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Related Concept Videos

Acid-Catalyzed Ring-Opening of Epoxides02:24

Acid-Catalyzed Ring-Opening of Epoxides

9.0K
Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
9.0K
Base-Catalyzed Ring-Opening of Epoxides02:26

Base-Catalyzed Ring-Opening of Epoxides

10.3K
Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
10.3K
Base-Catalyzed Aldol Addition Reaction01:08

Base-Catalyzed Aldol Addition Reaction

4.6K
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound.
4.6K
Acid-Catalyzed Dehydration of Alcohols to Alkenes02:35

Acid-Catalyzed Dehydration of Alcohols to Alkenes

24.1K
In a dehydration reaction, a hydroxyl group in an alcohol is eliminated along with the hydrogen from an adjacent carbon. Here, the products are an alkene and a molecule of water. Dehydration of alcohols is generally achieved by heating in the presence of an acid catalyst. While the dehydration of primary alcohols requires high temperatures and acid concentrations, secondary and tertiary alcohols can lose a water molecule under relatively mild conditions.
24.1K
Acid-Catalyzed Aldol Addition Reaction01:15

Acid-Catalyzed Aldol Addition Reaction

3.3K
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1.
3.3K
Acid-Catalyzed Hydration of Alkenes02:45

Acid-Catalyzed Hydration of Alkenes

17.4K
Alkenes react with water in the presence of an acid to form an alcohol. In the absence of acid, hydration of alkenes does not occur at a significant rate, and the acid is not consumed in the reaction. Therefore, alkene hydration is an acid-catalyzed reaction.
17.4K

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Related Experiment Video

Updated: Feb 10, 2026

Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase
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Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase

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A third type of hydrogenase catalyzing H2 activation.

Seigo Shima1, Rudolf K Thauer

  • 1Max-Planck-Institut für Terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, D-35043 Marburg, Germany. shima@mpi-marburg.mpg.de

Chemical Record (New York, N.Y.)
|February 17, 2007
PubMed
Summary

This review details the iron-sulfur cluster-free hydrogenase (Hmd), a unique enzyme catalyzing molecular hydrogen activation. It features a mononuclear iron cofactor, distinct from other hydrogenases, with a proposed H(2) binding site.

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An Efficient Method for the Synthesis of Peptoids with Mixed Lysine-type/Arginine-type Monomers and Evaluation of Their Anti-leishmanial Activity
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Protease- and Acid-catalyzed Labeling Workflows Employing 18O-enriched Water
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Area of Science:

  • Biochemistry
  • Enzymology
  • Bioinorganic Chemistry

Background:

  • Molecular hydrogen (H2) activation is crucial in chemistry and biology.
  • Hydrogenases catalyze H2 cleavage, with [FeFe]- and [NiFe]- types previously known.
  • These known hydrogenases contain dinuclear metal centers and iron-sulfur clusters.

Purpose of the Study:

  • To review the structure and function of iron-sulfur cluster-free hydrogenase (Hmd).
  • To highlight Hmd as a third, phylogenetically distinct class of hydrogenase.
  • To elucidate the active site of Hmd and its proposed role in H2 binding.

Main Methods:

  • Review of existing literature on hydrogenase structures and functions.
  • Analysis of crystal structures of [FeFe]- and [NiFe]-hydrogenases.
  • Focus on the structural and functional characterization of the iron-sulfur cluster-free hydrogenase (Hmd).

Main Results:

  • Identified a third class of hydrogenase, the iron-sulfur cluster-free hydrogenase (Hmd).
  • Hmd possesses a mononuclear iron active site, unlike the dinuclear centers of other hydrogenases.
  • The Hmd active site contains an iron cofactor with CO, sulfur, and N/O ligands, and an open coordination site for H2 binding.

Conclusions:

  • The iron-sulfur cluster-free hydrogenase (Hmd) represents a novel class of hydrogen-activating enzymes.
  • Hmd's unique mononuclear iron active site is proposed to bind and activate H2.
  • This discovery expands our understanding of biological hydrogen activation mechanisms.