Oxidised mannan as a novel adjuvant inducing mucosal IgA production.

Mannan, oxidatively coupled to recombinant protein antigens, has here been tested as a possible adjuvant for the production of antibody on the mucosa. Given intranasally, but not intraperitoneally, mannan markedly enhanced the production of IgA, IgG1 and IgG2a in the serum, and IgA locally in the lung and at remote mucosal sites, including tears, vaginal and salivary secretions. Oxidative coupling was critical to its action, since neither mannan simply mixed with protein nor mannan–protein conjugates which had been reduced by treatment with sodium borohydride, acted as adjuvants. Oxidatively coupled mannan was compared with the widely studied mucosal adjuvant, cholera toxin (CT). The use of oxidised mannan as an adjuvant induced better responses than CT judged by the induction of IgA in serum, vaginal washings and saliva. Thus, oxidised mannan, which is non-toxic and can be administered without injection, is a suitable adjuvant coupled with protective antigens for vaccinating against a number of infections that occur via the mucous membranes.

Oxidised mannan-listeriolysin O conjugates induce Th1/Th2 cytokine responses after intranasal immunisation

Clearance of infectious organisms does not always require polarised Th1 or Th2 responses and it may be advantageous for both Th1 and Th2 responses to be elicited for effective protection against an invading pathogen. It was the aim of this study to investigate oxidised mannan as a possible Th1/Th2 adjuvant. Oxidised mannan was conjugated to two candidate antigens and delivered intranasally to mice. Immunisation with the oxidised conjugate resulted in significant antigen specific proliferative responses, IL-2, IFN-γ and IL-4 production when compared to unconjugated controls.

Infrared study of methyl formate and formaldehyde adsorption on reduced and oxidised silica-supported copper catalysts

Infrared spectra are reported of methyl formate and formaldehyde adsorbed at 300 K on silica, Cu/SiO2 reduced in hydrogen and Cu/SiO2 which had been oxidised by exposure to nitrous oxide after reduction. Silanol groups on silica form hydrogen bonds with carbonyl groups in weakly adsorbed methyl formate molecules. Methyl formate ligates via its carbonyl groups to Cu atoms in the surface of reduced copper. A low residual concentration of surface oxygen on copper promoted the slow reaction of ligated methyl formate to give a bridging formate species on copper and adsorbed methoxy groups. Methyl formate did not ligate to an oxidised copper surface but was rapidly chemisorbed to give unidentate formate and methoxy species. Formaldehyde slowly polymerises on silica to form trioxane and other oxymethylene species. The reaction is faster over Cu/SiO2 which, in the reduced state, also catalyses the formation of bridging formate anions adsorbed on copper. The reaction between formaldehyde and oxidised Cu/SiO2 leads to both unidentate and bidentate formate and adsorbed water.

Infrared study of the adsorption of formic acid on silica-supported copper and oxidised copper catalysts

Infrared spectra are reported of formic acid adsorbed at 300 K on a reduced copper catalyst (Cu/SiO2) and a copper surface which had been oxidised by exposure to nitrous oxide. Formic acid was weakly adsorbed on the silica support. Ligation of formic acid to the copper surface occurred only on the reduced catalyst. Dissociative adsorption resulted in the formation of unidentate formate on the oxidised catalyst. The presence of reduced copper metal instigated a rapid reorientation to a bidentate formate species.

Infrared study of CO adsorption on reduced and oxidised silica-supported copper catalysts

FTIR spectra are reported of CO adsorbed on silica-supported copper catalysts prepared from copper(II) acetate monohydrate. Fully oxidised catalyst gave bands due to CO on CuO, isolated Cu2+ cations on silica and anion vacancy sites in CuO. The highly dispersed CuO aggregated on reduction to metal particles which gave bands due to adsorbed CO characteristic of both low-index exposed planes and stepped sites on high-index planes. Partial surface oxidation with N2O or H2O generated Cu+ adsorption sites which were slowly reduced to Cu° by CO at 300 K. Surface carbonate initially formed from CO was also slowly depleted with time with the generation of CO2. The results are consistent with adsorbed carbonate being an intermediate in the water-gas shift reaction of H2O and CO to H2 and CO2.

