No description available.

A theoretical analysis of the orientation of biofunctionalized thiolate has been made by changing the surface configuration. The results show that it is possible to match the experimental data by changing the molecular density and also that it is possible to match the experimental data using only hollow sites in the gold surface as placements for the molecules. Some configurations that match available data using only hollow sites positions have been suggested. Moving away from the (sqrt(3) x sqrt(3)) R30° configuration result in a large energy gain for Bor Capped.

Universiẗat, Diss., 2006--Würzburg. / Erscheinungsjahr an der Haupttitelstelle: 2005. Dateien im PDF-Format.

No description available.

Siehe S. 132 im pdf-file / Siehe S. 140 im pdf-file

DNA-modified surfaces have been widely studied for microarray and biosensor applications, in particular sequence-specific detection of DNA, for which electrochemical and optical signs can be produced. Variations in the organization and surface density of adsorbed DNA are known to affect the sensitivity and reliability of assays performed using such surfaces, however most measurements of such surfaces to date have little to no spatial resolution, limiting the information that can be gathered regarding the heterogeneity of the organization of adsorbed DNA molecules. We have applied in situ epi-fluorescence microscopic imaging in conjunction with electrochemical measurements to fluorescently labelled thiolate DNA, adsorbed on polycrystalline gold electrodes with a mercaptohexanol (MCH) passive layer. Spatially resolved information on the organization of adsorbed DNA on the surface is gathered within an area measuring 520by 730micrometres with a 0.96 micrometre resolution. The technique has enabled us to investigate "hotspots" (regions of anomalously bright fluorescence) and regional variation in fluorescence; since molecular fluorescence is quenched as a function of distance from the metal substrate, potential modulation with consequent DNA reorientation or layer specificity of the adsorption. Furthermore, an alternative means to the conventional preparation of thiolate-DNA / MCH monolayers has been developed. In this new method, a gold substrate passivated with MCH is subsequently immersed in an aqueous solution of 5'hexylthiol modified DNA. Through a ligand exchange process, DNA is immobilized forming a mixed MCH / DNA monolayer. Samples prepared via the new method display fewer hotspots and improved fluorescence switching of the DNA during electromodulation for samples made with single stranded (ss) DNA and with double stranded (ds) DNA. Measurement of the DNA surface concentration using ruthenium (III) hexaammine chloride with cyclic voltammetry for self assembled monolayers (SAMs) prepared via the new method are on the order of 1% of the maximum grafting density obtainable for both ssDNA and dsDNA by conventional methods.

DNA-modified surfaces have been widely studied for microarray and biosensor applications, in particular sequence-specific detection of DNA, for which electrochemical and optical signs can be produced. Variations in the organization and surface density of adsorbed DNA are known to affect the sensitivity and reliability of assays performed using such surfaces, however most measurements of such surfaces to date have little to no spatial resolution, limiting the information that can be gathered regarding the heterogeneity of the organization of adsorbed DNA molecules. We have applied in situ epi-fluorescence microscopic imaging in conjunction with electrochemical measurements to fluorescently labelled thiolate DNA, adsorbed on polycrystalline gold electrodes with a mercaptohexanol (MCH) passive layer. Spatially resolved information on the organization of adsorbed DNA on the surface is gathered within an area measuring 520by 730micrometres with a 0.96 micrometre resolution. The technique has enabled us to investigate "hotspots" (regions of anomalously bright fluorescence) and regional variation in fluorescence; since molecular fluorescence is quenched as a function of distance from the metal substrate, potential modulation with consequent DNA reorientation or layer specificity of the adsorption. Furthermore, an alternative means to the conventional preparation of thiolate-DNA / MCH monolayers has been developed. In this new method, a gold substrate passivated with MCH is subsequently immersed in an aqueous solution of 5'hexylthiol modified DNA. Through a ligand exchange process, DNA is immobilized forming a mixed MCH / DNA monolayer. Samples prepared via the new method display fewer hotspots and improved fluorescence switching of the DNA during electromodulation for samples made with single stranded (ss) DNA and with double stranded (ds) DNA. Measurement of the DNA surface concentration using ruthenium (III) hexaammine chloride with cyclic voltammetry for self assembled monolayers (SAMs) prepared via the new method are on the order of 1% of the maximum grafting density obtainable for both ssDNA and dsDNA by conventional methods.

