Computational Physics

In silico studies have been helpful in identifying the potential lead molecules with reduced cost. The chemical structure of a drug determines its physicochemical properties, and further determinates its absorption, distribution, metabolism, excretion and toxicity properties and ultimately affect the pharmacological activity. Medical chemists can regulate the pharmacological activity of drug molecule by modifying their structure. Unsaturated(contain two double or triple bonds), partially unsaturated(contain at least one double or triple bond) and saturated(contain no double bond or triple bonds) ring systems are important components of a drug. In this study, a serious of 27 five-membered heterocyclics were subjected to frontier molecular orbital(FMO) analysis and nonlinear optical(NLO) property identification by using density functional theory(DFT) calculations. DFT based global reactivity descriptor calculations have emerged as powerful tools for studying the reactivity, selectivity and stability of chemical and biological systems. Molecular orbital analysis exhibits relatively high(low) energy gap of the studied molecules, indicating that it would be kinetically stable(unstable). Pharmacokinetic properties and toxicity risks were studied using various programs like OSIRIS and Molsoft. In addition, we also verified the drug score, which combines drug likeness, cLogP, LogS, molecular weight(MW), and toxicity risks in one value and this may be used to judge the compounds overall potential to qualify for a drug.

The Fourier transform infrared, FT-Raman and NMR spectra of Naphthalene-1-ly acetic acid (NAA) have been recorded and analyzed. Harmonic vibrational frequencies have been investigated with the help of Density functional theory (DFT) with 6-31+G(d, p) and 6-31++G(2d, 2p) basis sets. The Gauge-Invariant Atomic Orbital Approach (GIOA) is used to calculate the proton and carbon chemical shifts of the title compound. The natural bond orbital analysis of the title compound is also reported in order to understand the stability of the molecule which arises from hyper-conjucative intermolecular interactions and charge delocalization. The polarizability (?), first order hyper-polarizability (?) and second order hyper-polarizability (?) values of the investigated molecule have been computed using DFT quantum mechanical calculations. The molecular orbital contributions are studied by the density of energy states (DOSs). The reactivity sites are by mapping the electron density into the electrostatic potential surface (MEP). Mulliken analysis of atomic charges is also calculated. The electron density-based local reactivity descriptors such as Fukui functions were calculated to explain the chemical selectivity or reactivity site in NAA. Hirshfeld surface and fingerprint plots reveal that the complex structure is stabilized mainly by H…H, C…C, C…H intermolecular interactions. Finally, molecular docking studies have been carried out in the active site of NAA was also investigated.

The FT-IR and FT-Raman spectra of 2-hydroxy-4-methyl-3-nitropyridine (HMNP) have been recorded and analyzed. The optimized geometry, and harmonic vibrational wave numbers of HMNP have been investigated with the help of B3LYP scaled quantum mechanical (SQM) method supplemented with 6-311++G** basis set. The infrared and Raman spectra were predicted theoretically from the calculated intensities. The observed and simulated spectra were found to be well comparable.

The FT-IR and FT Raman spectra of 2,4-dihydroxy-3-nitropyridine (DHNP) molecule have been recorded in the region 4000-400cm-1 and 3500-50cm-1 respectively. Optimized geometrical parameters, harmonic vibrational frequencies and depolarization ratio have been computed by HF and density functional theory (DFT) using B3LYP/6-311++G(d,p) method and basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analysed and compared with theoretically predicted vibrational frequencies. The calculated HOMO and LUMO energies shows that charge transfer occur within molecule. Unambiguous vibrational assignments of all the fundamentals was made using the total energy distribution (TED).

In this study, the solid phase FT-IR and FT-Raman spectra of the 2-hydroxy-4-methyl-5-nitropyridine (HM5NP) was recorded in the range 4000–400 cm^–1 and 3500–100 cm^–1, respectively. Theoretical information on the optimized geometry, harmonic vibrational frequencies, Infrared and Raman intensities were obtained by means of density functional theory (DFT) using standard B3LYP/6-311++G** level. This information was used in the assignment of the various fundamentals. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.

The vibrational spectroscopy of o-nitrobenzaldehyde (ONBH) by means of quantum chemical calculation has been studied. The FT-Raman and FT-IR spectra of ONBH have been recorded in the region 3500-50cm-1 and 4000-400cm-1 respectively. The fundamental vibrational frequencies and intensity of vibrational bands have been evaluated using density functional theory (DFT) with standard B3LYP/6-31+G(d,p) and B3LYP/6-31++G(d,p) basis set combinations for optimized geometries. The observed FT-IR and FT-Raman vibrational frequencies have been anlaysed and compared with theoretically predicted vibrational frequencies. The assignments of bands to various normal modes of molecule have also been carried out. The electric dipole moment (?) and the first hyper polarazibility (?) values of the investigated molecule have been computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occur with in the molecule.

In this paper, we present the hyperchaotic dynamics of a four-dimensional autonomous Van der Pol–Duffing oscillator circuit. This circuit, which is capable of realizing the behavior of every member of Van der Pol–Duffing family, consists of just four linear elements (inductors and capacitors), a negative conductor and a cubic non-linear element. The route followed is a transition from regular behavior to Chaos and then to hyperchaos through period three-doubling bifurcation, as the system parameter is varied. The hyperchaotic dynamics, characterized by more than one positive Lyapunov exponents, is described by a set of four coupled first-order ordinary differential equations. This has been investigated extensively using laboratory experiments and numerical analysis.

The solid phase FTIR and FT-Raman spectra of 2,3,4,5,6-pentafluoroaniline(PFA) have been recorded in the region 4000-400 cm-1 and 3500-100 cm-1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculation based on the density functional theory (DFT) using the standard HF/6-31+G(d,p) and B3LYP/6-31+G(d,p) methods and basis set combination. A close agreement between the observed and calculated frequencies by refinement of the scale factor. The values of electric dipole moment (? and First-order hyperpolarizability(?) of the compound were computed using ab-initio quantum mechanical calculations.The calculation results also show that the PFA molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. HOMO and LUMO energy gap explains the eventual charge transfer interaction taking place within the molecule. Temperature dependence of various thermodynamic properties like heat capacity, enthalpy, Gibb’s free energy, entropy is increase with increase in temperature. And magnetic susceptibility of the title compound at different temperatures is calculated.

The experimental FT-IR (4000 - 400 cm-1) and FT? Raman (3500 ? 100 cm-1) spectra of o-(salicyloyloxy) benzoiacid (OSBA) have been recorded. Quantum chemical calculation of energies, geometric, vibrational wave numbers of OSBA are carrier out using DFT/B3LYP method 6-31+G (d) and 6-311++G (d, p) basic sets. The optimized geometrical parameters obtained by B3LYP method shows a good agreement with experimental data. The complete vibrational assignments were performed on the basics of potential energy distribution (PED) of the vibrational modes calculated with scaled quantum mechanical method. The calculated HOMO and LUMO energies allow the calculation of atomic and molecular properties and they also show that charge transfer occurs in the molecule. Details of molecular picture of OSBA, Mulliken atomic charge and molecular electrostatic potential map, respectively

Vibrational spectral analysis of 2,3,4,5,6-pentafluoroaniline (PFA) was recorded using FT-IR and FT-Raman spectroscopic techniques in the region 4000-400 cm^-1 and 3500-100 cm^-1, respectively. The equilibrium geometry, and harmonic vibrational frequencies of PFA have been investigated with the help of HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) methods. The observed and calculated frequencies are found to be in good agreement.