Search

Many chemical and physical factors govern the mobility of metal contaminants in soils and clay systems; some of these chemical factors include mineralogical composition, cation exchange capacity, organic matter content, pH and the ionic strength of soil water. This makes understanding and therefore predicting the fate of metal contaminants in soils a complex undertaking. There were two broad objectives in this study. The first was to investigate binary and ternary sorption systems, with the aim to understand the effects that factors such as pH, ionic strength, organic matter and metal concentrations, have on sorption of simple clay minerals (bentonite and kaolinite) with metals (cadmium, caesium, nickel and strontium). The second was to investigate the retention of heavy metals and radionuclides by well characterised organic-rich and organic-poor clay soils, breaking them down to their individual components to help understand the effects of each component separately, the study also tested to see if the additivity principle holds for these heavy metals and radionuclides, the additivity principle presumes that the overall sorption behaviour of a complex mixture is a summation of the weighted individual sorption behaviours of its constituents. The study also determined the relationship between the natural organic matter (NOM) content and cation exchange capacity (CEC) of the soils and how these affect the mobility of the metals, while also considering the relative importance of the speciation of the metals. Two British clay soils (Mercia Mudstone and London Clay) and two Nigerian soils (an organic-rich Ikeja Loam and the other organic-poor Magodo Laterite) were characterised by X-ray diffraction (XRD) analysis. Batch techniques were employed for the sorption studies, and radiometric techniques, ICP-OES and ICP-MS were used to quantify metal distribution between phases. The sorption of dissolved organic matter to clay minerals is very dependent on pH; this dependence is greater with increasing concentration of organic matter. The formation of metal-humate complexes is dependent on the nature of the metal and pH. Caesium exhibits no discernible sorption to humic acid, cadmium sorption is enhanced by increasing alkalinity but this enhancement is slightly reduced in higher concentrations of humic acid, nickel sorption is mostly unaffected by pH except in higher concentrations of humic acid and enhanced only under very low concentrations of humic acid, while strontium sorption to humic acid is reduced with increasing alkalinity. The nature and preference of humic acid sorption for these metals are vital to understanding the role played by humic acid in the ternary sorption studies of metals, humic acid and clay minerals. Strongly acidic conditions dominate other factors affecting sorption such as ionic strength in sorption of metals to clay minerals. Caesium sorption to bentonite at pH 4 is poor and almost unaffected by ionic strength of the electrolyte solution; saturation of sorption sites is reached with low amounts of adsorbed caesium. Strontium also binds poorly to bentonite at pH 4, more so than caesium, but an ionic strength effect on sorption still exists and is discernible even under these conditions. Increasing alkalinity has the expected effect of increasing sorption capacity of bentonite for both metals. Bentonite has poor sorption properties, having low affinity for caesium and strontium, but has greater affinity for caesium than strontium. The presence of humic acid can enhance or suppresses sorption, this varies from metal to metal and from solid to solid, the degree of enhancement or suppression also depends on humic acid concentration. Kaolinite has better sorption properties than bentonie. Cadmium has greater sorption affinity for kaolinite in the absence of humic acid, but nickel sorption is more enhanced in the presence of humic acid. Although the presence of humic acid enhances cadmium and nickel sorption to kaolinite, low humic acid concentration provides the best conditions for maximum sorption of both metals. High concentrations of humic acid lead to colloid formation which block access of metals with larger hydration radii to sorption sites while also encouraging the formation of humic acid-metal complexes. As with bentonite, caesium and strontium are both poorly sorbed by kaolinite. Unlike with cadmium and nickel however, the enhancement of strontium sorption is supported by higher concentrations of humic acid, these confirm a greater preference for the formation of S-HA-Sr ternary and lower preference for the formation HA-Sr binary complexes. The presence of humic acid inhibits caesium binding, and retention but this reduces with increasing alkalinity, while the reverse is the case with strontium whose retention is very poor and improved in the presence of humic acid and increasing alkalinity. Both caesium and strontium are poorly sorbed and retained by kaolinite but their retention improves with increasing humic acid concentration and pH. Cadmium and nickel also exhibit poor retention to kaolinite but their retentions are more improved under alkaline conditions and higher humic acid concentrations, nickel more so than cadmium. Similar sorption affinities were exhibited by the British (London Clay and Mercia Mudstone) and Nigerian soils (Magodo Laterite and Ikeja Loam) for the metals studied, showing the significance of soil constituent contribution to sorption behaviour. Both British clay matrices have affinity for the metals in the order Cs >> Cd ≈ Ni >> Sr, London Clay has the greater sorption capacity for all the metals, the clay mineral content of Mercia Mudstone is almost entirely made up of Illite while London Clay contains a mixture of smectite, illite and kaolinite with smectite being the most prevalent clay mineral phase. These confirm that smectite-rich clay systems will exhibit better sorption and retention capacities for metal contaminants. Both Nigerian soils showed the same order of affinity for all the metals Cd >> Ni >> Cs >> Sr, cadmium s preferential sorption to kaolinite was observed in its greater sorption and retention by the Nigerian soils which are kaolinite-rich. This preferential sorption of cadmium by kaolinite is confirmed by the Standard Addition experiment where its contribution to cadmium sorption is clearly evident, a trend not replicated with nickel as the sorbing metal. The presence of organic matter in soils or clay systems improves their metal sorption capacity significantly, especially true for insoluble organic matter, however its significance is reduced as pH increases. The contribution of organic matter also depends on the sorption affinity of the metal for organic matter; metals such like strontium are more affected by organic matter presence. The overall sorption behaviour of complex systems such as soils is difficult to attribute to their individual constituents. The laterite soils can be considered a relatively simple soil system containing only four constituents in significant quantities, yet it is difficult to replicate its sorption behaviour using a replicate proportioned mixture of its constituent phases. The additively calculated sorption profiles for the synthetic laterite were different from those obtained experimentally, the reason for this is that the existence of significant particle size differences between the natural and synthetic soils give rise to differences in the availability of sorption sites which is evident from the different CEC values measured for both systems.

Protein (mis)folding into highly ordered, fibrillar structures, amyloid fibrils, is a hallmark of several, mainly neurodegenerative, disorders. The mechanism of this supra-molecular self-assembly reaction, as well as its relationship to protein folding are not well understood. In particular, the molecular origin of the metastability of the soluble state of proteins with respect to the aggregated states has not been clearly established. In this dissertation, it is demonstrated, that highly accurate kinetic experiments, using a novel biosensing method, can yield fundamental insight into the dynamics of proteins in the region of the free energy landscape corresponding to protein aggregation. First, a section on Method development describes the extension and elaboration of the previously established kinetic assay relying on quartz crystal microbalance measurements for the study of amyloid fibril elongation (Chapter 3). This methodology is then applied in order to study in great detail the origin of the various contributions to the free energy barriers separating the soluble state of a protein from its aggregated state. In particular, the relative importance of residual structure, hydrophobicity (Chapter 4) and electrostatic interactions (Chapter 5) for the total free energy of activation are discussed. In the last part of this thesis (Chapter 6), it is demonstrated that this biosensing method can also be used to study the binding of small molecules to amyloid fibrils, a very useful feature in the framework of the quest for potential inhibitors of amyloid formation. In addition, it is shown that Thioflavin T, to-date the most frequently employed fluorescent label molecule for bulk solution kinetic studies, can in the presence of potential amyloid inhibitor candidates be highly unreliable as a means to quantify the effect of the inhibitor on amyloid formation kinetics. In summary, the work in this thesis contributes to both the fundamental and the applied aspects of the field of protein aggregation.

This thesis is concerned with the study of different effects in protein ultrafiltration including device configuration, solution chemistry and membrane charge In the recent and more established literature membrane fouling remains a challenging problem that limits the wider application of ultrafiltration. Thus, investigations which can aid understanding and potentially reduce membrane fouling are of particular interest and in this study the problem has been addressed from several different angles Polyethersulfone membranes were studied at varying pH and two ionic strengths using bovine serum albumm and lysozyme as the model proteins. The study was conducted both in a stirred cell and a crossflow configuration in order to evaluate the influence of different system hydrodynamics on filtration This work was further substantiated through the application of filtration models An attempt was also made to modify the membrane surface by low temperature plasma modification with the intention to preferentially alter the characteristics of the membrane surface Both unmodified and plasma-modified polyethersulfone membranes were characterised using a range of analytical methods including flux data, streaming potential, contact angle and MWCO measurements to aid results interpretation. The research showed that MWCO data quoted by manufacturers is mostly greater than that obtained during laboratory studies The MWCO technique was also used to highlight differences between the unmodified and plasma-modified membranes demonstrating that the modification resulted in a membrane with tighter pores in the lower molecular weight region. Concentration polarisation effects were found to be reduced as a result of the plasmamodification The study of protein filtration at different pH and ionic strengths demonstrated that ionic strength effects were more pronounced than pH effects It was also shown that changes m the ionic strength can be used to alter the degree of protein rejection for the given system concentration polarisation was found to be higher during crossflow filtration compared to stirred cell filtration The thesis adds to existing knowledge in the area of ultrafiltration emphasizing the importance of device configuration, solution chemistry as well as the potential of charged membranes

