Using the ion migration in various gel mediums governed by a direct electric field is a well-know... more Using the ion migration in various gel mediums governed by a direct electric field is a well-known technique, especially in analytical chemistry, to separate charged chemical species. This approach is also suitable for generating different-sized crystals and controlling the pattern formation in gels. Here we present a synthesis of zeolitic imidazolate framework-8 in an agarose gel driven by a direct electric field. We investigate the effect of an applied electric current on the macroscopic pattern formed in the gel, morphology, size, and dispersity of the ZIF-8 crystals. Upon increasing the electric current, the average size of the particles and dispersity of the samples decreased along the gel tube from the liquid-gel interface of the anodic side. This trend is opposite to the results obtained in synthesising particles utilizing only diffusion for mass transport. The electric field caused peak-doubling in the X-ray diffraction (XRD) pattern. To support the experimental observations, we developed a reaction-diffusion-migration model, which qualitatively describes the pattern formation observed in experiments.
Reaction Kinetics, Mechanisms and Catalysis, Jan 7, 2022
In the past decade, much effort has been devoted to using chemical clock-type reactions in materi... more In the past decade, much effort has been devoted to using chemical clock-type reactions in material design and driving the self-assembly of various building blocks. Urea-urease enzymatic reaction has chemical pH clock behavior in an unbuffered medium, in which the induction time and the final pH can be programmed by the concentrations of the reagents. The urea-urease reaction can offer a new alternative in material synthesis, where the pH and its course in time are crucial factors in the synthesis. However, before using it in any synthesis method, it is important to investigate the possible effects of the reagents on the enzymatic reaction. Here we investigate the effect of the reagents of the zeolite imidazole framework-8 (zinc ions and 2-methylimidazole) on the urea-urease reaction. We have chosen the zeolite imidazole framework-8 because its formation serves as a model reaction for the formation of other metal-organic frameworks. We found that, besides the inhibition effect of the zinc ions which is well-known in the literature, 2-methylimidazole inhibits the enzymatic reaction as well. In addition to the observed inhibition effect, we report the formation of a hybrid urease-zinc-2-methylimidazole hybrid material. To support the inhibition effect, we developed a kinetic model which reproduced qualitatively the experimentally observed kinetic curves.
Strategies for designing autonomous oscillatory systems have gained much attention in the past fe... more Strategies for designing autonomous oscillatory systems have gained much attention in the past few decades. A broadly accepted and used strategy for the generation of forced oscillations in the originally non-oscillatory subsystems is to couple a pH (driving) oscillator to a pH-sensitive substance (forced oscillatory subsystem) in a one-compartment system. The forced oscillatory subsystem comprises pH-sensitive components, which inevitably generate negative feedback and affect the characteristics of the driving oscillatory system. Here, we present a different approach by separating the driving and forced oscillatory systems into a two-compartment system using a silicone membrane, and the forced oscillations of the absorbance of a pH-sensitive chemical species (methyl red dye) were realized by the transport of carbon dioxide through the membrane generated periodically by the driving pH oscillator. The transported carbon dioxide produced the pH change in the separated compartment by carbon dioxide−hydrogen carbonate−carbonate equilibria and created forced oscillations of a pHsensitive chemical species manifested in the oscillation of its absorbance at a fixed wavelength. This approach avoids any feedback from the forced oscillatory system to the driving system via the cross-membrane transport of the chemical species from the forced to the driving oscillatory system. Additionally, we present that this carbon dioxide coupling to the methyl red dye can be used to estimate the carbon dioxide content in both liquid and gas phases.
