Valence structures of aromatic bioactive compounds: a combined theoretical and experimental study

Abstract

Valence electronic structures of three recently isolated aryl bioactive compounds, namely 2-phenylethanol (2PE), p-hydroxyphenylethanol (HPE) and 4-hydroxybenzaldehyde (HBA), are studied using a combined theoretical and experimental method. Density functional theory-based calculations indicate that the side chains cause electron charge redistribution and therefore influence the aromaticity of the benzene derivatives. The simulated IR spectra further reveal features induced by the side chains. Solvent effects on the IR spectra are simulated using the polarizable continuum model, which exhibits enhancement of the O-H stretch vibrations with significant red-shift of 464 cm À1 in 2PE. A significant spectral peak splitting of 94 cm À1 between O(4)-H and O(8)-H of HPE is revealed in an aqueous environment. Experimental measurements for valence binding energy spectra for 2PE, HPE and HBA are presented and analyzed using outer-valence Green function calculations. The experimental (predicted) first ionization energies are measured as 9.19 (8.79), 8.47 (8.27) and 8.97 (8.82) eV for 2PE, HPE and HBA, respectively. The frontier orbitals (highest occupied molecular orbitals, HOMOs, and lowest unoccupied molecular orbitals, LUMOs) have similar atomic orbital characters although the HOMO-LUMO energy gaps are quite different.

From building blocks of proteins to drugs: a quantum chemical study on structure–property relationships of phenylalanine, tyrosine and dopa

“…Moreover, it is ascertained that the SAOP model slightly overestimates the outermost valence IPs, especially the IP of the HOMOs, whereas the OVGF produces more accurate IPs in this region. 51,53,56,61 Hence combining both the SAOP and OVGF models can, therefore, achieve good correlation between the calculated valence IPs and the experiments.…”

“…Here, the et-pVQZ basis set denotes the even-tempered polarized valence quadruple-zeta Slater-type basis set and the OVGF/TZVP is the outer valence Greens function combined with the triple zeta valence polarized basis set. The DFT based SAOP model and the Green's function based OVGF model have been efficient in calculating the accurate valence IPs for amino acids 36,52,56 and other bio-molecules 49,54,61,62 . The former model is able to calculate the IPs in the entire valence space, while the latter is applicable for calculations of the outer valence IPs with required accuracy.…”

“…The former model is able to calculate the IPs in the entire valence space, while the latter is applicable for calculations of the outer valence IPs with required accuracy. Moreover, it is ascertained that the SAOP model slightly over-estimates the outermost valence IPs, especially the IP of the HOMOs, whereas the OVGF produces more accurate IPs in this region 51,53,56,61 . Hence combining both the SAOP and OVGF models can, therefore, achieve good correlation between the calculated valence IPs and the experiments.…”

“…The DFT based statistical average of orbital potentials (SAOP) and the Green's function based OVGF model have been efficient in calculating the accurate valence ionization potentials (IPs) for amino acids 36,52,56 and other biomolecules. 49,54,61,62 The former model is able to calculate the IPs in the entire valence space, while the latter is applicable for calculations of the outer valence IPs with required accuracy. Moreover, it is ascertained that the SAOP model slightly overestimates the outermost valence IPs, especially the IP of the HOMOs, whereas the OVGF produces more accurate IPs in this region.…”

Probing Intramolecular Interaction of Stereoisomers Using Computational Spectroscopy

“…Experimental measurements, rather than capturing a single molecular state, often detect a weighted average of all possible isomers due to effects such as temperature and Frank-Condon effects, requiring additional information for assignment and insight into the physico-chemical origin of properties. [10][11][12][13][14] An understanding of preferred conformation, active conformation, property changes from the conformational restriction, and strategies to develop conformationally restricted analogues is crucial to the chemical design of new compounds.…”