form were studied using the Fourier Transform Infrared (FTIR) and Raman spectroscopy combined with theoretical calculations derived from the theory of the functional of the density (DFT). Here, the structural and vibrational properties were predicted using the hybrid B3LYP/6-31G∗ method. The complete vibrational assignments were performed using the scaled mechanical force fields (SQMFF) methodology and their internal normal coordinates. The natural bond orbital (NBO) and atoms in molecules (AIM) calculations predicted high stabilities for the dihydrated species in gas and aqueous solution phases. The little variation observed in the dipole moment for the dihydrated species in solution could be related to a small perturbation of water hydration shell and short hydrogen bonds, as revealed by NBO and AIM studies. The lower volume expansion, low solvation energy and the higher nucleophilicity index observed for trehalose species in solution, in relation to maltose and sucrose could probably explain that different water molecules are around of trehalose/water mixtures generating higher “rigidity” in trehalose, as was experimentally reported in the literature. On the other hand, the low f(νO–H)H2O force constant value for trehalose, as compared with maltose and lactose could justify the very fragile character from the trehalose/water system to the temperature and concentration changes, as was experimentally observed from viscosity and Raman scattering studies. Keywords: Trehalose, Molecular structure, Vibrational spectra, DFT calculations, Force field

In this work, the structural, topological and vibrational properties of an isothiazole derivatives series with antiviral activities in gas and aqueous solution phases were studied by using DFT calculations. The self consistent reaction field (SCRF) method was combined with the polarized continuum (PCM) model in order to study the solvent effects and to predict their reactivities and behaviours in both media. Thus, the 3-mercapto-5-phenyl-4-isothiazolecarbonitrile (I), 3-methylthio-5-phenyl-4-isothiazolecarbonitrile (II), 3-Ethylthio-5-phenyl-4-isothiazolecarbonitrile (III), S-[3-(4-cyano-5-phenyl)isothiazolyl] ethyl thiocarbonate (IV), 5-Phenyl-3-(4-cyano-5-phenylisothiazol-3-yl) disulphanyl-4-isothiazolecarbonitrile (V) and 1,2-Bis(4-cyano-5-phenylisothiazol-3-yl) sulphanyl Ethane (VI) derivatives were studied by using the hybrid B3LYP/6-31G* method. All the properties were compared and analyzed in function of the different R groups linked to the thiazole ring. This study clearly shows that the high polarity of (I) probably explains its elevated antiviral activity due to their facility to traverse biological membranes more rapidly than the other ones while in the (IV) and (V) derivatives the previous hydrolysis of both bonds increasing their antiviral properties inside the cell probably are related to their low S-R bond order values. In addition, the complete vibrational assignments and force constants are presented.

In this work, the structural, electronic and vibrational properties of 6-Nitro-1,3-benzothiazole-2(3 H )-thione and their 2-thiol tautomer were studied by using density functional theory (DFT) and self consistent reaction force (SCRF) calculations in gas phase and, in formamide, aqueous, DMSO and acetone solutions. The solvation energies were computed taking into account the solvent effects by using the polarized continuum (PCM) and solvation (SM) models. The atomic charges, electrostatic potentials, bond order, energy stabilizations, topological properties were calculated together with the gap energies and some descriptors in order to predict the reactivities and behaviour of both tautomers in the different media. The dipole moment and solvation energy values for both forms show different behaviours with the permittivity values of the solvents. The studies by infrared spectroscopy reveal the presence of both tautomers and of the two dimers of thione in the solid phase, as supported by the weak IR bands at 1702, 1525, 1303 and 1292 cm −1 and the shoulder at 915 cm −1 . Moreover, the strong IR band at 3062 cm −1 , the bands of the media intensities at 680 and 466 cm −1 and, the very weak band at 499 cm −1 support the presence of the thione form. The higher electrostatic potentials on the NO 2 group of the thiol tautomer and their low electrophilic index show that thiol is better electron donor than thione while, thione has the highest reactivities in all the solvents and in gas phase than thiol. Here, the complete assignments of the normal vibration modes of thione and thiol in gas phase and in the four solvents are reported for the first time.

In this work, the influence of the different S═O, S−O, N⋯H, O⋯H, Na⋯O bonds present in the structures of the powerful laxative drug, sodium picosulphate in gas and aqueous solution phases were studied combining the density functional theory (DFT) calculations with the experimental available infrared, 1H NMR and UV-visible spectra. The structural, topological, electronic and vibrational properties were investigated in both media by using the hybrid B3LYP/6-31G* method and the integral equation formalism variant polarised continuum model (IEFPCM). Here, the characteristics of the S═O, S−O, N⋯H, O⋯H, Na⋯O bonds were completely revealed by using atomic charges, natural bond orbital (NBO) and atoms in molecules (AIM) studies. The infrared, 1H NMR, 13C NMR and UV-visible spectra are in reasonable concordance with those experimental available in the literature. The vibrational analysis of sodium picosulphate was performed considering C3V symmetries for both SO42− groups and the complete assignments of the 126 vibration modes were reported in gas phase and aqueous solution together with their corresponding force fields. In addition, the reactivities of sodium picosulfate increase in solution due to their ionic characteristic which probably justifies their behaviour as a stimulant cathartic and their easy metabolic conversion, as reported in the literature.

In the present work, the structural, topological and vibrational properties of five members of the series C8H13N3O5POR (RH, (CH2)3OCH2CH3, (CH2)3O(CH2)7CH3, (CH2)3O(CH2)13CH3 and (CH2)3O(CH2)15CH3), where the first and the latter members are the two potential antiviral agents, cidofovir and brincidofovir, respectively, were studied by using density functional theory (DFT), natural bond orbital (NBO), atoms in molecules theory (AIM), frontier orbitals and molecular electrostatic potential (MEP) calculations and the hybrid B3LYP/6-31G∗ method. Here, the changes in the properties were followed modifying the side chain from cidofovir to brincidofovir. This study reveals clearly the differences in the properties when they change the longitude of the side chain. The high dipole moment value of brincidofovir together with the large side chain could explain the ability of brincidofovir to traverse biological membranes more rapidly than cidofovir while the low bond order that presents the POR bond in brincidofovir probably supports the quick removal of its side chain inside the cell. The frontier orbitals predicted a high reactivity and a higher electrophilicity index for brincidofovir, as compared with cidofovir. The complete assignment of the 90 vibration modes of cidofovir was proposed. Keywords: Brincidofovir, Vibrational spectra, Molecular structure, Force field, DFT calculations