Redox-aktive Modifizierung von Kieselgeloberflächen durch Bildung von Silizium-Kohlenstoff-Bindungen

The thesis deals with the immobilization of redox-active molecules on a simplified interphase system. Spherical, monodispere and non-porous silica particles, synthesized by a modified Stöber process, are used as the solid matrix. The key step of the surface modification is the formation of a hydrolytically stable silicon-carbon bond from surface silicon hydride groups. The latter are produced selectively and in high yields by a new synthetic strategy involving a chlorination-reduction sequence at high temperature. The silicon-carbon bond is obtained from a free radical induced hydrosilylation reaction between the surface Si-H groups and terminal C=C groups. Both photochemical and thermal activations are used. A dehydrogenative coupling between terminal alkynes and Si-H groups is also successfully applied for the Si-C bond formation. Ferrocene is covalently bound on the Stöber particle surface via the photochemical hydrosilylation route. Cyclic voltammetry of the ferrocene modified particles indicates that ferrocene units over the whole particle surface are electrochemically accessible by an electron hopping mechanism. Silica surfaces are also modified with alkyl chains via the thermal hydrosilylation route. These materials display good performance as HPLC separation phases.Die Doktorarbeit befasst sich mit der Immobilisierung von redox-aktiven Molekülen in einem vereinfachten Interphasensystem. Als feste Matrix werden sphärische, nicht-poröse und monodisperse Kieselgelpartikel verwendet, die nach einem modifizierten Stöber-Prozess synthetisiert werden. Die Erzeugung einer stabilen Silizium-Kohlenstoff-Bindung aus Silizium-Hydrid-Oberflächengruppen stellt den Schlüsselschritt zur Oberflächenmodifizierung dar. Diese Bindungen werden selektiv und in hoher Ausbeuten durch eine neuartige Synthesestrategie, nämlich einer Chlorierungs-Reduktions-Sequenz bei hoher Temperatur, hergestellt. Die Silizium-Kohlenstoff-Bindung wird durch eine radikalische Hydrosilylierungsreaktion zwischen der hydrid-modifizierten Kieselgeloberfläche und terminalen C=C Gruppen erhalten. Sowohl photochemische wie thermische Aktivierungen werden verwendet. Eine Dehydrokondensierung zwischen einem terminalen Alkin und den Si-H Gruppen wird ebenfalls erfolgreich für die Herstellung der Si-C Bindung angewandt. Ferrocen wird kovalent an der Stöberpartikeloberfläche durch photochemische Hydrosilylierung gebunden. Cyclische Voltammetrie der redox-aktiv modifizierten Partikel zeigt, dass die Ferrocen-Einheiten über die ganze Partikeloberfläche durch einen electron hopping'-Mechanismus elektrochemisch zugänglich sind. Kieselgeloberflächen werden auch mit Alkylketten durch eine thermische Hydrosilylierung modifiziert. Die erhaltenen Materialen zeigen gute Eigenschaften als HPLC Trennphasen

The rehabilitation of tropical soils using compost and vermicompost is affected by the presence of endogeic earthworms

As soil engineers, earthworms play a key role in soil organic matter turnover and ecosystem functioning. Numerous studies have shown their positive influence on plant growth and soil quality. At the same time, organic matter inputs in compost or vermicompost, produced in the presence of earthworms, are valuable soil amendments that may increase plant growth. However, whether the combination of earthworm activity and organic matter amendments can be a successful approach for soil rehabilitation remains insufficiently studied. The aim of the present study was to determine the interactions between Dichogaster bolaui , an endogeic earthworm species, and compost or vermicompost produced by Eisenia andrei , an epigeic earthworm species, in a degraded tropical soil. We assessed nutrient availability and natural vegetation recovery. Treatments with and without D. bolaui earthworms were compared. The incorporation of both types of organic matter improved soil quality (i.e., higher pH, more C and nutrients) and led to the recovery of vegetation growth (i.e., development of seedlings and higher above- and belowground biomass). Mineral nutrients, on the other hand, had no effect on vegetation development and led to more pollution of groundwater (i.e., higher concentrations of N-NH 4 +, N-NO 3 - , K and P). Although we could not draw definite conclusions about whether vermicompost had a more positive effect on plant growth than compost, this substrate improved soil chemical properties compared with compost. Dichogaster bolaui enhanced leaching of N-NH 4 + , N-NO 3 - and K when mineral nutrients were used. However overall, D. bolaui had a neutral impact on plant growth when combined with compost, but a negative effect when in combination with vermicompost inputs. In conclusion, this experiment demonstrated that organic matter amendment is an interesting alternative for the rehabilitation of tropical soils. However, negative interactions can occur between local endogeic earthworms and vermicompost

Complete Protection of O 2 -Sensitive Catalysts in Thin Films

International audienceEnergy conversion schemes involving dihydrogen hold great potential for meeting sustainable energy needs, but widespread implementation cannot proceed without solutions that mitigate the cost of rare metal catalysts and the O 2 instability of biological and bioinspired replacements. Recently, thick films (>100 μm) of redox polymers were shown to prevent O 2 catalyst damage but also resulted in unnecessary catalyst load and mass transport limitations. Here we apply novel homogeneous thin films (down to 3 μm) that provide protection from O 2 while achieving highly efficient catalyst utilization. Our empirical data are explained by modeling, demonstrating that resistance to O 2 inactivation can be obtained for nonlimiting periods of time when the optimal thickness for catalyst utilization and current generation is achieved, even when using highly fragile catalysts such as the enzyme hydrogenase. We show that different protection mechanisms operate depending on the matrix dimensions and the intrinsic catalyst properties and can be integrated together synergistically to achieve stable H 2 oxidation currents in the presence of O 2 , potentially enabling a plethora of practical applications for bioinspired catalysts under harsh oxidative conditions

