a-technical-guide-for-performing-spectroscopic-measurements-on-metal

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

quantifying-effects-antimicrobials-on-vitro-biofilm-architecture

Quantifying the Effects of Antimicrobials on <em>In vitro</em> Biofilm Architecture using COMSTAT Software

Biofilms are aggregates of microorganisms that rely on a self-produced matrix of extracellular polymeric substance for protection and structural ...

visualization-pseudomonas-aeruginosa-within-sputum-cystic-fibrosis

Visualization of <em>Pseudomonas aeruginosa</em> within the Sputum of Cystic Fibrosis Patients

Early detection and eradication of Pseudomonas aeruginosa within the lungs of cystic fibrosis patients can reduce the chance of developing chronic ...

Hospital for Sick Children

Virginia Polytechnic and State Institute

We report the photo-induced degradation of and cargo release from a nanoscale metal-organic framework (nMOF) incorporating photo-isomerizable 4,4'-azobenzenedicarboxylate (AZB) linkers. The structure matches a UiO-type framework where 12 4,4'-azobenzenedicarboxylate moieties are connected to a ZrO(OH) cluster, referred to as UiO-AZB. Due to the incorporation of photo-isomerizable struts, the degradation of UiO-AZB is accelerated by irradiation with white light (1.3 ± 0.1% h under dark conditions vs. 8.4 ± 0.4% h when irradiated). Additionally, we show slow release of Nile Red (NR) which is triggered by irradiation (0.04 ± 0.01% h under dark conditions vs. 0.36 ± 0.02% h when irradiated).

Cargo delivery on demand from photodegradable MOF nano-cages.

The dominant charge transfer mechanism in a vast number of metal-organic frameworks (MOFs) is that of redox hopping, a process best explained through the motion of electrons via self-exchange reactions between redox centers coupled to the motion of counter-balancing ions. Mechanistic studies of redox hopping transport in MOFs reveal characteristics that recall pioneering studies in linear redox polymers. When MOFs are employed as electrocatalysts, consideration must be given to both the catalytic properties - turn-over frequency (TOF) and energetic requirements (overpotential, TON) - and the charge transport properties - rate of charge hopping, measured via an apparent diffusion coefficient (Dapp). Herein, we provide a mathematical framework to provide constraints to MOF catalyst development by relating Dapp, TOF, and film thickness in the context of providing 10 mA cm-2 of catalytic current. Lastly with the mechanistic studies discussed as a foundation, design rules for future MOF electrocatalysts are provided and the challenges to the community to optimize MOF charge transport are laid out.

The role of redox hopping in metal-organic framework electrocatalysis.

A series of Ru(ii)LL' (L = 2,2'-bipyridyl, L' = 2,2'-bipyridine-5,5'-dicarboxylic acid), RuDCBPY, -containing zirconium(iv) coordination polymer thin films have been prepared as sensitizing materials for solar cell applications. These metal-organic framework (MOF) sensitized solar cells, MOFSCs, each are shown to generate photocurrent in response to simulated 1 sun illumination. Emission lifetime measurements indicate the excited state quenching of RuDCBPY at the MOF-TiO interface is extremely efficient (>90%), presumably due to electron injection into TiO. A mechanism is proposed in which RuDCBPY-centers photo-excited within the MOF-bulk undergo isotropic energy migration up to 25 nm from the point of origin. This work represents the first example in which a MOFSC is directly compared to the constituent dye adsorbed on TiO (DSC). Importantly, the MOFSCs outperformed their RuDCBPY-TiO DSC counterpart under the conditions used here and, thus, are solidified as promising solar cell platforms.

Ruthenium(ii)-polypyridyl zirconium(iv) metal-organic frameworks as a new class of sensitized solar cells.

A nano metal-organic-framework (nanoMOF) was employed as a first-of-its kind drug delivery vehicle (DDV) for the photo-controlled release of therapeutics with simultaneous breakdown of the carrier into small molecules.

Photo-triggered release of 5-fluorouracil from a MOF drug delivery vehicle.

Sensitized upconversion is explored in three metal-organic frameworks (MOFs) constructed from the anthracene dicarboxylate (ADC) derivatives and zirconium nodes, 9,10-ADC (9,10-MOF), 2,6-ADC (2,6-MOF) and 1,4-ADC (1,4-MOF). Selective excitation of surface-bound Pd(ii) mesoporphyrin IX (PdMP) gives rise to delayed fluorescence (τ = 370 ± 30 ns) from anthracene in the 9,10-MOF. The overall upconversion efficiency of the Pd@9,10-MOF is 0.46 ± 0.05% with a threshold intensity of 104 ± 26 mW cm-2.

Sensitized photon upconversion in anthracene-based zirconium metal-organic frameworks.

Solid-state electrochemiluminescence (ECL) has drawn increasing attention due to its advantages over solution-phase ECL, such as reducing the consumption of expensive reagents and enhancing the ECL signal. Herein we report a ruthenium(ii)-polypyridyl doped zirconium(iv) metal-organic framework (MOF) film, UiO-67-Ru@FTO, for solid-state electrochemiluminescence. With tripropylamine (TPA) as a coreactant, UiO-67-Ru@FTO exhibited high ECL intensity and good stability. A linear relationship was found between the ECL intensity and TPA concentration in a wide range of 0.04-20 mM. Additionally, UiO-67-Ru@FTO was successfully used for dopamine detection, implying its great potential in real-life applications.

Ruthenium(ii)-polypyridyl doped zirconium(iv) metal-organic frameworks for solid-state electrochemiluminescence.

We present the synthesis and photophysical characterization of a water stable PCN-223(freebase) metal organic framework (MOF) constructed from meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP). The photophysical properties of the synthesized crystalline material were studied using a wide range of steady-state and time-resolved spectroscopic techniques. Quenching experiments performed on TCPP and PCN-223 demonstrated that the extent and the rate of quenching in the MOF is significantly higher than the monomeric ligand. Based on these results, we propose that upon photo-excitation, the singlet excitation energy migrates across neutral TCPP linkers until it is quenched by a N-protonated TCPP linker. The N-protonated linkers act as trap states that deactivate the excited state to the ground state. Variable temperature measurements aided in understanding the mechanism of singlet-singlet energy transfer in the PCN-223 MOF. The rate of energy transfer and the total exciton hopping distance in PCN-223 were calculated in order to quantify the energy transfer characteristics of PCN-223. Nanosecond transient absorption spectroscopy was used to study the triplet excited state photophysics in both the free ligand and PCN-223 MOF. Furthermore, femtosecond transient absorption spectroscopy was employed to get a better understanding of the photophysical processes taking place in the ligand and MOF on ultrafast timescales. Efficient energy transfer (Förster radius = 54.5 Å) accompanied with long distance exciton hopping (173 Å) was obtained for the PCN-223 MOF.

Light harvesting and energy transfer in a porphyrin-based metal organic framework.

Metal-organic frameworks (MOFs) provide a suitable platform for stable and efficient heterogeneous photoelectrochemical oxidation catalysis due to their highly ordered structure, large surface area, and synthetic tunability. Herein, a mixed-linker MOF comprising of a photosensitizer [Ru(dcbpy)(bpy)] (bpy = 2,2'-bipyridine, dcbpy = 5,5'-dicarboxy-2,2'-bipyridine) and catalyst [Ru(tpy)(dcbpy)Cl] (tpy = 2,2':6',2''-terpyridine) that were incorporated into the UiO-67 framework and grown as thin films on a TiO-coated, fluorine-doped tin oxide (FTO) electrode (RuB-RuTB-UiO-67/TiO/FTO). When used as an electrode for the photoelectrochemical oxidation of benzyl alcohol, the mixed-linker MOF film showed a faradaic efficiency of 34%, corresponding to a 3-fold increase in efficiency relative to the RuB-UiO-67/TiO/FTO control. This increase in catalytic efficiency is ascribed to the activation of RuTB moieties via oxidation by photogenerated RuB. Transient absorption spectroscopy revealed the delayed appearance of RuTB* or RuTB formation, occurring with a lifetime of 21 ns, due to energy and/or electron transfer. The recovery kinetics of the charge separated state was increased (283 μs) in comparison to single-component control experiments (105 μs for RuB-UiO-67/TiO/FTO and 7 μs for RuTB-UiO-67/TiO/FTO) indicating a cooperative effect that could be exploited in chromophore/catalyst MOF motifs.

