The electrical properties of metal-molecular nanoparticle networks are studied both theoretically and experimentally. Benzenedithiol-aluminum cluster linear chains, Y-shaped and H-shaped networks are modeled with semi-empirical methods to study the electronic properties of such structures. The HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) gaps of the benzenedithiol-Al cluster networks decrease several eV compared to the isolated benzenedithiol molecule. Frontier energy levels become more closely spaced as the size of the molecular networks increase, accompanied with an increased HOMO energy and decreased LUMO energy, indicating a decreased energy barrier to electron transport. Delocalized spatial distribution of the frontier orbitals indicates a high probability for electron transmission and corresponds well with peaks near the HOMO-LUMO gap in the electronic density of states. Self-assembled molecular networks consisting of dithiol/thiol molecules and 30 nm colloidal gold nanoparticles are fabricated with a solution-based method. Electrical measurements performed on these nanostructures show a typically linear current-voltage characteristic while nonlinear I-V curves are also observed for networks built of benzenedithiol or hexane/octanethiol molecules. Further analysis with atomic force microscopy shows that the network’s conductance is determined by the molecule’s conductivity and network dimensions. Circuit model consisting of networked molecular resistors is applied to study the interconnections between the particles within the network and the simulated values of the network’s conductance is consistent with the measured values. Theoretical and experimental study on the electrical properties of metal-molecular nanoparticle networks reveals the influence of molecules and metallic particles on determining the network’s conductivity. Such self-assembled networks can be used to implement several circuit elements, such as resistors, diodes, etc., and more complicated computation components such as nanocells, memristors, etc. The electrical properties of the networks can be tuned by proper choice of molecules, metallic particles and network geometry making them promising for future molecular electronic circuits. / Graduate

There is a continued interest in the properties of arsenic thiolate compounds for both industrial and biological uses. Recent discoveries in the medicinal properties of such compounds have resulted in a sustained need for the synthesis of new dithiarsolane compounds for research as anti-leukemic compounds. Close analogues of the 2-halo arsenic dithiolates, namely those with an arsenic-carbon bond instead of an arsenic-halide bond, have recently been shown to have some efficacy towards leukemia cells. Based on the hydrolytic character and the active role of glutathione with arsenic in vivo, the compounds reported here may also have such activity. Arsenic compounds have demonstrated biological activity in the literature, thus the hypothesis of this thesis is cyclized arsenic thiolates can be synthesized with the appropriate characteristics as to be potentially useful medicinal agents as well as provide new structural and reaction information. A series of arsenic and antimony di- and trithiolates has been synthesized and characterized. Those compounds include 2-chloro-1,3,2-dithiarsolane, 2-bromo- 1,3,2-dithiarsolane, 2-iodo-1,3,2-dithiarsolane, 2-chloro-1,3,2-dithiarsenane, 2-bromo- 1,3,2-dithiarsenane, 2-iodo-1,3,2-dithiarsenane, 3-chloro-4H,7H-5,6-benz-1,3,2- dithiarsepine, 2-chloro-benzo-1,3,2-dithiarsole, 1,2-bis-dithiarsolan-2-ylmercapto-ethane, tris-(pentafluorophenylthio)-arsen, bis(2-(1,3,2-benzodithiarsol-2ylsulfanyl)- benzenesulfide), 2-chloro-benzo-1,3,2-dithiastibole, and bis(2-(1,3,2-benzodithistibol)- 1,2-benzenedithiol. Elucidation of the pH characteristics of arsenic dithiolates within the human toxicity reaction pathway is an area of interest. It has been shown that the aqueous arsenic dithiolate stability depends on the size of the ring. 2-Chloro-1,3,2-dithiarsolane has been shown to be somewhat stable at both low and high pH as well as neutral pH. 1,2-bis- Dithiarsolan-2-ylmercapto-ethane is completely stable in a neutral aqueous solution. Glutathione does not permanently bind to arsenic even in overwhelming excess. In particular, these fully characterized compounds determine how reactive the AsS and AsCl linkages are under environmental and biological conditions, and provide a source of new reagents to examine in medical applications. Future applications may include the incorporation of the reported compounds in filtration and remediation technologies with further modification.

