Fragmentation mechanisms of oxidized peptides elucidated by SID, RRKM modeling, and molecular dynamics

The gas-phase fragmentation reactions of singly charged angiotensin II (AngII, DR⁺VYIHPF) and the ozonolysis products AngII+O (DR⁺VY*IHPF), AngII+3O (DR⁺VYIH*PF), and AngII+4O (DR⁺VY*IH*PF) were studied using SID FT-ICR mass spectrometry, RRKM modeling, and molecular dynamics. Oxidation of Tyr (AngII+O) leads to a low-energy charge-remote selective fragmentation channel resulting in the b ₄ +O fragment ion. Modification of His (AngII+3O and AngII+4O) leads to a series of new selective dissociation channels. For AngII+3O and AngII+4O, the formation of [MH+3O] ⁺ −45 and [MH+3O] ⁺ −71 are driven by charge-remote processes while it is suggested that b ₅ and [MH+3O] ⁺ −88 fragments are a result of charge-directed reactions. Energy-resolved SID experiments and RRKM modeling provide threshold energies and activation entropies for the lowest energy fragmentation channel for each of the parent ions. Fragmentation of the ozonolysis products was found to be controlled by entropic effects. Mechanisms are proposed for each of the new dissociation pathways based on the energies and entropies of activation and parent ion conformations sampled using molecular dynamics.     

Localization in one dimensional correlated random potentials

The localization length of one-dimensional disordered systems with statistically correlated random potentials is studied both numerically and analytically. The results indicate that the localization length generally increases when the correlation function is positive. In the presence of anticorrelation effects the localization length may be shorter than in the uncorrelated case.     

Atomgewichte

Ohne Zusammenfassung     

Steplike currents in confined two dimensional systems

In a confined two dimensional system of non-interacting electrons in a normal constant magnetic field, the current is calculated along the sample as a response to an electric field in the same direction which is switched on and then off. The resulting stationary current is shown to be a step-like function of the electron density.     

Kalk

Ohne Zusammenfassung