Accelerated d-Fructose Acid-Catalyzed Reactions in Thin Films Formed by Charged Microdroplets Deposition

Abstract

Thin films derived by the deposition of charged microdroplets generated in the ESI source of a mass spectrometer act as highly concentrated reaction vessels in which the final products of an ion–molecule reaction can be isolated by their precipitation onto a solid surface under ambient conditions. In this study, the ESI Z-spray source supplied to a Q-TOF Ultima mass spectrometer was used to investigate the d-fructose acid-catalyzed reactions by microdroplets deposition onto a stainless-steel target surface. High conversion ratios of d-fructose into 5-hydroxymethylfuraldehyde (5-HMF), 5-methoxymethylfuraldehyde (5-MMF), and difructrose anhydrides (DFAs) were obtained with HCl and KHSO4 as metal-free catalysts by using synthetic conditions under which the same products in bulk are not formed. Furthermore, the reaction outcome was found to be highly sensitive to the catalyst and the solvent employed as well as to the ESI source parameters influencing the thin film formation from microdroplets deposition onto the solid surface.

Sulfuric Acid Catalyzed Esterification of Amino Acids in Thin Film

“…In the last few years, several milestone reactions of organic chemistry have been studied in the microdroplets generated into the electrospray ionization (ESI) source of a mass spectrometer. − It has been demonstrated that in the confined volume of the charged microdroplets the reaction rates are accelerated up to 10 5 times compared with the same process in bulk. Moreover, the microdroplets landing onto a solid surface generate a thin film by which the neutral products of the reaction can be separated and quantified. − The thin film retains the peculiar confined volume of the microdroplets needed for reaction acceleration, but it is characterized by a longer lifetime that allows one to extend the reaction time to any desired value. Low molecule solvation, formation of highly reactive transient ionic species, extreme pH value, and a high interfacial electric field are some of the parameters invoked to explain the strong acceleration factors observed in confined volumes with respect to the same processes in bulk. − From this point of view, the carboxylic acid esterification reaction, similarly to other dehydration reactions, − may benefit from the peculiar fast solvent evaporation operative in the microdroplet/thin film system.…”

Mobilized Electrospray Device for On-Tissue Chemical Derivatization in MALDI-MS Imaging

“…3 Finally, Duenãs et al found a fourfold improvement in unique spectral features with electrospray deposition compared to TM sprayer deposition for GT derivatization. 11 As both the neutral and charged spray depositions result in heterogeneous reaction systems that feature the similarity of producing thin films as the individual droplets dry on surface, 7,12,13 improvement in reaction efficiency compared to bulk is anticipated for both. However, no work has focused on directly investigating and discussing the improvement in reaction efficiency between a charged spray and a neutral pneumatic spray for MALDI derivatization.…”

Kinetic Study of the Maillard Reaction in Thin Film Generated by Microdroplets Deposition

“…The electrospray ionization (ESI) source of a mass spectrometer operating under ambient conditions can be considered as a miniaturized laboratory by which the reactions taking place at the liquid-gas interface can be easily studied [1][2][3][4][5][6][7]. The charged microdroplets generated in the ESI process represent confined reaction volumes where the rate of the chemical reactions can be accelerated hundreds of times with respect to the same processes performed in bulk [8][9][10][11][12][13][14][15]. The reaction acceleration was attributed to the greater mobility of reagents at the interface, to the extremely high pH values, and to the strong electric field created at the droplets' interface [16][17][18][19].…”

“…Under these conditions, the final products of the reactions can be collected by continuously supplying the microdroplets onto the target surface. Based on the results obtained on the gas-phase ionic reactions of biomass-derived sugars [20][21][22][23], we have recently extended their gas-phase reactivity to the confined volume of the thin films as a further step to tentatively scale up the observed processes for industrial applications [10].…”