Síntese, caracterização e polimerização eletroquímica de monômeros derivados de pirrol visando à aplicação em química forense para a revelação de impressões digitais latentes

Abstract

Fingerprints are important in criminal investigations, as they can serve as evidence to identify criminals and/or connect them with the crime scene. In this work, we present a methodology proposal based on the electrodeposition of new conjugated polymers in an aqueous medium. To this end, the synthesis of three new pyrrole derivatives was performed through the reactions of Clauson-Kaas, esterification and bimolecular nucleophilic substitution (SN2). Synthesized monomers were obtained with good chemical yield and they were characterized by one-dimensional / two-dimensional Nuclear Magnetic Resonance (1D / 2D NMR) and Fourier Transform Infrared (FTIR). Polymeric films were synthesized by electrochemical polymerization using the potentiostatic method (PST), by chronoamperometry, and using the galvanostatic method (GST), by chronopotentiometry. For both methods, an electrochemical cell was used containing the aqueous solution with the monomer (0.01 mol L-1) and the electrolyte LiClO4 (0.1 mol L-1), the reference electrode (Ag / AgCl), the auxiliary electrode (Platinum) and the working electrode (stainless steel plate). These methods were also used to obtain the copolymer film formed between PySSO3Na and 3,4-ethylenedioxythiophene (EDOT) monomers. The characterization of the copolymer was made by comparing the absorption bands present in the FTIR spectra of the pure monomers and the copolymer. The electrodeposition was carried out on metallic substrates (stainless steel), containing latent fingerprints (IDLs), applying a recent development method based on polymeric deposition on a conductive substrate. The polymer is deposited between the ridges of the fingerprint, resulting in the “negative” image of the IDL, consequently, revealing it. The quality evaluation of the revealed fingerprints was performed using the Griaule Forensic Fingerprint software, in which it was possible to identify the minutiae present in the fingerprints, and the Bandey Scale, obtaining a grade 4 for all post-treatment images with the software. In addition, Scanning Electron Microscopy (SEM) analysis was performed, and thus it was possible to visualize the polymer-sebaceous residues interface, showing that such materials are morphologically distinct, as well as identifying fingerprint minutiae.