substrate

Examples of substrate in the following topics:

• Enzyme Catalysis

  • They do this by binding the reactant(s), known as the substrate(s), to an active site within the enzyme.
  • At the active site, the substrate(s) can form an activated complex at lower energy.
  • This model proposes that the binding of the reactant, or substrate, to the enzyme active site results in a conformational change to the enzyme.
  • Electrostatic catalysis: electrostatic attractions between the enzyme and the substrate can stabilize the activated complex.
  • An enzyme catalyzes a biochemical reaction by binding a substrate at the active site.

• Overview of Reducing Agents

  • Note that Lithium Aluminum Hydride (LiAlH4) is the strongest reducing agent listed, and it reduces all the substrates.
  • In a similar sense, acyl chlorides are the most reactive substrate.

• Hydrogenation

  • Hydrogenation reactions, which involve the addition of hydrogen to substrates, have many important applications.
  • Hydrogenation reactions generally require three components: the substrate, the hydrogen source, and a catalyst.
  • The reaction is carried out at varying temperatures and pressures depending on the catalyst and substrate used.
  • Homogeneous catalysts are soluble in the solvent that contains the unsaturated substrate.
  • The metal binds the substrate and then transfers one of the hydrogen atoms from the metal to the substrate via migratory insertion.

• Reactions of Coordination Compounds

  • Complexes that have unfilled or half-filled orbitals often show the capability to react with substrates.
  • Most substrates have a singlet ground-state; that is, they have lone electron pairs (e.g., water, amines, ethers).
  • These substrates need an empty orbital to be able to react with a metal center.
  • Some substrates (e.g., molecular oxygen) have a triplet ground state.
  • Metals with half-filled orbitals have a tendency to react with such substrates.

• Introduction to Chemical Reactivity

  • Chemical Reaction: A transformation resulting in a change of composition, constitution and/or configuration of a compound (referred to as the reactant or substrate).
  • Reactant or Substrate: The organic compound undergoing change in a chemical reaction.

• Hydroboration

  • Stereoselectivity refers to the preferential formation in a chemical reaction of one product stereoisomer (enantiomer or diastereomer) over another, as a result of inherent reaction specificity, or the influence of chiral features in the substrate, reagent, catalyst or environment.
  • When this selectivity results in the formation of an excess of one enantiomer over the other from an achiral or racemic substrate it is sometimes called asymmetric induction.
  • Since the substrate, reagents and products are all achiral, this diastereospecificity lies in the nature of the reactions themselves.

• Anionic Chain-Growth Polymerization

  • Only monomers having anion stabilizing substituents, such as phenyl, cyano or carbonyl are good substrates for this polymerization technique.

• Epoxidation

  • For primary allylic alcohols of the type shown above, Sharpless epoxidation achieves the remarkable conversion of an achiral substrate into a chiral product with high enantioselectivity.
  • In the reaction of secondary allylic alcohols, where substituent R2 or R3 is an alkyl group (diagram below), the allylic alcohol substrate is chiral and the enantiomers react at different rates via diastereomeric transition states.
  • This rate difference results in a kinetic resolution of this substrate.
  • Enantioselectivity requires the presence of a chiral feature in a substrate, reagent or catalyst.

• By Structural Change

  • In an addition reaction the number of σ-bonds in the substrate molecule increases, usually at the expense of one or more π-bonds.
  • The reverse is true of elimination reactions, i.e. the number of σ-bonds in the substrate decreases, and new π-bonds are often formed.

• Radical Recombination Reactions

  • This requirement is satisfied by appropriate steroid substrates, as demonstrated in the second diagram above.