Origin of the Bathochromic Shift of Astaxanthin in Lobster Protein: 2D Electronic Spectroscopy Investigation of beta-Crustacyanin

Author(s)
Niklas Christensson, Karel Zidek, Nikki Cecil M. Magdaong, Amy M. LaFountain, Harry A. Frank, Donatas Zigmantas
Abstract

We report on ultrafast spectroscopy study of β-crustacyanin, the

carotenoprotein responsible for the coloration of the lobster shell.

β-Crustacyanin is formed by two closely positioned astaxanthin molecules

encapsulated in protein. The 2D electronic spectroscopy together with

two-color pump–probe was applied to investigate the electronic

structure, the excited-state dynamics, and the influence of the

excitonic interaction between the two carotenoids in β-crustacyanin. By

using the ∼20 fs laser pulses tuned to absorption bands of the S0–S2 and S1–Sn transitions of carotenoids, we were able to trace full excitation relaxation dynamics, starting with S2–S1

relaxation on the ∼30 fs time scale and finishing with the ground-state

recovery of 3.2 ps. Superimposed on the relaxation dynamics in the 2D

spectra, we observed long-lived beating signals at the characteristic

frequencies of astaxanthin vibrational modes. We assign these

oscillations to the ground-state vibrational wavepacket dynamics. All

major features of the 2D spectra, including amplitude and phase maps of

the long-lived oscillations, were reproduced by employing the

exciton-vibronic model. Consistent modeling of all optical properties of

β-crustacyanin (including absorption and circular dichroism spectra)

points to the relatively weak coupling between the two astaxanthin

molecules (∼250 cm–1). This implies that the excitonic

coupling provides insignificant contribution to the bathochromic shift

in β-crustacyanin. We discuss the origin of the shift and propose that

it is caused by two major effects: conformational changes of astaxanthin

molecules (increase in effective conjugation length) together with

increased charge-transfer character of the S2 state. We put the bathochromic shift in the broad perspective of other “blue” carotenoids properties.

Organisation(s)
Electronic Properties of Materials
External organisation(s)
Lund University, University of Connecticut
Journal
The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical
Volume
117
Pages
11209-11219
No. of pages
11
ISSN
1520-6106
DOI
https://doi.org/10.1021/jp401873k
Publication date
09-2013
Peer reviewed
Yes
Austrian Fields of Science 2012
1030 Physics, Astronomy, 104002 Analytical chemistry
Keywords
Portal url
https://ucrisportal.univie.ac.at/en/publications/06175f88-dfae-4eb4-908c-2c4000776c8b