PHOTOPHYSICS AND CATALYSIS OF PORPHYRINOIDS
Year of Dissertation:
2011
Organic nanoparticles (ONP) of metalloporphyrins can be versatile catalysts for the selective oxidation of alkenes and other hydrocarbons. Herein, we report the catalytic activity of ONP of 5,10,15,20-tetrakis-[4-(1'H,1'H,2'H,2'H-heptadecafluorodecane-1-thiol)-2,3,5,6-tetrafluorophenyl] porphyrinato iron(III), Fe(III)TPPF84, and 5,10,15,20-tetakis-(2,3,4,5,6-pentafluorophenyl) porphyrinato manganese(III), Mn(III)TPPF20, for cyclohexene oxidation using molecular oxygen as an oxidant in water under ambient conditions. While the solvated metalloporphyrins catalytically oxidize alkenes to the corresponding epoxide in halogenated solvent with a modest turn-over numbers (TON), 10-30 nm ONP of these metalloporphyrins have enhanced catalytic activity with up to a 4-fold greater TON and yields only allylic oxidation products. These ONP catalytic systems facilitate a greener reaction since ca. 89% of the reaction medium is water, molecular oxygen is used in place of man-made oxidants, and the ambient reaction conditions require less energy. The enhanced catalytic activity of these ONP is unexpected because the metalloporphyrins in the nanoaggregates are in the close proximity and the TON should diminish by self-oxidative degradation. The fluorous alkanes in Fe(III)TPPF84 stabilize the ONP towards self-oxidative degradation. Sequential dipping of indium-tin-oxide electrodes into solutions of tetra cationic porphyrins and tetra anionic polyoxometalates results in the controlled formation of nm thick films. The potential applications of these robust films on electrodes range from catalysts to sensors. This chapter focuses on the electrochemistry of the multilayered films where it is found that the oxidation and reduction potentials of each species remain largely the same as found in solution. Photophysical properties of Porphyrinoids bearing four rigid hydrogen bonding motifs on the meso positions, self-assembled into a cofacial cage with four complementary bis(decyl)melamine units in dry solvents are presented here. Self-assembly was investigated by NMR spectroscopy, dynamic light scattering, and atomic force microscopy. The phototphysical properties of the cage formation involve the measurement of their absorption and emission spectra and the fluorescence life time in dry THF. The hydrocarbon chains on the bis(decyl)melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates.
Fabrication of Quantum Dot Encoded Silica Beads for High-throughput Screening Applications
Year of Dissertation:
2011
The focus of this research is on the development of optically barcoded silica gel microbeads, synthesized to be used in high throughput screening platforms, using suspension methods for bead synthesis developed specifically for rapid gelation. In suspension methods for particle manufacture, precursor droplets are first formed in a continuous phase immiscible with the droplet phase. The droplets are then solidified into particles. Silica is chosen as the bead material because it can very easily be functionalized to anchor probe molecules which is necessary to function as a capture element in high throughput screening applications. The optical code embedded into the microbeads consists of the spectral signature (the emission spectrum) of a collection of luminescent species. In particular, for this study, multicolor semiconductor nanocrystals or quantum dots (QDs) are used. Each type of QD emits electromagnetic waves at a set wavelength (color), and sets of QDs will be incorporated in differing quantities to form the code. The encoding QDs are dispersed in the pre-gel droplet phase, and are surface functionalized so as not to partition in the continuous phase. In this way, the QDs are effectively trapped in the droplets as they gel to microbeads, which allows for a quantitative loading necessary for optical coding.
MICROSTRUCTURAL ENVIRONMENTS AND REDOX STATES OF IRON IN RANDOM AND ORDERED POROUS SILICA MATRICES
Author:
Don Anton Amarasinghe
Year of Dissertation:
2009
In our previous studies we have shown that the refractive index of porous Vycor glass can be changed by doping with iron and at the lower end of the iron loading, the refractive index shows a fairly linear increase with the loading. This allows us to create refractive index patterns in porous Vycor glass. The exact mechanisms regarding image formation in the Vycor glass and the factors that affect the image quality are still being investigated. In this study we analyzed the cross-sectional distribution of iron and the lateral diffusion of iron during the heat treatment in order to understand the contrast variations. The study also focused on microstructural changes of iron particles from the surface to the interior of the porous Vycor glass. The other objective of the study is to understand microstructural variations of iron in regular pore structured materials such as MCM-41 and random pore networks such as xerogel and PVG.
Gold and Zinc Oxide Nanoparticle Coated Peptide Nanotubes Fabrication and Their Electrical Transport Properties Study
Year of Dissertation:
2012
There is a growing interest in attempts in using biomolecular as the 1D nanotube templates to grow inorganic nanoparticles (NPs) in controlled morphology and structure. One of the research motivations for this combination is to take advantage of the catalytic activity for the room-temperature material growth and the ability of self-assembly into controlled structures on a large scale. One approach to fabricate such nanotube is by using a glycine-based peptide nanotube as template, and on template sidewall immobilizing biomineralizing peptide, which can selectively bind to the target metal/semiconductor precursor and mediate the formation of the inorganic material on templates incorporating these peptides.
