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Reactivity of Ammonia Ligands of the Antitumor Agent Cisplatin: A Unique Dodecanuclear Pt 4 ,Pd 4 ,Ag 4 Platform for Four Cytosine Model Nucleobases
Author(s) -
Kampf Gunnar,
Sanz Miguel Pablo J.,
Morell Cerdà Marta,
Willermann Michael,
Schneider Alexandra,
Lippert Bernhard
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800586
Subject(s) - nucleobase , chemistry , adduct , crystallography , metal , stereochemistry , ethylenediamine , reactivity (psychology) , supramolecular chemistry , platinum , crystal structure , inorganic chemistry , catalysis , dna , organic chemistry , medicine , biochemistry , alternative medicine , pathology
Abstract The reaction of a potential mono(nucleobase) model adduct of cisplatin, cis ‐[Pt(NH 3 ) 2 (1‐MeC‐ N3 )(H 2 O)] 2+ ( 6 ; 1‐MeC: 1‐methylcytosine), with the electrophile [Pd(en)(H 2 O) 2 ] 2+ (en: ethylenediamine) at pH≈6 yields a kinetic product X which is likely to be a dinuclear Pt,Pd complex containing 1‐MeC − ‐ N3 , N4 and OH bridges, namely cis ‐[Pt(NH 3 ) 2 (1‐MeC − ‐ N3 , N4 )(OH)Pd(en)] 2+ . Upon addition of excess Ag + ions, conversion takes place to form a thermodynamic product, which, according to 1 H NMR spectroscopy and X‐ray crystallography, is dominated by a μ ‐NH 2 bridge between the Pt II and Pd II centers. X‐ray crystallography reveals that the compound crystallizes out of solution as a dodecanuclear complex containing four Pt II , four Pd II , and four Ag + entities: [{Pt 2 (1‐MeC − ‐ N3 , N4 ) 2 (NH 3 ) 2 (NH 2 ) 2 (OH)Pd 2 (en) 2 Ag} 2 {Ag(H 2 O)} 2 ](NO 3 ) 10 ⋅ 6 H 2 O ( 10 ) is composed of a roughly planar array of the 12 metal ions, in which the metal ions are interconnected by μ‐ NH 2 groups (between Pt and Pd centers), μ ‐OH groups (between pairs of Pt atoms), and metal–metal donor bonds (Pt→Ag, Pd→Ag). The four 1‐methylcytosinato ligands, which are stacked pairwise, as well as the four NH 3 ligands and parts of the en rings, are approximately perpendicular to the metal plane. Two of the four Ag ions (Ag2, Ag2′) of 10 are labile in solution and show the expected behavior of Ag + ions in water, that is, they are readily precipitated as AgCl by Cl − ions. The resulting pentanuclear complex [Pt 2 Pd 2 Ag(1‐MeC − ) 2 (NH 2 ) 2 (OH)(NH 3 ) 2 (en) 2 ](NO 3 ) 4 ⋅ 7 H 2 O ( 11 ) largely maintains the structural features of one half of 10 . The other two Ag + ions (Ag1, Ag1′) of 10 are remarkably unreactive toward excess NaCl. In fact, the pentanuclear complex [Pt 2 Pd 2 AgCl(1‐MeC − ) 2 (NH 2 ) 2 (OH)(NH 3 ) 2 (en) 2 ](NO 3 ) 3 ⋅ 4.5 H 2 O ( 12 ), obtained from 10 with excess NaCl, displays a Cl − anion bound to the Ag center (2.459(3) Å) and is thus a rare case of a crystallized “AgCl molecule”.