Pyrene Linkers Research Articles

Quantitative Mid‐Infrared Plasmonic Biosensing on Scalable Graphene Nanostructures

AbstractGraphene nanostructures, exhibiting tunable and nanoscale‐confined mid‐infrared (mid‐IR) plasmons, prevail as a powerful spectroscopic platform for novel surface‐enhanced molecular identification. Particularly, graphene shows exciting opportunities for biosensing applications due to its versatile functionalization methods with different biomolecular building blocks (e.g., enzymes, proteins, and DNA). Here, a quantitative bioassay based on the mid‐IR localized surface plasmon resonance (LSPR) modulation in functionalized graphene nanostructures is demonstrated. Specifically, vitamin B12 (vB12) using the specific recognition elements on modified graphene nanoribbons (i.e., pyrene linkers via π − π stacking + anti‐vB12 antibody fragments via amide bond) is detected. Different concentrations of vB12 spotted on an arrayed panel of a single chip are quantified by the graphene LSPR shifts, where a limit of detection (LOD) of 53.5 ng mL−1 is obtained. The upscaling potential of the bioassay using large area nanostructured graphene films produced by nanoimprinting 2D hole arrays is illustrated. The integration of quantitative bioassay with scalable graphene nanostructures shows promising routes of graphene‐based mid‐IR platforms toward prospective industrial applications.

An iron-porphyrin grafted metal–organic framework as a heterogeneous catalyst for the photochemical reduction of CO2

Photocatalytic reduction of carbon dioxide (CO2) into value-added carbon products is a promising strategy for dealing with carbon emission. Selected metal–organic frameworks (MOFs) have been shown promise in photocatalytic CO2 reduction owing to their photochemical activity and structural modularity. Here, we take advantage of displaceable nonstructural ligands on the nodes of a pyrene-based MOF, NU-1000, to graft a molecular catalyst, tetra(4-carboxyphenyl) porphyrin iron (III) chloride (Fe-TCPP). The pyrene linkers in the MOF absorb photons and transfer electrons to the porphyrin catalyst, resulting in a self-contained photocatalyst. The obtained Fe-TCPP@NU-1000 heterogeneous catalysts exhibit activity for CO2 photoreduction under illumination at 390 nm, with a TON for CO of 22 in 2 h. Molecular hydrogen is co-evolved. Leaching of the grafted catalyst from the MOF ultimately limits performance.

Precise Spatial‐Designed Metal‐Organic‐Framework Nanosheets for Efficient Energy Transfer and Photocatalysis

AbstractHigh‐efficiency photocatalysis in metal‐organic frameworks (MOF) and MOF nanosheets (NSs) are often limited by their short‐lived charge separation as well as self‐quenching. Here, we propose to use the energy‐transfer process (EnT) to increase charge separation, thus enhancing the catalytic performance of a series of MOF NSs. With the use of NS, the photocatalyst can also be well isolated to reduce self‐quenching. Tetrakis(4‐carboxyphenyl) porphyrin (H4TCPP) and 1,3,6,8‐tetrakis(p‐benzoic acid)pyrene (H4TBAPy) linkers were chosen as the acceptor and donor moieties, respectively. Accounting for the precise spatial design afforded by the MOF NSs, the donor and acceptor moieties could be closely positioned on the NSs, allowing for an efficient EnT process as well as a high degree of site isolation. Two templates, donor‐on‐acceptor NS and acceptor‐on‐donor NS catalysts, were successfully synthesized, and the results show that the second one has much enhanced catalytic performances over the first one due to site‐isolated active photocatalysts.

Precise Spatial-Designed Metal-Organic-Framework Nanosheets for Efficient Energy Transfer and Photocatalysis.

High-efficiency photocatalysis in metal-organic frameworks (MOF) and MOF nanosheets (NSs) are often limited by their short-lived charge separation as well as self-quenching. Here, we propose to use the energy-transfer process (EnT) to increase charge separation, thus enhancing the catalytic performance of a series of MOF NSs. With the use of NS, the photocatalyst can also be well isolated to reduce self-quenching. Tetrakis(4-carboxyphenyl) porphyrin (H4 TCPP) and 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4 TBAPy) linkers were chosen as the acceptor and donor moieties, respectively. Accounting for the precise spatial design afforded by the MOF NSs, the donor and acceptor moieties could be closely positioned on the NSs, allowing for an efficient EnT process as well as a high degree of site isolation. Two templates, donor-on-acceptor NS and acceptor-on-donor NS catalysts, were successfully synthesized, and the results show that the second one has much enhanced catalytic performances over the first one due to site-isolated active photocatalysts.

