This project is aimed to study charged supramolecular adducts and naked ions in the gas phase through the application of advanced hyphenated techniques based on mass spectrometric and spectroscopic devices. Object of the study is the structural characterization of the investigated species in order to ascertain: 1) the chemical identity of both the m/z selected ions and their relevant fragments obtained by MSn (typically n=2, 3) dissociation; 2) the nature and the strength of the non-covalent interactions responsible of the actual conformation of free charged molecules (intramolecular interactions) and supramolecular organization within ionic clusters (intracomplex interactions), including chiral systems. To this end a crucial role is played by in-silico simulations of the experimental gas-phase results obtained through theoretical calculations. Gas Phase investigation of the structure of single species and supramolecules offer an exclusive, "intimate" view of the non-covalent interactions in act, without any interference by environmental factors (e.g. solvation, pH, ionic strength, counterion), whose role in condensed phase can affect the intrinsic behavior of the system. Because of the ubiquitous nature of the solvent, the effect of environmental factors is difficult to evaluate in condensed phase, but it clearly emerge from the comparison of gas-phase experiments on the same system.
The present project is aimed to investigate:
1) representative DNA adducts relevant as biomarkers of exposure to genotoxic substances and for cancer risk assessment, in order to test the potentiality of the IRMPD spectroscopy in discriminating the nature of the modifications and the base sites in which they took place;
2) the time dependent structural characteristics of the proton bound complexes [C¿H¿G]+ formed between the home made macrocycle rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene (C) and D-(+)-Galactosamine (G).
Following the first application of electrospray ionization (ESI) in 1968, development of atmospheric pressure ionization source stimulated the applications of Mass Spectrometry (MS) based techniques to ever wider sectors of chemical, biological and medical science, as for example, biochemistry, catalysis, separation sciences, environmental analysis, sensors, chemical logic gates, molecular machines, nanomaterials, drugs design, omics techniques, medical diagnostics, and many others, but the lack of structural resolving power limits pure MS applications especially when isomeric species are involved, as often happens in -omics procedures (proteomics, glycomics, metabolomics, etc). Hyphenated spectroscopic (IRMPD) and Ion Mobility (IM) methods, developed over the past few decades, allow now the IR action spectra of shape-selected ions be performed. Thus, detailed structural information can be obtained by comparison of experimental and theoretical IR spectra of the isolated ions.
Therefore, we expect that the combined application of these methodologies will give an unequivocal answer to specific analytical questions, starting from the structural analysis of isomeric DNA adducts and their MSn fragmentation products, which is the first topic of this project. Moreover, when applied to parent and daughter ions in MSn experiments, ESI-(FAIMS)-IT-IRMPD spectroscopy provides unambiguous information regarding to the fragmentation pathways, which is invaluable for better understanding the mechanisms of unimolecular processes in mass spectrometry environment, and even more for building reliable spectra libraries.
As a second topic of this project, the same methodology will be applied to the proton bound complexes [C¿H¿G]+ between the home made macrocycle rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methyl resorcin[4]arene (C) and D-(+)-Galactosamine (G). In addition to studying the anomeric preference for alpha- and beta-G guests, the aim is to obtain detailed information about the nature of the non-covalent interactions at play in the formation of two very different [C¿H¿G]+ aggregates, whose existence is suggested by their fast/slow kinetics behavior in previous ligand-exchange experiments. Time dependent formation of [C¿H¿G]+ supramolecular host-guest complexes is interesting in view of potential application as age detector for food or other perishable goods, whereas the fast/slow kinetics behavior may help in understanding the mechanisms of guest release, fundamental in engineering nano-encapsulated drugs.
This research lays at the border of two aggregation states, i.e. solution and the gas-phase, given that the solution composition and/or the (supra)molecular features are sometimes maintained thoughout the ion source, but mostly they are partially altered or strongly affected by the ESI conditions, wherein unexpected aggregation-types or unfavourite conformations can be freezed and survive in the gas-phase.