Electrocatalysis of oxygen reduction on multi-walled carbon nanotube supported copper and manganese phthalocyanines in alkaline media

Manganese phthalocyanine (MnPc) and copper phthalocyanine (CuPc)-modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat treated at four different temperatures to investigate the effect of pyrolysis on the oxygen reduction reaction (ORR) activity of these electrocatalysts. The MWCNT to metal phthalocyanine ratio was varied. Scanning electron microscopy (SEM) was employed to visualise the surface morphology of the electrodes and the x-ray photoelectron spectroscopic (XPS) study was carried out to analyse the surface composition of the most active catalyst materials. The ORR was studied in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. Glassy carbon (GC) electrodes were modified with carbon nanotube-supported metal phthalocyanine catalysts using Tokuyama AS-4 ionomer. The RDE results revealed that the highest electrocatalytic activity for ORR was achieved upon heat treatment at 800 °C. CuPc-derived catalyst demonstrated lower catalytic activity as compared to the MnPc-derived counterpart, which is in good agreement with previous literature, whereas the activity of MnPc-based catalyst was higher than that reported earlier.     

Responsive lanthanide luminescent cyclen complexes: from switching/sensing to supramolecular architectures

This article highlights some of the recent developments in the use of responsive cyclen based lanthanide luminescent devices, focusing on Eu(III), Tb(III), Nd(III) and Yb(III) complexes, where the photophysical properties, such as the excited state lifetimes, quantum yield/intensity and emission polarisation are modulated by the local chemical environment, e.g. ions and molecules, or through self-assembly of either f-f or mixed f-d cyclen complexes.     

Water-assisted self-assembly of harmonic single and triple helices in a polymeric coordination complex

A novel two-dimensional coordination polymer containing infinite, coherently pitched single and triple helical motifs is formed by the self-assembly of Cd2+, succinate, water and a bipyridyl ligand.     

Development of a capillary electrophoretic method for the separation of diastereoisomers of a new human immunodeficiency virus protease inhibitor

A capillary electrophoretic (CE) method was developed for the separation of diastereoisomers of a new human immunodeficiency virus (HIV) protease inhibitor TMC114. In total 16 isomers of this drug have been synthesized (eight pairs of enantiomers). We succeeded in the separation of the eight diastereoisomers, but no enantiomers could be separated. Because of the high similarity and water-insolubility of these isomers, the separation is a real challenge. Different CE modes were tried out: capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), micellar electrokinetic capillary chromatography (MEKC), and microemulsion electrokinetic capillary chromatography (MEEKC). Only MEEKC offered resolution of these compounds.     

New cobalt(II) and zinc(II) coordination frameworks incorporating a pyridyl-pyrazole ditopic ligand

The metal-directed assembly of new molecular frameworks incorporating 4-(4-pyridyl)pyrazole (L), containing non-linear coordination vectors, is presented. Three metallo-arrays of types [Co(LH)2(NO3)4], [Co(LH)2(H2O)4][NO3]4.H2O and [Zn2(L-H)2Cl2].2EtOH are reported. The cobalt(II) in [Co(LH)2(NO3)4] displays distorted octahedral geometry, with the two protonated pyridyl-pyrazole ligands coordinated through their pyrazole nitrogen atoms in a trans-orientation; the remaining four coordination sites are occupied by nitrate anions. Two internal hydrogen bonds occur between each pyrazole NH and the oxygens of adjacent coordinated nitrato ligands. Short intermolecular hydrogen bonds also occur between the two pyridinium hydrogens and bound nitrate ligands on different molecules to yield a two-dimensional hydrogen-bonded array. Two of these arrays interpenetrate to form an extended two dimensional layer; such layers stack throughout the crystal structure. A second product of type [Co(LH)2(H2O)4][NO3]4.H2O exists as two crystallographically independent, but chemically similar, forms. In each form, the two protonated pyridyl-pyrazole ligands occupy trans positions about the cobalt, with the remaining four coordination sites being filled by water molecules to yield a distorted octahedral coordination geometry. Intramolecular hydrogen-bonding is observed between the two non-coordinated pyrazoyl nitrogen atoms and bound water oxygen atoms. The third complex, [Zn2(L-H)2Cl2].2EtOH, contains dimer units consisting of two zinc(II) ions bridged by two pyrazoylate groups in which the coordination geometry of each zinc approximates a tetrahedron. Each zinc is bound to two deprotonated pyridine-pyrazole ligands (L-H), one pyridyl group (from a different dimeric unit) and one chloro ligand. Each pyridyl nitrogen thus connects each of these zinc dimers to an adjacent dimer unit, forming a three-dimensional network containing small voids. The latter are occupied by ethanol molecules which form hydrogen bonds to the chloro ligands.     

