The DLVO theory states that the interaction between two lyophobic particles in aqueous media can be predicted by the sum of two surface forces, i.e., the electrical double-layer and van der Waals forces. This theory, which was developed 50 years ago, served as a backbone for colloid chemistry. However, various experiments conducted in recent years showed that it is applicable only to those particles whose advancing water contact angles (qa) are in the range of 15-60o. For example, direct surface force measurements conducted between silica substrates, whose qa values are less than 15o, exhibited the existence of repulsive hydration forces at relatively short separation distances. On the other hand, substrates, for which qa is greater than 60o, exhibit long-range attractive hydrophobic forces not considered in the DLVO theory . These extraneous attractive forces play important roles in many industrial applications. It is, therefore, the objective of the present study to measure the hydrophobic and hydration forces under different conditions. The measurements were conducted using both the Surface Forces Apparatus (SFA) and the Atomic Force Microscope (AFM). Mica and Silica were used as substrates, and the effects of dioctylammonium-hydrochloride (DOAHCl), octanol, methanol, ethanol, trifluoroethanol (TFE), pyridine, CaCl2, MgCl2 and sodium oleate were studied. A Mark IV SFA was used to conduct force measurements between mica surfaces in aqueous solutions of DOAHCl, which is a secondary amine. At 7x10-6M DOAHCl, the mica surfaces were rendered electrically neutral, and net attractive hydrophobic forces were observed. The measured forces can be represented by a double-exponential function with the larger decay length (D2) of 5.1 nm. The measured hydrophobic forces are substantially stronger than those reported in literature between self-assembled monolayers of soluble single-chain surfactants such as dodeylammonium hydrochloride (DAHCl) and cetyltrimethylammonium bromide (CTAB). Appearance of the strong hydrophobic forces is due to the likelihood that the double-chain cationic surfactant can create a higher hydrocarbon chain packing density than the single-chain cationic surfactants such as DAHCl and CTAB. Force measurements were also conducted using the AFM between a silica plate and a glass sphere in aqueous solutions of methanol, ethanol, TFE and pyridine to study their effect on the hydration force. It was observed that in Nanopure water, silica surfaces exhibit a strong short-range hydration repulsion, which can be represented by a double-exponential function with its longer decay length (D2) of 2.4 nm. In solutions containing 15% methanol, however, the hydration force disappears completely. This observation can be attributed to the displacement of the water molecules H-bonded to the silanol group by methanol, which in turn destroys the water structure in the vicinity of the silica surface. Methanol can displace water from the silanol group because it is more basic than the water. Ethanol, on the other hand, cannot cause the hydration forces to disappear, suggesting that it is less effective than methanol in displacing the H-bonded water molecules from the silanol groups, possibly due to steric hindrance. In the presence of triflouroethanol (TFE) and pyridine, hydration forces change little, which suggest that they are not effective in disturbing the water structure in the vicinity of silica. Finally, an AFM was used to measure the hydrophobic forces between silica surfaces coated with oleate. Since this surfactant is anionic, and the silica surface is negatively charged in alkaline solutions, it was necessary to reverse the charge of the silica substrate. In the present work, CaCl2 and MgCl2 were used as activators. It was found that hydrophobic forces are observed at pHs where the CaOH+ or MgOH+ ion concentrations reach maximum, suggesting that the singly charged hydroxo-complexes are the activating species. A model developed in the proposed work suggests that a significant part of the free energy of adsorption comes from the lateral interactions between neighboring hydroxo-complexes on the surface. It is also suggested that oleate adsorbs on silica as basic calcium oleate and basic magnesium oleate. These species may be H-bonded to the silanol groups on surface. The force measurements were also conducted between hydrophobic (silanated) silica surfaces in CuCl2 solutions. The results show that the hydrophobic force decreases most significantly at the pH where the concentration of the CuOH+ ions reaches maximum, which suggests that the singly charged hydroxo-complexes are more surface-active than their unhydrolyzed counterpart. The driving forces for the adsorption of the CaOH+ ions may include the electrostatic attraction from the surface and the lateral interaction between neighboring hydroxo-complexes on the surface. / Ph. D.

