Preparation And Solution Properties Of Helical Sulfonium-based Polypeptides And Their Polyelectrolyte Complexes

Polyelectrolyte complex is a complex formed by electrostatic interaction between polyanion and polycation.At present,many advanced research work is being carried out in the field of polyelectrolyte complexes,which often combine the properties of two different polymers without losing their properties.Before that,the properties of polyelectrolyte complex composed of?-helical polypeptides have not been studied.Herein,a polyelectrolyte complex composed of?-helical cationic polypeptides(PPBLG-DMS-I)and polysaccharides(?-carboxymethyl dextran sodium salt,CMD)was prepared.The structure of the intermediate and the product were characterized by a series of instruments,and the properties of the solution were studied.The specific content of the whole work is as follows:In this paper we designed and synthetized a series of sulfonium-based polypolypeptides(PMTBLG)with different degree of polymerization through unilateral esterification,cyclization and controlled ultrafast ring opening polymerization,PPBLG-DMS-I were synthesized by alkylation of methylthio groups with high grafting efficiency(97%).The consumption rate of NCA monitored by FTIR shows that when the initial monomer/initiator ratio([M]₀/[I]₀)is within 100,the polymerization can be completed quickly within 25 min.The polymer structure investigated by the instruments shows that we have successfully obtained the target product.The Circular Dichroism and FTIR results indicate that PPBLG-DMS-I adopt?-helical conformation in both aqueous and solid phases,and the secondary structure in aqueous solution has good temperature stability,when concentration of Na Cl?5mg·ml^-1,or p H?9.5,in aqueous solution the transformation occured from helical to random coil conformation.We tested the solubility of PMTBLG and PPBLG-DMS-I in a series of solvents.Unlike polypeptides with imidazole or pyridine groups,when the PPBLG-DMS-I concentration is 20 mg·ml^-1,there is no temperature response in aqueous solution in the range of 20-70?.After that,we used PPBLG-DMS-I and CMD to obtain the aqueous solution system of polyelectrolyte complex formed by electrostatic interaction.Due to the difference of cation/anion mass ratio(R_CAs)and polypeptide concentration,the aggregation size of the polyelectrolyte complex in aqueous solution at room temperature varies in the range of 450-600 nm.As the temperature rises 40?,aggregation size reduced by 300 nm.Under low salt concentrations(<6 mg·ml^-1),the polyelectrolyte complex solution exhibits a salt-induced sharp phase transition.As p H changes,the solution exhibits a p H induced phase transition.By using the CD,the change of the secondary structure of the polymer before and after the composite is explored when the environmental factors change,we found that the composite system has a stabilizing effect on the helical comformation of the polypeptide.Meanwhile,the effect of the secondary structure,degree of polymerization and alkylation on the properties of the polyelectrolyte complex solution were investigated.It was found that the helical comformation had a great effect on the salt-induced and p H-induced phase transition range and aggregation size of the polyelectrolyte complex,the degree of polymerization has little effect on the polyelectrolyte complex,and the degree of alkylation mainly affects the aggregation size of the polyelectrolyte complex in aqueous solution.With the increase of alkylation degree,the aggregation size decreases slightly.