The objective of this dissertation research was to investigate initiation mechanisms for CO2 localized corrosion on mild steel, encompassing the effects of chloride, oxygen, and acetic acid. In CO2 corrosion, iron in steel will be oxidized to ferrous ions under deareated conditions. The ferrous and carbonate ions can combine to form FeCO3 and precipitate once exceeding the solubility limit. When the precipitation of FeCO3 occurs evenly on the steel surface it forms a compact and protective layer. This acts as a diffusion barrier hindering the mass transfer of electrochemical species and covers/blocks the surface making it unavailable for corrosion, which enhances the resistance of mild steel to further uniform CO2 corrosion. However, there are various scenarios where localized corrosion may occur. When the environment becomes more aggressive, the FeCO3 could be partially removed. This leads to localized regions of the bare steel surface that become exposed to the corrosive solution and, subsequently, localized corrosion could be initiated.To study CO2 localized corrosion, two-stage experiments were performed: (1) a uniform protective FeCO3 layer was first formed on a carbon steel with high initial FeCO3 saturation; (2) localized CO2 corrosion scenarios were then developed by adding additional salts (NaCl or NaClO4), oxygen or acetic acid to challenge the protective FeCO3 layer.The experiments were conducted in a two-liter glass cell with a three-electrode system, working electrode (X65 carbon steel), reference electrode (Ag/AgCl saturated electrode), and counter electrode (platinum). Electrochemical measurements (linear polarization resistance) were carried out to observe electrochemical behaviors and calculate the corrosion rates. Weight loss was also used to determine general corrosion rates. Fe2+ concentration was measured using spectrophotometry in order to study the solubilization of FeCO3. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and profilometry by infinite focus microscopy (IFM) were used to determine pitting.The results in non-ideal solutions showed that no localized corrosion was initiated by introducing more salt. The introduction of acetic acid resulted in localized corrosion. When oxygen was introduced, severe pitting occurred. A new water chemistry model based on Oddo & Tomson’s equation was proposed by the author. Based on EQCM results, a new model to calculate the solubility constant of iron carbonate in non-ideal solution at 80℃ was developed based on Sun & Nesic model.

One aspect of the biocomplexity of eukaryotic cells is the compartmentalized ionic strength, which impacts a myriad of biological functions. In this thesis, we investigate a class of environmental ionic strength sensors (mCerulean3–linker–mCitrine) that can be genetically encoded in site-specific compartments in living cells. In these sensors, mCerulean3–mCitrine acts as a Förster resonance energy transfer (FRET) pair that is tethered by two oppositely charged α-helices in the linker region. We hypothesize that as the ionic strength is increased, the attractive force between these charged alpha helices will be screened by the dissolved ions, resulting in an increase in the donor–acceptor distance (i.e., reduced FRET efficiency). To test this hypothesis, we investigated the rotational dynamics of these sensors using a newly developed time-dependent polarization anisotropy approach of the acceptor (mCitrine) emission, following pulsed excitation of the mCerulean3 (donor) in cleaved and intact mCerulean3–linker–mCitrine sensors (KE, RD, and RE) in different Hofmeister salt solutions (namely, KCl, NaCl, NaI, and Na2SO4). Our results show that the rotational dynamics of the intact and cleaved sensors are distinct under the excitation-detection conditions. Importantly, the FRET efficiency decreases and the donor-acceptor distance increases as the environmental ionic strength increases, with slight sensitivity to the Hofmeister salt type. In contrast, FRET efficiency of E6G2 with electrostatically neutral amino acids in the linker region exhibits salt-independent rotational and FRET dynamics. Our time-resolved anisotropy data were also used to test existing theorical models concerning the steady-state anisotropy of these hetero-FRET sensors, while revealing the ionic strength effects on the angle between the dipole moments of the donor and acceptor in these sensors. Using our complementary, traditional time-resolved fluorescence method, we optimized our time-resolved anisotropy approach for FRET analysis and developed a theoretical model using Debye ionic screening of the two charged alpha helices in the linker region. These results help establishing time-resolved anisotropy of donor-acceptor pairs as a quantitative means for FRET analysis, which complement other traditional methods such as time-resolved fluorescence.

