PhD / Electrostatics of aerosols for inhalation is a relatively new research area. Charge properties of these particles are largely unknown but electrostatic forces have been proposed to potentially influence lung deposition. Investigation on the relationship between formulation and aerosol charging is required to understand the fundamental mechanisms. A modified electrical low pressure impactor was employed to measure the particles generated from metered dose inhalers and dry powder inhalers. This equipment provides detailed size and charge information of the aerosols. The particles were sized by impaction onto thirteen stages. The net charges in twelve of the size fractions were detected and recorded by sensitive electrometers. The drug deposits were quantified by chemical assay. The aerosol charge profiles of commercial metered dose inhalers were product-dependent, which was due to differences in the drug, formulation, and valve stem material. The calculated number of elementary charges per drug particle of size ≤ 6.06 μm ranged from zero to several ten thousands. The high charge levels on particles may have a potential effect on the deposition of the aerosol particles in the lung when inhaled. New plastic spacers marketed for use with metered dose inhalers were found to possess high surface charges on the internal walls, which was successfully removed by detergent-coating. Detergent-coated spacer had higher drug output than the new ones due to the reduced electrostatic particle deposition inside the spacer. Particles delivered from spacers carried lower inherent charges than those directly from metered dose inhalers. Those with higher charges might be susceptible to electrostatic forces inside the spacers and were thus retained. The electrostatic low pressure impactor was further modified to disperse two commercial Tubuhaler® products at 60 L/min. The DPIs showed drug-specific responses to particle charging at different RHs. The difference in hygroscopicity of the drugs may play a major role. A dual mechanistic charging model was proposed to explain the charging behaviours. The charge levels on drug particles delivered from these inhalers were sufficiently high to potentially affect deposition in the airways when inhaled. Drug-free metered dose inhalers containing HFA-134a and 227 produced highly variable charge profiles but on average the puffs were negatively charged, which was thought to be due to the electronegative fluorine atoms in the HFA molecules. The charges of both HFAs shifted towards neutrality or positive polarity with increasing water content. The spiked water might have increased the electrical conductivity and/or decreased the electronegativity of the bulk propellant solution. The number of elementary charges per droplet decreased with decreasing droplet size. This trend was probably due to the redistribution of charges amongst small droplets following electrostatic fission of a bigger droplet when the Raleigh limit was reached.

Thesis (Ph. D.)--Ohio University, June, 2004. / Includes bibliographical references (p. 167-171).

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Mechanical Engineering, 2009. / Includes bibliographical references.

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Yiacoumi, Sotira, Committee Chair ; Tsouris, Costas, Committee Co-Chair ; Pavlostathis, Spyros, Committee Member ; Tannenbaum, Rina, Committee Member ; Sherrill, David, Committee Member.

Thesis (Ph.D.)--Ohio University, June, 2004. / Title from PDF t.p. Includes bibliographical references (p. 167-171)

Nous avons déterminé par diffusion de rayons X le potentiel d’interaction entre deux bicouches, une première adsorbée sur un substrat solide et une deuxième flottant à proximité. Nous montrons que les interactions dans ces systèmes fortement hydratés sont deux ordres de grandeur plus faibles que dans les travaux précédents menés sur des phases multilamellaires. Cette caractéristique est attribuée à la répulsion électrostatique due à la faible fraction de lipides ionisés. Nous avons de plus accès aux potentiels de répulsion entropique, et testons les différents modèles théoriques existants.Les effets d’un champ électrique sur les membranes ont également été étudiés. Nous montrons que le champ induit une tension négative et une rigidité positive, et mène à la déstabilisation d’une bicouche supportée sous certaines conditions.Finalement, nous mesurons les propriétés de membranes chargées par diffusion de rayons X, nous permettant d’accéder aux limites de la théorie de Poisson-Boltzmann. / We have determined by grazing incidence X-ray scattering the interaction potential between two lipid bilayers, one adsorbed on a solid surface and the other floating close by. We find that interactions in this highly hydrated system are two orders of magnitude softer than in previously reported work on multilayer stacks. This is attributed to the weak electrostatic repulsion due to the small fraction of ionized lipids in defectless supported bilayers. We also access the entropic repulsion potentials, allowing us to discriminate between the different existing models.The effects of an electric field on the properties of membranes have also been studied. We show that the field induces a negative tension and an increase of the rigidity. We also show that it is possible to destabilize a supported bilayer by an electric field under certain conditions.Finally, we measure the properties of charged membranes using X-ray scattering, giving access to the limits of the Poisson-Boltzmann theory.

