Reversible Charge Trapping in Bis-Carbazole-Diimide Redox Polymers with Complete Luminescence Quenching Enabling Nondestructive Read-Out by Resonance Raman Spectroscopy

The coupling of substituted carbazole compounds through carbon–carbon bond formation upon one-electron oxidation is shown to be a highly versatile approach to the formation of redox polymer films. Although the polymerization of single carbazole units has been proposed earlier, we show that by tethering pairs of carbazoles double sequential dimerization allows for facile formation of redox polymer films with fine control over film thickness. We show that the design of the monomers and in particular the bridging units is key to polymer formation, with the diaminobenzene motif proving advantageous, in terms of the matching to the redox potentials of the monomer and polymer film and thereby avoiding limitations in film thickness (autoinsulation), but introduces unacceptable instability due to the intrinsic redox activity of this moiety. The use of a diimide protecting group both avoids complications due to <i>p</i>-diamino-benzene redox chemistry and provides for a redox polymer in which the photoluminescence of the bis-carbazole moiety can be switched reversibly (on/off) with redox control. The monomer design approach is versatile enabling facile incorporation of additional functional units, such as naphthalene. Here we show that a multicomponent carbazole/naphthalene containing monomer (<b>APCNDI</b>) can form redox polymer films showing both p- and n- conductivity under ambient conditions and allows access to five distinct redox states, and a complex electrochromic response covering the whole of the UV/vis–NIR spectral region. The highly effective quenching of the photoluminescence of both components in poly-<b>APCNDI</b> enables detailed characterization of the redox polymer films. The poly-<b>APCNDI</b> films show extensive charge trapping, which can be read out spectroscopically in the case of films and is characterized as kinetic rather than chemical in origin on the basis of UV/vis–NIR absorption and resonance Raman spectroscopic analyses. The strong resonantly enhanced Raman scattering for the various oxidized and reduced states of <b>APCNDI</b> enables nondestructive “read-out” of the state of the polymer, including that in which charges are trapped kinetically at the surface, making poly-<b>APCNDI</b> highly suitable for application as a component in organic nonvolatile memory devices

Failures and successes in the quest of hybrid systems for efficient catalysis

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Inorgánica. Fecha de lectura: 13-03-2015This thesis has been carried out in the Department of Inorganic Chemistry at the Autonomous University of Madrid and focused on the study of hybrid systems with potential use in a variety of catalytic processes. After the general introduction, in the second chapter is presented a comprehensive analysis of the H2 activation process achieved by active species generated by the reaction of H2O2 with non-heme iron compound [Fe (BPMCN) (OTf)2] (BPMCN= N,N’-bis(2-pyridylmethyl)-1,2-diaminocyclohexane). This study was derived from the original idea of designing a tandem catalytic process from H2 + O2 mixture until the formation of epoxides and H2O from reaction with olefins. However, what was observed is that depending on the presence of acetic acid in the reaction medium, H2 molecule is activated with varying efficiency by the non-heme iron species with high oxidation state. In the third chapter of this thesis, different strategies for supramolecular or covalent functionalization of graphene oxide (GO) designing for GO- porphyrin hybrids are presented. In the fourth chapter, a procedure of sonication of graphite is reported in various mixtures of water and organic solvent, producing stable suspensions of few layers graphene. Optimized spray deposition processes of these graphene suspensions resulted in transparent coatings with excellent electrical conductivity vs transparency ratios. In the fifth chapter is presented the design of electrodes with high surface area, based on carbon microfibers, which can be chemically modified (by an oxidation process using H2SO4 / H2O2) to make them active in electrocatalytic processes for H2 generationEsta tesis se ha llevado a cabo en el departamento de Química Inorgánica en la Universidad Autónoma de Madrid y se ha centrado en el estudio de sistemas híbridos con potencial uso en diversos procesos catalíticos. Después de la introducción general, en el segundo capítulo se ha presentado un análisis exhaustivo del proceso de activación de H2 logrado por las especies activas generadas por reacción de H2O2 con el compuesto de hierro no hemo [Fe(BPMCN)(OTf)2] (BPMCN= N,N’-bis(2-pyridylmethyl)-1,2-diaminocyclohexane). Este estudio se derivó de la idea original de diseñar un proceso catalítico tipo tándem desde la mezcla H2 + O2 hasta la formación de epóxidos y H2O a partir de reacción con olefinas. Sin embargo, lo que se observó fue que en función de la presencia de ácido acético en el medio de reacción, se activa con más o menos eficiencia la molécula de H2 por la correspondiente especie de hierro no hemo con elevado estado de oxidación. En el tercer capítulo de esta tesis se presentan diferentes estrategias de funcionalización supramolecular o covalente de óxido de grafeno para obtener híbridos de GO-porfirina. En el cuarto capítulo se reporta un procedimiento de sonicación de grafito en varias mezclas de agua y disolvente orgánico que produce suspensiones muy estables de grafeno de pocas capas. La optimización de procesos de deposición por pulverización de estas suspensiones de grafeno ha resultado en recubrimientos transparentes con una excelente relación transparencia vs conductividad eléctrica. En el quinto capítulo se presenta el diseño electrodos de elevada área superficial, basados en fibra de carbono, los cuales pueden ser químicamente modificados (mediante un proceso de oxidación usando H2SO4/H2O2) para hacerlos activos en procesos electrocatalíticos para la generación de H2

