Accelerated Non-Enzymatic Fatty Acid Esterification during Microdroplet Collision: A Method for Enhanced Sustainability

Abstract

Accelerated non-enzymatic and metal-free “reaction and extraction” of sugar esters at the interface of two immiscible liquid microdroplets is demonstrated. The bimolecular reaction occurs by collision of microdroplets originating from two home-built electrospray sonic ion sources, carrying sugar molecules in water and long-chain fatty acids in toluene, respectively. Our method shows that the rate of reaction is enhanced ∼107 times in comparison to the bulk, initiated by ultrasonic activation. Such a high rate of reaction in the microdroplets can be attributed to factors such as surface activity, concentration enhancement, partial solvation, and temperature-assisted dehydration of the species occurring in microdroplets. We provide evidence for an interfacial nucleophilic addition–elimination reaction mechanism. This method of synthesis is extended to 18 similar reactions. Microdroplet synthesis offers a sustainable method for biphasic reactions, eliminating the need for phase transfer reagents and activating agents such as acids/bases, metals, or enzymes.

Simultaneous and Spontaneous Oxidation and Reduction in Microdroplets by the Water Radical Cation/Anion Pair

“…Microdroplet chemistry is a relatively new field that has engendered much recent interest and the topic has been reviewed [1, 2] . Chemical reactions in micron‐sized droplets under ambient conditions are often orders of magnitude faster than the equivalent bulk reactions [3–9] . The catalyst‐like role of microdroplets makes them excellent tools for rapid chemical derivatization [10, 11] and small‐scale synthesis [3, 12–17] .…”

“…[1,2] Chemical reactions in micron-sized droplets under ambient conditions are often orders of magnitude faster than the equivalent bulk reactions. [3][4][5][6][7][8][9] The catalystlike role of microdroplets makes them excellent tools for rapid chemical derivatization [10,11] and small-scale synthesis. [3,[12][13][14][15][16][17] The observed reaction acceleration is explained by the peculiar environment at the droplet air/ solution interface, where reactants are only partially solvated [1,2,18,19] and which is characterized by a high electric field.…”

Simultaneous and Spontaneous Oxidation and Reduction in Microdroplets by the Water Radical Cation/Anion Pair

“…[ 1 , 2 ] Chemical reactions in micron‐sized droplets under ambient conditions are often orders of magnitude faster than the equivalent bulk reactions. [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ] The catalyst‐like role of microdroplets makes them excellent tools for rapid chemical derivatization[ 10 , 11 ] and small‐scale synthesis. [ 3 , 12 , 13 , 14 , 15 , 16 , 17 ] The observed reaction acceleration is explained by the peculiar environment at the droplet air/solution interface, where reactants are only partially solvated[ 1 , 2 , 18 , 19 ] and which is characterized by a high electric field.…”

Aqueous microdroplets enable abiotic synthesis and chain extension of unique peptide isomers from free amino acids

“…Interfacial chemistry appears to play a crucial role in facilitating biomolecule transformations in aqueous environments, as has been demonstrated in biphasic systems ( 91 ), cell condensates, and subcompartments ( 98 ), as well as in microdroplets ( 12 , 13 , 21 , 29 , 42 , 51 – 53 , 99 , 100 ). The observed generation of peptides from free amino acids at the air–water interface of pure water droplets, the simplest of all prebiotic systems, suggests that settings such as atmospheric aerosols or sea spray may have provided a unique and ubiquitous environment to overcome the energetic hurdles associated with condensation and polymerization of biomolecules in water.…”

“…Of particular interest is the observation that the air–water interface of monolayers and thin films ( 28 – 31 ), inverted micelle aerosols ( 12 ), Leidenfrost droplets ( 32 – 36 ), and charged or neutral microdroplets ( 37 – 46 ) all reveal vastly different chemical kinetics compared to bulk, with rate constants increased by up to six orders of magnitude ( 47 , 48 ). This interfacial acceleration phenomenon has been reported for prebiotically relevant reactions including condensation ( 12 , 21 , 29 , 49 – 53 ), redox ( 54 , 55 ), nucleophilic addition ( 41 , 43 ), and ultraviolet-initiated photopolymerization reactions ( 56 ).…”