Protein aggregation and physical stability are perpetual concerns in medicine and industry. Misfolded protein can form ordered protein aggregates, amyloids, which are associated with a host of neurodegenerative diseases in mammals and control heritable traits in fungi and yeast. Industrially, amorphous aggregates reduce the efficacy of protein-based therapeutics and activity of enzymes during production and storage. This work studies ion-specific and solvent-based effects on protein physical stability. We show that ion-specificity significantly affects amyloid formation kinetics, aggregate morphology, thermostability, frangibility, and, most intriguingly, prion infectivity in vivo. Forming amyloid in chaotropic or kosmotropic solutions generates predominately weak or strong prion variants, respectively. Ion-specific effects also influenced amorphous aggregation of model proteins and antibodies. To quantify protein - protein stability/affinity, we developed a rapid and reliable diffusion-based technique. Our technique was able to resolve relative differences in colloidal stability between various saline and saccharide solutions. In all, this dissertation expands our understanding of ion-specific and water-mediated interactions with prion proteins and protein dispersions.

Inspirados por las investigaciones realizadas en los campos de la plasmónica y los metamateriales, en este trabajo hemos estudiado la difusión de la luz por pequeñas partículas (nanopartículas en el rango del visible) con propiedades ópticas arbitraria, tanto convencionales (dieléctricas como metálicas) como no convencionales (con permeabilidad magnética distinta de 1). El trabajo está principalmente enfocado en controlar la propiedades (principalmente la dirección) de la luz difundida por una partícula mediante la manipulación de sus constantes ópticas. Las principales aplicaciones de este estudio se pueden concentrar en los campos de los biosensores y/o de las comunicaciones ópticas. Es por esto que hemos considerado tanto partículas aisladas como sistemas de partículas(dímeros principalmente). / Inspired by the last researches on plasmonics and metamaterials, this work is devoted to the study of light scattering by small particles (nanoparticles in the visible range) with arbitrary optical properties, both conventional and non-conventional. We focused the analysis on the control of the directionality of light scattering by tunning the optical constants of the scatterer. This could be interesting for the design of futuristic optical communications and/or for the generation of improved biosensores. For this reason, isolated particles and also clusters of them (mainly dimers) were considered.

Bacterioferritin, an iron storage protein having a 24-subunit quaternary structure, was used as a model for the study of host-guest interactions and guest encapsulation, making use of its spherical cage-like structure. A hexahistidine-affinity tag fused to the C-terminus of each bacterioferritin subunit was constructed. The C-terminus of each subunit points toward the inside of the cavity, while the N-terminus is exposed on the surface of the protein. The hexaHistag was able to form strong interactions with a nickel-nitrilotriacetic acid linked dye molecule (guest) and this interaction was used in attempts to develop a principle to control guest molecule encapsulation within the spherical cavity of the 24-mer bacterioferritin protein molecule. The procedure involved (1) subunit dissociation under acidic pH, (2) affinity controlled dye-Histag binding with exposed C-terminal hexahistidine residues and (3) reassociation of the subunits at neutral pH. The encapsulation conditions involving step 1 and 3 were studied preliminarily using laser light scattering to measure size (hydrodynamic radius) of the protein particle with apoferritin as a model system as it resembles the size and structure of bacterioferritin. In order to encapsulate guest molecules, the emptied shell of bacterioferritin was generated by site-directed mutagenesis resulting in ferroxidase- as well as heme-free bacterioferritin mutants (E18A/M52L/E94A), and these mutants were used to examine protein stability before conducting encapsulation experiments. However, wild-type bacterioferritin possessed highest stability in maintaining its multisubunit structure; hence, it was used for the encapsulation studies. It was found that 100% bacterioferritin with hexahistidine tag at the C-terminus, and a combination of 60% bacterioferritin with hexahistidine tag at the C-terminus and 40% bacterioferritin without hexahistidine tag at the C-terminus yielded similar amounts of encapsulated guest molecules. This suggested that all hexahistidine at the C-terminus were not equally available for dye molecule binding.

Bacterioferritin, an iron storage protein having a 24-subunit quaternary structure, was used as a model for the study of host-guest interactions and guest encapsulation, making use of its spherical cage-like structure. A hexahistidine-affinity tag fused to the C-terminus of each bacterioferritin subunit was constructed. The C-terminus of each subunit points toward the inside of the cavity, while the N-terminus is exposed on the surface of the protein. The hexaHistag was able to form strong interactions with a nickel-nitrilotriacetic acid linked dye molecule (guest) and this interaction was used in attempts to develop a principle to control guest molecule encapsulation within the spherical cavity of the 24-mer bacterioferritin protein molecule. The procedure involved (1) subunit dissociation under acidic pH, (2) affinity controlled dye-Histag binding with exposed C-terminal hexahistidine residues and (3) reassociation of the subunits at neutral pH. The encapsulation conditions involving step 1 and 3 were studied preliminarily using laser light scattering to measure size (hydrodynamic radius) of the protein particle with apoferritin as a model system as it resembles the size and structure of bacterioferritin. In order to encapsulate guest molecules, the emptied shell of bacterioferritin was generated by site-directed mutagenesis resulting in ferroxidase- as well as heme-free bacterioferritin mutants (E18A/M52L/E94A), and these mutants were used to examine protein stability before conducting encapsulation experiments. However, wild-type bacterioferritin possessed highest stability in maintaining its multisubunit structure; hence, it was used for the encapsulation studies. It was found that 100% bacterioferritin with hexahistidine tag at the C-terminus, and a combination of 60% bacterioferritin with hexahistidine tag at the C-terminus and 40% bacterioferritin without hexahistidine tag at the C-terminus yielded similar amounts of encapsulated guest molecules. This suggested that all hexahistidine at the C-terminus were not equally available for dye molecule binding.

