Florian Mertens

Proton and Water Activity-Controlled Structure Formation in Zinc Carboxylate-Based Metal Organic Frameworks

The contributions of terephthalic acid and Zn(2+)-coordinated water in N,N-diethylformamide (DEF) to the overall proton activity in the synthesis of MOF-5 (Zn4O(BDC)3, BDC = 1,4-benzenedicarboxylate) were quantitatively determined by combined electrochemical and UV-vis spectroscopic measurements. Structural transformations of zinc carboxylate-based metal organic frameworks due to their exposure to environments with variable water concentrations and the chemical means necessary to revert these transitions have been investigated. It was found that the water-induced structural transition of MOF-5 to the hydroxide structure Zn3(OH)2(BDC)2 x 2 DEF (MOF-69c) can be reverted by a thermal treatment of the obtained compound and its subsequent exposure to anhydrous DEF. MOF-5 syntheses from simple carboxylates as well as a water-free synthesis based on nitrate decomposition are presented. The latter demonstrates that nitrate can serve as the sole source for the oxide ion in MOF-5.

Main-Group and Transition-Element IRMOF Homologues

A simple two-component procedure was developed to synthesize not only classical zinc-based IRMOFs represented by MOF-5 but also the cobalt and beryllium homologues of this most prominent MOF. The procedure is the first manifestation of mirroring the IRMOF series with other metal centers taken from main-group as well as transition-metal elements. Because of the existence of many suitable precursors, the procedure promises the generation of a large number of IRMOF homologues. Since the IRMOF series together with the MIL series is the MOF group with the largest number of representatives, the possibility of choosing the metal centers of the secondary building units from an extended set will tremendously expand the number of obtainable structures in a predictive, crystal-engineering-type way. Use of metal centers other than zinc will allow the addition of new features to the existing IRMOF structures, such as magnetic properties in the example of cobalt.

High‐Separation Performance of Chromatographic Capillaries Coated with MOF‐5 by the Controlled SBU Approach

Recently developed MOF surface-coating techniques, the controlled SBU approach (CSA) for the generation of MOF-5, and the use of self-assembled monolayers have been combined to generate a wall-bonded, crosslinked stationary phase for gas chromatographic capillary columns displaying excellent performance in the separation of natural gas components. The chromatographic performance of this new type of column has been compared to the state-of-the-art solution for this separation problem, namely a coated silica column of the porous layer open tubular (PLOT) type. Chromatographic parameters such as separation, resolution, and tailing factors, as well as plate numbers and heights in the case of isothermal operation, have been determined. Kinetic and thermodynamic parameters characterizing the analyte-stationary phase interaction have been determined for various C1-C4 analytes.

HKUST-1 as an open metal site gas chromatographic stationary phase—capillary preparation, separation of small hydrocarbons and electron donating compounds, determination of thermodynamic data

The development of cyclic preparation techniques based on the application of an SBU (secondary building unit) precursor and a linker solution for the generation of MOF (metal–organic framework) coatings were used to prepare HKUST-1 (Hong Kong University of Science and Technology-1) coated capillary gas-chromatographic columns. As a prerequisite for the conducted preparation of the coatings some optimisation of the procedure for the generation of the MOF material at room temperature was carried out. Beside the demonstration of their general suitability for the separation of permanent gases, the capillaries were used to perform isothermal retention time measurements with analytes possessing electron donating capabilities, such as aromatic or oxygen containing compounds. Since HKUST-1 possesses SBUs with open metal sites, the heat of adsorption and the adsorption entropy were determined to address the question whether or not coordinative contributions may affect the analyte–MOF interaction.

TURBULENCE AND STANDING WAVES IN OSCILLATORY CHEMICAL REACTIONS WITH GLOBAL COUPLING

Using the model of the complex Ginzburg–Landau equation with global coupling, the influence of long‐range interactions on the turbulent state of oscillatory reaction–diffusion systems is investigated. Experimental realizations of such a system are, e.g., oscillatory reactions on single crystal surfaces where some of the phenomena we simulate have been observed experimentally. We find that strong global coupling suppresses turbulence by transforming it into a pattern of standing waves or into uniform oscillations. Weaker global coupling gives rise to an intermittent turbulent state which retains partial synchrony.

Breakdown of global coupling in oscillatory chemical reactions

The effects of global coupling through the gas phase in oscillatory surface chemical reactions are investigated using a model which represents the complex Ginzburg–Landau equation with an additional integral term. Depending on the parameters of the model, global coupling is found to have either a synchronizing or desynchronizing effect. Respectively, the breakdown of global coupling requires the presence of strong supercritical inhomogeneities or spontaneously occurs in a uniform system.

