Verified Solution • 2025–26 Session moderate

QJEEAdv12Chde78: JEE Advanced 2012 Chemistry - Class 12 JEEAdv12Chde78 Solution: The substituents R 1 and R 2 for nine peptides are listed in…

The substituents R1 and R2 for nine peptides are listed in the table given below. How many of these peptides are positively charged at pH = 7.0 ?

IIT-JEE 2012 Paper 1 Offline Chemistry - Biomolecules Question 10 English

Peptide R1{R_1} R2{R_2}
I H H
II H CH3C{H_3}
III CH2COOHC{H_2}COOH H
IV CH2CONH2C{H_2}CON{H_2} (CH2)4NH2{(C{H_2})_4}N{H_2}
V CH2CONH2C{H_2}CON{H_2} CH2CONH2C{H_2}CON{H_2}
VI (CH2)4NH2{(C{H_2})_4}N{H_2} (CH2)4NH2{(C{H_2})_4}N{H_2}
VII CH2COOHC{H_2}COOH CH2CONH2C{H_2}CON{H_2}
VIII CH2OHC{H_2}OH (CH2)4NH2{(C{H_2})_4}N{H_2}
IX (CH2)4NH2{(C{H_2})_4}N{H_2} CH3C{H_3}

Step-by-Step Verified Solution

For basic amino acids with pH > 7, peptides will exist as cations. For example, when the substituents are basic, that is R1 = CH2CONH2 and R2 = (CH2)4NH2 or when R1 = (CH2)4NH2 and R2 = (CH2)4NH2 or when R1 = CH2OH and R2 = (CH2)4NH2 or when R1 = (CH2)4NH2 and R2 = CH3.

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