Electrochemical oxidation of meglumine in a pharmaceutical formulation using a nanocomposite anode

The electrocatalytic oxidation of meglumine and gadoterate meglumine (Gd-DOTA) on a TiO2-Ni(SO4)0.3(OH)1.4 composite anode was investigated in alkaline medium (5 M KOH) using cyclic voltammetry and chronoamperometry. The composite was prepared by hydrothermal method and the morphology and structure of the produced nanoparticles were studied by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, atomic force microscopy, BET surface area analysis and Fourier transform infrared spectroscopy. The characterization revealed the formation of Ni(SO4)0.3(OH)1.4 nanobelts dispersed on TiO2 nanoaggregates. The composite was coated onto a porous graphite rod, showing good adherence without requiring any binder (according to their anodic and cathodic charges). The supported composite was electrocatalytic, allowing the oxidation of meglumine, either as pure reagent or contained in gadoterate meglumine solutions. Electrochemical methods allowed determining the kinetic parameters, such as the electron transfer coefficient α, the total number of electrons n and the standard heterogeneous rate constant k0 for the reaction of meglumine. The chronoamperometric tests informed about the good stability of the composite anode upon meglumine oxidation at +0.6 V for 10 h. The electrochemical oxidation of meglumine in a commercial pharmaceutical formulation (Dotarem®) was corroborated via ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry

Multilayer graphene in the interplay with different photocatalyst architectures for the hydrogen evolution reaction

The use of graphene as co-component for nanostructured materials has led to the claim of improving efficiencies of solar cells, fuel cells and particular in photocatalytic systems for solar water splitting. As a result of exceptional conductivity properties it is believed that graphene might always enhance the separation of charge carriers, consequently increasing photocatalytic performances. However, herein is demonstrated that employing graphene in different configurations, i.e. powder suspension, multicomponent aerogel and electrode, the photocatalytic enhancement is rather case sensitive.Die Verwendung von Graphen als Co-Komponente in Solarzellen, Brennstoffzellen oder in photokatalytischen Systemen zur Wasserspaltung führte zu der allgemeinen Annahme, dass mittels dieser Materialien ein effizienterer Betrieb möglich ist. Als Folge seiner außergewöhnlichen Leitfähigkeit wird angenommen, dass Graphen immer durch Ladungsträgertrennung konsequenterweise die photokatalytische Leistungsfähigkeit erhöht. Die verschiedenen Studien dieser Arbeit zeigten jedoch, dass der Einfluss vielmehr fallsensitiv, wie beim Einsatz in multikomponenten Suspensionen, Aerogelen oder Elektroden, ist

New analytical applications of gold nanoparticles

The work includes improvements of surface technology, new analytical applications of metallic nanoparticles and optimization of technological steps for production of different types of metallic nanoparticles in discrete and continuous modes. The technology of LbL deposition was optimized and applied for immobilization of metallic nanoparticles. SPR detection was used for the determination of optimal deposition conditions and on-line monitoring of the deposition process. Simple approach for automation of LbL deposition allowing one to deposit up to hundreds of layers was developed. The technology was proved by electrochemical analysis for deposition of electrochemically active polymers. A new diffusion based semi-quantitative assay for detection of sugars was suggested. Electrochemical oxidation of glucose and dopamine on electrodes modified with gold nanoparticles was studied. Conditions for electrochemical analysis of these substances in the presence of typical natural interferents were evaluated. A combination of voltammetry and impedance spectroscopy was used to demonstrate a formation of insulating layer on gold surface, this resulted in explanation of anomalous shape of voltammetric curves. A combination of electrochemical and SPR measurements demonstrated directly a formation of an insulating layer on the electrode surface and was used for optimization of the assay conditions. The results indicate a possibility to develop an enzyme free sensors for glucose and dopamine. It was discovered that gold nanoparticles are effective nucleating agents for protein crystallization. Nanoparticles induce protein crystallization at lower supersaturation and increase the number of protein crystals formed at higher supersaturation. The fact that this technology works with so different proteins as lysozyme and ferritin allows one to suggest that it may be also applied for many other proteins including the ones which are reluctant to crystallization by known technologies. Irreversible freezing indicators based on gold nanoparticles were developed. The filling suspension containing nanoparticles, nucleation and stabilization agents were optimized in sense of stability and irreversibility of color changes. A large scale production of this indicator will be started in spring 2008

