Solvent-Free Synthesis of Amidated Carboxymethyl Cellulose Derivatives: Effect on the Thermal Properties.

The present work explores the possibility of chemically modifying carboxymethyl cellulose (CMC), a widely diffused commercial cellulose ether, by grafting of hydrophobic moieties. Amidation of CMC, at high temperature and in heterogeneous conditions, was selected as synthetic tool for grafting on CMC a panel of commercially available amines (bearing long aliphatic chains, alkyl aromatic and heteroaromatic groups, more or less spaced from the cellulose backbone). The reaction was successfully carried out in absence of solvents, catalysts and coupling agents, providing a promising and more sustainable alternative to conventional amidation procedures. Relationships between the chemical structure of the obtained CMC derivatives and their thermal properties were carefully studied, with a particular attention to the thermal behavior. Grafting of aromatic and heteroaromatic alkyl amines, presenting a linear alkyl chain between CMC backbone and a terminal bulky moiety, allowed for efficiently separating the polysaccharide chains, improving their mobility and resulting in a consequent lowering of the glass transition temperature (Tg). The Tg values obtained (90-147 °C) were found to be closely dependent on both the size of the aliphatic spacer, the structure of the aromatic ring and the extent of amidation.

Sodium and acidic alginate foams with hierarchical porosity: Preparation, characterization and efficiency as a dye adsorbent.

A novel approach for the preparation of sodium alginate foams by ice-templating, followed by freeze-drying was described. Important effects of the preparation parameters on the macroporous structure of the final materials could be evidenced. A functionalization procedure for the preparation of acidified macro/meso-porous foams with high surface area was optimized and the efficiency of one alginic acid foam was demonstrated for the adsorption of a basic dye (methylene blue) from aqueous solution. The comparison of the maximum monolayer adsorption capacity of this adsorbent with the values already reported for other biosorbents clearly identified alginic acid foams as competitive sorbents for the removal of methylene blue from aqueous solutions.

Boronic acid-modified alginate enables direct formation of injectable, self-healing and multistimuli-responsive hydrogels.

One-step functionalization of alginate with boronic acid groups allowed spontaneous formation of biocompatible hydrogels under basic conditions without additional complementary molecules or crosslinking agents. The dynamic nature of boronate ester bonds formed with vicinal diols present on alginate pyranose rings provided remarkable self-healing, injectable and multi-stimuli responsive properties to the material.

Keratin Protein-Catalyzed Nitroaldol (Henry) Reaction and Comparison with Other Biopolymers.

Here we describe a preliminary investigation on the ability of natural keratin to catalyze the nitroaldol (Henry) reaction between aldehydes and nitroalkanes. Both aromatic and heteroaromatic aldehydes bearing strong or moderate electron-withdrawing groups were converted into the corresponding ß-nitroalcohol products in both DMSO and in water in the presence of tetrabutylammonium bromide (TBAB) as a phase transfer catalyst. Negligible background reactions (i.e., negative control experiment in the absence of keratin protein) were observed in these solvent systems. Aromatic aldehydes bearing electron-donating groups and aliphatic aldehydes showed poor or no conversion, respectively. In general, the reactions in water/TBAB required twice the amount of time than in DMSO to achieve similar conversions. Moreover, comparison of the kinetics of the keratin-mediated nitroaldol (Henry) reaction with other biopolymers revealed slower rates for the former and the possibility of fine-tuning the kinetics by appropriate selection of the biopolymer and solvent.

DNA-catalyzed Henry reaction in pure water and the striking influence of organic buffer systems.

In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry) reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA). Both heteroaromatic aldehydes (e.g., 2-pyridinecarboxaldehyde) and aromatic aldehydes bearing strong or moderate electron-withdrawing groups reacted satisfactorily with nitromethane obeying first order kinetics and affording the corresponding ß-nitroalcohols in good yields within 24 h. In contrast, aliphatic aldehydes and aromatic aldehydes having electron-donating groups either did not react or were poorly converted. Moreover, we discovered that a number of metal-free organic buffers efficiently promote the Henry reaction when they were used as reaction media without adding external catalysts. This constitutes an important observation because the influence of organic buffers in chemical processes has been traditionally underestimated.