Semiempirical, ab initio and density functional studies on structural and electronic properties of trans- and cis-cAMPB(H2O)

Structural changes of a water-soluble cyclic azobenzene peptide containing the photoswitch (4-aminomethyl)-phenylazobenzoic acid (AMPB) and a bioactive peptide motif, cAMPB(H2O) (peptide motif Lys-Ser-Ala-Thr-Ser-Asp-Lys-Lys), were studied with quantum mechanical methods. Quantum-mechanical investigations of the ground-state geometry of trans-cAMPB(H2O) and cis-cAMPB(H2O) were performed by using the semiempirical molecular orbital method PM3, HF and density functional methods. We report the structural properties, energy, dipole moment, polarizability, HOMO-LUMO gap and other properties of the trans and cis configurations of cAMPB(H2O) calculated using the PM3, ab initio HF and B3LYP functionals. The absorption spectrum of each studied molecule was obtained by semiempirical ZINDO/S and TD-DFT methods and compare with experimental data.