4-Phosphoryl Pyrazolones for Highly Selective Lithium Separation from Alkali Metal Ions

Effective receptors for the separation of Li⁺ from a mixture with other alkali metal ions under mild conditions remains an important challenge that could benefit from new approaches. In this study, it is demonstrated that the 4-phosphoryl pyrazolones, H L ²-H L ⁴, in the presence of the typical industrial organophosphorus co-ligands tributylphosphine oxide (TBPO), tributylphosphate (TBP) and trioctylphosphine oxide (TOPO), are able to selectively recognise and extract lithium ions from aqueous solution. Structural investigations in solution as well as in the solid state reveal the existence of a series of multinuclear Li⁺ complexes that include dimers (TBPO, TBP) as well as rarely observed trimers (TOPO) and represent the first clear evidence for the synergistic role of the co-ligands in the extraction process. Our findings are supported by detailed NMR, MS and extraction studies. Liquid-liquid extraction in the presence of TOPO revealed an unprecedented high Li⁺ extraction efficiency (78 %) for H L ⁴ compared to the use of the industrially employed acylpyrazolone H L ¹ (15 %) and benzoyl-1,1,1-trifluoroacetone (52 %) extractants. In addition, a high selectivity for Li⁺ over Na⁺, K⁺ and Cs⁺ under mild conditions (pH ∼8.2) confirms that H L ²-H L ⁴ represent a new class of ligands that are very effective extractants for use in lithium separation.     

2′‐De­oxy‐5‐propynyl­cytidine: a nucleoside forming two solid‐state conformations

The title compound, 4‐amino‐1‐(2‐deoxy‐β‐d ‐erythropentofuranosyl)‐5‐(prop‐1‐ynyl)pyrimidin‐2(1H)‐one, C₁₂H₁₅N₃O₄, shows two conformations in the crystalline state which differ mainly in the glycosylic bond torsion angle and the sugar pucker. Both mol­ecules exhibit an anti glycosylic bond conformation, with torsion angles χ = −135.0 (2) and −156.4 (2)° for mol­ecules 1 and 2, respectively. The sugar moieties show a twisted C2′‐endo sugar pucker (S‐type), with P = 173.3 and 192.5° for mol­ecules 1 and 2, respectively. The crystal structure is characterized by a three‐dimensional network that is stabilized by several inter­molecular hydrogen bonds between the two conformers.     

6‐Aza‐2′‐deoxy­uridine and N3‐anisoyl‐6‐aza‐2′‐deoxy­uridine

In 2‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐1,2,4‐triazine‐3,5(2H,4H)‐dione (6‐aza‐2′‐deoxy­uridine), C₈H₁₁N₃O₅, (I), the conformation of the glycosylic bond is between anti and high‐anti [χ = −94.0 (3)°], whereas the derivative 2‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐N⁴‐(2‐methoxy­benzoyl)‐1,2,4‐triazine‐3,5(2H,4H)‐dione (N³‐anisoyl‐6‐aza‐2′‐deoxy­uridine), C₁₆H₁₇N₃O₇, (II), displays a high‐anti conformation [χ = −86.4 (3)°]. The furanosyl moiety in (I) adopts the S‐type sugar pucker (²T₃), with P = 188.1 (2)° and τ_m = 40.3 (2)°, while the sugar pucker in (II) is N (³T₄), with P = 36.1 (3)° and τ_m = 33.5 (2)°. The crystal structures of (I) and (II) are stabilized by inter­molecular N—H⋯O and O—H⋯O inter­actions.     

The 7‐bromo derivative of 2‐amino‐2′‐deoxytubercidin fluorinated at the sugar moiety

The title compound, 2,4‐diamino‐5‐bromo‐7‐(2‐deoxy‐2‐fluoro‐β‐d ‐arabinofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine, C₁₁H₁₃BrFN₅O₃, shows two conformations of the exocyclic C4′—C5′ bond, with the torsion angle γ (O5′—C5′—C4′—C3′) being 170.1 (3)° for conformer 1 (occupancy 0.69) and 60.7 (7)° for conformer 2 (occupancy 0.31). The N‐glycosylic bond exhibits an anti conformation, with χ = −114.8 (4)°. The sugar pucker is N‐type (C3′‐endo; ³T₄), with P = 23.3 (4)° and τ_m = 36.5 (2)°. The compound forms a three‐dimensional network that is stabilized by several intermolecular hydrogen bonds (N—H...O, O—H...N and N—H...Br).