The invention concerns the use of a collection of compounds of general formula (I), wherein: n is 0 or 1; p represents an integer between 1 and 6; r represents an integer between 1 and 12; R1 and R'1 represent in particular a hydrogen atom; R2 represents an amino acid side chain or an amino acid derivative; R3 represents a group derived from a carboxylic acid, bearing a basic entity; R4 represents in particular an alkyl group containing 1 to 10 carbon atoms; and A represents a hydrogen atom, a protecting group or a tracing group, in particular a fluorophor, a colouring agent or a quencher, for determining, through binding studies, ligands of receptors whose ligand is unknown or whose ligand useful for carrying out specific affinity binding assays is unknown.