Histidine coordinated to Chl a is a distinct characteristic of Chl a in vivo. By usinghistidine analogue of 1-methylimidazole (C4H6N2) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between...Histidine coordinated to Chl a is a distinct characteristic of Chl a in vivo. By usinghistidine analogue of 1-methylimidazole (C4H6N2) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between C4H6N2and Chl a in CCI4, we have obtained that: (i) In pure CCI4 solvent, Chl a molecule is in five-coordinate state, and two Chl a molecules form an asymmetric compact-dimer with strong coupling interaction. We propose that the two Chl a molecules are connected by two unequally coordinated Mg-O bonds (the two oxygen atoms come from the C=O of C131 keto and C17 ester, respectively); (ii) when the molar ratio of C4H6N2/Chl a is 0.5 or 1 (corresponding to 2Chl a #1C4H6N2 and 2Chl a ·2C4H6N2, respectively), significant changes have been observed in the absorption, CD and MCD spectra, which indicate that the Chl a remains in dimer form, but the coupling interaction between them reduces greatly. We postulate that C4H6N2 replaces the ligation of C=O of C17 ester and C131 keto to Mg atoms展开更多
文摘Histidine coordinated to Chl a is a distinct characteristic of Chl a in vivo. By usinghistidine analogue of 1-methylimidazole (C4H6N2) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between C4H6N2and Chl a in CCI4, we have obtained that: (i) In pure CCI4 solvent, Chl a molecule is in five-coordinate state, and two Chl a molecules form an asymmetric compact-dimer with strong coupling interaction. We propose that the two Chl a molecules are connected by two unequally coordinated Mg-O bonds (the two oxygen atoms come from the C=O of C131 keto and C17 ester, respectively); (ii) when the molar ratio of C4H6N2/Chl a is 0.5 or 1 (corresponding to 2Chl a #1C4H6N2 and 2Chl a ·2C4H6N2, respectively), significant changes have been observed in the absorption, CD and MCD spectra, which indicate that the Chl a remains in dimer form, but the coupling interaction between them reduces greatly. We postulate that C4H6N2 replaces the ligation of C=O of C17 ester and C131 keto to Mg atoms
