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Edwin C Constable

Publications and source records attributed to Edwin C Constable.

At least 19 recordsLinked to original sources
PubMed2006

Quantification of single-stranded nucleic acid and oligonucleotide interactions with metal ions by affinity capillary electrophoresis: part I.

The interactions between oligonucleotides and inorganic cations have been measured by capillary zone electrophoresis. With increasing concentrations of divalent cations (Ca(2+), Mg(2+), Mn(2+) and Ni(2+)) in the running buffer, the migration behavior was evaluated by calculation of the binding constants. Besides these fundamental studies of binding equilibria, different buffer components, tris(hydroxymethyl)aminomethane and 3-(N-morpholino)propanesulfonic acid, have been investigated and their effects on metal ion binding quantified.

Calcium↗
PubMed2006

Understanding the structural properties of a dendrimeric material directly from powder X-ray diffraction data.

Complete structure determination of an early-generation dendrimeric material has been carried out directly from powder X-ray diffraction data, using the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement. This work represents the first application of modern direct-space techniques for structure determination from powder X-ray diffraction data in the case of a dendrimeric material and paves the way for the future application of this approach to enable complete structure determination of other dendrimeric materials that cannot be prepared as single crystal samples suitable for single crystal X-ray diffraction studies.

Letter↗
PubMed2006

Structural development of free or coordinated 4'-(4-pyridyl)-2,2':6',2''-terpyridine ligands through N-alkylation: new strategies for metallamacrocycle formation.

A series of N-alkylated derivatives of [Ru(pytpy)(2)]2+ (pytpy=4'-(4-pyridyl)-2,2':6',2''-terpyridine) has been synthesised and characterised. These include both model and functionalised complexes that complement previously reported iron(II) analogues. Reaction of [Ru(pytpy)(2)]2+ with bis[4-(bromomethyl)phenyl]methane leads to the formation of a [2+2] ruthenamacrocycle. Related ferramacrocycles could not be accessed by this route, and instead were prepared in two steps by first reacting bis[4-(bromomethyl)phenyl]methane or 4,4'-bis(bromomethyl)biphenyl with two equivalents of pytpy, and then treating the resulting bis(N-alkylated) product with iron(II) salts.

Alkylation↗
PubMed2006

A hydrogen-bonded dimer of 13-hydroxy-13-[(triisopropylsilyl)ethynyl]pentacen-6(13H)-one.

The title compound, C33H34O2Si, has been obtained as a product in the synthesis of 6,13-bis[(triisopropylsilyl)ethynyl]-6,13-dihydropentacene-6,13-diol. The solid-state structure reveals a dimer, with strong hydrogen bonds holding the two molecules in a face-to-face arrangement [O...O = 2.746 (2) A and O-H...O = 173 (2) degrees ]. Within each dimer, the pentacene units are pi-stacked (the distance between the mean least-squares planes of 22 C atoms is 3.60 A).

Journal Article↗
PubMed2005

Metal-directed synthesis and photophysical studies of trinuclear v-shaped and pentanuclear x-shaped ruthenium and osmium metallorods and metallostars based upon 4'-(3,5-dihydroxyphenyl)-2,2':6',2''-terpyridine divergent units.

A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, {M(tpy)2} motifs (M=Ru or Os; tpy=2,2':6',2''-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)]2+ (X=Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited {Ru(tpy)2}* domains is most significant.

Journal Article↗
PubMed2005

Formation of [2 + 2] diruthenium(II) metallomacrocycles from ligands containing 2,2':6',2''-terpyridine domains linked through flexible polyethyleneoxy spacers.

The syntheses of three ligands containing two terpy metal-binding domains linked through flexible polyethyleneoxy spacers are described. These ligands have been utilised as building blocks in a two-step process for the formation of a series of dinuclear ruthenium(II) metallomacrocycles of the type [Ru2L2]4+. Employing a two-step methodology allows the formation of homoleptic ([Ru2L2]4+) and heteroleptic ([Ru2LL']4+) species in which the ligands differ in the length of the polyethyleneoxy spacer connecting each terpy motif. Homoleptic metallomacrocycles have been characterised through single crystal X-ray diffraction studies, while 2D-NMR spectroscopy has been employed for the characterisation of the heteroleptic species.

Journal Article↗
PubMed2005

Octyl-decorated Fréchet-type dendrons: a general motif for visualisation of static and dynamic behaviour using scanning tunnelling microscopy?

A detailed STM study of monolayers of 3,5-bis[(3,5-bisoctyloxyphenyl)methyloxy]benzaldehyde and 3,5-bis[(3,5-bisoctyloxyphenyl)methyloxy]benzyl alcohol adsorbed on graphite is presented. Very highly resolved scanning tunnelling microscopy images are observed at room temperature in air allowing the analysis of the conformation of the adsorbed molecules. These long-chain alkyl-decorated Fréchet-type dendrons are a powerful assembly motif and initially form a pattern based on trimeric units, assembled into hexagonal host structures with a pseudo-unit cell of seven molecules, one of which remains highly mobile. Over time, the supramolecular ordering changes from a trimeric into a dimeric pattern. The chirality arising from the adsorption onto a surface of the dendrons is discussed.

