Ab initio study of the electronic singlet excited-state properties of tryptophan in the gas phase: The role of alanyl side-chain conformations

Antioxidant properties of ethenyl indole: DPPH assay and TDDFT studies

Ethenyl indole exhibits antioxidant activity in a substituent dependent manner. Ethenyls bearing strong electron withdrawing substituents show weak or no antioxidant activities, whereas ethenyls with electron donating substituents exhibit antioxidant properties comparable to vitamin E.

Molecular dynamics simulations and in vitro analysis of the CRMP2 thiol switch

The collapsin response mediator protein CRMP2 (gene: DPYSL2) is crucial for neuronal development. The homotetrameric CRMP2 complex is regulated via two mechanisms: first by phosphorylation and second by the reduction and oxidation of the Cys504 residues of two adjacent subunits. Here, we have analysed the effects of this redox switch on the protein in vitro combined with force field molecular dynamics (MD). Earlier X-ray data reveal the structure of the rigid body of the molecule but lack the flexible C-terminus with the important sites for phosphorylation and redox regulation. An in silico model for this part was established by replica exchange simulations and homology modelling, which is consistent with the CD spectroscopy results of the recombinant protein. Thermofluor data indicated that the protein aggregates at bivalent ion concentrations below 200 mM. In simulations the protein surface was covered under these conditions by a large number of ions, which most likely prevent aggregation. A tryptophan residue (Trp295) in close proximity to the forming disulphide allowed the measurement of the structural relaxation of the rigid body upon reduction by fluorescence quenching. We were also able to determine the second-order rate constant of CRMP2 oxidation by H₂O₂. The simulated solvent accessible surface of the hydroxyl group of Ser518 significantly increased upon reduction of the disulphide bond. Our results give the first detailed insight into the profound structural changes of the tetrameric CRMP2 due to oxidation and indicate a tightly connected regulation by phosphorylation and redox modification.

Solvation by Glycerol at Temperatures from 353 to 77 K: Its Solvatochromic Characterization and Use to Block the Molecular Structure of Conformationally Flexible Structures

Glycerol is UV/vis spectroscopically characterized by using suitable solvatochromic polarity probes spanning a wide temperature range of 353 to 77 K. For the first time we find experimental evidence that, when the solvent preserves its internal structure in a broad range of temperatures, all solvatochromically derived solvent parameters (i.e., SP, SdP, SA, and SB) also maintain their values unchanged. On the basis of these solvatochromic measurements, it is shown that, below 180 K, glycerol efficiently blocks the molecular structure of conformationally flexible solutes.

The first UV absorption band ofl-tryptophan is not due to two simultaneous orthogonal electronic transitions differing in the dipole moment

The difference between the emission spectrum ofl-tryptophan in ethanol obtained at 113 K and at 293 K.

Action spectroscopy of a protonated peptide in the ultraviolet range

Action spectroscopy of substance P, a model undecapeptide, has been probed from 5.2 eV to 20 eV.

Contribution of synchrotron radiation to photoactivation studies of biomolecular ions in the gas phase

Photon activation of ions in the visible and ultraviolet range attracts a growing interest, partly for its promising applications in tandem mass spectrometry. However, this task is not trivial, as it requires notably high brilliance photon sources. Hence, most of the work in that field has been performed using lasers. Synchrotron radiation is a source continuously tunable over a wide photon energy range and which possesses the necessary characteristics for ion activation. This review focuses on the array of applications of synchrotron radiation in photon activation of ions ranging from near UV to soft X-rays.

Ultrafast Nonradiative Relaxation Channels of Tryptophan

The nonradiative relaxation channels of gas-phase tryptophan excited along the S1-S4 excited states (287-217 nm) have been tracked by femtosecond time-resolved ionization. In the low-energy region, λ ≥ 240 nm, the measured transient signals reflect nonadiabatic interactions between the two bright La and Lb states of ππ* character and the dark dissociative πσ* state of the indole NH. The observed dynamical behavior is interpreted in terms of the ultrafast conversion of the prepared La state, which simultaneously populates the fluorescent Lb> and the dissociative πσ* states. At higher energies, after excitation of the S4 state, the tryptophan dynamics diverges from that observed in indole, pointing to the opening of a relaxation channel that could involve states of the amino acid part. The work provides a detailed picture of the processes and electronic states involved in the relaxation of the molecule, after photoexcitation in the near part of its UV absorption spectrum.