Adriana S. Ribeiro

Effects of UV irradiation on the wettability of chitosan films containing dansyl derivatives

The morphological and wetting properties of chitosan films containing dansyl derivatives have been investigated. By means of dynamic contact angle measurements, we study the modification of surface properties of chitosan-based films due to UV irradiation. The results were analyzed in the light of the molecular-kinetic theory which describes the wetting phenomena in terms of the statistical dynamics for the displacement of liquid molecules in a solid substrate. Our results show that the immobilization of dansyl groups in the chitosan backbone leads to a pronounced enhancement of the UV sensitivity of polymeric films.

Synthesis of (R)-(−) and (S)-(+)-3-(1-pyrrolyl)propyl- N-(3,5-dinitrobenzoyl)-α-phenylglycinate and derivatives. A suitable chiral polymeric phase precursor

Abstract A synthetic route to obtain ( R )-(−) ( 1 ), ( S )-(+)-3-(1-pyrrolyl)propyl- N -(3,5-dinitrobenzoyl)-α-phenylglycinate ( 2 ) and derivatives is described. In a first step, pyrrole derivatives were prepared using the Clauson-Kaas method. The esterification, second step, was performed using basic conditions due to sensitivity of the pyrrole group toward acidic conditions. A tautomeric equilibrium involving the stereogenic center induces the product epimerization. The substitution of DMAP and Et 3 N by a highly hindered base, proton-sponge ® , furnished the final products without racemization. The ee of 1 , 2 and of the corresponding methyl esters ( 3 and 4 ) were determined by 1 H NMR analysis in the presence of optically active Eu(tfc) 3 . Epimerization was not observed in the preparation of the carboxylate salts ( 5 – 8 ).

Preparação e caracterização de nanocompósitos poliméricos baseados em quitosana e argilo minerais

In this work nanocomposites based on chitosan and different clays were prepared using polyethyleneglycol (PEG) as plasticizer. The samples obtained were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), thermogravimetric analysis (TGA/DTG) and by mechanical characterization (tensile test) with the aim of investigating the interactions between chitosan and clay. The nanocomposite films prepared using sodium bentonite (Ben) showed an increase of 81.2% in the maximum tensile stress values and a decrease of 16.0% in the Youngs modulus when compared to the chitosan with PEG (QuiPEG) films, evidencing that the introduction of the clay into the polymer matrix provided a more flexible and resistant film, whose elongation at break was 93.6% higher than for the QuiPEG film.

Conjugated conducting polymers with electrochromic and fluorescent properties

We here describe recent progress in conjugated polymers research for the design of materials that present both electrochromic and fluorescent properties. We focus on the importance of electrochemical techniques as important tools for the preparation of materials deposited onto electrode surfaces through electropolymerisation and the investigation of their properties according to the applied potential in order to apply them in optoelectronic devices. The first section is devoted to a brief overview concerning structure and properties of conjugated polymers. Next, we focus on recent advances concerning the synthesis, electrochemical and optical properties of the conjugated electrochromic and fluorescent polymers. Last, we underline the possibilities of application of such materials as active layers for electrochromic devices and organic light emitting diodes (OLEDs), and also as fluorescent electrochemical sensors.