Mechanoenzymatic Transformations in the Absence of Bulk Water: A More Natural Way of Using Enzymes

Abstract

Mechanochemical enzymatic reactions without bulk water have emerged as a low‐waste and efficient method to access useful chemicals and to depolymerize biomass components in a single step. This emergent mechanoenzymatic reaction strategy is able to take advantage of the stereospecificity, regio‐ and stereoselectivity, as well as renewability of enzymes, while avoiding bulk solvents, offering the opportunity to control the direction of the reaction, bypassing reactant solubility issues, and enabling reactions with water‐sensitive substrates or products. Enzymes are traditionally used in dilute aqueous solution, which is quite different from their crowded, water‐depleted natural environment. This review outlines recent work which demonstrates that enzymes can be equally or even more efficient under mechanochemical conditions, without bulk aqueous or organic solvent.

Sustainability Assessment of Mechanochemistry by Using the Twelve Principles of Green Chemistry

“…[174] In recent years, mechanochemistry has also experienced an expansion from metal-catalyzed, [9i,175] and organocatalyzed reactions [9e,176] to biocatalytic reactions. [177,178] To date, hydrolytic enzymes, such as lipases, [179][180][181] proteases, [143,182] and glucosidases, [183,184] among others, [177,178,185] have proven stable to catalyze mechanochemical reactions by ball milling and extrusion techniques (Scheme 12). Since enzymes are generally biodegradable and renewable their use in mechanochemical reactions truly enhances the sustainability of chemical synthesis.…”

Efficient Enzymatic Hydrolysis of Biomass Hemicellulose in the Absence of Bulk Water

“…In the remainder of this manuscript, enzyme loading will be described as the mass of protein per total initial solid mass used, i.e., the combined mass of the substrate and of the enzyme preparation. The enzymatic reactions reported herein proceed either via ball milling with or without subsequent aging (static incubation) at 55 °C, or via multiple cycles of milling and aging—a process known as reactive aging (RAging) [29,30,31,32]. Unless mentioned otherwise, milling was performed at 30 Hz and room temperature, in 10 mL teflon jars containing two stainless steel balls (7 mm in diameter).…”

“…Recent studies by our group, and others [22,23,24,25,26,27,28,29,30,31,32], have established that enzymes can function very well without bulk organic or aqueous solvent. In particular, our group has demonstrated that in the absence of bulk water, cellulases can efficiently catalyze cellulose hydrolysis to glucose [29,30], and chitinases can favor the clean depolymerization of chitin to N -acetylglucosamine [31].…”

Rapid mechanoenzymatic saccharification of lignocellulosic biomass without bulk water or chemical pre-treatment

“…Not only were enzymes reported to tolerate mechanical stress, [33][34][35][36][37][38][39][40][41][42] but they were also found to remain active in moist solid mixtures. 43 Static incubation of enzymatic reaction mixtures without bulk water may provide a better mimic of the natural environment of enzymes, and especially so for enzymes that are secreted by soil microorganisms that thrive on moist surfaces rather than dilute aqueous solutions. 67,68 By minimizing the total volume of the reaction mixture, the herein presented mechanochemically-activated enzymatic processes greatly facilitate handling and mixing, and curtail waste associated with processing and depolymerization of polysaccharide biomass.…”

“…Our group, and others, have recently demonstrated that enzymes can function surprisingly well in the absence of aqueous or organic solvent, and that their activity can be facilitated by mechanical mixing. 33,34,43,[35][36][37][38][39][40][41][42] This emerging area of research, mechanoenzymology, may provide a solution to the solids effect challenge. In particular, we recently developed a mechanoenzymatic technique ( Fig.…”