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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Design and Application of Bile-Salt/Lanthanide Based Hydrogels

Bhowmik, Sandip January 2013 (has links) (PDF)
Chapter 1: Introduction to the luminescent properties of lanthanides Luminescence properties of trivalent lanthanides have been explored extensively over the past few decades owing to their unique properties. Lanthanides emission is known to be due to intra-configurational f-f transitions. Because the partially filled 4f shell is well shielded from its 26 environment by the closed 5sand 5pshells, the ligands in the first and second coordination sphere perturb the electronic configurations of the trivalent lanthanide ions only to a very limited extent. This leads to interesting properties such as long lifetimes, sharp line-like emissions etc. which in turn make lanthanides very attractive choice for commercial optical applications. Despite this, the scope of applications remained limited because of the low molar extinction coefficient values of the forbidden lanthanide f-f transitions. However, this problem has been successfully addressed by complexing the lanthanide ion with suitable ligands which can sensitize it resulting in a significant increase in the emission intensity (so called “antenna effect”). The strategy worked very well and resulted in widespread applications of lanthanides form biology to optoelectronics. This chapter discusses elementary ideas regarding the mechanism of sensitization and relevant examples that traces various applications of such lanthanide complexes from the current literature. Chapter 2: A self-assembled Europium Cholate hydrogel: a novel approach towards lanthanide sensitization Luminescent lanthanides can be of great value in a number of possible applications but their scope is limited by their intrinsic low molar absorptivities. Though this problem can be circumvented by complexing the lanthanide ion with suitable chelating ligands to improve the luminescence properties drastically, the design of such systems often involves meticulous planning and laborious synthetic steps to obtain a ligand suitable for the job. It is therefore desirable to have a simpler version of a sensitizing system that does not require the complexities of a chelating ligand but can sensitize trivalent lanthanides with comparable efficiency. It was observed in our group that divalent metal ions (Ni2+, Zn2+, Cu2+, Coetc.) form hydrogels on addition of sodium cholate. We extended to obtain hydrogels of trivalent lanthanides. Furthermore, when the gel was doped with pyrene, a ten-fold increase in the intensity of Eu(III) emission was observed (Fig 2). Thus we established a unique way to sensitize lanthanides in a hydrogel media by non-coordinating chromophores. The approach was completely modular in nature and avoids any laborious synthesis. We also tried other derivatives of pyrene as sensitizers and found that 1-pyreneboronic acid also caused similar sensitization of Eu(III). Fig 2. (a) Schematic representation of the sensitization process (the arrangement of molecules in the gel fiber is arbitrary). Eu-cholate (5 mM/15 mM) gel (a) normal light and (b) 354 nm UV excitation in the presence of 6 μM pyrene Further studies revealed, that 2,3-dihydroxynapthalene (DHN) can sensitize Tb(III) in a similar hydrogel. We also demonstrated Tb(III) to Eu(III) energy transfer process occurring in the gel when doped with DHN. This allowed us to achieve a hydrogel system with tunable luminescence properties (by varying relative ratios of Tb(III) and Eu(III) ). When the effect of divalent metal ions on such energy transfer processes were explored, it was observed that the luminescence from the composite gel of Tb(III)/ Eu(III) is tunable by Zn(II) and through proper manipulation of concentrations one can obtain white light emitting gel (Fig 3). Fig 3. Effect of Zn(II) (from left to right 0 mM, 2.8 mM, 11.3 mM) on Tb3+ (4.5 mM)/Eu3+ (0.11mM)/ sodium cholate (13.6 mM) gels. b) Tb/Eu/Zn-cholate gel (Tb3+ (4.4 mM), Eu3+ (0.11 mM), Zn2+ (7.4 mM), NaC (13.6 mM, DHN 0.2 mM) under 365 nm UV lamp (c) CIE 1931 diagram depicting the luminescence as white (black spot). Chapter 3. A “Pro-Sensitizer” based Sensing of Enzymes using Tb(III) Luminescence in a Hydrogel matrix This chapter descirbes design and realisation of a sensor system based on Tb(III) luminescnece for the detection of enzymes. The idea involved synthesizing a covalently modified DHN molecule by attaching appropriate enzyme cleavable units. We coined the term “pro-sensitizer”to describe the modified molecule which would not sensitize Tb(III) in the gel matrix but when proper enzymes are applied the free form of DHN would be released triggering a luminescence response from Tb(III). This would enable us to monitor the acitivities of the particular enzyme by examining the luminescence intensity enhancement with time (Fig 4) Fig 4. A “pro-sensitizer” based approach to detect different types of enzymes in a hydrogel matrix through Tb(III) luminescence. We applied the idea to develop a novel luminogenic gel probe for inexpensive and rapid detection of three different hydrolases, lipase, β–glucosidase and α-chymotrypsin. The corresponding “pro-sensitizer”for each enzyme were synthesized (Fig 5).The sensing technique depends on the gel matrix to provide the nessesary platform for lanthanide sensitization. Thereofore, it enjoys an edge over the contemporary techniques that typically involve specially designed and synthesized multidentate chelating ligands for this purpose. We also determined important kinetic parameters of all the enzymes, thus enabling us to have a better insight into the activity of the enzymes in the hydrogel matrix. Fig 4. Pro-sensitizers molecules for (1) lipase, (2) β-glucosidase and (3)α-chymotrypsin Chapter 4. A novel approach towards templated synthesis of lanthanide trifluoride nanoparticles Nanomaterials with excellent optical properties have been of special interest. Lanthanide derived nanoparticles, owing to their unique physical properties, provide an excellent choice for applications such as biolabels, lasers, optical amplifiers, and optical-display phosphors. Several types of lanthanide nanoparticles or nanocrystals are reported in the literature such as Nd2O3, Eu2O3, Gd2O3, Tb2O3, and Y2O3. Among them lanthanide fluoride nanoparticles have emerged as the best choice because of their low phonon energy, and thus minimum quenching of emissive Lnions thereby allowing maximum efficiency for several optical applications. In previous literature precedence, LnF3 nanoparticles were typically synthesized following conventional approaches which necessitate use of high temperatures, high pressures (hydrothermal techniques) and capping ligands. In this chapter, we demonstrated a simpler synthesis of LnF3 nanoparticles at ambient temperatures without the requirement of added capping agents. The room temperature synthesis of LnF3 was unprecedented and was achieved simply by diffusing NaF solution through the hydrogels of corresponding Ln-cholate gels. The nanoparticles were characterized by transmission electron microscopy (TEM) and by powder XRD analysis which established the presence of very small (3-4 nm) nanoparticles mono-dispersed uniformly over the the gel matrix (Fig 6). The LnF3 containing xerogels of Tb(III) and Eu(III) cholate gels were also shown to be highly emissive. Fig 6. HRTEM images of a) TbF3, b) GdF3, c) NdF3 and d) DyF3 in their corresponding gel media.
12

