Commencement Program, May (1987)

https://red.mnstate.edu/commencement/1145/thumbnail.jp

Polyoxometalate-Embedded Metal–Organic Framework as an Efficient Copper-Based Monooxygenase for C(sp³)–H Bond Oxidation via Multiphoton Excitation

The complex and precise structure of natural monooxygenases makes it difficult to clone their structure and activity, and the reported artificial copper-based monooxygenase catalysts for the oxidation of inert C(sp3)–H bonds exhibit limited catalytic activities. Inspired by monooxygenases, we report a metal–organic framework (SiW12@CuMOF-1) comprising a binuclear copper HAT catalyst, photosensitizing nicotinamide adenine dinucleotide (NAD+) mimic bridging ligand, and embedded polyoxometalate. SiW12@CuMOF-1 accelerates the oxidative dehydrogenation of 3,5-DTBC with a catalytic efficiency comparable to that of natural polyphenol oxidase. In the presence of pyridine hydrochloride, irradiation of SiW12@CuMOF-1 afforded the highly active chlorine radical and CuI species via a ligand-to-metal charge transfer process. The chlorine radical abstracts a hydrogen atom selectively from C(sp3)–H bonds to generate the radical intermediate. The CuI species interacted with the active oxygen species 1O2 that formed from the photoinduced energy transfer from the excited state of the NAD+ mimics, giving the active oxygen species O2•– for further oxidization. The well-modified binuclear copper sites cleave the O–O bond to give the final products selectively. Meanwhile, the embedded polyoxometalates interacted with the alcohol substrates via hydrogen bonding interactions to help the catalytic conversion with high efficiency. The well-defined structural characters, the finely modified catalytic properties, and the sustainable multiphoton excitation photocatalytic processes provide a new avenue to develop robust artificial enzymes with uniform active sites and improved catalytic performances

Polyoxometalate-Embedded Metal–Organic Framework as an Efficient Copper-Based Monooxygenase for C(sp³)–H Bond Oxidation via Multiphoton Excitation

The complex and precise structure of natural monooxygenases makes it difficult to clone their structure and activity, and the reported artificial copper-based monooxygenase catalysts for the oxidation of inert C(sp3)–H bonds exhibit limited catalytic activities. Inspired by monooxygenases, we report a metal–organic framework (SiW12@CuMOF-1) comprising a binuclear copper HAT catalyst, photosensitizing nicotinamide adenine dinucleotide (NAD+) mimic bridging ligand, and embedded polyoxometalate. SiW12@CuMOF-1 accelerates the oxidative dehydrogenation of 3,5-DTBC with a catalytic efficiency comparable to that of natural polyphenol oxidase. In the presence of pyridine hydrochloride, irradiation of SiW12@CuMOF-1 afforded the highly active chlorine radical and CuI species via a ligand-to-metal charge transfer process. The chlorine radical abstracts a hydrogen atom selectively from C(sp3)–H bonds to generate the radical intermediate. The CuI species interacted with the active oxygen species 1O2 that formed from the photoinduced energy transfer from the excited state of the NAD+ mimics, giving the active oxygen species O2•– for further oxidization. The well-modified binuclear copper sites cleave the O–O bond to give the final products selectively. Meanwhile, the embedded polyoxometalates interacted with the alcohol substrates via hydrogen bonding interactions to help the catalytic conversion with high efficiency. The well-defined structural characters, the finely modified catalytic properties, and the sustainable multiphoton excitation photocatalytic processes provide a new avenue to develop robust artificial enzymes with uniform active sites and improved catalytic performances

A Metal–Organic Tetrahedron as a Redox Vehicle to Encapsulate Organic Dyes for Photocatalytic Proton Reduction

The design of artificial systems that mimic highly evolved and finely tuned natural photosynthetic systems is a subject of intensive research. We report herein a new approach to constructing supramolecular systems for the photocatalytic generation of hydrogen from water by encapsulating an organic dye molecule into the pocket of a redox-active metal–organic polyhedron. The assembled neutral Co₄L₄ tetrahedron consists of four ligands and four cobalt ions that connect together in alternating fashion. The cobalt ions are coordinated by three thiosemicarbazone NS chelators and exhibit a redox potential suitable for electrochemical proton reduction. The close proximity between the redox site and the photosensitizer encapsulated in the pocket enables photoinduced electron transfer from the excited state of the photosensitizer to the cobalt-based catalytic sites via a powerful pseudo-intramolecular pathway. The modified supramolecular system exhibits TON values comparable to the highest values reported for related cobalt/fluorescein systems. Control experiments based on a smaller tetrahedral analogue of the vehicle with a filled pocket and a mononuclear compound resembling the cobalt corner of the tetrahedron suggest an enzymatic dynamics behavior. The new, well-elucidated reaction pathways and the increased molarity of the reaction within the confined space render these supramolecular systems superior to other relevant systems