Infrared study of the adsorption of methanol on oxidised and reduced Cu/SiO2 catalysts

Infrared spectra are reported of methanol adsorbed at 295 K on reduced Cu/SiO2 and on Cu/SiO2 which had been preoxidised by exposure to excess nitrous oxide. Methanol was chemisorbed on reduced Cu/SiO2 to give methoxy species on both silica and copper, gave a trace of formate on copper via reaction with residual surface oxygen, and was weakly adsorbed at SiOH sites on the silica support. Heating the adsorbed species at 393 K led to the loss of methoxy groups on copper and the concomitant formation of a bidentate surface formate. Heating reduced Cu/SiO2 in methanol at 538 K initially gave both gaseous and adsorbed (on Cu) methyl formate which subsequently decomposed to CO and hydrogen. The reactions of methanol with oxidised Cu/SiO2 were similar to those for the reduced catalyst although surface oxygen promoted the formation of surface methoxy groups on copper. Subsequent heating at 393 K led first to unidentate formate before the appearance of bidentate formate.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces. Part 2. -- A fourier-transform infrared spectroscopy study of methanol adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

FTIR spectra are reported of methanol adsorbed at 295 K on ZnO/SiO 2, on reduced Cu/ZnO/SiO2 and on Cu/ZnO/SiO2 which had been preoxidised by exposure to nitrous oxide. Methanol on ZnO/SiO2 gave methoxy species on ZnO and SiO, in addition to both strongly and weakly physisorbed methanol on SiO2. The corresponding adsorption of methanol on reduced Cu/ZnO/SiO2 also gave methoxy species on Cu and a small amount of bridging formate. Reaction of methanol with a reoxidised Cu/ZnO/SiO2 catalyst resulted in an enhanced quantity of methoxy species on Cu. Heating adsorbed species on Cu/ZnO/SiO2 at 393 K led to the loss of methoxy groups on Cu and the concomitant formation of formate species on both ZnO and Cu. The comparable reaction on a reoxidised Cu/ZnO/SiO2 catalyst gave an increased amount of formate species on ZnO and this correlated with an increased quantity of methoxy groups lost from Cu. An explanation is given in terms of adsorption of formate and formaldehyde species at special sites located at the copper/zinc oxide interface.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces: Part 1. -- A Fourier-transform infrared study of formic acid and formaldehyde adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

Fourier-transform infrared (FTIR) spectra are reported of formic acid and formaldehyde on ZnO/SiO2, reduced Cu/ZnO/SiO2 and reoxidised Cu/ZnO/SiO2 catalyst. Formic acid adsorption on ZnO/SiO2 produced mainly bidentate zinc formate species with a lesser quantity of unidentate zinc formate. Formic acid on reduced Cu/ZnO/SiO2 catalyst resulted not only in the formation of bridging copper formate structures but also in an enhanced amount of formate relative to that for ZnO/SiO2 catalyst. Formic acid on reoxidised Cu/ZnO/SiO2 gave unidentate formate species on copper in addition to zinc formate moieties. The interaction of formaldehyde with ZnO/SiO2 catalyst resulted in the formation of zinc formate species. The same reaction on reduced Cu/ZnO/SiO2 catalyst gave bridging formate on copper and a remarkable increase in the quantity of formate species associated with the zinc oxide. Adsorption of formaldehyde on a reoxidised Cu/ZnO/SiO2 catalyst produced bridging copper formate and again an apparent increase in the concentration of zinc formate species. An explanation in terms of the adsorption of molecules at special sites located at the interface between copper and zinc oxide is given.

Infrared study of CO, CO2, H2 and H2O interactions on potassium-promoted reduced and oxidised silica-supported copper catalysts

