A novel type of spin traps 1 derived from the pyrimidoquinoxaline N-oxide heterocyclic core is reported.EPR technique was used to evaluate their ability to trap methyl radicals generated in a Fenton reaction in the presence of DMSO. All the synthesized nitrones showed spin trapping properties and the corresponding nitroxides 2 were characterized by EPR. The novel spin traps showed remarkably persistent signals, as confirmed in a competition experiment with DMPO. The addition rate constants leading to the spin adducts (k add ) were determined, and very good correlations were found with steric and electronic parameters of the parent nitrones. The spin adducts decomposition rate constants (k dec ) and the corresponding half-life times (t 1/2 ) were also determined. DFT and MP2 calculations were used in order to rationalize the adducts hfcc and the structural factors influencing their addition and decomposition rates.

Lacustrine sequences were obtained from Laguna Verde and Laguna Gemelas Este, two small lakes 43 located east of the southern Patagonian Ice Field and close to the village of El Chaltén in Argentinian 44 Patagonia. Four tephra layers were identified in each of these short sedimentary sequences and 45 characterised using individual glass-shard tephra chemistry to determine provenance. In order to 46 understand the impact of the tephra deposits on lake ecosystems, bulk sediment geochemistry and 47 diatom assemblages were analysed. Age-depth models for the cores were established by radiometric 48 dating using 137 Cs and 210 Pb measurements. 49

The behaviour of some N,N'-disubstituted hexahydropyrimidines, a class of naturally occurring compounds of biological and biomedical interest, has been studied in both electron ionization (EI) and electrospray ionization (ESI) modes coupled with collisional experiments (ESI-MSn). In both techniques, the [M-H]+ ions are highly abundant, even if their formation is generated by two different mechanisms, i.e. H. loss from the M+. species in the case of EI and hydride (H-) abstraction from the molecules in the case of ESI. Furthermore, due to the low, step-by-step internal energy deposition typical of collisional experiments performed in an ion trap mass spectrometer, different fragment ions were observed in EI and ESI-MSn collisions. In both cases, the ions can be related to the original structure and allow us to identify the positions in which the different substituents are present.