ABSTRACT
Microelectrode arrays are commonly used to study the electrophysiological behavior of cells. Recently, there has been a growing interest in fabricating three-dimensional microelectrode arrays. Here, we present a novel process for the fast fabrication of epoxy-based 3D microelectrode array platforms with the assistance of laser-patterning technology. To this end, we photopatterned 3D pillars as scaffolds using epoxy-based dry films. Electrodes and conductor traces were fabricated by laser patterning of sputtered platinum films on top of the 3D structures, followed by deposition of parylene-C for insulation. Microelectrodes at the tip of the 3D structures were exposed using a vertical laser ablation process. The final electrodes demonstrated a low impedance of â¼10 kΩ at 1 kHz in electrochemical impedance spectroscopy measurements under physiological conditions. We investigated the maximum compression force of the 3D structures, which could withstand approximately 0.6 N per pillar. The 3D microelectrode arrays were used to record extracellular signals from HL-1 cells in culture as a proof of principle. Our results show regular firing of action potentials recorded at the tip of the 3D structures, demonstrating the possibility of recording cell signals in non-planar environments.
ABSTRACT
An electrochemical (EC) sensor based on metalloporphyrin metal-organic framework (MOF) for the detection of parathion-methyl (PM) has been developed. The prepared MOF-525(Fe) exhibits great signal enhancement toward the electrochemical detection of PM owing to its unique structural properties and electrochemical activities. Under optimal experimental conditions, the as-prepared MOF-525(Fe) based EC sensor exhibited excellent PM sensing performance with a wide linear detection range (0.1 µM-100 µM) and low limit of detection (LOD, 1.4 nM). Compared to its corresponding Fe metalloporphyrin (linker), MOF-525(Fe) exhibited a superior sensitivity (28.31 µA cm-2·µM-1), which is 3.7 times higher than the sensitivity of FeTCPP linker (7.56 µA cm-2·µM-1) towards PM. The improved performance is associated with the high specific surface area and the large pore channels of MOF-525(Fe) facilitating a better interaction between PM and the Fe metalloporphyrin active sites, especially in the lower concentration range. Moreover, a possible affinity of the PM molecules toward Zr6 clusters may also contribute to the selective enrichment of PM on MOF-525(Fe). This EC sensor further demonstrated high selectivity in the presence of interfering molecules. The recovery results further confirm accurate PM sensing in actual samples, which suggests promising applications for the rapid detection of environmental organophosphates by metalloporphyrin MOFs.
Subject(s)
Biosensing Techniques , Electrochemical Techniques , Limit of Detection , Metal-Organic Frameworks , Metalloporphyrins , Methyl Parathion , Zirconium , Metal-Organic Frameworks/chemistry , Electrochemical Techniques/methods , Biosensing Techniques/methods , Metalloporphyrins/chemistry , Zirconium/chemistry , Methyl Parathion/analysisABSTRACT
Reaction of neutral olefin complexes of ruthenium and molybdenum with GaTMP (TMP = 2,2,6,6-tetramethylpiperidinyl) by substitution leads to the formation of respective five- and six-coordinated homoleptic products. [Ru(GaTMP)5] (1) and [Mo(GaTMP)6] (2) were isolated and characterized. Core structure geometries were analyzed using continuous shape measure, and the complexes were subjected to DFT calculations unveiling competing π-interactions between the transition metal center and the amido substituent with the unoccupied pπ orbitals of the gallium.
ABSTRACT
Key strategies in cluster synthesis include the use of modulating agents (e.g., coordinating additives). We studied the influence of various phosphines exhibiting different steric and electronic properties on the reduction of the Au(I) precursor to Au(0) clusters. We report a synthesis of the bimetallic clusters [Au6(AlCp*)6] = [Au6Al6](Cp*)6 (1) and [HAu7(AlCp*)6] = [HAu7Al6](Cp*)6 (2) (Cp* = pentamethylcyclopentadiene) using Au(I) precursors and AlCp*. The cluster [Au2(AlCp*)5] = [Au2Al5](Cp*)5 (3) was isolated and identified as an intermediate species in the reactions to 1 and 2. The processes of cluster growth and degradation were investigated by in situ 1H NMR and LIFDI-MS techniques. The structures of 1 and 2 were established by DFT geometry optimization. These octahedral clusters can both be described as closed-shell 18-electron superatoms.
