[Show abstract][Hide abstract] ABSTRACT: The synthesis of a series of banana-shaped structures has been carried out, in which the bend unit is formed by a 4,4’-methylenedianiline or 3,3’-methylenedianiline core bearing two symmetric pyridylimine linkages to di- and tri- alkoxyphenylester moieties on the side arms. The molecules, in addition to providing an elongated aromatic central core associated with liquid crystal (LC) molecules, also provide binding sites for metals. The methylenedianiline spacer incorporates phenylene groups that sterically prevent the two binding sites from co-ordinating to a single metal centre and the central methylene unit introduces enhanced flexibility into the ligand backbone. Furthermore, complexes have been formed by the co-ordination between 3, 3’-methylenedianiline containing ligands and Cu (I) ions [Cu2(3a-c)2][PF6]2. Electrospray Mass Spectrometry (ESMS) and Fast Atom Bombardment Mass Spectrometry (FABMS) showed the formation of dimeric species; [Cu (L)2][PF6]2. Finally,thermal analysis of the ligands (1a-d, 2a-d, 3a-c and 4a-d) andCu complexes [Cu2(3a-c)2][PF6]2 has been carried out in order to investigate the phase properties of these materials. None of the banana-shaped ligands and the metal complexes [Cu2(3a-c)2][PF6]2 showed any mesophases.
[Show abstract][Hide abstract] ABSTRACT: The enantiomeric resolution of an extended range of di-metallo supramolecular triple-helical molecules are reported. The ligands for all complexes are symmetric with two units containing an aryl group linked via an imine bond to a pyridine. Alkyl substituents have been attached in different positions on the ligand backbone. Previous work on the parent compound, whose molecular formula is [Fe(2)(C(25)H(20)N(4))(3)]Cl4, showed that it could be resolved into enantiomerically pure solutions using cellulose and 20 mM aqueous sodium chloride. In this work a range of mobile phases have been investigated to see if the separation and speed of elution could be increased and the amount of NaCl co-eluted with the compounds decreased. Methanol, ethanol and acetonitrile were considered, together with aqueous NaCl : organic mixtures. Effective separation was most often achieved when using 90% acetonitrile : 10% 20 mM NaCl (aq) w/v, which gives scope for scaling up to incorporate the use of HPLC. The overall most efficient (i.e. fastest) separation was generally achieved where the cellulose column was packed with 20 mM NaCl (aq) and the column first eluted with 100% acetonitrile, then with 75% ethanol : 25% 20 mM NaCl (aq) until the M enantiomer had fully eluted and finally with 90% acetonitrile : 10% 20 mM NaCl (aq) until the P enantiomer had been collected. The sequence of eluents ensured minimum NaCl accompanying the enantiomers and minimum total solvent being required to elute the enantiomers, especially the second one, from the column. No helicate with a methyl group on the imine bond could be resolved and methyl groups on the pyridine rings also have an adverse effect on resolution.
Full-text · Article · Mar 2007 · Dalton Transactions
[Show abstract][Hide abstract] ABSTRACT: The effect of changes in the angles at the connection points of linear/circular helicates is explored as a route to control the nuclearity and architecture of metallo-supramolecular arrays. This effect is probed by changing the geometry of the metal centre used to assemble bis-pyridylimine ligands that contain a 1,3-bis(aminomethyl) benzene spacer group. Tetrahedral metal ions favour linear dimers, whereas octahedral nickel(II) predominantly gives a triangular circular helicate. Five-coordinate copper(II) falls in the middle of these extremes and results in the formation of solvent-dependent mixtures of dimer and trimer. The trinuclear, triangular, circular helicate structures, which result from coordination to copper(II) and nickel(II), are structurally characterised by X-ray crystallography and reveal that the units can aggregate into hexagonal arrays that contain anion-filled tube-like channels in the solid state.
[Show abstract][Hide abstract] ABSTRACT: The DNA binding of a dicationic pyridylimine-based dicopper(I) metallosupramolecular cylinder is reported together with its ability to act as an artificial nuclease. The cylinder binds strongly to DNA; more strongly than the spherical dication [Ru(phen)(3)](2+) (phen=1,10-phenanthroline), but more weakly than the corresponding tetracationic cylinders. DNA coiling effects are not observed with this dication, in contrast to the situation with the previously reported tetracationic cylinder involving a similar ligand. Linear dichroism (LD) data suggests that the dicopper cylinder binds in a different orientation from that of the tetracationic iron cylinder. Furthermore, the dicopper cylinder shows DNA-cleavage activity in the presence of peroxide. Of particular note is that the cylinder displays a marked and unusual ability to cleave both DNA strands at the same site, probably reflecting its dinuclear nature and possibly its mode of binding to the DNA.