Here we show a time-programmed and autonomous synthesis of zeolitic imidazole framework-8 (ZIF-8)... more Here we show a time-programmed and autonomous synthesis of zeolitic imidazole framework-8 (ZIF-8) using a methylene glycolsulfite clock reaction. The induction period of the driving clock reaction, thus, the appearance of the ZIF-8 can be adjusted by the initial concentration of one reagent of the chemical clock. The autonomously synthesized ZIF-8 showed excellent morphology and crystallinity. Metal-organic frameworks (MOFs) are unique 2D or 3D hierarchical porous materials self-assembled from metal cations and organic linkers. 1,2 MOFs have been used in gas storage, 3-5 gas separation, 5,6 chromatography, 7,8 heterogeneous catalysis, 9,10 and targeted drug delivery. 11,12 The recent trend is that various MOFs have been applied in electronic applications since they have special and unique charge transport properties. 13,14 There are several synthetic routes that have been exploited to generate MOF structures. The most robust and firstly developed technique is the solvothermal method, in which metal salts and organic linkers are dissolved in a solvent and mixed in a reactor. The common solvents used include N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), methanol, and acetonitrile. 15-17 The temperature of the synthesis is generally greater than the room temperature. Later, other powerful techniques have been developed such as electrochemical, hydrothermal, mechanochemical, microwave-assisted, and flowdriven routes. 18-22 In the framework of environmental sustainability, there is an increasing demand to develop green synthesis methods to generate high stability and high porosity MOF crystals using water as a solvent. Moreover, an aqueous environment allows to take advantage of the aqueous acid-base chemistry to gain better control over the environmental conditions and would permit to implement smart synthetic routes by employing known autonomous chemical systems. Using these systems (such as clock reactions, enzymatic reactions) to drive the self-assembly of various components and supramolecular gelation has recently gained much interest due to its versatile applicability. 23-30 The main idea in these applications is that the building blocks of the system (such as nanoparticles, polymers, macromolecules) are sensitive to the response generated by the autonomous driving system (pH, redox potential, concentration of the product). 31-34 It should be noted that usually, these driving systems contain harsh (e.g., oxidative) initial reagents and intermediate products that may interfere with the building blocks limiting the applicability of these autonomous systems. 35 Therefore, the application of autonomous chemical reactions in materials synthesis and design remains challenging. However, the application of these reactions may provide two very important benefits for the synthesis. First, the process is autonomous and starts after a given time (induction period) that can be efficiently programmed by adjusting the experimental conditions (concentration of the initial reagents, temperature). This differs from the regular synthesis methods, in which the synthesis starts immediately after mixing the reagents. Secondly, in classical approaches, the experimental factors such as temperature, pH, and solvent composition remain fixed in the course of the synthesis. In chemical clock-type reactions (including autocatalytic and enzymatic reactions) the concentration of the products (for example, the concentration of the hydrogen ions, i.e., pH) and the rate of its change, which drive the synthesis, change continuously in time. The rate of the concentration change in the
The trifluoromethylation of aromatic and heteroaromatic cores has attracted considerable interest... more The trifluoromethylation of aromatic and heteroaromatic cores has attracted considerable interest in recent years due to its pharmacological relevance. We studied the extension of a simple copper-catalyzed trifluoromethylation protocol to alkoxy-substituted iodopyridines and their benzologs. The trifluoromethylation proceeded smoothly in all cases, and the desired compounds were isolated and characterized. In the trifluoromethylation of 3-iodo-4-methoxyquinoline, we observed a concomitant O-N methyl migration, resulting in the trifluoromethylated quinolone as a product. Overall, the described procedure should facilitate the broader use of copper-catalyzed trifluoromethylation in medicinal chemistry.
Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscilla... more Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscillations manifest in the temporal periodic change of one or several physical quantities describing the systems. In chemistry and biology, this physical quantity is the concentration of the chemical species. In most chemical oscillatory systems operating in batch or open reactors, the oscillations persist because of the sophisticated chemical reaction networks incorporating autocatalysis and negative feedback. However, similar oscillations can be generated by periodically changing the environment providing non-autonomous oscillatory systems. Here we present a new strategy for designing a non-autonomous chemical oscillatory system for the zinc–methylimidazole. The oscillations manifested in the periodic change of the turbidity utilizing the precipitation reaction between the zinc ions and 2-methylimidazole (2-met) followed by a partial dissolution of the formed precipitate due to a synergetic...
A methylene glycol–sulfite chemical clock was used to synthesize zeolitic imidazole framework-8 i... more A methylene glycol–sulfite chemical clock was used to synthesize zeolitic imidazole framework-8 in a time-programmed and autonomous way.
In the past decade, much effort has been devoted to using chemical clock-type reactions in materi... more In the past decade, much effort has been devoted to using chemical clock-type reactions in material design and driving the self-assembly of various building blocks. Urea-urease enzymatic reaction has chemical pH clock behavior in an unbuffered medium, in which the induction time and the final pH can be programmed by the concentrations of the reagents. The urea-urease reaction can offer a new alternative in material synthesis, where the pH and its course in time are crucial factors in the synthesis. However, before using it in any synthesis method, it is important to investigate the possible effects of the reagents on the enzymatic reaction. Here we investigate the effect of the reagents of the zeolite imidazole framework-8 (zinc ions and 2-methylimidazole) on the urea-urease reaction. We have chosen the zeolite imidazole framework-8 because its formation serves as a model reaction for the formation of other metal–organic frameworks. We found that, besides the inhibition effect of th...