Dans cette thèse, les caractéristiques de l’adsorption de dithiols sur des métaux sont étudiées en utilisant principalement l’XPS à haute résolution sur synchrotron, TOF DRS at LEED. L’objectif est de caractérisé les couches auto-assemblées de dithiols formées par évaporation sous vide, comprendre la transition de dithiols d’une phase couchée vers une phase debout, et des processus de réarrangement et de dissociation. Nous avons constaté que sur Au (111) une phase couchée de butanedithiol (C4DT) pouvait être remplacé par un octanethiol pour former une phase debout mixte, et aussi que la phase C4DT debout pouvait être formée lors d’exposition rapide à des grandes doses de vapeurs de C4DT.Cela montre que la phase couchée ne doit pas empêcher la formation d'une phase debout. L'adsorption de 1,4-benzenedimethanethiol (BDMT) sur Au (111), Ag (111), Au (110), Cu (111), Cu (100) et de Pd (111) ont été étudiés dans cette thèse. La phase debout peut être formée dans certains cas, lorsque la surface n'est pas très réactive. Dans le cas de Cu et Pd, la dissociation de BDMT a été observée et un sulfure de surface a été formé sur Pd. On a étudié également l'interaction entre les atomes de chalcogène (S et Se) et certains métaux en rapport avec le travail de l'auto assemblage. Les informations détaillées sur leurs caractéristiques d'adsorption devraient aider à résoudre des ambiguïtés dans la caractérisation des assemblages de thiols et sulfures. Lors de l’adsorption de Se atomes sur Au surface on observe la chemisorption de Se et la formation de structures de Se₈, tandis que pour l'Ag le séléniure d'argent est formé. L’adsorption de soufre sur des (111), Cu (100) et de Pd (111) résulte en la sulfuration et des structures ordonnées intéressantes ont été observées. / In this thesis, the characteristics of SAMs of dithiol molecules adsorption on metals are investigated mainly by HRXPS based on synchrotron radiation, TOF-DRS and LEED. The aim is to characterize self-assembled dithiol monolayers formed by evaporative assembly, to understand the transition of dithiols from a lying down phase to standing up phase, and eventually existence of rearrangement and dissociation processes. We found that on Au(111) a lying down phase of butanedithiol (C4DT) could be substituted by octanethiols to form a mixed standing up phase, and also that standing-up C4DT phase could be formed upon rapid very large exposure to C4DT vapors. This shows that the lying down phase should not impede formation of the standing up one. The adsorption of 1,4-benzenedimethanethiol (BDMT) on Au(111), Ag(111), Au(110), Cu(111), Cu(100) and Pd(111) were investigated in this thesis. The standing up phase could be formed in some cases, when the surface is not very reactive. In case of Cu and Pd dissociation of BDMT was observed and surface sulphide was formed on Pd. Also the interaction between chalcogen atoms (S and Se) and some metals was investigated in relation to the self assembly work. The detailed information about their adsorption characteristics should help in resolving ambiguities in characterization of thiol and sulphide assemblies. The result of Se atoms adsorption on Au surface shows chemisorbed Se and Se₈ features, while for Ag the silver selenide is formed. S atoms adsorption on Cu(111), Cu(100) and Pd(111) surfaces result in metal sulfidation and some interesting structures were observed.

The interest in biosensors can be attributed to the first described enzyme containing sensor used to detect levels of glucose in 1962. Although research into biosensors was initially slow to pick up, the field has become increasingly popular and research has been widespread for the last 20 years. The continuing research into biosensors is crucial as this will improve current devices to become smaller, faster and more economical and yield new biosensors. This thesis is mostly concerned with the development of an integral component of a biosensor, the redox mediator. Complexes of ruthenium incorporating electron rich sulfur-donor ligands such as naphthalenedithiol should possess interesting redox qualities which could be used to produce better mediators. A second area covered in this thesis is in the structural studies of a series of iridium and rhodium complexes. Two classes of ruthenium complexes with sulfur-donor ligands have been prepared. The first class incorporates the ruthenium bis-bipyridine moiety while the second contains pentamethylcyclopentadienyl ruthenium. Most complexes synthesised exhibited reversible oxidation waves in the region of -0.1 to 0.2 V vs. Ag/Ag⁺. Their possible use as redox mediators was hindered by several factors, particularly difficulties in purification. They also exhibited oxygen sensitivity and low stability when in solution.The second area covered in this thesis is to further understand the bonding of the ligands used in the above study. A series of pentamethylcyclopentadienyl iridium and rhodium complexes were synthesised with three different dithiolato ligands. Two of the three ligands studies produced structures that included more than one metal centre leading to straining of the ligand. In order to study the monomeric form, the clusters were opened with a neutral phosphine ligand. Both the Ir…S and Rh…S bond lengths of all the complexes were within expected parameters.

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<p>The study and understanding of molecular interactions is fundamentally important in today's field of life sciences and there is a demand for well designed surfaces for biosensor applications. The biosensor has to be able to detect specific molecular interactions, while non-specific binding of other substances to the sensor surface should be kept to a minimum.                                                                                                                                                                                The objective of this master´s thesis was to design sensor surfaces based on self-assembled monolayers (SAMs) and evaluate their structural characteristics as well as their performance in Biacore systems. By mixing different oligo (ethylene glycol) terminated thiol compounds in the SAMs, the density of functional groups for bimolecular attachment could be controlled.  Structural characteristics of the SAMs were studied using Ellipsometry, Contact Angle Goniometry, IRAS and XPS. Surfaces showing promising results were examined further with Surface Plasmon Resonance in Biacore instruments.<p>Mixed SAM surfaces with a tailored degree of functional COOH groups could be prepared. The surfaces showed promising characteristics in terms of stability, immobilization capacity of biomolecules, non-specific binding and kinetic assay performance, while further work needs to be dedicated to the improvement of their storage stability. In conclusion, the SAM based sensor surfaces studied in this thesis are interesting candidates for Biacore applications.</p></p>

The study and understanding of molecular interactions is fundamentally important in today's field of life sciences and there is a demand for well designed surfaces for biosensor applications. The biosensor has to be able to detect specific molecular interactions, while non-specific binding of other substances to the sensor surface should be kept to a minimum.                                                                                                                                                                                The objective of this master´s thesis was to design sensor surfaces based on self-assembled monolayers (SAMs) and evaluate their structural characteristics as well as their performance in Biacore systems. By mixing different oligo (ethylene glycol) terminated thiol compounds in the SAMs, the density of functional groups for bimolecular attachment could be controlled.  Structural characteristics of the SAMs were studied using Ellipsometry, Contact Angle Goniometry, IRAS and XPS. Surfaces showing promising results were examined further with Surface Plasmon Resonance in Biacore instruments.Mixed SAM surfaces with a tailored degree of functional COOH groups could be prepared. The surfaces showed promising characteristics in terms of stability, immobilization capacity of biomolecules, non-specific binding and kinetic assay performance, while further work needs to be dedicated to the improvement of their storage stability. In conclusion, the SAM based sensor surfaces studied in this thesis are interesting candidates for Biacore applications.