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Coordination Chemistry in Water of a Free and a Lipase-Embedded Cationic NCN-Pincer Platinum Center with Neutral and Ionic Triarylphosphines

By B. Wieczorek, D.J.M. Snelders, H.P. Dijkstra, C. Versluis, M. Lutz, A.L. Spek, M.R. Egmond, R.J.M. Klein Gebbink and G. van Koten


The coordination chemistry in aqueous media was studied for the platinum center of low-molecular-weight cationic NCN-pincer platinum complexes [RC6H2(CH2NMe2)2-3,5-Pt(H2O)-4]+ (R = −(CH2)3P(═O)(OEt)(OC6H4NO2-4) (1(OH2)), H (2(OH2))) as well as of the platinum center of the NCN-pincer platinum cation embedded in the lipase cutinase (cut-1; molecular weight 20 619.3) with various anionic, neutral, and cationic triarylphosphines. A 31P NMR study of the coordination of triarylphosphines to the cationic NCN-pincer platinum center in low-molecular-weight [2(OH2)][OTf] in both D2O and Tris buffer (Tris = tris(hydroxylmethyl)aminomethane) showed that the phosphine–platinum coordination is strongly affected by Tris buffer molecules. Two crystal structures of a NCN-pincer platinum–phosphine and a NCN-pincer platinum–ethanolamine coordination complex with ethanolamine as a functional model of Tris with hydrogen bridges, provoking a dimeric supramolecular structure, confirmed that the coordination observed in solution occurred in the solid state as well. A 31P NMR and ESI-MS study of the lipase cut-1 showed that the coordination of various triarylphosphines to the enzyme-embedded platinum center is affected by the surrounding protein backbone, discriminating between phosphines on the basis of their size and charge. By using 31P NMR spectroscopy and ESI-MS spectrometry, study of the coordination of triarylphosphines to cut-1 was possible, thereby avoiding the need for the application of laborious biochemical procedures. To the best of our knowledge, this is the first example of a study involving the selective binding of organic ligands to the metal center of a semisynthetic metalloprotein, unequivocally demonstrating that the well-established coordination chemistry for small-molecule complexes can be transferred to biological molecules. This initial study allows future explorations in the field of selective protein targeting and identification, as in protein profiling or screening studie

Year: 2012
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