Biomedical subjects

Ian G Dance

Publications and source records attributed to Ian G Dance.

6 recordsLinked to original sources

PubMed2006

cis-[PtBr2{PPh2(4-catechol)}2]: synthesis, crystal structure, and computational modelling of its binding to nanocrystalline TiO2.

The complex cis-[PtBr(2){PPh(2)(4-catechol)}(2)]1 has been synthesized by cleavage of the four methyl groups from cis-[PtCl(2){PPh(2)(4-veratrole)}(2)] using BBr(3), followed by work-up in the presence of excess bromide. An X-ray crystal structure of 1.(ethanol)(2) confirms that the two catechol rings are adjacent to each other and approximately parallel, and therefore well structured to act as double bidentate ligands for adjacent metal atoms on the surface of a nanocrystal. The crystal packing of 1.(ethanol)(2) involves intermolecular hydrogen-bonding interactions and a parallel fourfold phenyl embrace between PPh(2) moieties. Density functional calculations have demonstrated that conformational variability of the aryl rings in cis-[PtBr(2){PPh(2)(4-catechol)}(2)] is energetically feasible, and two conformations of cis-[PtBr(2){PPh(2)(4-catechol)}(2)] as a complex ligand for Ti atoms on the various surfaces of the anatase and rutile structures of TiO(2) have been assessed for geometrical commensurability. Three structural models for adsorbates of cis-[PtBr(2){PPh(2)(4-catechol)}(2)] on TiO(2) are developed for anatase (110), anatase (101), and rutile (001).

Journal Article↗

PubMed2004

Localization of a catalytic intermediate bound to the FeMo-cofactor of nitrogenase.

Nitrogenase catalyzes the biological reduction of N(2) to ammonia (nitrogen fixation) as well as the reduction of a number of alternative substrates, including acetylene (HC identical with CH) to ethylene (H2C=CH2). It is known that the metallocluster FeMo-cofactor located within the nitrogenase MoFe protein component provides the site of substrate reduction, but the exact site where substrates bind and are reduced on the FeMo-cofactor remains unknown. We have recently shown that the alpha-70 residue of the MoFe protein plays a significant role in defining substrate access to the active site; alpha-70 approaches one face of the FeMo-cofactor, and when valine is substituted by alanine at this position, the substituted nitrogenase is able to accommodate a reduction of the larger alkyne propargyl alcohol (HC identical with CCH(2)OH, propargyl-OH). During this reduction, a substrate-derived intermediate can be trapped on the FeMo-cofactor resulting in an S = 1/2 spin system with a novel electron paramagnetic resonance spectrum. In the present work, trapping of the propargyl-OH-derived or propargyl amine (HC identical with CCH(2)NH(2), propargyl-NH(2))-derived intermediates is shown to be dependent on pH and the presence of histidine at position alpha-195. It is concluded that these catalytic intermediates are stabilized and thereby trapped by H-bonding interactions between either the-OH group or the-NH(3)(+)group and the imidazole epsilon-NH of alpha-195(His). Thus, for the first time it is possible to establish the location of a bound substrate-derived intermediate on the FeMo-cofactor. Refinement of the binding mode and site was accomplished by the use of density functional and force field calculations pointing to an eta(2) coordination at Fe-6 of the FeMo-cofactor.

Acetylene↗

PubMed2004

Substrate interactions with nitrogenase: Fe versus Mo.

Biological nitrogen reduction is catalyzed by a complex two-component metalloenzyme called nitrogenase. For the Mo-dependent enzyme, the site of substrate reduction is provided by a [7Fe-9S-Mo-X-homocitrate] metallocluster, where X is proposed to be an N atom. Recent progress with organometallic model compounds, theoretical calculations, and biochemical, kinetic, and biophysical studies on nitrogenase has led to the formulation of two opposing models of where N(2) or alternative substrates might bind during catalysis. One model involves substrate binding to the Mo atom, whereas the other model involves the participation of one or more Fe atoms located in the central region of the metallocluster. Recently gathered evidence that has provided the basis for both models is summarized, and a perspective on future research in resolving this fundamental mechanistic question is presented.

Bacterial Proteins↗

PubMed2003

Tetraphenylarsonium iodide, a new determination.

The reported crystal structures of Ph(4)P(+).I(-) and Ph(4)As(+).I(-) have been re-examined. An apparent instance of substitutional dimorphism could not be reproduced and, contrary to an earlier report, tetraphenylarsonium iodide, [As(C(6)H(5))(4)]I or Ph(4)As(+).I(-), was found to be isostructural with the phosphorus compound. The cation and anion are both located on -4 symmetry sites. The crystal packing involves linear chains of cations in fourfold phenyl embraces.

