published_or_final_version / abstract / toc / Chemistry / Master / Master of Philosophy

Cationic gemini surfactants have been used for delivery of DNA into cells. These cationic surfactants are known to strongly bind to DNA to form a complex. In the dilute regimen, when the gemini-DNA complexes are mixed with helper neutral lipids, they undergo spontaneous assembly to form particles that are able to transfect DNA into the cells. In this study, the structure of several gemini surfactants, gemini-DNA complexes and gemini-DNA-neutral lipids complexes were systematically examined by small angle x-ray scattering (SAXS). The gemini surfactants were found to form micelles of varying shapes and arrangements modulated by the nature of spacer region and tail lengths. This includes ellipsoidal and worm-like micelles (as in the case of the 12- s-12 series) and disk-shaped hexagonally packed micelles (as in the case of 16-3-16). In addition to the study of the gemini surfactants, the effect of varying the DNA: gemini charge ratio on the DNA-gemini assembly was studied. The scattering pattern has shown that in the presence of excess gemini surfactants, free unbound surfactants exist in the solution. Upon the addition of neutral lipids, DNA-gemini-neutral lipid complexes are formed. The scattering patterns of the latter showed evidence of a strong interaction of the neutral lipids with the free gemini surfactants and the overcharged DNA-gemini complexes. Effectively, overcharging DNA-gemini complexes seem to aid in its incorporation into the neutral lipid matrix. These findings shed the light on the structure of DNA-gemini-neutral lipid systems and provide insights into the factors that influence the spontaneity of the self-assembly process. More importantly, the presented work provides a general strategy that can be applied to the study of similar systems using small angle x-ray scattering. A helium and vacuum chambers were made to enable testing the feasibility of the technique at the Canadian Light Source. Further, a pipeline was written to automate the reduction and analysis of SAXS data.