Nanocelluloses (NCs) have emerged throughout soft materials sciences as a green building block for the bottom-up design of functional materials. This thesis addresses the self-assembly and aggregation of NCs into (I) 3D soft materials and (II) at 2D fluid interfaces to foster the understanding of NC colloidal behavior and facilitate this bottom-up approach. In part (I) optical, mechanical, and structural analyses are combined to map the phase behavior of cellulose nanocrystal (CNC) aqueous dispersions. CNCs undergo a transition from isotropic dispersion to cholesteric liquid crystals at increasing volume fraction. Ion-induced charge screening initially decreases the cholesteric volume fraction, but induces the arrest of CNCs into attractive glasses beyond a critical ionic strength. CNC attractive glasses have received little attention, but may be of great interest as they exhibit gel-like mechanical properties while remaining optically active owed to entrapped nematic domains. At higher ionic strength CNCs aggregate into hydrogels. Using four salts with different size and valency, it was confirmed that gelation derives entirely from CNC attractive forces, refuting previous speculations of ionic bridging. Ultimately, the hydrogels were demonstrated to qualify as injectable biocompatible drug carriers for sustained and pH-responsive drug delivery. NCs have been widely used for the stabilization of biocompatible Pickering emulsions in the past decade, however, their behavior at fluid interfaces remained poorly understood. In part (II), the first ever protocol for the formation of NC interfacial films is presented. This provided insights into NC adsorption kinetics, isotherms, and energy by dynamic surface tension measurements, as well as enabling the analysis of NC interfacial structure and coverage by reflectivity and film displacement techniques. NC adsorption is limited by its surface charge, and is promoted at lower charge density or by salt-induced charge screening. NCs orient laterally in the interfacial plane and form discontinuous monolayers. The inability of NCs to stabilize foams, an ongoing enigma in the field, could be attributed to an energetically more favorable contact angle at oil-water compared to air-water interfaces. Adsorption experiments at different oils revealed that NC adsorption is less stable at oils with increasing polarity, which in turn impedes emulsion stability. These insights provide the long-missed fundamental understanding of NC adsorption at fluid interfaces, and will facilitate the formulation of NC Pickering emulsions in the future.

Nitrate (NO3-) is a reactive nitrogen compound and can be utilized by living organisms. Industrial nitrogen fixation methods have greatly increased the production of reactive nitrogen and ultimately increased concentration of nitrate in natural waters. In natural streams, nitrate is recognized as a pollutant that can lead to some serious health issue for humans. Therefore, knowing the nitrate concentration in streams is critical to the environment and human health. Nitrate is not a major ion in natural waters. It would be very helpful if nitrate concentration could be estimated from other frequently measured parameters of stream, allowing ones to predict the nitrate concentration from other, more easily measure parameters. The largest data set of ionic composition of streams that has ever been compiled was used to examine the relationships among nitrate concentrations, major ion concentrations, and two bulk measurements of ionic content, ionic strength and specific conductance.

Protein therapeutics offer numerous advantages over small molecule drugs and are rapidly becoming one of the most prominent classes of therapeutics. Unfortunately, they are delivered almost exclusively by injection due to biological obstacles preventing high bioavailability via the oral route. In this work, numerous approaches to overcoming these barriers are explored. PH-Responsive poly(itaconic acid-co-N-vinylpyrrolidone) (P(IA-co-NVP)) hydrogels were synthesized, and the effects of monomer ratios, crosslinking density, microparticle size, protein size, and loading conditions were systematically evaluated using in vitro tests. P(IA-co-NVP) hydrogels demonstrated up to 69% greater equilibrium swelling at neutral conditions than previously-studied poly(methacrylic acid-co-N-vinylpyrrolidone) hydrogels and a 10-fold improvement in time-sensitive swelling experiments. Furthermore, P(IA-co-NVP) hydrogel microparticles demonstrated up to a 2.7-fold improvement in delivery of salmon calcitonin (sCT) compared to methacrylic acid-based systems, with a formulation comprised of a 1:2 ratio of itaconic acid to N-vinylpyrrolidone demonstrating the greatest delivery capability. Vast improvement in delivery capability was achieved using reduced ionic strength conditions during drug loading. Use of a 1.50 mM PBS buffer during loading yielded an 83-fold improvement in delivery of sCT compared to a standard 150 mM buffer. With this improvement, a daily dose of sCT could be provided using P(IA-co-NVP) microparticles in one standard-sized gel capsule. P(IA-co-NVP) was also tested with larger proteins urokinase and Rituxan. Crosslinking density provided a facile method for tuning hydrogels to accommodate a wide range of protein sizes. The effects of protein PEGylation were also explored. PEGylated sCT displayed lower release from P(IA-co-NVP) microparticles, but displayed increased apparent permeability across a Caco-2 monolayer by two orders of magnitude. Therefore, PEG-containing systems could yield high bioavailability of orally delivered proteins. Finally, a modified SELEX protocol for cellular selection of transcellular transport-initiating aptamers was developed and used to identify aptamer sequences showing enhanced intestinal perfusion. Over three selection cycles, the selected aptamer library showed significant increases in absorption, and from an initial library of 1.1 trillion sequences, 5-10 sequences were selected that demonstrated up to 10-fold amplification compared to the naïve library. These sequences could provide a means of overcoming the significant final barrier of intestinal absorption.

