Journal of Physical Chemistry A, Vol.119, No.21, 5218-5223, 2015
Plasmonic Circular Dichroism of 310-and alpha-Helix Using a Discrete Interaction Model/Quantum Mechanics Method
Plasmonic circular dichroism (CD)of chiral molecules in the near field of plasmonic nanoparticles (NPs) May be used to enhance molecular CD signatures or to induce a CD signal at the plasmon resonance. A recent few-states theory explored these effects for model systems and showed an orientation dependence of the Sign of the induced pp signal for spherical NPs. Here, we use the discrete interaction model/quantum. mechanical (DIM/QM) method to simulate the CD and plasmonic CD of the and alpha-helix conformations of a short alanine peptide. We find that the interactions between the molecule and the plasm:on lead to significant changes in the CD spectra. In the plasmon region, we find that the sign of the CD depends strongly on the orientation of the molecule as well: as specific interactions with the NP through image dipole effects. A small enhancement of the CD is found in the molecule region of the spectrum, however, the molecular signatures maybe significantly altered through interactions with the NP. We also show that the image dipole effect can result in induced plasmonic CD even for achiral molecules. Overall, we find that the specific interactions with the NP can lead to large changes to the CD spectrum that complicates the interpretation of the results.