SYNTHESES AND STRUCTURES OF RHENIUM(VII) AND MANGANESE(VII) OXIDE FLUORIDES, MANGANESE(V, IV) FLUORIDES, AND THE FIRST OXIDE OF XENON(II)

Ivanova, Maria January 2016 (has links)
This Thesis extends the chemistry of group VII transition metal oxide fluorides, namely ReO3F and MnO3F. The fundamental chemistry of ReO3F has been significantly extended with the development of its high-yield and high-purity synthesis. This has been achieved by solvolysis of Re2O7 in anhydrous HF (aHF) followed by reaction of the water formed with dissolved F2 at room temperature. The improved synthesis has allowed the Lewis acid and fluoride-ion donor-acceptor properties of ReO3F to be further investigated. The Lewis acid-base complex, (HF)2ReO3F·HF, was obtained by dissolution of ReO3F in aHF at room temperature and was characterized by vibrational spectroscopy with aid of quantum-chemical calculations and single-crystal X-ray diffraction at −173 °C. The HF molecules are F-coordinated to rhenium, representing the only known example of an HF complex with rhenium. The study of the fluoride-ion acceptor properties of ReO3F resulted in the syntheses and characterization of the [{ReO3(μ-F)}3(μ3-O)]2−, [ReO3F3]2−, and [ReO3F2]− anions. The [{ReO3(μ-F)}3(μ3-O)]2− anion was obtained as the [N(CH3)4]+ salt by the reaction of stoichiometric amounts of ReO3F and [N(CH3)4]F in CH3CN solvent. The anion was structurally characterized in CH3CN solution by 1D and 2D 19F NMR spectroscopy and in the solid state by Raman spectroscopy and a single-crystal X-ray structure determination of [N(CH3)4]2[{ReO3(μ-F)}3(μ3-O)]·CH3CN. The structure of the [{ReO3(μ-F)}3(μ3-O)]2– anion consists of three ReO3F units linked to each other through dicoordinate bridging fluorine atoms (F) and a central tricoordinate bridging oxygen atom (O3). Calculated vibrational frequencies and Raman intensities of the [{MO3(μ-F)}3(μ3-O)]2− (C3v) and [{MO3(μ-F)}3(μ3-F)]− (C3v) anions (M = Re, Tc) have been used to assign the Raman spectrum of [N(CH3)4]2[{ReO3(μ-F)}3(μ3-O)]·CH3CN. The fac-[ReO3F3]2− and [ReO3F2]− anions have been synthesized by the reactions of ReO3F with CsF and KF in aHF, and by reaction of ReO3F with NOF. Additionally, the [ReO3F2]− anion has been synthesized by the reaction of ReO3F with [NH4]F in aHF. Both anions were characterized by Raman spectroscopy in the solid state and single-crystal X-ray diffraction. The calculated vibrational frequencies of the fac-[ReO3F3]2− (C3v) and [(µ-F)4(ReO3F)4]4− (C4v) anions were used to assign the Raman spectra of fac-[ReO3F3]2− and [ReO3F2]−, respectively. The rhenium atoms in the open-chain, fluorine-bridged [ReO3F2]− anion and the monomeric fac-[ReO3F3]2− anion are six-coordinate with a facial arrangement of the oxygen ligands. The fluoride-ion donor properties were established by the reactions of ReO3F with excess AsF5 and SbF5/SO2ClF. Both reactions resulted in the formation of white friable solids, µ-O(ReO2F)(AsF5)∙2AsF5 and [ReO3][Sb3F16]. The [ReO3][Sb3F16] salt is stable at room temperature and decomposes to [ReO2F2][SbF5], when maintained at 45 oC under dynamic vacuum. The µ-O(ReO2F)(AsF5)∙2AsF5, however, slowly decomposes at 0 oC to ReO3F and AsF5. Both products were characterized by Raman spectroscopy in the solid state with aid of quantum-chemical calculations. The vibrational analyses revealed that the geometry of [ReO3][Sb3F16] is consistent with a trigonal pyramidal arrangement of oxygen atoms around rhenium, whereas in µ-O(ReO2F)(AsF5)∙2AsF5, ReO3F interacts with one of the AsF5 molecules through an O-bridge, which represents the first example of such type of bonding. The reactions of µ-O(ReO2F)(AsF5)∙2AsF5 and [ReO3][Sb3F16] with CH3CN resulted in the formation of the white salts, [O3Re(NCCH3)3][PnF6] (Pn = As, Sb), which were characterized by Raman