Ranking Protons in order of Increasing Acidity Using pKa Values
TLDRThe video script discusses the dipeptide carnosine, composed of beta-alanine and histidine, and its role as an antioxidant. It explains the process of ranking the acidity of protons in carnosine by estimating their pKa values. The carboxylic acid in amino acids has a lower pKa due to electron-withdrawing effects, while the amino group's pKa is influenced by the amino acid's context. The alpha hydrogen adjacent to the amide carbonyl group has a high pKa due to its ability to delocalize a negative charge. The imidazole ring of histidine has a unique pKa, and the script concludes with the ranking of protons from least to most acidic in carnosine.
Takeaways
- 🧬 Carnosine is a dipeptide composed of beta-alanine and histidine amino acids.
- 🛡️ It acts as an antioxidant and can resist the effects of glycation.
- 📊 To rank the acidity of protons in carnosine, PKa values are essential.
- 🔢 The carboxylic acid in a regular amino acid has a PKa around 2 to 3, lower than the typical 4 to 5 due to the electron-withdrawing effect of the alpha carbon's nitrogen.
- 🌐 The nitrogen on the alpha carbon of the carboxylic acid in an amino acid reduces its PKa.
- 🔗 Carnosine's structure includes an amide linkage between the two amino acids.
- 🌀 The PKa of the protonated amine group in an amino acid is approximately 9 to 10, lower than the general 10 to 11 for most amines.
- 🌡️ The alpha proton adjacent to the carbonyl group in an amide has a PKa around 30.
- 🔑 The hydrogen on the imidazole ring of histidine has a PKa around 6 to 7.
- 📝 The acidity of protons in carnosine can be ranked from least to most acidic based on their PKa values.
- 📉 The ranking order from least to most acidic is: Proton C (least acidic), Proton B, Proton A, Proton D (amino proton), and Proton E (most acidic).
Q & A
What is carnosine and what is its composition?
-Carnosine is a dipeptide composed of the amino acids beta-alanine and histidine. It is known for its antioxidant properties and its ability to resist the effects of glycation.
Why is it important to rank the protons in carnosine by acidity?
-Ranking the protons in carnosine by acidity helps in understanding the reactivity of different parts of the molecule, which is crucial for its biological functions and interactions.
What is the approximate pKa range for a regular carboxylic acid?
-The approximate pKa range for a regular carboxylic acid is around four to five.
How does the presence of an amino group affect the pKa of a carboxylic acid in an amino acid?
-The presence of an amino group, due to its electron-withdrawing effect, reduces the pKa of the carboxylic acid in an amino acid, typically to a range of two to three.
What is the role of the amide linkage in the dipeptide carnosine?
-The amide linkage in carnosine joins the two amino acids, beta-alanine and histidine, together, forming the dipeptide structure.
What is the approximate pKa for the protonated amine group in an amino acid?
-The approximate pKa for the protonated amine group in an amino acid is between nine to ten.
What is the pKa of the alpha proton adjacent to the carbonyl group in an amide?
-The pKa of the alpha proton adjacent to the carbonyl group in an amide is around 30.
How does the presence of a double bond affect the pKa of a hydrogen atom one carbon away?
-The presence of a double bond can slightly lower the pKa of a hydrogen atom one carbon away due to the potential for electron delocalization into the ring, with a range of 40 to 60.
What is the pKa value for the imidazole ring of histidine in carnosine?
-The pKa value for the imidazole ring of histidine in carnosine is around six to seven.
How can the acidity of protons in carnosine be ranked from least to most acidic?
-The acidity of protons in carnosine can be ranked from least to most acidic as follows: proton C (least acidic), proton B, proton A, proton D, proton E (most acidic).
Outlines
🧪 Carnosine's Antioxidant Properties and Proton Acidity Ranking
This paragraph delves into the chemical composition and properties of carnosine, a dipeptide made from beta-alanine and histidine. It highlights carnosine's role as an antioxidant that combats glycation. The main focus is on ranking the acidity of various protons within the carnosine molecule based on their pKa values. The explanation includes a detailed analysis of how different functional groups and their positions affect the pKa, such as the carboxylic acid in amino acids, the amino group in the context of an amino acid, the alpha hydrogen adjacent to the carbonyl group in an amide, and the imidazole ring in histidine. The paragraph concludes with a ranked list of the protons from least to most acidic, starting with proton C and ending with the carboxylic acid proton.
📉 Continuing the Proton Acidity Ranking in Carnosine
Building upon the previous discussion, this paragraph continues to rank the acidity of protons in the carnosine molecule. It details the order of protons from least to most acidic, following the carboxylic acid proton. The ranking includes the amidazole proton, the ammonium or amino proton, and the alpha hydrogen next to the amide. The paragraph provides a clear sequence of protons based on their acidity, which is crucial for understanding the reactivity and behavior of carnosine in various chemical environments.
Mindmap
Keywords
💡Dipeptide
💡Amino Acids
💡Antioxidant
💡Glycation
💡pKa Values
💡Carboxylic Acid
💡Electron Withdrawing Effects
💡Amide Linkage
💡Alpha Proton
💡Imidazole Ring
💡Allylic Hydrogens
Highlights
Carnosine is a dipeptide composed of beta-alanine and histidine.
Carnosine acts as an antioxidant and can resist glycation effects.
The task is to rank the protons in carnosine by increasing acidity.
Labeling approximate pKa values helps in ranking protons' acidity.
A regular carboxylic acid has a pKa of around 4 to 5.
In amino acids, the carboxylic acid pKa drops to around 2 to 3.
The presence of an electronegative nitrogen on the alpha carbon reduces the carboxylic acid pKa.
A dipeptide like carnosine is formed by two amino acids joined through an amide linkage.
Beta-alanine and histidine are the two amino acids in carnosine.
The pKa for a protonated amine in an amino acid is around 9 to 10.
The alpha proton adjacent to an amide carbonyl group has a pKa of around 30.
The pKa for an alpha hydrogen next to a ketone is 19, and for an ester, it's 25.
The pKa for a regular carbon away from a double bond is similar to an alkane but slightly lower.
Allylic hydrogens have a high pKa, ranging from 40 to 60.
The imidazole ring in histidine has a pKa of around 6 to 7.
The carboxylic acid proton in carnosine is the most acidic with the lowest pKa.
The amidazole proton is the second most acidic, followed by the ammonium or amino proton.
The alpha hydrogen next to the amide is less acidic than the amidazole proton.
The final proton mentioned is the least acidic in the sequence.
Transcripts
Browse More Related Video
5.0 / 5 (0 votes)
Thanks for rating: