Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

13. Alcohols and Carbonyl Compounds

Oxidizing Agent

Organic Chemistry

13. Alcohols and Carbonyl Compounds

Oxidizing Agent

Previous problemNext problem

4:37 minutes

Problem 40

Textbook Question

Lipoic acid is often found near the active sites of enzymes, usually bound to the peptide by a long, flexible amide linkage with a lysine residue.

(a) Is lipoic acid a mild oxidizing agent or a mild reducing agent? Draw it in both its oxidized and reduced forms.
(b) Show how lipoic acid might react with two Cys residues to form a disulfide bridge.
(c) Give a balanced equation for the hypothetical oxidation or reduction, as you predicted in part (a), of an aldehyde by lipoic acid.

Verified step by step guidance

Step 1: Analyze the structure of lipoic acid. Lipoic acid contains a disulfide bond (-S-S-) in its oxidized form, which can be reduced to two thiol groups (-SH). This indicates that lipoic acid can act as a mild oxidizing agent by accepting electrons and breaking the disulfide bond.

Step 2: Draw the oxidized and reduced forms of lipoic acid. The oxidized form has the disulfide bond (-S-S-), while the reduced form has two thiol groups (-SH). Use the provided images to confirm the structures.

Step 3: To show how lipoic acid reacts with two cysteine (Cys) residues to form a disulfide bridge, consider the thiol groups (-SH) on the cysteine residues. Lipoic acid in its oxidized form can accept electrons from the thiol groups, forming a disulfide bridge between the two cysteine residues and reducing lipoic acid to its thiol form.

Step 4: Write a balanced equation for the hypothetical oxidation or reduction of an aldehyde by lipoic acid. In this reaction, the aldehyde (RCHO) is oxidized to a carboxylic acid (RCOOH), while lipoic acid is reduced from its oxidized disulfide form to its reduced thiol form. The balanced equation would involve the transfer of electrons and protons.

Step 5: Summarize the role of lipoic acid in enzymatic reactions. Lipoic acid often acts as a cofactor near enzyme active sites, facilitating redox reactions by cycling between its oxidized and reduced forms. This flexibility makes it an important molecule in biochemical processes.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation and Reduction

Oxidation and reduction are fundamental chemical processes involving the transfer of electrons between species. Oxidation refers to the loss of electrons, while reduction involves the gain of electrons. In the context of lipoic acid, understanding its role as either a mild oxidizing or reducing agent is crucial for predicting its reactivity with other molecules, such as aldehydes or cysteine residues.

Disulfide Bridge Formation

A disulfide bridge is a covalent bond formed between the sulfur atoms of two cysteine residues, resulting in a -S-S- linkage. This bond is significant in stabilizing the three-dimensional structure of proteins. In the case of lipoic acid, its ability to react with cysteine residues to form disulfide bridges is essential for its function in enzymatic reactions and cellular processes.

Chemical Structure of Lipoic Acid

Lipoic acid is a dithiol compound characterized by two thiol (-SH) groups and a flexible aliphatic chain. Its structure allows it to exist in both oxidized (disulfide form) and reduced (dithiol form) states. Recognizing these forms is vital for understanding how lipoic acid interacts with other biomolecules and its role in redox reactions within biological systems.

Watch next

Master Reagents with a bite sized video explanation from Johnny

Start learning