Effects Of Environment On Absorption And Fluorescence Spectra Of Carotenoid Aggregates

This paper takes carotenoids and chlorophyll as research objects,and uses Raman spectroscopy,UV-VIS absorption spectroscopy,and fluorescence spectroscopy to study the effects of environment on the absorption and fluorescence spectra of carotenoid aggregates.The variable temperature Raman spectroscopy study of?-carotene aggregates in ethanol aqueous solution showed that the?-carotene aggregates remained weakly coupled aggregates at 77 K,while showing a temperature dependence of similar H-type aggregates in ethanol aqueous solution;The changes of the absorption and emission spectra of carotenoids aggregates in ethanol aqueous solutions with different pH values were discussed,the physical laws of the effect of solution pH on the formation of carotenoids and chlorophyll aggregates as well as energy and electron transfer were obtained.The Raman spectra of carotenoid aggregates in ethanol aqueous solution at room temperature and their variation with temperature were studied.The raman vibration mode is stable when the temperature decreases from 295 K to 77 K.Due to changes in frequency shift and resonance conditions,the CC stretching vibration mode of?-carotene aggregates shows a relatively small frequency shift compared to organic solvents.Through the peak splitting treatment of the experimental results,it is shown that the Raman peak at 1522cm^-1 can be deconvolved into two overlapping vibration modes.The frequency shift trend of the two modes is similar,but their resonance enhancement is different.The 0-0 and 0–1 bands of the?-carotene aggregates behave differently before and after the solution phase transition by background extraction when lowering the temperature.The solution phase transition also leads to a dramatic fluorescence quenching of the?-carotene aggregates.With continuous cooling,it can be found that in the solid state,the fluorescence enhancement of the 0-1 band can be found,while the 0-0 band shows a decreasing trend.The results showed that?-carotene aggregates remained weakly coupled aggregates at 77K,while exhibiting temperature dependence similar to H-type aggregates in ethanol aqueous solution.The spectra of all-trans?-carotene,lutein and chlorophyll a in ethanol aqueous solutions with different pH values were studied respectively.The geometric structure of chlorophyll a changed with the increase of hydrogen bond under acidic conditions,and the porphyrin ring of chlorophyll a was deformed,resulting in the absorption spectrum red-shift and fluorescence quenching.With the increase of acidity,it was confirmed that chlorophyll a formed H-type and J-type aggregates in acidic ethanol aqueous solution through the splitting and shifting of the spectrum.Under alkaline conditions,the Q band of the chlorophyll a absorption spectrum has a smaller blue shift,while the fluorescence spectrum has a weaker blue shift and quenching.Analysis of?-carotene absorption spectrum shows that acidic conditions are favorable for the formation of J-type and H-type aggregates.The blue shift of the absorption spectrum of lutein indicates that lutein forms H-type aggregates under acidic conditions.The effects of temperature and pH on the absorption and fluorescence spectrum of carotenoid aggregates were discussed,and the temperature-dependent properties of carotenoid aggregates were obtained.The experimental results have a reference value for elucidating the mechanism of disorder-induced aggregation fluorescence,and provide a new idea for the research of pH on chlorophyll a and energy transfer during photosynthesis in plants.