A neutral receptor that binds anions by hydrogen bonds even in water is the cyclopeptide reported in this article. This property results from the particular structure of the complex in which the ...anions are effectively shielded from the surrounding solvent, as can be seen in the iodide complex shown.
The excited state dynamics of the isolated and protonated peptide H(2)N-Leu-Trp-COOH are analyzed by fs pump-probe spectroscopy. The peptides are brought into the gas phase by electrospray ...ionization, and fs pump-probe excitation is detected by fragment ion formation. The pump laser addressed the excited pipi* state of the indole chromophore of the amino acid tryptophan. The subsequent excited state dynamics agreed with a biexponential decay with time constants of 500 fs and 10 ps. This is considerably shorter than the lifetime of neutral tryptophan in solution and in proteins, but similar to isolated, protonated tryptophan. Several models are discussed to explain the experimental results but the detailed quenching mechanism remains unresolved.
The excited state dynamics of protonated adenine in the gas phase were investigated by femtosecond pump–probe transient mass spectroscopy. Adenine was protonated in an electrospray ionization source ...and transferred to a Paul trap. Two femtosecond laser pulses at 266 nm and 800 nm excited the lowest electronic ππ* state and probed the excited‐state dynamics by monitoring ion fragment formation. The measured excited state decay is monoexponential with a lifetime shorter than 161 fs. This agrees with a theoretical prediction of very fast internal conversion via a conical intersection with the ground state.
Photostability of adenine: Femtosecond pump–probe transient mass spectrometry was used to investigate the excited‐state dynamics of protonated adenine in the gas phase. Fragmentation patterns are similar to those found for high‐energy collision‐induced dissociation mass spectra, and experimental evidence agrees well with predictions that a conical intersection to the ground state is accessed without a barrier.
Electron transfer dissociation (ETD) is commonly employed in ion traps utilizing rf fields that facilitate efficient electron transfer reactions. Here, we explore performing ETD in the HCD collision ...cell on an Orbitrap Velos instrument by applying a static DC gradient axially to the rods. This gradient enables simultaneous three dimensional, charge sign independent, trapping of cations and anions, initiating electron transfer reactions in the center of the HCD cell where oppositely charged ions clouds overlap. Here, we evaluate this mode of operation for a number of tryptic peptide populations and the top-down sequence analysis of ubiquitin. Our preliminary data show that performing ETD in the HCD cell provides similar fragmentation as ion trap-ETD but requires further optimization to match performance of ion trap-ETD.
The cover picture shows
the potential energy scheme of protonated adenine. The adenine molecule in front is in the ground‐state equilibrium geometry whereas the molecule in the back shows the ...nonplanar structure after absorption of an UV photon. In their Article on page 751 Nolting et al. investigate the excited state dynamics of protonated adenine by femtosecond pump–probe transient mass spectrometry in the gas phase.
We describe the preparation and characterization of Al-AlOx-Ag tunnel junctions and calculate the energy distribution of the tunneling hot electrons in the range 0–2.5 eV above the Fermi level of ...silver. Because the mean free path of the hot electrons is of the order of the thickness of the silver film of the junction, which is at the same time the electrode in contact with an electrolyte, new surface effects can be studied. Hot electrons can be injected into the nonhydrated electron band in water. Hot electrons also cause hydrogen evolution at electrode potentials more positive than the ones needed in common electrochemistry. We observed the emission of hot electrons into silver during transients of hydrogen oxidation at silver and during oxidation of overpotential hydrogen on platinum clusters deposited on the silver electrode. The tunnel current at constant tunnel voltage can be changed by faradaic reactions, but surprisingly also by nonfaradaic reactions; this is assigned to a mesoscopic quantum phenomenon.
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