Issue 20, 2005

Excited state tautomerization of azaindole

Abstract

Fluorescent tryptophan analogs, like azatryptophan, offer an advantage for exploring protein and peptide structure and dynamics. The chromophoric moieties, azaindole, of the azatryptophan analogs are investigated for their potential as fluorescent probes. The photophysical properties of 4-azaindole (4AI) and 5-azaindole (5AI) and their tautomers are characterized through computational and experimental methods. Both 4AI and 5AI undergo excited state tautomerization in the presence of 1 M NaOH. The protonated forms of 4AI and 5AI have a fluorescence emission of 415 and 410 nm, respectively, while the tautomers of 4AI and 5AI have a fluorescent emission of 480 and 450 nm, respectively. Gas phase computations (B3LYP/6–31+G**) show that the N1H azaindole tautomer is lower in energy in the ground state by as much as 12.5 kcal mol−1, while the NnH azaindole tautomer is lower in energy in the excited state by as much as 18.1 kcal mol−1. Solvent effects on the tautomer energy differences were computed using the isodensity polarized continuum model (IPCM). The polarity of the solvent helps to reduce the energy difference between the tautomers in the ground state by as much as 5.8 kcal mol−1, but not enough to reverse the ground state tautomer preference.

Graphical abstract: Excited state tautomerization of azaindole

Article information

Article type
Paper
Submitted
12 May 2005
Accepted
10 Aug 2005
First published
14 Sep 2005

Org. Biomol. Chem., 2005,3, 3701-3706

Excited state tautomerization of azaindole

M. T. Cash, P. R. Schreiner and R. S. Phillips, Org. Biomol. Chem., 2005, 3, 3701 DOI: 10.1039/B506652B

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements