The hydrolysis of iron(III) ions in aqueous solution forms a series of soluble hydroxide complexes with associated equilibrium constants. The solubility of iron(III) is controlled by the various soluble hydroxide complexes, and can, in theory, be calculated from the pH and equilibrium constants. Experimental verification of the calculated solubility has proven difficult due to the lack of sensitive analytical techniques and the presence of colloidal ferric hydroxide interferences. Recently, electrochemical methods for the determination of low levels of iron(III) have been developed using adsorptive cathodic stripping voltammetry which relies on the interfacial accumulation of the chelate of iron with Solochrome Violet RS on a hanging mercury drop electrode. The purpose of this investigation was to experimentally verify the calculated solubility of iron(III) in the pH 4-12 region using adsorptive cathodic stripping voltammetry. The ubiquitous nature of iron requires background levels of iron be reduced below the experimental concentrations to be determined. Attempts to lower the background levels of iron were ineffective as concentrations below about 10-8M iron could not be attained. Verification of the calculated solubility of iron(III) was unsuccessful as background concentrations of iron(III) and tr.e presence of colloidal ferric hydroxide hindered the experimental results. The dissolution of the ferric hydroxide colloids coupled with the background levels of iron resulted in the determination of experimental concentrations which exceeded theoretical values by two to four orders of magnitude.

Zero-valent iron (ZVI) has been successfully used for the degradation of a wide range of organic contaminants in groundwaters in recent years. The rate of degradation of contaminants by ZVI may be enhanced by use of nanoscale zero valent iron (nZVI) particles which possess higher surface area than the more widely used granular materials. However, the most widely used method of producing nZVI involves the reduction of FeIII by sodium borohydride is expensive. Dithionite can be used to reduce Fe(II) and produce cost effective nZVI under conditions of high pH and in the absence of oxygen. The efficiency of trichloroethylene (TCE) degradation using dithionite nZVI particles (nZVIS2O4) is similar to that of the conventional borohydride particles (nZVIBH4). Oxidation of benzoic acid using the nZVIS2O4 particles results in different byproducts than those produced when nZVIBH4 particles are used. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH addition is not the primary oxidation pathway when one is using the nZVIS2O4 particles. It is proposed that sulfate radicals (SO4−) are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVIS2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions. Low yields of oxidants limit the application of nZVI. It has recently been demonstrated that nZVI oxidative efficiency can be enhanced in presence of ethlylendiaminetetraacetic acid (EDTA). Additional insight into the nZVI-mediated process has been obtained from comparative studies of degradation of benzoic acid by nZVI particles and Fenton reagents in the absence and presence of EDTA at different pH. The efficiency of nZVI degradation is significantly hindered by the rapid aggregation of the iron nanoparticles, which may result in a decrease in available reactive surface area. These effects of aggregation can be overcome by surface modification through adsorption of capping agents which provide steric and electrosteric repulsive interactions between particles. Several high molecular weight (HMW) organic polymers have been used for preventing agglomeration of nZVI particles, such as water soluble starch, sodium carboxymethyl cellulose (CMC) and alginate. The degradation capabilities of different functionalized nZVIS2O4 particle were investigated. Iron-based bimetallic particles in which metals such as Pd and Ni have been combined with Fe, have been found to both enhance rates of halogenated organic contaminants reduction and generate more fully dehalogenated products relative to unamended iron. The results presented in this thesis demonstrate that formation of bimetallic particles with nZVI formed from the more cost effective dithionite reduction of ferrous salts also results in dramatic enhancement in reducing ability. The oxidising ability of nZVIBH4 particles can be enhanced dramatically by addition of polyoxometallates (POMs), redox catalysts which result in enhanced production of hydrogen peroxide. The extent of enhancement is quantified by examination of the oxidation of formic acid (to CO2) and kinetic modelling of the results obtained used to investigate the mechanism of the POM-mediated oxidation process.

Integral membrane proteins perform a wide range of biological processes, including respiration, signal transduction and molecular transport. Structural information is necessary for a full understanding of the mechanisms by which integral membrane proteins work. Ferrous iron transporter protein B (FeoB) is an integral membrane protein of Escherichia coli which is considered to transport ferrous iron in to bacteria. But there are no definite proofs or clear indications of the precise mechanism of ferrous transport. By expressing and crystallizing the G-protein domain (FeoGP) and FeoB, it will be helpful to know about the iron transport system. In order to express FeoB and FeoGP, expression vector pFeoB (FeoB in pGEX-4T-1) and pFeoGP (FeoB in pGEX-4T-1) were made. FeoB and FeoGP proteins were expressed and purified. Using vapour diffusion method crystallization trials of FeoB and FeoGP were done. Crystals of FeoGP are observed and no crystal formation for FeoB. Native crystals of FeoGP diffracted to 2.2 ?? resolution, and mant-GMPPNP crystals to 2.6 ??. Preliminary data processing indicate space group P212121 for native crystals, with cell dimensions 46 x 119 x 146 ??. The data set is 100% complete, Rmerge 0.08, and I/ ?? 3.2.

