title: Excited-state interactions in flurbiprofen-tryptophan dyads.
abstract: Fluorescence and laser-flash photolysis measurements have been performed on two pairs of diastereomeric dyads that contain the nonsteroidal anti-inflammatory drug (S)- or (R)-flurbiprofen (FBP) and (S)-tryptophan (Trp), which is a relevant amino acid present in site I of human serum albumin. The fluorescence spectra were obtained when subjected to excitation at 266 nm, where approximately 60% of the light is absorbed by FBP and approximately 40% is absorbed by Trp; the most remarkable feature observed in all dyads was a dramatic fluorescence quenching, and the residual emission was assigned to the Trp chromophore. In addition, an exciplex emission was observed as a broad band between 380 and 500 nm, especially in the case of the (R,S) diastereomers. The fluorescence lifetimes (tauF) at lambdaem=340 nm were clearly shorter in the dyads than in Trp-derived model compounds; in contrast, the values of tauF at lambdaem=440 nm (exciplex) were much longer. On the other hand, the typical FBP triplet-triplet transient absorption spectrum was obtained when subjected to laser-flash photolysis, although the signals were less intense than when FBP was directly excited under the same conditions. The main photophysical events in FBP-Trp dyads can be summarized as follows: (1) most of the energy provided by the incident radiation at 266 nm reaches the excited singlet state of Trp (1Trp*), either via direct absorption by this chromophore or by singlet singlet energy transfer from excited FBP (1FBP*); (2) a minor, yet stereoselective deactivation of 1FBP* leads to detectable exciplexes and/or radical ion pairs; (3) the main process observed is intramolecular 1Trp* quenching; and (4) the first triplet excited-state of FBP can be populated by triplet-triplet energy transfer from excited Trp or by back-electron transfer within the charge-separated states.
authors.affiliation: Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universidad Politécnica de Valencia, Camino de Vera s/n, E-46022 Valencia, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Vayá
authors.forename: M Consuelo
authors.initials: MC
authors.lastname: Jiménez
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Miranda
mesh_terms: D000097:Acetonitriles; D004146:Dioxanes / Q000737:chemistry; D005480:Flurbiprofen / Q000737:chemistry*; D006801:Humans; D015394:Molecular Structure; D010777:Photochemistry; D012709:Serum Albumin / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D004146:Dioxanes; D012709:Serum Albumin; D005480:Flurbiprofen; D014364:Tryptophan; C025223:1,4-dioxane; C032159:acetonitrile