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02:36Crown Ethers
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Crown ethers are cyclic polyethers that contain multiple oxygen atoms, usually arranged in a regular pattern. The first crown ether was synthesized by Charles Pederson while working at DuPont in 1967. For this work, Pedersen was co-awarded the 1987 Nobel Prize in Chemistry. Crown ethers are named using the formula x-crown-y, where x is the total number of atoms in the ring and y is the number of ether oxygen atoms. The term 'crown' refers to the crown-like shape that these ether...
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02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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01:17Thermal Electrocyclic Reactions: Stereochemistry
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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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01:13Introduction to Mechanisms of Enzyme Catalysis
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For many years, scientists thought that enzyme-substrate binding took place in a simple "lock-and-key" fashion. This model stated that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a more refined view scientists call induced fit. The induced-fit model expands upon the lock-and-key model by describing a more dynamic interaction between enzyme and substrate. As the enzyme and substrate come together, their interaction causes...
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02:34Enzymes
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Inside living organisms, enzymes act as catalysts for many biochemical reactions involved in cellular metabolism. The role of enzymes is to reduce the activation energies of biochemical reactions by forming complexes with its substrates. The lowering of activation energies favor an increase in the rates of biochemical reactions.
Enzyme deficiencies can often translate into life-threatening diseases. For example, a genetic abnormality resulting in the deficiency of the enzyme G6PD...
Enzyme deficiencies can often translate into life-threatening diseases. For example, a genetic abnormality resulting in the deficiency of the enzyme G6PD...
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![[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2Ffiles%2Fmedia%2Fscience-education%2Fscience-education-thumbs%2F12422.jpg&w=3840&q=75)
01:21[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement
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The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
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Tunable and Switchable Catalysis Enabled by Cation-Controlled Gating with Crown Ether Ligands.
Sebastian Acosta-Calle1, Alexander J M Miller1
1Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States.
Accounts of Chemical Research
|March 28, 2023
Summary
Researchers developed dynamic catalysts that respond to external stimuli, enabling switchable and tunable chemical reactions. This innovation mimics natural enzymes by controlling substrate access, paving the way for advanced catalysis.
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Area of Science:
- Catalysis
- Supramolecular Chemistry
- Organometallic Chemistry
Background:
- Catalysis is crucial in pharmaceuticals, chemicals, and fuels.
- Current catalysts are typically optimized for single reactions.
- Dynamic catalysts responding to stimuli offer significant innovation potential.
Purpose of the Study:
- To develop design principles for cation-controlled catalysis.
- To achieve substrate gating in synthetic catalysts outside of macromolecular environments.
- To create catalysts with adjustable activity and selectivity.
Main Methods:
- Designed catalysts at the interface of organometallic chemistry and supramolecular chemistry.
- Incorporated a macrocyclic crown ether into a pincer ligand to create "pincer-crown ether" ligands.
- Explored iridium, nickel, and palladium pincer-crown ether catalysts for substrate gating.
Main Results:
- Developed cation-controlled catalysts capable of substrate gating.
- Demonstrated switchable catalysis where cation addition/removal altered reaction rates or selectivity.
- Achieved tunable catalysis by varying salt concentration to modulate activity.
Conclusions:
- Pincer-crown ether catalysts enable cation-controlled substrate gating.
- This approach allows for switchable and tunable catalytic processes.
- Findings provide design principles for advanced, dynamic synthetic catalysts.