Intramolecular interactions of L‐phenylalanine: Valence ionization spectra and orbital momentum distributions of its fragment molecules

Abstract

Intramolecular interactions between fragments of L-phenylalanine, i.e., phenyl and alaninyl, have been investigated using dual space analysis (DSA) quantum mechanically. Valence space photoelectron spectra (PES), orbital energy topology and correlation diagram, as well as orbital momentum distributions (MDs) of L-phenylalanine, benzene and L-alanine are studied using density functional theory methods. While fully resolved experimental PES of L-phenylalanine is not yet available, our simulated PES reproduces major features of the experimental measurement. For benzene, the simulated orbital MDs for 1e(1g) and 1a(2u) orbitals also agree well with those measured using electron momentum spectra. Our theoretical models are then applied to reveal intramolecular interactions of the species on an orbital base, using DSA. Valence orbitals of L-phenylalanine can be essentially deduced into contributions from its fragments such as phenyl and alaninyl as well as their interactions. The fragment orbitals inherit properties of their parent species in energy and shape (ie., MDs). Phenylalanine orbitals show strong bonding in the energy range of 14-20 eV, rather than outside of this region. This study presents a competent orbital based fragments-in-molecules picture in the valence space, which supports the fragment molecular orbital picture and building block principle in valence space. The optimized structures of the molecules are represented using the recently developed interactive 3D-PDF technique.

Dynamical (e,2e) studies of tetrahydrofurfuryl alcohol

“…30,31 The DGTZVP basis set of Godbout et al 32 has been proven to be a good basis set for orbital momentum distribution calculations, 33 which can also be applied to larger molecules. 34 The ionization potential energies of THFA are calculated using the outer valence Green function OVGF/DGTZVP model. The ith momentum-space wave function i ( p) of THFA is produced according to the Dirac transformation theory, 30 in which the ith molecular orbital can be transformed from the coordinate space representation…”

Positron scattering from chiral enantiomers

“…The former is for validation purposes and the latter is for a more accurate MCP geometry determination. The DGTZVP basis set due to Godbout et al [33] has proven to be a good basis set for orbital momentum distribution calculations [34,35], which can also be applied to larger molecules [36]. We thus also chose to use it here.…”

Fragment based electronic structural analysis of l-phenylalanine using calculated ionization spectroscopy and dual space analysis

“…However, the high symmetry benzene (D 6h ) possesses ve pairs of occupied doubly degenerate orbitals in its valence space, i.e., 1e 1g , 3e 2g , 3e 1u , 2e 2g and 2e 1u , in which, two of the MOs (2e 2g and 2e 1u ) appear in the inner valence and the other orbitals (1e 1g , 3e 2g and 3e 1u ) are in the outer valence region. 12 It is noted in this diagram that the orbital correlations are not strictly on the one-to-one basis, since "free fragments" employed in the present study are molecules saturated by hydrogen atoms. Hence the orbital correlations are matched by their orbital characteristics of the molecules.…”

“…In molecular orbital theory, information of valence orbital topology is useful as changes in the orbitals are indicators of chemical bonding. 12 Fig. 8 displays the inner (a) and outer valence (b) orbital diagrams of the related fragments, in which the le side panel presents the orbital correlations in the A/B scheme, whereas the right side panel displays the correlation in the G/T scheme.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Like other amino acids, Phe takes a neutral structure in the gas phase presenting a number of low energy conformers. 7,10,16,21,22 However, with the presence of even a few water molecules, Phe takes a zwitterion form.…”