spectroscopy. The reactivity of ReO3F has been extended to the synthesis of a new Re(VII) oxide fluoride, (μ-F)4{[μ-O(ReO2F)2](ReO2F2)2}, which was synthesized by the reaction of 1:3 molar ratio of ReO3F and ReO2F3. The compound, (μ-F)4{[μ-O(ReO2F)2](ReO2F2)2}, a rare example of an O-bridged rhenium oxide fluoride, has been characterized by single-crystal X-ray diffraction and solid-state Raman spectroscopy. The vibrational assignments of (μ-F)4{[μ-O(ReO2F)2](ReO2F2)2} were confirmed by 18O-enrichment and quantum-chemical calculations. The improved synthesis of ReO3F has also led to the synthesis and characterization of the novel [XeOXeOXe]2+ cation as its [μ-F(ReO2F3)2]− salt by the low-temperature reaction of ReO3F and XeF2 in aHF. The [XeOXeOXe]2+ cation provides an unprecedented example of a xenon(II) oxide and a noble-gas oxocation as well as a rare example of a noble-gas dication. The crystal structure of [XeOXeOXe][µ-F(ReO2F3)2]2 consists of a planar, zigzag-shaped [XeOXeOXe]2+ cation (C2h symmetry) that is fluorine bridged through its terminal xenon atoms to two [µ-F(ReO2F3)2]– anions. The Raman spectra of the natural abundance and 18O-enriched [XeOXeOXe]2+ salts are consistent with a centrosymmetric (C2h) cation geometry. Quantum-chemical calculations were used to aid in the vibrational assignments of [Xe16/18OXe16/18OXe][µ-F(Re16/18O2F3)2]2 and to assess the bonding in [XeOXeOXe]2+ by NBO, QTAIM, ELF, and MEPS analyses. Ion pair interactions occur through Re–Fμ---Xe bridges, which are predominantly electrostatic in nature and result from polarization of the Fμ-atom electron densities by the exposed core charges of the terminal xenon atoms. Each xenon(II) atom is surrounded by a torus of xenon valence electron density comprised of the three valence electron lone pairs. The positive regions of the terminal xenon atoms and associated fluorine bridge bonds correspond to the positive σ-holes and donor interactions that are associated with “halogen bonding”. The reactions of MnO3F with noble-gas fluorides, KrF2 and XeF6, have been studied as the possible synthetic routes to MnOF5 and MnO2F3. The reaction of MnO3F with KrF2 yielded a red solid, which was isolated as a crystalline solid at room temperature and its crystal structure was assigned to manganese(V) fluoride, MnF5. The crystal structure of polymeric MnF5 consists of MnF6-octahedra which are trans-coordinated through fluorine bridges. The geometrical parameters of MnF5 could not be reliably determined due to unresolved twinning issues. The reaction of MnO3F with KrF2 in the presence of K[HF2] yielded a red-orange solid mixture of K[MnF6] (soluble in HF) and MnF3 (insoluble in HF). The HF solution of the solid mixture was characterized by 19F NMR spectroscopy and the resonance observed in the 19F NMR spectrum was preliminary assigned to [MnF6] by comparison with the chemical shift observed in the 19F NMR spectrum of MnO3F. Additionally, MnO3F was characterized by 19F−55Mn COSY NMR and 55Mn NMR spectroscopies, the latter provided the first 1J(19F−55Mn) coupling constant. The K[MnF6] salt was also characterized by single-crystal X-ray diffraction. The resulting octahedral geometry is imposed by symmetry, therefore, the anticipated Jahn-Teller distortion, which would result in D4h symmetry for the [MnF6] anion, could not be observed. The reaction of MnO3F with XeF6 resulted in the isolation of [Xe2F11]2[MnF6] and [XeF5]2[MnF6]. Both salts were characterized by low-temperature single-crystal X-ray diffraction. The [Xe2F11]2[MnF6] salt was additionally characterized by low-temperature Raman spectroscopy with the aid of quantum-chemical calculations, whereas the assignment of the known Raman spectrum of [XeF5]2[MnF6] has been improved in the present work. / Thesis / Doctor of Philosophy (PhD)
13

