Titolo della tesi: From Phytochemicals to Metal-Based Drugs: Structure and Coordination Chemistry Investigated by Mass Spectrometry and Infrared Ion Spectroscopy
The structural characterization of bioactive compounds, including phytochemicals and their metal complexes, as well as metal-based drugs, is becoming an increasingly important area of research in several fields, such as drug discovery and food science. Among the numerous phytochemicals with beneficial activities for human health, (poly)phenolic compounds play a significant role. These compounds hold a broad spectrum of pharmacological activity, due to their structural conformation and their high capabilities as free radical scavengers and metal ion chelating agents. This thesis explores the relationship between the chemical structure and the activity of bioactive species, as well as characterizes the properties of metal complexes, in particular in their interaction with biological molecules. Indeed, as in the case of anticancer drugs, understanding their mechanisms of action is important for deliver new metal-based therapies. To achieve all these objectives, a combined contribution of several techniques has been involved in this thesis. Electrospray ionization mass spectrometry (ESI-MS) has demonstrated to be the most suitable and versatile technique for the analysis in gas-phase of ionic species formed in solution. In addition, infrared multiple photon dissociation action spectroscopy (IRMPD) provides the vibrational features of mass selected species in gas-phase without solvent effect. Calculations of potential geometries of the assayed ions are performed using density functional theory (DFT) methods, and the calculated IR spectra are compared with the experimental IRMPD spectra. In this way it is possible to interpret the experimental vibrational features and to determine the structure of the sampled gas-phase ions. Moreover, high resolution mass spectrometry (HR-MS), collision-induced dissociation (CID) and ion mobility MS (IM-MS), are exploited to complete these studies. This thesis will be presented in two main sections as follows.
The part A involves the structural characterization and isomeric discrimination of polyphenols belonging to the family of flavonoids. In particular, in chapter 3 a detailed structural characterization of bare deprotonated genistein has been performed. Chapter 4 is focused on discrimination of positive forms of naringenin and its structural isomer naringenin chalcone, providing the structural features necessary to discriminate the two isomers in complex natural matrices. Moreover, the spectroscopic analysis conducted on negative forms of naringenin and naringenin chalcone was aimed to the investigation of the proposed chalcone⮂flavanone isomerization, which should occurs, as hypothesized, during the deprotonation process in negative ionization mode (ESI(-)).
In part B the coordination sites of metal-complexes of bioactive compounds in binding with biomolecules (including amino acids, peptides and nucleobases) have been studied and clarified. Phenolic acids and metal-based drugs have been chosen as bioactive compounds for their particularly interest for pharmaceutical applications.
Chapter 5 is aimed to identify the Cu(II) coordination site in chlorogenic and rosmarinic acids and then to evaluate the impact of adding histidine to this system in the gas phase. IM-MS has been assessed to investigate how these phenolic compounds affect the Cu(II)-induced Aβ aggregation. Finally, in chapter 6 the structural characterization of complexes involving the binding of guanine and adenine with second- and third-generation of platinum drugs, namely carboplatin and oxaliplatin, is presented, providing insights into their biological activity.