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Related Concept Videos

Nucleophilic Acyl Substitution of Carboxylic Acid Derivatives01:15

Nucleophilic Acyl Substitution of Carboxylic Acid Derivatives

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Nucleophilic acyl substitution is an important class of substitution reactions involving a nucleophile and an acyl compound, such as carboxylic acids and their derivatives. In these reactions, the leaving group attached to the acyl group is substituted by a nucleophile. The general mechanism proceeds via two steps.
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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
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Overview of Fatty Acid Metabolism01:28

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Lipids also are sources of energy that power cellular processes. Like carbohydrates, lipids are composed of carbon, hydrogen, and oxygen, but these atoms are arranged differently. Most lipids are nonpolar and hydrophobic. Major types include fats and oils, waxes, phospholipids, and steroids.
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In an electrophilic aromatic substitution reaction, an electrophile substitutes for a hydrogen of an aromatic compound.
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SN1 Reaction: Stereochemistry02:15

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This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
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Preparation of Alcohols via Substitution Reactions01:38

Preparation of Alcohols via Substitution Reactions

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Overview
Alcohols can be synthesized from alkyl halides via nucleophilic substitution reactions. The highly polar carbon-halogen bond in the substrate makes halide a good leaving group.  The hydroxide ion or water can act as a nucleophile to take the place of halide and form an alcohol. The substitution reactions occur via two different reaction pathways, SN1 or SN2,  depending on the nature of carbon attached to the halide.
Primary alcohols are synthesized from primary alkyl halides, and the...
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Development of Photoswitchable Cholesterol Derivatives through Side Chain Replacement.

Michael D Zott1, Antonia Behnsen1, Laura Depta2

  • 1Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.

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|November 12, 2025
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Researchers developed photocholesterols (PChols), light-controllable cholesterol analogs. These compounds enable optical control over cholesterol transport proteins, aiding research into cholesterol

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Chemical Biology

Background:

  • Cholesterol is a vital lipid involved in membrane structure, signaling, and biosynthesis.
  • Understanding cholesterol's dynamic roles requires tools to precisely control its localization and interactions.

Purpose of the Study:

  • To create photoswitchable cholesterol analogs (photocholesterols, PChols) that mimic native cholesterol's properties.
  • To enable optical control over cholesterol binding to key transport proteins.

Main Methods:

  • Computationally guided design replacing cholesterol's side chain with azobenzene photoswitches.
  • Semisynthetic route utilizing transition metal-catalyzed cross-couplings and hydrogenations.
  • Characterization of photocholesterols' lipophilic profile and binding interactions.

Main Results:

  • Successful synthesis of photocholesterols (PChols) with retained lipophilicity.
  • Demonstrated optical control of PChols' binding to sterol transport proteins ORP1/2 and OSBP.

Conclusions:

  • Photocholesterols provide a novel tool for optically manipulating cholesterol transport.
  • This platform facilitates broader investigation into cholesterol's functions in cellular processes.