Terpyridine Groups Research Articles

Enantiomerically pure chiral coordination polymers: synthesis, spectroscopy, and electrochemistry in solution and on surfaces.

The two enantiomerically pure bridging ligands (+/-)-[ctpy-x-ctpy] have been prepared employing a two-fold stereospecific alkylation reaction of the enantiomerically pure, chiral terpyridyl-type ligands (+/-)-ctpy. The reaction of each of the enantiomerically pure bridging ligands with Fe(2+) gives rise to chiral coordination polymers whose formation and stoichiometry were followed spectrophotometrically. An assignment of the absolute configuration of the formed helical polymeric structures was carried out on the basis of circular dichroism studies. Highly ordered domains (as determined from STM imaging) of the enantiomerically pure chiral redox polymers could be prepared via the interfacial reaction, over an HOPG substrate, of the bridging ligand in CH(2)Cl(2) and FeSO(4) in water. The degree of polymerization was estimated to be up to 60 from analysis of the STM images of the highly ordered domains on HOPG. The helicality of the domains was compared to the configuration obtained from the circular dichroism studies. The electrochemical properties of the polymers were investigated using cyclic voltammetry and the results compared to those of the respective monomeric complexes. The redox behavior of the iron centers in the polymer was comparable to that of the monomeric complex [Fe((-)-ctpy)(2)](PF(6))(2) as well as to that of [Fe(tpy)(2)](PF(6))(2). The polymeric materials undergo electrodeposition following the two-electron reduction of each bridging ligand unit (one electron per terpyridine group). No ligand-mediated metal-metal interactions were evident from the cyclic voltammetric measurements, suggesting that the metal centers act independently. Moreover, oxidation of the metal centers within the polymeric materials did not give rise to electrodeposition.

Redox Active Ordered Arrays via Metal Initiated Self-Assembly of Terpyridine Based Ligands

The interfacial reaction of terpyridyl-pendant poly-amido amine (PAMAM) dendrimers (dend-n-tpy; n = 4, 8, 32) and of bis-terpyridine containing bridging ligands (tpy-bridge-tpy), dissolved in CH2Cl2, with aqueous Fe2+ or Co2+ gives rise to film formation on HOPG and Pt(111) single crystal surfaces. Molecularly resolved STM images reveal that these films form highly ordered 2-D trigonal arrays, which appear to be composed of one-dimensional polymeric strands with a repeat unit of (tpy-dendrimer-tpy-M)x, in the case of dendrimers, or (tpy-bridge-tpy-M)x, in the case of the bridging ligands. An extensive study with ligands of tailored architecture has been carried out, providing insight on the relationship between the ligand's molecular structure and that of the resulting films. The formation of ordered domains appears to be controlled, at least in part, by the rigidity of the molecule containing the terpyridine groups. Films derived from bridging ligands containing long chains did not give rise to observabl...

Toward artificial ribonucleases: design and synthesis of 2'-O-methyloligonucleotides with a terpyridine-copper(II) complex.

In order to construct an antisense 2'-O-methyloligonucleotide with an internal terpyridine-Cu(II) complex, a novel synthon was synthesized. This synthon was a 2'-deoxy-uridine-3'-phosphoramidite derivative with a terpyridine group at the 5'-O and a dimethoxytritylated hydroxypropyl group at the C-5. The antisense agent cleaved the RNA site-specifically and in a moderate yield.

Five-nuclear complexes of zinc (II) phthalocyanine with directly linked terpyridine ligands

The synthesis of a novel ligand, in which four terpyridine groups are directly connected to a zinc (II) phthalocyanine unit, is described. Preliminary absorption, electrochemical, and fluorescence results are indicative of strong electronic coupling among the metal centers.