Carbohydrates as Scaffolds for Bioactive Agents
Year of Dissertation:
2012
ABSTRACT
Genetically Modified Collagen-like Triple helix Protein as Biomimetic Template to Fabricate Metal/Semiconductor Nanowires
Year of Dissertation:
2011
Various metal and semiconductor nanowires have been developed as building blocks for electronics, optics, and sensors devices. Among these, new nanowires developed on biomolecular templates got more attention since the molecular recognition functions of these biomolecules with specific ligands can be employed to immobilize nanowires onto specific locations to establish desired device geometries. In order for their application in electronics, optics, and sensors device fabrications, after configuring device geometries with nanowires by the biomolecular recognition, we focused upon the biomineralization function of peptides on the nanotemplate sidewall to develop various material coatings such as metals and semiconductors for electronics and sensor applications. It should be noted that the coating morphology such as particle-domain size and inter-particle distance on the nanotemplates could be tuned by peptide sequences and conformations.
Europium Complexes as Probes for Biological and Materials applications
Author:
Laurence Bensaid-Geyer
Year of Dissertation:
2009
Europium is a widely used lanthanide due to its emission in the visible region and its long life time. It is often complexed with ligands in order to serve different purposes in various domains: these complexes can be used as photostable biological probes but also as photoelectronic devices. This thesis interest will lie on both aspects. In chapter 2, we focused on europium phosphonates for targeting bone cancer. As we look at the adsorption of europium phosphonate to bone, possible scenario can take place: the complex can adsorb to the bone and/or the europium can transchelate from the ligand. If the europium transchelate, we looked at the possibility of a europium incorporation into the hydroxyapatite (HA) structure. We prove the presence of europium within the HA structure using various analytical and spectroscopic methods such as elemental analysis, X&ndashray diffraction (XRD), Infra-red (IR), luminescence studies, X&ndashray absorption fine structure (XAFS), and other spectroscopic analysis (SEM, BSE and EDS). In another part, the actual adsorption of europium phosphonate onto HA surface was studied. The adsorption was demonstrated based on luminescence studies showing a change of europium environment. In chapter 3, solution behavior of lanthanide complexes of the &alpha2&ndashP2W17O6110- ligand was reported to identify trends that will facilitate rational synthesis of hybrid organic lanthanide polyoxometalate complexes. Based on 31P NMR studies, the equilibrium between the 1:1 and the 1:2 species, that was observed by Pope for the Ce(III) analog is prevalent for the early-mid lanthanides. This equilibrium is slightly dependent on pH but seems to be very much influenced by larger poorly hydrated cations which appear to favor the 1:2 species for the early to mid lanthanides while they do not appear to influence the equilibrium for the later lanthanides. For all counterions, we found the 1:1 species stable with no trace of the 1:2 species. Finally, in chapter 4, we investigated Eu&alpha1&ndashP2W17O617- (EuPOM) for a layer by layer deposition application with Zn(phen)32+ (Zn(phen)) and its potential as a electroluminescence device. The depositions were monitored by UV-vis. We successfully fabricated multilayer film via electrostatic interaction between the polyanion EuPOM7- and the polycation Zn(phen)32+ until reaching four bilayers when the layers appeared to strip off. Also luminescence studies showed that the multilayer film demonstrated an effective luminescence activity due to the energy transfer through space from the phenanthroline to the europium ion.
Synthesis and characterization of Lanthanide Aluminotungstates and Rhenium Polyoxometalates: Potential Application in Molecular Information Storage Devices
Year of Dissertation:
2011
Abstract
Design of Large Pore Ordered Mesoporous Silicas, Related Silica/Polymer Composites and Carbon Replicas
Year of Dissertation:
2010
This dissertation includes four chapters, namely, the introduction to development and current research interests in mesoporous materials, the "soft-templating" synthesis of large pore 2-D hexagonal ordered mesoporous silicas, the synthesis of mesoporous polymer/silica composites via surface-initiated controlled polymerization, and the "hard-templating" method to fabricate ordered mesoporous carbons.
COMPUTATIONAL STUDIES OF REACTIVE OXYGEN AND SULFUR SPECIES
Year of Dissertation:
2011
In this thesis, we summarized the use of computational chemistry methods to provide insight into the chemistry of reactive intermediates species like singlet oxygen, thiozone, radical and diradicals of mercapto-quinones, and benzyl alkynyl sulfides anions. The theoretical methods used included Density Functional Theory, and hybrid [Molecular Orbital:Molecular Orbital] methods and the Conductor-like Polarizable Continuum Model for condensed phase calculations.