Crown ether complexes of potassium and thallium(I) 2- and 4-nitrophenoxides

18-Crown-6 and dicyclohexano-18-crown-6 complexes of potassium 2- and 4-nitrophenoxide, and 18-crown-6 complexes of thallium(I) 2- and 4-nitrophenoxide have been synthesized. Solvent effects on the visible spectra of the nitrophenoxide anions are independent of the nature of the cation and the nature of the complexing agent. The 18-crown-6 complex of thallium(I) 2-nitrophenoxide is a 1:2 complex. All the other complexes are 1:1. X-ray crystallographic examination of the potassium dicyclohexano-18-crown-6 complexes showed the potassium ion is octacoordinated in the 2-nitrophenoxide and heptacoordinated in the 4-nitrophenoxide.     

Surface and curvature properties of neutron-rich nuclei

We use the extended Thomas-Fermi approximation and Skyrme-type interactions to describe the energy density of a semi-infinite slab of neutron-rich nuclear matter at zero temperature. We allow for the existence of a drip phase at low proton fractions in addition to the more dense nuclear phase. We determine various bulk properties of both phases when the system is in equilibrium. We extend the usual definition of the surface energy to apply to the case where drip is present. Assuming the density profile has the form of a Fermi function to a power, we perform a constrained variational calculation to determine the parameters of the density profile. The surface and curvature energies are calculated for proton fractions ranging from 0.5 (symmetric nuclear matter) to 0 (pure neutron matter) for typical Skyrme-type interactions. We find significantly different asymmetry dependences for different interactions. For proton fractions close to 0.5, our results are in close agreement with the predictions of the droplet model. We also present results of calculations for fission barrier properties and phase transitions between nuclei and bubbles to highlight the role of surface and curvature energies in the neutron-rich regime.     

Cluster bonding and energetics of the borane anions,BnHn2− (n = 5–12): A comparative study using bond length—bond enthal

Cluster bond enthalpies, E_L(BB), and orders, n?(BB), for the structurally characterised closo anions, B_nH_n^2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships E_L(BB) (kJ mol^?1) = 1.766 × 10¹¹ [L(BB)]^?4.0 and E_L(BB) (kJ mol^?1) = 318.8[n?(BB)]^0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, E_I, have been calculated using the relationships E_I(BB) = 297.9 I(BB) and E_I(BH) = 374.8I(BH) (enthalpies in kJ mol^?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of E_L and Σ E_L generally exceed those of E_I and Σ E_I by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of B_nH_n^2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ E_I values suggest that the anions are all of comparable stability, the ΣE_L values clearly show B₆H₆^2?, B₁₀H₁₀^2? and B₁₂H₁₂^2? to be more stable than B₈H₈^2?, B₉H₉^2? and B₁₁H₁₁^2?. The interatomic distances in B₇H₇^2? and in the unknown B₅ H₅^2? are estimated and used to assess their relative stabilities. The E_L values suggest that B₇ H₇^2? is of comparable stability to B₈H₈^2? etc., but show B₅H₅^2? as relatively unstable. The E_I values suggest that both of these anions should be relatively stable members of the series of closo anions.     

Salt-induced swelling-to-shrinking transition in polyelectrolyte multilayer capsules

We study the size of polyelectrolyte multilayer capsules as a function of ionic strength, temperature, and time. A dynamic micromechanical model is developed which successfully describes the experiments. The model includes the polymer-solvent surface tension, an electrostatic force which is strongly ionic strength dependent, and a temperature-dependent mobility parameter. The activation of >50 kT suggests that multiple ion pairs must be broken simultaneously in the process of chain rearrangement. In support of our physical model capsules can repeatedly swell and shrink by varying ionic strength.     

Triarylphosphine-stabilized platinum nanoparticles in three-dimensional nanostructured films as active electrocatalysts

Ligand-stabilized platinum nanoparticles (Pt NPs) can be used to build well-defined three-dimensional (3-D) nanostructured electrodes for better control of the catalyst architecture in proton exchange membrane fuel cells (PEMFCs). Platinum NPs of 1.7 +/- 0.5 nm diameter stabilized by the water-soluble phosphine ligand, tris(4-phosphonatophenyl)phosphine (TPPTP, P(4-C6H4PO3H2)3), were prepared by ethylene glycol reduction of chloroplatinic acid and subsequent treatment of the isolated nanoparticles with TPPTP. The isolated TPPTP-stabilized Pt NPs were characterized by multinuclear magnetic resonance spectroscopy (31P and 195Pt NMR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). The negatively charged TPPTP-Pt NPs were electrostatically deposited onto a glassy carbon electrode (GCE) modified with protonated 4-aminophenyl functional groups (APh). Multilayers were assembled via electrostatic layer-by-layer deposition with cationic poly(allylamine HCl) (PAH). These multilayer films are active for the key hydrogen fuel cell reactions, hydrogen oxidation (anode) and oxygen reduction (cathode). Using a rotating disk electrode configuration, fully mass-transport limited kinetics for hydrogen oxidation was obtained after 3 layers of TPPTP-Pt NPs with a total Pt loading of 4.2 microg/cm2. Complete reduction of oxygen by four electrons was achieved with 4 layers of TPPTP-Pt NPs and a total Pt loading of 5.6 microg/cm2. A maximum current density for oxygen reduction was reached with these films after 5 layers resulting in a mass-specific activity, i(m), of 0.11 A/mg(Pt) at 0.9 V. These films feature a high electrocatalytic activity and can be used to create systematic changes in the catalyst chemistry and architecture to provide insight for building better electrocatalysts.     

