since PEO contains aliphatic nonpolar CH2CH2 moiety and polar oxygen it can be considered as amphiphilic. During hydration, water molecules interact with polar oxygen of PEO and thus saturate these interaction sites which can not interact with charged interaction sites of polylysine and polyaspartate. In other words, water molecules compete with charged interaction sites of polylysine and polyaspartate. Water molecules are smaller and penetrate the PEO layer more easily. On the other hand the CH2CH2 moiety is not directly hydrated and is prone to interact with the hydrophobic or slightly polar uncharged peptides (polyglycine, polyvaline, and polyserine). That is why these peptides adsorb onto the PEO covered CNT in water while the charged peptides are repelled. One can argue that polylysine and polyaspartate are more sizeable. But polyvaline is comparable in size and is attracted in water and saline. Moreover, if the repulsion resulted from steric effects, it would be observed also in vacuum but in vacuum the charged peptides ALSO adsorb to PEO covered CNT.
Question
Very interesting work dear colleague! Can you explain why the hydratation is affected only positively and negatively charged peptides?
Re: Question
Dear Robi,
since PEO contains aliphatic nonpolar CH2CH2 moiety and polar oxygen it can be considered as amphiphilic. During hydration, water molecules interact with polar oxygen of PEO and thus saturate these interaction sites which can not interact with charged interaction sites of polylysine and polyaspartate. In other words, water molecules compete with charged interaction sites of polylysine and polyaspartate. Water molecules are smaller and penetrate the PEO layer more easily. On the other hand the CH2CH2 moiety is not directly hydrated and is prone to interact with the hydrophobic or slightly polar uncharged peptides (polyglycine, polyvaline, and polyserine). That is why these peptides adsorb onto the PEO covered CNT in water while the charged peptides are repelled. One can argue that polylysine and polyaspartate are more sizeable. But polyvaline is comparable in size and is attracted in water and saline. Moreover, if the repulsion resulted from steric effects, it would be observed also in vacuum but in vacuum the charged peptides ALSO adsorb to PEO covered CNT.
Greetings
Zuzana