OpenUCT :: Browsing by Author "Rodgers, Allen L"

Browsing by Author "Rodgers, Allen L"

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Open Access
The adsorption of nitrogen and argon by evaporated films of sodium chloride
(1969) Rodgers, Allen L; Linder, Peter W
An ultra-high vacuum apparatus has been designed and constructed. Pressures of the order of 1 x 10⁻⁸ torr have been attained routinely. The adsorption of nitrogen by Pyrex has been investigated and the results obtained have shown good agreement with those in the literature. Rigorously cleaned evaporated films of sodium chloride have been prepared and the adsorption of nitrogen and argon by them has been investigated. Isosteric heats and entropies of adsorption have been determined and theoretical entropies calculated. The appearance of a group of sites of uniform activity, hitherto unavailable owing to contamination of the surface, is postulated. The adsorption of nitrogen and argon has been found to be reasonably well represented by the immobile, localized model with indications of the adsorbed argon molecules occupying a different set of sites from the adsorbed nitrogen. Two novel methods for the preparation of evaporated films of alkali halides are suggested.
Open Access
Crystallization of calcium oxalate on molecularly imprinted polymer surfaces
(2004) Tewolde, Tewolde Siele; Egan, Timothy J; Rodgers, Allen L
Calcium oxalate (CaOx) is the most common component of human kidney stones. Heterogeneous nucleation is regarded as the key mechanism in this process. As such, crystallization of this substance has been studied in several different model systems. However, molecular imprinting has not been previously used in this field. In the present study, template crystals of calcium oxalate mono- and di-hydrate (COM and COD respectively) were used to imprint a copolymer of 6-methacrylamidohexanoic acid and divinylbenzene.
Open Access
Crystalluria in various groups of sportsmen
(1987) Cox, Tracy-Ann; Rodgers, Allen L
This thesis examines various groups of athletes to assess whether they are at risk with regard to kidney stone formation. Particle size distribution analysis (Coulter counter), ultra-structural analyses (SEM) and urine analysis were conducted. The background to various factors relating to stone formation is discussed as well as the general theory behind the techniques employed. The methods utilized and data obtained are described. Particle size distribution analysis and scanning electron· micrographs suggest that marathon runners and cyclists may be at risk with respect to stone formation. Dehydration and urinary tract trauma are thought to occur in the former whereas dehydration only is operative in the latter. Results obtained from Na/Ca ratio analyses are found to correspond with the particle size analyses thereby suggesting that this ratio may have potential as a useful index of stone-forming risk. The enormous spread of values amongst each class of athlete shows, however, that physical exertion is not the sole factor affecting the Na/Ca ratio.
Open Access
The design, development and testing of a non-invasive continuous crystalliser system for the study of calcium oxalate crystallisation processes
(1996) Bretherton, Tracy Ann; Rodgers, Allen L
The MSMPR was designed according to chemical engineering principles and tests showed that it conforms to the assumptions necessary for conventional MSMPR analysis. Various crystalliser offtakes and six system designs were developed and tested to allow measurements using the thermostatted flow cell. The flow cell allows for continuous measurement of the sample dispersion using a noninvasive monitoring instrument - a Malvern Particle Size Analyser. In this technique, measurement of the steady state crystal size distribution is based on a diffraction pattern produced by the particles in a parallel beam of monochromatic light. Comparative measurements were obtained by sampling directly from the crystalliser and analysing the product in a Coulter Counter. In this technique, the steady state crystal size distribution is measured by the change in resistance as particles, in an electrically conductive liquid, pass through the Coulter aperture. Due to the large volumes required by the crystalliser, it was necessary to pool urines. Aliquots of volume 1. 5 dm3 from the 24 hour urines of each of 8 male controls were pooled. The first series of experiments were performed to investigate the effect on calcium oxalate crystallisation of varying the concentration of sodium oxalate solutions used to initiate crystallisation, and also to investigate the effect of varying the temperature. A further series of experiments was performed to determine the effect of adding inhibitors individually (citrate, magnesium, chondroitin sulphate A) and in combination (citrate and magnesium). The inhibitor experiments were performed using two different approaches. In the first, the pooled urine was pre-treated with the inhibitor prior to being introduced into the crystalliser. In the second set of experiments, the inhibitor was introduced into the crystalliser via a separate, independent feed. It is suggested that these approaches represent crude models respectively of (a) the endogenous