I am really interested in polydopamine-based surface modification of materials. This method is impressive since it provides a functionalized surface that is reactive with amine (-NH2) and thiol (-SH) groups. However, there is one point I do not clearly understand that many researchers have used Tris buffer for polymerization of Dopamine while it might react with polydopamine.
Could you give me suggestion about this?
Thank you very much!
Do you imply the reactions between Tris with dopamine in the polymerization?
or Tris with polydopamine?
Thank you for your reply! It is reported that polydopamine layer can react with amine and thiol groups. This phenomena can be used to immobilize other molecules on this surface. However, Tris also contains amine group that might react with polydopamine. If it happens, the surface of polydopamine should be covered by Tris after polymerization step and can not react with other molecules. This point makes me confused. I just want to make it clear before carrying out experiments.
Thank you and I am still waiting for an explanation!
I see what you mean.
If you saw the mechanism of polymerization, Tris may even react with Dopamine by Michael addition.
In fact, Tris buffer pH 8.5 can be used for immobilization step.
1. The role of basic conditions is to shift the below balance to the right (quinone), make ways for reactions with nucleophiles (-NH2, -SH).
(poly)Dopamine (poly)Dopamine quinone + 2H+ + 2e
2. The primary amine group (-NH2) is attached to tertiary carbon atom in Tris marking it more difficult to directly contact and react with PDA than (many) primary or secondary amines in peptides, proteins because of space hindrance.
3. In immobilization, proteins are used with many primary amine groups, thereby, when some groups are attached, it creates a platform to the whole molecule adhered.
That's what I think.
Or you could change to another buffer, e.g. bicine buffer (pH 8) ^^
Just do it, bro. Don't think too much like I did.
I got the same thought when I was going through the polydopamine literature. I guess that Tris molecules are also getting incorporated in the polymer.
Any news about this are really welcome.
From my experience, I would say there is a reaction between poly/dopamine and Tris. For instance, If you change the buffer e.g. potassium chloride (pH 8.5) during polydopamine coating you will observe that the thickness is much higher in the presence of KCl over Tris. This can be also another explanation.
Please see the following papaer.
Langmuir, 2014, 30 (32), pp 9811–9818
DOI: 10.1021/la501560z
You will get your answer. Indeed it is belived that tris can be atteched to PDA during polimerization
Now I am trying coating without tris to see difference. My theory is because Tris is a buffer solution it keep the ph stable during reaction, otherwise pH will drop during reaction. I will share my results after some experiments.
Actually, in our group, we are using bicarbonate buffer (pH 8.5) as an alternative for Tris buffer to stabilize the pH. But the difference is unclear. Glad to get any news from your results, Deniz. Thank you.
To Funda Çıtak: About the thicker thickness of polydopamine layer in the presence of KCl over Tris, it seems that K+ ions assist the formation of polydopamine through cation-pi assembly. The detail information could be found in a new publication from Heashin Lee's group.(https://advances.sciencemag.org/content/4/9/eaat7457 ).
Any other point-of-views are appreciated!
It is already known that during the conversion of dopamine to polydopamine the pH decrees with reaction time when reaction is carried out in the NaOH solution. Please see doi https://doi.org/10.1007/s10856-013-4994-2. Thus, using the buffer indeed may stabilize the pH. Moreover, the different polymerization conditions i.e various buffers may influence the properties of polydopamine and the final composition of the material. See DOI: 10.1021/la501560z. I would say that the reason why people are using TRIS buffer it very simple. It was used in the Lee´s paper about polydopamine and people are just following. I would say that parameters influencing the PDA polymerization and its final properties are still interesting research pointy and we are missing the full understanding of dopamine conversion to polydopamine and we are not able to control fully this process.
Totally agree with you Radosław. The main issue here is the reactivity of polydopamine after incorporating with tris. Can it react with other amine/thiol-based molecules? Nowadays, polydopamine is widely use for conjugation of amine and thiol-containing molecules. Do you have any information related to the stability of polydopamine-thiol/amine linkage? Will it be as stable as the conjugation using conventional EDC/NHS or maleimide chemistry?
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