Thesis (Ph.D.)--University of Wisconsin--Madison, 2006. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

L'objectif principal de ce travail est la préparation de nanoparticules d'argent (AgNPs) stabilisées par des oligo-et polysaccharides et leur application en catalyse et pour la détection de lectines. Pour atteindre cet objectif, deux stratégies ont été utilisées, l'une utilisant le polysaccharide dextran comme stabilisant et l'autre utilisant des composés amphiphiles oligosaccharidiques dérivés du maltose, lactose, maltoheptaose et du xyloglucane. Dans les deux stratégies, la préparation des nanoparticules AgNPs a été optimisée en réalisant une analyse multifactorielle basée sur l'étude de la bande de résonance plasmonique de surface (SPR) des nanoparticules. Toutes les suspensions colloïdales stables de nanoparticules ont été caractérisées par spectroscopie ultraviolet-visible (UV-vis), microscopie électronique à transmission (TEM), diffraction des rayons X aux petits angles (SAXS) et par diffusion dynamique de lumière (DLS). Les activités catalytiques des nanoparticules ont été déterminées pour la réaction de réduction du p-nitrophénol (Nip) par NaBH4, dans l'eau ou dans des mélanges eau-éthanol. Parmi les différentes nanoparticules préparées, celles stabilisées par du dextran ou par le dérivé de maltoheptaose Mal7NAcC12 ont montré les meilleures propriétés catalytiques pour la réduction du Nip par NaBH4 avec des constantes de vitesse respectives de 1,41 et 1,11 s-1 m-2 L. Ces valeurs sont parmi les plus élevées de la littérature. L'effet du solvant et notamment de la présence d'éthanol sur les propriétés catalytiques des nanoparticules a également été évalué. Il a été montré que la présence d'éthanol inhibe l'activité des nanoparticules, probablement par formation d'une couche de solvant à la surface des particules entrant en compétition avec le réducteur. Enfin, trois systèmes différents (Ag-Mal7NAcC12 Ag-XGONAcC12 et Ag-LacNAcC12) ont été évalués comme biocapteurs potentiels pour la détection de lectines. Les nanoparticules Ag-Mal7NAcC12 en particulier ont permis la détection colorimétrique et sans marquage de la Concanavaline A. / The main goal of this work is the preparation, characterization and catalytic and lectins detection studies of silver nanoparticles (AgNPs) having sugar-based compounds as stabilizers. To achieve this goal two strategies were used, one using the polysaccharide dextran as stabilizer and other using amphiphile compounds based on oligosaccharides (maltose, lactose, maltoheptaose and xyloglucan). In both strategies the optimization of AgNPs preparation was realized using a multivariate analysis based in informations collected from the surface Plasmon resonance band (SPR) of AgNPs. All stable AgNPs were characterized by ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. The catalytic activities of AgNPs were determined over the p-nitrophenol (Nip) reduction reaction by NaBH4, as reducing agent, in water or water-ethanol mixtures. Two different types of amphiphiles were synthesized, one with an alkyne group in the junction of a sugar block with a hydrophobic block and the other type with a carboxylic acid group in the end of hydrophobic part. The amphiphiles were characterized by 1H and 13C NMR and mass spectrometry. The Nip reduction reaction with NaBH4 showed the best catalytic activity with AgNPs-dextran and Ag-Mal7NAcC12 nanoparticles with the rate constant normalized to the surface area of the NPs per unit volume of 1.41 and 1.11 s-1 m-2 L, respectively. These values are among the highest ones found in literature. The solvent effect in this reaction was evaluated by mixtures of water and ethanol. Applying a pseudo-monomolecular surface reaction as an experimental artifice, the obtained kinetic data were treated according to the Langmuir model, which combined with water/ethanol surface tension observations revealed that addition of ethanol inhibit the reaction, most probably by competing with BH4- ions for the nanoparticles surface, with the formation of a solvent monolayer. Finally, three different systems (Ag-Mal7NAcC12, Ag-XGONAcC12 and Ag-LacNAcC12) were tested as sensor for lectin detection and Ag-Mal7NAcC12 nanoparticles showed specific interaction with the Concanavalin A.