Coordination driven self-assembly of donor-acceptor linkers in 3D supramolecular frameworks: Ground state charge transfer and tunable porosity

We report the synthesis, structural characterization and photophysical properties of two 3D supramolecular architectures formed by the coordination driven self-assembly of pyrene and Schiff base linkers, as a donor-acceptor (D-A) pair. The monotopic functionality of the pyrene (as pyrenemonocarboxylic acid and pyrenebutyric acid) and ditopic Schiff base with Cd2+ render 1D coordination polymers (CPs), which are interdigitated via non-covalent interactions to form 3D supramolecular frameworks. The pyrenemonocarboxylic acid containing CP forms a dense structure, while the pyrenebutyric acid containing CP is porous and dynamic, as confirmed by the gas and solvent vapour adsorption experiments. Structural insight from the X-ray crystal structures and photophysical characterizations of the CPs reveal that pyrene and Schiff base form a stable charge transfer (CT) state. The variable alkyl chain lengths of the pyrene linkers tune the porosity, however, allow strong π-π and C–H-π interactions among the D-A units rendering facile CT, as confirmed by EPR and DFT calculations.

Pyrenyl Carbon Nanotubes for Covalent Bilirubin Oxidase Biocathode Design: Should the Nanotubes be Carboxylated?

Understanding the characteristics of nanomaterials in the context of electrode designs for bio-electrocatalysis is an emerging research direction. Applications for fuel cells, batteries, and biosensors are directly benefited. The objective of this study is to understand the influence of unfunctionalized multiwalled carbon nanotubes (MWNT) in comparison to carboxylated nanotubes (MWNT–COOH) for pi-pi stacking with 1-pyrenebutyric acid (Py) and covalent immobilization of bilirubin oxidase (BOD) enzyme toward the resulting oxygen reduction currents. We designed pyrolytic graphite-edge electrodes modified with MWNT/Py, MWNT–COOH/Py, or only MWNT–COOH for carbodiimide activation and BOD immobilization. The relative increase in surface –COOH groups as we move from MWNT to MWNT/Py to MWNT–COOH/Py modification is voltammetrically estimated. Although the MWNT–COOH/Py displayed the highest relative amount of surface −COOH groups, the oxygen reduction current was the largest for the BOD-immobilized MWNT/Py electrode than others. Results indicate that unfunctionalized MWNT is the optimal choice for pi-pi stacking with pyrene linkers and covalent BOD immobilization as biocathode for direct electrocatalysis with high current densities. Favorable hydrophobic MWNT surface to interact more closely with the electron-receiving T1 Cu site of BOD, as opposed to the relatively polar and more defective MWNT–COOH material due to functionalization, is suggested to be one of the underlying factors for the observed electrocatalytic trend.

Protein Detection using Quadratic Fit Analysis Near Dirac Point of Graphene Field Effect Biosensors.

Although graphene-based biosensors provid extreme sensitivity for the detection of atoms, gases, and biomolecules, the specificity of graphene biosensors to the target molecules requires surface decoration of graphene with bifunctional linkers such pyrene derivatives. Here, we demonstrate that the pyrene functionalization influences graphene's electrical properties by yielding partial formation of bilayer graphene which was confirmed by Raman 2D spectrum. Based on this observation, we introduce quadratic fit analysis of the nonlinear electrical behavior of pyrene-functionalized graphene near the Dirac point. Compared to the conventional linear fit analysis of the transconductance at a distance from the Dirac point, the quadratic fit analysis of the nonlinear transconductance near the Dirac point increased the overall protein detection sensitivity by a factor of 5. Furthermore, we show that both pyrene linkers and gating voltage near the Dirac point play critical roles in sensitive and reliable detection of proteins' biological activities with the graphene biosensors.

Pyrenyl Carbon Nanotubes for Covalent Bilirubin Oxidase Biocathode Design: Should the Nanotubes be Carboxylated?

AbstractUnderstanding the characteristics of nanomaterials in the context of electrode designs for bio‐electrocatalysis is an emerging research direction. Applications for fuel cells, batteries, and biosensors are directly benefited. The objective of this study is to understand the influence of unfunctionalized multiwalled carbon nanotubes (MWNT) in comparison to carboxylated nanotubes (MWNT−COOH) for pi‐pi stacking with 1‐pyrenebutyric acid (Py) and covalent immobilization of bilirubin oxidase (BOD) enzyme toward the resulting oxygen reduction currents. We designed pyrolytic graphite‐edge electrodes modified with MWNT/Py, MWNT−COOH/Py, or only MWNT−COOH for carbodiimide activation and BOD immobilization. The relative increase in surface −COOH groups as we move from MWNT to MWNT/Py to MWNT−COOH/Py modification is voltammetrically estimated. Although the MWNT−COOH/Py displayed the highest relative amount of surface −COOH groups, the oxygen reduction current was the largest for the BOD‐immobilized MWNT/Py electrode than others. Results indicate that unfunctionalized MWNT is the optimal choice for pi‐pi stacking with pyrene linkers and covalent BOD immobilization as biocathode for energy devices. Favorable hydrophobic MWNT surface to interact more closely with the electron‐receiving T1 Cu site of BOD, as opposed to the relatively polar and more defective MWNT−COOH material due to functionalization, is suggested to be one of the underlying factors for the observed electrocatalytic trend.

