title: Ultrafast light harvesting dynamics in the cryptophyte phycocyanin 645.
abstract: Steady-state and femtosecond time-resolved optical methods have been used to study spectroscopic features and energy transfer dynamics in the soluble antenna protein phycocyanin 645 (PC645), isolated from a unicellular cryptophyte Chroomonas CCMP270. Absorption, emission and polarization measurements as well as one-colour pump-probe traces are reported in combination with complementary quantum chemical calculations of electronic transitions of the bilins. Estimation of bilin spectral positions and energy transfer rates aids in the development of a model for light harvesting by PC645. At higher photon energies light is absorbed by the centrally located dimer (DBV, beta50/beta61) and the excitation is subsequently funneled through a complex interference of pathways to four peripheral pigments (MBV alpha19, PCB beta158). Those chromophores transfer the excitation energy to the red-most bilins (PCB beta82). We suggest that the final resonance energy transfer step occurs between the PCB 82 bilins on a timescale estimated to be approximately 15 ps. Such a rapid final energy transfer step cannot be rationalized by calculations that combine experimental parameters and quantum chemical calculations, which predict the energy transfer time to be 40 ps.
authors.affiliation: Department of Chemistry, 80 St. George Street, Institute for Optical Sciences, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Tihana
authors.initials: T
authors.lastname: Mirkovic
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Doust
authors.forename: Jeongho
authors.initials: J
authors.lastname: Kim
authors.forename: Krystyna E
authors.initials: KE
authors.lastname: Wilk
authors.forename: Carles
authors.initials: C
authors.lastname: Curutchet
authors.forename: Benedetta
authors.initials: B
authors.lastname: Mennucci
authors.forename: Roberto
authors.initials: R
authors.lastname: Cammi
authors.forename: Paul M G
authors.initials: PM
authors.lastname: Curmi
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Scholes
mesh_terms: D003198:Computer Simulation; D008027:Light; D008958:Models, Molecular; D008968:Molecular Conformation; D010798:Phycocyanin / Q000737:chemistry*; D013053:Spectrophotometry; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: C039637:phycocyanin 645; D010798:Phycocyanin