ABSTRACT
Poorly selective mixed-metal cluster synthesis and separation yield reaction solutions of inseparable intermetalloid cluster mixtures, which are often discarded. High-resolution mass spectrometry, however, can provide precise compositional data of such product mixtures. Structure assignments can be achieved by advanced computational screening and consideration of the complete structural space. Here, we experimentally verify structure and composition of a whole cluster ensemble by combining a set of spectroscopic techniques. Our study case are the very similar nickel/gallium clusters of M12, M13 and M14 core composition Ni6+xGa6+y (x + y ≤ 2). The rationalization of structure, bonding and reactivity is built upon the organometallic superatom cluster [Ni6Ga6](Cp*)6 = [Ga6](NiCp*)6 (1; Cp* = C5Me5). The structural conclusions are validated by reactivity tests using carbon monoxide, which selectively binds to Ni sites, whereas (triisopropylsilyl)acetylene selectively binds to Ga sites.
ABSTRACT
Porphyrin-based metal-organic frameworks (MOFs) are attractive materials for photo- and thermally activated catalysis due to their unique structural features related to the porphyrin moiety, guest-accessible porosity, and high chemical tunability. In this study, we report the synthetic incorporation of nonplanar ß-ethyl-functionalized porphyrin linkers into the framework structure of PCN-222, obtaining a solid-solution series of materials with different modified linker contents. Comprehensive analysis by a combination of characterization techniques, such as NMR, UV-vis and IR spectroscopy, powder X-ray diffraction, and N2 sorption analysis, allows for the confirmation of linker incorporation. A detailed structural analysis of intrinsic material properties, such as the thermal response of the different materials, underlines the complexity of synthesizing and understanding such materials. This study presents a blueprint for synthesizing and analyzing porphyrin-based mixed-linker MOF systems and highlights the hurdles of characterizing such materials.
ABSTRACT
Three new coordination polymers (CPs) constructed from the linker 1,4-di(dithiocarboxylate) (BDDTC2-)âthe sulfur-analog of 1,4-benzenedicarboxylate (BDC2-)âtogether with Mn-, Zn-, and Fe-based inorganic SBUs are reported with description of their structural and electronic properties. Single-crystal X-ray diffraction revealed structural diversity ranging from one-dimensional chains in [Mn(BDDTC)(DMF)2] (1) to two-dimensional (2D) honeycomb sheets observed for [Zn2(BDDTC)3][Zn(DMF)5(H2O)] (2). Gas adsorption experiments confirmed a 3D porous structure for the mixed-valent material [Fe2(BDDTC)2(OH)] (3). 3 contains a 1:1 ratio of Fe2+/3+ ions, as evidenced by 57Fe Mössbauer, X-band EPR, and X-ray absorption spectroscopy. Its empirical formula was established by elemental analysis, thermal gravimetric analysis, infrared vibrational spectroscopy, and X-ray absorption spectroscopy in lieu of elusive single-crystal X-ray diffraction data. In contrast to the Mn- and Zn-based compounds 1 and 2, the Fe2+/3+ CP 3 showed remarkably high electrical conductivity of 5 × 10-3 S cm-1 (according to van der Pauw measurements), which is within the range of semiconducting materials. Overall, our study confirms that sulfur derivatives of typical carboxylate linkers (e.g., BDC) are suitable for the construction of electrically conducting CPs, due to acceptedly higher covalency in metal-ligand bonding compared to the electrically insulating carboxylate CPs or metal-organic frameworks. At the same time, the direct comparison between insulating CPs 1 and 2 with CP 3 emphasizes that the electronic structure of the metal is likewise a crucial aspect to construct electrically conductive materials.
ABSTRACT
The forthcoming generation of materials, including artificial muscles, recyclable and healable systems, photochromic heterogeneous catalysts, or tailorable supercapacitors, relies on the fundamental concept of rapid switching between two or more discrete forms in the solid state. Herein, we report a breakthrough in the "speed limit" of photochromic molecules on the example of sterically-demanding spiropyran derivatives through their integration within solvent-free confined space, allowing for engineering of the photoresponsive moiety environment and tailoring their photoisomerization rates. The presented conceptual approach realized through construction of the spiropyran environment results in ~1000 times switching enhancement even in the solid state compared to its behavior in solution, setting a record in the field of photochromic compounds. Moreover, integration of two distinct photochromic moieties in the same framework provided access to a dynamic range of rates as well as complementary switching in the material's optical profile, uncovering a previously inaccessible pathway for interstate rapid photoisomerization.
ABSTRACT
Covalent hybrids of graphene and metal-organic frameworks (MOFs) hold immense potential in various technologies, particularly catalysis and energy applications, due to the advantageous combination of conductivity and porosity. The formation of an amide bond between carboxylate-functionalized graphene acid (GA) and amine-functionalized UiO-66-NH2 MOF (Zr6O4(OH)4(NH2-bdc)6, with NH2-bdc2- = 2-amino-1,4-benzenedicarboxylate and UiO = Universitetet i Oslo) is a highly efficient strategy for creating such covalent hybrids. Previous experimental studies have demonstrated exceptional properties of these conductive networks, including significant surface area and functionalized hierarchical pores, showing promise as a chemiresistive CO2 sensor and electrode materials for asymmetric supercapacitors. However, the molecular-level origin of the covalent linkages between pristine MOF and GA layers remains unclear. In this study, density functional theory (DFT) calculations were conducted to elucidate the mechanism of amide bond formation between GA and UiO-66-NH2. The theoretical calculations emphasize the crucial role of zirconium within UiO-66, which acts as a catalyst in the reaction cycle. Both commonly observed hexa-coordinated and less common hepta-coordinated zirconium complexes are considered as intermediates. By gaining detailed insights into the binding interactions between graphene derivatives and MOFs, strategies for tailored syntheses of such nanocomposite materials can be developed.
ABSTRACT
Late dinuclear transition-metal (especially group 10 and 11) homoleptic carbonyl complexes are elusive species and have so far not been isolated. A typical example is the 30-electron species [Ni2(CO)5], the structure and bonding of which is still debated. We show that, by using the AlCp* ligand (isolobal to CO), it is possible to isolate and fully characterize [Ni2(AlCp*)5] (1), which inspired us to revisit by DFT calculations, the bonding situation within [Ni2L5] (L = CO, AlCp*) and other isoelectronic species. The short Ni-Ni X-ray distance in 1 (2.270 Å) should not be attributed to the existence of a typical localized triple-bond between the metals, but rather to a strong through-bond interaction involving the three bridging ligands via their donating lone pairs and accepting π* orbitals. In contrast, in the isostructural 32-electron [Au2(AlCp*)5] (2) cluster an orbital with M-M antibonding and Al...Al bonding character is occupied, which is in accordance with the particularly long Au-Au distance (3.856 Å) and rather short Al...Al contacts between the bridging ligands (2.843 Å). This work shows that, unlike late transition-metal [M2(CO)x] species, stable [M2(AlCp*)x] complexes can be isolated, owing to the subtle differences between CO and AlCp*. We propose a similar approach for rationalizing the bonding in the emblematic 34 electron species [Fe2(CO)9].
ABSTRACT
Irradiation of [Ru(GaCp*)3(SiEt3)H3] (1) at 350 nm induces reductive elimination of dihydrogen and triethylsilane and generates unsaturated Ru/Ga species. This photochemically induced cascading reductive elimination processes generate the reactive intermediate [Ru(GaCp*)3], which can be trapped by diphosphine coordination to yield the stable complex [(dppe)Ru(GaCp*)3] (4). The photochemically generated RuGa3 species is catalytically active in the hydrogenation of alkynes, which is further investigated by 1H NMR and mass spectrometry. Formation of intermetallic Ru/Ga clusters is observed as a competing and for the catalytic activity of the species limiting side reaction.
