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The substituents R(1) and R(2) for nine ...

The substituents `R_(1)` and `R_(2)` for nine peptides are listed in the table given below. How many of these peptides are positively charged at `pH=7.0` ?

A

6

B

4

C

5

D

none of these

Text Solution

Verified by Experts

The correct Answer is:
B
The Amino acids at its isoelectric point is completely in zwitter ion form. Amino acids with additional acid group have isoelectric pH less than 7. increasing pH above isoelectric point makse them anionic. The amino acids with additional basic group have their isoelectric pH greater than 7 and decreasing pH below isoelectric point ( by adding acid solution ) makes them cationic . Thus four peptides with following `R_(1)` and `R_(2)` are basic and will remain protonated (catanioc ) at pH =7
`|:("Peptide",|,R_(1),|"R_(2)),(IV,CH_(2)CONH_(2),(CH_(2))_(4)NH_(2),),(VI,(CH_(2))_(4)NH_(2),(CH_(2))_(4)NH_(2),),(VIII,CH_(2)OH,(CH_(2))_(4)NH_(2),),(IX,(CH_(2))_(4)NH_(2),CH_(3),):|`
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