This work was supported by a grant from National Natural Science Foundation of China(29805003).
在丙酮溶液中合成得到镧-叶绿素a、钐-叶绿素a和铜-叶绿素a复合物,并研究了它们的紫外可见光谱(UV-Vis)、Fourier红外光谱(FT-IR)和EXAFS结构.镧-叶绿素a、钐-叶绿素a和铜-叶绿素a的UV-Vis谱、FT-IR谱与叶绿素a(含镁)的光谱性质相似,但与脱镁叶绿素a的光谱性质差异很大.证明了La3+、Sm3+、Cu2+已配位到脱镁叶绿素的卟啉环上,形成了镧-叶绿素a、钐-叶绿素a和铜-叶绿素a复合物.通过扩展X射线吸收精细结构谱(EXAFS)研究表明:合成镧-叶绿素a、钐-叶绿素a具有双层夹心结构.La(Ⅲ)、Sm(Ⅲ)夹于两个卟啉环之间, 与上下卟啉环上共八个N原子配位, La-N平均键长0.261 nm,Sm-N平均键长0.243 nm, 而铜-叶绿素a的EXAFS表明为一单层结构,Cu(Ⅱ)与卟啉环中的四个N原子配位,Cu-N平均键长0.197 nm.元素分析也证明镧-叶绿素a、钐-叶绿素a为双层结构,铜-叶绿素a为单层结构.
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.
洪法水,魏正贵,赵贵文,陶冶,胡天斗,刘涛,谢亚宁.金属叶绿素a配位结构的研究[J].生物化学与生物物理进展,2001,28(3):381-386
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