Structural And Vibrational Studies on Isomers of Antiviral Ribavirin Drug in Gas and Aqueous Environmental by Using The SQM Approach

Five stable isomers of antiviral ribavirin agent were theoretically determined in gas and aqueous solution by using the hybrid B3LYP/6-31G* method. Here, the solvent effects were studied with the self consistent reaction field (SCRF) methodology employing the polarized continuum (PCM) and the universal solvation model (SM). Structural, electronic and topological properties were reported for all isomers while the vibrational analyses were performed only for those two polymorphic structures experimentally observed in the solid phase by X-ray diffraction. Calculations have evidenced that C2 correspond to the polymorphic V1 structure while C5 to the polymorphic V2 structure. The high dipole moment values predicted for C2 and C5 in both media could probably explain their presences in the solid. Experimental available IR and Raman spectra of ribavirin in the solid state and normal internal coordinates were employed together with the scaled quantum mechanical force field (SQMFF) approach to perform the complete vibrational assignments in both media. Here, the 81 vibration modes expected for C2 and C5 in both media were completely assigned. The frontier orbitals studies reveal that C5 is the less reactive in both media. Here, the gap value observed for C5 is in agreement with the value recently reported for ribavirin by using B3LYP/6-311++G** calculations

A combined study on structures and vibrational spectra of the antiviral rimantadine using SQMFF and DFT calculations

In this research, a combined study on structures and vibrational spectra of antiviral rimantadine have been performed using hybrid B3LYP/6-311 thorn thorn G** calculations and the scaled quantum force field (SQMFF) proced-ure. Harmonic force fields and scaled force constants of Free Base (FB), Cationic (CA) and Hydrochloride (HCl) species derived from the antiviral rimantadine have been calculated in gas phase and in aqueous solution using normal internal coordinates and scaling factors. Good correlations were acquired comparing the theoretical IR, Raman, 1H- 13C-NMR and UV spectra of three species with the analogous experimental ones, suggesting probably, the presence of all them in both phases. The main force constants of three species have evidenced lower values than the corresponding to antiviral amantadine. The ionic character of N1-H33 center dot center dot center dot Cl36 bond of HCl species in aqueous solution evidence positive Mulliken charge on N1 atom indicating that this species is as CA one. Rimantadine presents higher solvation energies in water than other antiviral species, such as chloroquin, niclo-samide, cidofovir and brincidofovir. The FB and HCl species of rimantadine are slightly less reactive than the corresponding to amantadine while the opposite is observed for the CA species. The predicted ECD spectra for the FB and CA species show positive Cotton effect different from the negative observed for the HCl one. These different behaviours of three species of rimantadine could probably explain the differences observed in the in-tensities of bands predicted in the electronic spectra of these species.Peer reviewe

Effect of Long-Range Corrections on Intermolecular Interactions and Vibrational Assignments of Ethylene Oxide Dimer. A Combined DFT and SQFF Study

Theoretical structural and vibrational study for the ethylene oxide dimer have been performed by using the experimental structure determined by X-ray diffraction, the vibrational spectra and, the functional hybrids B3LYP/6-311++G** and WB97XD/6-311++G** methods. Here, the effects of dispersion on intermolecular interactions and on complete assignments of infrared and Raman spectra of dimer have been performed combining the Pulay´s scaled quantum mechanical force field (SQMFF) methodology with those two levels of calculations in order to fit the theoretical wavenumbers values to the experimental ones. Calculations including long-range corrections have revealed similar optimized energy, volume and frequencies to calculated with the B3LYP/6-31G* method, lower correlations in the geometrical parameters, higher stabilization energy, higher values in the topological parameters and higher scaled force constants than the obtained at B3LYP/6-311++G** level. Natural bond order (NBO) and atoms in molecules theory (AIM) studies with both methods reveal two types of intermolecular interactions (C-O···H and C-O···O) in the ethylene oxide dimer in accordance with the bands observed in the experimental Raman spectrum at low temperatures and with the experimental structure determined at 100 K. The nature of those interactions and their topological properties were studied by using NBO and AIM calculations. The studied properties for the ethylene oxide dimer were analyzed and compared with those obtained for the monomer. Similar assignments of the vibrational modes for dimer were obtained using the three different methods