Aluminium (Al) toxicity is a key factor limiting pasture production in the high country of New Zealand. Many high country soils are acidic, with a pH less than 5.5. Low soil pH makes Al soluble, leading to high concentations of exchangeable Al in soils and plant Al toxicity. Aluminium toxicity reduces plant vigour and yields; resticting root growth and limiting nutrient and water uptake. The harsh climatic conditions experienced in the high country could also play a role in the exacerbation of Al toxicity. Literature on the influence of low moisture extremes on exchangeable Al concentrations is scarce. Nomad white clover was grown for 10 months under glasshouse conditions at Lincoln University in two acidic high country soils collected from Omarama and Glenmore Stations, Central Otago. The trial was a full factorial design of two soil types, three soil moisture levels and four fertiliser treatments. Lime (100% CaCO3) was applied at three rates (0,2 and 8 t lime/ha) with one treatment of P and lime (2 t lime/ha and 150 mg P/kg). Sulphur was applied to all treatments at 120 kg S/ha (Gypsum). Plants were harvested four times during the experiment and yields were determined. Herbage was analysed for macro and micro nutrient concentrations by ICP-OES and NIRS. Soils were analysed for pH and exchangeable Al, with bulk soil samples also analysed for P and S contents at completion of the experiment. A significant interaction between soil moisture and exchangeable soil aluminium was observed for the Glenmore soil. The medium moisture treatment (23% VWC) had lower exchangeable Al, 4 mg/kg compared to the low (17% VWC) and high (33% VWC) moisture treatments which contained 5 and 5.6 mg exchangeable Al/kg respectively, for the zero lime treatment. The low Al Omarama soil in comparison, only contained Al concentrations of 1.3, 1.1 and 0.8 mg Al/kg in the same treatments at the completion of the experiment. This experiment did show an interesting interaction and strongly suggests that soil moisture influences exchangeable Al, but only when Al concentrations are greater than 4 mg Al/kg. Similar experiments are required using high Al soils to confirm this result. The Glenmore soil contained higher initial concentrations of exchangeable Al (6.6 mg Al/kg), had greater carbon stocks (6.9 kg C/m3) and produced higher shoot yields (10.6 g DM/pot) than the Omarama soil (3.8 mg Al/kg , 3.5 kg C/m3 and 7.8 g DM/pot). The high P fertility of the Glenmore soil (Olsen P 18) probably supressed soil Al affects on yield. High soil carbon may have also masked the effects of soil moisture on exchangeable Al for the Glenmore soil. Moisture treatments caused a significant growth limitation on the low moisture treatment (17% VWC), with a yield of 8.7 g DM/pot compared to 9.5 and 9.4 g DM/pot for the medium (23% VWC) and high (33% VWC) moisture treatments. Herbage nutrient concentrations were effected predicatably by lime and P addition. Shoot concentrations of P and Mo increased with lime addition, while shoot concentrations of Zn, Mn, B and Al decreased. Shoot nutrient uptake followed the same trends as concentration.

