Two-photon circular dichroism of molecular structures simulating l-tryptophan residues in proteins with secondary structures

Herein, we report on the calculation and the comparative analysis of the theoretical two-photon circular dichroism (TPCD) spectra of l-tryptophan (Trp) residues in proteins with secondary structures (α-helix, β-strand and random coil) conformation, down to the far-UV region (FUV). The examination of the TPCD spectra of the different conformers in each configuration reveals distinctive fingerprints in the FUV, a dark spectral region for electronic circular dichroism (ECD). Our results show the potential of FUV-TPCD to identify and study protein structures in a region never assessed before but filled with important structural information.