Study on Absorption Spectra of Lutein Aggregate with Experimental Analysis and Theoretical Calculation.

Compared with the monomer, aggregate exhibits unique features such as electron and energy transfer which can be understood with the study of absorption spectra. In the experimental the absorption spectra of lutein monomer in ethanol solution and aggregate in 1∶1 aqueous ethanol solution are detected by utilizing UV-lVis spectrophotometer. The vibration structure of excited state of lutein monomer is obtained with Gauss decomposition of the absorption spectra. Theoretically, the molecular parameters of excitation energy, vibration frequency of characteristic mode, Huang-Phys factor are calculated by means of simulation of the monomer absorption spectra described by temporal correlation function and Frenkel exciton model. The spectral calculation of the lutein aggregate is conducted by using these parameters and then the factors of the spectral changes affected by the aggregate structure are analyzed. Some conclusions are drawn from the analysis: (1) The absorption peak position of the aggregate is determined mainly by intermolecular interaction. The calculation shows that the interaction is about 2 000 cm-1 according 77 nm blue shift of absorption spectra from experiment result. (2) With the increase of molecular number of the aggregate the half-width of the absorption spectra decreases and the peak position blue shift slightly due to enhanced cooperation effect. (3) Disorder degree from environment has great influence on half-width for the greater disorder degree the larger half-width. The results of this paper will provide a theoretical reference for the further study of lutein aggregate function in biological and materials systems.

[The influence of temperature on the orientation of pigments in PS II].

The effect of temperature on the orientation of pigment in PSII was studied by the fluorescence excitation spectra and polarization fluorescence spectra of spinach thylakoid solution. The experimental results showed that in the temperature range of 15-45 degrees C the absorption band of chl a at 436 nm at room temperature red-shifted with increasing temperature. The excitation spectra intensity reached the maximum at the temperature of 35 degrees C, but greatly reduced with temperature at 65 and 78 degrees C. In the polarization fluorescence spectra the fluorescence peak of PSII didn't change with temperature from 15 to 45 degrees C. It was also found that the calculated fluorescence polarization degree increased with the temperature in the entire temperature range. The analysis indicated that temperature would affect the orientation of the pigments in PSII and the coupling strength between pigments so to change photosynthetic efficiency. The results will give a certain reference for the study of the energy absorption and transmission, regulation mechanism and also on solar cell materials.