Some asbestiform minerals may cause lung disease in humans such as asbestosis, mesothelioma, and lung cancer. Crocidolite, the asbestiform counterpart of the amphibole riebeckite, is particularly dangerous in cases of chronic exposure. Its pathogenic activity may result from the interaction of the fiber surfaces with physiological fluids. Fe removed from the fiber surface by molecular chelators present in the body can promote a series of reactions that yield the hydroxyl radicals (•OH) which are known to cause DNA damage. This breakdown of DNA may be part of the mechanism for crocidolite-induced pathogenesis. X-ray photoelectron spectroscopy (XPS) and solution chemistry were used to monitor the changes in surface composition of crocidolite fibers in a 50 mM NaCl solution at pH= 7.5 and 25°C in the presence of Fe chelators (citrate, EDTA, or desferrioxamine) for up to 30 days. The data show that the introduction of Fe chelators dramatically increases the rate at which Fe is released from the surface when compared to a control group where no chelators were added. In particular, XPS shows that Fe(III) is more effectively removed in the presence of the chelators. Past studies of the dissolution of Fe-containing silicates generally indicate that Fe removal is the rate-limiting step. Fe(III) is particularly insoluble under circumneutral conditions. However, our work suggests that crocidolite undergoes enhanced dissolution in the presence of a chelator. Therefore, based on our XPS and solution data, and assuming a typical fiber diameter, we can estimate that a crocidolite fiber will survive on the order of hundreds of years in lung-like conditions. This is at least two orders of magnitude longer than a chrysotile fiber of the same size, and corresponds well with the fiber content observed in human lung tissue. / Master of Science

Thesis: M.S., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1978 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Materials Science and Engineering