Impact of Different Groups on Properties of All Members of the Series of 1-X-Benzotriazole Derivatives (X= H, OH, NH2, Cl and CH3)

Here, the impact of different groups on the geometrical parameters, dipole moments, atomic charges, stabilization and solvation energies, molecular electrostatic potentials, densities rings, positions IR and UV bands and NMR chemical shifts of all members of the series of 1X-benzotriazole derivatives (X= H, CH3, Cl, NH2 and OH) have been investigated by using hybrid B3LYP/6-311++G** calculations because, so far, correlations among their properties neither the vibrational analyses are reported yet. The polarity of N-X bonds, electronegativity, donor/acceptor characteristics of the different X groups were analysed for all members. The polarity of N1-X4 bonds have influence on dipole moments, volumes and on bond lengths of both rings while the chlorinated derivative has a higher reactivity due to its higher global electrophilicity index. NBO and AIM studies reveal the strong influence of Cl on densities of both rings of CBT and, on this derivative. Harmonic force fields evidence very good correlations between stretching force constants and assignments

Theoretical Investigation on Monomer and Dimers of Inhibitor of Cytochrome P450 Enzymes: 1-Aminobenzotriazole

In this research, structures and properties of monomer and two dimers (1 and 2) of inhibitor of cytochrome P450 enzymes, 1-Aminobenzotriazole (ABT) have been studied by using functional hybrid B3LYP/6-311++G** calculations. The very good correlations observed between theoretical and experimental 1H-, 13C-NMR, FT-IR and FT-Raman spectra suggest that C-H···N interactions of dimeric species should be expected in the solid phase, as was observed in the experimental crystalline structure of a quinolin benzotriazole derivative. NBO and AIM calculations suggest that dimer 2 with inverted positions of its monomers could be present in the solid phase because it evidence higher stabilities in both media. On the other hand, frontier orbitals studies support a higher reactivity of dimer 2 of ABT higher than the monomer and dimer 1, for which, the presence of dimer 2 containing N-NH2 groups in ABT could justify the biological activities observed for this species with gap values between 4.5933 and 4.8164 eV different from antiviral agents containing the C-NH2 moiety, as amantadine and chloroquine whose gap values are around 4.3012-4.1116 eV. Finally, the presence of bands of monomer and of both dimers are predicted in the vibrational spectra and, hence, its completes assignments have been performed. The scaled force constants for the three studied species are also reported

Vibrational study and force field of the citric acid dimer based on the SQM methodology

We have carried out a structural and vibrational theoretical study for the citric acid dimer. The Density Functional Theory (DFT) method with the B3LYP/6-31G() and B3LYP/6-311++ G methods have been used to study its structure and vibrational properties. Then, in order to get a good assignment of the IR and Raman spectra in solid phase of dimer, the best fit possible between the calculated and recorded frequencies was carry out and the force fields were scaled using the Scaled Quantum Mechanic Force Field (SQMFF) methodology. An assignment of the observed spectral features is proposed. A band of medium intensity at 1242 cm - 1 together with a group of weak bands, previously not assigned to the monomer, was in this case assigned to the dimer. Furthermore, the analysis of the Natural Bond Orbitals (NBOs) and the topological properties of electronic charge density by employing Bader's Atoms in Molecules theory (AIM) for the dimer were carried out to study the charge transference interactions of the compound.Facultad de Ciencias Exacta

A crystallographic and vibrational study of cesium di-μ-aqua bis[tetraaquasodium(I)] decavanadate, Cs₄[Na₂(H₂O)₁₀](V₁₀O₂₈)

The title compound crystallizes in the triclinic space group P͞1, with a = 8.6161(4) Å, b = 10.591(1) Å, c = 11.406(1) Å, α = 67.976(7)°, β = 86.868(6)°, γ = 67.798(6)°, and Z = 1. The structure was refined to R1 = 0.0413. The decavanadate anion V₁₀O₂₈⁶⁻ and the [Na₂(H₂O)₁₀]²⁺ bridged cation are located at inversion centers. Partial deuteration of the substance indicates that the coordinated water molecules are strongly asymmetric, forming weak hydrogen bonds with acceptor oxygen atoms from the decavanadate anion. The infrared and Raman spectra are dominated by the water and decavanadate anion bands.Instituto de Física La PlataCentro de Química Inorgánic

