Li Wei-Shi, Jiang Dong-Lin, Suna Yuki, Aida Takuzo
Aida Nanospace Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), 2-41 Aomi, Koto-ku, Tokyo, 135-0064 Japan.
J Am Chem Soc. 2005 Jun 1;127(21):7700-2. doi: 10.1021/ja0513335.
Zinc porphyrin-appended dendrimers, 12PZn, 18PZn, 24PZn, and 36PZn, containing 12, 18, 24, and 36 zinc porphyrin units, respectively, were synthesized using zinc porphyrin dyad (2PZn) and triad (3PZn) as precursors. Although these dye-functionalized dendrimers all serve as chiroptical sensors for an asymmetric bipyridine (RR- and SS-Py2), the sensing capability is highly dependent on the structure of the dendritic scaffold. 2PZn, which is chiroptically silent toward Py2, turns cooperative and displays a large ICD (induced circular dichroism) response in the visible region when incorporated into 12PZn. Judging from the extents of contribution of each zinc porphyrin unit to the CD amplitudes ([Deltaepsilonmax]), the cooperativity in 24PZn (112 M-1 cm-1) is lower than that in 12PZn (196 M-1 cm-1) and much lower in dendron 4PZn (59 M-1 cm-1). In contrast, 3PZn, which is ICD-active toward Py2, hardly shows such an enhanced cooperativity when incorporated into 18PZn and 36PZn and dendron 6PZn, as well. Absorption spectroscopy suggests some unique conformational characteristics of the zinc porphyrin units in highly cooperative 12PZn.
分别含有12、18、24和36个锌卟啉单元的锌卟啉连接的树枝状大分子12PZn、18PZn、24PZn和36PZn，是以前体锌卟啉二元体（2PZn）和三元体（3PZn）为原料合成的。尽管这些染料功能化的树枝状大分子都可作为不对称联吡啶（RR-和SS-Py2）的手性光学传感器，但传感能力高度依赖于树枝状支架的结构。对Py2呈手性光学沉默的2PZn，当并入12PZn中时会变得协同，并在可见光区域显示出较大的诱导圆二色性（ICD）响应。从每个锌卟啉单元对圆二色性振幅（[Δεmax]）的贡献程度判断，24PZn（112 M-1 cm-1）中的协同性低于12PZn（196 M-1 cm-1），在树枝状分子4PZn（59 M-1 cm-1）中则低得多。相比之下，对Py2具有ICD活性的3PZn，当并入18PZn、36PZn以及树枝状分子6PZn中时，几乎没有表现出这种增强的协同性。吸收光谱表明，在高度协同的12PZn中，锌卟啉单元具有一些独特的构象特征。