presence of inhibitors and (b) the oral administration of such inhibitors. Each individual experiment was performed using three different urine pools. The steady state crystal size distributions obtained from both the Coulter and the Malvern instruments were used to determine nucleation and growth rates in each urine. Scanning electron microscopy was used to obtain qualitative and semi-quantitative data related to crystal morphology, number, size and degree of aggregation. Both nucleation and growth rates increased as the concentrations of the initiating sodium oxalate solutions increased. Nucleation and growth rates also increased with increasing temperatures. In the latter series of experiments, different calcium oxalate crystal phases precipitated at the various temperatures. Citrate inhibited nucleation and growth of calcium oxalate, irrespective of how it was admitted to the crystalliser. Magnesium was found to inhibit growth only and, like citrate, this role was independent of how it was introduced into the crystalliser. Although both inhibited growth, the effect of the citrate was greater. When both components were added in combination, inhibition was observed to be additive. In all cases, inhibitory effects increased with increasing concentration. Chondroitin sulphate A was found to inhibit nucleation; inhibition of growth was minimal at the concentrations tested. Aggregation of calcium oxalate crystals was found to be inhibited by chondroitin sulphate A. The results of the calcium oxalate crystallisation kinetic studies, obtained by using Malvern particle sizing and Coulter Counter techniques independently of each other, showed general agreement. These results, in turn, were in agreement with the published results of others, thereby lending confidence to the findings and highlighting the potential application of the non-invasive continuous crystalliser in urolithiasis research.
Open Access
The effect of Ascorbic acid ingestion on the risk of calcium oxalate kidney stone formation
(1995) Auer, Bronwyn Leigh; Rodgers, Allen L
This study was undertaken to investigate the effect of prolonged megadose ingestion of ascorbic acid on the risk of calcium oxalate kidney stone formation. Ten healthy male subjects (ages 20 to 30 years) participated in the study. Each was required to ingest a daily dose of 4 g ascorbic acid per day for a period of 5 days. Twenty-four hour urines were collected at various times prior to, during and after this protocol. During each 24 hour collection, aliquots were withdrawn and stored in the presence and absence of an EDTA preservative. Other aliquots were withdrawn for immediate ascorbate analyses. Urine samples were analysed for sodium, potassium, magnesium, calcium, citrate, oxalate, urate, phosphate and creatinine. A new flow-injection method was designed, developed and tested for the analysis of urinary ascorbate. Analytical data obtained from this method were compared with results obtained from a manual titration method using 2,6 dichlorophenolindophenol. While the accuracy of both methods was found to be similar, results obtained by the flow-injection were more repeatable. All urine samples were analysed for ascorbate by both methods. In vitro crystallization experiments were performed on each urine to determine the limit of metastability and the rate of calcium oxalate crystallization. All data were statistically compared using the method of least-squares. Prolonged ascorbic acid ingestion had no effect on urinary calcium and oxalate nor on several other biochemical risk factors including urinary citrate, sodium, chloride and creatinine. Calcium oxalate metastable limits and crystallization kinetics were also unaffected, as were values of the Tiselius risk index and calcium oxalate relative supersaturation. While risk-reducing changes in urinary magnesium and pH occurred, these were offset by risk-increasing changes in urinary potassium and phosphate. The investigation showed that in vitro conversion of ascorbate to oxalate occurs but that this can be prevented by the presence of EDTA in the collection vessel. The study also demonstrated that ingestion of large doses of ascorbic acid probably commences with high percentage absorption of the vitamin but that saturation is achieved within 24 hours. Continued ingestion results in less absorption with excess ascorbic acid being excreted unchanged in the urine. In a separate case study, prior to the commencement of the investigation described above, a healthy male participant was given a daily dose of 8g ascorbic acid in a protocol which was planned to last 9 days. Significant crystalluria and haematuria developed on the 8th day after which further ascorbic acid ingestion was immediately suspended. In this individual, several risk factors changed significantly. These were urinary oxalate excretion, metastable limit, Tiselius risk index and calcium oxalate relative supersaturation. This study shows that prolonged ingestion of large doses of ascorbic acid does not increase the risk of calcium oxalate kidney stone formation. However, the results of the special case study highlight the fact that in some individuals, renal handling of ascorbic acid may be impaired, leading to undesirable consequences.