Strategies for designing autonomous oscillatory systems have gained much attention in the past fe... more Strategies for designing autonomous oscillatory systems have gained much attention in the past few decades. A broadly accepted and used strategy for the generation of forced oscillations in the originally non-oscillatory subsystems is to couple a pH (driving) oscillator to a pH-sensitive substance (forced oscillatory subsystem) in a one-compartment system. The forced oscillatory subsystem comprises pH-sensitive components, which inevitably generate negative feedback and affect the characteristics of the driving oscillatory system. Here, we present a different approach by separating the driving and forced oscillatory systems into a two-compartment system using a silicone membrane, and the forced oscillations of the absorbance of a pH-sensitive chemical species (methyl red dye) were realized by the transport of carbon dioxide through the membrane generated periodically by the driving pH oscillator. The transported carbon dioxide produced the pH change in the separated compartment by c...
The beat in physical systems is a transparent and well-understood phenomenon. It may occur in for... more The beat in physical systems is a transparent and well-understood phenomenon. It may occur in forced oscillatory systems and as a result of the interference of two waves of slightly different frequencies. However, in chemical systems, the realization of the latter type of the beat phenomenon has been lacking. Here we show that a periodic titration of acid and alkaline solutions with each other using programmable syringe pumps in a continuous stirred-tank reactor exhibits the beat phenomenon in the temporal pH oscillation pattern if the time periods of sinusoidal inflow rates of the reagents are slightly different. Interestingly, the frequency of the chemical beat pattern follows the well-known relationship from physics, namely the frequency of the beat is equal to the absolute value of the difference of the two wave frequencies. Based on our strategy, we can design and engineer non-autonomous pH oscillatory systems, in which the characteristics of the temporal oscillations (amplitud...
Using the ion migration in various gel mediums governed by a direct electric field is a well-know... more Using the ion migration in various gel mediums governed by a direct electric field is a well-known technique, especially in analytical chemistry, to separate charged chemical species. This approach is also suitable for generating different-sized crystals and controlling the pattern formation in gels. Here we present a synthesis of zeolitic imidazolate framework-8 in an agarose gel driven by a direct electric field. We investigate the effect of an applied electric current on the macroscopic pattern formed in the gel, morphology, size, and dispersity of the ZIF-8 crystals. Upon increasing the electric current, the average size of the particles and dispersity of the samples decreased along the gel tube from the liquid-gel interface of the anodic side. This trend is opposite to the results obtained in synthesising particles utilizing only diffusion for mass transport. The electric field caused peak-doubling in the X-ray diffraction (XRD) pattern. To support the experimental observations, we developed a reaction-diffusion-migration model, which qualitatively describes the pattern formation observed in experiments.
Reaction Kinetics, Mechanisms and Catalysis, Jan 7, 2022
In the past decade, much effort has been devoted to using chemical clock-type reactions in materi... more In the past decade, much effort has been devoted to using chemical clock-type reactions in material design and driving the self-assembly of various building blocks. Urea-urease enzymatic reaction has chemical pH clock behavior in an unbuffered medium, in which the induction time and the final pH can be programmed by the concentrations of the reagents. The urea-urease reaction can offer a new alternative in material synthesis, where the pH and its course in time are crucial factors in the synthesis. However, before using it in any synthesis method, it is important to investigate the possible effects of the reagents on the enzymatic reaction. Here we investigate the effect of the reagents of the zeolite imidazole framework-8 (zinc ions and 2-methylimidazole) on the urea-urease reaction. We have chosen the zeolite imidazole framework-8 because its formation serves as a model reaction for the formation of other metal-organic frameworks. We found that, besides the inhibition effect of the zinc ions which is well-known in the literature, 2-methylimidazole inhibits the enzymatic reaction as well. In addition to the observed inhibition effect, we report the formation of a hybrid urease-zinc-2-methylimidazole hybrid material. To support the inhibition effect, we developed a kinetic model which reproduced qualitatively the experimentally observed kinetic curves.
