Determination of Coordination Structure on Metal-Substituted Chlorophyll a by Spectroscopy

2001 
La chlorophyll a, Sm chlorophyll a and Cu chlorophyll a were synthesized from pheophytin a, lanthanum, samarium and cuprum in the acetone solution. Their characteristics have been investigated by ultravioler visible (UV Vis), FT IR and extended X ray absorption fine structure spectra (EXAFS). The Soret band of UV Vis spectra of La chlorophyll a, Sm chlorophyll a and Cu chlorophyll a was more ultraviolet shift than that of pheophytin a, the Q band was more red shift than that of pheophytin a. FT IR spectra of La chlorophyll a, Sm chlorophyll a and Cu chlorophyll a was similar with chlorophyll, but different from pheophytin. UV Vis and IR spectra confirmed the coordination of La(Ⅲ), Sm(Ⅲ) and Cu(Ⅱ) to the porphyrin rings. By extended X ray absorption fine structure spectra method, it was found that the molecular structure of synthesized La Chlorophyll a, Sm chlorophyll a could be well fitted by the double decker sandwich structure model that La, Sm was surrounded by eight nitrogen atoms from two porphyrin rings. It is believed that chemical form of La chlorophyll a, Sm chlorophyll a was a sandwich structured complexes with the La N and Sm N bond length of average 0 261 nm and 0 243nm, respectively. Extended X ray absorption fine structure spectra showed that Cu chlorophyll a could be well fitted by the mono decker structure model that Cu was surrounded by four nitrogen atoms from porphyrin rings, Cu N bond length of average was 0 197 nm. Elemental analysis indicated that La chlorophyll a and Sm chlorophyll a have the double decker sandwich structure, Cu chlorophyll a has the mono decker structure.
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