Electron transfer from FAD-dependent glucose dehydrogenase to single-sheet graphene electrodes

Continuous glucose monitoring (CGM) is an emerging technology that can provide a more complete picture of the diabetes patient’s glucose levels. Amperometric blood glucose tests typically require redox mediators to facilitate charge transfer from the enzyme to the electrode, that are not ideal in CGM settings because of their potential toxicity or long-term stability issues. Direct electron transfer (DET) would eliminate this need and has therefore attracted substantial interest. However, most DET-based glucose biosensor studies so far have used glucose oxidase (GOx) leading to controversial results because the oxygen dependency may be misinterpreted as DET. Here, we overcome this challenge by using an oxygen-insensitive glucose dehydrogenase (GDH). To enable direct electron transfer, the enzyme was immobilized on the surface of high-quality single-layer graphene electrodes via short pyrene linkers (<1 nm). The biosensor strongly responded to glucose even without a redox mediator, implying direct electron transfer. Control measurements on different surfaces further confirm that the response is enzyme-specific. The activity of immobilized enzymes was confirmed by glucose measurements with a conventional ferrocenemethanol mediator as well as relatively unexplored redox mediator - nitrosoaniline. The influence of a most potent interferent in blood, ascorbic acid, was assessed. This is the first demonstration of application of single-layer graphene electrode to obtain DET from an oxygen insensitive enzyme (GDH), highlighting the potential of such devices for applications in CGM.

Observation of Direct Electron Transfer from Glucose Dehydrogenase to Single Sheet Graphene Electrode

Continuous glucose monitoring (CGM) is an emerging technology that can provide a more complete picture of the diabetes patient’s glucose levels. Amperometric blood glucose tests typically require redox mediators to facilitate charge transfer from the enzyme to the electrode, that are not ideal in CGM settings because of their potential toxicity or long-term stability issues. Direct electron transfer (DET) would eliminate this need and has therefore attracted substantial interest. However, most DETs studies so far have used glucose oxidase leading to controversial results because the oxygen dependency may be misinterpreted as DET. Here, we overcome this challenge by using an oxygen-insensitive glucose dehydrogenase. The biosensor strongly responded to glucose even without a redox mediator, implying direct electron transfer (Fig. 1 A). Control measurements on different surfaces further confirm that the response is enzyme-specific. To enable direct electron transfer, the enzyme was immobilized on the surface of high-quality single-layer graphene electrodes via short pyrene linkers (<1 nm) (Fig. 1 B). The activity of immobilized enzymes was confirmed by glucose measurements with relatively unexplored redox mediator - nitrosoaniline, and the influence of a most potent interferent in blood, ascorbic acid, was assessed (Fig. 1 C). This is the first demonstration of DET from an oxygen insensitive enzyme to single-layer graphene, highlighting the potential of such devices for applications in CGM. Figure 1

A Bismuth Metal-Organic Framework as a Contrast Agent for X-ray Computed Tomography.

A new bismuth metal-organic framework (MOF), bismuth-NU-901 (Bi-NU-901), featuring the scu topology and a pore with a diameter of ∼11 Å, was solvothermally synthesized, and its use as an X-ray computed tomography (CT) contrast agent was tested. X-ray CT is a common diagnostic method used in the medical field. Inside the body, contrast media enhance the distinction between tissues and organs of similar density. Bi-NU-901 consists of eight connected Bi6 nodes and tetratopic 1,3,5,8-(p-benzoate)pyrene linkers (TBAPy). Numerous material characterization studies including powder X-ray diffraction (PXRD), scanning transmission electron microscopy (STEM), and DFT pore size distribution support the scu structure. Additionally, given the framework's high density of nontoxic heavy atoms, Bi-NU-901 was evaluated as an X-ray computed tomography (CT) agent. Importantly, in vitro studies revealed this new bismuth MOF demonstrates ∼7 times better contrast intensity compared to a zirconium MOF featuring the same topology and ∼14 times better contrast than a commercially available CT contrast agent. These results suggest bismuth MOFs may be promising CT contrast agents.

Zirconium-Based Metal-Organic Frameworks for the Removal of Protein-Bound Uremic Toxin from Human Serum Albumin.

