Thesis (Ph. D.)--University of Virginia, 2001. / Includes bibliographical references (leaves 187-202). Also available online through Digital Dissertations.

Orientador: Rosehelene Marotta de Araújo / Banca: Silvio José Mauro / Banca: Maria Amélia Maximo de Araujo / Resumo: A finalidade deste trabalho foi verificar a passagem do ácido fosfórico em diferentes concentrações em dentina profunda, situado a 0,3mm da câmara pulpar, e observar as• alterações morfológicas da dentina pelo MEV. Setenta e dois corpos de prova, molares e pré-molares humanos hígidos, foram utilizados para este trabalho onde foi exposta a dentina oclusal. Através da máquina especialmente elaborada para o corte dos dentes, foi cortada a dentina deixando-a com espessura de 0,3 mm acima do corno pulpar. Os dentes foram aleatoriamente divididos em seis grupos de dez dentes cada: grupo 1 - controle ( sem tratamento ácido); grupo 2- ácido fosfórico a 10% sem sílica; grupo 3- ácido fosfórico a 32% sem sílica; grupo 4 - ácido fosfórico à 35% com sílica; grupo 5 - ácido fosfórico a 3 7% sem sílica e grupo 6 - ácido fosfórico a 50% líquido. Foi alojado na câmara pulpar dos corpos de prova, um papel de tornassol que atapetasse toda esta câmara, a fim de que quando aplicado o ácido fosfórico nas suas diferentes concentrações, pudéssemos avaliar a passagem mesmo. Cada concentração do ácido foi aplicada por quinze segundos e lavadas com spray água/ar. Observamos que: a) não houve a passagem do ácido fosfórico através da dentina com as diferentes concentrações estudadas; b) o ácido fosfórico a 10% sem sílica em corte transversal,demonstrou abertura parcial dos túbulos dentinários; c) o ácido fosfórico a 32% sem sílica, 35% com sílica, 37% sem sílica e 50% líquido demonstraram alterações morfológicas semelhantes; d) houve remoção preferencial da dentina peritubular; e) a sílica contida no ácido fosfórico a 35% não foi totalmente removida após abundantes lavagens / Abstract: The purpose of this study was to verify acid penetration of phosphoric acid at variable concentrations, into deep dentin, located at 0,3 mm from the pulp chamber, and a.tso observe dentin morphological changes with S.E.M. Occlusal dentin of human sound molars and premolars was exposed totaling 72 specimens. A special designed device was used to section teeth, obtaining 0.3 mm of remaining dentin over pulp horns. Teeth were randomly assigned to six groups with ten teeth each: group 1 - Control (no acid conditioning); group 2 - 10 % phosphoric acid: group 3 - 32 % phosphoric acid; group 4 - 35 % phosphoric acid with silica; group 5 - 37 % phosphoric acid; group 6 - 50 % phosphoric acid solution. A pH indicating paper was placed on pulp chamber walls in order to verify acid penetration of acid etchants. Each etchant was applied for 15 seconds, spray rinsed and air dried Conclusions: a) no acid penetration occurred through dentin; b) dentin tubules were partially open in crosscut 10 % phosphoric acid specimens; c) similar morphological changes were found for 50 % solution, 37 %, 35 % and 32 % phosphoric acid groups; d) most structural removal occurred at peritubular dentin; e) silica from 35% acid gel was not completely removed from dentin surface after thorough rinsing. / Mestre