Electrochemical immunosensors

Master'sMASTER OF SCIENC

Porézní borem dopované diamantové elektrody: Charakterizace a využití v elektroanalýze

Předkládaná disertační práce pojednává o nově připravených elektrodových materiálech na bázi porézního borem dopovaného diamantu (BDDpor) a jejich aplikačních možnostech v oblasti elektroanalýzy. Všechny nové BDDpor elektrody (v celkovém počtu dvanáct) byly důkladně elektrochemicky charakterizovány a porovnány, a ty s nejperspektivnějšími elektrochemickými vlastnostmi byly vybrány k vývoji spolehlivých voltametrických metod pro detekci nervového přenašeče dopaminu. Na začátku byl objasněn vliv vybraných parametrů přípravy na finální vlastnosti nově připravených BDDpor elektrod; konkrétně byly studovány tyto parametry: (1) porézní substrát použitý k depozici, (2) úroveň dopování borem, (3) doba růstu jednotlivých vrstev (porozita), (4) počet deponovaných vrstev (tloušťka), a (5) obsah nediamantových (sp2 ) uhlíkových nečistot. Změny v podmínkách depozice přirozeně vedly k přípravě BDDpor elektrod, které měly (i) odlišné strukturní a morfologické charakteristiky, které byly sledovány pomocí skenovací elektronové mikroskopie a Ramanovy spektroskopie, a (ii) rozličné fyzikální a elektrochemické chování, což bylo studováno za využití cyklické voltametrie. Na základě dalších parametrů, jako je náchylnost vůči adsorpci, stabilita signálů, citlivost a selektivita, byla testována vhodnost vybraných BDDpor...This dissertation thesis presents newly developed electrode materials based on porous boron- doped diamond (BDDporous) and their potential applications in electroanalysis. Particularly, these novel BDDporous electrodes (twelve in total) were thoroughly electrochemically characterised and compared, and the ones with the most promising properties were selected to develop reliable voltammetric methods for detecting the neurotransmitter dopamine. Initially, the impact of selected fabrication parameters on the final properties and electrochemical behaviour of novel BDDporous electrodes was clarified; the following factors were specifically studied: (1) deposition template used, (2) boron-doping level, (3) growth time of the individual layers (i.e., porosity), (4) number of deposited layers (i.e., thickness), and (5) content of non-diamond (sp2 ) carbon impurities. Alterations in deposition conditions naturally resulted in BDDporous electrodes with diverse (i) structural and morphological features, which were investigated by scanning electron microscopy and Raman spectroscopy, and (ii) physical and electrochemical characteristics, examined by cyclic voltammetry. Besides, to assess the suitability of selected BDDporous electrodes for dopamine detection, other parameters, such as susceptibility to...Department of Analytical ChemistryKatedra analytické chemieFaculty of SciencePřírodovědecká fakult

