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Alexander J Blake

Publications and source records attributed to Alexander J Blake.

At least 55 records · Page 3Linked to original sources
PubMed2004

Phenolate and phenoxyl radical complexes of Co(II) and Co(III).

The new phenol-imidazole pro-ligands (R)LH react with Co(BF(4))(2).6H(2)O in the presence of Et(3)N to form the corresponding [Co(II)((R)L)(2)] compound (R = Ph (1), PhOMe (2), or Bz (3)). Also, (Bz)LH, reacts with Co(ii) in the presence of Et(3)N and H(2)O(2) to form [Co(III)((Bz)L)(3)](4). The structures of 1.2.5MeCN, 2.2DMF, 3.4MeOH, and 4.4DMF have been determined by X-ray crystallography. 1, 2, and 3 each involve Co(II) bound to two N,O-bidentate ligands with a distorted tetrahedral coordination sphere; 4 involves Co(III) bound to three N,O-bidentate ligands in a mer-N(3)O(3) distorted octahedral geometry. [Co(II)((R)L)(2)](R = Ph or PhOMe) undergo two, one-electron, oxidations. The products of the first oxidation, [1](+) and [2](+), have been synthesised by the chemical oxidation of 1 and 2, respectively; these cations, formulated as [Co(II)((R)L*)((R)L)(2)](+), comprise one phenoxyl radical and one phenolate ligand bound to Co(II) and are the first phenoxyl radical ligand complexes of tetra-coordinated Co(II). 4 undergoes two, one-electron, ligand-based oxidations, the first of which produces [4](+), [Co(III)((Bz)L*)((Bz)L)(2)](+). Unlike [1](+) and [2](+), product of the one-electron oxidation of [Co(II)((Bz)L)(2)], [3](+), is unstable and decomposes to produce [4](+). These studies have demonstrated that the chemical properties of [M(II)((R)L*)((R)L)(2)](+)(M = Co, Cu, Zn) are highly dependent on the nature of both the ligand and the metal centre.

Journal Article↗
PubMed2004

Synthesis and biological evaluation of new inhibitors of UDP-Galf transferase--a key enzyme in M. tuberculosis cell wall biosynthesis.

Two iminosugars have been designed and synthesized as potential inhibitors of UDP-Galf transferase, an enzyme involved in Mycobacterium tuberculosis cell wall biosynthesis. The design is based on a proposed model of the transition state for the transferase reaction. One of the two racemic compounds is the first reported inhibitor of the target enzyme from M. smegmatis.

Catalysis↗
PubMed2004

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II).

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.

Journal Article↗
PubMed2004

The synthesis and electronic structure of a novel [NiS4Fe2(CO)6] radical cluster: implications for the active site of the [NiFe] hydrogenases.

A novel [NiS4Fe2(CO)6]cluster (1: 'S(4)'=(CH(3)C(6)H(3)S(2))(2)(CH(2))(3)) has been synthesised, structurally characterised and has been shown to undergo a chemically reversible reduction process at -1.31 V versus Fc(+)/Fc to generate the EPR-active monoanion 1(-). Multifrequency Q-, X- and S-band EPR spectra of (61)Ni-enriched 1(-) show a well-resolved quartet hyperfine splitting in the low-field region due to the interaction with a single (61)Ni (I=3/2) nucleus. Simulations of the EPR spectra require the introduction of a single angle of non-coincidence between g(1) and A(1), and g(3) and A(3) to reproduce all of the features in the S- and X-band spectra. This behaviour provides a rare example of the detection and measurement of non-coincidence effects from frozen-solution EPR spectra without the need for single-crystal measurements, and in which the S-band experiment is sensitive to the non-coincidence. An analysis of the EPR spectra of 1(-) reveals a 24 % Ni contribution to the SOMO in 1(-), supporting a delocalisation of the spin-density across the NiFe(2) cluster. This observation is supported by IR spectroscopic results which show that the CO stretching frequencies, nu(CO), shift to lower frequency by about 70 cm(-1) when 1 is reduced to 1(-). Density functional calculations provide a framework for the interpretation of the spectroscopic properties of 1(-) and suggest that the SOMO is delocalised over the whole cluster, but with little S-centre participation. This electronic structure contrasts with that of the Ni-A, -B, -C and -L forms of [NiFe] hydrogenase in which there is considerable S participation in the SOMO.

