Can the Side Chains of Q and L Form a Hydrogen Bond at pH 8.1?

🔬 Understanding the Side Chains

Glutamine (Q): This amino acid has a polar, uncharged side chain containing an amide group (-CONH₂). The amide group has both a hydrogen bond donor (NH₂) and an acceptor (C=O), making it highly capable of participating in hydrogen bonding.

Leucine (L): Leucine has a nonpolar, aliphatic side chain (isobutyl group). It lacks polar functional groups and therefore cannot act as a hydrogen bond donor or acceptor under physiological or slightly basic conditions.

⚖️ Impact of pH 8.1

At pH 8.1 (slightly basic), the ionization states of side chains are mostly unaltered for both Q and L:

• Q remains uncharged and polar, still capable of forming hydrogen bonds.
• L remains nonpolar and hydrophobic, with no change in bonding capability.

🧬 Can a Hydrogen Bond Form Between Them?

For a hydrogen bond to occur, there must be:

• A hydrogen donor (usually –OH or –NH)
• An electronegative atom (like O or N) as the acceptor

Q provides these groups, but L does not. Therefore, Q can participate in H-bonding, but L cannot form such a bond with Q due to the absence of compatible functional groups.

✅ Final Conclusion

The side chains of Q (Glutamine) and L (Leucine) cannot form a hydrogen bond at pH = 8.1 or any physiological pH. This is due to the nonpolar, hydrophobic nature of leucine’s side chain.

🔍 Therefore, the interaction is not possible based on hydrogen bonding principles.