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Christopher E Anson

Publications and source records attributed to Christopher E Anson.

At least 19 recordsLinked to original sources
PubMed2007

Polymeric organometallic architectures of novel P-Se anions.

The characterisation of a series of compounds obtained from Woollins' reagent (W.R.) offers a novel approach to organometallic coordination polymers. The syntheses were achieved by nucleophilic ring-opening reactions of W.R. with metal salts and crystallisation using solvent-diffusion techniques. One-dimensional coordination polymers are formed as a result, and we demonstrate that the dimensionality of the polymers can be influenced by using hydrated metal salts or by the construction of heterometallic arrangements.

Anions↗
PubMed2006

Synthesis, molecular characterization, and biological activity of novel synthetic derivatives of chromen-4-one in human cancer cells.

The synthesis and characterization of Schiff base derivatives of 3-formylchromone 3-6 (FPA-120 to FPA-123), the minimal biologically active structural motif of soy isoflavone, genistein, and their copper(II) complexes 7-10 (FPA-124 to FPA-127) are reported here. These copper complexes possess distorted square-planar geometries capable of stabilizing Cu2+/Cu+ redox forms. The molecular modeling study revealed that the key interaction of the metal complexes was with amino acids in the pleckstrin homology (PH) and the kinase domain of the PKB (Akt) protein. Copper complex 7 significantly forms stronger charge interactions in the kinase domain than genistein, leading to better stabilization in the active pocket. In vitro evaluation of copper complexes against hormone-independent and metastatic breast (BT20), prostate (PC-3), and K-ras mutant (COLO 357) and K-ras wild-type (BxPC-3) pancreatic cancer cells revealed that 7 was the most potent compound which exhibited PKB (Akt protein) inhibitory activities and caused NF-kappaB inactivation in a well-established orthotopic pancreatic tumor model using COLO 357 cells. An inverse relationship was observed between IC50 values of the anti-proliferative activities and the Cu2+/Cu+ redox couple for these compounds, which may provide a rapid screen for evaluating the efficacy of active metallodrugs affecting redox-sensitive transcription factors such as NF-kappaB and its upstream target, the PKB (Akt) pathway, in multiple cancers.

Animals↗
PubMed2006

Polymeric arrangements of P-Se anions and a first insight into their reactivity.

The reactions of the P/Se-precursor Woollins' reagent [PhP(Se)mu-Se]2 with alkali-metal salts offer new perspectives for the synthesis of metal aggregates containing P-Se anions. Depending on the alkali-metal thiolates polymeric arrangements of [PhPSe3]2- or [PhPSe2Se-SeSe2PPh]2- dianions are observed and the mechanisms of their formation described.

Journal Article↗
PubMed2006

New valence-sandwich [Mn(II)4Mn(III)4Mn(II)4] aggregate showing single-molecule magnet behavior.

The reaction of manganese(II) acetate, 1,1,1-tris(hydroxymethyl)methane (H3thme), and triethylamine in methanol leads to the formation of [Mn12O2(OMe)2(thme)4(OAc)10(H2O)4].2MeOH. The [Mn(III)4Mn(II)8] core consists of a central [Mn(III)4O6] rhombus sandwiched by two [Mn(II)4O7] fragments. Frequency-dependent ac susceptibility and hysteresis loops in the magnetization indicate single-molecule magnet behavior with a pure quantum-tunneling regime of relaxation below 0.2 K.

Journal Article↗
PubMed2006

Modelling calcium carbonate biomineralisation processes.