The increasing applications of different nanomaterials in the myriad of nano-enabled products and their potential for leaching have raised considerable environmental, health and safety (EHS) concerns. As systematic studies investigating potential anomalies in the morphology and anatomy of crop plants are scarce, herein we report on the developmental responses of two agriculturally significant crop plants, maize (Zea mays L.) and cabbage (Brassica oleracea var. capitata L.), upon in vitro exposure to nanoparticles of citrate-coated silver (Citrate-nAg) and zinc oxide (nZnO). Analyses involve histology of the primary root morphology and anatomy using light microscopy, metal biouptake, moisture content, rate of germination, and root elongation. Comparative toxicity profiles of the ionic salts (AgNO3 and ZnSO4) are developed. Notably, we uncover structural changes in maize primary root cells upon exposure to Citrate-nAg, nZnO, AgNO3, and ZnSO4, possibly due to metal biouptake, suggesting potential for functional impairments in the plant growth and development. Citrate-nAg exposure results in lower Ag biouptake compared to AgNO3 treatment in maize. Microscopic evidence reveals 'tunneling-like effect' with nZnO treatment, while exposure to AgNO3 leads to cell erosion in maize root apical meristem. In maize, a significant change in metaxylem count is evident with Citrate-nAg, AgNO3, and ZnSO4 treatment, but not with nZnO treatment (p>0.1). In both maize and cabbage, measures of germination and root elongation reveal lower nanoparticle toxicity compared to free ions. As moisture data do not support osmotically-induced water stress hypothesis for explaining toxicity, we discuss other proximate mechanisms including the potential role of growth hormones and transcription factors. These findings highlight previously overlooked, anatomically significant effects of metal nanoparticles, and recommend considering detailed anatomical investigations in tandem with the standard developmental phytotoxicity assays (germination and root elongation) as the latter ones appear less sensitive for screening plant responses to nanomaterial insults.

The increasing applications of different nanomaterials in the myriad of nano-enabled products and their potential for leaching have raised considerable environmental, health and safety (EHS) concerns. As systematic studies investigating potential anomalies in the morphology and anatomy of crop plants are scarce, herein we report on the developmental responses of two agriculturally significant crop plants, maize (Zea mays L.) and cabbage (Brassica oleracea var. capitata L.), upon in vitro exposure to nanoparticles of citrate-coated silver (Citrate-nAg) and zinc oxide (nZnO). Analyses involve histology of the primary root morphology and anatomy using light microscopy, metal biouptake, moisture content, rate of germination, and root elongation. Comparative toxicity profiles of the ionic salts (AgNO3 and ZnSO4) are developed. Notably, we uncover structural changes in maize primary root cells upon exposure to Citrate-nAg, nZnO, AgNO3, and ZnSO4, possibly due to metal biouptake, suggesting potential for functional impairments in the plant growth and development. Citrate-nAg exposure results in lower Ag biouptake compared to AgNO3 treatment in maize. Microscopic evidence reveals 'tunneling-like effect' with nZnO treatment, while exposure to AgNO3 leads to cell erosion in maize root apical meristem. In maize, a significant change in metaxylem count is evident with Citrate-nAg, AgNO3, and ZnSO4 treatment, but not with nZnO treatment (p>0.1). In both maize and cabbage, measures of germination and root elongation reveal lower nanoparticle toxicity compared to free ions. As moisture data do not support osmotically-induced water stress hypothesis for explaining toxicity, we discuss other proximate mechanisms including the potential role of growth hormones and transcription factors. These findings highlight previously overlooked, anatomically significant effects of metal nanoparticles, and recommend considering detailed anatomical investigations in tandem with the standard developmental phytotoxicity assays (germination and root elongation) as the latter ones appear less sensitive for screening plant responses to nanomaterial insults.

A strategy based on reticulating metal ions and organic ligands into atomically precise gold and silver nanoclusters (NCs) with high monodispersity has been advanced to a point that allows the design of NCs with strict stoichiometries, functionalities and valence. Of the Ag NCs discovered, Ag44 is the most studied, not only due to its high absorption that transcends the visible spectrum suitable for photovoltaics but also because of its long excited state lifetime, as revealed by nanosecond transient absorption spectroscopy. A major principle discovered in this dissertation is the ability to produce Ag44 in scalable amounts and with high stability in addition to modulation of the functional groups of the organic ligands via a fast and complete ligand exchange process. This new discovery has led to the development of synthetic designs in which new sizes were obtained by varying the reaction parameters (e.g., ligands functionality, reaction temperature and time), namely, Ag29 using dithiols and phosphines. The synthesized NCs possess tetravalent functionalities that facilitate their crystallization and characterization. Furthermore, Ag29 glows red and is therefore a possible candidate for sensing and imaging applications.

Zeolites with encapsulated metal nanoparticles have attracted a wide attention in heterogeneous catalysis due to their high catalytic activity, selectivity, and stability. The PhD thesis was focused on design and synthesis of metal@zeolite catalysts with small and uniformly distributed metal nanoparticles. The main interests were encapsulation of metal nanoparticles into zeolites by co-crystallization strategy and 2-dimensional to 3-dimensional zeolite transformation approach. The PhD work was performed at the Department of Synthesis and Catalysis at J. Heyrovský Institute of Physical Chemistry and Department of Physical and Macromolecular Chemistry, Faculty of Science at Charles University under the supervision of Prof. Jiří Čejka. Zeolites are inorganic crystalline aluminosilicates with microporous framework structures. The micropores of zeolites provide the ideal microenvironment to accommodate metal nanoparticles. During metal nanoparticles formation in zeolite micropores, they can be limited by a rigid framework, preventing the aggregation and leaching of metal during the reaction process. Furthermore, the diameters of zeolite micropores are usually in the range of 0.3-1.5 nm, which can be used to discriminate molecules depending on their size and shape, thus endowing the metal@zeolite...

