Determination of double decker sandwich structured La-substituted chlorophyll a by EXAFS

Double decker sandwich lanthanoid porphyrins have been synthesized and char acterized systematically. Chlorophyll. is a representative of natural porph yrin derivatives, It is therefore interesting to study the chemical form of lanthanide in chlorophyll. We synthesized Lanthanum(III) Chlorophyll a der ivatives, whose UV - vis and IR spectra confirm the coordination of La(III) to the porphyrin rings. MCD spectra show the special bands in Soret band r egion, which indicate a transition from sandwich structure porphyrin comple xes. By extended X - ray absorption fine structure (EXAFS) method, it is fo und that the molecular structure of synthesized La - Chl a can be well fitt ed by the double decker sandwich structure model that La is surrounded by e ight nitrogen atoms from two porphyrin rings. The MCD and EXAFS results ind icate that the La in chlorophyll a exist as a sandwich shaped complexes wit h an average La - N bond length of 0.261 nm. To our best knowledge, this is the first example of La - Chl a with a double decker sandwich molecular st ructure.