Scanning electrochemical microscopy as a local probe of oxygen permeability in cartilage

The use of scanning electrochemical microscopy, a high-resolution chemical imaging technique, to probe the distribution and mobility of solutes in articular cartilage is described. In this application, a mobile ultramicroelectrode is positioned close (not, vert, similar1 μm) to the cartilage sample surface, which has been equilibrated in a bathing solution containing the solute of interest. The solute is electrolyzed at a diffusion-limited rate, and the current response measured as the ultramicroelectrode is scanned across the sample surface. The topography of the samples was determined using Ru(CN)64−, a solute to which the cartilage matrix was impermeable. This revealed a number of pit-like depressions corresponding to the distribution of chondrocytes, which were also observed by atomic force and light microscopy. Subsequent imaging of the same area of the cartilage sample for the diffusion-limited reduction of oxygen indicated enhanced, but heterogeneous, permeability of oxygen across the cartilage surface. In particular, areas of high permeability were observed in the cellular and pericellular regions. This is the first time that inhomogeneities in the permeability of cartilage toward simple solutes, such as oxygen, have been observed on a micrometer scale

The deposition and chemistry of manganese and zinc in non-aqueous solutions

The electrodeposition of manganese and zinc from non-aqueous solvents was investigated using microelectrodes. Good quality data, free from iR distortion was obtained. Zinc deposition from ZnBr2/TBABF4/THF was found to be simple and rapid. The deposition process proved to be completely reversible. Manganese deposition from three distinct systems was also investigated, i.e., MnBr2/TBABF4/THF, MnBr2/LiBr/THF and MnBr2/TBABF2/TBABF4/DMF. In all cases the deposition reaction proved to be complex and not completely reversible. Analysis of the deposits formed showed that they contained large amounts of some `MnBr' species. It was found that in all the above cases nucleation was instantaneous and was followed by three dimensional growth which was under electron transfer control. The synthesis and reactions of organomanganous reagents was also studied. Manganese alkyls, synthesised from BuLi and MnBr2, were found to react selectively with acid chlorides to give good ketone yields under relatively mild conditions. The solvent and choice of organomanganous species were found to be very important. Organomanganous reagents were also synthesised directly using manganese powder. A Reformatsky type reaction was carried out where an organomanganous species synthesised by reaction of manganese powder with ethyl bromoacetate, was reacted with benzaldehyde. Relatively good yields of the β-acetoxy ester product were obtained, although it was evident that side reactions were occurring.</p