Application of Quantum Mechanical Calculations and Symmetry in Chemistry; Vibration Frequencies, Corrosion Inhibition and Prodrugs

Ab initio quantum chemistry is based solely on established laws of nature: Over the last two decades powerful molecular modeling tools have been developed which are capable of accurately predicting structures, energetics, reactivity and other properties of molecules. Computational chemistry is not a replacement for experimental studies, but plays an important role in enabling chemists to:

Explain and rationalise known chemistry, explore new or unknown chemistry, many molecular properties can be computed, these include; Bond energies and reaction energies, structures of ground-excited-and transition-states, atomic charges and electrostatic potentials, vibrational frequencies (IR and Raman), transition energies and intensities for UV and IR spectra, NMR chemical shifts, dipole moments, polarisabilities and hyperpolarisabilities, reaction pathways and mechanisms

This book was focused on three applications to show the importance of quantum chemistry calculations in chemical applications supporting experimentation.

The first application was for the electrical, chemical properties, vibration frequencies, and absorption intensities of SWCNTs which vary significantly according to the symmetry, chirality, and diameter, making the experimental determination of these structural properties important. The vibrational density of states contains information on the structure of carbon nanotubes, particularly at low frequencies. The signicant changes in the frequencies and relative intensities of these peaks open up a route to distinguish among structurally di-erent nanotubes. With our results, more structural information can be obtained from experiments.

The second application is the initial evaluation for the inhibition ability of new organic compounds as inhibitors towards carbon steel corrosion in acidic or basic solutions, using the quantum mechanical method of PM3 and Density Functional Theory (DFT) of B3LYP with a level of 6-311++G (2d, 2p) to calculate the geometrical structure, physical properties, and inhibition efficiency parameters, in a different media, all calculated at the equilibrium geometry. The results correlated with the experimental %IE. The local reactivity has been studied through Mulliken charges population analysis.

The third application concerns the using of suggested new prodrug designs for improving active drug solubility and consequently bioavailability, increasing permeability and absorption and modifying the drug’s distribution profile with enhanced efficacy, reduced toxicity, and side effects. Over the years, innovations in new drug therapy have become, more complex, time-consuming and costly. Theoretically in our prodrug design, a computational approach were performed by Gaussian 09 program. A comparison was made between the total energy of the reactants and the energies and transitional states up to the final products. The theoretical study of the proposed primary drugs aims to study the possibility of improving the properties of prodrugs and to study the possibility of obtaining new alternatives to approved prodrugs. Correlations between experimental and calculated values were to verify and confirm the possibility of adopting the final results.