Topical therapies for the treatment of nail diseases are preferable. They reduce the likelihood of adverse effects associated with systemic medications and increase patient compliance. Due to the imperviousness of nail, however, topical delivery is challenging. The nail selects for the penetration of small, hydrophilic molecules. Most pharmaceutical agents are large and highly lipophilic, and are therefore unable to diffuse across the nail at therapeutic concentrations. Iontophoresis has been proposed as a mechanism to overcome the nail barrier to concurrently deliver and load the nail with drug. To optimize a transungual iontophoretic drug system, the transport barrier properties of the human nail plate during iontophoresis were characterized. Specifically, the effects of ionic strength, pH, and organic solvents on the barrier properties of nail were assessed in vitro through nail hydration/gravimetric, uptake, and transport studies. Permselectivity towards tetraethylammonium ion (TEA) was inversely related to ionic strength in both passive and iontophoretic transport. The permeability and transference number of TEA were higher at lower ionic strengths under symmetric conditions due to increased partitioning of TEA into the nail. Transference numbers were lower under asymmetric conditions compared with their symmetric counterparts. Nail hydration was independent of ionic strength and pH under moderate pH conditions and increased significantly under extreme pH conditions (pH >11). Likewise, nail permeability for water was pH-independent at pH 1 to 10 and an order of magnitude higher at pH 13. The results of passive and iontophoretic transport of Na and Cl ions are consistent with the published permselective properties of nail. Interestingly, extremely acidic conditions (e.g., pH = 1) altered nail permselectivity with the changes lasting several days at the higher pH conditions. Hydronium and hydroxide ion competition to iontophoretic transport was generally negligible at pH 3–11 but ion competition was significant at the extreme pH values studied. Nail uptake and permeability increased with increases in the organic solvent concentration for ethanol (EtOH), propylene glycol (PPG), and polyethylene glycol-400 (PEG). These changes coincided with differences in the solution viscosity as well as with changes in the barrier properties of the nail of which hydration was the most likely explanation. The more pronounced results for PPG and PEG as compared with those for EtOH are likely due to the differences in the viscosity and molecular size of the different organic solvents. There are four main practical implications from these results. First, the results suggest that positively charged drugs can effectively partition into the nail at low donor concentration due to ion-to-nail charge interactions. Second, the pretreatment of nail with solutions of extremely acidic pH (pH 11) may be useful for enhancing transungual permeability. Third, the results suggest that pH modulations – between pH 3 and 11 – necessary to increase drug solubility will not affect drug transport. Fourth, these results suggest that increased drug solubility brought about by the use of organic solvents may be counteracted by increased nail barrier resistivity.

MUDGAL, PRASHANT. Aggregation Mechanisms of a Whey Protein Model System at Low pH. (Under the direction of Dr. Christopher R. Daubert and Dr. E. Allen Foegeding) Recently, there has developed increasing interest in cold-thickening whey protein ingredients for food applications where heat may not be desirable and because of their nutritional benefits over conventionally-used starches and hydrocolloids. In previous studies, a procedure allowing for the production of a cold-thickening whey protein ingredient, without any addition of salt or heat, was developed. This procedure involved pH adjustment to 3.35, thermal gelation, followed by drying and milling to a powder. Originally, this procedure was applied to whey protein isolates, but also worked with concentrates. Although, these modified powders provide certain benefits, such as instant thickening without addition of heat or salts, these ingredients were prepared at low pH and yield astringent flavors that limit use in practical applications. To effectively tailor the original modification process to expand the functionality and utility of cold-thickening modified whey protein ingredients, the basic mechanism behind the cold-thickening must be explained. β-Lactoglobulin (β-lg) is the major component of whey protein products and was selected as a model system to investigate the cold-thickening mechanisms. Concentration effects on β-lg modification were studied at low pH using capillary and rotational viscometry, transmission electron microscopy (TEM), and high performance liquid chromatography coupled with multi-angle laser light scattering (HPLC-MALS). From the results of the capillary viscometry, a critical concentration (Cc ~ 6.4 % w/w protein) was identified below which no significant thickening functionality could be achieved. Microscopy revealed formation of flexible fibrillar network at pH 3.35 during heating at all concentrations. These flexible fibrils had a diameter of approximately 5 nm and persistence length of about 35 nm as compared to more linear and stiff fibrils formed at pH 2 and low ionic strength (I) conditions. Under similar heating conditions at concentrations above Cc, larger aggregates similar to microgels were observed. However, at concentrations below Cc, isolated fibrils were observed with an average contour length of about 130 nm. In further investigations, concentration effects were studied together with ionic strength (CaCl2) effects on the β-lg cold-thickening mechanism using light scattering, microscopy, and rotational viscometry. A slight increase in I (up to 20 mM) with β-lg concentrations above the critical concentration resulted in an increased thickening function from modified powders. The network characteristics remained fine stranded with small addition of CaCl2, and increased aggregation was observed at all concentrations. The aggregates formed during heating persisted in dried powders; however, freeze concentration effects during freezing further enhanced thickening function as obtained from the reconstituted modified powders. The size of the aggregates formed during the modification process was found to be dependent on the initial protein concentration from kinetic studies using light scattering and rheology. A nucleation and growth mechanism best fit the aggregation at pH 3.35, and nucleation was found to be a rate limiting step below the critical concentration. Above the critical concentration, nucleation occurred rapidly leading to a higher degree of aggregation and formation of large aggregates. By manipulating concentration and heating times, it seemed feasible to control the degree of aggregation and the size of aggregates between 106 to 108 Da. According to electrophoretic studies, disulfide linked aggregates were formed upon heating during the modification procedure. However, disulfide interactions alone could not explain the observed concentration dependent thickening differences. Some acid hydrolysis occurred at pH 3.35 and with additional hydrolysis of β-lg with the enzyme pepsin, solution viscosities increased by about two logs. Likely, formation of pre-aggregates during hydrolysis may explain increased aggregation and higher viscosities.

