Vibrational dynamics of plant light-harvesting complex LHC II investigated by quasi- and inelastic neutron scattering

Vibrational dynamics of the light-harvesting complex II (LHC II) from spinach was investigated by quasi- and inelastic neutron scattering (QENS and INS) at three different temperatures of 80, 160, and 285K. QENS/INS spectra of solubilised LHC II and of the corresponding buffer solution were obtained separately and exhibit characteristic inelastic features. After subtraction of the buffer contribution, the INS spectrum of LHC II reveals a distinct Boson peak at ∼ 2.5meV at 80K that shifts towards lower energies if the temperature is increased to 285K. This effect is interpreted in terms of a "softening" of the protein matrix along with the dynamical transition at ∼ 240K. Our findings indicate that INS is a valuable method to obtain the density of vibrational states not only at cryogenic, but also at physiological temperatures.