The Dynamic Model for Aerosol Nucleation (DMAN) is a model which simulates nucleation, gas-phase chemistry, coagulation and condensation/evaporation for a multi-component atmospheric aerosol population. We developed an updated version of DMAN which includes the condensation of organic vapors on nanoparticles, using the recently developed Volatility Basis Set framework, and simulates the gas phase chemistry using the chemical mechanism SAPRC-99. The simulations were performed for two locations with different organic sources; Hyytiala (Finland) and Finokalia (Greece). Initially, we compared the results of the extended DMAN model with the old version which does not include the condensation of organics. The condensation of organics neglecting the Kelvin effects resulting in an approximate doubling of the growth rate of new particles. The number predicted concentration of particles above 3 nm (N3) and 100 (N100) increased at both locations. The increase of surface tension decreased dramatically the growth rate and the diameter that the new particles reached. The predicted concentration of N100 decreased at Hyytiala but increased at Finokalia, while the concentration of N3 decreased in both locations. Condensation of semi-volatile organic vapors, assuming realistic values of the organic surface energy, cannot explain the observed growth rates in Hyytiala during typical nucleation events. The simulations with production and condensation of low-volatility organics and a surface tension of 0.025 N m-1 indicate that the model can reproduce well the field measurements. The addition of chemical aging reactions converting semi-volatile organic aerosol (OA) to low volatility compounds helped the model to better reproduce the observed growth of the fresh particles. At Hyytiala, the organics are the major components during the growth process of new particles. The low-volatility secondary OA helps the growth initially, but after a few hours most of the growth is due to semi-volatile secondary OA components. At Finokalia, the simulation shows that the organic components have a complementary role for the growth contributing 45% of the total mass of new particles. / Το Δυναμικό Μοντέλο Πυρηνογένεσης Σωματιδίων (DMAN) είναι ένα μοντέλο το όποιο προσομοιώνει την πυρηνογένεση, την χημεία στην αέρια φάση, την συσσωμάτωση και την συμπύκνωση/εξάτμιση για ένα πολυσυστατικό πληθυσμό σωματιδίων. Εμείς αναπτύξαμε μια ανανεωμένη έκδοση του DMAN, το όποιο περιλαμβάνει και την συμπύκνωση των οργανικών ατμών πάνω στα νανοσωματίδια, χρησιμοποιώντας την πρόσφατη προσέγγιση Volatility Basis Set και προσομοιώνοντας την αέρια χημεία με την χρήση του χημικού μηχανισμού SAPRC-99. Οι προσομοιώσεις πραγματοποιήθηκαν για δυο τοποθεσίες με διαφορετικές πήγες οργανικών: Hyytiala (Φινλανδία) και Φινοκαλιά (Ελλάδα). Αρχικά, εμείς συγκρίναμε τα αποτελέσματα του εκτεταμένου DMAN μοντέλου με την παλιά έκδοση, η όποια δεν περιλαμβάνει την συμπύκνωση των οργανικών. Η συμπύκνωση των οργανικών παραμελώντας το Kelvin effect έχει σαν αποτέλεσμα τον διπλασιασμό του ρυθμού ανάπτυξης των νέων σωματιδίων. Η προβλεπόμενη συγκέντρωση αριθμού των σωματιδίων πάνω από 3 nm (N3) και 100 (N100) αυξήθηκε και στις δύο τοποθεσίες. Η αύξηση της επιφανειακής τάσης μειώνει δραματικά το ρυθμό ανάπτυξης και την διάμετρο που φτάνουν τα νέα σωματίδια. Η προβλεπόμενη συγκέντρωση των N100 μειώθηκε στη Hyytiala αλλά αυξήθηκε στην Φινοκαλιά, ενώ η συγκέντρωση του Ν3 μειώθηκε και στις δύο περιοχές. Η συμπύκνωση των ημι-πτητικών οργανικών ατμών, θεωρώντας ρεαλιστικές τιμές της επιφανειακής ενέργειας των οργανικών ατμών, δεν μπορεί να εξηγήσει το παρατηρούμενο ρυθμό ανάπτυξης στην Hyytiala κατά τη διάρκεια μιας τυπικής μέρας με πυρηνογένεση. Οι προσομοιώσεις με παραγωγή και συμπύκνωση οργανικών με χαμηλή πτητικότητα και επιφανειακή τάση 0.025 N m-1 δείχνουν ότι το μοντέλο μπορεί να αναπαράγει καλά τις μετρήσεις πεδίου. Η προσθήκη των χημικών αντιδράσεων γήρανσης μετατρέπουν τα ημι-πτητικά οργανικά αεροζόλ (ΟΑ) σε ενώσεις με χαμηλή πτητικότητα, αυτές βοηθούν το μοντέλο να αναπαράγει καλύτερα την παρατηρούμενη ανάπτυξη των φρέσκων σωματιδίων. Στην Hyytiala, τα οργανικά είναι τα κύρια συστατικά κατά τη διαδικασία της ανάπτυξης νέων σωματιδίων. Τα χαμηλής πτητικότητας δευτερογενή ΟΑ βοηθά στην ανάπτυξη αρχικά, αλλά μετά από μερικές ώρες το μεγαλύτερο μέρος της αύξησης οφείλεται στα ημι-πτητικά δευτερογενή ΟΑ. Στη Φινοκαλιά, η προσομοίωση δείχνει ότι τα οργανικά συστατικά έχουν ένα συμπληρωματικό ρόλο για την ανάπτυξη συμβάλλοντας 45% της συνολικής μάζας των νέων σωματιδίων.

The purpose of this dissertation was two-fold: 1) explore the micelle structure and microenvironment of monorhamnolipids (mRL), produced by Pseudomonas aeruginosa ATCC 9027, and their mixtures with synthetic surfactants in order to postulate possible applications of these materials in industrial products and 2) examine the effects of mRL on commercial metal oxide nanoparticle (NP) aqueous dispersion behavior to reveal the potential impact of microbial secondary metabolites on NP fate and transport in the environment. The mixing behavior of mRL with cetylpyridinium chloride (CPC) was measured using surface tensiometry. Electrostatics resulted in cooperative enhancement in mixture properties, but were not significant until α(CPC) ≥ 0.25. Steady-state and time resolved fluorescence quenching measurements in mRL micelles revealed that quenching proceeded via a combined static and dynamic mechanism. Static quenching was preferred in mRL illustrating the reactants form a globular micelle. Changing the structure of the reactants displayed changes in the degree and mechanism of quenching further supporting this aggregate model. Fluorescence measurements on mRL-Tween 20 micelles supported that a geometrically-driven shape transition occurs as mRL decreases. The corresponding decrease in probe lifetime indicated the polarity of the micelle was decreasing. Tween "sealed" the mRL micelles making them less susceptible to water penetration. The effect of mRL on metal oxide NP dispersions was evaluated on adsorption strength, NP aggregate size and stability, and zeta potential under different conditions. Silica NPs showed little adsorption of mRL and was impervious to all variables in altering the solution stable aggregate size. NP aggregate size decreased at very high mRL concentrations due to osmotic and electrosteric repulsions of mRL micelles in solution. Titania, despite expectations, indicated fairly low adsorption of mRL and displayed similar aggregate dispersion stability as that of silica. Spectroscopic investigations exposed that the commercial titania NPs were contaminated with silica altering NP surface properties. Zinc oxide (ZnO) dispersions were substantially affected by the adsorption of mRL. Without mRL, ZnO NPs were unstable independent of pH. The addition of mRL stabilized the ZnO dispersions and lowered the zeta potentials. Furthermore, mRL coating prevented the dissolution of ZnO, the major factor implicated in ZnO toxicity.

