Investigations of the metastable decay of DNA under ultraviolet matrix-assisted laser desorption/ionization conditions with post-source-decay analysis and hydrogen/deuterium exchange

The fragmentation of positive ions of DNA under the conditions of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was investigated by post-source decay (PSD) analysis and hydrogen/deuterium (H/D) exchange. Spectra of five different synthetic 4mer oligonucleotides were recorded. As a main result the hypothesis was confirmed that for these ions all fragment ions result from processes, initiated by protonation/deuteration of a suitable base followed by a loss of this base as a neutral or ion and further backbone cleavages. The three bases adenine, guanine, and cytosine all exhibit comparable lability for fragmentation. The spectra show evidence for an interaction of the adenine base with the phosphate backbone. Signals of fragments containing TT- and CT-cycloadducts were observed in the spectra.     

On uniqueness for an inverse problem in inhomogeneous elasticity

We consider the scattering of time-harmonic elastic waves inan isotropic medium which is characterized by constant Lamécoefficients and an inhomogeneous mass density. We prove thata knowledge of the far-field pattern for all incident planewaves and a single frequency provides sufficient informationto determine the mass density uniquely. To this end we constructa periodic Faddeev-type fundamental solution for the Navierequation and derive the existence of complex geometrical opticssolutions to the Navier equation.