Palladium-Catalyzed Oxidative Heck Coupling Reaction for Direct Synthesis of 4-Arylcoumarins Using Coumarins and Arylboronic Acids

An efficient protocol for the direct synthesis of 4-arylcoumarins via palladium-catalyzed oxidative Heck coupling reaction of coumarins and arylboronic acids was developed. 4-Arylcoumarins were obtained in moderate to excellent yields, and the reaction also showed tolerance toward functional groups such as hydro, methoxy, diethylamino, nitro, and chloro groups

Confinement Effect in Metal–Organic Framework Cu₃(<b>BTC</b>)₂ for Enhancing Shape Selectivity of Radical Difunctionalization of Alkenes

The radical difunctionalization of alkenes plays a vital role in pharmacy, but the conventional homogeneous catalytic systems are challenging in selectivity and sustainability to afford the target molecules. Herein, the famous readily available metal–organic framework (MOF), Cu3(BTC)2, has been applied to cyano-trifluoromethylation of alkenes as a high-performance and recyclable heterogeneous catalyst, which possesses copper(II) active sites residing in funnel-like cavities. Under mild conditions, styrene derivatives and various unactivated olefins could be smoothly transformed into the corresponding cyano-trifluoromethylation products. Moreover, the transformation brought about by the active copper center in confined environments achieved regio- and shape selectivity. To understand the enhanced selectivity, the activation manner of the MOF catalyst was studied with control catalytic experiments such as FT-IR and UV–vis absorption spectroscopy of substrate-incorporated Cu3(BTC)2, which elucidated that the catalyst underwent a radical transformation with the intermediates confined in the MOF cavity, and the confinement effect endowed the method with pronounced selectivities

Metal–Organic Frameworks with Phosphotungstate Incorporated for Hydrolytic Cleavage of a DNA-Model Phosphodiester

Five phosphotungstate-incorporated metal–organic frameworks {[Eu₄(dpdo)₉(H₂O)₁₆PW₁₂O₄₀]}­(PW₁₂O₄₀)₂·(dpdo)₃·Cl₃ (<b>1</b>); {ZnNa₂(μ-OH)­(dpdo)₄(H₂O)₄[PW₁₂O₄₀]}·3H₂O (<b>2</b>); {Zn₃(dpdo)₇}­[PW₁₂O₄₀]₂·3H₂O (3); and [Ln₂H­(μ-O)₂(dpdo)₄(H₂O)₂]­[PW₁₂O₄₀]·3H₂O (Ln = Ho for <b>4</b> and Yb for <b>5</b>) (dpdo = 4,4′-bipyridine-<i>N</i>,<i>N</i>′-dioxide) have been synthesized through a one-step hydrothermal reaction and characterized by elemental analyses, infrared (IR) spectroscopy, photoluminescence, and single-crystal X-ray diffraction (XRD). The structural analyses indicate that <b>1</b>–<b>5</b> display diversity structure from one-dimensional (1D) to three-dimensional (3D) series of hybrids. Kinetic experiments for the hydrolytic cleavage of DNA-model phosphodiester BNPP (bis­(<i>p</i>-nitrophenyl)­phosphate) were followed spectrophotometrically for the absorbance increase at 400 nm in EPPS (4-(2-hydroxyethyl)­piperazine-1-propane sulfonic acid) buffer solution, because of the formation of <i>p</i>-nitrophenoxide with <b>1</b>–<b>5</b> under conditions of pH 4.0 and 50 °C. Ultraviolet (UV) spectroscopy indicate that the cleavage of the phosphodiester bond proceeds with the pseudo-first-order rate constant in the range of 10^–7–10^–6 s^–1, giving an inorganic phosphate and <i>p</i>-nitrophenol as the final products of hydrolysis. The results demonstrate that <b>1</b>–<b>5</b> have good catalytic activity and reusability for hydrolytic cleavage of BNPP

Metal–Organic Polymers Containing Discrete Single-Walled Nanotube as a Heterogeneous Catalyst for the Cycloaddition of Carbon Dioxide to Epoxides

The cycloaddition of carbon dioxide to epoxides to produce cyclic carbonates is quite promising and does not result in any side products. A discrete single-walled metal–organic nanotube was synthesized by incorporating a tetraphenyl-ethylene moiety as the four-point connected node. The assembled complex has a large cross-section, with an exterior wall diameter of 3.6 nm and an interior channel diameter of 2.1 nm. It features excellent activity toward the cycloaddition of carbon dioxide, with a turnover number of 17,500 per mole of catalyst and an initial turnover frequency as high as 1000 per mole of catalyst per hour. Only minimal decreases in the catalytic activity were observed after 70 h under identical reaction conditions, and a total turnover number as high as 35,000 was achieved. A simple comparison of relative porous MOFs suggested that the cross-section of the channels is an important factor influencing the transport of the substrates and products through the channel

