Textbook Question
Explain why, when the guanidino group of arginine is protonated, the double-bonded nitrogen is the nitrogen that accepts the proton.
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Ch. 21 - Amino Acids, Peptides, and Proteins
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Chapter 22, Problem 8a
Draw the predominant form for glutamate in a solution with the following pH:
a. 0
Verified step by step guidance1
Identify the functional groups in glutamate: Glutamate is an amino acid with an amine group (-NH₂), a carboxylic acid group (-COOH), and a side chain containing another carboxylic acid group (-COOH).
Understand the pKa values of the functional groups: The pKa values for glutamate are approximately 2.1 for the α-carboxylic acid group, 4.1 for the side chain carboxylic acid group, and 9.7 for the α-amino group.
Compare the pH of the solution (pH = 0) to the pKa values: At pH = 0, the solution is highly acidic, meaning the environment will protonate all ionizable groups in glutamate.
Determine the protonation state of each group: At pH = 0, both carboxylic acid groups (-COOH) will remain in their protonated form, and the amine group (-NH₂) will be protonated to form -NH₃⁺.
Draw the structure of glutamate in its fully protonated form: The α-carboxylic acid group and the side chain carboxylic acid group will both be -COOH, and the α-amino group will be -NH₃⁺. Ensure the correct connectivity of the molecule is shown.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Amino Acids and Their Ionization
Amino acids, like glutamate, can exist in different ionic forms depending on the pH of the solution. At low pH, amino acids tend to be protonated, meaning they carry a positive charge. Understanding the ionization of amino acids is crucial for predicting their behavior in various pH environments.
Recommended video:
Guided course
04:10
The 7 Ionizable Amino Acids
Glutamate Structure
Glutamate is an amino acid with a carboxylic acid group, an amine group, and a side chain that also contains a carboxylic acid. This structure allows glutamate to participate in acid-base reactions, influencing its charge and predominant form in solution. Recognizing its functional groups is essential for determining its ionization state.
Recommended video:
Guided course
03:04Drawing Resonance Structures
pH and Its Effect on Charge
pH is a measure of the hydrogen ion concentration in a solution, affecting the protonation state of molecules. At a pH of 0, the environment is highly acidic, leading to an abundance of protons. This high proton concentration will influence the ionization of glutamate, resulting in a predominantly positively charged form.
Recommended video:
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01:34Calculating formal and net charge.
Related Practice
Textbook Question
a. Which amino acid has the lowest pI value?
b. Which amino acid has the highest pI value?
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Textbook Question
Explain why, when the imidazole ring of histidine is protonated, the double-bonded nitrogen is the nitrogen that accepts the proton.
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Textbook Question
Draw the predominant form for glutamate in a solution with the following
pH: b. 3
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Textbook Question
Alanine has pKa values of 2.34 and 9.69. Therefore, alanine exists predominately as a zwitterion in an aqueous solution with pH >____ and pH <____.
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Textbook Question
Why is the pKa of the arginine side chain greater than the pKa of the lysine side chain?
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