Interaction of (amine)M(II) complexes (amine=dien, en; M=Pd, Pt) with purine nucleoside 2′-, 3′- and 5′-monophosphates—the role of the phosphate site for specific metal fragment–nucleotide recognition by macrochelation

The pH-dependent interaction of [Pd(dien)(H2O)]2+ with adenosine and guanosine 2′- and 3′-monophosphates at molar ratios R=1 and 3 has been studied by potentiometric and NMR techniques. The absence of additional intramolecular stabilisation of the N7 coordination mode by (amine)NH⋯O(phosphate) hydrogen bonding, as for 5′-AMP2− or 5′-GMP3−, leads to reversal of the intrinsic binding ratio log [β(BM1)/β(M7B)] in favour of N1 coordination for mononuclear (dien)Pd(II) complexes of the purine 2′- and 3′-nucleotides. Outer-sphere κ2N7,O(phosphate) macrochelation is also responsible for the formation of a specific μ-N1,N7 bridged cyclic tetramer [{(en)Pd(5′-GMP)}4]4− in the pH range 5.5–9.5. Both inner- and outer-sphere κ2N3,O(phosphate) macrochelation lead at R=3 to a dramatic enhancement of (en)Pd(II) binding to N3 of 2′-GMP3− in comparison to 3′- or 5′-GMP3−. Reaction of [{Pt(dien)}2(2′-GMP-μ-N1,N7)]+ with [Pt(en)(H2O)2]2+ affords both types of macrochelate at approximately 1:1 ratio, namely [{Pt(dien)}2(2′-GMP-μ3-N1,N3,N7,O(P)){Pt(en)}3+ and [{Pt(dien)}2(2′-GMP-μ3-N1,N3,N7) {Pt(en)H2O)}]3+ with respectively direct (en)PtO(phosphate) and outer-sphere (amine)NH⋯O(phosphate) hydrogen bonding. Following HPLC separation, these trinuclear products could be characterised by NMR and FAB-MS.