Design and synthesis of a 4-(2'-pyridyl)-1,2,3,5-dithiadiazolyl cobalt complex

The 4-(2'-pyridyl)-1,2,3,5-dithiadiazolyl neutral radical 1 has been prepared for use as a spin-bearing bidentate ligand. The coordination of this ligand to bis(hexafluoroacetylacetonato)cobalt affords a thermally stable complex 2. Magnetic susceptibility measurements of the crystalline complex indicate ferromagnetic coupling between the ligand-centered spin and the unpaired electrons of the high-spin Co(II).     

The role of non-coordinating anions in homogeneous olefin polymerization

We present an overview of homogeneous olefin polymerization catalysts in which chain initiation and propagation involves a metallocenium ion (e.g. Cp₂ZrMe⁺) that can be produced by equilibrium or irreversible CH₃⁻ transfer. The Kaminsky catalyst is an example of the former. Complexes of (C₆F₅)₃B with water, alcohols, mercaptans, silanols and oximes are strong acids which can protonate dialkylmetallocenes to produce weakly-coordinated metallocenium salts that are hydrocarbon soluble and which produce high molecular weight poly-1-olefins. Polymer molecular weight is correlated with the steric and electronic effects of the ligands attached to the metal.     

The solution phase characterization of poly(ferrocenyldimethylsilane)s by small‐angle neutron scattering

A series of monodisperse (M_w/M_n < 1.1) poly(ferrocenyldimethylsilane)s was prepared with number‐averaged degrees of polymerization, 〈z〉_n, of 9, 33, 206, and 506 ( 2 – 5 , respectively), as determined by gel permeation chromatography (GPC). The polymers were studied by small‐angle neutron scattering (SANS) in solution with the aim of obtaining the radius of gyration, R_g, the weight‐averaged molecular weight, M_w, and the polydispersity index, M_w/M_n. Data were collected over the range 0.008 < Q/Å^?1 < 0.5 and for a series of concentrations (weight fraction, w = 0.0063, 0.0125, 0.025, and 0.05). The scattered intensity, I(Q), was fitted to a model based on a Schultz–Zimm distribution of isolated chains with excluded volume. A comparison of the molecular weight and size data determined by GPC and SANS indicated an acceptable agreement between the values for R_g, M_w and M_w/M_n. The results of this study demonstrate the potential utility of SANS to fully characterize metallopolymers, and other polymer systems where traditional methods cannot be applied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4011–4020     

Manganese Triacetate Oxidation of 3β, 3aβ, 6-Trimethyl-3a, 7aβ-dihydro-2(3H), 5(4H)-benzofurandione

The manganese triacetate oxidation of hindered α¹-positions in a model enone, 3β, 3aβ, 6-trimethyl-3a, 7aβ-dihydro-2(3H), 5(4H)-benzofurandione, provided a procedure for the introduction of the α′-hydroxyenone functionality characteristic of the A ring of certain quassinoids.     

Engineering Multifunctional Capsules through the Assembly of Metal–Phenolic Networks

Metal–organic coordination materials are of widespread interest because of the coupled benefits of inorganic and organic building blocks. These materials can be assembled into hollow capsules with a range of properties, which include selective permeability, enhanced mechanical/thermal stability, and stimuli‐responsiveness. Previous studies have primarily focused on the assembly aspects of metal‐coordination capsules; however, the engineering of metal‐specific functionality for capsule design has not been explored. A library of functional metal–phenolic network (MPN) capsules prepared from a phenolic ligand (tannic acid) and a range of metals is reported. The properties of the MPN capsules are determined by the coordinated metals, allowing for control over film thickness, disassembly characteristics, and fluorescence behavior. Furthermore, the functional properties of the MPN capsules were tailored for drug delivery, positron emission tomography (PET), magnetic resonance imaging (MRI), and catalysis. The ability to incorporate multiple metals into MPN capsules demonstrates that a diverse range of functional materials can be generated.     

Four cytotoxic N4‐substituted thiosemicarbazones derived from 2‐hydroxynaphthalene‐1‐carboxaldehyde

The X‐ray crystal structures are reported of four novel and potentially O,N,S‐tridentate donor ligands that demonstrate antitumour activity. These ligands are 1‐[(4‐methyl­thio­semicarbazono)methyl]‐2‐naphthol, C₁₃H₁₃N₃OS, (III), 1‐[(4‐ethylthio­semicarbazono)­methyl]‐2‐naphthol, C₁₄H₁₅N₃OS, (IV), 1‐[(4‐phenyl­thio­semicarbazono)­methyl]‐2‐naphthol, C₁₈H₁₅N₃OS, (V), and 1‐[(4,4‐di­methyl­thio­semicarbazono)­methyl]‐2‐naphthol di­methyl sulfoxide solvate, C₁₄H₁₅N₃OS·C₂H₆OS, (VI). These chelators are N4‐substituted thio­semicarbazones, each based on the same parent aldehyde, namely 2‐­zhydroxynaphthalene‐1‐carboxaldehyde isonicotinoylhydrazone. Conformational variations within this series are discussed in relation to the optimum conformation for metal‐ion binding.     

Chemical composition and antimicrobial activity of the essential oils of Onychopetalum amazonicum R.E.Fr.

The essential oils from leaves, twigs and trunk bark of Onychopetalum amazonicum R.E. Fr. (Annonaceae), obtained by hydrodistillation, were analysed by GC and GC–MS, and also were evaluated for in vitro antimicrobial activity. Forty-one compounds, which correspond to 75.0–92.2% of the oil components, were identified. Major compounds were sesquiterpenes, including (E)-caryophyllene, caryophyllene oxide, spathulenol, α-gurjunene, allo-aromadendrene and α-epi-cadinol. The oils were evaluated for antimicrobial activities against four bacteria strains and five pathogenic fungi. The oil of the trunk bark exhibited good activity against Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 10538 and Kocuria rhizophila ATCC 9341, with a minimal inhibitory concentration of 62.5 μg/mL. The essential oil composition and the antimicrobial evaluation are reported for the first time for the genus Onychopetalum.     

NMR structural characterization from one‐bond 13C?13C couplings: Complete assignment of a hydrogen‐poor depsidone

The connectivity, conformation, tautomeric form, and dynamics of a new depsidone (perisalazinic acid) were characterized using one‐bond ¹³C? ¹³C NMR scalar couplings (¹J_CC) obtained from the INADEQUATE experiment. Characterization of perisalazinic acid using more conventional NMR techniques is problematic due to the extremely limited number of C? H protons present. In the present study, 81 candidate structures were considered and a best fit structure was selected by comparing computed ¹J_CC values for each candidate to 15 experimental values. Of the six flexible moieties in perisalazinic acid, three are adequately represented by a single orientation stabilized by intramolecular hydrogen bonding. The three remaining groups are present as mixtures of conformers with two sites consisting of a pair of conformations and another disordered over six orientations. This study demonstrates the feasibility of complete three‐dimensional structural characterization of an unknown using only theoretical and experimental ¹J_CC values.     

Report on the standardization workshop, 11th ICTAC 1996

This was a very well attended meeting with the numbers reflecting an increasing world-wide demand for certified reference materials. This is an inevitable consequence of the growth of schemes for the accreditation of the quality of measurement.