https://doi.org/10.1140/epjd/e2002-00155-6
The role of enhanced aromatic π-electron donating aptitude of the tyrosyl sidechain with respect to that of phenylalanyl in intramolecular interactions
1
Department of Biomedical Sciences, School of Medicine
Creighton University, 2500 California Plaza, Omaha, NE 68178, USA
2
Global Institute Of Computational Molecular and Material Science @ Velocet,
210 Dundas St. W., Toronto, Ontario, Canada M5G 2E8
3
Department of Chemistry, University of Toronto, Lash Miller Chemical Laboratories,
80 St. George St., Toronto, Ontario, Canada M5S 3H6
Corresponding authors: a gchass@fixy.org - b slovas@bif1.creighton.edu - c barrym@creighton.edu - d icsizmad@fixy.org
Received:
1
February
2002
Revised:
28
May
2002
Published online:
13
September
2002
An exhaustive ab initio and DFT search for energetically stable conformers from the
topologically possible set was undertaken on the N-acetyl-phenylalanyl-N-methylamide and N-acetyl-tyrosyl- systems. The geometries of all 81 phenylalanyl and 162 tyrosyl
possible rotamers, described under the rules outlined by Multi-Dimensional Conformational
Analysis (MDCA), were attempted at each of the RHF/3-21G, RHF/6-31G(d) and B3LYP/6-31G(d) levels of theory. A total of 32 and 66 stable conformational minima were found for the
phenylalanyl and tyrosyl amino acid diamides, respectively, at the B3LYP/6-31G(d) level. From
the tyrosyl set, 33 unique conformers emerge when the orientation of the dihedral angle (p-OH
orientation) is disregarded. A total of 31 conformers were common to both sets and showed nearly
identical geometries. The comparison of the optimized DFT geometries of the two systems showed
near by perfect linear fits with R2 values of 0.9997, 0.9994, 0.9997, and 0.9996 for
the
,
,
, and
dihedral angles, respectively. Relative energies of the matching 31 conformers also
fitted to
a linear plot with an R2 value of 0.9985. The geometric centroid of the aromatic ring in the
sidechain of both systems was found to be within 4.1 Å of the H and O atoms of the peptide
groups, in 21 and 2 of the conformers, respectively. None of the non-matching conformers
showed any such interaction distance ≤4.1 Å.
PACS: 31.15.Ar – Ab initio calculations / 31.50.Bc – Potential energy surfaces for ground electronic states / 33.15.Bh – General molecular conformation and symmetry; stereochemistry
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002