Abstract
Abstract The synthesis of poly(L-glutamic acid) (PG) was investigated. Reduction of poly(benzyl-L-glutamate) by the palladium/charcoal catalyst proved to be an effective method for obtaining polyglutamic acid pure and particularly exhibiting in the α-helix secondary structure. The structure of this synthetic polypeptide was assessed by infrared spectroscopy, gel permeation chromatography, proton nuclear magnetic resonance spectroscopy, temperature-modulated differential scanning calorimetry and wide-angle powder X-ray diffraction methods. The α-helical PG was, for the first time, combined with multi-walled carbon nanotubes (MWCNTs). The obtained PG was demonstrated to be a promising matrix to disperse MWCNTs, forming MWCNT/PG biocomposites.
Highlights
The Poly(L-glutamic acid) (PG) is a homo-polyamide that is made of L-glutamic acid units connected by amide bonds
It should be noted that when applying another previously reported method to synthesize poly(L-glutamic acid) (PG) homopolymer such as reduction of PBG with phosphonium iodide in acetic acid[8], we found that the recovered PG after purification and Figure 7. 1H NMR spectrum of PLGA obtained by hydrogenolysis of PBG at 10 wt% of Pd/C, 50 oC, 90 bar, for 1 day
In addition to characteristic diffraction peaks attributed to the structure of α-helical PG, the multi-walled carbon nanotubes (MWCNTs)/PG composite showed a characteristic diffraction peak at q = 18.3 nm-1 (d = 0.34 nm), which can be assigned to the diffracted pattern peak (002) of CNTs42-44
Summary
The Poly(L-glutamic acid) (PG) is a homo-polyamide that is made of L-glutamic acid units connected by amide bonds. Poly(glutamic acid) and its derivatives have attracted plenty of research for a variety of applications in industrial fields, such as medicine, cosmetics, food and water treatments[1,2]. The ring-opening polymerization of glutamate NCA monomers bearing these substituents often resulted in polyamides with relatively low molecular weights low yields[9,11] These carboxylic protected polyglutamates can be in the α-helix conformation, the PGs resulted after removal of the protected groups have low molecular weights and a high propensity for forming β-sheet aggregates. We first studied the synthesis of poly(Lglutamic acid) via palladium(Pd)/charcoal (C)-catalyzed hydrogenation of PBG (Scheme 1), which was later used as a biomaterial matrix for dispersing multi-walled carbon nanotubes. Amine-initiated ring-opening polymerization of benzyl-L-glutamate NCA produced PBG with well-defined secondary structure and high yield[13]. The effects of the CNT content on CNT dispersibility and mechanical properties of the nanocomposites were investigated
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