Made available in DSpace on 2015-01-26T13:21:25Z (GMT). No. of bitstreams: 0 Previous issue date: 1997-03-04Bitstream added on 2015-01-26T13:30:30Z : No. of bitstreams: 1 000036234.pdf: 4116221 bytes, checksum: 868e565d3f58d838039c7a0ba8c15bda (MD5) / A finalidade deste trabalho foi verificar a passagem do ácido fosfórico em diferentes concentrações em dentina profunda, situado a 0,3mm da câmara pulpar, e observar as• alterações morfológicas da dentina pelo MEV. Setenta e dois corpos de prova, molares e pré-molares humanos hígidos, foram utilizados para este trabalho onde foi exposta a dentina oclusal. Através da máquina especialmente elaborada para o corte dos dentes, foi cortada a dentina deixando-a com espessura de 0,3 mm acima do corno pulpar. Os dentes foram aleatoriamente divididos em seis grupos de dez dentes cada: grupo 1 - controle ( sem tratamento ácido); grupo 2- ácido fosfórico a 10% sem sílica; grupo 3- ácido fosfórico a 32% sem sílica; grupo 4 - ácido fosfórico à 35% com sílica; grupo 5 – ácido fosfórico a 3 7% sem sílica e grupo 6 - ácido fosfórico a 50% líquido. Foi alojado na câmara pulpar dos corpos de prova, um papel de tornassol que atapetasse toda esta câmara, a fim de que quando aplicado o ácido fosfórico nas suas diferentes concentrações, pudéssemos avaliar a passagem mesmo. Cada concentração do ácido foi aplicada por quinze segundos e lavadas com spray água/ar. Observamos que: a) não houve a passagem do ácido fosfórico através da dentina com as diferentes concentrações estudadas; b) o ácido fosfórico a 10% sem sílica em corte transversal,demonstrou abertura parcial dos túbulos dentinários; c) o ácido fosfórico a 32% sem sílica, 35% com sílica, 37% sem sílica e 50% líquido demonstraram alterações morfológicas semelhantes; d) houve remoção preferencial da dentina peritubular; e) a sílica contida no ácido fosfórico a 35% não foi totalmente removida após abundantes lavagens / The purpose of this study was to verify acid penetration of phosphoric acid at variable concentrations, into deep dentin, located at 0,3 mm from the pulp chamber, and a.tso observe dentin morphological changes with S.E.M. Occlusal dentin of human sound molars and premolars was exposed totaling 72 specimens. A special designed device was used to section teeth, obtaining 0.3 mm of remaining dentin over pulp horns. Teeth were randomly assigned to six groups with ten teeth each: group 1 - Control (no acid conditioning); group 2 - 10 % phosphoric acid: group 3 - 32 % phosphoric acid; group 4 - 35 % phosphoric acid with silica; group 5 - 37 % phosphoric acid; group 6 - 50 % phosphoric acid solution. A pH indicating paper was placed on pulp chamber walls in order to verify acid penetration of acid etchants. Each etchant was applied for 15 seconds, spray rinsed and air dried Conclusions: a) no acid penetration occurred through dentin; b) dentin tubules were partially open in crosscut 10 % phosphoric acid specimens; c) similar morphological changes were found for 50 % solution, 37 %, 35 % and 32 % phosphoric acid groups; d) most structural removal occurred at peritubular dentin; e) silica from 35% acid gel was not completely removed from dentin surface after thorough rinsing.

