A novel tetranuclear hydrogenphosphate-bridged Cu(II) cluster. Synthesis, structure, spectroscopy and magnetism of [Cu4(dpyam)4(μ4,η-HPO4)2(μ-X)2]X2(H2O)6 (X = Cl, Br)

Two novel tetranuclear compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu₄(dpyam)₄(μ₄,η³-HPO₄)₂(μ-X)₂]²⁺ (in which dpyam = di-2-pyridylamine and X = Cl (1), Br (2)) have been synthesised and characterised structurally and magnetically. The Cu(II) ions in the structures each display a square-pyramidal geometry, with two tridentate hydrogenphosphato groups bridging four copper atoms in a μ₄,η³ coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(II) ions is additionally bridged by halide ions, with relatively long Cu-X distances (2.551(3)-2.604(3) Å for 1 and 2.707(1)-2.766(2) Å for 2) and subsequently also a small Cu-X-Cu angle (65.7(1)° and 65.1(1)° for 1 and 61.6(1)° and 62.4(1) for 2) and a large Cu-X-Cu angle (95.5(1)° and 96.5(1)° for 1 and 91.1(1)° and 92.6(1)° for 2). Cu?Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) Å for 1 and from 2.834(1) to5.233(1) Å in 2. The lattice structures are stabilised by extensive intermolecular hydrogen bonds. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer pairs of Cu(II) ions which vary from 22 to 46 cm⁻¹ in 1 and 12 to 33 cm⁻¹ in 2 and a moderately strong antiferromagnetic interaction between the inner Cu(II) ions of −79 cm⁻¹ in 1 and −83 cm⁻¹ in 2, via the Cu-O-P-O-Cu pathway.     

An unprecedented tetranuclear Cu(II) cluster, exclusively bridged by two μ3,η-hydrogenphosphate anions: synthesis, structure, and magnetic properties

A novel tetranuclear μ₃,η³- Cu(II) complex with a new coordination mode of a hydrogenphosphato bridge, [Cu₄(di-2-pyridylamine)₄(μ₃,η³-HPO₄)₂(H₂O)₂(NO₃)₂](NO₃)₂(H₂O)₂ has been synthesised and characterised structurally, spectroscopically and magnetically. The geometry around the Cu(II) ions is distorted square pyramidal for Cu(1) and an intermediate between square pyramidal and trigonal pyramidal. The magnetic susceptibility measurements have been fit for a weak antiferromagnetic interaction of J = −10.3(1) cm⁻¹ between outer Cu ions and J = −5.3(2) cm⁻¹ between inner Cu atoms.     

Development of amperometric α-ketoglutarate biosensor based on ruthenium-rhodium modified carbon fiber enzyme microelectrode

A rapid and highly sensitive miniaturized amperometric biosensor for the detection of α-ketoglutarate (α-KG) based on a carbon fiber electrode (CFE) is presented. The biosensor is constructed by immobilizing the enzyme, glutamate dehydrogenase (GLUD) on the surface of single carbon fiber modified by co-deposition of ruthenium (Ru) and rhodium (Rh) nanoparticles. SEM and EDX shed useful insights into the morphology and composition of the modified microelectrode. The mixed Ru/Rh coating offers a greatly enhanced electrocatalytic activity towards the detection of β-nicotinamide adenine dinucleotide (NADH), with a substantial decrease in overpotential of ～ 400 mV compared to the unmodified CFE. It also imparts higher stability with minimal surface fouling, common to NADH oxidation. Further modification with the enzyme, GLUD leads to effective amperometric biosensing of α-KG through monitoring of the NADH consumption. A very rapid response to dynamic changes in the α-KG concentrations is observed with a response time of 6s. The current response is linear between 100 and 600 μM with a sensitivity of 42 μAM(-1) and a detection limit of 20 μM. This proof of concept study indicates that the GLUD-Ru/Rh-CFE biosensor holds great promise for real-time electrochemical measurements of α-KG.     

Synthesis, crystal structure and magnetic properties of a polynuclear Cu(II) complex: catena-poly[aqua(di-2-pyridylamine)copper(II)(μ-formato-O,O′)nitrate]

The synthesis, X-ray structure, spectroscopic and magnetic properties of a zig-zag formato-bridged chain complex with the formula [Cu(dpyam)(μ-O₂CH)(OH₂)]_n(NO₃)_n (1) (in which dpyam = di-2-pyridylamine) is described.The geometry of the copper(II) ion is distorted square pyramidal with a basal plane consisting of two nitrogen atoms of the dpyam ligand (Cu-N distances 1.987(3) and 2.010(3) Å) and two oxygen atoms of two different formato ligands (Cu-O distances 1.974(2) and 1.975(2) Å). A coordinated water molecule occupies the axial position at a distance of 2.222(3) Å. The copper atoms are bridged unsymmetrically by a formato anion in a syn-anti arrangement, resulting in a polymeric zig-zag chain structure.The magnetic susceptibility measurements (5-280 K) agree with a very weak ferromagnetic chain interaction between the Cu centres with a J value of 0.75 cm⁻¹.     

