The application of radiochemical techniques to the study of surface reactions

The aim of the investigation was to find the mechanism of selective catalysis in the Rosenmund reaction, i.e. the catalytic hydrogenation of acid chlorides to aldehydes under such conditions that no further hydrogenation takes place. Benzoyl chloride was chosen as the primary reactant in all the experiments. A detailed examination was made of the purity of the reagents. The reaction conditions were investigated to find the procedure necessary in order to give an optimum yield of aldehyde. The effect of controlled amounts of added impurities in the reaction mixture and in the synthesis of the catalyst was also examined. A range of selective poisons for the reaction was investigated and it was found that the most powerful poison, i.e. the one which gave the largest yield of aldehyde with the minimum amount of poison added, was tetramethylthiourea. It was shown that decomposition or hydrogenation of all the poisons took place during the reaction. Elementary sulphur was found to be an efficient poison if added under the correct conditions. Palladium sulphide (PdS) catalysts decomposed with loss of sulphur under the reaction conditions and required addition of a sulphur poison in order to give a yield of aldehyde. The effect of temperature on the reaction was also studied and it was found that the reaction products varied with the temperature. To distinguish between consecutive and simultaneous reaction mechanisms, C14 labelled aldehyde was added to a hydrogenation. A loss of activity showed that the reaction proceeded in a stepwise manner, i.e. the primary reaction product could react further by being readsorbed on the catalyst surface. As an aid to the elucidation of the mechanism, the adsorption of reactants on the catalyst surface was investigated by means of a liquid scintillation counter. An accurate method of determining the partition ratio of a reactant, between solvent and catalyst, in the presence of scintillation quenching effects was discovered. The adsorption of aldehyde was examined and there was shown to be a correlation between the amount of aldehyde on the catalyst surface and the rate of reaction at the corresponding concentration A mechanism for the selective action of the poison in the Rosenmund reaction was postulated to explain these results

Effect of surface treatments of titanium dioxide pigments on the cure of polyester/triglycidyl isocyanurate powder coatings

Titanium dioxide pigments will typically have an inorganic surface coating based on a blend of alumina and silica and an organic treatment. Both the organic and inorganic treatments can influence the cure characteristics of polyester powder coatings. This paper attempts to explore the connectivity between the nature of the coating and the cure behavior of a typical heat-cured epoxidized isocyanurate formulation. It is found that a high silica:alumina content in the inorganic pacification layer significantly retards the cure process, but is influenced by the nature of the organic treatment. The organic surface treatment may accelerate or retard the initial cure process and gelation times. Elemental analysis indicates that some of the pigments studied have a significantly higher zirconium content and exhibited enhanced cure rates compared with those with the lower zirconium content. This paper illustrates the potential effects of different grades of titanium dioxide on the cure of polyester powder coatings

Interaction with nanoscale topography: Adhesion quantification and signal transduction in cells of osteogenic and multipotent lineage

Polymeric medical devices widely used in orthopedic surgery play key roles in fracture fixation and orthopedic implant design. Topographical modification and surface micro-roughness of these devices regulate cellular adhesion, a process fundamental in the initiation of osteoinduction and osteogenesis. Advances in fabrication techniques have evolved the field of surface modification; in particular, nanotechnology has allowed the development of nanoscale substrates for the investigation into cell-nanofeature interactions. In this study human osteoblasts (HOBs) were cultured on ordered nanoscale pits and random nano craters and islands. Adhesion subtypes were quantified by immunofluorescent microscopy and cell-substrate interactions investigated via immuno-scanning electron microscopy. To investigate the effects of these substrates on cellular function 1.7 k microarray analysis was used to establish gene profiles of enriched STRO-1+ progenitor cell populations cultured on these nanotopographies. Nanotopographies affected the formation of adhesions on experimental substrates. Adhesion formation was prominent on planar control substrates and reduced on nanocrater and nanoisland topographies; nanopits, however, were shown to inhibit directly the formation of large adhesions. STRO-1+ progenitor cells cultured on experimental substrates revealed significant changes in genetic expression. This study implicates nanotopographical modification as a significant modulator of osteoblast adhesion and cellular function in mesenchymal populations

Genomic expression of mesenchymal stem cells to altered nanoscale topographies

The understanding of cellular response to the shape of their environment would be of benefit in the development of artificial extracellular environments for potential use in the production of biomimetic surfaces. Specifically, the understanding of how cues from the extracellular environment can be used to understand stem cell differentiation would be of special interest in regenerative medicine.In this paper, the genetic profile of mesenchymal stem cells cultured on two osteogenic nanoscale topographies (pitted surface versus raised islands) are compared with cells treated with dexamethasone, a corticosteroid routinely used to stimulate bone formation in culture from mesenchymal stem cells, using 19k gene microarrays as well as 101 gene arrays specific for osteoblast and endothelial biology.The current studies show that by altering the shape of the matrix a cell response (genomic profile) similar to that achieved with chemical stimulation can be elicited. Here, we show that bone formation can be achieved with efficiency similar to that of dexamethasone with the added benefit that endothelial cell development is not inhibited. We further show that the mechanism of action of the topographies and dexamethasone differs. This could have an implication for tissue engineering in which a simultaneous, targeted, development of a tissue, such as bone, without the suppression of angiogenesis to supply nutrients to the new tissue is required. The results further demonstrate that perhaps the shape of the extracellular matrix is critical to tissue development