At the molecular level the entropic “hydrophobic effect” is responsible for high interfacial energies between hydrophobic solids and aqueous liquids, the low solubility of apolar solutes in aqueous solvents, and self-assembly in biological processes, such as vesicle formation and protein folding. Although it is known that a strong attraction between apolar molecules exists at the molecular level, it is not clear how this force scales up to objects with dimensions in the range 100 nm–1 m. This work sets out to measure the forces between particles with a radius of about 10 µm. Because we can only measure the total force, which includes the van der Waals force and the electrostatic forces, it is important to isolate the effect of “hydrophobicity”. We do this by measuring for systems where the particles are very hydrophobic (water contact angle, θ ~110°) and the van der Waals and electrostatic forces are very small. Under these conditions we find that the total force is very small: it is similar to the van der Waals force at separations exceeding 5 nm. Many early works on the hydrophobic force reported surface force at over 100 nm of separation. However, many of these strong, long-ranged attractive forces are likely caused by submicron interfacial bubbles, known as nanobubbles. Nanobubbles were imaged with an atomic force microscope to better understand their stability and dependence on solution properties, such as initial concentration of dissolved gas and changes in gas concentration. We found that nanobubbles still formed in degassed solutions and that lowering the dissolved gas concentration did not reduce the bubble size, implying that nanobubbles do not form from dissolved gas in the liquid phase or do not contain gas and are instead water vapor. Furthermore, addition of an oxygen scavenger agent, sodium sulfite, to a liquid phase that had been pressured with oxygen did not reduce bubble size which could be evidence that nanobubbles are impermeable to gas diffusion across the gas liquid interface, do not form from the dissolved gas in the surrounding liquid, or do not contain gas and are instead water vapor. / Ph. D.

Interactions between proteins and contact surfaces can have important implications in the food industry. Such interactions contribute to the course of fouling of membrane surfaces and they appear to mediate bacterial and spore adhesion to some degree as well. In addition to protein and solution properties, interfacial behavior is strongly influenced by contact surface properties. Among these, hydrophobicity and the potential to take part in acid-base interaction have received considerable attention, but in a quantitative sense we know very little about their respective influences on protein adsorption. It was the purpose of this research to quantify the equilibrium adsorptive behavior of the milk protein β-lactoglobulin as it is influenced by the presence of different contact surface functional groups. Monocrystalline and polished silicon surfaces were modified to be hydrophilic by oxidation and hydrophobic by silanization with dichlorodiethylsilane (DDES), dichlorodimethylsilane (DDMS), and dichlorodiphenylsilane (DDPS), each used at concentrations of 0.82, 3.3, and 82 mM. Surface hydrophobicities were evaluated with contact angle methods. Adsorption isotherms were constructed after allowing each modified silicon surface to independently contact β-lactoglobulin (0.01 M phosphate buffer, pH 7.0) at concentrations ranging between 200 and 2000 mg/L for eight h at room temperature. Surfaces were then rinsed and dried. Optical properties of the bare- and film-covered surfaces, necessary for calculation of adsorbed mass, were obtained by ellipsometry. Plots of adsorbed mass as a function of protein concentration exhibited attainment of plateau values beyond a protein concentration of about 200 mg/L. At high silane concentration, the plateau values associated with surfaces exhibiting ethyl groups were observed to be greatest followed by those exhibiting phenyl, methyl, then hydrophilic (OH) groups. At the low DDMS and DDES concentrations (0.82 and 3.3 mM), adsorbed mass did not increase beyond that value recorded for the hydrophilic surface. This is likely due to some critical spacing of methyl and ethyl groups being required to produce a favorable hydrophobic effect on adsorption. For surfaces treated with dichlorodiphenylsilane, adsorbed mass increased with silane concentration. Apparently, a favorable acid-base interaction effected by the hydrophilic surface is inhibited by the presence of small amounts of methyl and ethyl groups, but somewhat less inhibited by the presence of phenyl groups because the latter have the ability to undergo acid-base interaction. / Graduation date: 1993

