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Biomedical subjects

Neil Robertson

Publications and source records attributed to Neil Robertson.

14 recordsLinked to original sources
PubMed2007

DiscoverySpace: an interactive data analysis application.

DiscoverySpace is a graphical application for bioinformatics data analysis. Users can seamlessly traverse references between biological databases and draw together annotations in an intuitive tabular interface. Datasets can be compared using a suite of novel tools to aid in the identification of significant patterns. DiscoverySpace is of broad utility and its particular strength is in the analysis of serial analysis of gene expression (SAGE) data. The application is freely available online.

Animals↗
PubMed2006

Structural and magnetic properties of [BDTA]2[MCl4] [M = Cu (1), Co (2), and Mn (3)], revealing an S = 1/2 square-lattice antiferromagnet with weak magnetic exchange.

We report the synthesis and structural and magnetic characterization of model square or rectangular antiferromagnets [BDTA]2[MCl4] [BDTA = benzo-1,3,2-dithiazolyl; M = Cu (1), Co (2), and Mn (3)]. All of these compounds display a molecular structure of sandwich layers of [MCl4]2- between two sheets of [BDTA]+ molecules. Consideration of likely superexchange pathways suggests that 1 presents a model square lattice of S = 1/2 moments, while 2 and 3 present model rectangular lattices with S = 3/2 and 5/2, respectively. Magnetic susceptibility measurements indicate that all of these materials have modest antiferromagnetic exchange fields, with near-neighbor exchange J/k(B) running from 0.018(1) through 0.35(3) to 2.10(2) K as M runs from Mn to Co to Cu. No signature of any three-dimensional magnetic ordering could be observed down to 1.8 K. 1 is of particular interest because it belongs to a similar class of magnets as the high-Tc superconducting cuprates but has a much smaller exchange field; it has been proposed that the application of a magnetic field to this type of magnet can induce novel quantum states in this class of magnet, but the observation of such states is only experimentally feasible for small exchange. More detailed characterization of 1 by heat capacity measurements showed a broad cusp centered at 1.3 K in the absence of an applied magnetic field but failed to observe any sign of long-range order down to 0.33 K; this suggests that interplane magnetic exchange is weak.

Journal Article↗
PubMed2006

Combined magnetic and single-crystal X-ray structural study of the linear chain antiferromagnet [(CH3)4N][MnCl3] under varying pressure.

The magnetic susceptibility and single-crystal X-ray structure of the one-dimensional Heisenberg antiferromagnetic chain tetramethylammonium manganese trichloride (TMMC) have been studied under pressure as a facile route to develop structure-property relationships. The X-ray structure of TMMC was determined at 0, 2.1, 3.8, 6.8, 12.2, and 17.0 kbar using diamond-anvil cell techniques and synchrotron radiation. The space group is confirmed to be P6(3)/m up to 17 kbar, and structural refinement shows that the Mn-Mn separations between and along the chains change by about 3.4 and 2.5%, respectively, over 17 kbar. A structural transition from hexagonal to monoclinic symmetry possibly occurs at 17 kbar, associated with a loss of crystal quality. Variable-temperature magnetic susceptibility data were taken at 0, 0.3, 1.5, 2.9, 4.0, 5.2, and 6.5 kbar and show that the intrachain coupling constant changes from -6.85 to -7.81 K over this range. The interchain coupling constant of -0.54 K can also be extracted from the Fisher model modified for interacting chains. The pressure-temperature diagram shows the slope of the intrachain antiferromagnetic coupling with pressure, DeltaT(IAF)/DeltaP, changes from 0.5 to 1.6 K/kbar at 2 kbar where the structure changes from P2(1)/a to P2(1)/m. Comparison of the magnetic and structural data are consistent with the power-law relationship developed by Bloch where J proportional, variant r-n, r = Mn...Mn separation and n approximately 10.

Journal Article↗
PubMed2006

Optimizing dyes for dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) have emerged as an important cheap photovoltaic technology. Charge separation is initiated at the dye, bound at the interface of an inorganic semiconductor and a hole-transport material. Careful design of the dye can minimize loss mechanisms and improve light harvesting. Mass application of DSSCs is currently limited by manufacturing complexity and long-term stability associated with the liquid redox electrolyte used in the most-efficient cells. In this Minireview, dye design is discussed in the context of novel alternatives to the standard liquid electrolyte. Rapid progress is being made in improving the efficiencies of such solid and quasi-solid DSSCs which promises cheap, efficient, and robust photovoltaic systems.

Journal Article↗
PubMed2006

Structural, spectroscopic and magnetic properties of M[R2P(E)NP(E)R'2]2 complexes, M = Co, Mn, E = S, Se and R, R' = Ph or iPr. Covalency of M-S bonds from experimental data and theoretical calculations.

