PLD-assisted VLS growth of aligned ferrite nanorods, nanowires, and nanobelts-synthesis, and properties

We report here a systematic synthesis and characterization of aligned alpha-Fe2O3 (hematite), epsilon-Fe2O3, and Fe3O4 (magnetite) nanorods, nanobelts, and nanowires on alumina substrates using a pulsed laser deposition (PLD) method. The presence of spherical gold catalyst particles at the tips of the nanostructures indicates selective growth via the vapor-liquid-solid (VLS) mechanism. Through a series of experiments, we have produced a primitive "phase diagram" for growing these structures based on several designed pressure and temperature parameters. Transmission electron microscopy (TEM) analysis has shown that the rods, wires, and belts are single-crystalline and grow along <111>m or <110>h directions. X-ray diffraction (XRD) measurements confirm phase and structural analysis. Superconducting quantum interference device (SQUID) measurements show that the iron oxide structures exhibit interesting magnetic behavior, particularly at room temperature. This work is the first known report of magnetite 1D nanostructure growth via the vapor-liquid-solid (VLS) mechanism without using a template, as well as the first known synthesis of long epsilon-Fe2O3 nanobelts and nanowires.     

Natural products as an inspiration in the diversity-oriented synthesis of bioactive compound libraries

The purpose of diversity-oriented synthesis is to drive the discovery of small molecules with previously unknown biological functions. Natural products necessarily populate biologically relevant chemical space, since they bind both their biosynthetic enzymes and their target macromolecules. Natural product families are, therefore, libraries of pre-validated, functionally diverse structures in which individual compounds selectively modulate unrelated macromolecular targets. This review describes examples of diversity-oriented syntheses which have, to some extent, been inspired by the structures of natural products. Particular emphasis is placed on innovations that allow the synthesis of compound libraries that, like natural products, are skeletally diverse. Mimicking the broad structural features of natural products may allow the discovery of compounds that modulate the functions of macromolecules for which ligands are not known. The ability of innovations in diversity-oriented synthesis to deliver such compounds is critically assessed.     

A Review of Microdialysis Sampling Systems

The most important aspects of microdialysis are a theoretical understanding of the process, the microdialysis membrane and the design of the microdialysis probe including the inner cannula dimensions. Several efforts have been made to theoretically account for the processes that take place during microdialysis. These have been employed to develop optimal sampling conditions so as to increase the applicability of the technique for in situ sampling and as a sample clean-up technique prior to chromatography. On the occasion of Prof. Lo Gorton’s 60th birthday, this review highlights the challenge presented by low analyte recoveries that is the major bottleneck in the wider use of microdialysis. The discussion concludes by considering how to increase analyte recovery through a multiple probe approach or by an increase in recovery in the light of the advantages of nanotechnology. Both approaches could impact on the use of microdialysis as a sampling and sample clean-up technique for liquid chromatography.     

Optical spectra of protected diamine 10-bond-bridged intervalence radical cations related to N,N,N'N'-tetraalkylbenzidine

The optical absorption spectra of the delocalized intervalence radical cations of seven o,o'-linked benzidine derivatives that have the nitrogens protected as 9-(9-aza-bicyclo[3.3.1]nonan-3-one) derivatives are discussed and compared with that of the p-phenylene radical cation. The linking units are CH2, CH2CH2, NMe, S, SO2, and C=O, and we also studied H,H (the unlinked benzidine). The lowest-energy absorption band is assigned as the transition from the antibonding combination of symmetrical N and aromatic orbitals to the antibonding combination of the antisymmetric N and aromatic orbitals using TD-DFT calculations, and a good correlation between the observed transition energies and those calculated using the simple Koopmans theorem-based "neutral in-cation geometry" calculations on the UB3LYP/6-31G* structures is found. The use of the two-state model that equates the electronic interaction through the bridge between the amino groups with half of the lowest transition energy is seriously incorrect for these and other delocalized intervalence compounds. The problem of extracting the electronic interactions that actually are involved from calculated transition energies is discussed.     

Sample preparation for chromatography: an African perspective

Africa as a continent has its unique challenges for analytical chemists in sample preparation for chromatographic analyses. The areas of agriculture, environment, food and health provide formidable challenges when it comes to method development, for example, drought can result in inadequate supplies of good quality water. The testing of water quality necessitates the development of assay methods that can be employed to not only determine the quantities of pesticides associated with malaria and tsetse fly eradication programmes, but also to monitor mycotoxins or neurotoxins. Urbanisation has also meant that endocrine disruptors such as phthalate esters need to be monitored. This review will profile some of the activities by analytical chemists practising in the African continent, who seek to address some of the challenges in sample preparation for chromatographic analyses.     

