I'm trying to quaternize the free primary amine of my α-Poly-L-Lysine, to achieve a higher zeta potential and thus more stability of my nanoparticles. However, my approaches so far have not worked at all.
I added methyl iodide in a 30x and 100x molar excess to an aqueous solution of my Poly-Lysine (1 mg/ml). I adjusted the pH with NaHCO3 to 8.24. I stirred the solution for 3 days at room temperature, dialysed and freeze dried my solution, but nothing happened. I'm still left with the same Poly-Lysine that I started with.
Another thing I tried is adding GTMAC to the primary amine of the Poly-Lysine. I made two formulations, adding GTMAC in a 40:1 ratio to the 1 mg/ml Poly-Lysine solution. 1 reaction was carried out at pH 5, the other one in a pH 7.4 PBS buffer. I stirred the solutions at 75 °C over night, again dialysed & freeze dried the solutions, but again nothing happened to my Poly-Lysine.
Does anyone know why it appears to be so unreactive? May it be the low concentration (1mg/ml) of my polymer?
Please note that I'm not a trained chemist but a pharmacist. I'm happy about any suggestions on what I could alter to get the reaction going.
Thanks in advance,