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PDase II activity was determined using a synthetic substrate, the 2,4-dinitrophenyl ester of thymidine 3'-phosphate. The enzyme activity was estimated in fractions obtained by differential centrifugation of homogenates of epithelial cells fromt.the small intestinal mucosa of guinea pigs and rats. In guinea pig preparations PDase II occurred with highest specific activity in those fractions rich in succinate dehydrogenase and acid phosphatase. A lysosomal location for the guinea pig enzyme was indicated by its structure-linked latency and by its association with particles which underwent a characteristic decrease in equilibrium density when Triton WR-1339 was injected into the animals. With rat preparations a much greater proportion of the PDase II activity was found in the soluble fraction after uult-ra;c;entrifugation. The rat enzyme exhibited a lower degree of latency and administration of Triton WR-1339 had no effect. The rat enzyme activity in these crude preparations further differed from that of the guinea pig in other respects; it was more labile at 60°C, exhibited a slightly lower pH optimum, had a higher molecular weight as determined by gel filtration chromatography and displayed a much smaller tendency to aggregate under Llow salt conditions. Both enzymes were purified by chromatography on DEAE-cellulose, CM-cellulose and agarose, the extensive purification (550 fold) of the rat enzyme being largely due to its behaviour oh the latter material where it was found to bind tenaciously in low ionic strength solutions. On the other hand, only a fifteen-fold purification of the guinea pig enzyme was obtained because of its tendency tofform insoluble aggregatesdduring the chromatographic steps. In the main, the properties of the partially purified enzymes were quite similar. Both displayed pH optima between pH 6 and 7, were inhibited in solutions of high ionic strength, were unaffected' by divalent cations or EDTA, were similarly inactivated by heating at a temperature of 60°G displayed discontinuous Arrhenius plots _5 and exhibited Km values of the order 2-5x10 M for dTpDNP. In most casestfche differences between the enzymes were just differences of degree and could probably be accounted for byethe different extents to which the enzymes were purified. A more extensive characterization of the highly purified rat PDase was carried out. The fall-off in PDase II reaction rate observed at high enzyme levels with dTpDNP as substrate was found to be due to competitive inhibition of the enzyme by dTp, a reaction product which showed a of 2x10 M. The isoelectric point of PDase II was estimated by electrofocusing but since multiple peaks of activity were found at pH 3.4, 4.2-4.5, and pH 7.2 a conclusive result was not obtained. Polyacrylamide gel electrophoresis of purified rat PDase II indicated that the pattern obtained was, in part, dependent on whether the preparation was fresh or not; freshly purified PDase II contained up to 10 bands in gels stained for protein whereas only 1-2 bands were obtained when the preparations were "aged". A molecular weight of 150000-170000 for the enzyme was estimated in experiments performed by gel-filtration chromatography on dextran and agarose gels. Investigation of the interaction with, and hydrolysis by, rat PDase II of a number of possible phosphodiester substrates indicated that'-, the enzyme required a nucleoside 3'-phosphoryl residue for the initiation of hydrolysis which then proceeded in a 5'+3' direction. Finally, the effect of some enzyme inhibitors was investigated. PDase II activity was inhibited in the presence; of NEM, PCMB, PCMPS and iodoacetic acid. It was further found that the inactivation by iodoacetic acid could be prevented by the presence of a PDase substrate or, better still, by dTp. This is good evidence that iodoacetate alkylates an essential residue at the active center of PDase II and is the first time that such an effect has been shown for a PDase. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Solid phosphoric acid is a catalyst used for the upgrading of light olefins into fuels. To delve into the mechanism of olefin dimerisation over the catalyst, the oligomerisation of 1- hexene was investigated over a wide range of operating conditions. The reaction progression of 1-hexene dimerisation over solid phosphoric acid was interpreted by means of kinetic experiments for both a linear hexene (1-hexene) and a branched hexene (2,3-dimethylbutene). The reaction rate for both reagents was described by using an elementary kinetic model. From the experimental data it was shown that the rate of dimerisation of branched hexenes was faster than the rate observed for linear hexene dimerisation. To correlate the two sets of kinetic data, the reaction network was expanded to incorporate skeletal isomerisation of 1-hexene with dimerisation only taking place by the co-dimerisation of linear and branched hexenes and the dimerisation of branched hexenes. The fit of the kinetic equation demonstrated that the reaction rate of 1-hexene is essentially