Open Access
Qualitative and semi-quantitative physico-chemical characterization of some calcium phosphate implant and bone samples
(1991) Schindler, Gustav Joseph; Rodgers, Allen L
Ten calcium phosphate implant substances (six of natural origin, four of synthetic origin) and several bone samples from a single human skeleton have been qualitatively and semi-quantitatively characterized with respect to several physico-chemical properties. Analysis involved the techniques of X-ray powder diffraction, infra-red spectroscopy, inductively-coupled plasma atomic emission spectroscopy, atomic absorption spectroscopy, and thermal decomposition. In addition, a series of adsorption/exchange experiments were conducted in which implant and bone samples were exposed to progressively increasing concentrations of aqueous Ca²⁺ and Na⁺ ions. X-ray powder diffraction showed that the implants consist of only hydroxyapatite while bones contain small amounts of CaO as well. a-Cell parameters of the implants of natural origin were larger than those of both synthetic implants and bones. The a-cell sizes of the latter two types of samples resembled each other. The c-cell sizes were similar for all samples. The degrees of crystallinity of all implants were higher than those of bone, possibly indicating lower CO₃ contents in the former. %Mass contents of various elements were determined by ICP for implants and bones. Statistical analysis on the bone values showed that variation of elemental concentrations not attributable to experimental error occurred in bone from different regions of the body, but not across the surface of any particular bone. Ratios of Ca/P and Mg/Ca were calculated for all samples, and showed differences between implants and bone due to higher calcium levels in the former. Infrared spectroscopy was used in order to determine %CO₃ values in all the samples. It is suggested that bone contains higher levels of CO₃ than the implants. This was confirmed by analysis of the shapes of certain bands in the spectra of all samples and correlated with XRD results. All samples were subjected to heat up to a maximum of 900°C. XRD scans were recorded after heating to 650°C and 900°C. Percentage mass losses were also recorded at various stages throughout the heating process. Some of the implants revealed traces of tricalcium phosphate (β-TCP) and Cao after heating to 900°C. All bones revealed traces of CaO after heating to 900°C. a-Cell parameters were calculated for all samples and revealed very slight changes in size. Implants exhibited most of these changes after heating to 650°C, while bones did so only after heating to 900°C. Surface chemistry studies further confirmed chemical differences between implants and bone by virtue of the fact that neither exogenous Ca²⁺ nor Na⁺ adsorbed/exchanged with ions in the implants, while bone exhibited a clear saturation curve for each exogenous ion. It is suggested that the techniques and experiments described in this thesis might be utilized by other investigators in the hope of establishing guidelines for the selection of appropriate implant substances.
Open Access
Scientific aspects of urolithiasis : quantitative stone analyses and crystallization experiments
(1986) Wandt, Michael Alexander Erich; Rodgers, Allen L
This thesis describes two aspects of the various scientific approaches to the study of urolithiasis. In the first instance, the theory, development and results of three quantitative analytical procedures are described while in the second, crystallization experiments in a rotary evaporator are presented. Of the different methods of quantitative X-ray powder diffraction analyses, the 'internal standard method' and a microanalytical technique were identified as being potentially the two most useful procedures for the quantitative analysis of urinary calculi. 'Reference intensity ratios' for 6 major stone phases were determined and were used in the analysis of 20 calculi by the 'internal standard method'. It is concluded that the attainment of accurate results using this procedure is not easily achieved because of problems such as the unavailability of standards which realistically mimic stone composition, sample preparation, overlap of reflections from sample components and standards and the requirement of 'infinitely thick' specimens ( > 250 mg). For the microanalytical technique, micro-quantities of 10 calculi from the original 20 were deposited on silver filters and were quantitatively analysed using both, the attenuation of the Ag peak and the separately measured absorption coefficients μ*· Inductively coupled plasma atomic emission spectroscopic (ICP-AES) methods were also investigated, developed and used in this study. Various procedures for the digestion of calculi were tested and a mixture of HNO₃ and HClO₄ was eventually found to be the most successful. The major elements Ca, Mg, and Pin 41 calculi were-determined. For the determination of trace elements, a new microwave-assisted digestion procedure was developed and used for the digestion of 100 calculi. Thereafter the major elements Ca, Mg and P together with the minor and trace elements Al, Cu, Fe, K, Li, Mn, Mo, Na, Pb, S, Sr and Zn in all 100 stones were simultaneously determined. The data so obtained were subjected to 3 types of statistical