title: Sensitization of lanthanides by nonnatural amino acids.
abstract: The sensitization of Eu(III) and Tb(III) by ethylenediaminetetraaceticacid (EDTA)-derivatized tryptophan (Trp), 7-azatryptophan (7AW) and 5-hydroxytryptophan (5HW) has been examined. These Trp analogs were utilized in the present study because they can be incorporated into proteins in place of native Trp residues and because they absorb strongly beyond 305 nm (where Trp absorbance goes to zero), allowing selective excitation of such species in the presence of other Trp-containing proteins. All three indole derivatives were able to sensitize Tb(III) luminescence, with the relative sensitization being in the order Trp > 5HW > 7AW. On the other hand, only the 7AW-EDTA complex was able to sensitize Eu(III) luminescence, likely owing to a better spectral overlap between 7AW emission and Eu(III) absorbance. The sensitized emission of Tb(III) and Eu(II) displayed the expected long emission lifetimes at 545 nm [for Tb(III)] and 617 nm [for Eu(III)], indicating that long-lifetime lanthanide emission could be produced using nonnatural amino-acid donors. Thus, 7AW- and 5HW-sensitized lanthanide emissions should prove to be useful in biophysical studies, such as the use of fluorescence energy transfer to probe biomolecular interactions in vivo.
authors.affiliation: Department of Chemistry, McMaster University, Hamilton, Ontario, Canada. brennanj@mcmaster.ca
authors.forename: John D
authors.initials: JD
authors.lastname: Brennan
authors.forename: Alfredo
authors.initials: A
authors.lastname: Capretta
authors.forename: Kelvin
authors.initials: K
authors.lastname: Yong
authors.forename: David
authors.initials: D
authors.lastname: Gerritsma
authors.forename: Kulwinder K
authors.initials: KK
authors.lastname: Flora
authors.forename: Amy
authors.initials: A
authors.lastname: Jones
mesh_terms: D000596:Amino Acids / Q000494:pharmacology*; D005063:Europium / Q000528:radiation effects; D028581:Lanthanoid Series Elements / Q000528:radiation effects*; D049449:Luminescence; D015335:Molecular Probes / Q000528:radiation effects; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000494:pharmacology*; D013725:Terbium / Q000528:radiation effects; D014364:Tryptophan / Q000031:analogs & derivatives / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: D000596:Amino Acids; D028581:Lanthanoid Series Elements; D015335:Molecular Probes; D017319:Photosensitizing Agents; D013725:Terbium; D005063:Europium; D014364:Tryptophan