First-principles simulation of amide and aromatic side chain ultraviolet spectroscopy of a cyclic dipeptide.

By combining time-dependent density functional theory (TDDFT) and molecular dynamics (MD) simulations, we calculate the ultraviolet absorption and circular dichroism (CD) of a cyclic dipeptide, cyclo(L-Pro-D-Tyr), in the 185-300 nm region. The absorption is dominated by the phenol chromophore of tyrosine. The CD spectrum shows both phenol and amide units transitions. A crude coherent two-dimensional ultraviolet spectrum (2DUV) calculated by neglecting the two-excitation states shows a cross-peak between two transitions of the phenol in the tyrosine side chain. Additional cross-peaks between the side chain and the backbone are observed when using a chirality-induced pulse polarization configuration.