Preparation and Characterization of Graphite‐Epoxy Composite Modified with Zinc Hexacyanoferrate and Their Electrochemical Behaviour in Presence of Substituted Anilines

The growth of zinc hexacyanoferrate (ZnHCF) hybrid film on the surface of graphite‐epoxy composite (GEC) electrodes was demonstrated by cyclic voltammetry. Surface morphology of the hybrid film was investigated by using scanning electron microscopy. The effect of the type of monovalent cations on the redox behaviour of hybrid film was also studied. This effect indicated that the radius of the hydrated cation mainly determines the ion permeability of the film.     

Reversible and Selective CO2 to HCO2− Electrocatalysis near the Thermodynamic Potential

Reversible catalysis is a hallmark of energy‐efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition‐state barriers. Using these criteria, we demonstrate reversible CO₂/HCO₂^? conversion catalyzed by [Pt(depe)₂]²⁺ (depe=1,2‐bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO₂ reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO₂ reduction, H₂ evolution is negligible and the Faradaic efficiency for HCO₂^? production is nearly quantitative. A free‐energy analysis reveals H₂ evolution is endergonic, providing a thermodynamic basis for highly selective CO₂ reduction.     

Hierarchical Functionalized Polymeric‐Ceramic Coatings on Mg‐Ca Alloys for Biodegradable Implant Applications

Magnesium‐based implants present several advantages for clinical applications, in particular due to their biocompatibility and degradability. However, degradation products can affect negatively the cell activity. In this work, a combined coating strategy to control the implant degradation and cell regulation processes is evaluated, including plasma electrolytic oxidation (PEO) that produces a 13 µm‐thick Ca, P, and Si containing ceramic coating with surface porosity, and breath figures (BF) approach that produces a porous polymeric poly(ε‐caprolactone) surface. The degradation of PCL‐PEO‐coated Mg hierarchical scaffold can be tailored to promote cell adhesion and proliferation into the porous structure. As a result, cell culture can colonize the inner PEO‐ceramic coating structure where higher amount of bioelements are present. The Mg/PEO/PCL/BF scaffolds exhibit equally good or better premyoblast cell adhesion and proliferation compared with Ti CP control. The biological behavior of this new hierarchical functionalized scaffold can improve the implantation success in bone and cardiovascular clinical applications.     

Electrospun Nanofibers Sorbents for Pre-Concentration of 1,1-dichloro-2,2 bis-(4-chlorophenyl)ethylene with Subsequent Desorption by Pressurized Hot Water Extraction

Electrospun polystyrene (PS) nanofibers (130–500 nm) incorporating a potassium salt of imidazole-1-carbodithioate were evaluated as potential sorbents for the pre-concentration of a model organochlorine pesticide; 1,1-dichloro-2,2bis-(4-chlorophenyl)ethylene (DDE). The efficiencies of DDE (0.25–1.0 μg L^?1) adsorption by the nanofiber sorbent followed by desorption employing pressurized hot water extraction (PHWE) were investigated and monitored using gas chromatography with electron capture detection (GC-ECD). Parameters such as time, temperature and pressure of extraction, sample volume, DDE concentration and sorbent mass were optimized. The maximum adsorption of DDE (0.50 μg L^?1) on electrospun PS and carbodithioate incorporated PS nanofibers was at 43.7 and 94.6%, respectively, in 20 min. Incorporation of carbodithiote doubled the adsorption efficiency of PS and achieved LOD of 0.000234 μg L^?1 for DDE. The optimal DDE desorption on the PHWE system was 93.8% in 10 min. It would seem that the use of electrospun nanofibers as sorbent material with subsequent desorption by PHWE has great potential and thus warrants further investigations. This approach as it uses water as an extraction solvent for an organochlorine pesticide provides an opportunity to eliminate organic solvents, especially for procedures aimed at monitoring organic pollutants in the environment.     

Thermal and odd–even behaviour in a homologous series of lithium n-alkanoates

Thermotropic phase transition temperatures, enthalpies and entropies of phase changes and odd–even alternation, in a homologous series of anhydrous lithium n-alkanoates, LiC_nH_2n?1O₂ (LiC_8–19 inclusive), have been investigated by differential scanning calorimetry (d.s.c.), hot stage polarizing microscopy and solid state ¹³C NMR spectroscopy. The number of phases observed, between the room temperature microcrystalline solid and isotropic melt, shows a clear dependence on chain length. For LiC_8–13, only one intermediate lamellar II crystalline phase is observed. For LiC_14–19, a lamellar II and high temperature phase are evident. The high temperature phase is characterized by pre-melting and disordering of hydrocarbon chains as they change from nearly all-trans to one with increased gauche conformers. It is probably a solid rotator phase. Odd–even alternation in melting temperature, density and some thermodynamic data result from the relative distance between methyl groups, from opposite layers in a bi-layer. Molecular models indicate that the methyl groups in odd chains are more favourably orientated which lead to a more energetically favoured staggered conformer. As a consequence, the methyl groups, for odd chains, are in closer proximity than even chains. This subtle change in the molecular lattice could account for the presence of polymorphic structures on cooling from the melt.