Non-aqueous solvation of n-octanol and ethanol: spectroscopic and computational studies

Raman spectroscopy was used to examine the interactions of the free O-H bonds in n-octanol and ethanol with the organic solvents carbon tetrachloride (CCl(4)), cyclohexane, and benzene. These spectra reveal that the solvents CCl(4) and cyclohexane have a small effect on the free O-H peak of alcohols, whereas benzene as a solvent significantly red-shifts the free O-H band. Calculated spectra were generated via MP2/6-31G* calculations and the B3LYP/6-31+G**//MP2/6-31G*-derived Boltzmann populations of each ethanol complex and are consistent with the experimental results. Additional spectra were calculated using Boltzmann populations derived from single-point energies at the polarizable continuum model (PCM) level with the B3LYP/6-31+G** level of theory to take overall solvent effects into account, and these simulated spectra are also largely consistent with the experimental results. Analysis of the computational results reveals a lengthening of the O-H bond from the O-H interaction with the delocalized electronic structure of benzene as well as a bimodal distribution of the free O-H peak of the alcohol/benzene mixtures due to two distinctly different types of alcohol/benzene complexes.     

A new technique to examine individual pollutant particle and fibre deposition and transit behaviour in live mouse trachea

During respiration, particles suspended in the air are inhaled and unless cleared by airway defences they can remain and affect lung health. Their size precludes the use of standard imaging modalities so we have developed synchrotron phase-contrast X-ray imaging (PCXI) methods to non-invasively monitor the behaviour of individual particles in live mouse airways. In this study we used these techniques to examine post-deposition particle behaviour in the trachea. PCXI was used to monitor the deposition and subsequent behaviour of particles of quarry dust and lead ore; fibres of asbestos and fibreglass; and hollow glass micro-spheres. Visibility was examined in vitro and ex vivo to avoid the complicating effects of surrounding tissue and respiratory or cardiac motion. Particle behaviour was then examined after deposition onto the tracheal airway surfaces of live mice. Each particle and fibre looked and behaved differently on the airway surface. Particles lodged on the airway shortly after deposition, and the rate at which this occurred was dependent on the particle type and size. After the live-imaging experiments, excised airway samples were examined using light and electron microscopy. Evidence of particle capture into the airway surface fluids and the epithelial cell layer was found. PCXI is a valuable tool for examining post-deposition particulate behaviour in the tracheal airway. These first indications that the interaction between airways and individual particles may depend on the particle type and size should provide a novel approach to studying the early effects of respired particles on airway health.     

Miklós–Manickam–Singhi conjectures on partial geometries

In this paper we give a proof of the Miklós–Manickam–Singhi (MMS) conjecture for some partial geometries. Specifically, we give a condition on partial geometries which implies that the MMS conjecture holds. Further, several specific partial geometries that are counterexamples to the conjecture are described.     

Impact of grain-dependent boron uptake on the electrochemical and electrical properties of polycrystalline boron doped diamond electrodes

A combination of high-resolution electrical and electrochemical imaging techniques, in conjunction with cathodoluminescence (CL), is used to investigate the electrochemical behavior of oxygen-terminated highly doped polycrystalline boron doped diamond (BDD). The BDD has a dopant density approximately 5 x 10(20) atoms cm(-3), grain size ca. 5-40 microm, and thickness 500 microm. CL imaging demonstrates that boron uptake is nonuniform across the surface of BDD, and conducting atomic force microscopy (C-AFM) highlights how this impacts on the local conductivity. While C-AFM shows no evidence for enhanced grain boundary conductivity, two characteristic conductivity domains are found with resistances of ca. 100 kOmega and ca. 50 MOmega. With the use of scanning electrochemical microscopy (SECM), local heterogeneities are also observed in the electroactivity of the BDD surface, consistent with the two different types of conducting regions. Local currents of the magnitude expected for metal-like behavior are observed in some regions, suggesting degenerative doping of the grains (supported by CL studies). In other regions, slower electron transfer is apparent. However, even for the reduction of Ru(NH(3))(6)(3+), which occurs at potentials far negative of the flat-band potential for oxygen-terminated BDD, all areas of the surface show some electroactivity. This study highlights that the spatially heterogeneous conductivity and corresponding electroactivity of BDD are readily resolved using a combination of C-AFM, SECM, and CL.