Binding Sites↗
PubMed2004

Co-ordination chemistry of amino pendant arm derivatives of 1,4,7-triazacyclononane.

The binding properties of 1,4,7-triazacyclononane ([9]aneN3) to metal cations can be adapted through sequential functionalisation of the secondary amines with aminoethyl or aminopropyl pendant arms to generate ligands with increasing numbers of donor atoms. The new amino functionalised pendant arm derivative of 1,4,7-triazacyclononane ([9]aneN3), L1, has been synthesised and its salt [H2L1]Cl2 characterised by X-ray diffraction. The protonation constants of the ligands L1-L4 having one, two or three aminoethyl or three aminopropyl pendant arms, respectively, on the [9]aneN3 framework, and the thermodynamic stabilities of their mononuclear complexes with CuII and ZnII have been investigated by potentiometric measurements in aqueous solutions. In order to discern the protonation sites of ligands L1-L4, 1H NMR spectroscopic studies were performed in D2O as a function of pH. While the stability constants of the CuII complexes increase on going from L1 to L2 and then decrease on going from L2 to L3 and L4, those for ZnII complexes increase from L1 to L3 and then decrease for L4. The X-ray crystal structures of the complexes [Cu(L1)(Br)]Br, [Zn(L1)(NO3)]NO3, [Cu(L2)](ClO4)2, [Ni(L2)(MeCN)](BF4)2, [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O have been determined. In both [Cu(L1)(Br)]Br and [Zn(L1)(NO3)]NO3 the metal ion is five co-ordinate and bound by four N-donors of the macrocyclic ligand and by one of the two counter-anions. The crystal structures of [Cu(L2)](ClO4)2 and [Ni(L2)(MeCN)](BF4)2 show the metal centre in slightly distorted square-based pyramidal and octahedral geometry, respectively, with a MeCN molecule completing the co-ordination sphere around NiII in the latter. In both [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O the metal ion is bound by all six N-donors of the macrocyclic ligand in a distorted octahedral geometry. Interestingly, and in agreement with the solution studies and with the marked preference of CuII to assume a square-based pyramidal geometry with these types of ligands, the reaction of L4 with one equivalent of Cu(BF4)2.4H2O in MeOH at room temperature yields a square-based pyramidal five co-ordinate CuII complex [Cu(L6)](BF4)2 where one of the three propylamino pendant arms of the starting ligand has been cleaved to give L6.

Journal Article↗
PubMed2004

Lanthanide complexes of new nonadentate imino-phosphonate ligands derived from 1,4,7-triazacyclononane: synthesis, structural characterisation and NMR studies.

The polyamino ligand 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane (1) has been used to synthesise two new ligands by Schiff-base condensation with methyl sodium acetyl phosphonate to give ligand L and methyl sodium 4-methoxybenzoyl phosphonate to give ligand L1 in the presence of lanthanide ion as templating agent to form the complexes [Ln(L)] and [Ln(L1)](Ln = Y, La, Gd, Yb). Both ligands L and L1 have nine donor atoms comprising three amine and three imine N-donors and three phosphonate O-donors and form Ln(III) complexes in which the three pendant arms of the ligands wrap around the nine-coordinate Ln(III) centres. Complexes with Y(III), La(III), Gd(III) and Yb(III) have been synthesised and the complexes [Y(L)], [Gd(L)] and [Gd(L1)] have been structurally characterised. In all the complexes the coordination polyhedron about the lanthanide centre is slightly distorted tricapped trigonal prismatic with the two triangular faces of the prism formed by the macrocyclic N-donors and the phosphonate O-donors. Interestingly, given the three chiral phosphorus centres present in [Ln(L)] and [Ln(L1)] complexes, the three crystal structures reported show the presence of only one diastereomer of the four possible. 1H, 13C and 31P NMR spectroscopic studies on diamagnetic [Y(L)] and [La(L)] and on paramagnetic [Yb(L)] complexes indicate the presence in solution of all the four different diastereomers in varying proportions. The stability of complexes [Y(L)] and [Y(L1)] in D2O in both neutral and acidic media, and the relaxivity of the Gd(III) complexes, have also been investigated.