Journal Article↗

PubMed2002

Metal Cyanide Ions Mx(CN)y]+,- in the gas phase: M = Fe, Co, Ni, Zn, Cd, Hg, Fe + Ag, Co + Ag.

The generation of metal cyanide ions in the gas phase by laser ablation of M(CN)(2) (M = Co, Ni, Zn, Cd, Hg), Fe(III)[Fe(III)(CN)(6)] x xH(2)O, Ag(3)[M(CN)(6)] (M = Fe, Co), and Ag(2)[Fe(CN)(5)(NO)] has been investigated using Fourier transform ion cyclotron resonance mass spectrometry. Irradiation of Zn(CN)(2) and Cd(CN)(2) produced extensive series of anions, [Zn(n)(CN)(2n+1)](-) (1 < or = n < or = 27) and [Cd(n)(CN)(2n+1)](-) (n = 1, 2, 8-27, and possibly 29, 30). Cations Hg(CN)(+) and [Hg(2)(CN)(x)](+) (x = 1-3), and anions [Hg(CN)(x)](-) (x = 2, 3), are produced from Hg(CN)(2). Irradiation of Fe(III)[Fe(III)(CN)(6)] x xH(2)O gives the anions [Fe(CN)(2)](-), [Fe(CN)(3)](-), [Fe(2)(CN)(3)](-), [Fe(2)(CN)(4)](-), and [Fe(2)(CN)(5)](-). When Ag(3)[Fe(CN)(6)] is ablated, [AgFe(CN)(4)](-) and [Ag(2)Fe(CN)(5)](-) are observed together with homoleptic anions of Fe and Ag. The additional heterometallic complexes [AgFe(2)(CN)(6)](-), [AgFe(3)(CN)(8)](-), [Ag(2)Fe(2)(CN)(7)](-), and [Ag(3)Fe(CN)(6)](-) are observed on ablation of Ag(2)[Fe(CN)(5)(NO)]. Homoleptic anions [Co(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n+2)](-) (n = 1-3), [Co(2)(CN)(4)](-), and [Co(3)(CN)(5)](-) are formed when anhydrous Co(CN)(2) is the target. Ablation of Ag(3)[Co(CN)(6)] yields cations [Ag(n)(CN)(n-1)](+) (n = 1-4) and [Ag(n)Co(CN)(n)](+) (n = 1, 2) and anions [Ag(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n-1)](-) (n = 1, 2), [Ag(n)Co(CN)(n+2)](-) (n = 1, 2), and [Ag(n)Co(CN)(n+3)](-) (n = 0-2). The Ni(I) species [Ni(n)(CN)(n-1)](+) (n = 1-4) and [Ni(n)(CN)(n+1)](-) (n = 1-3) are produced when anhydrous Ni(CN)(2) is irradiated. In all cases, CN(-) and polyatomic carbon nitride ions C(x)N(y)(-) are formed concurrently. On the basis of density functional calculations, probable structures are proposed for most of the newly observed species. General structural features are low coordination numbers, regular trigonal coordination stereochemistry for d(10) metals but distorted trigonal stereochemistry for transition metals, the occurrence of M-CN-M and M(-CN-)(2)M bridges, addition of AgCN to terminal CN ligands, and the occurrence of high spin ground states for linear [M(n)(CN)(n+1)](-) complexes of Co and Ni.

Journal Article↗

PubMed2002

Crystal engineering of hydroxy group hydrogen bonding: design and synthesis of new diol lattice inclusion hosts.

The diols 7-11 have been synthesized, and their X-ray crystal structures determined, to learn how to influence and control lattice hydroxy group hydrogen bonding using crystal engineering ideas. To obtain new lattice inclusion hosts precise structural rules can be defined which enable the necessary supramolecular interactions to be duplicated. In this manner the helical tubuland 10 and ellipsoidal clathrate 11 hosts were obtained for the first time and their chloroform inclusion compounds characterized. New synthetic routes were utilized to obtain the bicyclo[3.3.2]decane and 9-thiatricyclo[4.3.1.1(3,8)]undecane frameworks present in these compounds. The solid-state conformations of bicyclo[3.3.2]decane derivatives 9 and 10 are compared with prior predictions and studies made on this uncommon ring system.

Journal Article↗