Atomic layer deposition of Al²O³ on NF³-pre-treated graphene

Junige, Marcel, Oddoy, Tim, Yakimovab, Rositsa, Darakchievab, Vanya, Wenger, Christian, Lupinac, Grzegorz, Kitzmann, Julia, Albert, Matthias, Bartha, Johann W. 06 September 2019 (has links)
Graphene has been considered for a variety of applications including novel nanoelectronic device concepts. However, the deposition of ultra-thin high-k dielectrics on top of graphene has still been challenging due to graphene's lack of dangling bonds. The formation of large islands and leaky films has been observed resulting from a much delayed growth initiation. In order to address this issue, we tested a pre-treatment with NF³ instead of XeF² on CVD graphene as well as epitaxial graphene monolayers prior to the Atomic Layer Deposition (ALD) of Al²O³. All experiments were conducted in vacuo; i. e. the pristine graphene samples were exposed to NF³ in the same reactor immediately before applying 30 (TMA - H²O) ALD cycles and the samples were transferred between the ALD reactor and a surface analysis unit under high vacuum conditions. The ALD growth initiation was observed by in-situ real-time Spectroscopic Ellipsometry (irtSE) with a sampling rate above 1 Hz. The total amount of Al²O³ material deposited by the applied 30 ALD cycles was cross-checked by in-vacuo X-ray Photoelectron Spectroscopy (XPS). The Al²O³ morphology was determined by Atomic Force Microscopy (AFM). The presence of graphene and its defect status was examined by in-vacuo XPS and Raman Spectroscopy before and after the coating procedure, respectively.
14

Die Aktivierung von reaktionsträgen kleinen Molekülen an koordinativ ungesättigten Beta-Diketiminato-Nickelkomplexen

