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Guest‐dependent conformation of 18‐crown‐6 tetracarboxylic acid: Relation to chiral separation of racemic amino acids
Author(s) -
Nagata Hiroomi,
Nishi Hiroyuki,
Kamigauchi Miyoko,
Ishida Toshimasa
Publication year - 2008
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.20550
Subject(s) - chemistry , chirality (physics) , amino acid , crown ether , cationic polymerization , stereochemistry , glycine , ring (chemistry) , crystallography , enantiomer , organic chemistry , ion , chiral symmetry , biochemistry , physics , quantum mechanics , nambu–jona lasinio model , quark
(+)‐18‐Crown‐6 tetracarboxylic acid (18C6H 4 ) has been used as a chiral selector for various amines and amino acids. To further clarify the structural scaffold of 18C6H 4 for chiral separation, single crystal X‐ray analysis of its glycine + (1), H 3 O + (2), H 5 O 2 +(3), NH 4 +(4), and 2CH 3 NH 3 +(5) complexes was performed and the guest‐dependent conformation of 18C6H 4 was investigated. The crown ether ring of 18C6H 4 in 3 , 4 , and 5 took a symmetrical C 2 or C 2 ‐like conformation, whereas that in 1 and 2 took an asymmetric C 1 conformation, which is commonly observed in complexes with various optically active amino acids. The overall survey of the present and related complexes suggests that the molecular conformation of 18C6H 4 is freely changeable within an allowable range, depending on the molecular shape and interaction mode with the cationic guest. On the basis of the present results, we propose the allowable conformational variation of 18C6H 4 and a possible transition pathway from its primary conformation to the conformation suitable for chiral separation of racemic amines and amino acids. Chirality, 2008. © 2008 Wiley‐Liss, Inc.