I'm trying to thiolate Poly(Acrylic acid) (PAA) with L-cysteine using EDC (or EDAC), however prior to the addition of L-cys, when I add EDC to PAA large clumps form in solution.
1g of PAA was dissolved in 100ml of deionized water, and 2ml of EDC was dissolved 10ml of water. The pH of both solutions was adjusted to approximately pH 5. The EDC solution was added dropwise to the PAA dropwise over 30 minutes, with stirring. The polymer started to clump together upon the addition of the EDC and failed to dissolve fully. Any suggestions as to why this may be happening?
Dear Ellen Kennedy, I think the pH is not the appropriate one. COOH groups should be in their neutral state (lower pH, say less than pH 2). Please have a look at the following paper and the references therin, mainly ref.4. My Regards
10.1016/j.ejpb.2006.11.017
@ Ellen Kennedy The formation of clumps in the solution of PAA and EDC could be due to aggregation or crosslinking of the PAA molecules. This can occur when the EDC activates the carboxylic acid groups in the PAA, leading to the formation of ester or amide bonds between neighboring PAA chains. To avoid this issue, you can try decreasing the concentration of EDC, adding a small amount of EDC first and then gradually increasing the concentration, or adjusting the pH of the solution to reduce the reactivity of the carboxylic acid groups. Additionally, the addition of L-cysteine to the reaction mixture should reduce the formation of clumps by competing with the PAA chains for the activation of the carboxylic acid groups by the EDC.
Simply, In the reaction between PAA and L-cysteine, the EDC acts as a coupling reagent, facilitating the formation of a thioester bond between the carboxylic acid group of the PAA and the thiol group of L-cysteine. The formation of clumps in the reaction mixture can affect the efficiency of the thiolation reaction and lead to reduced yields and/or poor reaction homogeneity. To prevent clumping, it is important to optimize the reaction conditions, such as the concentration of EDC and L-cysteine, the pH of the reaction mixture, and the reaction time. You may also consider adding a small amount of a solubilizing agent, such as a surfactant, to improve the solubility of the PAA and prevent clumping. Additionally, controlling the reaction temperature and stirring the reaction mixture can also help minimize clumping.
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