abstract: Molecular dynamics simulations were used to study properties of water at the interface with nanometer-size solutes. We simulated nonpolar attractive Kihara cavities given by a Lennard-Jones potential shifted by a core radius. The dipolar response of the hydration layer to a uniform electric field substantially exceeds that of the bulk. For strongly attractive solutes, the collective dynamics of the hydration layer become slow compared to bulk water, as the solute size is increased. The statistics of electric field fluctuations at the solute center are Gaussian and tend toward the dielectric continuum limit with increasing solute size. A dipolar probe placed at the center of the solute is sensitive neither to the polarity excess nor to the slowed dynamics of the hydration layer. A point dipole was introduced close to the solute-water interface to further study the statistics of electric field fluctuations generated by the water. For small dipole magnitudes, the free energy surface is single-welled, with approximately Gaussian statistics. When the dipole is increased, the free energy surface becomes double-welled, before landing in an excited state, characterized again by a single-welled surface. The intermediate region is fairly broad and is characterized by electrostatic fluctuations significantly in excess of the prediction of linear response. We simulated a solute having the geometry of C180 fullerene, with dipoles introduced on each carbon. For small dipole moments, the solvent response follows the results seen for a single dipole; but for larger dipole magnitudes, the fluctuations of the solute-solvent energy pass through a second maximum. The juxtaposition of the two transitions leads to an approximately cubic scaling of the chemical potential with the dipole strengh. Umbrella sampling techniques were used to generate free energy surfaces of the electric potential fluctuations at the heme iron in Cytochrome B562. The results were unfortunately inconclusive, as the ionic background was not effectively represented in the finite-size system. / Dissertation/Thesis / Ph.D. Chemistry 2012

Doctor of Philosophy / Department of Physics / Jeremy D. Schmit / Diseases such as Alzheimer’s, Parkinson’s, eye lens cataracts, and Type 2 diabetes are the results of protein aggregation. Protein aggregation is also a problem in pharmaceutical industry for designing protein based drugs for long term stability. Disordered states such as precipitates and gels and ordered states such as crystals, micro tubules and capsids are both possible outcomes of protein–protein interaction. To understand the outcomes of protein–protein interaction and to find the ways to control forces, it is required to study both kinetic and equilibrium factors in protein–protein interactions. Salting in/salting out and Hofmeister effects are familiar terminologies used in protein science field from more than a century to represent the effects of salt on protein solubility, but they are yet to be understood theoretically. Here, we build a theory accounting both attractive and repulsive electrostatic interactions via the Poisson Boltzmann equation, ion–protein binding via grand cannonical partition function and implicit ion–water interaction using hydrated ion size, for describing salting in/salting out phenomena and Hofmeister and/or salt specific effect. Our model free energy includes Coulomb energy, salt entropy and ion–protein binding free energy. We find that the salting in behavior seen at low salt concentration near the isoelectric point of the protein is the output of Coulomb energy such that the addition of salt not only screens dipole attraction but also it enhances the monopole repulsion due to anion binding. The salting out behavior appearing after salting in at high salt concentration is due to a salt mediated depletion interaction. We also find that the salting out seen far from the isoelectric point of the protein is dominated by the salt entropy term. At low salt, the dominant effect comes from the entropic cost of confining ions within the aggregates and at high salt, the dominant effect comes from the entropy gain by ions in solution by enhancing the depletion attraction. The ion size has significant effects on the entropic term which leads to the salt specificity in the protein solubility. Crystal growth of anisotropic and fragile molecules such as proteins is a challenging task because kinetics search for a molecule having the correct binding state from a large ensemble of molecules. In the search process, crystal growth might suffer from a kinetic trap called self–poisoning. Here, we use Monte Carlo simulation to show why protein crystallization is vulnerable to the poisoning and how one can avoid such trap or recover crystal growth from such trap during crystallization. We show that self–poisoning requires only three minimal ingredients and these are related to the binding affinity of a protein molecule and its probability of occurrence. If a molecule attaches to the crystal in the crystallographic state then its binding energy will be high but in protein system this happens with very low probability (≈ 10−5). On the other hand, non–crystallographic binding is energetically weak, but it is highly probable to happen. If these things are realized, then it will not be surprising to encounter with self–poisoning during protein crystallization. The only way to recover or avoid poisoning is to alter the solution condition slightly such as by changing temperature or salt concentration or protein concentration etc.