The S/Se-containing bidentate ligands LH of the type R2P(E)NHP(E)R'2, E = S, Se and R, R' = Ph or iPr have been employed to synthesize ML2 (M = Mn, Co) complexes which contain the biologically important MS4 core. Theoretical calculations on the LH and L- forms of the ligands probe the geometric and electronic changes induced by the deprotonation of the LH form, which are correlated with structural data from X-ray crystallography. These results reflect the flexibility of the ligands, which enables them to be rather versatile with respect to the formation of ML2 complexes with varied geometries and MEPNPE metallacycle conformations. A series of old and new ML2 complexes have been synthesized and their structural, spectroscopic and magnetic properties characterized in detail. The nephelauxetic ratio beta of the CoL2 complexes provides evidence of covalent interactions, whereas the EPR properties of the MnL2 complexes are interpreted on the basis of predominant ionic interactions, between the metal center and the ligands, respectively. Additional evidence for the existence of covalent interactions in the CoL2 complexes (R = Ph, iPr, or mixed Ph/iPr), is offered by comparisons between their 31P NMR. The aforementioned notations are supported by extensive theoretical calculations on the ML2 (E = S, R = Me) modelled structures, which probe the covalent and ionic character of the M-S bonds when M = Co or Mn. Wider implications of the findings of the present study on the M-S covalency and its importance in the active sites of various metalloenzymes are also discussed.

Benzene Derivatives↗
PubMed2006

Photogeneration of titanium(III) from titanium(IV) citrate in aqueous solution.

Current interest in the biochemistry of Ti(IV) arises from its widespread use in white pigments and its potential in therapeutic agents. Citrate is known to form strong complexes with Ti(IV). We show here that Ti(III) citrate is generated in a facile manner and in good yield by the action of UV radiation on Ti(IV) citrate in aqueous solution. The Ti(III)-citrate species formed was isolated and characterised by UV-Visible spectroscopy, showing an absorption at 547 nm (epsilon=100 M(-1)cm(-1)), and by electron paramagnetic resonance (EPR) spectroscopy giving a resonance at g=1.949 (linewidth=60G) . An X-ray structure of the parent Ti(IV) complex in the form [TiNa(3)(C(6)H(6)O(7))(2)(C(6)H(5)O(7))(H(2)O)(6.8)].2H(2)O is reported along with a study of the reaction of Ti(IV)-citrate with N,N-ethylenebis(o-hydroxytoluene)glycine (EHTG), which was more rapid than those of other related Ti(IV) complexes.

Citric Acid↗
PubMed2005

Synthesis of nitrogen and sulfur macrocycles with cis exogenous oxygen and sulfur donor atoms.

A series of new N4 and N8 macrocycles has been prepared, that includes cis-exogenous O2, S2 and S/O atoms to allow chelation to a metal external to the macrocyclic ring. We found that thioamide units within the macrocycles were unstable to attack by secondary amines and thus alkylated precursors containing only tertiary amines could lead to exogenous-S2 macrocycles. Cyclisation of alkylated tetraamine precursors with dimethyloxalate or dithiooxamide led to both N4 and N8 macrocycles via 1 + 1 and 2 + 2 cyclisation reactions with exogenous-O2 or S2 respectively. Alkylation of preformed exogenous-O2 macrocycles was explored and led to alkyl substitution at the secondary amine nitrogens in the ring, however synthesis of these species was overall lower yielding than cyclisation using alkylated tetraamine precursors. Thionation of an exo-O2 macrocycle using an analogue of Lawesson's Reagent led to formation of the analogous exogenous-S2 and exogenous-O,S macrocycles. Related S2N2 macrocycles with exogenous-O2 were prepared by a cyclisation route but could not be isolated free of larger ring analogues.

Journal Article↗
PubMed2005

Synthesis, structural characterization, and magnetic studies of polynuclear iron complexes with a new disubstituted pyridine ligand.

A series of novel polyiron species have been prepared from the reaction of iron chloride with the 2,5-disubstituted pyridines H2L(n) (H2L1) = N,N'-bis(n-butylcarbamoyl)pyridine-2,6-dicarboxamide; H2L2 = N,N'-bis(n-ethylcarbamoyl)pyridine-2,6-dicarboxamide). By small modifications of the experimental conditions under which the reactions are carried out, it has been possible to prepare the quadruply stranded diiron(II) complex [Fe2(mu-H2L1)4(mu-Cl)2][FeCl4]2 (1), the metallamacrocycle [Fe2(mu-H2L1)2(THF)4Cl2][FeCl4]2 (2), the hexairon(III) compound [Fe6(L1)2(mu-OMe)6(mu4-O)2Cl4] (3), and the mixed-valence trinuclear iron complexes [Fe3(L(n))3(mu3-O)] (n = 1, 4; n = 2, 5). The X-ray crystal structures of 3 and 5 and magnetic studies for all the compounds are herein presented. Interestingly, the structural analysis of 5 at room temperature indicates that one of the iron centers is Fe(III) while the other two have an average valence state between Fe(II) and Fe(III). The five complexes herein presented demonstrate the great versatility that the new ligand has as a building block for the formation of supramolecular coordination assemblies.

Journal Article↗
PubMed2005

[BDTA]2[Cu(mnt)2]: an almost perfect one-dimensional magnetic material.

[BDTA]2[Cu(mnt)2] (BDTA = benzo-1,3,2-dithiazolyl, mnt = maleonitriledithiolate) was crystallized in the space group P with an inversion center on Cu giving a stacked structure with each metal complex anion sandwiched by two cations. Short intermolecular S...S contacts give rise to a one-dimensional chain lateral to the stacking axis. Variable-temperature magnetic susceptibility and EPR measurements indicate that the salt behaves as an ideal one-dimensional Heisenberg antiferromagnetic material from 2 K < or = T < or = 300 K, with a coupling constant of J/k(B) = 16-17 K; the very low temperature magnetic properties are in quantitative agreement with the predictions of quantum field theory. DFT calculations are consistent with the formation of a one-dimensional magnetic chain with interstack interactions mediated by the BDTA counterions.

Journal Article↗
PubMed2005

Synthesis, structure, and properties of [Pt(II)(diimine)(dithiolate)] dyes with 3,3'-, 4,4'-, and 5,5'-disubstituted bipyridyl: applications in dye-sensitized solar cells.

A family of [Pt(II)(diimine)(dithiolate)] complexes of general formula [Pt{X,X'(CO(2)R)(2)-2,2'-bipyridyl}(maleonitriledithiolate)] (where X = 3, 4, or 5 and R = H or Et) have been synthesized, spectroscopically and electrochemically characterized, and attached to a TiO(2) substrate to be tested as solar cell sensitizers. A single-crystal X-ray structure showing a large torsion angle between the bipyridyl rings was determined for [Pt{3,3'(CO(2)Et)(2)-2,2'-bipyridyl}(maleonitriledithiolate)].MeCN. The effect of changing the position of the bipyridyl substituents from 3,3' to 4,4' and 5,5' is discussed with reference to structural and electronic changes seen within the different members of the family of molecules. The first UV/vis/NIR spectroelectrochemical study of complexes of this general formula is discussed. All three complexes (where R = H) were tested as solar cell sensitizers, with the 3,3'-disubstituted bipyridyl complex giving an intermediate dye loading value but superior photovoltaic performance to those of the other two. The performance of this sensitizer is then compared with that of a well-known Ru polypyridyl sensitizer, the ditetrabutylammonium salt of [RuL(2)(NCS)(2)] (L = 2,2'-bipyridyl-4,4'-dicarboxylato), commonly called N719.

Journal Article↗
PubMed2004

Synthesis, structure, and complexation of a large 28-mer macrocycle containing two binding sites for either anions or metal ions.

The "one-pot" synthesis and characterization of a large 28-mer macrocycle (H(4)L(2)) with oxamido units capable of complexing guest ions through oxygen or nitrogen donor atoms is reported. Single-crystal structure determination of H(8)L(2)(NO(3))(4) and (Cu(2)[H(2)L(2)](H(2)O)(2))(NO(3))(2) demonstrated that the macrocycle contains two sites capable of complexing two nitrate anions or two copper(II) ions, involving a large structural reorganization in the conformation of the macrocyclic framework on coordination of the copper(II) ions when compared to the nitrate. Electrochemical and magnetic susceptibility measurements on the dinuclear Cu(II) complex and the related mononuclear and trinuclear Cu(II) complexes derived from the related 14-mer macrocycle were carried out and illustrate the role of the oxamido groups in mediating metal-metal interaction and delocalization.

Journal Article↗
PubMed2003

A comparison of potential molecular wires as components for molecular electronics.

The field of electronics using single-molecule components has recently received much attention as a possible new design concept for the continued miniturisation of electronics. Molecular wires are the conceptually simplest components of such electronic systems and several different compound types have been used to produce molecular wires. Examples of some of the most promising families of molecular wires are presented, namely conjugated hydrocarbons, carbon nanotubes, porphyrin oligomers and DNA. Discussion centres around their potential use in functioning electronic architectures in terms of their electronic properties, ease and controllability of synthesis and potential for self-assembly.

Base Pairing↗