Strategies for designing autonomous oscillatory systems have gained much attention in the past fe... more Strategies for designing autonomous oscillatory systems have gained much attention in the past few decades. A broadly accepted and used strategy for the generation of forced oscillations in the originally non-oscillatory subsystems is to couple a pH (driving) oscillator to a pH-sensitive substance (forced oscillatory subsystem) in a one-compartment system. The forced oscillatory subsystem comprises pH-sensitive components, which inevitably generate negative feedback and affect the characteristics of the driving oscillatory system. Here, we present a different approach by separating the driving and forced oscillatory systems into a two-compartment system using a silicone membrane, and the forced oscillations of the absorbance of a pH-sensitive chemical species (methyl red dye) were realized by the transport of carbon dioxide through the membrane generated periodically by the driving pH oscillator. The transported carbon dioxide produced the pH change in the separated compartment by carbon dioxide−hydrogen carbonate−carbonate equilibria and created forced oscillations of a pHsensitive chemical species manifested in the oscillation of its absorbance at a fixed wavelength. This approach avoids any feedback from the forced oscillatory system to the driving system via the cross-membrane transport of the chemical species from the forced to the driving oscillatory system. Additionally, we present that this carbon dioxide coupling to the methyl red dye can be used to estimate the carbon dioxide content in both liquid and gas phases.
Here we show a time-programmed and autonomous synthesis of zeolitic imidazole framework-8 (ZIF-8)... more Here we show a time-programmed and autonomous synthesis of zeolitic imidazole framework-8 (ZIF-8) using a methylene glycolsulfite clock reaction. The induction period of the driving clock reaction, thus, the appearance of the ZIF-8 can be adjusted by the initial concentration of one reagent of the chemical clock. The autonomously synthesized ZIF-8 showed excellent morphology and crystallinity. Metal-organic frameworks (MOFs) are unique 2D or 3D hierarchical porous materials self-assembled from metal cations and organic linkers. 1,2 MOFs have been used in gas storage, 3-5 gas separation, 5,6 chromatography, 7,8 heterogeneous catalysis, 9,10 and targeted drug delivery. 11,12 The recent trend is that various MOFs have been applied in electronic applications since they have special and unique charge transport properties. 13,14 There are several synthetic routes that have been exploited to generate MOF structures. The most robust and firstly developed technique is the solvothermal method, in which metal salts and organic linkers are dissolved in a solvent and mixed in a reactor. The common solvents used include N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), methanol, and acetonitrile. 15-17 The temperature of the synthesis is generally greater than the room temperature. Later, other powerful techniques have been developed such as electrochemical, hydrothermal, mechanochemical, microwave-assisted, and flowdriven routes. 18-22 In the framework of environmental sustainability, there is an increasing demand to develop green synthesis methods to generate high stability and high porosity MOF crystals using water as a solvent. Moreover, an aqueous environment allows to take advantage of the aqueous acid-base chemistry to gain better control over the environmental conditions and would permit to implement smart synthetic routes by employing known autonomous chemical systems. Using these systems (such as clock reactions, enzymatic reactions) to drive the self-assembly of various components and supramolecular gelation has recently gained much interest due to its versatile applicability. 23-30 The main idea in these applications is that the building blocks of the system (such as nanoparticles, polymers, macromolecules) are sensitive to the response generated by the autonomous driving system (pH, redox potential, concentration of the product). 31-34 It should be noted that usually, these driving systems contain harsh (e.g., oxidative) initial reagents and intermediate products that may interfere with the building blocks limiting the applicability of these autonomous systems. 35 Therefore, the application of autonomous chemical reactions in materials synthesis and design remains challenging. However, the application of these reactions may provide two very important benefits for the synthesis. First, the process is autonomous and starts after a given time (induction period) that can be efficiently programmed by adjusting the experimental conditions (concentration of the initial reagents, temperature). This differs from the regular synthesis methods, in which the synthesis starts immediately after mixing the reagents. Secondly, in classical approaches, the experimental factors such as temperature, pH, and solvent composition remain fixed in the course of the synthesis. In chemical clock-type reactions (including autocatalytic and enzymatic reactions) the concentration of the products (for example, the concentration of the hydrogen ions, i.e., pH) and the rate of its change, which drive the synthesis, change continuously in time. The rate of the concentration change in the
The trifluoromethylation of aromatic and heteroaromatic cores has attracted considerable interest... more The trifluoromethylation of aromatic and heteroaromatic cores has attracted considerable interest in recent years due to its pharmacological relevance. We studied the extension of a simple copper-catalyzed trifluoromethylation protocol to alkoxy-substituted iodopyridines and their benzologs. The trifluoromethylation proceeded smoothly in all cases, and the desired compounds were isolated and characterized. In the trifluoromethylation of 3-iodo-4-methoxyquinoline, we observed a concomitant O-N methyl migration, resulting in the trifluoromethylated quinolone as a product. Overall, the described procedure should facilitate the broader use of copper-catalyzed trifluoromethylation in medicinal chemistry.
Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscilla... more Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscillations manifest in the temporal periodic change of one or several physical quantities describing the systems. In chemistry and biology, this physical quantity is the concentration of the chemical species. In most chemical oscillatory systems operating in batch or open reactors, the oscillations persist because of the sophisticated chemical reaction networks incorporating autocatalysis and negative feedback. However, similar oscillations can be generated by periodically changing the environment providing non-autonomous oscillatory systems. Here we present a new strategy for designing a non-autonomous chemical oscillatory system for the zinc–methylimidazole. The oscillations manifested in the periodic change of the turbidity utilizing the precipitation reaction between the zinc ions and 2-methylimidazole (2-met) followed by a partial dissolution of the formed precipitate due to a synergetic...
A methylene glycol–sulfite chemical clock was used to synthesize zeolitic imidazole framework-8 i... more A methylene glycol–sulfite chemical clock was used to synthesize zeolitic imidazole framework-8 in a time-programmed and autonomous way.
In the past decade, much effort has been devoted to using chemical clock-type reactions in materi... more In the past decade, much effort has been devoted to using chemical clock-type reactions in material design and driving the self-assembly of various building blocks. Urea-urease enzymatic reaction has chemical pH clock behavior in an unbuffered medium, in which the induction time and the final pH can be programmed by the concentrations of the reagents. The urea-urease reaction can offer a new alternative in material synthesis, where the pH and its course in time are crucial factors in the synthesis. However, before using it in any synthesis method, it is important to investigate the possible effects of the reagents on the enzymatic reaction. Here we investigate the effect of the reagents of the zeolite imidazole framework-8 (zinc ions and 2-methylimidazole) on the urea-urease reaction. We have chosen the zeolite imidazole framework-8 because its formation serves as a model reaction for the formation of other metal–organic frameworks. We found that, besides the inhibition effect of th...
Strategies for designing autonomous oscillatory systems have gained much attention in the past fe... more Strategies for designing autonomous oscillatory systems have gained much attention in the past few decades. A broadly accepted and used strategy for the generation of forced oscillations in the originally non-oscillatory subsystems is to couple a pH (driving) oscillator to a pH-sensitive substance (forced oscillatory subsystem) in a one-compartment system. The forced oscillatory subsystem comprises pH-sensitive components, which inevitably generate negative feedback and affect the characteristics of the driving oscillatory system. Here, we present a different approach by separating the driving and forced oscillatory systems into a two-compartment system using a silicone membrane, and the forced oscillations of the absorbance of a pH-sensitive chemical species (methyl red dye) were realized by the transport of carbon dioxide through the membrane generated periodically by the driving pH oscillator. The transported carbon dioxide produced the pH change in the separated compartment by c...
The beat in physical systems is a transparent and well-understood phenomenon. It may occur in for... more The beat in physical systems is a transparent and well-understood phenomenon. It may occur in forced oscillatory systems and as a result of the interference of two waves of slightly different frequencies. However, in chemical systems, the realization of the latter type of the beat phenomenon has been lacking. Here we show that a periodic titration of acid and alkaline solutions with each other using programmable syringe pumps in a continuous stirred-tank reactor exhibits the beat phenomenon in the temporal pH oscillation pattern if the time periods of sinusoidal inflow rates of the reagents are slightly different. Interestingly, the frequency of the chemical beat pattern follows the well-known relationship from physics, namely the frequency of the beat is equal to the absolute value of the difference of the two wave frequencies. Based on our strategy, we can design and engineer non-autonomous pH oscillatory systems, in which the characteristics of the temporal oscillations (amplitud...
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Papers by Norbert Német