The structure-directing influence of the organic dicarboxylates malonate, succinate, glutarate and adipate as templating species on the hydrothermal formation of CaCO(3) was investigated at different temperatures (60, 80, 90, 120, 150 and 190 degrees C) and with a range of molar ratios of [Ca(2+)]/[templating species] (20, 14.3, 10, 7.7, 5, 1, 0.5 and 0.33). In the presence of the dicarboxylates, one, two or three polymorphs of CaCO(3) - calcite, aragonite and vaterite - could be formed, depending on the reaction conditions. In addition changes in crystal morphology were observed for the CaCO(3) polymorphs depending on the concentration of the template. In contrast, synthesis under ambient conditions of temperature and pressure resulted only in calcite formation, although template-dependent morphological changes were again observed. Crystalline products were all characterized by powder X-ray patterns and SEM (Scanning Electron Microscopy) micrographs. The ambient reactions with the chelating, dinucleating carboxylato ligands H(3)heidi and H(5)hpdta produce more profound changes in calcite morphology. With H(3)heidi rounded calcite crystals with shapes similar to that of otoliths are formed and with H(5)hpdta the formation of microtrumpets of constructed from bundles of nanocrystals of calcite is observed. The possible mode of action of these ligands on calcite formation is discussed in the context of known coordination chemistry with other metal ions.

Calcium Carbonate↗
PubMed2006

Dynamic chemical devices: photoinduced electron transfer and its ion-triggered switching in nanomechanical butterfly-type bis(porphyrin)terpyridines.

A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (alpha,omega)-diamine substrates to the Zn(II)-porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the eta3-terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs.

Chemical Phenomena↗
PubMed2006

A close look at short C-CH3...potassium contacts: synthetic and theoretical investigations of [M2Co2(mu3-OtBu)2(mu2-OtBu)4(thf)n] (M = Na, K, Rb, thf = tetrahydrofuran).

Agostic interactions of the type Si-CH3M+ (M = alkali metal) are frequently mentioned in discussions of solid-state structures of trimethylsilyl compounds and the purpose of this work was to elucidate if they also exist in the related tert-butyl species by using density functional theory. The compounds [M2Co2(mu3-OtBu)2(mu2-OtBu)4(thf)n] (M = Na, n = 2; M = K, n = 0; M = Rb, n = 1) have been synthesised and their crystal structures determined. Close contacts of methyl groups with K atoms are observed in the solid-state structure of [K2Co2(mu3-OtBu)2(mu2-OtBu)4], and calculations of the rotational barrier of a tert-butoxy group about the axis through the C-O bond were performed. It was shown that apparent short C-CH3K distances are in this case a consequence of the packing in the extended solid-state structure.

Journal Article↗
PubMed2005

Unusual syntheses, structures, and electronic properties of compounds containing ternary, T3-type supertetrahedral M/Sn/S anions [M5Sn(mu3-S)4(SnS4)4](10- (M = Zn, Co).

A recently discovered series of quaternary compounds of the general type [K(m)(ROH)(n)()][M(x)Sn(y)()Se(z)] (R = H, Me), containing ternary anions with [SnSe(4)](4-)-coordinated transition metal centers (M = Co, Mn, Zn, Cd, Hg) has now been extended by the synthesis and characterization of the two ortho-thiostannate-coordinated species, [Na(10)(H(2)O)(32)][M(5)Sn(mu(3)-S)(4)(SnS(4))(4)].2H(2)O (M = Zn (1), Co (2)). The central structural motifs of compounds 1 and 2 are highly charged [M(5)Sn(mu(3)-S)(4)(SnS(4))(4)](10-) anions, being the first T3-type supertetrahedral ternary anions reported to date. The exposure of single crystals of 2 to a dynamic vacuum for several hours resulted in the reversible formation of a partially dehydrated, but still monocrystalline material of the composition [Na(10)(H(2)O)(6)][Co(5)Sn(mu(3)-S)(4)(SnS(4))(4)] (3). The loss of 28 of the 34 water molecules only slightly affects the internal structure of the ternary anion in 3 and leads to a significant compacting of the crystal structure with closer linkage of the [Co(5)Sn(5)S(20)](10-) cluster units via the Na(+) cations. Magnetic measurements on 3 show that the ground state of the Co/Sn/S cluster is S = 1/2, indicating a significant antiferromagnetic coupling between the Co centers, which has also been rationalized by DFT investigations of the electronic situation in the ternary subunits of 1-3.

Journal Article↗