Photoelectrochemical alcohol oxidation by mixed-linker metal-organic frameworks.

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) is a promising synthetic route for 2,5-furandicarboxylic acid (FDCA) production. Here, we prepared a nickel(ii)-modified covalent-organic framework (COF) film TpBpy-Ni@FTO for HMF electrooxidation. With a high conversion of HMF (96%), TpBpy-Ni@FTO afforded a 58% FDCA yield. This work underlines the great potential of COF-based materials in electrocatalysis.

Nickel(II)-modified covalent-organic framework film for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF).

Herein, the synthetic methods for preparation of a novel light-responsive metal-organic framework (MOF) UiO-AZB-F are outlined. Upon irradiation with green light, the framework demonstrates controlled release of chemotherapeutic drug cargo with simultaneous breakdown into low toxicity small molecule components.

Green-light-responsive metal-organic frameworks for colorectal cancer treatment.

Solvent plays a key role in biological functions, catalysis, and drug delivery. Metal-organic frameworks (MOFs) due to their tunable functionalities, porosities and surface areas have been recently used as drug delivery vehicles. To investigate the effect of solvent on drug adsorption in MOFs, we have performed integrated computational and experimental studies in selected biocompatible MOFs, specifically, UiO-AZB, HKUST-1 (or CuBTC) and NH-MIL-53(Al). The adsorption of three drugs, namely, 5-fluorouracil (5-FU), ibuprofen (IBU), and hydroxyurea (HU) were performed in the presence and absence of the ethanol. Our computational predictions, at 1 atmospheric pressure, showed a reasonable agreement with experimental studies performed in the presence of ethanol. We find that in the presence of ethanol the drug molecules were adsorbed at the interface of solvent and MOFs. Moreover, the computationally calculated adsorption isotherms suggested that the drug adsorption was driven by electrostatic interactions at lower pressures (<10 Pa). Our computational predictions in the absence of ethanol were higher compared to those in the presence of ethanol. The MOF-adsorbate interaction ( ) energy decreased with decrease in the size of a drug molecule in all three MOFs at all simulated pressures. At high pressure the interaction energy increases with increase in the MOFs pore size as the number of molecules adsorbed increases. Thus, our research shows the important role played by solvent in drug adsorption and suggests that it is critical to consider solvent while performing computational studies.

ArticleTotal : 3	Year
Publication title Cited by 2	2023
Publication title Cited by 11	2020
Publication title Cited by 7	2020

Article	Year
Cargo delivery on demand from photodegradable MOF nano-cages. Dalton transactions (Cambridge, England : 2003)\| PubMed ID: 28181621	2017
The role of redox hopping in metal-organic framework electrocatalysis. Chemical communications (Cambridge, England)\| PubMed ID: 29809219	2018
Ruthenium(ii)-polypyridyl zirconium(iv) metal-organic frameworks as a new class of sensitized solar cells. Chemical science\| PubMed ID: 29896356	2016
Photo-triggered release of 5-fluorouracil from a MOF drug delivery vehicle. Chemical communications (Cambridge, England)\| PubMed ID: 29926872	2018
Sensitized photon upconversion in anthracene-based zirconium metal-organic frameworks. Chemical communications (Cambridge, England)\| PubMed ID: 29946618	2018
Ruthenium(ii)-polypyridyl doped zirconium(iv) metal-organic frameworks for solid-state electrochemiluminescence. Dalton transactions (Cambridge, England : 2003)\| PubMed ID: 30431029	2018
Light harvesting and energy transfer in a porphyrin-based metal organic framework. Faraday discussions\| PubMed ID: 31017129	2019
Photoelectrochemical alcohol oxidation by mixed-linker metal-organic frameworks. Faraday discussions\| PubMed ID: 33107542	2021
Nickel(II)-modified covalent-organic framework film for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF). Chemical communications (Cambridge, England)\| PubMed ID: 33140756	2020
Green-light-responsive metal-organic frameworks for colorectal cancer treatment. Chemical communications (Cambridge, England)\| PubMed ID: 35380568	2022
Modelling drug adsorption in metal-organic frameworks: the role of solvent. RSC advances\| PubMed ID: 35479687	2021

Amanda J. Morris

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JoVE Journal Publications

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