Graduate School of Life Sciences, Ritsumeikan University, Shiga, Japan.
Photochem Photobiol. 2014 Jan;90(1):121-8. doi: 10.1111/php.12173. Epub 2013 Oct 21.
Zinc complex of pyropheophorbide-b, a derivative of chlorophyll-b, was covalently dimerized through ethylene glycol diester. The synthetic homo-dyad was axially ligated with two methanol molecules from the β-face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto-carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, (1) H NMR and IR spectra. All the synthetic zinc chlorin homo- and hetero-dyads consisting of pyropheophorbides-a, b and/or d took the above methanol-locked and π-π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo-dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo-dyads partially took such supramolecules. The J-type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads.
叶绿酸 b 的衍生物原脱镁叶绿酸 b 的锌络合物通过乙二醇二酯发生共价二聚。合成的同二聚体从β-面轴向连接两个甲醇分子，两个非对映异构体配位的甲醇物种都与相邻叶绿素的酮羰基形成氢键，在复合物中形成一个折叠构象。通过可见光谱、（1）H NMR 和 IR 光谱证实了溶液中形成的折叠构象。所有由原脱镁叶绿酸 a、b 和/或 d 组成的锌叶绿酸同二聚体和异二聚体在 1%（v/v）甲醇和苯中均采取上述甲醇锁定和π-π堆积超分子结构，给出比相应单体叶绿素复合物更长波长的最红（Qy）电子吸收带。其他锌叶绿素和细菌叶绿素同二聚体在相同溶液中完全形成类似的折叠构象，而锌反叶绿素和卟啉同二聚体部分形成这种超分子。J 型聚集到折叠构象和复合 Qy 带的红移值取决于二聚体中卟啉类部分的电子和空间因素。