Journal Article↗
PubMed2005

Conformational analysis of self-organized monolayers with scanning tunneling microscopy at near-atomic resolution.

We describe the synthesis and a novel approach to the conformational analysis of 2,2'-bipyridines (bpy) bearing aromatic rich Frechet-type dendritic wedges of the first and second generation as substituents. The evaporation of solutions of these new ligands on graphite surfaces under ambient conditions results in the formation of self-organized monolayers. Scanning tunneling microscopy (STM) investigations of the monolayers under ambient conditions (air, 298 K) gave images at submolecular and near-atomic resolution. The analysis of the STM images includes the following processes: (i) identification and reproduction of potential homoconformational domains, (ii) exclusion of improper data using quality criteria for drift and feedback artifacts, (iii) compilation of running averages and checking for averaging artifacts, (iv) analysis of three-dimensional and contour plots, (v) calculation of the HOMO properties of the free molecules, and (vi) final conformational assignment based on all accessible information. Following this procedure, two different conformations could be assigned to domains observed in the monolayers of the first-generation (G1) and second-generation (G2) dendritic compounds. Homoconformational domains are observed side-by-side. The different conformations arise from syn or anti arrangements at the ether substituents. An additional conformational effect is found upon treating the G1 domains with HCl gas, when a partial rearrangement of the bpy from trans to cis occurs, concomitant with protonation.

Journal Article↗
PubMed2005

Hairpin helicates: a missing link between double-helicates and trefoil knots.

We have prepared a novel ligand in which two qpy metal-binding domains are linked by a polyoxyethylene spacer. The new ligand reacts with copper(ii) salts to form dinuclear double helicates with a hairpin structure. The hairpin complex and a model complex have been structurally characterised. The hairpin structure is formed regioselectively as the head-to-tail (HT) stereoisomer. Detailed electrochemical and spectroelectrochemical studies of the complexes are reported.

Journal Article↗
PubMed2005

Conducting polymers containing in-chain metal centers: electropolymerization of oligothienyl-substituted {M(tpy)2} complexes and in situ conductivity studies, M = Os(II), Ru(II).

The electropolymerization of a series of Ru and Os bis-terpyridine complexes that form rodlike polymers with bithienyl, quaterthienyl, or hexathienyl bridges has been studied. Absorption spectroscopy, scanning electron microscopy, and cyclic voltammetry have been used to characterize the monomers and resulting polymer films. The absolute dc conductivity of the quaterthienyl-bridged {Ru(tpy)2} and {Os(tpy)2} polymers is unusually large and independent of the identity of the metal center at 1.6 x 10(-3) S cm(-1). The maximum conductivity occurs at the formal potential of each redox process, which typically is observed for systems where redox conduction is the dominant charge transport mechanism. Significantly, the dc conductivity of the metal-based redox couple observed in these polymers is 2 orders of magnitude higher thanthat of a comparable nonconjugated system.

Journal Article↗
PubMed2004

Self-assembled monolayers of Ru/Os dinuclear complexes: probing monolayer structure and interaction energies by electrochemical means.

Monolayers of [Ru(bpy)2(micro-1)M2][PF6]4 salts (M = Os, Ru; bpy = 2,2'-bipyridine, 1 = 4'-(2,2'-bipyridin-4-yl)-2,2':6',2' '-terpyridine, tpy = 2,2':6',2' '-terpyridine, and 2 = 4'-(4-pyridyl)-2,2':6',2' '-terpyridine) were self-assembled on platinum and investigated by fast-scan electrochemistry. The electrochemistry of the complexes in solution and confined to the surface in self-assembled monolayers (SAMs) exhibited an almost ideal behavior. Scan-rate-dependent measurements of the peak current density (jp) were used to determine interaction energies within the monolayer. It is shown that the tpy coordination sites of the dinuclear complexes interact more strongly within the SAM than the bipyridine-coordinated fragments. This result was supported by peak potential shifts, which are due to interaction forces in SAMs. The alignment of the rodlike complexes relative to the surface is discussed, and the results of molecular mechanics calculations indicate that the species adopt a tilted orientation.

Adsorption↗
PubMed2004

Chiral induction in a ribose-decorated metallostar through intrinsic and interionic diastereomeric interactions.

A ribose-functionalized bpy ligand has been prepared and shown to give modest diastereomeric excesses of Lambda-[FeL(3)](2+) complexes; interconversion of Delta and Lambda cations is relatively fast, and in CHCl(3), the favored complexes with Delta- or Lambda-TRISPHAT counterions are homochiral, (Delta(+)Delta(-)) or (Lambda(+)Lambda(-)). In the case of the Delta-TRISPHAT salt, a single diastereomer is observed (de > or = 96%).

Circular Dichroism↗
PubMed2004

Preparation and structural characterisation of terpy-cored dendrimers and dendriplexes.

2,2':6',2''-Terpyridine (terpy) ligands and their iron(II) and cobalt(II) complexes bearing first and second generation Frechet-type dendritic wedges have been prepared and structurally characterised. The rotational freedom within the dendritic wedge results in a great diversity in conformational space. Structural studies are reported on first generation species and their metal complexes, and the variety of inter- and intramolecular interactions which dominate the conformation of the dendrimer and the packing of the molecules (ions) in the lattice are discussed.

Journal Article↗