Studies on the Film Formation of Polysaccharide Based Furan-2-Carboxylic Acid Esters

Novel thiol- amine- and amino acid functional xylan derivatives synthesized by thiol-ene reaction

In the present work, novel thioether xylans were synthesized via a simple procedure using water as solvent. First, allyl groups were introduced on the backbone of xylan by etherification of allyl chloride in aqueous alkaline conditions at 40°C, providing degree of substitution (DS) values up to 0.49. On the second step, the allyl groups were reacted with thioacetic acid, cysteamine hydrochloride or cysteine providing novel thiol-, amine- or amino acid functionalized xylans. The presented modular approach offers broad possibilities for developing new polysaccharide based materials. The thioacetic acid - ene reaction is reported for the first time for polysaccharide modification, yielding a protected thiol that can be stored at atmospheric conditions and can be deprotected by simple hydrolysis just prior to use, providing a versatile water soluble polythiol. The free thiol-groups were utilized for hydrogel formation through thiol-thiol oxidative coupling, allowing good control over the hydrogel shape, such as 3D hydrogel scaffolds and cross-linked foams. Further, the thiol-containing xylan was used to modify filter paper surface by a simple dipping method, which provides a novel and convenient way for introducing thiol-functionality on paper surface.

Thermoresponsive xylan hydrogels via copper-catalyzed azide-alkyne cycloaddition

In the present work, hydrogels of birch wood xylan and thermoresponsive poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEG-PPG-PEG) were prepared using copper catalyzed alkyne-azide cycloaddition (CuAAC) in aqueous reaction conditions. First, reactive azide groups were introduced on the backbone of xylan by etherification of 1-azido-2,3-epoxypropane in alkaline water/isopropanol-mixture at ambient temperature, providing degree of substitution (DS) values up to 0.28. On the second step, the azide groups were reacted with propargyl bifunctional PEG-PPG-PEG utilizing CuAAC, leading to formation of crosslinked hydrogels. The novel xylan derivatives were characterized with liquid and solid state nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA). The temperature controlled swelling behavior of the developed hydrogels was evaluated in the range of 7-70 °C by water absorption and compressive stress-strain measurements, which showed a reduction in water content and change in stiffness with increasing temperature. The morphology of the hydrogels at different temperatures was studied by scanning electron microscopy (SEM), which showed a reduction in pore size with increasing temperature.

Xylan and Xylan Derivatives – Basis of Functional Polymers for the Future

This review highlights xylan and xylan derivatives. It depicts the occurrence and structural diversity of the biopolymer, followed by a presentation of different ways of isolation from biomass. The determination of characteristics, i.e., molecular weight, interaction with other polysaccharides, thermal behaviour, and the biological activity of xylan are reviewed. The application potential arising from the structural features of the unmodified xylan is pointed out. Special attention is concentrated on the possibilities of the modification of functional properties by chemical functionalization of the biopolymers in order to design advanced materials. Within this review recent results in the field are accompanied with selected results of our own work.

Xylan-based nanoparticles: prodrugs for ibuprofen release

Esterification of xylan with ibuprofen via activiation of the carboxylic acid with N,N'-carbonyldiimidazole (CDI) yields products of high drug loadings. Subsequent sulfation of xylan ibuprofen esters using the gentle agent SO(3)/DMF was successfully carried out in order to modify hydrophobicity of the xylan esters. The structure of the novel xylan esters was evaluated by means of NMR spectroscopy. The resulting xylan derivatives self assemble into spherical nanoparticles with mean diameters ranging from 162 to 472 nm. Preliminary stability measurements indicate that hydrolytic stability decreases with increase in degree of substitution of sulfate groups. Thus, a new concept toward improved drug delivery from polysaccharide-based nanoparticles can be established here.