Στην παρούσα εργασία διερευνήθηκε περαιτέρω η δυνατότητα ανάπτυξης νανοσωματιδίων ελεγχόμενης χορήγησης και (παθητικής) στόχευσης σισπλατίνας με βάση τα PLGAmPEG συμπολυμερή. Αρχικά μελετήθηκε η επίδραση των συνθηκών παρασκευής στο μέγεθος των λαμβανομένων νανοσωματιδίων και στην φόρτωση και την ενκαψακίωση της σισπλατίνας σε PLGA(40)mPEG(5) νανοσωματίδια. Στη συνέχεια έγινε μελέτη της αντικαρκινικής δραστικότητας νανοσωματιδίων φορτωμένων με σισπλατίνη, τριών διαφορετικών πολυμερικών συστάσεων PLGA(7)mPEG(5) PLGA(31)mPEG(5) και PLGA(57)mPEG(5), έναντι LNCaP καρκινικών κυττάρων προστάτη και σύγκριση αυτής με την δραστικότητα του ελεύθερου φαρμάκου απέναντι στην ίδια καρκινική σειρά. / In the present work was investigated further the possibility of growth of nanoparticles with PLGAmPEG copolymers. Initially it was studied the effect of preparation conditions in the size of the nanoparticles and in the loading and the encapsulation of cisplatin in PLGA(40)mPEG(5) nanoparticles. Afterwards we studied the anticancer efficacy of cisplatin loaded nanoparticles , of three different polymeric constitution PLGA(7)mPEG (5), PLGA(31)mPEG(5) and PLGA(57)mPEG(5), opposite of LNCaP cancer cells and comparison of this with the efficacy of the free medicine towards the same cancer cells.

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Plasmonic resonances are characterized by enhanced optical near field and subwavelength power confinement. Light is not only scattered but also simultaneously absorbed in the metal nanostructures. With proper structural design, plasmonic-enhanced light absorption can generate nanoscopically confined heat power in metallic nanostructures, which can even be temporally modulated by varying the pump light. These intrinsic characters of plasmonic nanostructures are investigated in depth in this thesis for a range of materials and nanophotonic applications.   The theoretical basis for the photothermal phenomenon, including light absorption, heat generation, and heat conduction, is coherently summarized and implemented numerically based on finite-element method. Our analysis favours disk-pair and particle/dielectric-spacer/metal-film nanostructures for their high optical absorbance, originated from their antiparallel dipole resonances.   Experiments were done towards two specific application directions. First, the manipulation of the morphology and crystallinity of Au nanoparticles (NPs) in plasmonic absorbers by photothermal effect is demonstrated. In particular, with a nanosecond-pulsed light, brick-shaped Au NPs are reshaped to spherical NPs with a smooth surface; while with a 10-second continuous wave laser, similar brick-shaped NPs can be annealed to faceted nanocrystals. A comparison of the two cases reveals that pumping intensity and exposure time both play key roles in determining the morphology and crystallinity of the annealed NPs.   Second, the attempt is made to utilize the high absorbance and localized heat generation of the metal-insulator-metal (MIM) absorber in Si thermo-optic switches for achieving all-optical switching/routing with a small switching power and a fast transient response. For this purpose, a numerical study of a Mach-Zehnder interferometer integrated with MIM nanostrips is performed. Experimentally, a Si disk resonator and a ring-resonator-based add-drop filter, both integrated with MIM film absorbers, are fabricated and characterized. They show that good thermal conductance between the absorber and the Si light-guiding region is vital for a better switching performance.   Theoretical and experimental methodologies presented in the thesis show the physics principle and functionality of the photothermal effect in Au nanostructures, as well as its application in improving the morphology and crystallinity of Au NPs and miniaturized all-optical Si photonic switching devices. / <p>QC 20140331</p>

