Characterisation by X-ray photoelectron spectroscopy of surface layers of poly(vinyl alcohol) on particles formed by dispersion polymerisation of divinylbenzene

Well-defined dispersions of polydivinylbenzene in methanol and a binary liquid mixture of methanol and water were stabilised by samples of partially hydrolysed poly(vinyl alcohol) (PVOH). Mean particle diameters in the range 0.3–1.0 m were produced in dispersion polymerisations. In order to assess surface coverage by PVOH, alcohol groups in the stabilising surface layer were derivatised with trifluoroacetic anhydride. Characterisation of trifluoroacetate groups by X-ray photoelectron spectroscopy permits the quantitative determination of atomic fluorine. The relative concentrations of surface fluorine are in agreement with expectation based on the degrees of hydrolysis of 35 mol% and 72.5 mol% of the PVOH stabilisers. Treatments based on broadscan and high-resolution spectra permit reasonable estimates of the layer thickness for PVOH chains collapsed onto the surface of dry particles. Calculations of the area occupied per PVOH chain are consistent with estimates for other stabilising chains in hydrocarbon media.     

Quantum dot-labelled polymer beads by suspension polymerisation

CdSe quantum dots with polymerisable ligands have been incorporated into polystyrene beads, via a suspension polymerisation reaction, as a first step towards the optical encoding of solid supports for application in solid phase organic chemistry.     

A comparison of electron-transfer rates of ferrocenoyl-linked DNA

Electron transfer (ET) through two configurations of double-stranded (ds)-DNA was investigated by the attachment of a ferrocenoyl (Fc)-labeled and thiol-labeled DNA to Au electrodes. The first configuration positions the Fc moiety on the same strand as the thiolate, whereas the second configuration positions the Fc group on the complementary strand. The subtle difference in structure leads to a difference in E0' values (29 mV) and in ET rate constants (25 vs 115 s-1). The results have led to a further understanding of electron transfer in ds-DNA, and several models of ET are proposed.     

Optimality in transient markov chains and linear programming

It is shown how a discrete Markov programming problem can be transformed, using a linear program, into an equivalent problem from which the optimal decision rule can be trivially deduced. This transformation is applied to problems which have either transient probabilities or discounted costs.This research was supported by the National Research Council of Canada, Grant A7751.     

Anomalous thresholds and the Isgur-Wise function

The original de Rafael-Taron bound on the slope of the Isgur-Wise function at zero recoil is known to be violated in QCD by singularities appearing in an unphysical region. To be consistent, quark models must have corresponding singularity structures. In an existing relativistic quark-loop model, the meson-quark-antiquark vertex is such that the required singularity is an anomalous threshold. We also discuss the implications of another anomalous threshold, whose location is determined by quark masses alone.