[lip]

Out of Dopamine, Histamine , serotonin  and norepinephrine which one would be most hydrophobic and which one would be least hydrophobic. As per my knowledge Nerepinephrine would be most hydrophilic as it have three OH groups and one amine group. Dopamine would be next as it has two OH and one amine group. Then seretonine. as it has one hydroxyl one amino and one ring nitrogen group. Most hydrphobic would be histamine. It has one amino groups and  two imidazole ring nitrogens. It this a correct argument?

[Babcock_Hall]

I would look at the formal charge of each one at physiological pH before coming up with a final order.

[lip]

Actually this is separation question. At Physiological PH all have +1 charge. at basic PH all are neutral .

[Babcock_Hall]

An imidazole ring might also protonate, depending on the side chains; that is a consideration with histamine.