The field of structural DNA nanotechnology utilizes DNA's powerful base-pairing molecular recognition criteria to help solve real challenges facing researchers in material science and nanotechnology, some of which include synthesis, sensing, catalysis, delivery, storage, optics, electronics, and scaffolding. In it, DNA is stripped away from any of its preconceived biological roles, and is treated as a powerful synthetic polymer. A subarea of research that our group has recently termed supramolecular DNA nanotechnology is emerging, and is proving to be a powerful complement to some of the already established rules of structural DNA nanotechnology. The work within this thesis falls under the umbrella of supramolecular DNA nanotechnology, and can conceptually be divided into three parts. (1) The first deals with the problem of discrete nanopartic1e organization. In it we present an approach for the facile and economical access to libraries of discrete nanoparticle assemblies that are addressable and switchable post-assembly. (2) The second deals with the synthesis of three-dimensional DNA assemblies. In it we present an approach for the facile construction of discrete three-dimensional DNA cages that can be structurally oscillated between pre-defined lengths, and adapt this approach to generate geometrically well-defined DNA columns of modular stiffness. (3) The last part deals with the use of small molecules to reprogram the assembly behavior of DNA. In it we use molecules to address the issue of error-correction, during and after the assembly process, and to facilitate the synthesis of "higher-order" DNA helices composed of more than two DNA strands. This work collectively offers a set of simple solutions to some of the bigger challenges currently facing researchers in DNA nanotechnology, and provides a snapshot of what is to be expected from tehe emerging discipline that is supramolecular DNA nanotechnology.

RuO2/carbon composites have attracted a lot of attention for use as supercapacitor electrodes due to their high power and energy capabilities. Methods for loading the RuO2 into the carbon include impregnation and electrochemical deposition. The first project involves impregnation of RuO2 nanoparticles into a mesoporous carbon powder. Structural changes of the RuO2 nanoparticles in the composite were induced by annealing at high temperatures, and X-ray diffraction (XRD) and X-ray absorption (XAS) were used to study the changes. In situ electrochemical-XAS experiments were also developed and performed to study the structural stability of the RuO2 nanoparticles in the composite as well as bulk RuO2•xH2O, with respect to changing potential. Preliminary work on the electrodeposition of RuO2•xH2O onto Au foil and carbon cloth was performed. An electrode with a high specific capacitance of the RuO2•xH2O component was achieved. However, further studies need to be performed to optimize the deposition solution.

Structure and bonding properties of gold (Au) nanoparticles (NPs) are of great interest due to the unique size-dependent quantum-confinement effect exhibited by structures on the nanoscale. As such, Au NPs have demonstrated their potential use in a variety of fields (e.g. imaging, drug delivery, catalysis). The popularity of Au NPs is largely due to its versatility in synthesizing different NP compositions and surfaces. In this thesis, structure and bonding in Au NPs was examined from both surface functionalization/ligand and composition/metal bonding perspectives. Functionalization of Au-surface with model biomolecule ligands enables formation and electroless deposition of Au NPs onto a biocompatible Ti substrate. Through variation of model biomolecule size and concentration with respect to a Au precursor, insight was gained into the formation mechanisms of Au NPs, and the processes that lead to deposition upon the Ti substrate. Furthermore, using extended X-ray absorption fine-structure (EXAFS) with sample spinning and glancing angle setup allowed us to resolve small differences in coordination, leading to new findings on fine-tuning of peptide-coated Au NP size on Ti substrates. To explicitly analyze Au NP structure and bonding from a metallic perspective, NP model systems with precisely controlled compositions were studied with ab initio calculations to compare local environment and electronic character. It was determined that while surface features may be structurally similar, the effect of local environment and geometry can affect the electronic character of these features. Finally, small Au NP samples were studied to understand the alloying effect. The position of a heteroatom dopant Pt atom within Au25 has been a disputed issue, with no definitive means of determination. Using a combination of EXAFS spectra and ab initio calculations, it was possible to determine that the Pt atom resides in the central position of the icosahedral core. Furthermore, Pt doping in Au25 resulted in a contraction of the surface Au structure, an unobserved phenomenon until now. Through the careful and systematic comparison of Au NP systems, this thesis will contribute to a better understanding of Au local structure and bonding in ligand-functionalized substrate-supported Au NPs, as well as compositionally precise Au nanoclusters.