A cell is considered to be the smallest unit of life. It carries out a variety of biochemical reactions through the activities of proteins and protein enzymes. In order to perform functions, proteins must be in their native folded state together with the correct environmental conditions. A slight change in pH or temperature could cause disruption to the electrostatic interactions within the protein, thus leading to conformational change and the loss of activity. Studies have shown that solubility could be enhanced by increasing the number of charges on the protein surface. And from the studies of extremophiles, we learned that the presence of non-polar aromatic residues could be a key for thermostable proteins. Thus, charges are important to determine the function and adaptation of proteins.Over the decades, large amount of protein sequence and structure information relating to molecular biology has been produced. By employing algorithms, computational and statistical techniques, it is possible to analyse these data to solve biological problems. Often these investigations are based mainly on sequences since their numbers outstrip the number of available structures. However, adding structures would allow us to investigate problems such as the relationship between charges, sequence, structure and functions, which is the aim of this study.In this thesis, the relationships between proteins and function were examined by various electrostatic features derived from charges and also geometric properties from structures. One interesting finding is that the averaged value of pH of maximum stability of proteins within a subcellular location was highly correlated to the pH of that subcellular compartment, which was due to pKas (of histidines), and their locations on the proteins. We also found that the size of the largest non-charged patch on the protein surface correlates with solubility and provides a predictor with a maximum accuracy of 76%. The use of novel charge-based methods shows little improvement in distinguishing between enzymes and non-enzymes. However, the method of using real charges with grid size of 1 angstrom has paved a way into the idea of using charges and dipoles pattern from enzyme active site to distinguish different enzymes. Finally, a web-tool for displaying conserved residues on 3D protein structure is made available to the public for identifying residues that may be of functional importance.

The research presented in this thesis is situated within an interpretivist paradigm. Within this paradigm, a qualitative case-study research approach was adopted. This seemed most appropriate in my research project since the main focus is on elicitation of prior knowledge and incorporation of such knowledge into 'hands-on' and 'minds-on' practical activities with a view to improving conceptual development. For the purposes of this research project, I designed an interactive teaching and learning unit in electrostatics as an attempt to put into practice a learner-centred approach. This approach, in my view, is in line with the new curriculum in South Africa. The emerging central theme of this thesis is the notion of active participation by learners during teaching and learning. This study was carried out over a period of two years and involved my grade 9 learners, who participated voluntarily. The research process documented in this thesis has been conceptualised into two phases. Phase one was concerned with the elicitation of learners' prior knowledge around lightning. In phase two, learners were engaged in 'hands-on' and 'minds-on' practical activities, and key concepts were identified to ensure conceptual development. The data was collected using a variety of data collection tools, namely: focus group interviews, follow-up whole-class semi-structured interviews, worksheets, videotaped lessons and photographs. The analysis of data revealed that learners come to class with prior knowledge concerning lightning. Within this prior knowledge it was found that there were both ‘scientific’ and ‘non-scientific’ concepts. The identification of key concepts during practical activities was found to be very useful in promoting learning. However, the incorporation of prior knowledge into practical activities posed a challenge and needs further research. iv This research study also highlights some insights into some of the complexities of elicitation and incorporation of learners' prior knowledge, and conceptual development in science classrooms. It also demonstrates the challenges and possibilities during teaching and learning as well as the realities of the demands of the new curriculum and OBE in South Africa, in particular, in historically disadvantaged schools