Holze, Patrick 06 September 2016 (has links)
Kleine Moleküle wie Treibhausgase, aber auch Distickstoff und Disauerstoff stehen im Fokus der chemischen Forschung. Solche Moleküle sind durch ihr Vorkommen in der Atmosphäre ubiquitär vorhanden, preiswert und könnten als Synthesebausteine für die Darstellung von komplexeren Molekülen verwendet werden. In dieser Arbeit wurde die Reaktion koordinativ ungesättigter Diketiminato-Nickelkomplexe ([LNi] Komplexe) mit kleinen Molekülen untersucht. Zunächst wurden die Mechanismen der N2-Aktivierung durch reduzierte [LtBuNiI]- und [LMe6NiI] Komplexe miteinander verglichen. Dabei konnte das distickstoffaktivierende Schlüsselintermediat identifiziert und strukturell charakterisiert werden. Weiter wurden die N2-Komplexe [(LtBuNiI)( 1 1 N2)] bzw. K2[(LtBuNiI)( 1 1 N2)], die Vorläufer für [LNiI]- und [LNi0]– Komplexfragmente darstellen, hinsichtlich ihrer Potentials zur Aktivierung der reaktionsträgen Treibhausgase SF6 und NF3 untersucht. Über Reaktionen von Übergangsmetallkomplexen mit NF3 war bis dahin noch nicht berichtet worden; zur Umsetzung von SF6 existierten wenige Publikationen, in denen aber sehr viele mechanistische Fragen offengeblieben sind. Die Mechanismen der SF6- und NF3-Aktivierung wurden durch Kombination einer Vielzahl von ex- und in situ Analysen beleuchtet. Im Falle der SF6 Aktivierung gelang es zudem, ein Nickel(I)-Intermediat zu isolieren. Ein Produkt beider Systeme war der Fluorido-Nickel(II)-Komplex [LtBuNiIIF], dessen Reaktionsverhalten ebenfalls studiert wurde. Doch nicht nur Komplexe mit Nickelatomen in niedrigen Oxidationsstufen erwiesen sich für die Aktivierung kleiner Moleküle geeignet, sondern auch kationische [LtBuNiII(D)]+-Komplexe. Diese Nickel(II)-Komplexe reagierten mit fluorierten Molekülen, N2O sowie O2, was bemerkenswert ist, da Nickel(II)-Komplexe üblicherweise inert gegenüber O2 sind. Im Zuge der O2-Studien wurde ein metastabiler Oranoperoxidkomplex isoliert und strukturell charakterisiert, was beispiellos in der Literatur ist. / Current research focuses on the activation of small molecules like greenhouse gases, thermodynamically stable molecules like N2 and kinetically stabilized molecules like O2, which are all abundant in the atmosphere. Thus, it appears to be alluring to use them as cheap and readily available building blocks for the synthesis of value-added compounds. This dissertation deals with the reaction of low-coordinate diketiminate nickel complexes [LNi] and such small molecules. Initially, the mechanisms of the dinitrogen activation by reduced [LtBuNiI] and [LMe6NiI] complexes were studied. As a result, the key intermediate [(LtBuNiI)x(3 Br)xKx] (x > 1) was identified and structurally characterized. Subsequently, the nickel complexes [(LtBuNiI)( 1 1 N2)] and K2[(LtBuNiI)( 1 1 N2)], which represent sources for [LtBuNiI] and [LtBuNi0]– moieties, were applied to the activation of the inert, but very efficient greenhouse gases SF6 and NF3. Prior to these investigations, no transition metal complex had been reported to react with NF3. Publications dealing with the conversion of SF6 had been scarce, too, while at same time, the mechanisms involving its activation had been speculative. The mechanisms of the NF3 and SF6 activation reactions were deduced combining numerous ex-situ and in situ analytical methods. In case of the SF6 activation, even an intermediate could be isolated. In both systems, the nickel fluoride complex [LtBuNiIIF] was formed and its reaction behaviour was also studied. Furthermore, not only [LtBuNiI]- and [LtBuNi0]– moieties proved to be reactive towards small molecules, but also cationic [LtBuNiII(D)]+ complexes, which were specifically developed for this purpose. The reactions of [LtBuNiII(D)]+ complexes with fluorinated molecules (e. g. PhF, NF3), O2 and N2O were studied. In course of the O2 activation, a metastable organoperoxide complex was isolated and structurally characterized, which is unparalleled in the literature.
15

Electron Transfer and Other Reactions Using Atomic Metal Anions

Butson, Jeffery M. 04 February 2014 (has links)
The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-.
16

Electron Transfer and Other Reactions Using Atomic Metal Anions

Butson, Jeffery M. January 2014 (has links)
The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-.

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