Bryce E. Williamson

Reaction of gold substrates with diazonium salts in acidic solution at open-circuit potential.

The reaction of gold substrates with p-nitrobenzene diazonium tetrafluoroborate (NBD) in 0.1 M H(2)SO(4) at open-circuit potential (OCP) is demonstrated to proceed by electron transfer from gold to the NBD cation. Electrochemical, atomic force microscopy, and X-ray photoelectron spectroscopy analyses reveal the formation of multilayer films with the same composition as electrografted films. The film growth characteristics (surface concentration and film thickness vs time) also follow those observed during electrografting, consistent with electron transfer from the substrate to the diazonium cation. The OCP of the gold substrate increases during the period of film growth ( approximately 60 min) and then decreases to close to its initial value. The increase corresponds to accumulation of positive charge as electrons are transferred to NBD; the discharge process is tentatively attributed to slow oxidation of adventitious impurities in the reaction solution. Films formed at OCP or by electrografting from aqueous acid solution are markedly less stable to sonication in acetonitrile than are those electrografted from acetonitrile. Increased amounts of physisorbed material in films prepared in aqueous media or bonding of aryl groups to different gold sites in the two media are tentatively proposed to account for the different stabilities.

Chiral, single-molecule nanomagnets: synthesis, magnetic characterization and natural and magnetic circular dichroism

The first three chiral dodecamanganese clusters that behave as single-molecule magnets are reported. All reveal natural optical activity, which is stronger for the 2-chloropropionate derivative than for either the (S)-6-methoxy-α-methyl-2-naphthaleneacetate or the (S)-2-phenylbutyric acetate compounds. For the cluster with 2-chloropropionate moieties at its periphery, the magnetic circular dichroism was investigated and found to display large optical hysteresis, which depends on the direction in which the magnetic field direction is swept.

Patterning of metal, carbon, and semiconductor substrates with thin organic films by microcontact printing with aryldiazonium salt inks.

Surface modification through reduction of aryldiazonium salts to give covalently attached layers is a widely investigated procedure. However, realization of potential applications of the layers requires development of patterning methods. Here, we demonstrate that microcontact printing with poly(dimethylsiloxane) stamps inked with aqueous acid solutions of aryldiazonium salts gives stable organic layers on gold, copper, silicon, and graphitic carbon surfaces. Depending on the substrate-diazonium salt combination, the layers range from relatively irregular multilayers to smooth films with close to monolayer thickness. After printing, surface attached aminophenyl and carboxyphenyl groups retain their usual reactivity toward amide bond formation with solution species, and hence, the method is a simple route to patterned, covalently attached, reactive tether layers. Multicomponent patterned films can be prepared by printing a second modifier onto a film-coated surface. Microcontact printing using aryldiazonium salt inks is experimentally very simple and is applicable to the broad range of substrates capable of spontaneously reducing aryldiazonium salts.

The effectiveness of N2O in depleting stratospheric ozone

Recently, it was shown that of the ozone-depleting substances currently emitted, N2O emissions (the primary source of stratospheric NOx) dominate, and are likely to do so throughout the 21st century. To investigate the links between N2O and NOx concentrations, and the effects of NOx on ozone in a changing climate, the evolution of stratospheric ozone from 1960 to 2100 was simulated using the NIWA-SOCOL chemistry-climate model. The yield of NOx from N2O is reduced due to stratospheric cooling and a strengthening of the Brewer-Dobson circulation. After accounting for the reduced NOx yield, additional weakening of the primary NOx cycle is attributed to reduced availability of atomic oxygen, due to a) stratospheric cooling decreasing the atomic oxygen/ozone ratio, and b) enhanced rates of chlorine-catalyzed ozone loss cycles around 2000 and enhanced rates of HOx-induced ozone depletion. Our results suggest that the effects of N2O on ozone depend on both the radiative and chemical environment of the upper stratosphere, specifically CO2-induced cooling of the stratosphere and elevated CH4 emissions which enhance HOx-induced ozone loss and remove the availability of atomic oxygen to participate in NOx ozone loss cycles.