Journal Article↗
PubMed2004

Conformational and stereochemical flexibility in cadmium(II) complexes of aza-thioether macrocycles.

The synthesis and crystal structures of four CdII macrocyclic complexes containing mixed N-, O- and S-donors, [Cd(NO3)2([12]aneN2S2)] (1), [Cd(NO3)2([12]aneNS3)] (2), [Cd(NO3)2([15]aneNO2S2)] (3) and [Cd(NO3)([15]aneN2O2S)]NO3 (4), are presented. The metal ion is coordinated outside of the macrocyclic cavity in the complexes of the smaller macrocycles ([12]aneN2S2 and [12]aneNS3) while the flexibility of the larger macrocycles in and allows very different conformations to be adopted with a 'butterfly' geometry in and a flattened geometry in. No correlation between the number of sulfur donors and Cd-S bond distance in these types of complexes is observed, although the number and binding mode of the nitrato ligands is determined by the conformation and binding mode of the macrocycle. The position of the nitrato ligand also influences, through steric conflicts with the macrocyclic donor atoms, the bond distances in both ligand systems.

Journal Article↗
PubMed2004

Early-late, mixed-metal compounds supported by amidophosphine ligands.

The sequential syntheses, structural characterisation and reactivity studies of a series of discrete early-late mixed-metal complexes supported by the unique amidophosphine ligand m-(But2CH)N(C6H4)PPh2L1 are described. This ligand was synthesised using a Schiff-base/ButLi protocol and the resultant lithium salt LiL1 found to adopt a tetrameric structure in the solid state in which both two-coordinate N-Li-N and eta6:eta6-arylLi metallocene bonding motifs are present. Reaction between HL1 and labile Pt(II) and Pd(II) chlorides formed MCl2(HL1)2 complexes 4 (M = Pt) and 5 (M = Pd) in which a weak N-H...pi(aryl) hydrogen bonding interaction was identified in the solid-state structure of 4. These compounds were found to be inert to transamination and protonolysis reactions with Ti amides and alkyls; instead, stepwise alkyl transfer from Ti to Pt, resulting in Pt(CH2SiMe3)2(HL1)2 6 was observed. Access to mixed-metal complexes was achieved using an early-metal-first approach. Reaction between the metalloligand TiCl2(L1)2 and labile Group 10 and group 9 compounds resulted in the formation of TiCl2(mu-L1)2PtCl2 8, TiCl2(mu-L1)2PtMe2 9, TiCl2(mu-L1)2PdCl2 10, TiCl2(mu-L1)2NiBr2 11, and [TiCl2(mu-L1)2RhCl(CO)]2 12. In the solid state, the Group 4/10 compounds 8, 9 and 10 adopt similar structures that exhibit both intramolecular But2C-H...Cl-Ti hydrogen bonding and arylNP pi-stacking interactions; this hydrogen-bonding interaction is conserved in solution. Unlike the above Group 4/10 complexes, the Ti-Rh complex 12 adopts a tetranuclear structure in the solid state that is stabilised by similar hydrogen-bonding and pi-stacking interactions. The Group 4/10 complexes were assessed as catalysts for olefin polymerisation and cross-coupling reactions. In combination with MAO, the mixed-metal complexes 8 and 10 were poor ethylene polymerisation catalysts and resulted in polymers of both high molecular weight and polydispersity. The Ti-Ni complex 11 formed oligomeric material only, while the mononuclear Ti metalloligand TiCl2(L1)2 gave the best results, showing low activity (6.14 kg mol(-1) bar(-1) h(-1)) and moderate polydispersity (12). The Ti-Pd complex 10 was assessed in arylamination and Suzuki-Miyaura reactions. While little or no catalytic activity was observed in arylamination reactions, 10 was found to effect Suzuki coupling between activated aryl bromides and phenylboronic acid at 80 degrees C. Unlike with TiCl2(L1)2, reactions between 8 and the reducing agents C8K or Mg led to intractable mixtures. However, the cyclic voltammetry of both compounds indicated that a reversible one-electron reduction process occurs at a similar potential (ca. -0.7 V) and was assigned to the formation of the monohalides TiCl(L1)2 and TiCl(mu-L1)2PtCl2. The reactivity of the metallocage TiCl(mu-L3)3Pt was also investigated. While reduction reactions were unsuccessful, the metallocage reacted with CO to form the Ti-Pt carbonyl, TiCl(mu-L3)3Pt(CO) 13. The X-ray crystal structure of 13 revealed that accommodation of CO at the Pt centre has caused the cage expansion and loss of agostic aryl-H...Pt interactions. Furthermore, reaction of TiCl(mu-L3)3Pt with excess MeI resulted in the formation of the Ti(IV)-Pt(II) complex trans-TiCl2(mu-L3)2(kappa1-L3MeI)Pt(Me)I.

