The development of a multiarm metal-centered DNA building block as a precursor for the construction of supramolecular assemblies has relied upon the preparation of a Ni(II)-1,4,8,11-tetrazacyclotetradecane ligand (cyclam) functionalized with four linkers. This complex can be incorporated into a support-bound DNA sequence and the remaining three linkers can then be elongated by DNA synthesis. The result is a Ni(II)-cyclam complex tethering four 20-mer DNA strands. This building block, designed to be tetrahedral in nature, can in principle be used to form tetrahedral assemblies. These assemblies can be designed to be of known size and composition or permitted to grow into complexes of essentially infinite size, ideally the macroscopic version of a crystal.

Nucleic acids can assemble into higher-order structures on the basis of complementary Watson-Crick base pairing. This selfassembly process has been exploited by a number of researchers [1][2][3][4] in the "bottom-up" approach to the generation of nonbiological structures of nanoscale dimensions. [5] In some studies, these assemblies have been based solely upon complementary DNA hybridization in which branch points are created by double-crossover structures [6,7] (generated as immobile junctions [8][9][10] ) that are similar to those of DNA recombination intermediates; higher-order DNA networks can be made by this approach. [11,12] In other cases, DNA sequences have been tethered to multifunctional organic cores [13,14] or inorganic complexes [15][16][17][18][19] that are capable of selfassembling into more-complex networks such as dendrimers. [20,21] Oligonucleotides have been tethered to gold nanoparticles, [2,22,23] and complementary hydrogen bonding resulted in the formation of large assemblies that were used for diagnostics. [24,25] Nucleic acids can also be functionalized by conjugation, and this approach has led to the development of nanostructures and devices, [26,27] DNA-protein conjugates, [24] and the assembly of two-and three-dimensional networks. DNA-based nanoscale assemblies have been used for the construction of nanowires. [28,29] Herein we describe the preparation of six-oligonucleotide-armed ruthenium(ii) tris-(bipyridyl)-centered complexes as precursors for the generation of supramolecular nanoscale assemblies.In the present monomer design, we chose [Ru(bpy) 3 ] 2+with a Ru II ion bound to three bipyridine (bpy) ligands as a core, and the DNA arms were tethered at the 4-and 4'-positions of each bipyridine ligand (Figure 1). Although [Ru(bpy) 3 ] 2+ exists in two enantiomeric forms, substitution at all three 4 and 4' sites results in an octahedral arrangement of the substituents in both enantiomers. First, enantiomerically pure DNA-[Ru(bpy) 3 ] 2+ conjugates should be attainable by appropriate chromatographic resolution of the Ru complexes as has been described for related ruthenium complexes, [30][31][32] followed by their incorporation into DNA conjugates. However, such chromatographic separations are not yet routine, and successful isomer resolution still depends in part upon the nature of the complex. The choice of sequences

Ruthenium(II) bis(terpyridine) complexes have been prepared with two triethylene glycol linkers to which DNA sequences have been attached; hybridization at various complex ratios results in linear arrays of varying lengths.

Nucleic acids can assemble into higher-order structures on the basis of complementary Watson-Crick base pairing. This selfassembly process has been exploited by a number of researchers [1][2][3][4] in the "bottom-up" approach to the generation of nonbiological structures of nanoscale dimensions. [5] In some studies, these assemblies have been based solely upon complementary DNA hybridization in which branch points are created by double-crossover structures [6,7] (generated as immobile junctions [8][9][10] ) that are similar to those of DNA recombination intermediates; higher-order DNA networks can be made by this approach. [11,12] In other cases, DNA sequences have been tethered to multifunctional organic cores [13,14] or inorganic complexes [15][16][17][18][19] that are capable of selfassembling into more-complex networks such as dendrimers. [20,21] Oligonucleotides have been tethered to gold nanoparticles, [2,22,23] and complementary hydrogen bonding resulted in the formation of large assemblies that were used for diagnostics. [24,25] Nucleic acids can also be functionalized by conjugation, and this approach has led to the development of nanostructures and devices, [26,27] DNA-protein conjugates, [24] and the assembly of two-and three-dimensional networks. DNA-based nanoscale assemblies have been used for the construction of nanowires. [28,29] Herein we describe the preparation of six-oligonucleotide-armed ruthenium(ii) tris-(bipyridyl)-centered complexes as precursors for the generation of supramolecular nanoscale assemblies.In the present monomer design, we chose [Ru(bpy) 3 ] 2+with a Ru II ion bound to three bipyridine (bpy) ligands as a core, and the DNA arms were tethered at the 4-and 4'-positions of each bipyridine ligand (Figure 1). Although [Ru(bpy) 3 ] 2+ exists in two enantiomeric forms, substitution at all three 4 and 4' sites results in an octahedral arrangement of the substituents in both enantiomers. First, enantiomerically pure DNA-[Ru(bpy) 3 ] 2+ conjugates should be attainable by appropriate chromatographic resolution of the Ru complexes as has been described for related ruthenium complexes, [30][31][32] followed by their incorporation into DNA conjugates. However, such chromatographic separations are not yet routine, and successful isomer resolution still depends in part upon the nature of the complex. The choice of sequences