analyses involving direct correlations, scatter plots and a relatively new multivariate analysis of logarithmic data known as a 'covariance biplot'. Several interesting correlations were obtained. Fluoride concentrations in two stone collections - 20 calculi from India and 42 from South Africa - were determined using a fluoride-ion sensitive electrode and the HNO₃/HClO₄ digestion procedure used for the ICP study. Direct measurement of fluoride proved unsuccessful thereby necessitating the investigation and development of a diffusion technique. Using this method the fluoride content of both collections was determined. A series of crystallization experiments involving a standard reference artificial urine was carried out in a rotary evaporator. The effect of pH and urine composition was studied by varying the former and by including certain components (uric acid, urea, creatinine, MgO, methylene blue, chondroitin sulphate A, fluoride) in the reference solution. Crystals formed in these experiments were subjected to qualitative and semi-quantitative X-ray powder diffraction analyses. Scanning electron microscopy of several deposits was also carried out. Similar deposits to those observed in calculi were obtained with the fast evaporator. The results presented suggest that this system provides a simple, yet very useful means for studying the crystallization characteristics of urine solutions. The quantitative analytical procedures described in detail in this thesis can serve as model techniques for other workers involved in stone research. Together with other approaches such as the crystallization experiments discussed, these procedures can lead to a better understanding of the aetiological processes which govern stone formation.
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A study of crystal matrix extract and urinary prothrombin fragment 1 from a stone-prone and stone-free population.
(Springer, 2001) Durrbaum, Dawn; Rodgers, Allen L; Sturrock, Edward D
South African blacks are immune to urinary calculi whereas whites have an incidence rate similar to that reported in Western societies. Urinary prothrombin fragment 1 (UPTF1) and the crystal matrix extract (CME) from which it is derived have been shown to be potent inhibitors of crystal growth and aggregation in undiluted human urine. The objective of the present study was to isolate CME and UPTF1 from the urines of black and white subjects in order to assess whether either might contribute to the black population's relative stone immunity. CME was isolated from freshly precipitated calcium oxalate (CaOx) crystals and a crystallization study was conducted in synthetic urine. Coulter Counter, 14C-oxalate deposition, and scanning electron microscopy data demonstrated that the extracts from both race groups strongly inhibited CaOx nucleation. The extract derived from the black subjects inhibited nucleation to a greater extent than that from the whites. A phase conversion from COM to COD in the presence of the extracts, in support of the inhibitory effect of CME, was also observed. Purified UPTF1 isolated from both groups' CME was subjected to rigorous biochemical characterization involving matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, protein sequencing by Edman degradation, and amino acid analyses. No differences in molecular weight or amino acid sequence and composition were identified. It is suggested that the more potent inhibitory activity of the extract derived from the black subjects might be related to this group's relative stone immunity.
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Synergism between urinary prothrombin fragment 1 and urine: a comparison of inhibitory activities in stone-prone and stone-free population groups
(De Gruyter, 2002) Webber, Dawn; Rodgers, Allen L; Sturrock, Edward D
South African blacks rarely form kidney stones compared with whites. This study investigated whether purified urinary prothrombin fragment 1 (UPTF1) derived from blacks is a more potent inhibitor of calcium oxalate crystallisation than that from whites. UPTF1 was purified from the urine of both population groups and their inhibitory activities were compared in a cross-over design in which each protein was tested in ultrafiltered urine from both population groups. Coulter Multisizer, [14C]-oxalate deposition and scanning electron microscopy experiments were used to monitor crystallisation. The study has demonstrated for the first time that UPTF1 promotes nucleation and that inhibitory activity is synergistically dependent upon urine composition. The activity of the whites' UPTF1 was greater than that of the blacks in the whites' urine (e.g. particle size decrease: 31.7% vs. 25.2%), while the blacks' UPTF1 was superior to that of the whites in the blacks' urine (e.g. particle size decrease: 46.5% vs. 32.4%). In addition, when tested in their respective endogenous urines, the blacks' UPTF1 demonstrated superior inhibitory activity on an absolute scale (e.g. particle size decrease: 46.5% vs. 31.7%). Thus, the urine composition of black South Africans may influence their UPTF1 conformation, conferring greater efficacy for inhibition of calcium oxalate crystallisation.

Browsing by Author "Rodgers, Allen L"

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