Uremic toxins often accumulate in patients with compromised kidney function, like those with chronic kidney disease (CKD), leading to major clinical complications including serious illness and death. Sufficient removal of these toxins from the blood increases the efficacy of hemodialysis, as well as the survival rate, in CKD patients. Understanding the interactions between an adsorbent and the uremic toxins is critical for designing effective materials to remove these toxic compounds. Herein, we study the adsorption behavior of the uremic toxins, p-cresyl sulfate, indoxyl sulfate, and hippuric acid, in a series of zirconium-based metal-organic frameworks (MOFs). The pyrene-based MOF, NU-1000, offers the highest toxin removal efficiency of all the MOFs in this study. Other Zr-based MOFs possessing comparable surface areas and pore sizes to NU-1000 while lacking an extended aromatic system have much lower toxin removal efficiency. From single-crystal X-ray diffraction analyses assisted by density functional theory calculations, we determined that the high adsorption capacity of NU-1000 can be attributed to the highly hydrophobic adsorption sites sandwiched by two pyrene linkers and the hydroxyls and water molecules on the Zr6 nodes, which are capable of hydrogen bonding with polar functional groups of guest molecules. Further, NU-1000 almost completely removes p-cresyl sulfate from human serum albumin, a protein that these uremic toxins bind to in the body. These results offer design principles for potential MOFs candidates for uremic toxin removal.

Organic Linker Effect on the Growth and Diffusion of Cu Clusters in a Metal–Organic Framework

One reason that metal nanoparticles encapsulated in metal−organic frameworks are of interest is that confinement effects on the particle size and shape may lead to superior catalytic activity. The interior of a metal–organic framework has the potential to influence nucleation and aggregation of metal nanoparticles and to strongly affect their in situ shape and electronic properties. We apply density functional theory and ab initio molecular dynamics (AIMD) to model the nucleation and diffusion of Cun (n = 1–19) clusters on the tetratopic 1,3,6,8-(p-benzoate)pyrene (TBAPy4–) linkers of NU-1000 frameworks. We find that Cu atoms and Cu clusters are stabilized by the TBAPy linker, especially by the edge site of aromatic rings. The stabilization increases when the Cu cluster interacts with two linkers. We identified the most favorable site for Cu cluster adsorption as the window site that connects the c pore and the triangular pore. A Pt atom is found to bind much more strongly than a Cu atom on the TBAPy link...

Computational Linker Design for Highly Crystalline Metal–Organic Framework NU-1000

NU-1000 is a metal–organic framework (MOF) with Zr6(μ3–OH)4(μ3–O)4(OH)4(OH2)4 nodes (called Zr6 nodes) and tetratopic 1,3,6,8-tetrakis(p-benzoate)pyrene (TBAPy) linkers. NU-1000 has pores of 31 A diameter, and it has smaller pores connected perpendicularly to these large pores; this nanoporous structure makes it suitable as a catalyst or a support for catalysis. However, as ordinarily synthesized, NU-1000 has disordered Zr6 nodes populated in its large pores, and this introduces nonuniformity into the crystal and complicates structural characterization. We have examined possible MOF morphologies composed of Zr6 nodes and TBAPy linkers, and we propose that the extra Zr6 nodes in the large pores of NU-1000 are structurally similar to those of an NU-901 phase, which differs from NU-1000 in the relative orientation of Zr6 nodes and the linker conformations. This polymorphism comes from two rotamers of the TBAPy linkers; in NU-1000 the benzoates at the 1 and 3 positions and the 6 and 8 positions are disrotator...

Impact of metal-alkoxide functionalized linkers on H2 binding: A density functional study

The effect of metal-alkoxide functionalization of different organic linkers on the H2 binding is investigated employing DFT approach. While analyzing the H2 binding interaction of magnesium-alkoxide modified benzene, naphthalene, anthracene and pyrene linkers, we find their comparable affinity toward H2 molecules. Six-member alkoxide ring containing naphthalene and pyrene systems interact with the H2 molecules in a comparatively better way than their five-member analogues. AIM, NBO and LMO-EDA analyses have been performed to comprehend the bonding nature between Mg center and the H2 molecules. Polarization along with the charge transfer interactions play significant role in stabilizing the systems.

Metal–Organic Framework Thin Films Composed of Free-Standing Acicular Nanorods Exhibiting Reversible Electrochromism

A uniform and crack-free metalorganic framework (MOF) thin film composed of free-standing acicular nanorods was grown on a transparent conducting glass substrate. The MOF thin film exhibits electrochromic switching between yellow and deep blue by means of a one-electron redox reaction at its pyrene-based linkers. The rigid MOF stabilizes the radical cations of the pyrene linkers at positive applied potential, resulting in the reversible color change of the MOF film. The regular and uniform channels of the MOF allow ions to migrate through the entire film. The MOF thin film thus exhibits a remarkable color change and rapid switching rate.