ABSTRACT
Cooperative behavior and orthogonal responses of two classes of coordinatively integrated photochromic molecules towards distinct external stimuli were demonstrated on the first example of a photo-thermo-responsive hierarchical platform. Synergetic and orthogonal responses to temperature and excitation wavelength are achieved by confining the stimuli-responsive moieties within a metal-organic framework (MOF), leading to the preparation of a novel photo-thermo-responsive spiropyran-diarylethene based material. Synergistic behavior of two photoswitches enables the study of stimuli-responsive resonance energy transfer as well as control of the photoinduced charge transfer processes, milestones required to advance optoelectronics development. Spectroscopic studies in combination with theoretical modeling revealed a nonlinear effect on the material electronic structure arising from the coordinative integration of photoresponsive molecules with distinct photoisomerization mechanisms. Thus, the reported work covers multivariable facets of not only fundamental aspects of photoswitch cooperativity, but also provides a pathway to modulate photophysics and electronics of multidimensional functional materials exhibiting thermo-photochromism.
ABSTRACT
The bimetallic, decanuclear Ni3 Ga7 -cluster of the formula [Ni3 (GaTMP)3 (µ2 -GaTMP)3 (µ3 -GaTMP)] (1, TMP=2,2,6,6-tetramethylpiperidinyl) reacts reversibly with dihydrogen under the formation of a series of (poly-)hydride clusters 2. Low-temperature 2D NMR experiments at -80 °C show that 2 consist of a mixture of a di- (2Di ), tetra- (2Tetra ) and hexahydride species (2Hexa ). The structures of 2Di and 2Tetra are assessed by a combination of 2D NMR spectroscopy and DFT calculations. The cooperation of both metals is essential for the high hydrogen uptake of the cluster. Polyhydrides 2 are catalytically active in the semihydrogenation of 4-octyne to 4-octene with good selectivity. The example is the first of its kind and conceptually relates properties of molecular, atom-precise transition metal/main group metal clusters to the respective solid-state phase in catalysis.
ABSTRACT
Leveraging size effects, nanoparticles of metal-organic frameworks, nanoMOFs, have recently gained traction, amplifying their scopes in electrochemical sensing. However, their synthesis, especially under eco-friendly ambient conditions remains an unmet challenge. Herein, an ambient and fast secondary building unit (SBU)-assisted synthesis (SAS) route to afford a prototypal porphyrinic MOF, Fe-MOF-525 is introduced. Albeit the benign room temperature conditions, Fe-MOF-525(SAS) nanocrystallites obtained are of ≈30 nm size, relatively smaller than the ones conventional solvothermal methods elicit. Integrating Fe-MOF-525(SAS) as a thin film on a conductive indium tin oxide (ITO) surface affords Fe-MOF-525(SAS)/ITO, an electrochemical biosensor. Synergistic confluence of modular MOF composition, analyte-specific redox metalloporphyrin sites, and crystal downsizing contribute to its benchmark voltammetric uric acid (UA) sensing. Showcasing a wide linear range of UA detection with high sensitivity and low detection limit, this SAS strategy coalesces ambient condition synthesis and nanoparticle size control, paving a green way to advanced sensors.
Subject(s)
Biosensing Techniques , Metal Nanoparticles , Metal-Organic Frameworks , Benchmarking , Temperature , Electrochemical Techniques/methods , Metal-Organic Frameworks/chemistry , Metal Nanoparticles/chemistry , Biosensing Techniques/methodsABSTRACT
Flexible porous frameworks are at the forefront of materials research. A unique feature is their ability to open and close their pores in an adaptive manner induced by chemical and physical stimuli. Such enzyme-like selective recognition offers a wide range of functions ranging from gas storage and separation to sensing, actuation, mechanical energy storage and catalysis. However, the factors affecting switchability are poorly understood. In particular, the role of building blocks, as well as secondary factors (crystal size, defects, cooperativity) and the role of host-guest interactions, profit from systematic investigations of an idealized model by advanced analytical techniques and simulations. The review describes an integrated approach targeting the deliberate design of pillared layer metal-organic frameworks as idealized model materials for the analysis of critical factors affecting framework dynamics and summarizes the resulting progress in their understanding and application.
