Regioselective synthesis of polysaccharide-amino acid ester conjugates

Dextran Macroinitiator for Synthesis of Polysaccharide-b-Polypeptide Block Copolymers via NCA Ring-Opening Polymerization

Synthesis of polysaccharide-b-polypeptide block copolymers represents an attractive goal because of their promising potential in delivery applications. Inspired by recent breakthroughs in N-carboxyanhydride (NCA) ring-opening polymerization (ROP), we present an efficient approach for preparation of a dextran-based macroinitiator and the subsequent synthesis of dextran-b-polypeptides via NCA ROP. This is an original approach to creating and employing a native polysaccharide macroinitiator for block copolymer synthesis. In this strategy, regioselective (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) oxidation of the sole primary alcohol located at the C-6 position of the monosaccharide at the nonreducing end of linear dextran results in a carboxylic acid. This motif is then transformed into a tetraalkylammonium carboxylate, thereby generating the dextran macroinitiator. This macroinitiator initiates a wide range of NCA monomers and produces dextran-b-polypeptides with a degree of polymerization (DP) of the polypeptide up to 70 in a controlled manner (Đ < 1.3). This strategy offers several distinct advantages, including preservation of the original dextran backbone structure, relatively rapid polymerization, and moisture tolerance. The dextran-b-polypeptides exhibit interesting self-assembly behavior. Their nanostructures have been investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and adjustment of the structure of block copolymers allows self-assembly of spherical micelles and worm-like micelles with varied diameters and aspect ratios, revealing a range of diameters from 60 to 160 nm. Moreover, these nanostructures exhibit diverse morphologies, including spherical micelles and worm-like micelles, enabling delivery applications.

Reductive amination of oxidized hydroxypropyl cellulose with ω-aminoalkanoic acids as an efficient route to zwitterionic derivatives

Zwitterionic polymers, with their equal amounts of cationic and anionic functional groups, have found widespread utility including as non-fouling coatings, hydrogel materials, stabilizers, antifreeze materials, and drug carriers. Polysaccharide-derived zwitterionic polymers are attractive because of their sustainable origin, potential for lower toxicity, and possible biodegradability, but previous methods for synthesis of zwitterionic polysaccharide derivatives have been limited in terms of flexibility and attainable degree of substitution (DS) of charged entities. We report herein successful design and synthesis of zwitterionic polysaccharide derivatives, in this case based on cellulose, by reductive amination of oxidized 2-hydroxypropyl cellulose (Ox-HPC) with ω-aminoalkanoic acids. Reductive amination products could be readily obtained with DS(cation) (= DS(anion)) up to 1.6. Adduct hydrophilic/hydrophobic balance (amphiphilicity) can be influenced by selecting the appropriate chain length of the ω-aminoalkanoic acid. This strategy is shown to produce a range of amphiphilic, water-soluble, moderately high glass transition temperature (Tg) polysaccharide derivatives in just a couple of efficient steps from commercially available building blocks. The adducts were evaluated as crystallization inhibitors. They are strong inhibitors of crystallization even for the challenging, poorly soluble, fast-crystallizing prostate cancer drug enzalutamide, as supported by surface tension and Flory-Huggins interaction parameter results.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Facile fabrication of reusable starch sponge with adjustable crosslinked networks for efficient nest-trap and in situ photodegrade methylene blue

The fabrication of reusable natural polysaccharide sponges with nanoscale dispersed photocatalysts to achieve robust photocatalytic efficiency is desirable yet challenging. Herein, inspired by the nesting behavior when fishing, we designed reusable starch sponge with chemically anchored nano-ZnO into carboxylated starch matrix by thermoplastic interfacial reactions and solvent replacement for absorbing and photodegrading methylene blue (MB) in situ. The plasticization and interfacial reactions promoted a simultaneous increase in the reactivity of the starch hydroxyl/carboxyl groups and the specific surface area of ZnO. Meanwhile, the crosslinked networks of starch sponge could be adjusted by varying the ZnO and carboxylic groups contents. The results of photodegradation experiments revealed the recyclable closed-loop process of attraction-trapping-photodegradation of MB was successfully realized, achieving the effect of killing three birds with one stone. The reusable starch sponge with homogeneous dispersion of nano-ZnO by constructing three-dimensional porous channels possessed the high enrichment capacity and the remarkable photocatalysis efficiency with 150 mg/L ZnO. Under UV irradiation, the starch sponge degraded 97 % of MB with 1.67 × 10-3 min-1 photodegradation rate constant even after five cycles, which exceeded most existing photocatalytic systems. Overall, the reusable starch sponge with adjustable structure provided new insights for multifunctional bio-based photocatalyst loading systems.

Synthesis and Characterization of Multi-Reducing-End Polysaccharides

Site-specific modification is a great challenge for polysaccharide scientists. Chemo- and regioselective modification of polysaccharide chains can provide many useful natural-based materials and help us illuminate fundamental structure-property relationships of polysaccharide derivatives. The hemiacetal reducing end of a polysaccharide is in equilibrium with its ring-opened aldehyde form, making it the most uniquely reactive site on the polysaccharide molecule, ideal for regioselective decoration such as imine formation. However, all natural polysaccharides, whether they are branched or not, have only one reducing end per chain, which means that only one aldehyde-reactive substituent can be added. We introduce a new approach to selective functionalization of polysaccharides as an entrée to useful materials, appending multiple reducing ends to each polysaccharide molecule. Herein, we reduce the approach to practice using amide formation. Amine groups on monosaccharides such as glucosamine or galactosamine can react with carboxyl groups of polysaccharides, whether natural uronic acids like alginates, or derivatives with carboxyl-containing substituents such as carboxymethyl cellulose (CMC) or carboxymethyl dextran (CMD). Amide formation is assisted using the coupling agent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM). By linking the C2 amines of monosaccharides to polysaccharides in this way, a new class of polysaccharide derivatives possessing many reducing ends can be obtained. We refer to this class of derivatives as multi-reducing-end polysaccharides (MREPs). This new family of derivatives creates the potential for designing polysaccharide-based materials with many potential applications, including in hydrogels, block copolymers, prodrugs, and as reactive intermediates for other derivatives.