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 31.7% to 12.0%) for the chitosan Schiff bases by using solid state CPMAS (13)C NMR is performed. A linear correlation between the DS obtained for the secondary amino chitosans by (1)H NMR (55.3-10.2%) and those obtained by CPMAS (13)C NMR (34.4-13.8%) has allowed us to calculate an empirical correlation factor that could be applied on chitosan-based aromatic systems. The new chiral-labelled chitosan derivatives exhibit a stable fluorescent behaviour, which was used to explore solvent sensoring applications.

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. Correlations of (19)F NMR chemical shifts of tetrafluoroborate anion for most of the synthesized tri-arylpyrylium tetrafluoroborate complexes with both the pyrylium cation molecular weight and the standard substituent Hammett constants, demonstrate anion-π(+) interaction to act between the polyatomic anion BF4(-) and the pyrylium aromatic system. DFT calculations reveal that an additional (C-H)(+)-anion hydrogen bond involving the H(5) of pyrylium ring exists for these fluorescent dyes that show a tunable cup-to-cap shape cavity. The strong fluorescence emission observed for some representative pyrylium tetrafluoroborates described herein, makes them a promising class of tunable emission wavelength dyes for laser technology applications.

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

A general approach to enantiopure conformationally constrained sugar derived α/ß- and α/γ-peptides has been established. Five-membered ring α/ß-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 22.3 mg/100g) were detected among these varieties. Boiling the fruits for 30 minutes did not affect total carotenoid content, but did change the amount of some specific carotenoids, mainly by the production of Z-isomers. Peach palm varieties had the same carotenoids, but in different proportions, presenting mainly, all E-beta-carotene (26.2% to 47.9%), Z-gamma-carotene (18.2% to 34.3%) and Z-lycopene (10.2% to 26.8%). When antioxidant activity was evaluated using DPPH, it was observed that the variety with higher percentages of beta-carotene (54.1%) presented the higher activity. This is one of the first reports in carotenoid content and antioxidant activity in well typified varieties of Bactris gasipaes, whose results could have a positive impact in the consumption of certain peach palm varieties.

Carotenoid composition and antioxidant activity of the raw and boiled fruit mesocarp of six varieties of Bactris gasipaes / Composición de carotenoides y actividad antioxidante del mesocarpo crudo y hervido del fruto de seis variedades de Bactris gasipaes

Se determinó la concentración y composición de carotenoides a seis variedades de Bactris gasipaes, mediante espectrofotometría y HPLC con un detector de arreglo de diodos. Las diferencias en el contenido de carotenoides totales fueron significativas entre las variedades estudiadas (1.1 a 22.3 mg/100g). El hervir los frutos por 30 minutos no afectó de forma significativa el contenido de carotenoides totales, pero sí la concentración de algunos carotenoides, principalmente de los isómeros Z. Las distintas variedades presentaron los mismos carotenoides pero en diferente proporción, principalmente: todo E-ß-caroteno (26.2 por ciento - 47.9 por ciento), Z-y-caroteno (18.2 por ciento a 34.3 percent) y Z-licopeno (10.2 por ciento a 26.8 por ciento). Al evaluarse la actividad antioxidante con DPPH, se observó que la variedad con el mayor porcentaje de ß-caroteno presentó la mayor actividad. Este es uno de los primeros reportes de composición de carotenoides de Bactris gasipaes bien tipificados, cuyo resultado puede incidir directamente en el consumo de ciertas poblaciones de Bactris.

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 22.3 mg/100g) were detected among these varieties. Boiling the fruits for 30 minutes did not affect total carotenoid content, but did change the amount of some specific carotenoids, mainly by the production of Z-isomers. Peach palm varieties had the same carotenoids, but in different proportions, presenting mainly, all E-ß-carotene (26.2 percent to 47.9 percent), Z-y-carotene (18.2 percent to 34.3 percent) and Z-lycopene (10.2 percent to 26.8 percent). When antioxidant activity was evaluated using DPPH, it was observed that the variety with higher percentages of ß-carotene (54.1 percent) presented the higher activity. This is one of the first reports in carotenoid content and antioxidant activity in well typified varieties of Bactris gasipaes, whose results could have a positive impact in the consumption of certain peach palm varieties.