New Reactions in Metal-based and Enzymatic Catalysis

Aquesta tesi doctoral es proposa investigar noves funcions catalítiques a partir d'estratègies ben establertes en catàlisi asimètrica, amb l'objectiu de desenvolupar processos enantioselectius no convencionals des del punt de vista del mecanisme. En el primer projecte, es va mostrar com la irradiació de llum visible podria desviar la reactivitat d'un complex quiral d'iridi (III)--allil amb la funció ben establerta d'electròfil a l'estat fonamental per convertir-se en un oxidant d'un sol electró a l'estat excitat. La fotoexcitació d'aquest complex d'organoiridi quiral va permetre la implementació d'un acoblament creuat C-C enantioselectiu basat en un mecanisme radical inassolible en el domini tèrmic. El mètode ens va permetre acoblar alcohols allílics de bencil racèmics i 4-alquil-dihidropiridines (DHP), que van generar radicals α-amino després de l'oxidació per l'estat excitat del complex d'iridi(III). La reacció va transcórrer sota irradiació de 460 nm a temperatura ambient i va proporcionar els productes allílics desitjats amb alts rendiments i excés enantiomèric. En el segon projecte, es va mostrar com la modificació genètica d'un enzim ben establert la va convertir en un biocatalitzador multifuncional, que podria impulsar una reacció en biocascada nova des del punt de vista del mecanisme ja que l'enzim catalitzava tots els passos de la seqüència en cascada amb un alt control estereoscòpic. Aquests biocatalitzadors multifuncionals pertanyien a la família d'enzims 4-oxalocrotonat tautomerasa (4-OT) i podien fer tant l'activació amb enamina d'aldehids com l'activació amb ions imini d'enals de forma seqüencial. Això ens va permetre implementar les versions enzimàtiques de les dues reaccions en cascada clàssiques en organocatàlisi descrites per Enders per a la síntesi de carbaldehids de ciclohexens altament enriquits i complexos. El nostre protocol biocatalític va coincidir, i de vegades va superar, el mètode organocatalític en termes d'eficiència i estereoselectivitat.La presente tesis doctoral se propone de investigar nuevas funciones catalíticas a partir de estrategias bien establecidas en catálisis asimétrica, con el objetivo de desarrollar procesos enantioselectivos no convencionales desde el punto de vista del mecanismo. En el primer proyecto, se mostró cómo la irradiación de luz visible podría desviar la reactividad de un complejo quiral de iridio (III)--alilo con la función bien establecida de electrófilo en el estado fundamental para convertirse en un oxidante de un solo electrón en el estado excitado. La fotoexcitación de este complejo de organoiridio quiral permitió la implementación de un acoplamiento cruzado C-C enantioselectivo basado en un mecanismo radical inalcanzable en el dominio térmico. El método nos permitió acoplar alcoholes alílicos de bencilo racémicos y 4-alquil-dihidropiridinas (DHP), que generaron radicales α-amino tras la oxidación por el estado excitado del complejo de iridio(III). La reacción transcurrió bajo irradiación de 460 nm a temperatura ambiente y proporcionó los productos alílicos deseados con altos rendimientos y exceso enantiomérico. En el segundo proyecto, se mostró cómo la modificación genética de una enzima bien establecida la convirtió en un biocatalizador multifuncional, que podría impulsar una reacción en biocascada novedosa desde el pnto de vista del mecanismo ya que la enzima catalizaba todos los pasos de la secuencia en cascada con un alto control estereoscópico. Estos biocatalizadores multifuncionales pertenecían a la familia de enzimas 4-oxalocrotonato tautomerasa (4-OT) y podían realizar tanto la activación con enamina de aldehídos como la activación con iones iminio de enales de forma secuencial. Esto nos permitió implementar las versiones enzimáticas de las dos reacciones en cascada clásicas en organocatálisis descritas por Enders para la síntesis de carbaldehídos de ciclohexenos altamente enriquecidos y complejos. Nuestro protocolo biocatalítico coincidió, y en ocasiones superó, el método organocatalítico en términos de eficiencia y estereoselectividad.The objective of this research thesis was to upgrade established strategies of asymmetric catalysis by disclosing novel catalytic functions, useful to develop mechanistically-divergent enantioselective processes. In the first project, visible light irradiation was used to divert the well-established reactivity of a chiral iridium(III)--allyl complex that functioned as a general electrophile in the ground state. Upon excitation it became instead a single electron transfer (SET) oxidant in the excited state. The photoexcitation of this chiral organoiridium complex enabled a mechanistically-novel enantioselective radical C-C cross coupling that was unattainable in the thermal domain. The method allowed us to couple racemic benzyl allylic alcohols and 4-alkyl-dihydropyridines (DHPs), which delivered α-amino radicals upon SET oxidation by the excited state of the iridium(III) complex. The reaction proceeded under 460 nm irradiation at room temperature and afforded the desired allylic products in high yields and enantiomeric excess. In the second project, we used the genetic modification of a well-established enzyme to turn it into a multifunctional biocatalyst, which could drive a mechanistically-novel biocascade reaction by catalyzing all the steps of the cascade sequence with high stereocontrol. Our new multifunctional biocatalysts belonged to the 4-oxalocrotonate tautomerase (4-OT) family of enzymes and they could perform both the enamine activation of linear aldehydes and the iminium ion activation of enals in a sequential way. This allowed us to implement the enzymatic versions of the two classic organocascade reactions reported by Enders for the synthesis of complex and highly enantioenriched cyclohexene carbaldehyde scaffolds. Our biocatalytic protocol matched, and sometimes surpassed, the organocatalytic approach in terms of efficiency and stereoselectivity