Dye-sensitized solar cells (DSSCs), based on use of a black counter electrode (BCE) and thin TiO2 electrode (photoelectrode), have been developed to reduce related manufacturing costs. Despite their effectiveness in lowering manufacturing cost, the above DSSCs have a low photovoltaic performance, owing to their insufficient light harvesting efficiency. This work presents a novel metal-based light scattering layer (MLSL), which can be formed either on a black counter electrode or on a thin TiO2 electrode, to reflect the light passing through the latter. The proposed MLSL increases the light harvesting efficiency from the interior of the cell, thus enhancing the photovoltaic performance of DSSC. Experimental results indicate that the proposed MLSL also reduces the internal resistance, as well as increases the electron collection efficiency of DSSC, subsequently increasing the power conversion efficiency by 116%. This work also designs a low-cost external lightguide (EL), which is disposed on the exterior of photoelectrode of DSSC, to direct light towards the dye-covered nanoporous TiO2 film (D-NTF) of the photoelectrode. Incorporating EL can increase the light harvesting efficiency from the exterior of the cell, thus enhancing the photovoltaic performance of DSSC. Furthermore, in addition to increasing the light harvesting efficiency by 30.69%, the proposed EL increases the photocurrent density by 38.12% and power conversion efficiency by 25.09%.

Hydrogel micro- and nanoparticles (microgels and nanogels) are a promising class of drug delivery vehicles. Composed of hydrophilic polymers arranged into a cross-linked network structure, nanogels show several attractive features for the delivery of macromolecule therapeutics. For instance, the hydrated, porous internal cavity of the nanogel may serve as a high capacity compartment for loading macromolecules, whereas the periphery of the nanogel may be used as a scaffold for conjugating cell-specific targeting moieties. This dissertation presents recent investigations of nanogels as targeted delivery vehicles for oligonucleotides to cancer cells, while exploring new nanogel chemistries that enable future in vivo applications. For instance, synthetic efforts have produced particles capable of erosion into low molar mass constituents, providing a possible mechanism of particle clearance after repeated administration in vivo. In another example, the microgel network chemistry was tuned to promote the encapsulation of charged proteins. In parallel with those synthetic efforts, new light scattering methodologies were developed to accurately quantify the particle behaviors (e.g. loading, erosion). Using multiangle light scattering (MALS), changes in particle molar mass and radius were measured, providing a quantitative and direct approach for monitoring nanogel erosion and macromolecule encapsulation. The new particle chemistries demonstrated, together with enabling light scattering methods, will catalyze the development of improved delivery vehicles in the near future.

<p>In this thesis, size-exclusion chromatography (SEC) of woodpolymers dissolved in lithium chloride/N,N-dimethylacetamide(LiCl/DMAc) has been used to characterize the molar massdistributions (MMD) of wood polymers in pulp fibers afterchemical degradation.</p><p>Characterization of birch kraft pulps subjected to ozonedegradation and acid hydrolysis, respectively, rendereddifferent changes in the MMD. Ozone degradation resulted inlarge redistributions of the original MMD, observed as thedevelopment of a distinct fraction of cellulose withintermediate molar mass. Acid hydrolysis resulted in minorchanges of the original MMD compared to ozonation. Fiberssubjected to acid hydrolysis were considerably weaker thanozonated fibers. These results indicated that there aredifferences in how the two chemicals degrade the fiber.</p><p>The solubility of softwood kraft pulp fibers was enhanced byderivatization of the fiber polymers with ethyl-isocyanateduring simultaneous dissolution in LiCl/DMAc. Thederivatization made it possible to achieve reliable estimationsof the MMD, and hence molar masses, of softwood kraft pulps.The derivatization procedure made it possible to dissolve 90 %of softwood kraft pulps with kappa numbers over 50.</p><p>Severe alkaline degradation of birch and Norway spruce woodchips was studied both by varying the pulping time and byvarying the initial alkali concentration. Differences werefound in the MMD of the two fiber types, and the alkalinedegradation was found to affect polymers in the entire MMD.</p><p>Multi-angular laser light scattering (MALLS) was used as adetection technique with SEC on cellulosic samples. The MMD andaverage molar masses obtained through directstandardcalibration with commercial standards were compared with MMDand molar masses as obtained by MALLS-detection. Largediscrepancies were found, and two methods of correcting forthese discrepancies were developed.</p><p>Theoretical simulations of polymer degradation wereperformed. Random, or homogeneous degradation was used as amodel for alkaline cellulose chain scission, and a resemblancewith experimental data was observed. End-wise depolymerizationof cellulose was also simulated and the results are discussedin the light of experimentally observed MMD.</p><p><b>Keywords:</b>cellulose, kraft pulp, birch, spruce,ozonation, acid hydrolysis, degradation, MMD, sizeexclusionchromatography, light scattering, molar mass, chainscission</p>

