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

29. Amino Acids

Acid-Base Properties of Amino Acids

Organic Chemistry

29. Amino Acids

Acid-Base Properties of Amino Acids

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4:37 minutes

Problem 54d

Textbook Question

Draw the form of aspartate that predominates at the following pH values:
d. pH=11.0

Verified step by step guidance

Determine the pKa values of the functional groups in aspartate. Aspartate has three ionizable groups: the α-carboxyl group (pKa ≈ 2.1), the α-amino group (pKa ≈ 9.8), and the side-chain carboxyl group (pKa ≈ 3.9).

Compare the given pH (11.0) to each pKa value to determine the protonation state of each functional group. If the pH is higher than the pKa, the group will be deprotonated. If the pH is lower than the pKa, the group will remain protonated.

At pH 11.0, the α-carboxyl group (pKa ≈ 2.1) will be deprotonated, forming a negatively charged carboxylate ion \( \text{COO}^- \).

At pH 11.0, the side-chain carboxyl group (pKa ≈ 3.9) will also be deprotonated, forming another negatively charged carboxylate ion \( \text{COO}^- \).

At pH 11.0, the α-amino group (pKa ≈ 9.8) will be deprotonated, losing its proton and becoming a neutral \( \text{NH}_2 \) group. Combine these observations to draw the predominant form of aspartate at pH 11.0.

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Key Concepts

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

Amino Acid Structure

Amino acids, the building blocks of proteins, consist of a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain). Aspartate, specifically, has a carboxyl group in its side chain, which influences its ionization state depending on the pH of the environment.

pH and Ionization

pH is a measure of the acidity or basicity of a solution, affecting the ionization of functional groups in amino acids. At higher pH levels, such as pH 11.0, the environment is more basic, leading to the deprotonation of carboxyl groups and the potential protonation of amino groups, which alters the overall charge and form of the amino acid.

Zwitterion Form

A zwitterion is a molecule that has both positive and negative charges but is overall neutral. At physiological pH, aspartate exists predominantly as a zwitterion, but at pH 11.0, the carboxyl groups are fully deprotonated, resulting in a negatively charged form. Understanding this concept is crucial for predicting the predominant form of aspartate at different pH levels.

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Textbook Question

Glycine has pK_a values of 2.34 and 9.60. At what pH does glycine exist in the forms shown?

Textbook Question

Alanine has pK_a values of 2.34 and 9.69. Therefore, alanine exists predominately as a zwitterion in an aqueous solution with pH >____ and pH <____.

Textbook Question

Identify the location and type of charge on the hexapeptide Lys-Ser-Asp-Cys-His-Tyr at each of the following pH values:

d. pH=12

Textbook Question

Identify the location and type of charge on the hexapeptide Lys-Ser-Asp-Cys-His-Tyr at each of the following pH values:

c. pH=7

Textbook Question

Draw the form of aspartate that predominates at the following pH values: c. pH=6.0

Textbook Question

Draw the predominant form for glutamate in a solution with the following

pH: b. 3

Textbook Question

Draw the predominant form for glutamate in a solution with the following pH:

a. 0

Textbook Question

c. Which amino acid has the greatest amount of negative charge at pH = 6.20?

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Draw the form of aspartate that predominates at the following pH values: d. pH=11.0

Key Concepts

Amino Acid Structure

pH and Ionization

Zwitterion Form

Watch next

Draw the form of aspartate that predominates at the following pH values:
d. pH=11.0