Gas phase ionization energies of some important unsaturated steroids

• Published in: Structural chemistry 2015-02, Vol.26 (1), p.71-86
• Main Authors: Abyar, F., Farrokhpour, H., Tabrizchi, M.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Computer Applications in Chemistry; Original Research; Physical Chemistry; Theoretical and Computational Chemistry
• ISSN: 1040-0400; 1572-9001
• DOI: 10.1007/s11224-014-0469-4

Gas phase ionization energies of some important biological active unsaturated steroids, known as active molecules in biology, were calculated using an expensive ab initio method for the first time. The calculations were performed using symmetry-adapted cluster-configuration interaction methodology employing a large basis set (6–311++G(2df,pd)), and ten ionization energies were calculated for each steroid. In addition, thermochemistry calculations were performed to determine the Boltzmann population ratios (BPRs) of different conformers of each steroid in the gas phase. The calculated ionization energies, their intensities, and the BPRs of conformers were used to simulate the photoelectron spectrum of each steroid. The calculations showed that for some steroids, more than one conformer contribute to the photoelectron spectrum of steroid. The calculated photoelectron spectrum of each steroid was compared with its corresponding experimental spectrum reported in literature. This comparison showed that the applied theoretical model can predict very well the relative energy of the ionization bands. The spectral ionization bands of each steroid were assigned by natural bonding orbital calculations and the ionization energy of π CC of each steroid was determined.