Metal–Organic Frameworks with Phosphotungstate Incorporated for Hydrolytic Cleavage of a DNA-Model Phosphodiester

Five phosphotungstate-incorporated metal–organic frameworks {[Eu₄(dpdo)₉(H₂O)₁₆PW₁₂O₄₀]}­(PW₁₂O₄₀)₂·(dpdo)₃·Cl₃ (<b>1</b>); {ZnNa₂(μ-OH)­(dpdo)₄(H₂O)₄[PW₁₂O₄₀]}·3H₂O (<b>2</b>); {Zn₃(dpdo)₇}­[PW₁₂O₄₀]₂·3H₂O (3); and [Ln₂H­(μ-O)₂(dpdo)₄(H₂O)₂]­[PW₁₂O₄₀]·3H₂O (Ln = Ho for <b>4</b> and Yb for <b>5</b>) (dpdo = 4,4′-bipyridine-<i>N</i>,<i>N</i>′-dioxide) have been synthesized through a one-step hydrothermal reaction and characterized by elemental analyses, infrared (IR) spectroscopy, photoluminescence, and single-crystal X-ray diffraction (XRD). The structural analyses indicate that <b>1</b>–<b>5</b> display diversity structure from one-dimensional (1D) to three-dimensional (3D) series of hybrids. Kinetic experiments for the hydrolytic cleavage of DNA-model phosphodiester BNPP (bis­(<i>p</i>-nitrophenyl)­phosphate) were followed spectrophotometrically for the absorbance increase at 400 nm in EPPS (4-(2-hydroxyethyl)­piperazine-1-propane sulfonic acid) buffer solution, because of the formation of <i>p</i>-nitrophenoxide with <b>1</b>–<b>5</b> under conditions of pH 4.0 and 50 °C. Ultraviolet (UV) spectroscopy indicate that the cleavage of the phosphodiester bond proceeds with the pseudo-first-order rate constant in the range of 10^–7–10^–6 s^–1, giving an inorganic phosphate and <i>p</i>-nitrophenol as the final products of hydrolysis. The results demonstrate that <b>1</b>–<b>5</b> have good catalytic activity and reusability for hydrolytic cleavage of BNPP

Metal–Organic Frameworks with Phosphotungstate Incorporated for Hydrolytic Cleavage of a DNA-Model Phosphodiester

Five phosphotungstate-incorporated metal–organic frameworks {[Eu₄(dpdo)₉(H₂O)₁₆PW₁₂O₄₀]}­(PW₁₂O₄₀)₂·(dpdo)₃·Cl₃ (<b>1</b>); {ZnNa₂(μ-OH)­(dpdo)₄(H₂O)₄[PW₁₂O₄₀]}·3H₂O (<b>2</b>); {Zn₃(dpdo)₇}­[PW₁₂O₄₀]₂·3H₂O (3); and [Ln₂H­(μ-O)₂(dpdo)₄(H₂O)₂]­[PW₁₂O₄₀]·3H₂O (Ln = Ho for <b>4</b> and Yb for <b>5</b>) (dpdo = 4,4′-bipyridine-<i>N</i>,<i>N</i>′-dioxide) have been synthesized through a one-step hydrothermal reaction and characterized by elemental analyses, infrared (IR) spectroscopy, photoluminescence, and single-crystal X-ray diffraction (XRD). The structural analyses indicate that <b>1</b>–<b>5</b> display diversity structure from one-dimensional (1D) to three-dimensional (3D) series of hybrids. Kinetic experiments for the hydrolytic cleavage of DNA-model phosphodiester BNPP (bis­(<i>p</i>-nitrophenyl)­phosphate) were followed spectrophotometrically for the absorbance increase at 400 nm in EPPS (4-(2-hydroxyethyl)­piperazine-1-propane sulfonic acid) buffer solution, because of the formation of <i>p</i>-nitrophenoxide with <b>1</b>–<b>5</b> under conditions of pH 4.0 and 50 °C. Ultraviolet (UV) spectroscopy indicate that the cleavage of the phosphodiester bond proceeds with the pseudo-first-order rate constant in the range of 10^–7–10^–6 s^–1, giving an inorganic phosphate and <i>p</i>-nitrophenol as the final products of hydrolysis. The results demonstrate that <b>1</b>–<b>5</b> have good catalytic activity and reusability for hydrolytic cleavage of BNPP