Electron Withdrawing Groups and Steric Effects on the Methanogenic Toxicity

Abstract

Aims: This work highlights the influence of the additivity of withdrawing electronic groups attached to the aromatic ring on the inhibition of the production of methane gas by the methanogenic bacteria acetoclastic. Study Design: Anaerobic digestion of pig manure, anaerobic toxicity essay, Effect of additivity and the number of electron withdrawing groups on the methanogenic toxicity, relationship between the methanogenic toxicity, electron and steric effects.

Semi-empirical Approach on the Methanogenic Toxicity of Aromatic Compounds on the Biogas Production

“…However, this toxicity depends on the nature of the aromatic compounds, i.e. on the structural effects of the bound substituents on the benzene ring [6][7]. However, the substituents on the benzene ring, depending on their hydrophobic or hydrophilic nature made the latter more lipophilic or hydrophilic [6][7]29].…”

“…However, several parameters, namely : temperature, pH and potential of the environment, the tightness, cost and permanent monitoring of the digester, the nature of the substrate and the presence of inhibiting substances in the substrate to be biomethanized, limit the development of this technology, by blocking the biological activity of the archaeous plants [3][4][5]. Of all these parameters, the presence of inhibiting compounds, especially aromatic compounds, is currently one of the main causes of malfunction of this technology, as these compounds are naturally present in most organic waste and industrial effluents [6][7][8][9]10].…”

“…Our previous studies on methanogenic toxicity (MT) [6][7] have shown that the lipophilic character of the aromatic compound (quantified by the Log Poct value) as well as its electron density (influenced by the electro attracting or electrodonating character of its substituents) are at the basis of this toxicity. Since, the cell membranes of these methanogenic archae are nothing but lipoproteins (lipids), and on the other hand, the modification of the electron density on the aromatic ring considerably affects its reactivity towards the coenzyme M. In addition to their surfactant effects on cell membranes, thus modifying the cell diffusion and surface tension, aromatic compounds are also responsible for the disruption of certain interactions, in particular that between coenzyme M and the acetate substrate, at the expense of the formation of a complex by donor-acceptor charge transfer between coenzyme M and aromatic toxins [6][7]. This interaction probably leads to the blocking of the activity of coenzyme M on the acetate substrate.…”

“…This interaction probably leads to the blocking of the activity of coenzyme M on the acetate substrate. Nevertheless, the steric effects of the substituents on the aromatic ring may sometimes cause some restriction of the MT of the aromatic ring [7,11]. A good correlation between the structures of these aromatic compounds and their inhibitory effects on the bioactivity of acetoclastic methanogenic archaea.…”

Distortions and Deformations of Metaled Meso-Substituted and Unsubstituted Porphyrins and Derivatives in Crystal Structures

“…Studies on the aromatic rings such as benzene and others have shown that substitution and complexation influence the electronic density and lead to the new properties [9] [10].…”