Accelerating Electrochemical Reactions in a Voltage-Controlled Interfacial Microreactor

An Electrochemical Perspective on Reaction Acceleration in Microdroplets

Analytical techniques operating at the nanoscale introduce confinement as a tool at our disposal. This review delves into the phenomenon of accelerated reactivity within micro- and nanodroplets. A decade of accelerated reactivity observations was succeeded by several years of fundamental studies aimed at mechanistic enlightenment. Herein, we provide a brief historical context for rate enhancement in and around micro- and nanodroplets and summarize the mechanisms that have been proposed to contribute to such extraordinary reactivity. We highlight recent electrochemical reports that make use of restricted mass transfer to enhance electrochemical reactions and/or quantitatively measure reaction rates within droplet-confined electrochemical cells. A comprehensive approach to nanodroplet reactivity is paramount to understanding how nature takes advantage of these systems to provide life on Earth and, in turn, how to harness the full potential of such systems.

Ortho C-H Bond Activations in an Atmospheric Microwave Plasma Ion Source

C-H bond ortho-substitution reaction has always been a significant and challenging topic in organic chemistry. We proposed a synthesis method based on microwave plasma torches. High-resolution mass spectrometry was used to monitor rapid reaction products. 2-Alkylbenzimidazole can be formed through the reaction of phenylnitrenium ion and nitriles on a millisecond scale. This reaction can achieve the one-step formation of benzimidazoles from benzene ring single-substituted compounds without the addition of external oxidants or catalysts. A similar C-H bond activation reaction can be accomplished with ketones. Meanwhile, the microwave plasma reactor was modified, and the resulting 2-methylbenzimidazole was successfully collected, indicating the device has good application potential in organic reactions such as C-H bond activation reaction.

Pulsed Direct Current Arc-Induced Nanoelectrospray Ionization Mass Spectrometry

This study explores the innovative field of pulsed direct current arc-induced nanoelectrospray ionization mass spectrometry (DCAI-nano-ESI-MS), which utilizes a low-temperature direct current (DC) arc to induce ESI during MS analyses. By employing a 15 kV output voltage, the DCAI-nano-ESI source effectively identifies various biological molecules, including angiotensin II, bradykinin, cytochrome C, and soybean lecithin, showcasing impressive analyte signals and facilitating multicharge MS in positive- and negative-ion modes. Notably, results show that the oxidation of fatty acids using a DC arc produces [M + O - H]- ions, which aid in identifying the location of C═C bonds in unsaturated fatty acids and distinguishing between isomers based on diagnostic ions observed during collision-induced dissociation tandem MS. This study presents an approach for identifying the sn-1 and sn-2 positions in phosphatidylcholine using phosphatidylcholine and nitrate adduct ions, accurately determining phosphatidylcholine molecular configurations via the Paternò-Büchi reaction. With all the advantages above, DCAI-nano-ESI holds significant promise for future analytical and bioanalytical applications.

Interfacial Electromigration for Analysis of Biofluid Lipids in Small Volumes

Lipids are important biomarkers within the field of disease diagnostics and can serve as indicators of disease progression and predictors of treatment effectiveness. Although lipids can provide important insight into how diseases initiate and progress, mass spectrometric methods for lipid characterization and profiling are limited due to lipid structural diversity, particularly the presence of various lipid isomers. Moreover, the difficulty of handling small-volume samples exacerbates the intricacies of biological analyses. In this work, we have developed a strategy that electromigrates a thin film of a small-volume biological sample directly to the air-liquid interface formed at the tip of a theta capillary. Importantly, we seamlessly integrated in situ biological lipid extraction with accelerated chemical derivatization, enabled by the air-liquid interface, and conducted isomeric structural characterization within a unified platform utilizing theta capillary nanoelectrospray ionization mass spectrometry, all tailored for small-volume sample analysis. We applied this unified platform to the analysis of lipids from small-volume human plasma and Alzheimer's disease mouse serum samples. Accelerated electro-epoxidation of unsaturated lipids at the interface allowed us to characterize lipid double-bond positional isomers. The unique application of electromigration of a thin film to the air-liquid interface in combination with accelerated interfacial reactions holds great potential in small-volume sample analysis for disease diagnosis and prevention.

