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.

Two-Dimensional Electronic Spectroscopy Using Incoherent Light: Theoretical Analysis

“…Because the events are * ulnessd@cord.edu fast-usually nanosecond timescales or faster-it is natural for measurements to use femtosecond laser pulses. Most typical are pump-probe spectroscopy measurements [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], but technical advances [27][28][29][30][31][32][33][34][35][36] have made twodimensional electronic spectroscopy (2D ES) measurements of photosynthetic proteins [37][38][39][40][41][42][43][44][45][46] frequent as well.…”

Behavior of Poisson Bracket Mapping Equation in Studying Excitation Energy Transfer Dynamics of Cryptophyte Phycocyanin 645 Complex

“…6 Its structure was determined at 1.4 Å resolution by X-ray crystallography. 7 In the experiment, 3 the central DBV dimer was initially electronically excited with a laser pulse and the excitation energy was transferred to the MBV molecules. At the last stage, the four PCB molecules absorb the energy from the MBVs.…”

“…(6) with Eq. (4), followed by appropriate Wigner transformations, one can obtain (7) When the last summation is ignored, ,…”

Coherence dynamics in light-harvesting complexes with two-colour spectroscopy

“…Two of the chromophoric dihydrobiliverdin (DBV) molecules at the centre of the complex form a strongly coupled excitonic dimer, at the centre of the complex. These states are known as DBV+ the higher energy state and DBV-the lower energy state [4]. Another two chromophore molecules at the periphery are called mesobiliverdin (MBV) and also absorb along the blue edge of the absorption spectrum.…”

“…The structure of the complex is known to a high-resolution and shows 8 separate chromophore molecules held in a protein scaffold [4]. Two of the chromophoric dihydrobiliverdin (DBV) molecules at the centre of the complex form a strongly coupled excitonic dimer, at the centre of the complex.…”