Studies On Interactions Of Chlorophyll A With ZnO Nanoparticles

With the unique optical, electrical, magnetic and thermal properties which the bulk materials do not have, ZnO nanoparticles have been widely applied in many fields such as medicine, dope, food, cosmetics and so on. Due to the extensive application of ZnO nanoparticles, it has more opportunities to be diffused into the human survival environment. If adsorbed by leafs of green plants, nano-particles may exert toxicity on plants. Chlorophyll is an important pigment in plant photosynthesis, therefore it is especially important to study the influence of nanoparticles on chlorophyll pigments.In this paper, we have prepared a stable ZnO nanoparticle suspension by the sol-gel method and extracted pure chlorophyll a with the chromatographic analysis method from the fresh spinach leaf. We mix the two different solutions directly to obtain a compound system of ZnO nanoparticles and chlorophyll a molucules.The influences of ZnO nanoparticles on chlorophyll a in ethanol and benzene are studied by observing the changes in their UV-Vis absorption spectra, fluorescence spectra, and fourier transform infrared spectra (FTIR). For the chlorophyll a in ethanol (polarity solution), the absorption spectra have no change upon addition of ZnO nanoparticles, but the fluorescence spectra are quenched by ZnO in a orderly way. Two isoemissive points are observed in the fluorescence spectra when excited at 290 nm. We conclude that the main quenching mechanism is dynamic including the resonance energy transfering and the charge transfering between chlorophyll a and ZnO. For the chlorophyll a in benzene (non-polarity solution), its characteristic peaks in the absorption spectra and fluorescence spectra shift to longer wavelength and its fluorescence are quenched by ZnO too. An isoemissive point is observed at 654 nm when excited at 355 nm. Based on the Stern-Volmer relation I0 /I = 1+ K[Q], the quenching mechanism is attributed to static quenching. Besides, changes of Zn-O bond vibration peak in FTIR are also observed after the Chla molecules are absorbed onto ZnO nanoparticles. The above studies illustrate a strong interaction between Chla and ZnO nanoparticles through electrostatic or hydrogen bond and indicate that ZnO nanoparticles may exert negative effect on the photosynthesis process, where Chla plays an important role.