Volume 88, Issue 6

Different chiral bifunctional organocatalysts derived from trans -cyclohexane-1,2-diamine bearing different types of guanidine units able to form-hydrogen bonding activation have been designed. Conformational rigid 2-aminobenzimidazoles bearing a tertiary amino group have been used in enantioselective Michael type reactions of activated methylene compounds to nitroalkenes. The C 2 symmetric bis(2-aminobenzimidazole) derivatives the appropriate organocatalyst for the conjugate addition of 1,3-dicarbonyl compounds to maleimides as well as for the S N 1 reaction of benzylic alcohols with carbon nucleophiles. 2-Aminobenzimidazoles bearing a primary amino group have shown excellent catalytic activity in the Michael reaction of aldehydes to maleimides and nitroalkenes. Diastereomeric 2-aminopyrimidines bearing a prolinamide unit have been incorporated in the trans -cyclohexane-1,2-diamine scaffold and have been used for the inter- and intra-molecular direct aldol reaction under solvent-free conditions. For the Michael reaction of aldehydes with maleimides the primary amine 2-aminopyrimidine has shown excellent efficiency as organocatalyst. The bifunctional character of these organocatalysts has been demonstrated by means of DFT calculations.

Arylxanthones and arylacridones although not yet found in nature are becoming an important group of heterocyclic compounds due to their promising biological activities. Their central cores, xanthone and acridone, are recognized as interesting motifs for drug development mainly to be used in antitumour chemotherapy. The synthesis of this type of compounds is still scarce but several successful examples were recently published and a large variety of arylated xanthone and acridone derivatives were prepared. A systematic survey of the literature dedicated to their synthesis will be presented and discussed in this review.

In this work, chitosan was modified by the esterification with L-alanine in the presence of H 2 SO 4 as a catalyst to increase the number of amino groups with the aim of increasing the adsorption efficiency. Chitosan (CS) and chitosan-O-alanine (CS-Aln) were characterized and investigated by elemental analysis, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The results obtained from elemental analysis and IR indicated the presence of sulfuric acid after neutralization as a crosslinker between CS-Aln chains. Also CS-Aln is more amorphous than CS due to the ionic bonds of crosslinker. The removal of three heavy metals (Mn 2+ , Pb 2+ and Al 3+ ) and total organic carbon (TOC) from wastewater by CS and CS-Aln in the batch mode has been studied at different adsorbent dosages, temperatures and contact times. The maximum metal ions removal efficiency using CS achieved 99.6%, 99.1% and 98.9%, respectively, while by using CS-Aln 95.3%, 99.3% and 98.9% were achieved. However, the maximum adsorption capacity of TOC by CS achieved 50 mg/g and 89 mg/g by CS-Aln. The total maximum adsorption capacity of CS-Aln is higher than CS.

Chitin (β-(1-4)-poly-N-acetyl-D-glucosamine) is widely distributed in nature. A method for the preparation of chitin nanofibers (CNFs) is reported. CNFs are considered to have several potential applications because they have useful properties such as high specific surface area and porosity. More recently, beneficial effects of CNF as functional foods were reported. First, the anti-inflammatory effect of oral administration of chitin CNFs was demonstrated in a mouse model of inflammatory bowel disease (IBD). It was found that CNFs improved clinical symptoms and suppressed IBD. CNFs decreased the areas with nuclear factor-κB (NF-κB) staining in colon tissue. Second, the anti-obesity effects of surface-deacetylated chitin nanofibers (SDACNF) in a mouse model of high-fat diet-induced obesity was evaluated. SDACNFs suppressed the increase in body weight produced by the high-fat diet; however, CNFs did not suppress such weight gain. SDACNFs decreased serum levels of leptin. These results suggest that CNF and SDACNF are promising functional foods for patients with IBD or obesity.

In this article, a review of the research endeavors concerning ionic liquids, that have been used as media for dissolution, gelation, functionalization, and material preparation of chitin, is presented. Although chitin has been identified to show difficulty in solubility and processability, leading to mostly an unutilized organic resource, some ionic liquids have been found to dissolve chitin in certain concentrations. For example, the author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to 4.8 wt% and formed ion gels at higher contents of chitin. Cellulose/chitin binary ion gel and film were also obtained from the individually prepared polysaccharide solutions with ionic liquids. The binary ion gel was applied as a novel electrolyte for an electric double layer capacitor. Acetylation of chitin using acetic anhydride in AMIMBr gave chitin acetates with high degrees of substitution. The modification technique in the AMIMBr solvent was applied to the synthesis of a chitin macroinitiator for atom transfer radical polymerization (ATRP). Grafting of styrene by ATRP from the resulting macroinitiator was conducted to give chitin– graft –polystyrene. Self-assembled chitin nanofibers were fabricated in a methanol dispersion obtained by regeneration from the chitin ion gel with AMIMBr using methanol, which formed a film by subjecting the dispersion to filtration. Co-regeneration from the chitin ion gel coexisting poly(vinyl alcohol) (PVA) gave a self-assembled chitin nanofiber/PVA composite film. The self-assembled chitin nanofibers have also been used as a reinforcing agent for cellulose derivatives to produce composite films.