Self-assembled mononuclear palladium(II) based molecular loops

The meta-pyridine appended bidentate ligands L1, L2 and L3, crafted with flexible polyether spacer, are prepared by condensation of nicotinoyl chloride hydrochloride with di, tri-, and tetra-ethylene glycol, respectively. Self-assembled palladium(II) based mononuclear molecular loops of general formula cis-[Pd(N–N)(L)](NO3)2 are obtained exclusively by combining 1 equiv. of a ligand L with 1 equiv. of a cis-protected palladium(II) component, cis-[Pd(N–N)(NO3)2]. Complexation of 2 equiv. of L with 1 equiv. of palladium(II) nitrate also resulted mononuclear complexes, i.e. [Pd(L)2](NO3)2. The ligands used in the complexation reactions are L1, L2 and L3 where as the cis-protecting units N–N employed are ethylenediamine (en), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen). Thus 12 number of mononuclear complexes are prepared using all possible combination of above mentioned three number of ligands and four variety of palladium(II) components. Large chelate rings are realized irrespective of the spacer length or type of palladium(II) component used. All the resulted compounds are characterized by NMR and ESI-MS techniques and the structure of cis-[Pd(en)(L1)](NO3)2, cis-[Pd(bpy)(L1)](NO3)2 and [Pd(L3)2](NO3)2 are confirmed by single crystal X-ray diffraction. The binding abilities of cis-[Pd(phen)(L1)](NO3)2, cis-[Pd(phen)(L2)](NO3)2 and cis-[Pd(phen)(L3)](NO3)2 with DNA has been investigated by ethidium bromide displacement assay and gel electrophoresis.

Mononuclear self-assembled palladium(II) based molecular loops are prepared by combining meta-pyridine appended bidentate ligands crafted with flexible polyethylene glycol spacers with a variety of palladium(II) components. A family of 12 compounds with large chelate rings has been realized both in solution and a few in solid states. All the molecules are water soluble and exclusively mononuclear in nature.Figure optionsDownload as PowerPoint slideHighlights
► Water soluble mononuclear self-assembled Pd(II) based molecular loops.
► Molecular chair like structure demonstrated via crystallographic study.
► Binding of few molecular loops with DNA.