Nanosecond UV laser photoionization of aqueous tryptophan: temperature dependence of quantum yield, mechanism, and kinetics of hydrated electron decay

On the Formation of Radical Dications of Protonated Amino Acids in a “Microsolution” of Water or Acetonitrile and Their Reactivity Towards the Solvent

“…In fact, UV induced inactivation of proteins is caused partly by the degradation of photoionized tryptophan. [26] The procedure we have used is to collide AH (S) 1,2 [S water or acetonitrile] with O 2 . Water was chosen because it is an essential ingredient in biological environments, and acetonitrile because it is only a hydrogen acceptor in hydrogen bond formation and thereby represents a different case system.…”

Ultrafast excited-state dynamics of tryptophan in water observed by transient absorption spectroscopy

“…Nanosecond photolysis studies have reported an absorption band (k peak = 400-440 nm, s $ 20-45 ns) -termed as 'T 1 ' [12][13][14], that could qualify for being the primary photoproduct's signature. It has been observed only in conditions in which Trp's side chain ammonium group is protonated (NH þ 3 ), which seems to be the key side chain group for S 1 quenching [17,20], but due to insufficient time-resolution, a direct correlation of its formation with the S 1 quenching time is lacking.…”

“…In aqueous solution, besides sub-ps photo-ionization [9-11] and intersystem crossing [12][13][14] at long times, the intermediate, nanosecond time scale is characterized by a multi-exponential fluorescence decay. The latter has been rationalized on the basis of different rotameric configurations [15], and is thought to involve an excited-state proton [15][16][17][18] or charge-transfer [19,20], eventually leading to a primary photoproduct whose spectroscopic signature has not been identified so far.Nanosecond photolysis studies have reported an absorption band (k peak = 400-440 nm, s $ 20-45 ns) -termed as 'T 1 ' [12][13][14], that could qualify for being the primary photoproduct's signature. It has been observed only in conditions in which Trp's side chain ammonium group is protonated (NH þ 3 ), which seems to be the key side chain group for S 1 quenching [17,20], but due to insufficient time-resolution, a direct correlation of its formation with the S 1 quenching time is lacking.…”

“…It has been observed only in conditions in which Trp's side chain ammonium group is protonated (NH þ 3 ), which seems to be the key side chain group for S 1 quenching [17,20], but due to insufficient time-resolution, a direct correlation of its formation with the S 1 quenching time is lacking. Furthermore, T 1 is usually assigned to a triplet state of the protonated indole moiety [12][13][14], without a clear experimental proof though, since the usual quenching assays fail or give imprecise results for this short-lived species [13,14].As recognized in a few reports [7,20], ultrafast absorption experiments are lacking that would give evidence for the formation dynamics and the nature of the photoproduct resulting from S 1 quenching. We therefore performed femtosecond transient pump-probe spectroscopy studies on aqueous Trp.…”

Photoreactivity of biologically active compounds. XIX: Excited states and free radicals from the antimalarial drug primaquine

“…This may indicate a mixed mono and bi-photonic process; we have failed to observe significant transient absorbance at either 700 or 410 nm under experimental conditions that otherwise produce normal onephoton excitation in past experiments. Stevenson et al [25] note that the observed two photon power dependence is less with an experimental setup in which the laser and analyzing light beams are perpendicular (as in our experiment) than in an arrangement with collinear beams. In addition it is noted that at the powers and concentrations used in our experiments, saturation of absorption is likely.…”