Electrical properties of diamond surfaces functionalized with molecular monolayers

Recent studies have shown that semiconductor surfaces such as silicon and diamond can be functionalized with organic monolayers, and that these monolayer films can be used to tether biomolecules such as DNA to the surfaces. Electrical measurements of these interfaces show a change in response to DNA hybridization and other biological binding processes, but the fundamental nature of the electrical signal transduction has remained unclear. We have explored the electrical impedance of polycrystalline and single-crystal diamond surfaces modified with an organic monolayer produced by photochemical reaction of diamond with 1-dodecene. Our results show that, by measuring the impedance as a function of frequency and potential, it is possible to dissect the complex interfacial structure into frequency ranges where the total impedance is controlled by the molecular monolayer, by the diamond space-charge region, and by the electrolyte. The results have implications for understanding the ability to use molecularly modified semiconductor surfaces for applications such as chemical and biological sensing.     

Sorption of organic dyes by polyurethane foam

The sorption of fifty-nine organic dyes, indicators and stains by polyester and polyether-type polyurethane foams was investigated by use of aqueous solutions and powdered foam material. Comparisons were made with sorption from 50% methanol solutions for some dyes and also with solvent extractions done with diethyl ether or ethyl acetate for several dyes. The R(f) values for the dyes run on cellulose TLC plates in water or a mixed solvent mobile phase were compared to the distribution coefficients with polyurethane foam. The relationship between the structure of the test substances and their sorption is discussed.     

Ballistic impact to access the high-rate behaviour of individual silk fibres

A revision of a classic transverse fibre impact technique is presented, as applied to the problem of obtaining the high strain-rate constitutive behaviour of commercial Bombyx mori silk. Medium tenacity nylon was also studied. Two approaches are presented: firstly a fixed pre-stress, varied impact velocity method that derives stress–strain behaviour by inverse fit; and secondly a fixed impact velocity, varied pre-stress approach, assuming basic elastic jump conditions to obtain a locus of post-impact states. The post-impact stress–strain states obtained using the two approaches converge for silk but diverge for nylon. This we attribute to silk's fine structure being able to homogenise energy dissipation at static and dynamic deformation rates. However, the coarser microstructure of nylon results in a different loading path dependence, thus divergence in the two approaches. It was also noted that silk exhibited a comparatively stable level of impact energy absorption under varying pre-stress, when compared to nylon.     

Determination of total and non-water soluble iodine in atmospheric aerosols by thermal extraction and spectrometric detection (TESI)

Iodine has recently been of interest in atmospheric chemistry due to its role in tropospheric ozone depletion, modification of the HO/HO₂ ratio and aerosol nucleation. Gas-phase iodine chemistry is tightly coupled to the aerosol phase through heterogeneous reactions, which are dependent on iodine concentrations and speciation in the aerosol. To date, the only method available for total iodine determination in aerosols is collection on filters by impaction and quantification by neutron activation analysis (NAA). NAA is not widely available to all working groups and is costly to commission. Here, we present a method to determine total iodine concentrations in aerosol impact filter samples by combustion of filter sub-samples (∼5 cm²) at 1,000 °C, trapping in deionised water and quantification by UV/Vis spectroscopy. Both quartz and cellulose filters were analysed from four separate sampling campaigns. The method proved to be sensitive (3σ = 6 ng absolute iodine ≈ 3 pmol m⁻³) precise (RSD ∼ 5%) and accurate, as determined by external and standard addition calibrations. Total iodine concentrations ranged from 10 pmol m⁻³ over the Southern Ocean to 100 pmol m⁻³ over the tropical Atlantic, in agreement with previous estimates. The soluble iodine concentration (extracted with water and measured by ICP-MS) was then subtracted from the total iodine to yield non-water-soluble iodine (NSI). The NSI fraction ranged from 20% to 53% of total iodine, and thus can be significant in some cases.     

Double Molecular Encapsulation of Tetrahydrofuran by an Amphiphilic Calix-[4]-arene

The crystal structure of para-octanoylcalix-[4]-arene·2 tetrahydrofuran complex reveals double inclusion of the guest molecules, one deep in the aromatic cavity and the other held in a four-fingered molecular hand formed by the aliphatic chains, the inclusion changes the molecular packing from a bilayer system in the absence of guest, to a head-to-tail antiparallel chain packing.This revised version was published online in July 2005 with a corrected issue number.     

Access to macrocyclic endocyclic and exocyclic allylic alcohols by nickel-catalyzed reductive cyclization of ynals

Ni-catalyzed reductive macrocyclizations of ynals are reported. Disubstituted alkynes afford either endocyclic or exocyclic allylic alcohols depending on the ligand. Phosphine ligands favor the formation of endocyclic olefins, whereas N-heterocyclic carbene ligands favor the formation of exocyclic olefins. Terminal alkynes provide 1,2-disubstituted olefins with N-heterocyclic carbene ligands.     

The influence of intramolecular hydrogen bonding on the structure and E ↔ Z photoisomerization of urocanic acid derivatives

The molecular structures and E ? Z photoisomerization reactions of methyl urocanate and several urocanamides were investigated. All of the Z isomers possess intramolecular hydrogen bonds. The intramolecular hydrogen bonds may influence the efficiency of photoisomerization but do not totally inhibit its occurrence. The relative energies of the electronic absorption of the E and Z isomers depends on the mode of hydrogen bonding and are accurately predicted in the case of methyl urocanate using INDO/S-CI calculations. The solvent dependence of the absorption spectra of methyl urocanate can be related to the effects of inter- and intramolecular hydrogen bonding.