DNA-modified surfaces have been widely studied for microarray and biosensor applications, in particular sequence-specific detection of DNA, for which electrochemical and optical signs can be produced. Variations in the organization and surface density of adsorbed DNA are known to affect the sensitivity and reliability of assays performed using such surfaces, however most measurements of such surfaces to date have little to no spatial resolution, limiting the information that can be gathered regarding the heterogeneity of the organization of adsorbed DNA molecules. We have applied in situ epi-fluorescence microscopic imaging in conjunction with electrochemical measurements to fluorescently labelled thiolate DNA, adsorbed on polycrystalline gold electrodes with a mercaptohexanol (MCH) passive layer. Spatially resolved information on the organization of adsorbed DNA on the surface is gathered within an area measuring 520by 730micrometres with a 0.96 micrometre resolution. The technique has enabled us to investigate "hotspots" (regions of anomalously bright fluorescence) and regional variation in fluorescence; since molecular fluorescence is quenched as a function of distance from the metal substrate, potential modulation with consequent DNA reorientation or layer specificity of the adsorption. Furthermore, an alternative means to the conventional preparation of thiolate-DNA / MCH monolayers has been developed. In this new method, a gold substrate passivated with MCH is subsequently immersed in an aqueous solution of 5'hexylthiol modified DNA. Through a ligand exchange process, DNA is immobilized forming a mixed MCH / DNA monolayer. Samples prepared via the new method display fewer hotspots and improved fluorescence switching of the DNA during electromodulation for samples made with single stranded (ss) DNA and with double stranded (ds) DNA. Measurement of the DNA surface concentration using ruthenium (III) hexaammine chloride with cyclic voltammetry for self assembled monolayers (SAMs) prepared via the new method are on the order of 1% of the maximum grafting density obtainable for both ssDNA and dsDNA by conventional methods. / Science, Faculty of / Chemistry, Department of / Graduate

The research outlined in this dissertation focuses on understanding the role of metal-sulfur interactions as applied to bioinorganic and organometallic systems. This metal-sulfur interaction is analyzed using both gas-phase photoelectron spectroscopy (PES) and density functional theory (DFT). Gas-phase photoelectron spectroscopy is the most direct probe of electronic structure and is used in these studies to probe the molecular orbital energy levels of these model compounds, giving rise to an understanding of the metal and sulfur orbital interactions and characters (i.e. is an orbital primarily metal or sulfur based). Using density functional theory, orbital energies, overlap, and characters can be calculated and complement the PES experiments allowing for a detailed understanding of the electronic structure. The first part of my dissertation explains the design and implementation of a dual source gas-phase ultraviolet/X-ray photoelectron spectrometer (UPS/XPS). This gas-phase UPS/XPS can be used to quantify the bonding/antibonding character of frontier molecular orbitals, with specific applications to metal-sulfur interactions, allowing for a thorough analysis of the metal-sulfur interaction. The second part of the dissertation explores using model complexes, of the type Cp₂V(dithiolate) (where Cp is cyclopentadienyl and dithiolate is 1,2-ethenedithiolate or 1,2-benzenedithiolate), along with PES and DFT calculations to investigate the role of the pyranopterindithiolate cofactor and the d¹ electron configuration in modulating the redox potential and electron transfer in the active sites of molybdenum enzymes. This study shows that the d¹ electronic configuration offers a low energy electron transfer pathway for the reoxidation of the active site molybdenum center. The third part of the dissertation explores the use of model compounds that specifically focus on iron-thiolate interactions in biological systems, and the effect of electronic energy matching and sterics on the oxidation potential of this interaction. This study has shown that the metal-sulfur interaction is sensitive to the orientation of the thiolate ligand, and that during oxidation an “electronic-buffering effect” makes assigning a formal oxidation state to the metal center almost meaningless. All of these studies illustrate how the thiolate ligand can modulate the electron density and oxidation potential of the metal-sulfur interaction and the implication of this interaction to biological electron transfer.