Water-mediated interactions between non-polar moieties play a crucial role in driving self-assembly processes such as surfactant micellization, protein folding, and many other diverse phenomena. Among a variety of forces contributing to the self assembly, hydrophobic interactions play a dominant role. Historically, thermodynamic models describing hydrophobic effects have invariably relied on macroscopic thermodynamic properties to infer this molecular behavior. Experimental studies help to probe the spatial correlations between model hydrophobic solutes and to measure their waters of hydration in order to examine structural perturbations in the surrounding water induced by the solute, or to measure directly the attractive forces between hydrophobic surfaces. Further, molecular simulations can be used to derive entropic and enthalpic contributions to the free energy of hydrophobic hydration in terms of water structure surrounding simple, model hydrophobic solutes, such as methane. Based on the results for simple solutes, these methods can now be extended to investigate the hydrophobic hydration of more complex molecular solutes of arbitrary size and shape such as micelles. Atomistic simulations of chemical systems provide a new perspective towards testing the theories behind the ubiquitous phenomenon of hydrophobic effect, and probe the underlying thermodynamic signatures. In this context, my research work delves into the water-mediated interactions leading to the hydrophobic hydration of short chain alkanes, volumetric properties of unfolded polypeptides and self-assembly mechanism in polymer-surfactant systems. The first part of my research involves re-optimization of existing force field interaction parameters for the CHn alkane sites (n=0 to 4) to accurately reproduce the experimental hydration free energies of linear and branched chain alkanes over a range of temperatures. This Hydrophobic Hydration-Alkane (HH-Alkane) model accounts for polarization effects in the alkane hydration and can be extended to polypeptides in water. Subsequent discussions will focus on the results from extensive molecular simulations of tri- and tetrapeptides to quantify the accuracy of the simulation model in capturing the volumetric properties of unfolded polypeptides. Group additivity correlation was used to calculate the partial molar volumes of the neutral sidechains of amino acids, glycine backbone unit and both zwitterionic and N-acetyl/amide terminal units. The simulation results will be compared to the experimental results to validate these observations. In addition, the research explores the self-assembly and aggregation mechanism in anionic sodium dodecyl sulfate (SDS) surfactant- non-ionic Polyethylene Oxide (PEO) and Poly vinyl pyrrolidone (PVP) polymer systems. Potential of mean force calculations at multiple temperatures show an increasing trend in hydrophobic attractions within the polymer-micelle system. Also, these simulations provide interesting insights into the experimentally observed phenomena between the polymers and the micelles starting from pre-formed structure as well as random configurations. / 1 / Lalitanand N. Surampudi

Nisin is an antibacterial peptide, which when adsorbed on a surface can inhibit bacterial adhesion and viability. The ability of noncovalently immobilized nisin to withstand exchange by the milk proteins bovine serum albumin, ��-lactoglobulin, ��-lactalbumin, and ��-casein on surfaces that had been silanized with dichlorodiethylsilane to exhibit high and low hydrophobicities was examined using in situ ellipsometry. Kinetic behavior was recorded for nisin adsorption for 1h and 8h, followed in each case by rinsing in protein-free buffer solution, and sequential contact with a single milk protein for 4h. Concerning nisin adsorption to each surface, a higher adsorbed mass was consistently recorded on the hydrophilic relative to the hydrophobic surface, independent of adsorption time. While desorption was greater from the hydrophilic surface in the 1h test, the amount desorbed was quite similar on each surface in the 8h tests. The sequential data were consistent with the assumptions that nisin organization at the interface involved adsorption in at least two different states, possibly existing in more than one layer, and that in the absence of exchange, upon addition of the second protein adsorbed mass would increase by an amount equivalent to its experimentally observed monolayer coverage. The Mass of nisin exchanged was generally higher on the hydrophobic compared to the hydrophilic surface presumably because of the presence of a more diffuse outer layer in the former case. ��-casein was the most effective eluting agent among the proteins studied, while ��-lactalbumin was the least effective, apparently adsorbing onto the nisin layers with little exchange. Both bovine serum albumin and ��-lactoglobulin were moderately effective in exchanging with adsorbed nisin, with the amount of nisin removed by bovine serum albumin being more substantial, possibly due to its greater flexibility. / Graduation date: 1995

