In the 20 years, since the introduction of electrospray mass spectrometry (ESI-MS), the use of this technique in various fields of inorganic, organometallic, and analytical chemistry has been steadily increasing. In this study, the application of ESI-MS to the study of metal-ligand solution equilibria is reviewed (till 2004 included). In a first section, advantages and drawbacks of ESI-MS in this type of application are described. Subsequently, a list of ca. 300 studies is reported, in which ESI-MS was used to give number and stoichiometry of the species at equilibrium, or also to estimate their stability constants. All studies are classified according to the metal ions under examination. Other related applications, such as host-guest interactions and metal ion-protein binding studies, are briefly reviewed as well.

The thermodynamic properties of some copper complexes, among those frequently used as catalysts in controlled/living radical polymerization, has been studied in CH3CN + 0.1 M (C2H5)4NBF4. A combination of different techniques, namely potentiometry, spectrophotometry and cyclic voltammetry, has been used to determine the stability constants of all possible complexes of CuI and CuII present in binary and\ud ternary systems composed of CuI or CuII, a halide ion (X=Cl-, Br-) and a polyamine ligand (L = pentamethyldiethylenetriamine, tris(2-dimethylaminoethyl)amine). The binary Cu-X systems show only mononuclear CuXx complexes, where x=1, 2, 3, 4 for CuII, and x=1, 2 for CuI. Conversely, in the case of the binary Cu-L systems, besides the mononuclear complexes CuLl, where l=1 or 2, also dinuclear complexes Cu2L were found. The ternary systems give rise to a mixture of mononuclear and dinuclear\ud complexes of general formula CumLlXx. Besides the 1:1:1 complex obtained in all combinations, the following species were found: CuIILX2, CuI2LX and CuI2LX2. The stability constants of all these species were determined and used to construct speciation diagrams for both CuI and CuII species. Such diagrams show that often conditions favoring the quantitative formation of CuIIL, CuIIL2, or CuIILX can be easily realized, whereas isolation of a single predominant CuI species can hardly be achieved. Speciation diagrams for CuI as a function of CX/CCuI show interesting results that may be helpful in rationalizing the role of termination reactions in atom transfer radical polymerization

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The Cu 2+ complexes formed by a series of cyclen derivatives bearing sulfur pendant arms, 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis[2-(methylsulfanyl)ethyl]-4,10-diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S), were studied in aqueous solution at 25 °C from thermodynamic and structural points of view to evaluate their potential as chelators for copper radioisotopes. UV–vis spectrophotometric out-of-cell titrations under strongly acidic conditions, direct in-cell UV–vis titrations, potentiometric measurements at pH >4, and spectrophotometric Ag + –Cu 2+ competition experiments were performed to evaluate the stoichiometry and stability constants of the Cu 2+ complexes. A highly stable 1:1 metal-to-ligand complex (CuL) was found in solution at all pH values for all chelators, and for DO2A2S, protonated species were also detected under acidic conditions. The structures of the Cu 2+ complexes in aqueous solution were investigated by UV–vis and electron paramagnetic resonance (EPR), and the results were supported by relativistic density functional theory (DFT) calculations. Isomers were detected that differed from their coordination modes. Crystals of [Cu(DO4S)(NO 3 )]·NO 3 and [Cu(DO2A2S)] suitable for X-ray diffraction were obtained. Cyclic voltammetry (CV) experiments highlighted the remarkable stability of the copper complexes with reference to dissociation upon reduction from Cu 2+ to Cu + on the CV time scale. The Cu + complexes were generated in situ by electrolysis and examined by NMR spectroscopy. DFT calculations gave further structural insights. These results demonstrate that the investigated sulfur-containing chelators are promising candidates for application in copper-based radiopharmaceuticals. In this connection, the high stability of both Cu 2+ and Cu + complexes can represent a key parameter for avoiding in vivo demetalation after bioinduced reduction to Cu + , often observed for other well-known chelators that can stabilize only Cu 2+ .

New sulphur derivatives of cyclen, with potential complementary properties with respect to known compounds, have been synthesized and studied.