Final answer:
The carboxylation of graphene oxides via biotin-dependent enzymes utilizes carbonate as the carboxyl source, ATP for activation, and Mg2+ to reduce negative charge, resulting in carboxybiotin and subsequent transfer of the carboxyl group to a substrate like acetyl-CoA.
Step-by-step explanation:
The chemical mechanism during the carboxylation of graphene oxides involves several steps. Essential to this mechanism are biotin-dependent enzymes that facilitate the addition of a carboxyl group to a substrate. The process uses carbonate (HCO3-) as the source of the carboxyl group, ATP to activate it, and Mg2+ serves to reduce the overall negative charge.
Nucleophilic attack is central to this mechanism. Firstly, the biotin moiety attacks the activated carbonate to form carboxybiotin. Subsequently, the substrate performs a nucleophilic attack on the carboxybiotin, thus transferring the carboxyl group from biotin to the substrate. This mechanism is illustrated in scientific literature with acetyl-CoA as the substrate.
In another context, the enzyme rubisco catalyzes the carboxylation of ribulose bisphosphate (RuBP), where a different mechanism is observed. Here, carbon dioxide is added to RuBP, and the product is a six-carbon compound which then breaks down into two molecules of phosphoglycerate (PGA). This process does not involve biotin or ATP as in the previously described mechanism.