Abstract
Lanthanides (Ln) are metals in the f block that belong to the Rare Earth family. In aqueous environments, Ln are mainly found in the oxidized form with a +III state, and are commonly referred to as Ln(III) ions. Ln(III) are hard acids according to HSAB theory (Hard Soft Acids and Bases), which means that these ions will preferentially interact with hard bases such as carboxylates, phosphates, or amides for exemple. Ln(III) ions have a high coordination number (CN), which is generally 8 or 9 depending on the size of the ionic radius. Ln have similar chemical properties and unique and attractive physical properties, particularly for modern technologies. They are used in many technological applications such as renewable energy, lighting, medicine, and digital technology. Over the last few decades, the use and production of Ln has continued to increase, raising questions about their impact on environnemental and human health. However, only few datas are available on toxicology of Ln. Several types of biomolecules are involved in toxicity mechanisms, specially proteins. Due to their strong Lewis acidity, Ln(III) ions interact mainly with proteins through electrostatic bonds. These interactions, which are generally weak and easily disrupted, lead to isolation and identification difficulties of target proteins using separation methods commonly used in molecular biology. The objective of this thesis is to develop molecular probes that are able of covalently labeling proteins that interact with Ln. These probes are composed of four modules : (i) a ligand, (ii) a cleavable electrophile, (iii) a spacer group, and (iv) a fluorophore or biotin-type tag. (i) The ligand module must have affinity and selectivity for Ln in order to preferentially form a complex with Ln over other metals. The structures of ligands are inspired by the family of polyaminocarboxylate ligands (DTPA, EDTA, DOTA), which are known in the literature to have high affinity constants and good selectivity for these metals. (ii) The chosen cleavable electrophile module is acylimidazole, an electrophile with reactivity that can be modulated by complexation of the metal with the ligand module. (iii) The spacer module is an ethylene glycol chain whose purpose is to space the tag and ligand modules apart in order to avoid unwanted interactions. (iv) As its name suggests, the tag is used to label proteins and identify them. These probes are activated based on their low reactivity in an aqueous medium at physiological pH. In the presence of Ln(III) cations, the ligand module and imidazole group of the acylimidazole coordinate with Ln(III). This coordination, specially via the imidazole, leads to a decrease in electron density of carbonyl group of the acylimidazole, thereby increasing its reactivity. The probes then become activated and able of reacting rapidly with nucleophilic groups present on proteins. The work in this thesis has led to the design of a library of molecular probes whose coordination with Ln(III) has been characterized by Nuclear Magnetic Resonance (NMR). Activation of the probes in the presence of Ln(III) was then demonstrated in buffered aqueous media at physiological pH. Finally, the labeling efficiency on isolated proteins was evaluated for selected probes in terms of their reactivity and selectivity towards Ln, which had been demonstrated in previous studies.