controlled by the rate of skeletal isomerisation. Due to the large activation energy for skeletal isomerisation, low reaction temperatures favoured the co-dimerisation of linear and branched hexenes whereas at higher temperatures, the reaction rate was dominated by the dimerisation of branched hexenes. The product distribution indicated that, because of the fast rates of both cracking and secondary dimerisation (dimerisation of cracked products), the product distribution instantaneously reached a pseudo equilibrium after the dimerisation of hexenes. Therefore the carbon distribution was found to depend only on the reaction temperature, not on the residence time in the reactor. Solid phosphoric acid is a supported liquid phosphoric acid where the condensed state of the acid, e.g. ortho phosphoric acid (H3PO4) and pyro phosphoric acid (H4P2O7), is dependent on the quantity of water present in the reaction mixture. With a decrease in water content, the distribution of acid shifts and the ortho phosphoric acid becomes more condensed (H4P2O7, H5P3O9 etc.), i.e. high water content → low acid strength, low water content → high acid strength. The experiments completed at various degrees of catalyst hydration and free acid loading showed that the rate of reaction over solid phosphoric acid was dependent on the acid strength of the catalyst. The effect of acid strength on the reaction rate was integrated into the rate constants by means of an exponential dependency on acid strength. It was also shown that both the product distribution and the degree of branching remained unaffected by acid strength. The constant product indicates that the rate of cracking is limited by the rate of oligomerisation of hexenes, irrespective of the acid strength of the catalyst. Since the product from the dimerisation of 1-hexene could be used as fuel, the quality of the desired fuel would therefore depend solely on the reaction temperature, not on the hydration of the catalyst. The work performed in this thesis has been published in two peer-review articles: 1. Schwarzer R.B., Du Toit E. and Nicol W. (2008) Kinetic model for the dimerisation of 1-hexene over a solid phosphoric acid catalyst, Applied Catalysis A: General, 340, 119-124. 2. Schwarzer R.B., Du Toit E. and Nicol W. (2009) Solid phosphoric acid catalysts: The effect of free acid composition on selectivity and activity for 1-hexene dimerisation, Applied Catalysis A: General, 369, 83-89. / Thesis (PhD(Eng))--University of Pretoria, 2012. / Chemical Engineering / unrestricted

The practice of applying fertilizers to the soil by adding the liquid form to the irrigation water is increasing in popularity. There are several advantages maintained for such a method of application. Some of the advantages are: (A) Ease of application (B) No special equipment is required for application. (C) The fertilizer can be applied at any stage of plant growth without physical disturbance of the plant. (D) Penetration into the root zone may be greater than the dry fertilizers. Considerable phosphate fertilizer is used on soils of irrigated regions. If the behavior of liquid phosphoric acid after its incorporation with soil is such that it penetrates into the root zone and is otherwise as efficient as dry phosphate fertilizers in inducing favorable plant response, then it would seem practical to utilize the other advantages offered by applying the fertilizer in irrigation water. Commercial phosphoric acid (52% available P2O5) is produced by applying an excess of sulfuric acid to ground rock phosphate. This phosphoric acid is usually applied to an additional amount of phosphate rock to make concentrated superphosphate. A given quantity of phosphoric acid can yield more available phosphorus by applying it to rock phosphate than by using it directly as a fertilizer. Because of its potential value in producing concentrated superphosphate commercial phosphoric acid has been used very little as a fertilizer. There is insufficient research in which the comparative value of the acid as a fertilizer has been investigated the purpose of the studies reported in this paper are, to compare: (A) the value of commercial phosphoric acid and concentrated superphosphate as fertilizers when applied in equivalent amounts and, (B) the different methods of application and dilution of the phosphoric acid.

M.S.

The alkylation of various compositions of propane with ethylene at atmospheric pressure in the presence of various concentrations of ortho-phosphoric acids and mixtures of ortho-phosphoric acid and hydrochloric and sulfuric acids as catalyst was investigated. Physical conditions studied were (1) temperature ranging from 40 to 200°C., (2) length of run from six to eight hours, and (5) vapor feed rate from 100 to 200 eubie centimeters per minute. From the results obtained from this research, it is evident that pipe still vapors composed of ethylene and propane cannot be alkylated at atmospheric pressure and relatively low temperatures with the use of 85-100 per cent ortho-phosphoric acid as a catalyst. No mechanism of reaction has been proven. / M.S.