An Organic Chemist's Guide to Mediated Laccase Oxidation

Abstract

Laccases are oxidases that only require O 2 as a terminal oxidant. Thus, they provide an attractive green alternative to established alcohol oxidation protocols. However, laccases typically require catalytic amounts of mediator molecules to serve as electron shuttles between the enzyme and desired substrate. Consequently, laccase-mediator systems are defined by a multitude of parameters such as, e. g., the choice of laccase and mediator, the respective concentrations, pH, and the oxygen source. This complexity and a perceived lack of comparable data through-out literature represent an entry burden into this field. To provide a solid starting point, particularly for organic chemists, we herein provide a time-resolved, quantitative laccase and mediator screening based on the oxidation of anis alcohol as model reaction. We measured the redox potentials of mediators under the reaction conditions to relate them to their performance. Lastly, for particularly efficient laccase-mediator pairs, we screened important reaction parameters, resulting in an optimized setup for mediator-assisted laccase catalyzed oxidations.

Eco-friendly TEMPO/laccase/O2 biocatalytic system for degradation of Indigo Carmine: operative conditions and laccase inactivation

“…The Lineweaver–Burk plot was used to determine kinetics parameters: K M,eff (0.54 ± 0.05) mM and V max,eff (99 ± 5) nM s −1 . Previously, the elementary step of TEMPO enzymatic oxidation has been directly studied for TEMPO and laccase from T. versicolor , 17,18,25,36,37,65,67,68 and Michaelis constants K M were determined 1.8 mM, 68 1.314 mM, 25 0.393 mM. 37 Even though we studied the general process of IC decolorization instead of the oxidation reaction of TEMPO by laccase, we obtained a very close value K M,eff .…”

Laccase-Carrying Polylactic Acid Electrospun Fibers, Advantages and Limitations in Bio-Oxidation of Amines and Alcohols

“…The mechanism of TEMPO-mediated oxidation of alcohols and amines has been under continuous investigations [ 5 ]. Despite the radical nature of TEMPO, this mediator follows an ionic mechanism [ 38 ].…”

“…However, their low redox potential limits their broad application in the oxidation of simple non-aromatic amines or alcohols. To overcome this problem, the laccase mediator system (LMS) was developed: a low molecular weight redox mediator is oxidized by the enzyme and allowed to oxidize different substrates, then the reduced form of the mediator is restored by laccase using O 2 as the terminal oxidant [ 5 , 6 ]. Several synthetic and natural molecules are used as mediators in LMS, such as 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and its derivatives, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS), hydroxybenzotriazole (HOBt), violuric acid, or some phenolic compounds like syringaldehyde, methylsyringate, and p -coumaric acid [ 7 ].…”

Immobilizing white‐rot fungi laccase: Toward bio‐derived supports as a circular economy approach in organochlorine removal

“…Among LEs, Lacs are known for their efficiency as biocatalysts in the conversion of organic pollutants (Taghizadeh et al, 2020; Yaohua et al, 2019). Contrary to peroxidases, Lac requires only molecular oxygen as an enzyme‐harmless terminal oxidant (Obleser et al, 2022) and is composed of monomeric, dimeric, and tetrameric glycoproteins (Kumar & Chandra, 2020) and belongs to the multicopper oxidase superfamily (AA1) group of LEs (Asemoloye et al, 2021). This enzyme is capable of oxidizing multiple substrates, from nonphenols to larger organics (Asemoloye et al, 2021).…”