ABSTRACT
The advances made in the field of stimuli-responsive catalysis during the last five years with a focus on the novel recently-emerged directions and applications have been surveyed. Metal-free catalysts and organometallic complexes, as well as biomimetic systems and extended structures, which display switchable catalytic activity for a variety of organic transformations, are discussed. Light-activated systems comprised of photochromic molecules capable of modulating reaction rate, yield, or enantioselectivity based on geometric and electronic changes associated with photoisomerization are the focus of the detailed discussion. Alternative stimuli, including pH and temperature, which could be applied either alone or in combination with light, are also addressed. Recent advances clearly demonstrate that the capability to finely tune catalyst behavior via an external stimulus is a powerful tool that could alter the landscape of sustainable chemistry.
ABSTRACT
Syngas, a mixture of CO and H2 , is a high-priority intermediate for producing several commodity chemicals, e.g., ammonia, methanol, and synthetic hydrocarbon fuels. Accordingly, parallel sunlight-driven catalytic conversion of CO2 and protons to syngas is a key step toward a sustainable energy cycle. State-of-the-art catalytic systems and materials often fall short as application-oriented concurrent CO and H2 evolution requires challenging reaction conditions which can hamper stability, selectivity, and efficiency. Here a light-harvesting metal-organic framework hosting two molecular catalysts is engineered to yield colloidal, water-stable, versatile nanoreactors for photocatalytic syngas generation with highly controllable product ratios. In-depth fluorescence, X-ray, and microscopic studies paired with kinetic analysis show that the host delivers energy efficiently to active sites, conceptually yielding nanozymes. This unlocked sustained CO2 reduction and H2 evolution with benchmark turnover numbers and record incident photon conversions up to 36%, showcasing a highly active and durable all-in-one material toward application in solar energy-driven syngas generation.
ABSTRACT
Atomic-scale magnetic field sensors based on nitrogen vacancy (NV) defects in diamonds are an exciting platform for nanoscale nuclear magnetic resonance (NMR) spectroscopy. The detection of NMR signals from a few zeptoliters to single molecules or even single nuclear spins has been demonstrated using NV centers close to the diamond surface. However, fast molecular diffusion of sample molecules in and out of the nanoscale detection volumes impedes their detection and limits current experiments to solid-state or highly viscous samples. Here, we show that restricting diffusion by confinement enables nanoscale NMR spectroscopy of liquid samples. Our approach uses metal-organic frameworks (MOF) with angstrom-sized pores on a diamond chip to trap sample molecules near the NV centers. This enables the detection of NMR signals from a liquid sample, which would not be detectable without confinement. These results set the route for nanoscale liquid-phase NMR with high spectral resolution.
Subject(s)
Metal-Organic Frameworks , Nitrogen/chemistry , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Imaging , Diamond/chemistryABSTRACT
Metal active sites and sufficient porosity in metal-organic frameworks (MOFs) are crucial parameters determining the performances of catalysis, guest molecule adsorption, etc. Herein, through inâ situ introduction of Ru sites with different levels to Cu-BTC structure together with post-synthetic activation at 180 °C, a series of hierarchically porous CuRu-BTC (HP-CuRu-BTC) MOFs were obtained. Besides, selective thermal decomposition (STD) treatment was carried out at 240 °C to further tune the hierarchical pores and metal sites, yielding rare case of metal nanoparticles (NPs)@HP-CuRu-BTC composites. After full characterization by XRD, N2 physisorption, SEM, ICP and XPS, these HP-CuRu-BTC and NPs@HP-CuRu-BTC samples possess high surface area (682-1199â m2 g-1 ), hierarchical pores and highly distributed metal sites with reduced oxidation states (Cu+ and Ru2+ ), indicating regulation of both metal sites and hierarchical pores. The HP-CuRu-BTC and NPs@HP-CuRu-BTC were further employed as catalysts for the heterogeneous styrene oxidation reaction under mild condition. Compared to microporous Cu-BTC with unary metal component, HP-CuRu-BTC-3 and NPs@HP-CuRu-BTC-3 exhibited more than 2 times higher styrene conversion after 7â hours reaction under same condition.