The ability of Escherichia coli O157:H7 to survive in acidified vegetable products is of concern because of previously documented outbreaks associated with fruit juices. A study was conducted to determine the survival of E. coli O157:H7 in organic acids at pH values typical of acidified vegetable products (pH 3.2 and 3.7), under different atmospheres, and a range of ionic strengths (0.086 to 1.14). Determination of internal pH and catalase activity in acid solutions can explain how dissolved oxygen or D- versus L-lactic acid reduces the survival of Escherichia coli O157:H7 when the organism is exposed to low pH (3.2) values typical of fermented and acidified foods. All solutions contained 20 mM gluconic acid, which was used as a non-inhibitory low pH buffer to compare the individual acid effect to that of pH alone on the survival of E. coli O157:H7. E. coli O157:H7 cells challenged in buffered solution with ca. 5 mg/L dissolved oxygen (present in tap water) over a range of ionic strengths at pH 3.2 exhibited a decrease in survival as the ionic strength was increased over 6 h. Overall, under oxygen limiting conditions in an anaerobic chamber, there is no significant difference in the loss of viability of E. coli O157:H7 cells regardless of pH, acid type, concentration, or ionic strength. For lactate concentrations up to 40 mM, there was no significant difference in internal pH values when cells were incubated in D- versus L-lactic acid solutions. Unexpectedly, cells incubated under aerobic conditions maintained a significantly higher internal pH (ca. 5.8) than cells incubated under anaerobic conditions (ca. 5.4), regardless of the isomer of lactic acid used. Overall, catalase activity was higher when cells were in the presence of L-lactic acid versus D-lactic acid however there is a decrease in survival when cells are incubated in L-lactic acid. Under the conditions tested, differences in survival of E. coli O157:H7 between isomers of lactic acid and atmospheres is not a result of internal pH or catalase activity. However, the lower internal pH maintained by cells incubated anaerobically (5 mM lactic acid) results in a smaller pH gradient and decreases the accumulation of acid anions inside the cell, which may contribute to increased survival under anaerobic conditions. Many acid and acidified foods are sold in hermetically sealed containers with oxygen limiting conditions. Our results demonstrate that E. coli O157:H7 may survive better than previously expected from studies with acid solutions containing dissolved oxygen.

Silicate minerals are the most common mineral group in the earth's crust so it is not surprising that their weathering reactions dominate the chemistry of many earth surface processes. This project used forsterite as a model system to identify the important factors that affect silicate mineral dissolution rates and grain lifetimes in the weathering environment. I determined an empirical rate law for forsterite dissolution of forsterite in oxalic acid solutions: based on a series of 124 semi-batch reactor experiments over a pH range of 0 to 7 and total oxalate concentrations between 0 and 0.35 m at 25°C. These experiments show that oxalate-promoted dissolution rates depend upon both oxalate concentration and pH. I propose a reaction mechanism in which a hydrogen ion and an oxalate ion are simultaneously present in the activated complex for the reaction that releases H4SiO4 into solution. By analogy, I propose that water acts as a ligand in the absence of oxalate. I also ran 82 batch reactor experiments in magnesium and sodium sulfate and magnesium and potassium nitrate solutions. These experiments show that ionic strength up to 12 m, log mMg up to 4 m, and log mSO4 up to 3 m have no effect on forsterite dissolution rates. However, decreasing aH2O slows forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process.Forsterite dissolution rate data from previously published studies were combined with results from my experiments and regressed to produce rate laws at low and high pH. For pH < 5.05 or and for pH > 5.05 or I then developed a diagram that shows the effect rate-determining variables on the lifetime of olivine grains in weathering environments using these rate laws.

