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Circular dichroism of host–guest complexes of achiral pyridino‐ and phenazino‐18‐crown‐6 ligands with the enantiomers of chiral aralkyl ammonium salts
Author(s) -
Somogyi László,
Samu Erika,
Huszthy Péter,
Lázár Armand,
Aángyán J.G.,
Surján Péter R.,
Hollósi Miklós
Publication year - 2001
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/1520-636x(2001)13:2<109::aid-chir1006>3.0.co;2-r
Subject(s) - chemistry , circular dichroism , cotton effect , enantiomer , chromophore , crystallography , chirality (physics) , stereochemistry , exciton , photochemistry , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark
Circular dichroism (CD) spectroscopy was used for distinguishing different types of chiral interactions in host–guest complexes of achiral pyridino‐ and phenazino‐18‐crown‐6 ligands with chiral aralkyl ammonium salts. The general feature of the CD spectra of many homochiral (e.g., (R,R )‐host and (R )‐guest) and heterochiral (e.g., (R,R)‐ host and (S )‐guest) α‐(1‐naphthyl)ethylamine hydrogenperchlorate salt (NEA) complexes with chiral pyridino‐ and phenazino‐18‐crown‐6 hosts is exciton interaction. The most interesting example is the coupling of the transitions of the chiral guest NEA with the energetically close transitions of the achiral phenazino‐18‐crown‐6 host 6 . The CD spectrum of the complex is predominated by exciton coupling between the 1 B b transition of the chiral guest and the 1 B b transition of the achiral host. The redshifted intense spectra of the complexes of ( R )‐ or ( S )‐1‐phenylethylamine hydrogenperchlorate salt (PEA) with the achiral diester‐pyridino‐18‐crown‐6 host 4 are indicative of merging the π electron systems into one joint charge transfer chromophore. The appearance of weak bands with alternating sign in the spectrum of PEA complexes of the achiral “parent” pyridino‐18‐crown‐6 host ( 1 ) indicates the presence of two or more conformers. The CD spectra of the complexes of achiral phenazino‐18‐crown‐6 host 6 with PEA are also determined by π–π interaction. In addition to charge transfer bands, CD bands are also induced in the long‐wavelength spectral region of the achiral host. The weak π–π interaction between the achiral phenazino‐18‐crown‐6 host and methyl phenylglycinate hydrogenperchlorate (PGMA) or methyl phenylalaninate hydrogenperchlorate (PAMA) does not result in a definite spectral effect in the 1 L a region of the spectrum of the chiral guest, but its existence is proven by the weak CD bands induced in the long‐wavelength spectral region of the achiral host. Chirality 13:109–117, 2001. © 2001 Wiley‐Liss, Inc.