2005 Fiscal Year Final Research Report Summary
Synthesis of porphyrinoids with C_2 molecular symmetry and chiral recognition function
| Project/Area Number |
16350023
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Organic chemistry
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| Research Institution | Kobe University |
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Principal Investigator |
SETSUNE Jun-ichiro Kobe University, Faculty of Science, Department of Chemistry, Professor, 理学部, 教授 (10117997)
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| Co-Investigator(Kenkyū-buntansha) |
LINTULUOTO Juha Mikael Kobe University, Graduate School of Science and Technology, Department of Molecular Science and Material Engineering, Research Associate, 大学院・自然科学研究科, 助手 (20379481)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Molecular recognition / Porphyrinoid / Chirality induction / circular dichroism |
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| Research Abstract |
Molecular recognition of amino acids and sugars based on its chirality is of great interest in supramolecular chemistry. Expanded porphyrin with C_2 molecular symmetry is regarded as an potential host molecule for these purposes. Here, expanded porphyrins composed of 2,2'-bipyrrole unit(s) with C_2 molecular symmetry have been newly synthesized : octaphyrins composed of four 2,2'-bipyrrole units, expanded octaphyrins composed of four 1,4-bis (2-pyrrolyl) benzene units, and hexaphyrin composed of one 2,2'-bipyrrole and two gem-dimethyldipyrrylmethanes.
We have found that [32]octaphyrin(1.0.1.0.1.0.1.0) made of four parts of 2,2'-bipyrrole is rapidly oscillating between the figure eight enantiomeric forms especially when the ethyl group is existing at the bipyrrole 3,3'-position. The inversion of the chiral figure eight structure does not occur through unwinding of the molecular twist followed by rewinding in the opposite way but through an alternating stretching-compressing distortion of
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the rhombic cavity made of four panels of the planar dipyrrylmethene unit connected with four hinges of the bipyrrole 2,2'-bond. This rapid chirality change of the octaphyrin loop structure is the basis for the application to the chirality induction by complexation with optically active guest molecules. The CD spectrum is silent for octaphyrin free base absorbing at 570nm, whereas the first Cotton effect of the bisignate CD signal band at 639nm with shifting the absorption band to 649nm arises upon complexation of (R)-(-)-hexahydromandelic acid. The titration of the octaphyrin with (R)-(-)-mandelic acid shows that this band represents both 1:1 and 1:2 complexes which have the same chirality. Examination of eleven optically active carboxylic acids have shown that the sign of this induced Cotton effect is determined solely by the absolute configuration of the carboxylic acids. The present research has indicated the utility of octaphyrin as a tool for direct determination of absolute configuration of optically active compounds. Less
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