Seminars Archive

Functional and bioinspired materials from cellulose and other plant polysaccharides

Abstract
Cellulose is a natural biopolymer and an almost inexhaustible raw source. It has a hierarchically order supramolecular structure that can be advantageously exploited as model or building block for the preparation of a large class of functional materials. Cellulose nanofibers (CNF) can be obtained by cleaving the structure of native cellulose using different techniques. Among all of them, the regioselective oxidation of the C6 primary hydroxyls of the anhydroglucose units of cellulose to the corresponding carboxylate groups catalyzed by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) in presence of NaBr/NaClO system allows to prepare CNF few nanometers wide and few microns long (TOCNF). This approach is of particular interest due to its mild operative conditions, simplicity, and efficiency [1]. TOCNF were proposed by our group as template for the preparation of ceramic (TiO2 and TiO2/SiO2) porous materials possessing enhanced adsorption and photocatalytic properties with regard to different model molecules [2]. A new class of all-organic cellular solids with macro and micro porosity has been recently synthesized by combining TOCNF and branched polyethyleneimine (bPEI), via formation of amide-bonds (bPEI-TOCNF copolymer). The sponge-like materials obtained in this way have chelating amino groups as basic sites in the nano-porous structure, and show high performances in removing heavy metal ions and phenolic pollutants from contaminated water [3]. The same synthetic protocol has been also extended to generate a novel polymeric conjugate material from TOCNF and bPEI functionalized with pNO2-phenyl urea units, which can be successfully used for the heterogeneous and selective sensing of fluoride anions in DMSO solution [4]. Bioinspired aerogel functionalization by surface modification and coating is in high demand for biomedical and technological applications. Surface coating of TOCNF aerogels with a eumelanin thin film by ammonia-induced solid state polymerization (AISSP) of 5,6-dihydroxyindole (DHI) or 5,6-dihydroxyindole-2-carboxylic acid (DHICA) offers an innovative way for the preparation of original all-natural multifunctional biomaterials having potent antioxidant activity and strong adsorption capacity toward organic dyes [5]. Other than cellulose, polysaccharides from leguminous plants are also interesting to be investigated for the preparation of functional biomaterials. An aerogel obtained from laccase-oxidized galactomannans derived from fenugreek (FG, Trigonella foenum-graecum) has been recently proposed as versatile, biocompatible “delivery system” of active principles in food and non-food products [6]. Bibliography [1] A. Isogai, T. Saito, H. Fukuzumi, TEMPO-oxidized cellulose nanofibers, Nanoscale, 2011, 3, 71–85. [2] L. Melone, et al., Ceramic aerogels from TEMPO-oxidized cellulose nanofibre templates: Synthesis, characterization, and photocatalytic properties, Journal of Photochemistry and Photobiology A: Chemistry 2013, 261, 53– 60. [3] L. Melone et al., TEMPO-Oxidized cellulose cross-linked with branched polyethyleneimine: nanostructured adsorbent sponges for water- remediation, ChemPlusChem 2015, 80(9), 1408-1415. [4] L. Melone et al., Dip in colorimetric fluoride sensing by a chemically engineered polymeric cellulose/ bPEI conjugate in the solid state, RSC Advances 2015, 5(101), 83197-83205. [5] L. Panzella, L. Melone et al., Surface-functionalization of nanostructured cellulose aerogels by solid state eumelanin coating, Biomacromolecules 2016, 17(2), 564-571. [6] B. Rossi et al., An aerogel obtained from chemo-enzymatically oxidized fenugreek galactomannans as a versatile delivery system, Carbohydrate Polymers 2016, in press, doi: 10.1016/j.carbpol.2016.02.007.