Electric and Dielectric Behavior of Purified Galactomannan Films

Abstract

This work aimed to extract, purify, and to characterize galactomannan from Adenanthera pavonina L. by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and impedance spectroscopy (IS). Galactomannans (Gal) are polysaccharides, commonly found in the seed endosperm of the Fabaceae family, presenting a chemical structure formed by mannose and galactose, with units connected by glycosidic bonds of D-mannopyranose β(1→4) and by D-galactopyranose α(1→6). Due to their physical-chemical properties and biocompatibility, this biopolymer can be integrated into a vast range of biomedical devices, for example, as biosensors. Galactomannan was extracted from seeds of Adenanthera pavonina L., precipitated in ethyl alcohol, dehydrated, pulverized, and hermetically stored. Galactomannan films purified at 100% were prepared at a concentration of 5% and characterized by FTIR, XRD, and IS. In FTIR, characteristic monosaccharides of Gal were identified as β-D-manopyranose at 814 cm-1 and α-D-galactopyranose at 871 cm-1. From the diffractogram of purified Gal. (GP100), two diffraction peaks are observed at 5.8º and 20º, since the natural interaction of polysaccharides with water, intermediated by ethanol, causes changes related to crystalline-amorphous transitions. IS measurements in the frequency range between 10 Hz and 1 MHz, at room temperature, revealed the existence of a non-Debye relaxation phenomenon, observed using the electrical modulus function formalism (M*) and impedance formalism (Z*), ascribed to the short-range movement of charge carriers. For the purified and crude galactomannan films, we observed that the electrical resistivity is very high, reaching a magnitude of 109 Ω.mm, at the low-frequency region, decreasing to 108 Ω.mm for frequencies higher than 10 kHz. Because of this high impedance characteristic and biocompatibility, purified galactomannan can be easily used as an insulating substrate in biosensors.