title: Spectroscopy and quantum chemical modeling reveal a predominant contribution of excitonic interactions to the bathochromic shift in alpha-crustacyanin, the blue carotenoprotein in the carapace of the lobster Homarus gammarus.
abstract: To resolve the molecular basis of the coloration mechanism of alpha-crustacyanin, we used (13)C-labeled astaxanthins as chromophores for solid-state (13)C NMR and resonance Raman spectroscopy of [6,6',7,7']-(13)C(4) alpha-crustacyanin and [8,8',9,9',10,10',11,11',20,20']-(13)C(10) alpha-crustacyanin. We complement the experimental data with time-dependent density functional theory calculations on several models based on the structural information available for beta-crustacyanin. The data rule out major changes and strong polarization effects in the ground-state electron density of astaxanthin upon binding to the protein. Conformational changes in the chromophore and hydrogen-bond interactions between the astaxanthin and the protein can account only for about one-third of the total bathochromic shift in alpha-crustacyanin. The exciton coupling due to the proximity of two astaxanthin chromophores is found to be large, suggesting that aggregation effects in the protein represent the primary source of the color change.
authors.affiliation: Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, NL-2300 RA Leiden, The Netherlands.
authors.forename: Arjan A C
authors.initials: AA
authors.lastname: van Wijk
authors.forename: Arnold
authors.initials: A
authors.lastname: Spaans
authors.forename: Natallia
authors.initials: N
authors.lastname: Uzunbajakava
authors.forename: Cees
authors.initials: C
authors.lastname: Otto
authors.forename: Huub J M
authors.initials: HJ
authors.lastname: de Groot
authors.forename: Johan
authors.initials: J
authors.lastname: Lugtenburg
authors.forename: Francesco
authors.initials: F
authors.lastname: Buda
mesh_terms: D000818:Animals; D002247:Carbon Isotopes; D002352:Carrier Proteins; D008958:Models, Molecular; D008121:Nephropidae / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010860:Pigments, Biological / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D024341:Xanthophylls; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D002352:Carrier Proteins; D010860:Pigments, Biological; D011506:Proteins; D024341:Xanthophylls; C018494:crustacyanins; D019207:beta Carotene; C005948:astaxanthine