Amperometric sensing — Bioelectroanalysis

This editorial introduces to a Special Issue of Analytical and Bioanalytical Chemsitry dedicated to Amperometric Sensing. The progresses made in this scientific field are introduced and critically discussed

Suppressing hydrogen peroxide generation to achieve oxygen-insensitivity of a [NiFe] hydrogenase in redox active films

Redox-active films were proposed as protective matrices for preventing oxidative deactivation of oxygen-sensitive catalysts such as hydrogenases for their use in fuel cells. However, the theoretical models predict quasi-infinite protection from oxygen and the aerobic half-life for hydrogenase-catalyzed hydrogen oxidation within redox films lasts only about a day. Here, we employ operando confocal microscopy to elucidate the deactivation processes. The hydrogen peroxide generated from incomplete reduction of oxygen induces the decomposition of the redox matrix rather than deactivation of the biocatalyst. We show that efficient dismutation of hydrogen peroxide by iodide extends the aerobic half-life of the catalytic film containing an oxygen-sensitive [NiFe] hydrogenase to over one week, approaching the experimental anaerobic half-life. Altogether, our data support the theory that redox films make the hydrogenases immune against the direct deactivation by oxygen and highlight the importance of suppressing hydrogen peroxide production in order to reach complete protection from oxidative stress

The rehabilitation of tropical soils using compost and vermicompost is affected by the presence of endogeic earthworms

As soil engineers, earthworms play a key role in soil organic matter turnover and ecosystem functioning. Numerous studies have shown their positive influence on plant growth and soil quality. At the same time, organic matter inputs in compost or vermicompost, produced in the presence of earthworms, are valuable soil amendments that may increase plant growth. However, whether the combination of earthworm activity and organic matter amendments can be a successful approach for soil rehabilitation remains insufficiently studied. The aim of the present study was to determine the interactions between Dichogaster bolaui, an endogeic earthworm species, and compost or vermicompost produced by Eisenia andrei, an epigeic earthworm species, in a degraded tropical soil. We assessed nutrient availability and natural vegetation recovery. Treatments with and without D. bolaui earthworms were compared. The incorporation of both types of organic matter improved soil quality (i.e., higher pH, more C and nutrients) and led to the recovery of vegetation growth (i.e., development of seedlings and higher above- and belowground biomass). Mineral nutrients, on the other hand, had no effect on vegetation development and led to more pollution of groundwater (i.e., higher concentrations of N-NH4+, N-NO3-, K and P). Although we could not draw definite conclusions about whether vermicompost had a more positive effect on plant growth than compost, this substrate improved soil chemical properties compared with compost. Dichogaster bolaui enhanced leaching of N-NH4+, N-NO3- and K when mineral nutrients were used. However overall, D. bolaui had a neutral impact on plant growth when combined with compost, but a negative effect when in combination with vermicompost inputs. In conclusion, this experiment demonstrated that organic matter amendment is an interesting alternative for the rehabilitation of tropical soils. However, negative interactions can occur between local endogeic earthworms and vermicompost

Elucidating Electron Transfer Kinetics and Optimizing System Performance for Escherichia coli-Based Semi-Artificial H-2 Production

Both photo- and biocatalysis are well-established andintensivelystudied. The combination of these two approaches is also an emergingresearch field, commonly referred to as semi-artificial photosynthesis.Semi-artificial photosynthesis aims at combining highly efficientsynthetic light harvesters with the self-healing and potent catalyticproperties of biocatalysis. In this study, a semi-artificial photocatalyticsystem featuring Escherichia coli bacteria,which heterologously express the [FeFe] hydrogenase enzyme HydA1 fromgreen algae, is employed as a hydrogen gas production catalyst. Toprobe the influence of photochemistry on overall system performance,the E. coli whole-cell catalyst iscombined with two different photosensitizers and redox mediators.The addition of a redox mediator greatly improves the rates and longevityof the photocatalytic system, as reflected in increases of both theturn-over number (0.777 vs 10.9 & mu;mol H-2 mL(-1) OD600 (-1)) and the turn-over frequency(175 vs 334 & mu;mol H-2 mL(-1) h(-1) OD600 (-1)). The redoxmediator is found to both protect from photobleaching and enable electrontransport to the hydrogenase from an extracellular photosensitizer.However, E. coli cells are stronglyaffected by the photocatalytic system, leading to a decrease in cellintegrity and cell viability, possibly due to toxic decompositionproducts formed during the photocatalytic process. We furthermoreemployed steady-state and transient absorption spectroscopy to investigatesolution potentials and the kinetics of electron transfer processesbetween the sacrificial electron donor, photosensitizer, redox mediator,and the [FeFe] hydrogenase as the final electron acceptor. These resultsallowed us to rationalize the different activities observed in photocatalyticassays and offer a better understanding of the factors that influencethe photocatalytic performance of E. coli-based whole-cell systems