The relationship between the electrospray ionization behaviour and biological activity of some phosphino Cu(I) complexes Francesco Tisato 1 , Fiorenzo Refosco 1 , Marina Porchia 1 , Matteo Tegoni 2 , Valentina Gandin 3 , Cristina Marzano 3 , Maura Pellei 4 , Grazia Papini 4 , Lara Lucato 5 , Roberta Seraglia 5 and Pietro Traldi 5 * 1 CNR Istituto di Chimica Inorganica e delle Superfici, Corso Stati Uniti4, I 35127 Padova, Italy 2 Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita ` di Parma, Viale G.P. Usberti 17A, I 43100 Parma, Italy 3 Dipartimento di Scienze Farmaceutiche, Universita ` di Padova, Via Marzolo 5, I 35131 Padova, Italy 4 Scuola diScienze e Tecnologie, Universita ` di Camerino, Via S. Agostino 1, I 62032 Camerino Macerata, Italy 5 CNR Istituto di Scienze e Tecnologie Molecolari, Corso Stati Uniti4, I 35127 Padova (Italy) Received 10 February 2010; Revised 10 March 2010; Accepted 17 March 2010 Electrospray ionization mass spectrometry was usefully employed for the characterization of three phosphino copper(I)complexes of medicinalinterest.This technique revealed thatthe original [CuL 4 ] R pro-drugs (L ¼ hydrophilic tertiary phosphine) underwent dissociation with production of coordinative unsaturated [CuL 3 ] R and [CuL 2 ] R species, which represented key intermediates for the activation of potential biological properties. The more favoured was the displacement of the ligands from the [CuL 4 ] R parent complex, the more favoured was in turn the possibility for the metal ion to directly interactwith biological substrates,including pharmacologicaltargets related to cancer proliferation. An inverse correlation between the stability and the cytotoxic activity of the three copper(I) complexes investigated has been clearly established. Copyright # 2010 John Wiley & Sons, Ltd. Mass spectrometry can be employed to gain information on the chemical behaviour of molecules of biological interest, and this information can be validly employed for studies on structure-activity relationship (SAR). Thus, for example, the electron ionization induced fragmentation of some aryl- and heteroaryl-triazenes has been correlated to their mutagenic and antimetastatic properties. 1,2 More recently,a class of systematically active inhibitors of the intracellular activity of fatty acid amide hydrolase (FAAH) has been studied by mass spectrometry. 3–5 These compounds, characterized by an N- alkylcarbamic acid O-arylesterstructure,show an easy collisionally induced cleavage of the C(O)–O bond and the energetic ofthis decomposition process was found to be linearly correlated with their FAAH-inhibitory activity. The described findings can be easily explained by the fact that mass spectrometry results are strictly related to the chemistry of the molecules of interest, as the biochemical activity is. This approach was employed also in the present case,in order to gain information on the potential cytotoxic activity of some phosphino Cu(I) complexes. Copper is an essential trace element in all organisms living in oxygen-rich environ- ments. 6 It is a redox-active metal that readily switches from Cu(II) to Cu(I), or vice versa,both in conventional bench chemicalreactions, in physiologicalconditions and during mass spectrometric experiments. 7 The easy accessibility of differentredox statesand various coordination environ- ments allow this metal to interact with a variety of ligands, functional groups and different donor atoms including carboxylate oxygen, imidazole nitrogen,cysteine thiolate and methionine thioether sulfurs. In biology, copper is vital for the function of several enzymes and proteins involved, among others, in energy metabolism, mitochondrial respir- ation,antioxidation,collagen cross-linking, and catechol- amine biosynthesis processes. 6 The major functions of copper compounds involve oxidation–reduction reactions in which copper-containing biological molecules react directly with molecularoxygen to produce free radicals. 8–10 For this reason,free cellular copper concentration is maintained at extremely low levels. 11,12 Copper homeostasisin living organisms is regulated by both transcriptional controland selective transport mechanisms through a conserved group of proteins which contain unique cysteine-, methionine- and histidine-rich domains. 6 Altered levels of copper generatedisease states,as established in the case of Wilson disease (WD) and Menkes disease (MD), which are characterized by an overload or a deficiency of copper in the organism, respectively. 13 Investigations originally focused on Menkes and Wilson disorders have provided new insights into the field of copper homeostasis and, in particular,into the understanding of RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2010; 24:1610–1616 Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rcm.4553 *Correspondence to: P. Traldi, CNR Istituto di Scienze e Tecnologie Molecolari,Corso Stati Uniti 4, I 35127 Padova, Italy. E-mail:pietro.traldi@adr.pd.cnr.it Copyright # 2010 John Wiley & Sons, Ltd.