Electron paramagnetic resonance characterization of a humic acid-type polymer model

Abstract

Modelos de ácidos húmicos do tipo poliméricos tem mostrado semelhanças químicas com os ácidos húmicos naturais (AH). Devido à complexidade das substâncias húmicas (SH), esses modelos de ácidos húmicos do tipo poliméricos, no qual os sítios ligantes podem ser melhores definidos, podem ser usados no estudo de metais e outras aplicações. Neste estudo, obteve-se um polímero com características análogas às dos AH coletados em área de cultivo com sistema plantio direto por 9 anos, por meio de reações de síntese, através da polimerização oxidativa em meio alcalino utilizando como precursor a para-benzoquinona. Foi realizado um estudo do ácido húmico (AH) e do ácido húmico sintético (AHS) utilizando espectroscopia de ressonância paramagnética eletrônica (RPE Humic acid-type polymer models have been shown to be similar to natural humic acids (HA) in terms of chemical properties. Due to the complexity of humic substances (HS), this humic acid-type polymer models, in which the ligand sites are better defined, can be used in the study of metals and for other applications. In this study, a polymer with characteristics analogous to those of humic acids isolated from soil surface cultivated using a no-tillage system for nine years, was obtained by means of synthesis reactions, through oxidative polymerization in an alkaline medium using para-benzoquinone as precursor. An EPR spectroscopy study was made of natural humic acids (HA) and synthetic humic acids (SHA). A semiquinone-type free radical signal was detected in the SHA. The spectra showed similar signals for HA from soil and synthetic HA complexed with Fe 3+ , Cu 2+ and Mn 2+ ions.

EPR Spectroscopy as a Tool to Characterize the Maturity Degree of Humic Acids

“…The complex structure of HAs and its high variability make it difficult to characterize. Electron paramagnetic resonance (EPR) is one of the few methods that can provide structural information without artifacts or restrictive experimental conditions [ 4 ]. During humification that occurs in soils [ 4 ], semiquinone radicals are generated, among others, due to polymerization or depolymerization processes.…”

“…Electron paramagnetic resonance (EPR) is one of the few methods that can provide structural information without artifacts or restrictive experimental conditions [ 4 ]. During humification that occurs in soils [ 4 ], semiquinone radicals are generated, among others, due to polymerization or depolymerization processes. In the process of lignin (one of the main components of plant residues) oxidation, the carboxylic or aliphatic groups are lost and, this way, most of the radicals are generated, which are, in general, paramagnetic.…”

The Overlooked Occurrence of Environmentally Persistent Free Radicals in an Area with Low-Rank Coal Burning, Xuanwei, China

“…Thus, they are called EPFRs, in contrast to common free radicals with short lifetimes, such as reactive oxygen species. EPFRs have been shown to induce strong oxidative stress in vitro, leading to cytotoxicity, pulmonary pathologies, and environmental asthma. − Unfortunately, EPFRs have been detected in soil/sediment, suspended particles and natural organic matter . How is EPFR formation dependent on soil composition?…”

Molecular modeling of soil organic matter: Squaring the circle?

“…Photodegradation of HA was studied with model substances like tannic acid and/or p-hydroxybenzoic acid (Cowen and Al-Abadleh, 2009). Barriquello et al (2011) synthesized a polymer with characteristics analogous to those of humic acids isolated from soils, through oxidative polymerization in an alkaline medium using parabenzoquinone as precursor.…”