Conceptual framework relating predictor variables to observed patterns in patterns in growth.

<p>Red arrows imply positive relationship, blue arrows indicate a negative relationship.</p

The histidine effect. Electron transfer and capture cause different dissociations and rearrangements of histidine peptide cation-radicals.

International audienceElectron-transfer and -capture dissociations of doubly protonated peptides gave dramatically different product ions for a series of histidine-containing pentapeptides of both non-tryptic (AAHAL, AHAAL, AHADL, AHDAL) and tryptic (AAAHK, AAHAK, AHAAK, HAAAK, AAAHR, AAHAR, AHAAR, HAAAR) type. Electron transfer from gaseous Cs atoms and fluoranthene anions triggered backbone dissociations of all four N-C(alpha) bonds in the peptide ions in addition to loss of H and NH(3). Substantial fractions of charge-reduced cation-radicals did not dissociate on an experimental time scale ranging from 10(-6) to 10(-1) s. Multistage tandem mass spectrometric (MS(n)) experiments indicated that the non-dissociating cation-radicals had undergone rearrangements. These were explained as being due to proton migrations from N-terminal ammonium and COOH groups to the C-2' position of the reduced His ring, resulting in substantial radical stabilization. Ab initio calculations revealed that the charge-reduced cation-radicals can exist as low-energy zwitterionic amide pi* states which were local energy minima. These states underwent facile exothermic proton migrations to form aminoketyl radical intermediates, whereas direct N-C(alpha) bond cleavage in zwitterions was disfavored. RRKM analysis indicated that backbone N-C(alpha) bond cleavages did not occur competitively from a single charge-reduced precursor. Rather, these bond cleavages proceeded from distinct intermediates which originated from different electronic states accessed by electron transfer. In stark contrast to electron transfer, capture of a free electron by the peptide ions mainly induced radical dissociations of the charge-carrying side chains and loss of a hydrogen atom followed by standard backbone dissociations of even-electron ions. The differences in dissociation are explained by different electronic states being accessed upon electron transfer and capture

Experimental setup and first measurement of DNA damage induced along and around an antiproton beam

Radiotherapy employs ionizing radiation to induce lethal DNA lesions in cancer cells while minimizing damage to healthy tissues. Due to their pattern of energy deposition, better therapeutic outcomes can, in theory, be achieved with ions compared to photons. Antiprotons have been proposed to offer a further enhancement due to their annihilation at the end of the path. The work presented here aimed to establish and validate an experimental procedure for the quantification of plasmid and genomic DNA damage resulting from antiproton exposure. Immunocytochemistry was used to assess DNA damage in directly and indirectly exposed human fibroblasts irradiated in both plateau and Bragg peak regions of a 126 MeV antiproton beam at CERN. Cells were stained post irradiation with an anti-γ-H2AX antibody. Quantification of the γ-H2AX foci-dose relationship is consistent with a linear increase in the Bragg peak region. A qualitative analysis of the foci detected in the Bragg peak and plateau region indicates significant differences highlighting the different severity of DNA lesions produced along the particle path. Irradiation of desalted plasmid DNA with 5 Gy antiprotons at the Bragg peak resulted in a significant portion of linear plasmid in the resultant solution