Amphiphatic Molecules

[5words]

Question, for a compounds to be amphiphatic do the hydrophobic and hydrophilic parts need to be on opposite ends such as in proteins and Phospholipids?

I am asking because i thought the molecule below was Amphiphatic but mostly hydrophobic but however it turns out it is Hydrophilic!

Methyl 10B structure

image sharing

From the following question:

Why is methyl violet 10B retained by larger amounts of peptidoglycan?
A. Peptidoglycan and methyl violet 10B are both hydrophilic.
B. Mcthyl violet 10B can hydrogen bond with peptidoglycan's hydroryl groups.
C. Methyl violet 10B and peptidoglycan both have charges at neutral pH.
D. Peptidoglycan and methyl violet 10B are both hydrophobic.



@Next Step Tutor @NextStepTutor_2 @NextStepTutor_3 @aldol16

---

Members don't see this ad.

 

[aldol16]

An amphipathic molecule simply has both hydrophobic and hydrophilic parts. There's no requirement for them to be separated by any arbitrary distance. So in the methyl violet molecule you show, the charge makes the amine hydrophilic whereas the aromatic rings are hydrophobic. However, at the end of each ring is a nitrogen atom that is a good H-bond acceptor. Due to the three nitrogens, this molecule can be pretty easily solvated - it's soluble in water and EtOH.

 

[5words]

An amphipathic molecule simply has both hydrophobic and hydrophilic parts. There's no requirement for them to be separated by any arbitrary distance. So in the methyl violet molecule you show, the charge makes the amine hydrophilic whereas the aromatic rings are hydrophobic. However, at the end of each ring is a nitrogen atom that is a good H-bond acceptor. Due to the three nitrogens, this molecule can be pretty easily solvated - it's soluble in water and EtOH.

WOW , so the Nitrogen allow the lone pair of electron inside of the rings (after resonance) to interact with the solvent, thereby making it Hyprophilic.. Have you summed it right?

 

[akimhaneul]

So is the answer A? What about B?


Sent from my iPhone using SDN mobile

 

[5words]

So is the answer A? What about B?


Sent from my iPhone using SDN mobile

its A cant be B because of the resonance, so the Nitrogen wont donated its lone pair for the H bond.. in short, the N lone pair int readily available.

 

[aldol16]

WOW , so the Nitrogen allow the lone pair of electron inside of the rings (after resonance) to interact with the solvent, thereby making it Hyprophilic.. Have you summed it right?

Two things. Resonance delocalization of the nitrogen lone pairs into the ring is unfavorable for two reasons. First, you put a positive charge on nitrogen which doesn't really want a positive charge. Second, the molecule as drawn already has one of the nitrogen's lone pairs delocalized into the ring. You can't delocalize the other two nitrogen lone pairs readily without creating multiple charges. So there's more electron-density on the nitrogens than you think - probably enough for H-bonding.

 

[5words]

Two things. Resonance delocalization of the nitrogen lone pairs into the ring is unfavorable for two reasons. First, you put a positive charge on nitrogen which doesn't really want a positive charge. Second, the molecule as drawn already has one of the nitrogen's lone pairs delocalized into the ring. You can't delocalize the other two nitrogen lone pairs readily without creating multiple charges. So there's more electron-density on the nitrogens than you think - probably enough for H-bonding.

ok, i see it now... As a matter of fact, it's sp3 hybridized...So here H-bonding is not the better answer beacuse the ion-dipole interaction are stonger than H-bond (i.e dipole-dipole) and if so how do we reconcile the fact that we have 2 H-bond donating site vs a single ion-dipole interaction.. And the molecule is opting for Ion-dipole interaction to act with the peptidoglycan molecule.


Back to the original question , if like you've stated that this molecule has both hydrophilic and hydrophobic parts , why isn't it being consider amphiphatic? because i was stuck between A and C ..even though the resonance is unfavorable, there is some delocalization happening and on top of that Phenyl are electron-withdrawing group.. so i able to cross B... So i only crossed A because of amphiphatic vs hydrophilic.

 

[aldol16]

ok, i see it now... As a matter of fact, it's sp3 hybridized...So here H-bonding is not the better answer beacuse the ion-dipole interaction are stonger than H-bond (i.e dipole-dipole) and if so how do we reconcile the fact that we have 2 H-bond donating site vs a single ion-dipole interaction.. And the molecule is opting for Ion-dipole interaction to act with the peptidoglycan molecule.

Ah, I left out this part - although the electron density is there for a H-bond, H-bonding probably wouldn't occur in this case due to sterics. The amine is tri-substituted, meaning it would be hard for it to get close to the H-bond donor anyway. H-bonding also doesn't account for the whole effect - hydrophilicity is determined by more than just H-bonding. In this case, charge is a very important factor as well.

Back to the original question , if like you've stated that this molecule has both hydrophilic and hydrophobic parts , why isn't it being consider amphiphatic? because i was stuck between A and C ..even though the resonance is unfavorable, there is some delocalization happening and on top of that Phenyl are electron-withdrawing group.. so i able to cross B... So i only crossed A because of amphiphatic vs hydrophilic.

I would consider it at least moderately amphipathic. But that only means that parts of the molecule are hydrophobic and parts are hydrophilic. It's the hydrophilicity that you're interested in here, so that's the property you want to focus on. As for the specifics of the question, you'll have to ask the writers for why they chose that term instead of the other.