Photoelectron spectroscopy of biologically active molecules. 17. unsaturated steroids

Abstract

The assignment of the He1 photoelectron ( PE) spectra of the unsaturated steroids: estr4ene-3,17dione (1); estr-5( lO)ene-3,17dione (2); pregn-5ene-3,20-dione (3); 208-hydroxypregn4ene-3-one (4); 1 1~, 2 1 d i h y d r o x~~n e -3 , 2 0 -d i o n e (5); androst4ene-3,17dione (6); androsta-l,qdiene-3,17dione (7); androst-5en-l'l-one (8); and androst-5ene-3,17-dione (9) is attempted. This attempt is vested in an analysis of features, the results of quantum chemical calculations ( MNDO) , and correlative studies. A simple empirical method for the prediction of double-bond ioniiation energies of alkenes is described and applied. 1.Although the experimental values are readily obtained (e.g., by PE spectroscopy, multiphoton ionization, and mass spectrometry), the number of possible molecules increases so rapidly with the number of C-atoms that most of the larger molecules will never be either synthesized or isolated.2. The existing data suggest that a large range of I( xcc) values will be spanned by molecules with the same number of C-atoms but with different locations of the double bond.

Photoelectron Spectra of Some Important Biological Molecules: Symmetry-Adapted-Cluster Configuration Interaction Study

“…Valence ionization of biologically active compounds gives information about the frontier orbitals which significantly change in the species and chemical reactions. In this regard, there are numerous gas-phase He-I and He-II photoelectron spectra of different biological molecules in the literature. − Recently, photoelectron spectroscopy with the aid of high level of computational chemistry has significantly contributed to the determination of the vertical ionization energies and elucidation of the structure and dynamic of biomolecules and their solvated complexes in the gas phase. − For example, photoelectron spectroscopy along with the ab initio calculations was employed to determine the population ratios of different conformers and tautomers of amino acids and nucleotides in the gas phase . In another example, effect of solvation on the vertical ionization energies of amino acids and nucleotides in microhydration and bulk conditions has been also investigated both experimentally and theoretically. , …”