Vibrational study and force field of the citric acid dimer based on the SQM methodology

We have carried out a structural and vibrational theoretical study for the citric acid dimer. The Density Functional Theory (DFT) method with the B3LYP/6-31G() and B3LYP/6-311++ G methods have been used to study its structure and vibrational properties. Then, in order to get a good assignment of the IR and Raman spectra in solid phase of dimer, the best fit possible between the calculated and recorded frequencies was carry out and the force fields were scaled using the Scaled Quantum Mechanic Force Field (SQMFF) methodology. An assignment of the observed spectral features is proposed. A band of medium intensity at 1242 cm - 1 together with a group of weak bands, previously not assigned to the monomer, was in this case assigned to the dimer. Furthermore, the analysis of the Natural Bond Orbitals (NBOs) and the topological properties of electronic charge density by employing Bader's Atoms in Molecules theory (AIM) for the dimer were carried out to study the charge transference interactions of the compound.Facultad de Ciencias Exacta

Structural, harmonic force field and vibrational studies of cholinesterase inhibitor tacrine used for treatment of Alzheimer's disease

Different structures of free base (FB), two cationic forms (CA) and three hydrochloride forms (HCl) of cholinesterase inhibitor tacrine used for treatment of Alzheimer ’s disease was evaluated using hybrid B3LYP calculations in order to perform their complete vibrational assignments using the scaled harmonic force fields. Structures of anhydrous form of tacrine have been optimized in gas phase and in aqueous solution. The structure of form III HCl is in agreement with the experimental determined by X-ray diffraction while the predicted IR, Raman, 1H– 13C NMR and UV spectra show good correlations with the corresponding experimental ones. Energy values show that the three forms of HCl can exist in both media because these energetic values decrease from 35.15 kJ/mol in gas phase to 5.51 kJ/mol in solution. For the most stable species of tacrine, the following stability order using natural bond orbital (NBO) studies was found: form I HCl > form III HCl > form I CA > FB. CA presents the higher solvation energy value, as reported for hydrochloride species of alkaloids and antihypertensive agents. The structural parameters of form III of HCl present better concordance and corresponds to that experimental observed in the solid phase. Higher topological properties of form III together with the strong N2–H26⋯Cl31 interaction could justify the presence of this form in the solid phase and in solution and the higher stabilities in both media. The gap values support the higher reactivity of form III while FB is the less reactive species in both media. Complete vibrational assignments for FB, CA and HCl species together with the corresponding scaled force constants are reported

Structural and vibrational characterization of di-hydrated hydrochloride tacrine combining DFT with SQMFF approach

This research is a continuation of previously reported article on anhydrous freebase, cationic and hydrochloride tacrine. Here, structures and properties of di-hydrated species of cholinesterase inhibitor tacrine have been studied in gas phase and aqueous solution by using B3LYP/6-311G* and wB97XD/6-311G* levels of theory. Both methods show strong changes in the positions of two water molecules and similar solvation energies (-192.52 kJ/mol with the B3LYP method and -191.95 kJ/mol with the other one). The B3LYP method predicts low gap values for the anhydrous (2.4572 eV) and di-hydrated (3.2708 eV) species of tacrine in gas phase than the wB97XD/ 6-311G* method (7.2300 eV). Hence, higher reactivities are expected for the di-hydrated species in both media. Atoms in molecules (AIM) calculations support the lower stability of di-hydrated species in solution in agreement with its higher reactivity in this medium. Complete assignments of 104 vibration modes expected for di-hydrated hydrochloride by using the scaled mechanical force field (SQMFF) methodology have been reported. Both methods predict different assignments and scaled force constants presenting higher values those calculated with the wB97XD/6-311G* method. The predicted IR, Raman and 1H NMR spectra with both methods show good correlations with the corresponding experimental ones, however, better concordances between the 13C NMR and UV spectra are observed with the wB97XD/6-311G* method.Peer reviewe