Intrinsic to the many nano-enabled products are atomic-size multifunctional engineered nanomaterials, which upon release contaminate the environments, raising considerable health and safety concerns. This Ph.D. dissertation is designed to investigate (i) whether metals or oxide nanoparticles are more toxic than ions, and if MetPLATETM bioassay is applicable as a rapid nanotoxicity screening tool; (ii) how variable water chemistry (dissolved organic carbon (DOC), pH, and hardness) and organic compounds (cysteine, humic acid, and trolox) modulate colloidal stability, ion release, and aquatic toxicity of silver nanoparticles (AgNP); and (iii) the developmental responses of crop plants exposed to Ag- or ZnO- (zinc oxide) nanoparticles. Results suggest that the MetPLATEcan be considered a high-throughput screening tool for rapid nanotoxicity evaluation. Detectable changes in the colloidal diameter, surface charge, and plasmonic resonance revealed modulating effects of variable water chemistry and organic ligands on the particle stability, dissolution, and toxicity of AgNPs against Escherichia coli or Daphnia magna. Silver dissolution increased as a function of DOC concentrations but decreased with increasing hardness, pH, cysteine, or trolox levels. Notably, the dissociated Ag+ was inadequate to explain AgNP toxicity, and that the combined effect of AgNPs and dissolved Ag+ under each ligand treatment was lower than of AgNO3. Significant attenuation by trolox signifies an oxidative stress-mediated AgNP toxicity; its inability to attenuate AgNO3 toxicity, however, negates oxidative stress as Ag+ toxicity mechanism, and that cysteine could effectively quench free Ag+ to alleviate AgNO3 toxicity in D. magna. Surprisingly, DOC-AgNPs complex that apparently formed at higher DOC levels might have led daphnids filter-feed on aggregates, potentially elevating internal dose, and thus higher mortality. Maize root anatomy showed differential alterations upon exposure to AgNPs, ZnONPs, or their ions. Overall, various metal-based nanoparticles revealed lower toxicity than their ions against multiple organisms. This study showed that particle size, surface properties, and ion release kinetics of AgNPs modify following release into aquatic environment, suggesting potential implications to ecosystem health and functions, and that caution be applied when extending one species toxicity results to another because obvious differences in organism biology—supporting species sensitivity paradigm—can significantly alter nanoparticle or ionic toxicity.

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Research on metal nanoparticles (MNPs) synthesis and their applications for optoelectronic devices has been a recent interest in the fields of nanoscience and nanotechnology Photovoltaics are one of such systems in which MNPs have shown to be quite useful, due to unique physical, optical, magnetic, and electronic properties, including the metal nanoparticles synthesized in this research. Owing to the challenges with the most common physical and chemical methods of preparing MNPs, including the use of high temperatures, toxic reducing agents, and environmentally hazardous organic solvents, there is a critical need for a benign synthesis procedure for MNPs. In this work, a simple, versatile, and environmentally and economically responsible synthesis method for making iron, nickel, zinc, and bimetallic alloy nanoparticles (ANPs) has been developed and functionalization with organic capping agents were performed to form metal-organic hybrid nanocomposites with tunable properties. The size, shape, elemental composition, photophysical properties, and crystallinity of particles and their hybrids have been evaluated. Monometallic nanostructures of iron, nickel, and zinc oxide were synthesized via aqueous-phase reduction of metal(II) chloride salts with sodium borohydride. Upon optimization of the standard method described here, reaction parameters like reaction time, reagent molar ratios, and capping-agent molar ratio were evaluated. Characterization techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive x-ray (EDS), IR, and UV-visible spectroscopies, selected area electron diffraction (SAED), and power x-ray diffraction (XRD) were performed as necessary. Well-defined, reproducible nickel and iron nanoparticles were produced with average diameters of 26±4 nm and 50±26 nm, respectively, arranged into chain-like structures. Much smaller (6-9 nm) zinc oxide particles that self-assembled into single-particle thick, hexagonal hierarchical microstructures were formed from a modified standard method. Similarly, iron-nickel ANPs with the average size of 20.9±3.3 nm were also synthesized and successful grafting with the polymer capping agent, polyvinylpyrrolidone was confirmed. Because of size, ordered self-assembly, and benign synthesis procedure, the nanoparticles described here are ideal candidates for photovoltaic and thermoelectric device applications. Moreover, these particles have shown to disperse well in various organic and inorganic media, and therefore have wide versatility in thin-film deposition methods.