Schiff base

Synthesis

Schiff bases can be synthesized from an aliphatic or aromatic amine and a carbonyl compound by nucleophilic addition forming a hemiaminal, followed by a dehydration to generate an imine. In a typical reaction, 4,4'-oxydianiline reacts with o-vanillin:

Biochemistry

Schiff bases have been investigated in relation to a wide range of contexts, including antimicrobial, antiviral and anticancer activity. They have also been considered for the inhibition of amyloid-β aggregation.{{cite book|last1=Bajema|first1=Elizabeth A. |last2=Roberts|first2=Kaleigh F. |last3=Meade|first3=Thomas J. |editor1-last=Sigel|editor1-first=Astrid|editor2-last=Freisinger|editor2-first=Eva |editor3-last=Sigel|editor3-first=Roland K. O. |editor4-last=Carver|editor4-first=Peggy L. |title=Essential Metals in Medicine:Therapeutic Use and Toxicity of Metal Ions in the Clinic

Schiff bases are common enzymatic intermediates where an amine, such as the terminal group of a lysine residue, reversibly reacts with an aldehyde or ketone of a cofactor or substrate. The common enzyme cofactor pyridoxal phosphate (PLP) forms a Schiff base with a lysine residue and is transaldiminated to the substrate(s). Similarly, the cofactor retinal forms a Schiff base in rhodopsins, including human rhodopsin (via Lysine 296), which is key in the photoreception mechanism.

Coordination chemistry

The term Schiff base is normally applied to these compounds when they are being used as ligands to form coordination complexes with metal ions. One example is Jacobsen's catalyst. The imine nitrogen is basic and exhibits pi-acceptor properties. Several, especially the diiminopyridines are noninnocent ligands. Many Schiff base ligands are derived from alkyl diamines and aromatic aldehydes.

Chiral Schiff bases were one of the first ligands used for asymmetric catalysis. In 1968 Ryōji Noyori developed a copper-Schiff base complex for the metal-carbenoid cyclopropanation of styrene. Schiff bases have also been incorporated into metal–organic frameworks (MOF).

Conjugated Schiff bases

Conjugated Schiff bases absorb strongly in the UV-visible region of the electromagnetic spectrum. This absorption is the basis of the anisidine value, which is a measure of oxidative spoilage for fats and oils.

Historic references

References

Not in use--

References

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2. {{March6th
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4. "azomethines".
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