In dieser Arbeit konnten 69 neue und neuartige Koordinationspolymere sowie Komplexe mit schwefelhaltigen Liganden auf Selten-Erd-Chlorid-Basis synthetisiert und strukturell charak-terisiert werden. Durch die Umsetzung der Chloride mit dem Liganden Thiazol konnten bei Raumtemperatur, abhängig vom Ionenradius und der eingesetzten Menge Thiazol, sowohl Koordinationspolymere wie 1∞[LnCl3(thz)6]·thz (Ln = La, Ce), dimere Komplexe [Ln2Cl6(thz)8]·3(thz) (Ln = La, Ce, Pr, Nd), [Pr2Cl6(thz)8] sowie monomere Komplexe [LnCl3(thz)4]2·thz (Ln = Sm , Eu , Tb, Ho) erhalten werden. Mittels temperaturabhängiger Pulverdiffraktometrie und in-situ Infra-rotspektroskopie sowie DTA/TG-Messungen konnte exemplarisch an 1∞[LaCl3(thz)6]·thz und [Pr2Cl6(thz)8] gezeigt werden, dass stufenweise thermisch bedingt Thiazolmoleküle aus den Strukturen abgegeben werden bis hin zur Rückbildung des eingesetzten LnCl3. Unter der Vo-raussetzung, dass die flüchtige Komponente Thiazol resorbiert wird, ist daher ein Kreispro-zess denkbar. Ferner konnten zusätzlich wasserhaltige Phasen wie der vierkernige Cluster [Pr4Cl10(OH)2(thz)8(H2O)2] erhalten werden. Durch die Zugabe eines geeigneten Linkermoleküls in das Reaktionssystem aus trivalenten Lanthanidchloriden und Thiazol konnten unter solvothermalen Bedingungen eine Vielzahl an Koordinationspolymeren und Komplexen erhalten werden. Als Linker oder als end-on Ligan-den eigneten sich sowohl eine Reihe an ditopischer Pyridylliganden 4,4'-Biypridin (bipy), 1,2-Di-(4-pyridyl)ethen (dpe), trans-1-(2-Pyridyl)-2-(4-pyridyl)ethylen (tppe), 1,2-Di-(4-pyridyl)ethan (dpa), sowie die Diazine Pyrazin (pyz) und Pyrimidin (pym) oder auch Azole wie 1,2,4-Triazol (tzH) und Pyrazol (pzH). Mittels Einkristallstrukturanalyse und pulverdiffrakto-metrischer Methoden konnten die dreidimensionalen Gerüstverbindungen 3∞[LnCl3(dpa)2]·thz (Ln = Ce - Sm, Gd - Lu), die Schichtstrukturen 2∞[Ln2Cl6(bipy)3(thz)2]·thz (Ln = La, Ce), 2∞[LnCl3(tzH)2(thz)]·thz (Ln = Pr, Sm - Gd) und die strangartigen Koordinationspolymere 1∞[LnCl3(bipy)(thz)2]·thz (Ln = Pr, Nd), 1∞[LnCl3(bipy)(thz)2]·thz (Ln = Sm, Eu - Er, Yb), 1∞[Ln2Cl6(dpe)2(thz)4]·dpe (Ln = Ce, Nd), 1∞[LnCl3(dpe)(thz)2]· 0.5 (dpe) 0.5 (thz) (Ln = Sm, Gd - Dy, Er, Yb), 1∞[HoCl3(dpe)(thz)2]·thz, 1∞[La2Cl6(dpa)(thz)6], 1∞[Pr2Cl6(pyz) (thz)6], 1∞[Ln2Cl6(tzH)4(thz)2] (Ln = Pr, Sm, Gd) sowie die Komplexe [LnCl3(tppe)2(thz)2] (Ln = Nd, Tb, Ho, Er), [Ln2Cl6(pyz)(thz)6]·2(thz) (Ln = Tb, Er), [Ln2Cl6(pym)2(thz)4] (Ln = Tb , Er), [LnCl3(pzH)3(thz)2] (Ln = Pr, Gd) charakterisiert werden.   