Thesis(PhD)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Aminopolycarboxylic acids (APCAs) are chelating agents widely used to inactivate various metal ions by complex formation in industrial and household applications. Ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) are the widely used agents. Their use is under scrutiny due to their persistence in the environment because they cannot readily biodegrade. This led to the introduction of readily biodegradable agents namely ethylenediaminedisuccinic acid (EDDS) and iminodisuccinic acid (IDS) as alternatives especially to EDTA. Therefore, there was an interest to study the separation of EDDS, IDS and other APCAs using a simple, quick and accurate method. Capillary electrophoresis was used to determine the separation and speciation of iminodisuccinic acid with various metal ions at various pH levels. Speciation modelling was also utilized to compare and validate the presence and distribution of metal-ligand species. The obtained CE results were compared with speciation profiles and a reasonable agreement was obtained. The degradation studies at various time intervals for the metal-ligand (ML) complexes of DTPA, S,S-EDDS, IDS and R,S-IDS with various metal ions (Cd2+, Cr3+, Cu2+, Fe3+, Mn2+, Pb2+ and Zn2+) at pH 7 and 9 was evaluated using CE. New peaks were observed in some ML complexes when the pH was changed from pH 9 to 7. Sharp peaks were seen for CuL (L = DTPA, S,S-EDDS, IDS and R,S-IDS), FeDTPA and FeEDDS at both pH s. While small broad peaks were observed for FeIDS, CrL and MnL complexes. CuDTPA and CuEDDS complexes showed a greater stability over some considerable time as compared to CuIDS, CuR,S-IDS and other metal complexes at pH 9. This work also investigated the effect of various cationic electroosmotic flow (EOF) modifiers and counter anions on the CE separation of EDTA, EDDS and IDS as Cu(II) complexes. The performance of the modifiers was evaluated in terms of migration times, resolution and plate numbers. The best results were observed when Tetradecyltrimethylammonium bromide (TTAB) and Cetyltrimethylammonium bromide (CTAB) was used as modifiers in order to reverse the EOF in the fused silica capillary. This resulted in short analysis time and better peak shapes. The effect of different counteranions attached to EOF modifiers on the separation was also shown. It was also found that the counter anions of EOF modifiers used influences the separation of the complexes. The EOF modifiers namely Cetyltrimethylammonium chloride (CTAC) and Tetradecyltrimethylammonium chloride (TTAC) were further utilized for the determination of EDTA in South African river waters and industrial effluents. A method for the simultaneous separation of Fe (III) complexed with EDTA, S,S -EDDS and IDS was developed by CE and high-performance liquid chromatography (HPLC). The recalcitrant EDTA is used in combination with readily biodegradable analogues like EDDS and IDS in many commercial products. The methodology performance was evaluated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ) and reproducibility for both CE and HPLC methods. The LOD values obtained from HPLC were low when compared with CE. The applicability of both methods was demonstrated for the analysis of cosmetic products such as foam bath and shower cream. The results obtained by both CE and HPLC were found to be comparable and are in good agreement. / AFRIKAANSE OPSOMMING: Aminopolikarboksiel sure (APCAs) is komplekseer middels wat algemeen gebruik word om verskillende metaal ione te deaktifeer deur kompleks vorming in industriële en huishoudige toepassings. Etileendiamientetraasynsuur (EDTA) en dietileentriamienpentaasyn suur (DTPA) is die mees algemene APCA s. Hul gebruik word deesdae noukerig ondersoek as gevolg van hul volharding in die omgewing. Daar is n intense soektog na bio-afbreekbare agente soos etieleendiamiendisuksien suur (EDDS) and iminodisuksien suur (IDS) wat as plaasvervangers kan dien vir nieafbreekbare EDTA. Daar is dus n behoefte om te kyk na eenvoudige, vinnige en noukeurige metodes vir die bepaling van EDTA, EDTA , IDS en ander APCA s. Kapillere elektroforese (CE) was gebruik vir die skeiding en spesiering van iminodisuksien suur met verskillende metale by verskillende pH s. Spesiasie modellering was ook gebruik om die teenwoordigheid en verspreiding van metaal- spesies te vergelyk. Die CE uitslae was met die spesiasie profiele vergelyk en n redelike ooreenkoms was gevind. Die degraderings studies as n funksie van tyd was met CE bestudeer vir verskillende metal-ligand (ML) samestellings van DTPA, S,S-EDDS, IDS en R,S-IDS met verskillende metal ione (Cd2+, Cr3+, Cu2+, Fe3+, Mn2+, Pb2+ en Zn2+) by pH 7 en 9. Nuwe pieke was opgemerk in sommige ML samestellings wanneer die pH van pH 9 na 7 verander. Hoë pieke was vir CuL (L = DTPA, S,S-EDDS, IDS and R,S-IDS), FeEDTA en FeEDDS by alle pH s gevind. Lae, breë pieke was vir FeIDS, CrL en MnL komplekse gevind. CuDTPA en CuEDDS komplekse het n goeie stabiliteit gewys oor ʼn redelike tyd as dit met CuIDS, CuR,S-IDS en ander metal komplekses by pH 9 vergelyk word. In hierdie werk was die effek van verskillende kationiese elektro-osmotiese stroom (EOF) modifiseerders ook ondersoek. Veral die effek wat teen ioone op die CE skeidings het van EDTA, EDDS en IDS asook Cu(II) komplekse was ondersoek. Die effek van die modifiseerders was ondersoek en ge-evalueer in terme van migrasie tye, resolusie en plaat getalle. Die beste skeidingskondisies was bereik wanneer tetradesieltrimetielammonium bromied (TTAB) and setieltrimetielammonium bromied (CTAB) as modifiseerders gebruik word. Hierdie kondisies het ook aanleiding gegee tot korter ondersoek tye en beter piekvorme. Die effek van verskillende teen ioone wat aan die EOF modifiseerders gekoppel was het ook interresante resultate opgelewer. Die EOF modifiseerders setieltrimetielammonium chloried (CTAC) en tetradesieltrimetielammonium chloried (TTAC) was ook gebruik vir die bepaling van EDTA in Suid Afrikaanse rivier waters en industrieel afloop. ʼn Metode vir die gelyktydige skeiding van Fe(III) met EDTA, S,S’-EDDS en IDS was met behulp van CE en hoedruk vloeistof chromatography (HPLC) ontwikkel. Die metodologie was ondersoek ingevolge lineariteit, limiet van deteksie (LOD), limiet van kwantifisering (LOQ) en die herhaalbaarheid van CE en die HPLC metodes. Die LOD waardes verkry vanaf HPLC was swakker vergeleke met die verkry deur CE. Die toepaslikheid van al die metodes was vir die ontleding van kosmetiese produkte soos bad skuim en stortbad room getoets. Die uitslae deur CE en HPLC was vergelykbaar en ʼn goeie ooreenkoms was gevind.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

$EVWUDFW Application of radionuclides due to their unique nature is still attracting the interest of professionals from different branches of science. In this thesis, the unifying topic is the utilization of various radioactive labels on polymeric carriers for biomedicinal purposes. In the introductory part, the area of use of the investigated substances - in terms of their possible application in nuclear medicine, is presented to the reader. The experimental work is divided into three main sections dealing with synthesis and studying properties of appropriate selected polymers, their metal chelates and radiolabeling. First part of the study describes development of new strategies for labeling of polymeric carriers with radiometal cations and radioiodine, whereas in the following sections of the study synthesis and investigation of biocompatible polymer materials is discussed. New possible approaches in the diagnostics and therapy of cancer by using polymeric chelates as carriers are presented as well as the use of macroporous metal chelating polymer beads as potential therapeutics intended for radioembolization of liver malignancies and for the therapy of Wilson's disease. Investigated polymers have been shown to be non-toxic, to have good in vitro stability and to have the ability to be radiolabeled in...

