Textbook Question
Explain the order of elution (with a buffer of pH 4) of the following pairs of amino acids through a column packed with Dowex 50:
a. aspartate before serine
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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 18b
Explain the order of elution (with a buffer of pH 4) of the following pairs of amino acids through a column packed with Dowex 50:
b. serine before alanine
Verified step by step guidance1
Understand the context: Dowex 50 is a cation-exchange resin, meaning it binds positively charged species. The elution order of amino acids depends on their charge at the given pH, which is determined by their isoelectric point (pI) and the pH of the buffer.
Determine the isoelectric points (pI) of the amino acids: Serine has a pI of approximately 5.7, and alanine has a pI of approximately 6.0. At pH 4, both amino acids will be positively charged because the pH is below their respective pI values.
Compare the degree of positive charge: At pH 4, serine will have a slightly higher positive charge than alanine because its pI is lower. This means serine will interact more strongly with the Dowex 50 resin.
Analyze the elution behavior: Since serine binds more strongly to the resin, it will elute later than alanine. Alanine, with a weaker interaction, will elute first.
Conclude the order of elution: Based on the above reasoning, alanine will elute before serine through the Dowex 50 column at pH 4.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Ion Exchange Chromatography
Ion exchange chromatography is a technique used to separate charged molecules based on their affinity to the charged stationary phase. In this method, amino acids are separated as they interact with the resin, which can be positively or negatively charged. The order of elution depends on the net charge of the amino acids at a given pH, influencing their interaction with the resin.
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Metal Ion Catalysis Concept 1
Amino Acid Properties
Amino acids possess unique side chains that determine their charge and polarity at specific pH levels. At pH 4, serine, which has a polar hydroxyl group, remains neutral, while alanine, a non-polar amino acid, also remains neutral. However, the overall interactions with the resin can differ due to the presence of functional groups, affecting their elution order.
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04:10The 7 Ionizable Amino Acids
pH and Charge
The pH of the buffer solution significantly influences the ionization state of amino acids. At pH 4, the carboxyl group of both serine and alanine is deprotonated, while the amino group remains protonated, resulting in a net neutral charge. Understanding how pH affects the ionization of functional groups is crucial for predicting the elution order in ion exchange chromatography.
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01:34Calculating formal and net charge.
Related Practice
Textbook Question
A mixture of seven amino acids (glycine, glutamate, leucine, lysine, alanine, isoleucine, and aspartate) is separated by chromatography. Explain why only six spots show up when the chromatographic plate is coated with ninhydrin and heated.
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Textbook Question
Why is excess ammonia used in the preceding reaction?
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Textbook Question
What amino acid is formed using the N-phthalimidomalonic ester synthesis when the following alkyl halides are used in the third step?
b. CH3SCH2CH2Br
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Textbook Question
What amino acid is formed using the N-phthalimidomalonic ester synthesis when the following alkyl halides are used in the third step?
a.
Textbook Question
Explain why the pI of lysine is the average of the pKa values of its two protonated amino groups.
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