Exploring the light emission in fireflies

The School of Chemistry presents Dr Isabelle Navizet who will present a seminar entitled Exploring the light emission in firefly with theoretical tools as part of the school's Chemistry Seminar Programme.

Abstract:

The emitting light in fireflies arises from the electronic relaxation of oxyluciferin, an organic compound resulting from the oxidation of the D-luciferin substrate inside an enzyme called luciferase. The bioluminescence process results from three moities of the luciferin-luciferase system: the chemiluminophore, which opens the path to the excited state surface, the electon-donating fragment, which lowers the activation energy of the reaction of a charge transfer mechanism and a charge transfer controlling group which modulate the color emission, depending on the interactions between this moiety and the protein.^a 

In such systems, the use of quantum mechanical/molecular mechanical (QM/MM) methods is required. Accurate QM level is needed for dealing with charge transfer phenomena and taking into account the surrounding protein at the MM level is essential in order to understand the color modulation. The present lecture will discuss some of the results obtained on this system with calculations done with the coupling of the programs MOLCAS (CASPT2/CASSCF) and TINKER (AMBER force field).    

Our systematic theoretical investigation of all the possible light emitter structures of firefly shows that the phenolate-keto form of oxyluciferin is responsible for the light emission.^b Our theoretical results^c on the oxyluciferin-luciferase complex shows in agreement with recent experimental observations that the wavelength of the emitted light depends on the polarity of the microenvironment at the phenol/phenolate terminal of the benzothiazole fragment of oxyluciferin. Some last results^d show that even in the protein the molecule is almost planar like in the fluorescent molecule, this behaviour being different from the one^e in the bioluminescent coelenterate system.

[a] I. Navizet, Y. J. Liu, N. Ferré, D. Roca-Sanjuan, R. Lindh, ChemPhysChem, 2011, 12, 3064-3076.

[b] S. F. Chen, Y. J. Liu, I. Navizet, N. Ferré, W. H. Fang, R. Lindh, J. Chem. Theory Comput., 2011, 7, 798-803.

[c] I. Navizet, Y.-J. Liu, N. Ferré, H.-Y. Xiao, W.-H. Fang, R. Lindh, J. Am. Chem. Soc., 2010, 132, 706–712.

[d] I. Navizet, L. Yue, Y-J Liu, D Roca-Sanjuan,  N. Ferré and R. Lindh, JCPL, in preparation.

[e] D. Roca-Sanjuan , M. Delcey, I. Navizet, N. Ferré, Y. J. Liu, R Lindh, J. Chem. Theor. Comp., 2011, 7, 4060-4069.