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An accurate and generalized global retrieval algorithm from satellite observations is a prerequisite to understand the radiative effect of atmospheric aerosols on the climate system. Current operational aerosol retrieval algorithms are limited by the inversion schemes and suffering from the non-uniqueness problem. In order to solve these issues, a new algorithm is developed for the retrieval of non-spherical dust aerosol over land using multi-angular radiance and polarized measurements of the POLDER (POLarization and Directionality of the Earth’s Reflectances) and wide spectral high-resolution measurements of the MODIS (MODerate resolution Imaging Spectro-radiometer). As the first step to account for the non-sphericity of irregularly shaped dust aerosols in the light scattering problem, the spheroidal model is introduced. To solve the basic electromagnetic wave scattering problem by a single spheroid, we developed an algorithm, by transforming the transcendental infinite-continued-fraction-formeigen equation into a symmetric tri-diagonal linear system, for the calculation of the spheroidal angle function, radial functions of the first and second kind, as well as the corresponding first order derivatives. A database is developed subsequently to calculate the bulk scattering properties of dust aerosols for each channel of the satellite instruments. For the purpose of simulation of satellite observations, a code is developed to solve the VRTE (Vector Radiative Transfer Equation) for the coupled atmosphere-surface system using the adding-doubling technique. An alternative fast algorithm, where all the solid angle integrals are converted to summations on an icosahedral grid, is also proposed to speed-up the code. To make the model applicable to various land and ocean surfaces, a surface BRDF (Bidirectional Reflectance Distribution Function) library is embedded into the code. Considering the complimentary features of the MODIS and the POLDER, the collocated measurements of these two satellites are used in the retrieval process. To reduce the time spent on the simulation of dust aerosol scattering properties, a single-scattering property database of tri-axial ellipsoid is incorporated. In addition, atmospheric molecule correction is considered using the LBLRTM (Line-By-Line Ra- diative Transfer Model). The Levenberg-Marquardt method was employed to retrieve all the interested dust aerosol parameters and surface parameters simultaneously. As an example, dust aerosol properties retrieved over the Sahara Desert are presented.

Die Struktur von Netzwerken wird durch die Wahl der Netzwerkaufbaureaktion, der Ausgangsmoleküle und der Reaktionsbedingungen bestimmt. Es ist schwierig, wenn nicht gar unmöglich, geeignete Reaktionsparameter zu finden, die zum Aufbau homogener Netzwerkstrukturen führen. Die unterschiedliche Reaktivität der Ausgangsmoleküle resultiert in Unregelmäßigkeiten innerhalb der Netzwerkstruktur, z. B. durch inhomogene Verteilung der Vernetzungspunkte. Als Maß für die Heterogenität eines Netzwerkes kann die Streuintensität herangezogen werden. Diese besteht bei Netzwerken aus einem dynamischen und einem statischen Teil. In stark heterogenen Netzwerken überwiegt die statische Komponente der Streuintensität, die dynamischen Beiträge sind gering. Bei homogeneren Strukturen überwiegt die dynamische Komponente. Deshalb kann der Beitrag dynamischer Konzentrationsfluktuationen zur Gesamtstreuintensität als Maß für den Grad der Heterogenität dienen. Die meisten Netzwerke werden durch radikalische Copolymerisation von Monomeren und Vernetzern synthetisiert. Aufgrund der unterschiedlichen Reaktivitäten sind die entstehenden Strukturen stark heterogen. Die Verwendung anderer Mechanismen zum Netzwerkaufbau bietet eine Möglichkeit, homogenere Netzwerke zu erhalten. Vor allem die Vernetzung polymerer Ketten, ausgehend von einer homogenen halbverdünnten Lösung, ist eine strategisch interessante Variante. Ziel dieser Arbeit war die systematische Untersuchung des Einflusses der chemischen Zusammensetzung, der Netzwerkaufbaureaktion, der Polymerkonzentration und der Netzwerkdichte auf die thermodynamischen Eigenschaften (kooperative Diffusionskoeffizienten Dcoop) und die Netzwerkstruktur (Heterogenität) unterschiedlicher Netzwerksysteme. Am Beispiel von Polyacrylsäure (PAS) Netzwerken (radikalische Vernetzung) und Poly(styrol-co-maleinsäureanhydrid) (PScoMSA) Netzwerken (Vernetzung polymerer Lösungen) wurden zwei Netzwerksysteme untersucht, die sich hinsichtlich ihrer Aufbaureaktion unterscheiden. Mittels klassischer Netzwerkanalyse können diese Systeme sehr gut charakterisiert werden. Die kooperativen Diffusionskoeffizienten sowie die Netzwerkheterogenität wurden durch dynamische Lichtstreuung bestimmt.