Rotavirus NSP4, the first described viral enterotoxin, localizes to the plasma membrane of infected cells, possibly through interaction with caveolin-1. A direct interaction between NSP4 and caveolin-1, the structural protein of caveolae, was shown by yeast two-hybrid, peptide binding, and FRET analyses. To dissect the precise NSP4 binding domain to caveolin-1, mutants were prepared by altering either the charged or hydrophobic face of the NSP4 C-terminal amphipathic alpha-helix and examined for binding to caveolin-1. Replacing six charged residues with alanine (FLNSP4Ala) disrupted the charged face, while the hydrophobic face was disrupted by replacing selected hydrophobic residues with charged amino acids (aa) (FLNSP4HydroMut). In yeast two-hybrid and peptide binding assays, FLNSP4Ala retained its binding capacity, whereas FLNSP4HydroMut failed to bind caveolin-1. Mutants were generated with an Nterminal truncated clone (NSP446-175), which removed the hydrophobic domains and aided in yeast-two hybrid assays. These mutants exhibited the same binding pattern as FLNSP4 confirming that the N-terminus of NSP4 lacks the caveolin-1 binding site and NSP446-175 is sufficient for binding. Seven additional mutants were prepared from NSP4HydroMut in which individually charged residues were reverted to the original hydrophobic aa or were replaced with alanine. Analyses of the interaction of these revertants with caveolin-1 localized the NSP4 binding domain to one critical hydrophobic aa (L116) and one or two additional aa (I113, L127, and/or L134) on the hydrophobic face. Those mutants that bound caveolin-1 bound both the N- and C-terminal caveolin-1 peptides, but lacked binding to a centrally located peptide. These data suggest conformational and hydrophobic constraints play a role in the NSP4-caveolin-1 association. The mutant NSP4 molecules also were evaluated for transport to the plasma membrane. Mammalian cells were transfected with FLNSP4, FLNSP41-175Ala, and NSP41-175HydroMut plasmid DNA, surface biotinylated, and examined by IFA or Western blot for NSP4 expression. Epifluorescence revealed FLNSP4 and FLNSP4Ala were exposed on the cell surface in the absence of other viral proteins, whereas NSP4HydroMut remained intracellular. Further, NSP4-transfected cells displayed an intracellular association of with caveolin-1 or the caveolin-1 chaperone complex proteins. These data indicate NSP4 interacts with caveolin-1 in the absence of other viral proteins.

The transport of health-related organic micropollutans has been a major water quality and environmental issue in the past few decades. Because of their high toxicity, long environmental half-life and high bioaccumulation factors, many of the hydrophobic organic pollutants (HOPs) are listed as priority pollutants in many countries. Although not all of the chemical and physical factors should be considered in the fate of transportation of all chemicals, a simple one-dimensional mathematical model used to simulate all of the factors was conceptually developed (Bobba et al., 1996). In that study, most important parameters needed in the model were empirically fitted. For numerical simulation of the behaviors of pollutants in the environment, it is important to provide a feasible chemical and physical transport mechanism to describe the geo-chemical and geophysical interactions involved in the system. In this study a general two-dimensional hydrodynamic numerical simulation model is developed .This model can readily extend to a three-dimensional one. The model includes all possible physical and chemical factors that might affect the transport of the pollutants. For validation and demonstration purpose, only sorption-desorption between specified dissolved organic material and phase are studied in the present study. The hydrodynamic model is verified by comparing with the reported numerical results. The numerical model then incorporates the sorption-desorption terms and the sediment effects. From the results of the simulation, the sorption-desorption mechanism and sediment scavenge effect are founded to significantly affects the pollutants fate and transport of an outfall discharge.

No description available.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Joel P. Schneider, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 136-139). Also available on the World Wide Web.