Iron is an essential micronutrient that is required by some microorganisms in relatively large quantities. This is problematic for those inhabiting marine environments, where iron is highly insoluble and the dissolved fraction is predominantly strongly bound to organic compounds. Due to low supply and high demand, iron limits primary productivity in many oceanic waters, and may also limit growth of organisms in coastal waters under some circumstances. Recent incidents of explosive growth (???blooms???) of the noxious filamentous cyanobacterium Lyngbya majuscula in the coastal marine waters of Moreton Bay, Queensland, have prompted speculation that terrestrial human activities have increased iron availability to the organism, thus overcoming previous limitations on growth imposed by scarcity of the nutrient. This thesis describes work investigating the chemical form of iron in coastal waters under various environmental conditions and the way in which this influences its availability to L. majuscula. Chemical speciation of iron was investigated as a function of terrestrial-derived inputs of natural organic matter (NOM) of variable origin and sunlight in coastal marine waters, employing chemiluminescence-based and spectrophotometric techniques with high sensitivity and temporal resolution. These techniques allowed determination of iron and other chemical parameters at naturally occurring (typically nanomolar) concentrations. The mechanism of iron acquisition by L. majuscula was also investigated using a radioisotope-labelling labelling technique in addition to the other techniques described. Results indicated that iron speciation can be described by five classes: inorganic dissolved and organically complexed dissolved iron in both ferrous (reduced) and ferric (oxidised) forms, and precipitated inorganic iron. Simulation of laboratory results by numerical kinetic modelling of the processes investigated indicated that while the thermodynamic impetus is strongly towards precipitated iron, iron complexation by NOM and its reduction by sunlight-mediated processes and/or L. majuscula results in meta-stable dissolved species that are more readily available to L. majuscula. Superoxide is a critical intermediate in iron reduction by both sunlight and L. majuscula. Thus L. majuscula is capable of altering iron speciation to increase its availability, however uptake is also strongly dependent on environmental conditions and may be enhanced by increased inputs of iron, NOM and sunlight into coastal waters.

Superoxide, a reduced form of dioxygen is produced in natural waters from abiotic thermal processes such as iron(II) oxygenation photochemically, and biologically in natural waters. Superoxide is highly redox-active due to the presence of an unpaired electron and plays an important role in the geochemical cycling of trace metals and degradation of organic pollutants in natural waters. It also has a significant effect on the physiology of aquatic microorganisms and has been implicated in the growth of toxic microalga in coastal areas of Japan, Australia and Canada. The generation of superoxide by both biotic and photochemical pathways is described in this thesis and attention given to selected reactions of superoxide in simulated natural waters. Particular attention in this work has been given to the interaction of superoxide and iron and the impact of this interaction on iron availability to Chattonella marina, a red-tide phytoplankton frequently associated with fish-mortalities in Australia and Japan. Superoxide production from both phototchemical and biological sources is measured using a highly sensitive chemiluminescence technique and the effect of superoxide production on iron transformation under various environmental conditions is investigated by employing spectrophotometric techniques with high sensitivity and temporal resolution. The intermediacy of superoxide in iron acquisition mechanism by C. marina is also investigated using a radioisotope labeling technique. Our experimental results show that superoxide in natural waters is produced via reduction of dioxygen. The reduction of dioxygen takes place by transfer of electrons by the photo-excited quinone moieties present in natural organic matter or by reductases located on the outer cell membrane of organisms' surface. The experimental results suggest that the fate of iron in marine waters is closely related to the superoxidedioxygen redox couple. Superoxide can reduce a wide range of organically complexed iron(III) species to the more soluble iron(II) redox state, thus affecting its bioavailability. A simple kinetic model for redox-cycling of iron in the presence of superoxide is developed. In addition, by coupling the model for redox-cycling of iron with the forms of iron acquired by C. marina, a generalized mathematical model for iron acquisition is presented which satisfactorily describes all results obtained.

