The effect of ionic strength (I), pCO2, and temperature on the reaction kinetics of calcite was investigated in magnesium-free, phosphate-free, low calcium (mCa^2 ≈ 0.01 – 0.02 molal) simple KCl and NaCl solutions from both undersaturated and oversaturated conditions. First order kinetics were found sufficient to describe the dissolution rate data. Dissolution rates decreased with increasing I and were faster in KCl than NaCl solutions at the same I indicating that Na^ interacts more strongly with the calcite surface than K^ or that water is less available in NaCl solutions. Rates increased with increasing pCO2 and temperature, and their influence diminished at high I. Arrhenius plots yielded a relatively high activation energy (Ea ≈ 20 ± 2 kJ mol-1) which indicated that dissolution was dominated by surface controlled processes. These results are consistent with the hypothesis that the mole fraction of "free" solvent plays a significant role in the dissolution kinetics of calcite with a minimum value of ~45-50 percent required for dissolution to proceed in undersaturated solutions at 25-55 degrees C and pCO2 = 0.1 – 1 atm. Precipitation rates were modeled using the general and Davies and Jones rate equations yielding similar results. Reaction orders were found to typically range between 0.8 and 2.5 for both rate equations regardless of electrolyte. For both solutions, rate constants were found to range between 100.8 and 101.7 mmole m-2 hr-1 (general rate equation) and 101.5 and 102.2 mmole m-2 hr-1 (Davies and Jones rate equation). Under the experimental conditions employed and the resultant precision (~20-25 percent), I and pCO2 do not have a significant influence on the precipitation rate of calcite. Precipitation rates increased with temperature although Arrhenius plots yield a broad range of activation energies (Ea ≈ 15 – 28 kJ mol-1, R2 = 0.72). The relatively low calculated activation energies coupled with the precision of the results suggest the possibility of surface nucleation in the present results. Overall, these findings may be useful in understanding and predicting the interaction and reactivity of the host carbonate minerals in subsurface reservoirs to the injection of CO2 although much work needs to be completed at elevated temperatures and pressures.

ABSTRACT Hydrophobic organic pollutants (HOPs) are in general characterized by high toxicity, long environmental half-life and high bio-accumulation factors. Due to their hydrophobicity, HOPs tend to sorb onto particulates in natural aquatic environment and their degradation pathways and rates are altered with the change of the reaction media and the settlement of these particles. The influence of the dissolved organic matters (DOMs), termed as the third phase, on the sorption partition coefficient is observed because of their interactions with HOPs. This binding (between DOM and HOP) increases apparent solubility and mobility of the HOP and the sorption coefficient of HOP in aquatic system is reduced. On the purpose of obtaining data closer to the real world, many aquatic factors, such as the concentration and types of DOM, pH value and ionic strength, are studied intensively recently. Nevertheless, it is difficult to clarify the influence of ionic strength because the relationship between binding constant of DOM-HOP and ionic strength is ambiguous in the literature. As such, by applying fluorescence quenching method, we investigate the influence of ionic strength on the partition coefficient (Kdom) of PAHs (phenanthrene¡Bpyrene)-humic acid (HA) system. Results show that the interaction of HA and cations is the primary factor in the variations of the partition coefficient. It is believed that, as cations reacting with specific binding sites on HA, the molecules' configuration of HA is changed and the binding mechanism of PAHs and HA is altered. A "four-stage variation model" is then proposed to explain the relationship between the ionic strength and partition coefficient. Therefore, a non-constant trend of ionic strength effect is resulted and is used to explain the controversial findings in the literature. Furthermore, Mg++ is found to cause stronger effect than K+ owing to higher charge density. The introduction of Br- would complicate the fluorescence quenching mechanism of phenanthrene-HA system because it's a fluorescence quencher. However, effects of anions on the variation of Kdom are not as significant as cations in our system. The effects of ionic strength on the variation of Kdom for four humic acids are LHA¡ÖPHA¡]Peat humic acid¡^¡ÖSHHA¡]Summit Hill humic acid¡^¡ÖSRHA. Results from different humic acids indicate that the Suwannee River humic acid (SRHA) is not as sensitive as Leonardite humic acid (LHA) on the ionic strength effect because of lower hydrophobicity. The influence of ionic strength on the variation of Kdom for pyrene-HA system is also amplified because of pyrene's higher hydrophobicity compared with phenanthrene.

No description available.

This study investigates the influence of ionic strength on the binding constant (KDOC) between benzo(h)quinoline (BHQ) and LHA by using fluorescence quenching method. Being a basic polycyclic aromatic hydrocarbon, BHQ is the dominated solute as the solution¡¦s pH value is higher than BHQ¡¦s pKb. In contrast, BHQ+ is the major species as the solution¡¦s pH value is lower than BHQ¡¦s pKb. In a salty neutral or basic LHA solution, the cation will bind with the acidic functional groups of LHA, then the conformation of LHA would be coiled up to be small in size. Due to that, leading to the decrease of the corresponding BHQ¡¦s KDOC. Furthermore, the charge density of cation is an important factor in control of the variation of BHQ¡¦s KDOC. The lower charge density of cation is, the less BHQ¡¦s KDOC varied. Besides, SO4 2- may suppress the binding affinity between Na+ and the acidic function groups of LHA, so that lower variation of BHQ¡¦s KDOC was observed than that of Cl- in a Na+ contained LHA solution. In an acidic solution, cation will also bind with the acidic functional groups of LHA, leading to the decrease of the binding sites of BHQ+ on LHA and the corresponding BHQ+¡¦s KDOC. Besides, Mg2+ could provide more binding sites for the acidic functional groups of LHA than Na+, so that the variation of BHQ+¡¦s KDOC with Mg2+ addition is higher than that with Na+ addition.

