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Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
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α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base.  The reaction begins with the abstraction of  α hydrogen by the base to produce a nucleophilic enolate ion. This intermediate undergoes a subsequent nucleophilic substitution with the halogen to produce a monohalogenated carbonyl compound. If the starting substrate has more than one α hydrogen, it is difficult to stop the reaction...
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By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
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Halogenation of Alkenes

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Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
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A method involving the transformation of methyl ketones to carboxylic acids using excess base and halogen is called the haloform reaction. It begins with the deprotonation of α hydrogen to form an enolate ion which reacts with the electrophilic halogen to give an α-halo ketone. The step continues until all the α protons are substituted to form a trihalomethyl ketone. The resulting molecule is unstable, and in the presence of a hydroxide base, it readily undergoes nucleophilic...
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Alkyl Halides02:45

Alkyl Halides

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Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
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A selection assay for haloalkane dehalogenase activity based on toxic substrates.

Michael P C Fibinger1, Timo Davids2, Dominique Böttcher1

  • 1Department of Biotechnology and Enzyme Catalysis, Institute of Biochemistry, University of Greifswald, Felix-Hausdorff-Straße 4, D-17491, Greifswald, Germany.

Applied Microbiology and Biotechnology
|May 23, 2015
PubMed
Summary

A new high-throughput system uses natural selection to efficiently identify active haloalkane dehalogenase enzymes from large mutant libraries. This method accelerates enzyme discovery and evolution for industrial applications.

Keywords:
Continuous selection processGrowth assayHaloalkane dehalogenaseToxicity

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Area of Science:

  • Biotechnology and Molecular Biology
  • Enzyme Engineering
  • Evolutionary Biology

Background:

  • Haloalkane dehalogenases are enzymes crucial for bioremediation, but discovering active variants from large libraries is challenging.
  • Traditional screening methods often rely on artificial substrates, which are difficult to synthesize and may not reflect natural enzyme activity.
  • Evolutionary adaptation principles, specifically natural selection and survival of the fittest, offer a powerful framework for enzyme discovery.

Purpose of the Study:

  • To develop a smart, high-throughput screening system for identifying active haloalkane dehalogenase variants.
  • To leverage natural selection for efficient screening of large mutant libraries without artificial substrates.
  • To enable continuous directed evolution for enhanced haloalkane dehalogenase activity.

Main Methods:

  • A high-throughput system was designed based on the principle that only active haloalkane dehalogenase variants can detoxify halogenated alkanes, enabling cell survival and growth.
  • Inactive enzyme variants lead to cell starvation or death in the presence of toxic halogenated alkanes.
  • Three saturation libraries (over 10^6 cells) of inactive haloalkane dehalogenase variants (DhaA or DhlA) were screened using this system.

Main Results:

  • The system successfully screened large mutant libraries, retrieving active haloalkane dehalogenase enzymes.
  • An enrichment factor of approximately 340-fold was achieved for active wild-type enzymes compared to inactive variants.
  • The screening process was completed within a few days, demonstrating high throughput.

Conclusions:

  • The developed high-throughput system is effective for selecting active haloalkane dehalogenase variants from extensive mutant libraries.
  • This method bypasses the need for difficult-to-synthesize artificial substrates, using natural substrates for selection.
  • The system is applicable for continuous directed evolution, facilitating the development of improved haloalkane dehalogenases.