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Reduction of Alkenes: Catalytic Hydrogenation02:13

Reduction of Alkenes: Catalytic Hydrogenation

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Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
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Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation01:28

Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation

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Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...
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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction 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...
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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

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Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
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Oxidation Numbers03:14

Oxidation Numbers

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In redox reactions, the transfer of electrons occurs between reacting species. Electron transfer is described by a hypothetical number called the oxidation number (or oxidation state). It represents the effective charge of an atom or element, which is assigned using a set of rules.
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Hydrogen Bonds00:26

Hydrogen Bonds

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Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
Hydrogen Bonds Control the World!
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared....
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Modulation of Catalytic Promiscuity during Hydrogen Sulfide Oxidation.

Aaron P Landry1, David P Ballou1, Ruma Banerjee1

  • 1Department of Biological Chemistry , University of Michigan Medical School , Ann Arbor , Michigan 48109 , United States.

ACS Chemical Biology
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The mitochondrial sulfide oxidation pathway uses sulfide quinone oxidoreductase (SQR) to prevent toxic hydrogen sulfide (H2S) buildup. The enzyme

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Area of Science:

  • Biochemistry
  • Mitochondrial Biology
  • Enzymology

Background:

  • Hydrogen sulfide (H2S) is a signaling molecule requiring tight regulation to prevent toxicity.
  • Mitochondrial sulfide oxidation pathway, initiated by sulfide quinone oxidoreductase (SQR), detoxifies H2S.
  • SQR's substrate promiscuity in vitro raises questions about its in vivo specificity.

Purpose of the Study:

  • To investigate how the mitochondrial membrane environment affects SQR's substrate reactivity and promiscuity.
  • To assess the impact of alternate substrates like sulfite and methanethiol on SQR activity.
  • To understand how SQR maintains sulfide homeostasis in vivo.

Main Methods:

  • Spectroscopic and kinetic analyses of SQR.
  • Comparison of SQR in nanodiscs (ndSQR) versus detergent-solubilized SQR (sSQR).
  • Characterization of reactivity with alternate substrates including glutathione (GSH), sulfite, and methanethiol.

Main Results:

  • The membrane environment of ndSQR suppresses glutathione addition but enhances sulfite addition.
  • Methanethiol can act as both a substrate and a sulfur acceptor for SQR.
  • Elevated levels of alternate substrates can interfere with physiological sulfide oxidation.

Conclusions:

  • The mitochondrial membrane environment plays a crucial role in controlling SQR's substrate specificity.
  • Substrate availability and the membrane context work together to minimize promiscuous reactions.
  • These regulatory mechanisms are vital for maintaining cellular sulfide homeostasis.