Evidence for long-range excitation energy migration in macroaggregates of the chlorophyll a/b light-harvesting antenna complexes

We investigated the picosecond transient absorbance kinetics under singlet-singlet annihilation conditions and the steady-state spectroscopic features, absorbance, circular dichroism and low-temperature fluorescence spectra, in large, three-dimensional, stacked lamellar aggregates of the purified light-harvesting chlorophyll a/b complexes (LHCII) and its form of small aggregates. Our data strongly suggest that the macroorganizational parameters significantly influence the spectroscopic properties and strongly affect the energy migration pathways in the aggregates. In small aggregates (d approximate to 100 nm) of LHCII trimers the excitation energy migration could be characterized with a percolation type of excitation migration in a small cluster of chromophores. In contrast, in chirally organized macroaggregates (d approximate to 2-4 mu m), the annihilation kinetics were consistent with a model predicted for (infinitely) large three-dimensional aggregates, showing that LHCII macroaggregates can constitute a structural basis for long-range migration of the excitation energy.