Is Reaction Acceleration of Microdroplet Chemistry Favorable to Controlling the Enantioselectivity?

Microdroplet chemistry has been proven to amazingly accelerate many chemical and biological reactions in the past 2 decades. Current microdroplet accelerated reactions are predominantly symmetric synthetic but minorly asymmetric synthetic reactions, where stereoselectivity is scarcely concerned. This study selected unimolecular and bimolecular reactions, multicomponent Passerini reactions, and enzymatic ketone reduction as the model reactions to illustrate whether reaction acceleration of microdroplet chemistry is favorable to retaining a chiral center and controlling the enantioselectivity or not. The results illustrated that microdroplet chemistry did not disrupt pre-existing stereogenic centers in chiral starting materials during reactions but did harm to stereospecificity in asymmetric catalysis by chiral catalysts and chiral organic ligands with the exclusion of enzymatic reactions. Our preliminary study reminds us of more cautions to the product enantioselectivity when conducting asymmetric catalysis in microdroplets. We also hope this study may promote more valuable further research on the stereoselectivity of microdroplet chemistry.

Efficient and Selective Photogeneration of Stable N-Centered Radicals via Controllable Charge Carrier Imbalance in Cesium Lead Halide Nanocrystals

Despite the versatility of semiconductor nanocrystals (NCs) in photoinduced chemical processes, the generation of stable radicals has been more challenging due to reverse charge transfer or charge recombination even in the presence of sacrificial charge acceptors. Here, we show that cesium lead halide (CsPbX3) NCs can selectively photogenerate either aminium or aminyl radicals from amines, taking advantage of the controllable imbalance of the electron and hole populations achieved by varying the solvent composition. Using dihalomethane as the solvent, irreversible removal of the electrons from CsPbX3 NCs enabled by the photoinduced halide exchange between the NCs and the dihalomethane resulted in efficient oxidative generation of the aminium radical. In the absence of dihalomethane in solvent, the availability of both electrons and holes resulted in the production of an aminyl radical via sequential hole transfer and reductive N-H bond dissociation. The negative charge of the halide ions on the NC's lattice surface appears to facilitate the aminyl radical production, competing favorably with the reversible charge transfer reverting to the reactant.

Examination of electronically mismatched Diels-Alder reaction by on-line mass spectrometry

RATIONALE

Electronically mismatched Diels-Alder reactions have gained much attention as an alternative pathway for C-C bond formation. To facilitate the development of facile organic transformations, mechanistic investigations are required. Spectroscopic methods (NMR, electron paramagnetic resonance and UV-visible) are normally adopted for mechanistic examinations, but further improvements in directly obtaining structural information of short-lived intermediates are encouraged. Herein, an electronically mismatched Diels-Alder reaction between indole and 1,3-cyclohexadiene was studied using in situ electrospray ionization mass spectrometry (in situ ESI-MS). Based on direct sampling and detection of the in situ ESI-MS without sample pretreatment, the structures and dynamics of important intermediates were examined on-line.

METHODS

A syringe-based photocatalytic reactor and in situ ambient MS (AMS) evaluation system was constructed for mechanism studies. The role of oxygen was confirmed via control reaction employed in the N₂ -bubbled system. The stepwise cation radical-based pathway and the [2 + 2] cycloaddition process were determined through a series of experiments, including solvent evaluation, MS/MS experiments and dynamic monitoring.

RESULTS

The dependence of the reaction on solvent polarity demonstrated that the reaction occurs via the formation of cation radicals, which were captured, identified and dynamically monitored via in situ ESI-MS. Without pre-separation, the intermediate of [2 + 2] cycloaddition was identified and the cycloaddition process was thereby determined to be the combination of [4 + 2] cycloaddition and [2 + 2] cycloaddition. In addition, oxygen was proved to act as an electron mediator for both catalyst Ru(bpz)₃ (PF₆ )₂ and radical cations.

CONCLUSIONS

The mechanism of an electronically mismatched Diels-Alder reaction was successfully deduced by in situ MS associated with a syringe-based photocatalytic reactor. The structures and dynamics of cation radicals, the effect of O₂ for the reaction and the detailed process of [2 + 2] cycloaddition have been well demonstrated. This work could not only promote the understanding and development of facile photocatalytic transformations, but also enlarge the application range of AMS in on-line monitoring.