Every aerobic organism expresses cytochrome c oxidase to catalyze reduction of molecular oxygen to water, and takes advantage of this energy releasing reaction to produce an electrochemical gradient used in cellular energy production. The protein SCO (Synthesis of cytochrome c oxidase) is a required assembly factor for the oxidase, conserved across many species. SCO is implicated in the assembly of one of two copper centres (ie., CuA) of cytochrome oxidase. The exact mechanism of SCO’s participation in CuA assembly is not known. SCO has been proposed to bind and deliver copper, or alternatively to act in reductive preparation of the CuA site within the oxidase. In this body of work, the strength and stability of Cu(II) binding to Bacillus subtilis SCO is explored via electronic absorption and fluorescence spectroscopies and by calorimetric methods. An equilibrium dissociation constant (Kd) of 3.5x10-12 M was determined as an upper limit for the BsSCO-Cu(II) interaction, via differential scanning calorimetry. In the first reported case for a SCO homolog, dissociation kinetics of Cu(II) from BsSCO were characterized, and found to be dependent on both ionic strength and the presence of free Cu(II) in solution. Further differential scanning calorimetry experiments performed at high ionic strength support a two-step model of BsSCO and Cu(II) binding. The implications of this model for the BsSCO-Cu(II) interaction are presented in relation to the mechanism of interaction between SCO and the CuA site of cytochrome c oxidase. / Thesis (Master, Biochemistry) -- Queen's University, 2007-09-21 16:00:23.621

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

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.

In this study, we measured the binding constant, KCOC, between several humic acids and benzo(h)quinoline, a nitrogen contained PAHs via using fluorescence quenching method. KCOC of humic acids and phenanthrene, a parent PAHs, is also studied in comparison. Moreover, pH and ionic strength effect on the KCOC were investigated. According to our results, the phenanthrene¡¦s KCOC decreases as the pH increases due to the lower hydrophobicity of humic acid in higher pH values. The variation of benzo(h)quinoline¡¦s KCOC with pH exhibits a more complicated trend, with a maximum value at pH close to the pKb of benzo(h)quinoline. For pH lower than pKb, benzo(h)quinoline is protonated to be benzo(h)quinolinium, a cation, so that the ionic exchange is the dominant prosess in sorption mechanism. Therefore, the binding sites of humic acid increase with pH such that the KCOC increases with pH. In contrast, different mechanism involved in the binding for pH higher than pKb, neutral benzo(h)qunoline becomes dominant and hydrophobic interaction controls the binding prosess in sorption mechanism. At last, the composition of different functional groups of humic acid is also found significant in the binding affinity of benzo(h)qunoline or phenanthrene. Moreover, the benzo(h)qunoline¡¦s KCOC exhibits decreasing trend with increasing magnesium ionic strength because of the reduction of molecular size as well as the benzo(h)qunoline binding sites of humic acid. Findings from this study could provide valuable information for numerical simulation of transport and fates of HOPs in aquatic environment.

ABSTRACT Hydrophobic organic pollutants (HOPs) are in general characterized by high toxicity, long environmental half-life and high bio-accumulation factors. Due to their hydrophobicity, HOPs tend to sorb onto particles in environment. The influence of the dissolved organic matters (DOMs) on the sorption partition coefficient is observed because of their interactions with HOPs. This binding between DOM and HOPs increases apparent solubility and mobility of the HOPs in natural aquatic system. On the purpose of obtaining data closer to the real world, many aquatic factors, such as the concentration and types of DOM, pH value and ionic strength, are studied intensively recently. There are many studies about the mechanisms in the association of DOM and HOPs. Most of them assume achievement of equilibrium in their measurement. Recently, it was reported (Engebretson and von Wandruszka, 1998) that slow, revering, and even oscillating kinetics are observed. It is great concern and interest to those related studies in literatures. Complicated kinetic may in fact be a cause of the reproducibility problems for measurements of HOPs associated with both humic acid and metals. As such, by monitoring fluorescence intensity, we investigate the equilibrium kinetic of pyrene in HA solutions. In this study, results show that there are two stages of the fluorescence intensity after pyrene spiked into HA solutions: First, the fluorescence intensity decreases steeply due to the first dispersion of pyrene and the reaction of pyrene and HA (the front is dominance). Secound, fluorescence intensity decreases gently because of wall-effect. The dispersion rate of pyrene in HA solutions is difference with HA molecular size and quantity. As the ionic strength rising, cations reacting with specific binding sites on HA, the molecules¡¦ configuration of HA is changed, and less obstruct for dispersing of pyrene. It works as well as little molecular quantity. For second stage when ionic strength rising, wall- associations is less because of the hydrophobic-binding of pyrene and LHA is more stronger. Furthermore, it is not observed the ¡§migration¡¨ of Mg2+ within the LHA molecular structure as described by Engebretson and von Wandruszka .The reasons that make different results may depend on the species of humic acid. Therefore, the observations of Engebretson and von Wandruszka could not be used directly questioning those results in literatures. In addition, the effects of various cations (Mg2+, Ca2+and Sr2+) on Kdom are studied. It is believed different cation reacts with different specific binding sites on HA. As such, both charge density and affinity of cation with specific binding sites on HA should be considered in discussing the effects of metal ionic on the binding constants between PAHs and DOM.

No description available.