The role of structural changes in the excitation of chemical waves in the system Rh(110)/NO+H2

Previous investigations have demonstrated that the formation of chemical waves in the NO+H2 reaction on Rh(110) involves a cyclic transformation of the surface structure via various N,O-induced reconstructions, i.e., starting form the c(2×6)-O a cycle is initiated comprising the formation of a (2×3)/(3×1)-N and a mixed c(2×4)-2O,N structure. The stability and reactivity of these structures has been investigated in titration experiments as well as under stationary reaction conditions employing LEED, work function, rate measurements, and thermal desorption spectroscopy. It was shown that the c(2×6)-O and c(2×4)-2O,N structures exhibit a low reactivity whereas the (2×1)/(2×1)-N displays only a small to moderate decrease in catalytic activity (≈20%–30%) compared to the clean surface. On the basis of these results, an excitation mechanism for pulses in the NO+H2 reaction on Rh(110) was constructed consisting of the sequence c(2×6)-O, (2×1)/(3×1)-N c(2×4)-2O,N, c(2×6)-O.

Chip calorimetry for fast and reliable evaluation of bactericidal and bacteriostatic treatments of biofilms.

ABSTRACT Chip calorimetry is introduced as a new monitoring tool that provides real-time information about the physiological state of biofilms. Its potential for use for the study of the effects of antibiotics and other biocides was tested. Established Pseudomonas putida biofilms were exposed to substances known to cause toxicity by different mechanisms and to provoke different responses of defense and resistance. The effects of these compounds on heat production rates were monitored and compared with the effects of these compounds on the numbers of CFU and intracellular ATP contents. The real-time monitoring potential of chip calorimetry was successfully demonstrated by using as examples the fast-acting poisons formaldehyde and 2,4-dinitrophenol (DNP). A dosage of antibiotics initially increased the heat production rate. This was discussed as being the effect of energy-dependent resistance mechanisms (e.g., export and/or transformation of the antibiotic). The subsequent reduction in the heat production rate was attributed to the loss of activity and the death of the biofilm bacteria. The shapes of the death curves were in agreement with the assumed variation in the levels of exposure of cells within the multilayer biofilms. The new monitoring tool provides fast, quantitative, and mechanistic insights into the acute and chronic effects of a compound on biofilm activity while requiring only minute quantities of the biocide.

Potentials and limitations of miniaturized calorimeters for bioprocess monitoring.

In theory, heat production rates are very well suited for analysing and controlling bioprocesses on different scales from a few nanolitres up to many cubic metres. Any bioconversion is accompanied by a production (exothermic) or consumption (endothermic) of heat. The heat is tightly connected with the stoichiometry of the bioprocess via the law of Hess, and its rate is connected to the kinetics of the process. Heat signals provide real-time information of bioprocesses. The combination of heat measurements with respirometry is theoretically suited for the quantification of the coupling between catabolic and anabolic reactions. Heat measurements have also practical advantages. Unlike most other biochemical sensors, thermal transducers can be mounted in a protected way that prevents fouling, thereby minimizing response drifts. Finally, calorimetry works in optically opaque solutions and does not require labelling or reactants. It is surprising to see that despite all these advantages, calorimetry has rarely been applied to monitor and control bioprocesses with intact cells in the laboratory, industrial bioreactors or ecosystems. This review article analyses the reasons for this omission, discusses the additional information calorimetry can provide in comparison with respirometry and presents miniaturization as a potential way to overcome some inherent weaknesses of conventional calorimetry. It will be discussed for which sample types and scientific question miniaturized calorimeter can be advantageously applied. A few examples from different fields of microbiological and biotechnological research will illustrate the potentials and limitations of chip calorimetry. Finally, the future of chip calorimetry is addressed in an outlook.

Magnetic resonances in CsCuCl3

Abstract Transmission of mm-wave radiation through single crystals of CsCuCl3 was measured in magnetic fields up to 10 T. The q=0 spinwave gap was found by zero-field resonance in the temperature range between T=2K and TN=10.5K. For T=2K we got for the gap 98.5 GHz. The experimental field dependence of the resonance modes in configurations with the field parallel and perpendicular to the c-axis can be well explained by a simple model of three spinchains whose spins lie in the a,b-plane with 120° angle between one another at zero field. In the framework of our model we can determine the product of interchain exchange field and planar anisotropy field HexHd very accurately.