[Show abstract][Hide abstract] ABSTRACT: The effect of inter-strand and intra-strand interactions is explored in a metallo-supramolecular system in which the metal-ligand coordination requirements may be satisfied by more than one different supramolecular architecture. This is achieved by introducing alkyl substituents onto the spacers of readily prepared bis(pyridylimine) ligands. The alkyl substituents induce twisting within the ligand strand and this intra-strand effect favours formation of helical architectures. The alkyl substituents also introduce inter-strand CH.pi interactions into the system. For the smaller methyl group these are most effectively accommodated in a trinuclear circular helicate architecture. A solution mixture of dinuclear double-helicate and trinuclear circular helicate results from which, for copper(I), the trinuclear circular helicate crystallises. The CH.pi interactions endow the circular helicate with a bowl-shaped conformation and the triangular unit aggregates into a tetrahedral ball-shaped array. Low-temperature NMR studies indicate that the CH.pi interactions also confer a bowl-shaped conformation on the triangle in solution. The larger ethyl groups can sustain intra-strand CH.pi interactions in the lower nuclearity double-helical system and this is the unique architecture for that ligand system in both solution and the solid state. Crystal structures are described for both the copper(I) and silver(I) complexes. Thus we show that intra-strand interactions may be used to induce helicity within this system, while the nuclearity of the array can be prescribed by the inter-strand interactions.
[Show abstract][Hide abstract] ABSTRACT: Luminescent Ln-Pt2 metallohairpin complexes have been developed, and their intercalative recognition with DNA has been demonstrated with linear dichroism spectroscopy. The heterotrimetallic complexes were formed in a one-step reaction, by assembly of an aminopolycarboxylate ligand, a platinum terpyridine unit, and the lanthanide salt. The metallohairpin complexes bear a neutral lanthanide moiety and two positively charged platinum-containing intercalating units. The Nd(III) analogues are luminescent in the near infrared, and this near-IR luminescence is retained upon binding to DNA. The DNA recognition was demonstrated by linear dichroism spectroscopy. The linear dichroism spectra suggested that the complexes bind perpendicular to the DNA helical axis, confirming intercalative recognition accompanied by dramatic stiffening of DNA, which suggests bis-intercalation of the complex.
No preview · Article · Sep 2003 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: Bowls to balls: Triangular bowl-shaped copper(I) circular helicates based on pyridylimine ligands are assembled by mixing readily available reagents. The bowl-shaped topography of the triangles controls the supramolecular aggregation of four of these units into a chiral tetrameric ball-shaped structure (see picture) held together by face - edge (CH ⋯ π) π interactions and CH ⋯ F interactions.
No preview · Article · Nov 2002 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] ABSTRACT: Multiple competing molecular interactions (metal-ligand, pi-stacking and hydrogen-bonding) in the silver(I) complexes of 4'-thiomethyl-2,2':6',2"-terpyridine give rise to a range of different molecular architectures, in which the metal-ligand coordination requirements are satisfied in quite different ways. Polynuclear supramolecular spirals, aggregated mononuclear and aggregated dinuclear units are all structurally characterised. The metallo-supramolecular architecture obtained displays a remarkable dependence both on the choice of non-coordinated anion and the type of solvent used (coordinating or non-coordinating). The anion dependence is particularly surprising, since the anions are not integrated into the centre of the supramolecular structure. The solution behaviour is also solvent and anion dependent, with aggregation of planar mononuclear cations observed in acetonitrile, but oligonuclear spiral species implicated in nitromethane. The extraordinarily variable geometries of these systems suggest that they provide a novel example of the "frustration" principle, in which opposing tendencies cannot simultaneously be satisfied and identify an alternative approach to the design of metallo-supramolecular systems whose structure is responsive to external agents.
[Show abstract][Hide abstract] ABSTRACT: Enantiopure dinuclear silver(I) double helicates were prepared in simple one-pot reactions from commercially available starting materials and the pure complexes isolated as the hexafluorophosphate salts. The (R),(+) and (S),(−) enantiomers of 1,1′-binaphthalene-2,2′-diamine were used as spacer groups and reacted with pyridine-2-carbaldehyde to form chiral didentate imine ligands. These chiral ligands predetermine the chirality of the helicates: the R spacer gives a P helicate and the S spacer an M helicate. The dinuclear double helical structures are confirmed by single crystal X-ray analysis and their persistence in solution is supported by inter-strand NOE data. Enantiopure copper(I) dinuclear species were also prepared by similar one-pot procedures and analysed by 1H NMR, mass spectrometry and circular dichroism.
No preview · Article · Jan 2002 · Journal of the Chemical Society Dalton Transactions
[Show abstract][Hide abstract] ABSTRACT: Arc-shaped helicate units are readily prepared from simple pyridylimine ligands. The arc-shaped topography controls their aggregation and a four-unit circular array of 2.5 nm diameter results (see scheme).
No preview · Article · Mar 2001 · Angewandte Chemie