Addition of nano particles to cooling fluids has shown marked improvement in the heat transfer capabilities. Nanofluids, liquids that contain dispersed nanoparticles, are an emerging class of fluids that have great potential in many applications. There is a need to understand the fundamental behavior of nano dispersed particles with respect to their agglomeration characteristics and how it relates to the heat transfer capability. Such an understanding is important for the development and commercialization of nanofluids. In this work, the stability of nano particles was studied by measuring the zeta potential of colloidal particles, particle concentration and size. Two different sizes of silica nano particles, 10 nm and 20 nm are used in this investigation at 0.2 vol. % and 0.5 vol. % concentrations. The measurements were made in deionized (DI) water, buffer solutions at various pH, DI water plus HCl acid solution (acidic pH) and DI water plus NaOH solution (basic pH). The stability or instability of silica dispersions in these solutions was related to the zeta potential of colloidal particles and confirmed by particle sizing measurements and independently by TEM observations. Low zeta potentials resulted in agglomeration as expected and the measured particle size was greater. The heat transfer characteristics of stable or unstable silica dispersions using the above solutions were experimentally determined by measuring heat flux as a function of temperature differential between a nichrome wire and the surrounding fluid. These experiments allowed the determination of the critical heat flux (CHF), which was then related to the dispersion characteristics of the nanosilica in various fluids described above. The thickness of the diffuse layer on nano particles was computed and experimentally confirmed in selected conditions for which there was no agglomeration. As the thickness of the diffuse layer decreased due to the increase in salt content or the ionic content, the electrostatic force of repulsion cease to exist and Van der Waal's force of agglomeration prevailed causing the particles to agglomerate affecting the CHF. The 10nm size silica particle dispersions showed better heat transfer characteristics compared to 20nm dispersion. It was also observed that at low zeta potential values, where agglomeration prevailed in the dispersion, the silica nano particles had a tendency to deposit on the nickel chromium wire used in CHF experiments. The thickness of the deposition was measured and the results show that with a very high deposition, CHF is enhanced due to the porosity on the wire. The 10nm size silica particles show higher CHF compared to 20nm silica particles. In addition, for both 10nm and 20nm silica particles, 0.5 vol. % concentration yielded higher heat transfer compared to 0.2 vol. % concentration. It is believed that although CHF is significantly increased with nano silica containing fluids compared to pure fluids, formation of particle clusters in unstable slurries will lead to detrimental long time performance, compared to that with stable silica dispersions.

The response of cucumber (Cucumis sativus L.) plants to various root and shoot environments (solution depth, temperature, ionic strength, nitrogen and calcium level and light intensity) were studied. Cucumber plants were grown in continuously circulating-solution in a heated-glasshouse. Dry weights of leaves, stems and roots, leaf area, leaf number, root length and root number were measured as well as uptake of potassium, calcium and nitrogen. The relationship between shoot and root in terms of functional equilibrium equations was also examined. The results presented show that: 1. Shoot growth of cucumber plants was reduced if grown in solutions of less than 50mm in depth; 2. When roots were grown in shallow solution depths at 1 or 5mm the dry weight allocated to the root increased. The ratio of root number/root length(no./cm) also increased. Lowering solution temperature to 12.5±2.5°C enhanced the production of root number relctive to root length, and 5 and 2% of full strength and 5% of full strength nitrogen level solution stimulated the growth of root length relative to root number; 3. Under low solution temperature treatment leaf number was maintained at the expense of leaf area. Under low total ionic strength and low nitrogen solution, enhanced root length growth was at the expense of leaf area growth; 4. Low solution temperature enhanced the dry weight allocated to the stem relative to the leaf. Low total ionic strength and low nitrogen solution increased the dry weight allocated to the leaf relative to the stem; 5. The specific activity of root, represented by specific absorption rate, increased when the shoot was under light stress and, the specific activity of shoot, represented by unit shoot rate, increased when the root was under nitrogen-stress; 6. The form of equation developed by Thornley (∆M = fm∆W, where ∆M is the increment in weight of element M and ∆W the increment in total plant dry weight during a time period ∆t with fm a constant) showed a better relationship than the equation developed by Davidson [root mass x rate(absorption) ∝ leaf mass x rate(photosynthesis)] and subsequently used by Hunt in the form of mass ratio(root/shoot) ∝ l/activity ratio; 7. The equation developed by Chung et al, total plant weight/(leaf number/leaf area) ∝ total "k"/(root number/root length), where k represents the total contents of elements or compounds, showed a good approximation of the relationship between shoot and root under all the environmental stresses imposed with the exception of calcium uptake. The results support the concept that the activity of the root or shoot in carrying out its function is influenced by the demand created by the opposite organ and appears to be a better assumption than that which proposes that the activity of an organ is solely dependent on its own size.