Síntese e caracterização de amidos modificados e aplicação em eletrodos de pasta de carbono

Abstract

Starch is an energy reserve polysaccharide, commercially isolated from several plant sources such as potatoes, corn, cassava and rice, but there are limitations in its use in industry. Modifications to the starch structure have been widely studied and used in order to improve some characteristics of this polymer, such as its viscosity, stability and clarity, in order to use it in several areas. In this study, starches were modified using three methods, two adapted methods using succinic anhydride as reagent and another method using epichlorohydrin. In both procedures using succinic anhydride, a band close to 1724 cm-1 was observed in the infrared spectrum, referring to the C=O group, not observed in the native starch spectrum, which indicated the formation of the desired groups. In the 13C NMR analysis of the first product, the presence of two unreported signals in the spectrum of native starch was observed, one in the region of 175 ppm and the other in 31 ppm, which were attributed respectively to the C=O group and the groups methylene compounds located between carbonyls. The origin of only two peaks suggests symmetry in the product obtained, indicating that cross-linking (CL) has occurred. In the second procedure, several signals referring to carbonyls were observed in the 13C NMR spectrum in the region between 170 and 190 ppm and in the region between 20 and 45 ppm several signals attributed to methylenes. It is concluded that in addition to obtaining the same product as the previous reaction (CL), a product with the carboxylic acid function in the terminal chain called succinylated starch (SUC) was formed. The third procedure used epichlorohydrin as a reagent and was characterized by solid NMR. There were changes in the chemical displacements of C1 carbons, which indicates a change in the crystalline nature of the product obtained and C6 which shows that the reaction occurred preferentially in this carbon. Starches (native and modified) were applied to carbon paste electrodes (CPE) to check whether the starches would improve the electrochemical response. The use of starch, mainly the CPE/CLE sample, had a positive effect on the electrochemical performance of CPE. The presence of CLE starch in the carbon paste favored the electron transfer process, with the highest anode and cathode peak current values. This result was observed because, the LCE starch can attenuate the effect of the hydrophilic groups of the graphite structure, which would result in a lower capacitive current, as a consequence, the fared current referring to the anion redox process [Fe(CN)6]3-/4- has been maximized and the reversibility of the process has been increased. The EPC/CLE electrode was used to detect the drug sodium sulfacetamide, and this electrode in the presence of the analyte showed higher Ipa values when compared to the electrode modified with native starch (EPC/ST) and with the EPC without modification. Such results indicate that the new sensor obtained (EPC/CLE) can be considered a very promising alternative for the identification of drugs and other substances of biological interest.