Ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride in ionic liquids

Electrospinning and Post-Spun Chain Conformations of Synthetic, Hydrophobic Poly(α-amino acid)s

Electrospinning and post-spun conformations of hydrophobic poly(α-amino acid)s are described in this study. The poly(α-amino acid)s, poly(Gly), poly(l-Ala), poly(l-Val), and poly(l-Leu) were synthesized via corresponding N-carboxy-α-amino acid anhydrides. The average molecular weight and degree of polymerization of these polymers were determined by N-terminus labeling using 2,4-dinitrofluorobenzene and by viscometry in the case of poly(Gly). These poly(α-amino acid)s were electrospun from trifluoroacetic acid or trifluoroacetic acid/dichloromethane solutions. The FT-IR spectroscopy and wide-angle X-ray diffraction indicated that the electrospun poly(l-Ala) and poly(l-Leu) fibers predominantly adopts α-helical structure, whereas poly(l-Val) and poly(Gly) fibers exhibited mainly β-strand and random coil structures, respectively.

Mapping the Extra Solvent Power of Ionic Liquids for Monomers, Polymers, and Dry/Wet Globular Single-Chain Polymer Nanoparticles

Ionic liquids (ILs) have shown advantages in organic synthesis and catalysis, energy storage and conversion, and a variety of pharmaceutical applications. Understanding the miscibility behavior of IL/monomer, IL/polymer, and IL/polymer nanoparticle mixtures is critical for the use of ILs as green solvents in polymerization processes as well as to rationalize recent observations concerning the superior solubility of some proteins in ILs when compared to standard solvents. In this work, the most relevant results obtained in terms of extended three-component Flory-Huggins theory concerning the extra solvent power (ESP) of ILs when compared to traditional nonionic solvents for monomeric solutes (Case I), linear polymers (Case II), dry (i.e., without IL inside) globular single-chain polymer nanoparticles (SCNPs) (Case III), and wet (i.e., with IL inside) globular SCNPs (Case IV) are presented. Moreover, useful ESP maps are drawn for the first time for IL mixtures corresponding to Cases I, II, III, and IV at a constant temperature and pressure. Finally, a potential pathway to improve the miscibility of nonionic polymers in ILs is proposed.

The synthesis and characterization of hydroxyapatite-β-alanine modified by grafting polymerization of γ-benzyl-L-glutamate-N-carboxyanhydride

In this study, hydroxyapatite (HAP) was surface-modified by the addition of β-alanine (β-Ala), and the ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxy-anhydride (BLG-NCA) was subsequently initiated. HAP containing surface poly-γ-benzyl-l-glutamates (PBLG) was successfully prepared in this way. With the increase of PBLG content in HAP-PBLG, the solubility of HAP-PBLG increased gradually and it was ultimately soluble in chloroform. HAP-PLGA with surface carboxyl groups was obtained by the catalytic hydrogenation of HAP-PBLG. In the process of HAP modification, the morphology changes from rod to sheet and from flake to needle. The effect of BLG-NCA concentration on the character of hydroxyapatite-β-alanine-poly(γ-benzyl-l-glutamate) (HAP-PBLG) was investigated. The existence of amino acids on the HAP surfaces was confirmed in the resulting Fourier transform infrared (FTIR) spectra. The resulting powder X-ray diffraction patterns indicated that the crystallinity of HAP decreased when the ratio of BLG-NCA/HAP-NH₂ increased to 20/1. Transmission electron microscopy (TEM) indicated that the particle size of HAP-PBLG decreased significantly and that the resulting particles appeared less agglomerated relative to that of the HAP-NH₂ crystals. Furthermore, ¹H-NMR spectra and FTIR spectra revealed that hydroxyapatite-β-alanine-poly (l-glutamic acid) (HAP-PLGA) was able to successfully bear carboxylic acid groups on its side chains.

Synthesis and characterization of surface-modified PBLG nanoparticles for bone targeting: in vitro and in vivo evaluations

In this study, poly(γ-benzyl-l-glutamate) (PBLG) polypeptide derivatives were synthesized by ring-opening polymerization of amino acid N-carboxyanhydride using selected amine-terminated initiators. Alendronate, a targeting moiety that has a strong affinity for bone, was conjugated to PBLG. Monomethoxy polyethylene glycol (PEG) was used for a hydrophilic layer on the surface of the nanoparticles (NPs) to avoid reticuloendothelial system uptake. NPs were prepared by nanoprecipitation technique not only for PBLG or PBLG-PEG but also for composite polymers with different ratios. Fluorescein isothiocyanate would be attached to the NPs as a labeling agent. The size and morphology of NPs were evaluated by dynamic laser light scattering and transmission electron microscopy, and were found to be in a useful range (less than 80 nm) for bone-targeted drug delivery. In addition, the PEGylation of NPs was supported by isothermal titration calorimetry analysis. The bone-targeting potential of NPs was evaluated in vitro by calcium binding and hydroxyapatite affinity assays, and in vivo by fluorescent imaging experiments on rats. The targeted NPs showed bright fluorescent labeling in femur tissue. These results demonstrated the possibility of optimized NPs prepared with new PBLG derivatives to accumulate in bone successfully.

Synthesis of polypeptides by ring-opening polymerization of α-amino acid N-carboxyanhydrides

This chapter summarizes methods for the synthesis of polypeptides by ring-opening polymerization. Traditional and recently improved methods used to polymerize α-amino acid N-carboxyanhydrides (NCAs) for the synthesis of homopolypeptides are described. Use of these methods and strategies for the preparation of block copolypeptides and side-chain-functionalized polypeptides are also presented, as well as an analysis of the synthetic scope of different approaches. Finally, issues relating to obtaining highly functional polypeptides in pure form are detailed.

Recent developments in the utilization of green solvents in polymer chemistry

The use of solvents produces the largest amount of auxiliary waste in polymer science. Due to the fact that sustainable chemistry is becoming more and more important in polymer research, alternative reaction media have been investigated in order to reduce or replace the use of organic solvents. The most commonly used green solvents in polymer chemistry are water, supercritical carbon dioxide and ionic liquids. The progress of utilizing these green solvents in polymerization processes is reviewed and discussed in this critical review on the basis of results mainly published during the last five years (216 references).