Circular dichroism of host-guest complexes of achiral pyridino- and phenazino-18-crown-6 ligands with the enantiomers of chiral aralkyl ammonium salts

László Somogyi, Erika Samu, Péter Huszthy, Armand Lázár, J. G. Ángyán, Péter R. Surján, Miklós Hollósi

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12 Citations (Scopus)

Abstract

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 1Bb transition of the chiral guest and the 1Bb 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 1La 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.

Original languageEnglish
Pages (from-to)109-117
Number of pages9
JournalChirality
Volume13
Issue number2
DOIs
Publication statusPublished - Feb 15 2001

Keywords

  • Charge transfer band
  • Exciton coupling
  • Supramolecular interactions
  • π-π interaction

ASJC Scopus subject areas

  • Analytical Chemistry
  • Catalysis
  • Pharmacology
  • Drug Discovery
  • Spectroscopy
  • Organic Chemistry

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