Fluorescent imino and secondary amino chitosans as potential sensing biomaterials.

A variety of fluorescent imino and secondary amino chitosans were synthesized under very mild conditions by reaction of the biopolymer amino functions with aromatic aldehydes in an acidified methanolic suspension. Simultaneous reactions of several aldehydes with chitosan were successfully carried out, and kinetic studies showed that 1-pyrenecarboxaldehyde reacts the fastest among them. An unprecedented study on the evaluation of the degree of N-substitution (DS, ranging from 31.

Electronically tunable anion-π interactions in pyrylium complexes: experimental and theoretical studies.

Noncovalent interactions of anions with electron-deficient aromatic rings that have been studied so far involve non-heteroaromatic or nitrogen-based heteroaromatic systems. Here we report the first case of an organic oxygenated aromatic system, in particular the tri-aryl-pyrylium tetrafluoroborate system, for which noncovalent anion-π interactions of the pyrylium cation with the tetrafluoroborate anion have been experimentally detected and demonstrated by means of (19)F NMR spectroscopy in solution. A series of pyrylium tetrafluoroborate salts were synthesized in the presence of BF3·Et2O, by direct reaction of 4-substituted benzaldehydes with 4-substituted acetophenones or via the previously obtained chalcone of the less reactive ketone.

Synthesis of cyclically constrained sugar derived α/β- and α/γ-peptides.

A general approach to enantiopure conformationally constrained sugar derived α/β- and α/γ-peptides has been established. Five-membered ring α/β-peptides were synthesized via formyl C-glycofuranosides, easy available from hexose-derived azido-2-equatorial-OH-glycopyranosides by DAST-promoted ring contraction. By means of a regioselective oxidation with TEMPO at C-6 of hexose-derived 3-azido glycopyranosides as the key step, two- and three-residue α/γ-peptides having a six-membered ring were obtained in good yields and under very simple experimental conditions.

Carotenoid composition and antioxidant activity of the raw and boiled fruit mesocarp of six varieties of Bactris gasipaes.

Total carotenoid content and composition of carotenoids of six varieties of Bactris gasipaes were determined by spectrophotometry and HPLC, with photodiode array detector. Significant differences in total carotenoid content (1.1 to 22.