Graduation date: 1968

A detailed study of iron concentrations measured by the reducible, reactive ferrous, and extractable methods was conducted in Auke Bay, Alaska during June 1973 and in Hood Canal, Washington during October 1973 and April 1974. The concentrations by each method were generally highest at the bottom and decreased towards the surface with occasional pockets of high iron concentration water at the surface. In Hood Canal in October the maximum reactive ferrous iron concentration was observed at the bottom of the pycnocline. Large changes in the iron concentration were observed between successive surveys. The reducible iron method (range <0.8 to 187 μg Fe/L) measures colloidal ferric hydroxide plus easily dissolvable and reducible organically and inorganically bound iron. The reactive ferrous iron method (range <0.04 to 4.2 μg Fe/L) measures loosely bound organic and inorganic ferrous iron. The extractable iron method, as finally used, (range <4 to 170 μg Fe/L) measures that iron measured by reducible iron method plus up to twice the tightly bound organic iron. We have defined "available" iron (with quotes) as that iron which appears to be taken up by phytoplankton as determined by the correlation between the in situ iron concentration and the chlorophyll a concentration. Chlorophyll a concentration maxima generally occurred at the depth of the iron concentration minima, strongly supporting the idea that each method measures "available" iron. However, significant correlation coefficients for the regression of iron concentration versus chlorophyll a only support the "availability" of reactive ferrous iron and that phytoplankton prefer ferrous iron to ferric iron. This was one of the first extensive uses of Lewin and Chen's (1973) ferrous iron method and values observed were generally 2 to 100 times less than they reported. Changes occurring during water storage appear to be a function of p0₂. Major changes took place during the first five hours of storage. Interstitial water was greatly enriched in iron compared with the overlying water. The ferrous iron concentration was particularly high due to the low Eh of the sediments. Although the net flow of "available" iron is out of the sediment, the flux is small (approximately 3 x 10⁻⁵ μg Fe/m²sec). Most of the iron that appears to be coming from the sediment is probably being produced by bacterial decomposition as in the case of subsurface sources of iron associated with ammonia or urea maxima. Fresh water is a significant source of extractable and reactive ferrous iron into the well-mixed surface layer. Fresh water is also a source of organically bound iron. Zooplankton appear to produce "available" iron by eating or excretion. Light appears to cause the production of ferrous iron through an undetermined mechanism. / Graduation date: 1976

Contamination events at Oak Creek, which runs through Oregon State University Research lands, prompted investigations into alternate transport mechanisms for moving liquid effluent from OSU Diary lands to Oak Creek. Magnetometer surveys conducted at the Diary identified magnetic signatures spatially associated with sub-surface locations of drain tiles, a 12-inch pipe, and other features. These pipes may provide alternate methods of transporting effluent to Oak Creek. Magnetometer surveys in support of the contamination study identified an interesting variability in the Earth's local magnetic field. Magnetic signatures spatially associated with drain tiles appear strong in the western portion of the site, but fade out in the eastern part of the site. The cause of this variability was investigated by examining soil iron distributions. The Field-scale soil iron distribution was determined using a colorimetric analysis of extractions obtained from soil core samples. This study shows larger concentrations of iron in the western portion of the site where the magnetic signal is strong and lower concentrations of iron where the magnetic signal is lower. Tile-scale iron distribution over the drain tiles and in control units were analyzed using the same colorimetric technique. This study identified a disturbance to the natural iron distribution over the tile in the western part of the site due to soil mixing in the back-filled tile trench resulting in a contrast in the magnetic data. In the eastern part of the site, where there is no magnetic signature associated with the tile, the iron distribution over the tile looks similar to the control unit results. Analysis of the soils determined that excavating during tile installation disturbed soil horizons, but the iron has redistributed itself to the pre-tile configuration effectively erasing the magnetic contrast that existed shortly after tile installation. This project has shown that iron redistribution can adversely affect the ability of magnetometer surveys to identify drain tiles. This project also demonstrates that soils must be looked at as dynamic systems rather than the more common static system approach when evaluating the success of magnetometer surveys. Applying a dynamic view of soils can help ground-based remote sensing surveyors avoid costly, unproductive surveys. / Graduation date: 2003

Thesis (M.A.)--Virginia Polytechnic Institute and State University, 1984. / Vita. Abstract. Includes bibliographical references (leaves 146-153). Also available via the Internet.

Thesis (Ph. D.)--Purdue University, 2005. / Includes bibliographical references (p. 360-365). Also available online via the Purdue University e-Pubs website (http://docs.lib.purdue.edu/).