Dinuclear triply-bridged copper(II) compounds containing carboxylato bridges and di-2-pyridylamine as a ligand: synthesis, crystal structure, spectroscopic and magnetic properties

Three new triply-bridged dinuclear copper(II) compounds with carboxylato bridges, [Cu₂(μ-O₂CH)(μ-OH)(μ-Cl)(dpyam)₂](PF₆) (1), [Cu₂(μ-O₂CH)₂(μ-OH)(dpyam)₂](PF₆) (2) and [Cu₂(μ-O₂CCH₂CH₃)₂(μ-OH)(dpyam)₂](ClO₄) (3) (dpyam = di-2-pyridylamine) have been synthesized and characterized crystallographically and spectroscopically. Compound 1 consists of a dinuclear unit in which both copper(II) ions are bridged by three different ligands, i.e., formate, chloride and hydroxide anions, providing a distorted trigonal bipyramidal geometry with a CuN₂O₂Cl chromophore. Compounds 2 and 3 have two bridging formato ligands and two bridging propionato ligands, respectively, together with a hydroxo bridge. The carboxylato ligands in both compounds 2 and 3 exhibit different coordination modes. One is in a syn, syn η¹:η¹:μ₂ bridging mode and the other is in a monoatomic bridging mode. The structure of compound 2 involves a dinuclear unit, with a distorted trigonal bipyramidal geometry around each Cu(II) ion with a CuN₂O₃ chromophore. Compound 3 contains a non-centrosymmetric unit; the coordination environment around Cu(1) is a distorted square-pyramidal geometry and an intermediate geometry of sp and tbp around the Cu(II) ion. The Cu?Cu separations are 3.061, 3.113 and 3.006 Å for compounds 1, 2 and 3, respectively. The EPR spectra of all three compounds show a broad isotropic signal with a g value around 2.10.The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a moderate ferromagnetic interaction between the Cu(II) ions with a singlet-triplet energy gap (J) of 79.7, 47.8 and 24.1 cm⁻¹, for compounds 1, 2 and 3, respectively. Also a very weak intermolecular antiferromagnetic interaction was observed between the dinuclear units.     

Modulation of immune responses during HIV-malaria co-infection in pregnancy

Infection with either HIV or malaria during pregnancy often results in adverse outcomes for mother and child. Co-infection further increases the risks of these events, which include maternal anemia and babies with low birth weight. The immunological bases for the increased susceptibility of HIV-infected mothers to malaria and for the effect of co-infection on mother-to-child transmission of HIV are areas of major importance in public health. In this article, we review current data about humoral and cellular responses to HIV-placental-malaria co-infection and present an immunological hypothesis to explain the epidemiological findings.     

The coordination chemistry of mono(di-2-pyridylamine) copper(II) complexes with monovalent and divalent oxoanions: crystal structure, spectroscopic and magnetic properties of dinuclear [Cu(L)(μ-H2PO4)(H2PO4)]2 and polynuclear [Cu(L)(μ3-HPO4)]n

The crystal structures of two copper(II) complexes containing the ligand di-2-pyridylamine (dpyam) with monovalent H₂PO₄ ⁻ and divalent HPO₄ ²⁻ oxoanions, [Cu(dpyam)(μ-H₂PO₄-O,O^′)(H₂PO₄)]₂ (1) and [Cu(dpyam)(μ₃-HPO₄-O,O^′,O″)]_n (2), are reported and determined by X-ray crystallography. The dinuclear Cu(II) complex 1 was obtained by the reaction of dpyam with Cu(NO₃)₂ · 3H₂O and KH₂PO₄ in a water-ethanol (45/55) mixture. The molecules are linked into dinuclear units by two bridging didentate dihydrogenphosphate groups (endo/exo) in an equatorial-equatorial configuration giving a slightly distorted square pyramidal stereochemistry. The Cu-Cu contact distance of 5.136(2) Å is unusually large due to the exo/endo binding of the phosphate bridges. Complex 2 is a polymeric copper(II) derivative with helical [Cu(HPO₄)]₃ units surrounded by dpyam ligands and stabilized by intermolecular hydrogen bonds. Two nearest Cu(II) ions are bridged by a tridentate hydrogenphosphate group which is didentately coordinated to one copper(II) ion, and monodentately coordinated to another in an equatorial-equatorial configuration in an unusual bridging coordination mode. Each copper(II) ion in 2 exhibits a tetrahedrally distorted square-based geometry with the third oxygen atom (Cu-O=2.719(3) Å), from the hydrogenphosphate group weakly bound in an approximately axial position giving an extremely tetrahedrally distorted square-based pyramidal CuN₂O₂O^′ chromophore. The magnetic susceptibility measurements (5-300 K) reveals an antiferromagnetic interaction with J values of −2.85(1) and −26.20(2) cm⁻¹ for complexes 1 and 2, respectively. Some magneto-structural trends are discussed, along with their EPR and electronic reflectance spectra and compared with those of related complexes.