Excimer emission, cyclodextrins

As very different systems, Ueno et al. prepared a-helix peptides bearing y-cyclodextrin and one (16,17) or two (18) naphthalene units in their side chains (Fig. 2) [38], They are alanine-based peptides composed of 17 amino acid residues. The peptides 16 and 17, which have y-CD and one naphthalene unit, display a simple monomer emission and the fluorescence intensity slightly decreases with increasing guest concentration. On the other hand, the peptide 18, which has y-CD and two naphthalene units on both sides of the y-CD unit, exhibits considerable excimer emission in addition to the predominant monomer emission and the excimer emission decreases with increasing guest concentration. This indicates that 18 excludes the two naphthalene units from the y-CD cavity to the opposite directions upon guest accommodation. 

Inclusion complexes have also been shown to aid excimer formation provided that the cavity dimensions and polarity are appropriate. Thus Ueno et al. (1980) have shown that the lipophilic cavity of y-cyclodextrin can accommodate two molecules of sodium (l-naphthyl)methyl acetate and that this leads to enhanced excimer emission. Excimer formation by diaryl-methylammonium salts is promoted by y-cyclodextrin but not by a- and P-cyclodextrins (Emert et al., 1981a). The best results were obtained with compounds having fairly large aryl groups e.g. 4-biphenylyl and 1-naphthyl. The hydrophobic character of these groups helped to solubilise the compounds in the interior of the cyclodextrin. 

Polypeptide-grafted cyclodextrin bioconjugates Fluorescence 1 1 and 1 2 Excimer/ monomer emission bands ratio nd" 2012 [104]... 

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