Journal Article↗
PubMed2004

The imide tautomer of sulfasalazine.

The title compound, 5-[4-[(2-pyridylideneamino)sulfonyl]phenyldiazenyl]salicylic acid, C(18)H(14)N(4)O(5)S, crystallizes as the imide tautomer in the monoclinic space group P2(1)/c. In addition to an intramolecular O-H.O hydrogen bond, intermolecular O-H.O interactions link adjacent molecules into helices, which are connected by pairwise N-H.N interactions into two-dimensional hydrogen-bonded layers. Both the molecular conformation and the packing differ from those seen in the triclinic amide form [Filip et al. (2001). Acta Cryst. C57, 435-436].

Anti-Infective Agents↗
PubMed2003

Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane.

We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.

Journal Article↗
PubMed2003

Structure and electronic properties of an asymmetric thiolate-bridged binuclear complex: a model for the active site of acetyl CoA synthase.

The asymmetric binuclear complex [(dppe)Ni(mu-'S, S')Ni(L)](PF6)2 [L = (N, N'-diethyl-3,7-diazanonane-1,9-dithiolato)2-] shows a reversible one-electron reduction to afford a mixed-valent Ni(II) x Ni(I) species; the reduced complex has been characterised by EPR spectroscopy and mimics the redox active Nip site in the active A-cluster of acetyl coenzyme A synthase.

Aldehyde Oxidoreductases↗
PubMed2003

Intramolecular cyclization of 4,7-bis(2-bromoacetyl)-1-thia-4,7-diazacyclononane.

The reaction of 1-thia-4,7-diazacyclononane with bromoacetyl bromide in CHCl(3) affords the unexpected salt 4-(2-bromoacetyl)-8-oxo-1-thionia-4,7-diazabicyclo[5.2.2]undecane bromide, C(10)H(16)BrN(2)O(2)S(+).Br(-). Two units of the salt are linked by S.Br contacts about a crystallographic inversion centre, thus forming dimers that are linked by Br...Br contacts into extended ribbons. S...O contacts between these ribbons generate a two-dimensional sheet.

Journal Article↗
PubMed2003

Magnesium diiodide, MgI2.

Single crystals of magnesium diiodide have been grown and the structure solved for the first time from single-crystal X-ray diffraction data. This study confirms that MgI(2) is isostructural with CdI(2) (C6 or 2H structure type). The space group is P-3m1 with the Mg atom on a site with 3m symmetry (Wyckoff site 1a) and the I atom on a site with m symmetry (Wyckoff site 2d). Trends in the 2H structures of dihalides are discussed briefly.

Journal Article↗