Stimuli-responsive poly(ampholyte)s containing L-histidine residues: synthesis and protonation thermodynamics of methacrylic polymers in the free and in the cross-linked gel forms

Methacrylate-structured poly(ampholyte)s were synthesized in the homopolymer and copolymer forms starting from the N-methacryloyl-L-histidine (MHist) and the N-isopropylacrylamide (NIPAAm). They were also obtained in the cross-linked (hydrogel) form, showing a close thermodynamic behaviour as that shown by the corresponding soluble free polymer analogues. Viscometric data revealed that the minimum hydrodynamic volume of the polymer at its isoelectric point (pH 5) shifted to lower pHs as the NIPAAm content increased, and beyond a critical low MHist content the reduced viscosity decreased, even at low pHs. The phenomenon was attributed to hydrophobic forces between the isopropyl groups outweighing the repulsive electrostatic interactions of the polymer in the positively charged form. A similar behaviour was shown by the corresponding hydrogel. The latter also revealed a different phase transition phenomenon induced by external stimuli (temperature, pH, ionic strength, electric current) when compared to the acrylate-structured analogues. The polyMHist, as well as the corresponding monomer, was found for two days to be non toxic against the mouse osteoblasts (MC3T3-E1)

Correction: Wound healing properties of hyaluronan derivatives bearing ferulate residues

Correction for 'Wound healing properties of hyaluronan derivatives bearing ferulate residues' by Giuseppe Valacchi et al., J. Mater. Chem. B, 2015, DOI: 10.1039/c5tb00661a

Films made from poly(vinyl alcohol-co-ethylene) and soluble biopolymers isolated from postharvest tomato plant

Blended films were obtained from polyvinyl alcohol‐co‐ethylene (EVOH) with 52 kDa weight average molecular weight (Mw) and three water soluble biopolymers isolated from exhausted tomato plants hydrolysates. Two biopolymers contained mainly polysaccharides and had 27 and 79 kDa Mw, respectively. The third contained mainly lignin‐like C moieties and had 392 kDa MW. The films were fabricated with a biopolymer/EVOH w/w ratio ranging from 0.1 to 0.9. All blends had molecular weight and solubility which were substantially different from the starting materials. They were characterized for the chemical nature, and the thermal, rheological, and mechanical properties. Evidence of a chemical reaction between the biopolymers and EVOH was found. Generally, the films exhibited higher mechanical strength but lower strain at break then the neat EVOH. The best performing blended film was fabricated from the 27 kDa Mw polysaccharide. This contained less than 10% biopolymer. It exhibited 1043 MPa Young's modulus and 70% strain at break against 351 MPa modulus and 86% strain for neat EVOH. The results offer scope for investigating biopolymers sourced from other biowastes to understand more the reasons of the observed effects and exploit their full potential to modify or to replace synthetic polymers

Carboxymethylated-, hydroxypropylsulfonated- and quaternized xylan derivative films

Under alkaline/water conditions carboxymethyl, 2-hydroxypropylsulfonate and trimethylammonium-2-hydroxypropyl groups were introduced into xylan in one step with the goal to prepare film specimens. The materials were characterized by NMR, SEC-MALS, TG/DTG/DTA, AFM and mechanical testing. The properties of triple, double and mono-substituted materials were compared. The numerical molar masses of the specimens were from 12.3 to 17.6 kg/mol with Mw/Mn from 1.27 to 1.34. The elastic modulus values are decreasing in order: xylan (X; 7354 MPa)\u3ecarboxymethyl xylan (CX; 6090MPa)\u3e2-hydroxypropylsulfonate xylan (SX; 6000 MPa)\u3ecarboxymethyl/2-hydroxypropylsulfonate xylan (CSX; 4490 MPa)\u3equaternized xylan (QX; 3600 MPa)\u3ecarboxymethyl/quaternary/2-hydroxypropylsulfonate xylan (CQSX; 3380 MPa)\u3ecarboxymethyl/quaternary xylan (CQX; 2805 MPa). The onset temperatures of SX (214°C), CQSX (212°C), QSX (211°C) and CQX (207°C) were higher than for X (205°C). The roughness values of the film surfaces (3.634-18.667 nm) are higher on top than on the bottom of the specimen

Interfaces study of all-polysaccharide composite films

Films made of xylan (X) and quaternized chitosan (QC) were prepared and the interactions of the polysaccharides on interfaces were discussed. According to elemental analysis, the X film contained also cellulose (31%) which could not be separated from the water suspension. The QC sample was soluble in water due to the presence of quaternized glucosamine units (4%) despite the presence of equal amounts of chitosan (CS, 48%) and chitin (CT, 48%). According to mechanical tests on QC/X = 1/3 composite film, the modulus and tensile strength values were the best from all mixtures measured, but still not better than on the film from X. We assume this is due to the sorption of xylan onto the surface of insoluble cellulose fibrils in the X film. Cyclic voltammetry indicates that the incorporation of X into the QC film decreases the overall positive charge provided by the QC. The X composite with net negative charge is indeed a barrier against the diffusion of ferricyanide anions. Based on TG/DTG/DTA analysis, the onset temperatures (OT) are decreasing with increasing X content in the blended films. X and QC films exhibited the highest OT values in comparison with the blended samples. The lowest OT temperature was observed at QC/X = 1/3. We think it is due to the thermocatalytic effect of the 4-O-methyl-d-glucuronate in X and the QC quaternary groups on the thermolysis–thermo-oxidation mechanism. According to AFM, the QC/X = 1/3 film exhibited the largest roughness values on both sides of the films, likely due to having the highest density of electrostatic interactions. XRD profiles of the films indicate some crystalline residues of cellulose in the xylan component as well as some chitin in the QC component. We assume that the properties are the result of the combination of the electrostatic interactions of carboxyl and quaternary groups of the soluble components of X and QC bonded to the surface of insoluble cellulose fibrils by hydrogen bonds. This probably results in both synergistic and antagonistic effects expressed by the improved or diminished values of determined properties. © 2017, Institute of Chemistry, Slovak Academy of Sciences.26220120054, AUTO21 Network of Centres of Excellence; ERDF, European Regional Development Fund; COFORD, Programme of Competitive Forestry Research for Development; QU, Qatar University; 2/0087/11, SAIA, Slovak Academic Information Agency; 2/7030/7, SAIA, Slovak Academic Information Agency; 2/0007/13, SAIA, Slovak Academic Information Agency; 2/0100/14, SAIA, Slovak Academic Information Agency; 2003SP200280301; 2003SP200280203Slovak Granting Agency VEGA [2/7030/7, 2/0087/11, 2/0007/13, 2/0100/14]; Research & Development Operational Program - ERDF [ITMS 26220120054]; Qatar University [QUUG-CAM-2017-1]; [2003SP200280203]; [2003SP200280301

Humic acid-like matter isolated from green urban wastes. Part I: structure and surfactant properties

A humic acid-like substance (cHAL2) isolated from urban green wastes before composting was compared to a humic acid-like substance (cHAL) isolated from a mix of urban organic humid waste fraction and green residues composted for 15 days. cHAL2 was found to contain more aliphatic and O-alkyl C atoms relative to aromatic, phenol, and carboxyl C atoms, and to yield higher critical micellar concentration (cmc = 0.97 g L-1) and surface tension at the cmc (cmc = 37.8 mN/min water than cHAL (cmc = 0.40 g L-1; cmc = 36.1 mN/m). The results point out that biomass wastes may be an interesting source of biosurfactants with diversified properties that depend on the nature of waste and on its process of treatment