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On the origin and variation of colors in lobster carapace
University of Manchester, England.
DESY, Germany.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
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2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 26, 16723-16732 p.Article in journal (Refereed) Published
Abstract [en]

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation.

Place, publisher, year, edition, pages
Royal Society of Chemistry , 2015. Vol. 17, no 26, 16723-16732 p.
National Category
Chemical Sciences
URN: urn:nbn:se:liu:diva-120247DOI: 10.1039/c4cp06124aISI: 000356874000010PubMedID: 25797168OAI: diva2:842613

Funding Agencies|Bildungs- und Kultur-departement des Kantons Luzern, Switzerland; Swedish Research Council; Olle Engkvist Foundation; Nuffield Foundation; School of Chemistry, University of Manchester; European Molecular Biology Laboratory

Available from: 2015-07-21 Created: 2015-07-20 Last updated: 2015-11-19
In thesis
1. Computational Studies of Photobiological Keto-Enol Reactions and Chromophores
Open this publication in new window or tab >>Computational Studies of Photobiological Keto-Enol Reactions and Chromophores
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents computational chemistry studies of keto-enol reactions and chromophores of photobiological signicance.

The rst part of the thesis is concerned with two protein-bound chromophores that, depending on the chemical conditions, can exist in a number of dierent ketonic and enolic forms. The rst chromophore is astaxanthin, which occurs in the protein complex responsible for the deep-blue color of lobster carapace. By investigating how dierent forms of astaxanthin absorb UV-vis radiation of dierent wavelengths, a model is presented that explains the origin of the dramatic color change from deep-blue to red upon cooking of live lobsters.

The second chromophore is the oxyluciferin light emitter of fireflies, which is formed in the catalytic center of the enzyme firefly luciferase. To date, there is no consensus regarding which of the possible ketonic and enolic forms is the key contributor to the light emission. In the thesis, the intrinsic tendency of oxyluciferin to prefer one particular form over other possible forms is established through calculation of keto-enol and acid-base excited-state equilibrium constants in aqueous solution.

The second part of the thesis is concerned with two families of biological photoreceptors: the blue-light-absorbing LOV-domain proteins and the red-light-absorbing phytochromes. Based on the ambient light environment, these proteins regulate physiological and developmental processes by switching between inactive and active conformations. In both families, the conversion of the inactive into the active conformation is triggered by a chemical reaction of the respective chromophore.

The LOV-domain proteins bind a LOV-domain proteins bidn in flavin chromophore and regulate processes such as chloroplast relocation and phototropism in plants. An important step in the activation of these photoreceptors is a singlet-triplet transition between two electronically excited states of the flavin chromophore. In the thesis, this transition is used as a prototype example for illustrating, for the rst time, the ability of rst-principles methods to calculate rate constants of inter-excited state phosphorescence events.

Phytochromes, in turn, bind bilin chromophores and are active in the regulation of processes like seed germination and  flowering time in plants. Following two systematic studies identifying the best way to model the UV-vis absorption and fluorescence spectra of these photoreceptors, it is demonstrated that steric interactions between the chromophore and the apoprotein play a decisive role for how phytochromes are activated by light.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 76 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1713
National Category
Theoretical Chemistry
urn:nbn:se:liu:diva-122614 (URN)10.3384/diss.diva-122614 (DOI)978-⁠91-⁠7685-⁠922-⁠3 (print) (ISBN)
Public defence
2015-12-18, Nobel (BL32), B-huset, Campus Valla, Linköping, 13:15 (English)
Available from: 2015-11-19 Created: 2015-11-11 Last updated: 2015-11-26Bibliographically approved

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