Modulation of RNase H activity by modified DNA probes: Major groove vs minor groove effects

We have previously prepared ribozyme mimics and chemical nucleases from modified DNA containing pendant bipyridine and terpyridine groups. The ability of these modified DNA probes to support RNase H cleavage of complementary RNA is described. DNA/RNA duplexes were formed using DNA probes designed to deliver metal complexes via either the major groove or the minor groove of the duplex. The duplexes were treated with Escherichia coli RNase H. Modifications in the major groove produced the same RNA cleavage pattern as unmodified DNA probes. However, minor groove substituents inhibited RNA cleavage over a four-base region. Comparison was made with a DNA probe containing a 2′-OMe modification. Our results support enzyme binding in the minor groove of a DNA/RNA duplex. We do not observe cleavage directly across from the modified nucleoside. The RNA cleavage efficiency effected by RNase H and a DNA probe decreases as follows: unmodified DNA ≥ C-5 modified DNA ⪢ C2′-modified DNA > C1'-modified DNA. Results with 28-mer RNA substrates roughly parallel those obtained with a 159-mer RNA target. The differences observed between low and high MW RNA substrates can be explained by a much higher enzyme-substrate binding constant for the high MW target.

Self-assembly of a heteroduplex helicate from two different ligand strands and Cu(II) cations.

Cu(II) ions have been reacted with a 1/1 mixture of two linear ligands, one containing three 2,2'- bipyridine groups and the other three 2,2':6',2"-terpyridine groups. Absorption spectroscopy and fast atom bombardment mass spectrometry indicate the formation of a trinuclear complex containing one ligand of each kind. Determination of the crystal structure of this compound has confirmed that it is indeed a linear trinuclear complex in which two different ligands are wrapped in a helical fashion around the pentacoordinated metal ions. The central coordination geometry is trigonal bipyramidal; the two lateral Cu(II) ions are in a square pyramidal environment. Thus, a heteroduplex helicate is formed by the self-assembly of two different ligand strands and three specific metal ions induced by the coordination number and geometry of the latter. The self-assembly process may be considered to result from the reading of the steric and binding information present in the two ligands by Cu(II) ions through a pentacoordination algorithm. The same ligands have been shown earlier to yield homoduplex helicates from ions of tetrahedral and octahedral coordination geometry and strands of bidentate bipyridines and tridentate terpyridines, respectively. These two types of artificial double helical species may be related on one hand to the natural homoduplex nucleic acids and on the other hand to the DNA:RNA heteroduplex.

A monodentate 1,3-diphenyl-2-triazeno terpyridineplatinum(II) complex

The compound (l,3-diphenyl-2-triazeno )(2,2',2- terpyridine)platinum(II) perchlorate dimethylformamide solvate (1) is formed by reaction of dpt (dptH = 1,3-diphenyltriazene) and [Pt(tpy)Cl]Cl (tpy = terpyridine) in the presence of excess base (NEt3). There are two independent cations in the asymmetric unit. The platinum centers have a monodentate triazeno ligand with the remaining coordination sites occupied by the terpyridine group. The crystal packing is dominated by π-π stacking interactions, and metal-metal interactions are conspicuously absent.

A diphenylformamidinate-bridged terpyridineplatinum(II) dimer

The compound μ-N,N' -diphenylformamidinatobis[ 2,2',2-terpyridineplatinum(II)] perchlorate mono hydrate (1) is formed by reaction of diphenylformamidine and [Pt(tpy)Cl]Cl (tpy = terpyridine) in the presence of excess base. The two platinum centers are bridged by a single diphenylformamidinato ligand with the remaining coordination geometry completed by the terpyridine group. The platinum-platinum separation is 3.049 (1) A.

Mechanism of nucleophilic substitution in palladium(II) complexes of terpyridine

Rates of nucleophilic substitution reactions (i) [terpy = terpyridine; X = Cl, Br, I, N 3, NO2; Y = Cl, Br, N 3, I (NH 2) 2CS] have been [Pd(terpy)X] + Y − → [Pd(terpy)Y] + + X − (i) measured in methanol at 25°C and μ = 0.1. The results are compared with those relating to the analogous reactions (ii) [3-NHpd = 3-azapentane-l,5-diamine] on the quantitative basis of nucleophilic discrimination factors and intrinsic reactivities: [Pd(3-NHpd)X] + + Y − → [Pd(3-NHpd)Y] + + X − (ii) The larger reactivity of [Pd(terpy)X] + is interpreted on the assumption that the chelating terpyridine group enhances more effectively the electrophilicity of palladium(II) through π-interaction than 3-azapentane-1,5-diamine does.