The work presented in this thesis deals with the employment of Schiff base ligands used to synthesise novel 3d-4f polynuclear coordination clusters (PCCs) and the investigation into their potential magnetic, luminescent and catalytic properties. Chapter one provides a general introduction to the chemistry described in the thesis. It includes a general overview of 3d-4f PCC chemistry and the applications of these materials and previous synthetic strategies for the preparation of Schiff base PCCs. A rationale is presented for the ligands employed in the thesis and a synthetic strategy is devised for the synthesis of specific materials. The initial chapters are focused on the synthesis of 3d-4f PCCs with novel core topologies and the study of their magnetic properties. Several novel series of 3d-4f PCCs are presented with unique core topologies which are previously unobserved in 3d-4f PCC chemistry. In addition, some of the presented PCCs display single-molecule magnet (SMM) properties or a significant magnetocaloric effect (MCE). Chapter five bridges synthetic aspects discussed in the previous chapters, with a synthetic study targeting 3d-4f PCCs with a defect dicubane core (2,3M4-1) and introduces the term “isoskeletal” to describe PCCs which possess the same topology or related organic structures with the same host framework but different guests. Chapters seven to nine are focused on the development of a well characterised isoskeletal family of 3d-4f PCCs with a defect dicubane core and the investigation of their potential catalytic properties in a range of organic reactions including Michael Addition, Friedel-Crafts alkylations and multicomponent reactions. Characterisation of the 3d-4f PCCs is emphasised and verifies the stability of the 2,3M4-1 core in solution. An attempt at understanding the catalytic system and mechanistic aspects is undertaken, which is not explored in previously reported 3d-4f PCC co-operative catalysis. Chapter ten provides an overall conclusion to the work presented in the thesis, whilst highlighting the contributions of this work to the reported literature.

Soil-phosphorus relations have attracted the interest of many investigators since Liebig introduced his famous theory about the importance of the mineral matters to the plant in 1840. It was soon realized that phosphorus nutrition was a problem not easily solved for two reasons. 1. The added phosphorus fertilizers, soon after soil application are converted by some reactions in the soil to complex compounds far less soluble, consequently less available to the plant. Conclusions about this process led to controversial debates until it was discovered that a general statement covering all soils was impossible since the reactions involved in each case are different. 2. There was confusion caused by the use of two terms coined to express the plant's need for phosphorus. The first term, soluble phosphorus, was based on the assumption that nutrient absorption is a simple diffusion of ions from the soil solution into the roots while the second term, available phosphorus, was based on the observation that the plant absorbed more than that which could be estimated as soluble phosphorus from some insoluble sources. A general definition was given to the term available phosphorus as "that part of soil phosphorus which may be absorbed by ordinary crop plant in the production of plant substance." Later some restrictions were applied to regard the physical conditions of both soils and plants.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

A possible remediation strategy that involved washing with complexing reagents(s) [disodium ethylenediaminetetraacetate (Na2EDTA) alone or in combination with bis-(2-hydroxyethyl)dithiocarbamate (HEDC)] was evaluated with an urban soil that had been field contaminated with excesses of heavy metal (HMs). Heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) were targeted for removal. The aqueous solution that resulted from, washing was treated with zero-valent (ZV) magnesium (Mg0) or bimetallic mixture (Pd0/Mg 0 or Ag0/Mg0) to release the chelating reagent(s) from their heavy metal complexes. During this reaction, the heavy metals were precipitated from solution as hydroxides or became plated on to the surface of the excess ZV reagent. Thus, an appreciable fraction of the mobilized Pb and Cu and a portion of Zn became cemented to the surface of the ZV metal whereas most of the Fe and Mn were removed from solution as insoluble hydroxides. After filtration and pH re-adjustment, the demetallized solution was then returned to the soil to extract more heavy metals. After three washing cycles with the same reagent, it was observed that the sparing quantity of EDTA (10 mmoles) had mobilized 32--54% of the soil burden heavy metals (5 mmoles), but only 0.1% of the iron had been removed. / A 1:1 (mol/mol) mixture of EDTA and HEDC proved to be approximately equally efficient at HM extraction despite more than a three-fold reduction (3 mmoles) in the quantity of reagents. Three washing with the same reagent mobilized some 49% of the Pb, 18% of the Zn and 19% of the Mn but only 7% of the Cu and 1% of the Fe from the test soil.