Aggregation and site-selective spectroscopy of matrix-isolated metallophthalocyanines

Abstract Absorption, emission and selective excitation spectra are reported for the Q ( 1 E u ↔ 1 A 1g ) transition of zinc phthalocyanine (ZnPc) in Ar matrices. The dependence of the spectra on the method of sample preparation and subsequent treatment of the matrix are indicative of gas-phase aggregation of ZnPc. A simple matrix-preparation method is described that consistently yields samples dominated by well-isolated monomeric guest molecules. The variations of hole-burning efficiency with sample-preparation method and concentration, as well as its dependence on burn wavelength, indicate a role for inter-chromophore interactions and are consistent with a hole-burning mechanism that involves intermolecular triplet-state charge transfer followed by singlet recombination.

Spectroscopic and related evidence on the coloring and constitution of New Zealand jade

Abstract Infrared, optical absorption spectroscopy, and Mössbauer spectroscopy were used to investigate the color of jade from New Zealand. Spectroscopic results were supplemented by chemical analyses and petrological examination. Infrared spectra gave a quick identification of the matrix, optical absorption spectra gave information on color in relation to observed absorption bands, and Mössbauer spectra gave the distribution of Fe2+ and Fe3+ at the cation sites and also show how the Fe3+/Fe2+ ratio increases due to oxidative weathering. The development of the attractive flecking in the gem-quality jade is due to agglomerations of colloidally dispersed magnetite or chromite that can also lead to the formation of black spots. Darker samples are generally high in total iron, although not all lightly colored (or pale) samples are low in iron-cream or white unweathered nephrite can also contain high iron concentrations. Weathering under the climatic conditions where the samples occur can produce either a brown, hydrated iron oxide, or a whitish outer rind if the acidity is high enough to remove the oxide. In either case the nephrite matrix is unaltered. Two quite rare variations were found and ascribed to: (1) incomplete nephrite formation in samples developed in association with an unusual ultramafic protolithology and (2) the formation of chromian margarite giving rise to a bluish-green (pseudo) jade

Raman Spectra of Phosphate and Monofluorophosphate Ions in Several Dentally-Relevant Materials

Raman spectra of octacalcium phosphate, sodium monofluorophosphate and aqueous monofluorophosphate solutions were obtained, some at temperatures as low as 40°K. The internal modes of phosphate and mon

Dependence of catalytic activity and long-term stability of enzyme hydrogel films on curing time

Enzyme hydrogels were prepared on carbon film electrodes using glucose oxidase and an epoxide crosslinking agent. The catalytic activity of the gels was found to depend strongly on curing time. The competing effects of increased mechanical stability and decreased enzyme activity as curing time increases resulted in the highest catalytic activity for films cured for 24h at 25 degrees C. Weekly electrochemical measurements established that the long-term stabilities of all hydrogels cured for 24-72 h were similar, with close to half of the initial catalytic activity being retained after immersion for 3 months in agitated phosphate buffer solution at 25 degrees C.

Tuning the selectivity of a supported gold catalyst in solvent- and radical initiator-free aerobic oxidation of cyclohexene

The selectivity of supported gold catalysts in aerobic oxidation of cyclohexene under solvent-free conditions without addition of a radical initiator was tuned by either WO3 or the metal–organic framework MIL-101, used as a support/co-catalyst. WO3 was found to promote the formation of cyclohexene oxide via reaction of cyclohexenyl hydroperoxide with cyclohexene, while MIL-101 catalysed conversion of cyclohexenyl hydroperoxide to 2-cyclohexen-1-one.

Magnetic circular dichroism of the potassium atom “blue triplet” in a xenon matrix

Abstract The K/Xe “blue triplet” spectrum (730–790 nm) arises from K atoms in three distinct sites. Each site gives rise to a similar 2 S→ 2 P triplet pattern. The effective excited state spin-orbit coupling constant is −170 cm −1 compared to the values −213 and −196 cm −1 for Na/Xe and Li/Xe respectively.