FTIR spectra are reported of CO, CO2, H2 and H2O on silica-supported potassium, copper and potassium-copper catalysts. Adsorption of CO on a potassium/silica catalyst resulted in the formation of complexed CO moieties. Whereas exposure of CO2 to the same catalyst produced bands ascribed to CO2 -, bidentate carbonate and complexed CO species. Fully oxidised copper/silica surfaces gave bands due to CO on CuO and isolated Cu2+ cations on silica. Addition of potassium to this catalyst removed a peak attributed to CO adsorption on isolated Cu2+ cations and red-shifted the maximum ascribed to CO adsorbed on CuO. For a reduced copper/silica catalyst bands due to adsorbed CO on both high and low index planes were red-shifted by 10 cm-1 in the presence of potassium, although the strength of the Cu - CO bond did not appear to be increased concomitantly. An explanation in terms of an electrostatic effect between potassium and adsorbed CO is forwarded. A small maximum at ca. 1510 cm-1 for the reduced catalyst increased substantially upon exposing CO to a reoxidised promoted catalyst. Correspondingly, CO2 adsorption allowed the identification of two distinct carboxylate species, one of which was located at an interfacial site between copper and potassium oxide. Carboxylate species reacted with hydrogen at 295 K, on a reduced copper surface, to produce predominantly unidentate formate on potassium. In contrast no interaction was detected on a reoxidised copper catalyst at 295 K until a fraction of the copper surface was in a reduced state. Furthermore the interaction of polar water molecules with carboxylate species resulted in a perturbation of this structure which gave lower C----O stretching frequencies.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces. Part 3. -- Fourier-transform infrared study of methyl formate adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

FTIR spectra are reported of methyl formate adsorbed at 295 K on ZnO/SiO2, reduced Cu/ZnO/SiO2 and on Cu/ZnO/SiO2 which had been preoxidised by exposure to nitrous oxide. Methyl formate on ZnO/SiO2 gave adsorbed zinc formate species and strongly physisorbed molecular methanol on silica. The comparable reaction of methyl formate with reduced Cu/ZnO/SiO2 catalyst produced bridging formate species on copper and a diminished quantity of zinc formate relative to that formed on ZnO/SiO2 catalyst. This effect is explained in terms of site blockage on the ZnO surface by small copper clusters. Addition of methyl formate to a reoxidised Cu/ZnO/SiO2 catalyst produced a considerably greater amount of formate species on zinc oxide and methoxy groups on copper were detected. The increase in concentration of zinc formate species was rationalised in terms of rearrangement of unidentate copper formate species to become bonded to copper and zinc oxide sites located at the interface between these two components.

Studies on boundary lubrication properties of oxidised coconut and soy bean oils

Vegetable oils are a potential source of base oils for biodegradable lubricants, with limited oxidative stability. This study focuses on the effect of long-term ageing and the influence of oxidation products on the boundary lubrication performance of coconut and soy bean oils, by subjecting them to accelerated ageing in a dark oven at elevated temperature. The samples were collected at regular intervals and analysed for the changes in viscosity, percentage of free fatty acid and peroxide number compared to fresh oil samples. The boundary lubrication properties of these samples were evaluated using a four-ball tester. Increased wear observed with aged oil samples was linked to the destruction of triglyceride structure and formation of peroxides. The difference in the wear properties of soy bean oil to coconut oil was accounted by its high content of unsaturated fatty acids and its susceptibility to undergo oxidation. It was concluded that the coconut oil can perform as a better lubricant and has got a better storage life compared to soy bean oil.

Adsorption behaviour of an oxidised starch onto haematite in the presence of calcium

The adsorption behaviour of an oxidised starch AP as well as that of calcium onto haematite have been studied both individually and together. While the adsorption density of starch AP onto haematite is enhanced in the presence of calcium, the adsorption of calcium onto haematite is not promoted by starch AP. Flocculation tests on haematite ore fines in the presence of starch AP and calcium chloride reveal that the sequence in which calcium and starch are added governs the settling rates and turbidity values. Zeta potential, viscosity and conductivity measurements, and calcium ion binding studies with starch AP indicate calcium-starch interactions. Possible mechanisms involved in such interactions with respect to haematite flocculation have been discussed.

Wear of Al2O3-SiC-(Al,Si) melt oxidised ceramic composites

Al2O3-SiC-(Al,Si) cermets are fabricated using the melt oxidation route. The tribological properties of the composites are tested under adhesive sliding and two body abrasion conditions. Under adhesive conditions, the network of residual aluminium in the matrix plays a role in the formation of a thin tribofilm on the interface while in abrasion the hardness of the composite plays a prominent tribological role. The work suggests that microstructural control can make this low temperature composite competitive with the conventional high temperature monolithic ceramics. (C) 1999 Published by Elsevier Science S.A. All rights reserved.