Quantum Mechanical Investigation of the Oxidative Cleavage of the C–C Backbone Bonds in Polyethylene Model Molecules

Abstract

Recalcitrant plastic waste has caused serious global ecological problems. There is an urgent need to develop environmentally friendly and efficient methods for degrading the highly stable carbon skeleton structure of plastics. To that end, we used a quantum mechanical calculation to thoroughly investigate the oxidative scission of the carbon-carbon (C–C) backbone in polyethylene (PE). Here, we studied the reaction path of C–C bond oxidation via hydroxyl radical in PE. The flexible force constants and fuzzy bond orders of the C–C bonds were calculated in the presence of one or more carbocations in the same PE carbon chain. By comparison, the strength of the C–C bond decreased when carbocation density increased. However, the higher the density of carbocations, the higher the total energy of the molecule and the more difficult it was to be generated. The results revealed that PE oxidized to alcohol and other products, such as carboxylic acid, aldehyde and ketone, etc. Moreover, the presence of carbocations was seen to promote the cleavage of C–C backbones in the absence of oxygen.

Mechanism-Based Design of Efficient PET Hydrolases

“…Scientists have thus far succeeded in identifying and creating biocatalysts that appear to fit the need for PET waste depolymerization on an industrial and commercial scale. The fundamental understanding of interfacial biocatalysis on PET should be extended and transferred to address the challenges associated with the biotechnological degradation of other more abundant plastics such as polyolefins or more similar plastics such as polyamides (PA) and polyurethanes (PUR) with hydrolyzable backbones. ,, While the breakdown of carbon–carbon backbones in polyolefins can be energetically very challenging, , chemical and thermal pretreatments have been shown to enable subsequent biochemical transformation , and thus should be extensively studied in future research. On the other hand, the identification of putative PUR or PA hydrolases is envisioned as a result of collaborative large-scale research activities (e.g., the MIX-UP project and the upPE-T project) on plastic recycling.…”

Microbial enzymes will offer limited solutions to the global plastic pollution crisis

“…Within this framework, it is questionable, if it is possible to cleave C‐C bonds in larger polymers at all using enzymatic processes. Calculations on the free energy needed to crack the C‐C bonds and other challenges linked to polymer degradation imply that it might be almost impossible to establish enzymatic processes for many of the olefins (Jiang et al, 2021 ; Krueger et al, 2015a ).…”

Computational Exploration of Bio-Degradation Patterns of Various Plastic Types

“…Simultaneously, in silico simulations and analysis are becoming de facto prerequisites in many experimental settings to obtain an in-depth molecular interpretation of the enzymatic degradation of different plastic types. Jiang et al applied quantum mechanical calculation to understand the oxidation mechanism of the C-C bond in the PE plastic type [ 37 ]. Joo et al provide molecular insight into PET degradation using a combination of structure, sequence, and site-directed mutagenesis analysis, and Saini at el.…”