Ferner konnten die erhaltenen Verbindungen weitestgehend auf ihre photolumineszenz-spektroskopischen sowie thermischen Eigenschaften hin untersucht werden. Außerdem konn-ten auch durch direkte Schwefelkoordination an die Ln3+-Zentren eindimensionale Koordina-tionspolymere 1∞[PrCl2(amt)(py)3] (amt- = 3-Amino-5-mercapto-1,2,4-triazolat), [HNEt3]1∞[LnCl2(amt)2] (Ln = Ho, Er) und Komplexe [LnCl2(Mbim)(py)3]·py (Ln = Y, Er; Mbim = 2-Mercaptobenzimdiazolat) generiert werden / This thesis deals with the structural characterization of 69 novel coordination polymers and complexes synthesized with sulfur containing heterocyclic ligands and trivalent rare earth chlorides. Depending on the ionic radii of the used lanthanide chloride and the amount of the ligand thiazole coordination polymers as 1∞[LnCl3(thz)6]·thz (Ln = La, Ce), dimeric compounds [Ln2Cl6(thz)8]·3(thz) (Ln = La, Ce, Pr, Nd), [Pr2Cl6(thz)8] and monomeric complexes [LnCl3(thz)4]2·thz (Ln = Sm, Eu , Tb, Ho) were derived at room temperature. Using tempera-ture-dependent powder diffraction methods, in-situ IR-spectroscopy and DTA/TG measure-ments it was demonstrated that there is a stepwise, thermal induced release of thiazole molecules out of the structures to back-formation of crystalline lanthanide chloride in the cases of the coordination polymer 1∞[LaCl3(thz)6]·thz and the dimer [Pr2Cl6(thz)8]. This could be a cyclic process requiring the elusive ligand thiazole to be reabsorbed. Furthermore, hy-drous phases were also obtained like the tetranuclear cluster [Pr4Cl10(OH)2(thz)8(H2O)2]. It was possible to generate a series of various coordination polymers and complexes under solvothermal conditions adding suitable linker molecules into the reaction system of lantha-nide chloride and thiazole. Suitable linkers or end-on ligands are a range of ditopic pyridyl ligands like 4,4'-biypridine (bipy), 1,2-di-(4-pyridyl)ethene (dpe), trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene (tppe), 1,2-di-(4-pyridyl)ethane (dpa), diazine as pyrazine (pyz) and pyrimi-dine (pym) as well as azole like 1,2,4-triazole (tzH) and pyrazole (pzH). By single-X-ray struc-ture determination and powder diffraction it was possible to characterize three dimensional networks 3∞[LnCl3(dpa)2]·thz (Ln = Ce - Sm, Gd - Lu), layer structures 2∞[Ln2Cl6(bipy)3(thz)2]·thz (Ln = La, Ce), 2∞[LnCl3(tzH)2(thz)]·thz (Ln = Pr, Sm - Gd) and strand like coordination polymers 1∞[LnCl3(bipy)(thz)2]·thz (Ln = Pr, Nd), 1∞[LnCl3(bipy)(thz)2]·thz (Ln = Sm, Eu - Er, Yb), 1∞[Ln2Cl6(dpe)2(thz)4]·dpe (Ln = Ce, Nd), 1∞[LnCl3(dpe)(thz)2]·0.5 (dpe) 0.5 (thz) (Ln = Sm, Gd - Dy, Er, Yb), 1∞[HoCl3(dpe)(thz)2]·thz, 1∞[La2Cl6(dpa)(thz)6], 1∞[Pr2Cl6(pyz) (thz)6], 1∞[Ln2Cl6(tzH)4(thz)2] (Ln = Pr, Sm, Gd) as well as the complexes [LnCl3(tppe)2(thz)2] (Ln = Nd, Tb, Ho, Er), [Ln2Cl6(pyz)(thz)6]·2(thz) (Ln = Tb, Er), [Ln2Cl6(pym)2(thz)4] (Ln = Tb , Er), [LnCl3(pyr)3(thz)2] (Ln = Pr, Gd). Furthermore, nearly all of the generated structures were investigated with regards to their photoluminescent and thermal properties.   Moreover, one dimensional coordination polymers 1∞[PrCl2(amt)(py)3] (amt- = 3-amino-5-mercapto-1,2,4-triazolate), [HNEt3]1∞[LnCl2(amt)2] (Ln = Ho, Er) and complexes [LnCl2(Mbim)(py)3]·py (Ln = Y, Er; Mbim = 2-mercaptobenzimdiazolate) were obtained by direct coordination of sulfur at Ln3+-centers.