Jump to main content
Jump to site search

Issue 12, 2013
Previous Article Next Article

Stereodifferentiation in the intramolecular singlet excited state quenching of hydroxybiphenyltryptophan dyads

Author affiliations

Abstract

The photochemical processes occurring in diastereomeric dyads (S,S)-1 and (S,R)-1, prepared by conjugation of (S)-2-(2-hydroxy-1,1′-biphenyl-4-yl)propanoic acid ((S)-BPOH) with (S)- and (R)-Trp, have been investigated. In acetonitrile, the fluorescence spectra of (S,S)-1 and (S,R)-1 were coincident in shape and position with that of (S)-BPOH, although they revealed a markedly stereoselective quenching. Since singlet energy transfer from BPOH to Trp is forbidden (5 kcal mol−1 uphill), the quenching was attributed to thermodynamically favoured (according to Rehm–Weller) electron transfer or exciplex formation. Upon addition of 20% water, the fluorescence quantum yield of (S)-BPOH decreased, while only minor changes were observed for the dyads. This can be explained by an enhancement of the excited state acidity of (S)-BPOH, associated with bridging of the carboxy and hydroxy groups by water, in agreement with the presence of water molecules in the X-ray structure of (S)-BPOH. When the carboxy group was not available for coordination with water, as in the methyl ester (S)-BPOHMe or in the dyads, this effect was prevented; accordingly, the fluorescence quantum yields did not depend on the presence or absence of water. The fluorescence lifetimes in dry acetonitrile were 1.67, 0.95 and 0.46 ns for (S)-BPOH, (S,S)-1 and (S,R)-1, respectively, indicating that the observed quenching is indeed dynamic. In line with the steady-state and time-resolved observations, molecular modelling pointed to a more favourable geometric arrangement of the two interacting chromophores in (S,R)-1. Interestingly, this dyad exhibited a folded conformation in the solid state.

Graphical abstract: Stereodifferentiation in the intramolecular singlet excited state quenching of hydroxybiphenyl–tryptophan dyads

Back to tab navigation

Supplementary files

Publication details

The article was received on 23 Nov 2012, accepted on 11 Jan 2013 and first published on 11 Jan 2013


Article type: Paper
DOI: 10.1039/C3OB27278H
Citation: Org. Biomol. Chem., 2013,11, 1958-1963
  •   Request permissions

    Stereodifferentiation in the intramolecular singlet excited state quenching of hydroxybiphenyltryptophan dyads

    P. Bonancía, I. Vayá, D. Markovitsi, T. Gustavsson, M. C. Jiménez and M. A. Miranda, Org. Biomol. Chem., 2013, 11, 1958
    DOI: 10.1039/C3OB27278H

Search articles by author

Spotlight

Advertisements