In Situ Probing and Identification of Electrochemical Reaction Intermediates by Floating Electrolytic Electrospray Mass Spectrometry

The in-depth study of electrochemical (EC) synthesis can require a powerful mass spectrometry (MS) analytical platform which can discover and identify fleeting intermediates in EC reactions. Here we report a floating electrolytic electrospray ionization (FE-ESI) strategy that can perform EC processes in a floating electrolytic cell and monitor intermediates by high-resolution MS. Compared with previous EC-MS methods, a significant advantage of FE-ESI-MS is that it allows one to modulate the electrolytic and electrospray process individually, ensuring its high sensitivity in discovering intermediates and universality to investigate redox reactions in different scenarios. This powerful platform has been successfully used to investigate the EC reductive coupling of p-tolylboronic acid and p-nitrotoluene. A series of nitrene intermediates were discovered and identified by FE-ESI-MS, indicating that a hidden mechanism involving nitrene formation might play a key role in EC reductive coupling process.

Rapid Characterization of Antibodies via Automated Flow Injection Coupled with Online Microdroplet Reactions and Native-pH Mass Spectrometry

Microdroplet reactions have aroused much interest due to significant reaction acceleration (e.g., ultrafast protein digestion in microdroplets could occur in less than 1 ms). This study integrated a microdroplet protein digestion technique with automated sample flow injection and online mass spectrometry (MS) analysis, to develop a rapid and robust method for structural characterization of monoclonal antibodies (mAbs) that is essential to assess the antibody drug's safety and quality. Automated sequential aspiration and mixing of an antibody and an enzyme (IdeS or IgdE) enabled rapid analysis with high reproducibility (total analysis time: 2 min per sample; reproducibility: ∼2% coefficient of variation). Spraying the sample in ammonium acetate buffer (pH 7) using a jet stream source allowed efficient digestion of antibodies and efficient ionization of resulting antibody subunits under native-pH conditions. Importantly, it also provided a platform to directly study specific binding of an antibody and an antigen (e.g., detecting the complexes mAb/RSFV antigen and F(ab')2/RSVF in this study). Furthermore, subsequent tandem MS analysis of a resulting subunit from microdroplet digestion enabled localizing post-translational modifications on particular domains of a mAb in a rapid fashion. In combination with IdeS digestion of an antibody, additional tris(2-carboxyethyl)phosphine (TCEP) reduction and N-glycosidase F (PNGase F) deglycosylation reactions that facilitate antibody analysis could be realized in "one-pot" spraying. Interestingly, increased deglycosylation yield in microdroplets was found, simply by raising the sample temperature. We expect that our method would have a high impact for rapid characterization of monoclonal antibodies.

Catalyst-Free Accelerated Three-Component Synthesis of Betti Bases in Microdroplets

Due to their important roles in medicine and asymmetric metal catalysis, the formation of Betti bases has attracted wide interest in organic chemical community. Traditional multicomponent reaction methods for synthesizing Betti bases normally require long reaction times under harsh conditions (high temperature, microwave or ultrasonic irradiation, etc.) in the presence of various catalysts. In this study, we developed a mild, highly efficient and environmentally friendly method to synthesize Betti bases without the use of any catalysts in microdroplets. The Betti reaction was accelerated by 6.53×10³ in microdroplets by comparing the measured rate constant in bulk. Fifteen Betti bases were synthesized by the microdroplet method using a variety of aldehydes, naphthols and amines with 68-98 % yields at a scaled-up amount of 1.9 g h^-1 . Overall it is an attractive alternative to classic organic synthesis for the construction of Betti bases and derivatives.

Voltage-Controlled Divergent Cascade of Electrochemical Reactions for Characterization of Lipids at Multiple Isomer Levels Using Mass Spectrometry

Cascading divergent reactions in a single system is highly desirable for their intrinsic efficiency and potential to achieve multilevel structural characterization of complex biomolecules. In this work, two electrochemical reactions, interfacial electro-epoxidation and cobalt anodic corrosion, are divergently cascaded in nanoelectrospray (nESI) and can be switched at different voltages. We applied these reactions to lipid identification at multiple isomer levels using mass spectrometry (MS), which remains a great challenge in structural lipidomics. The divergent cascade reactions in situ derivatize lipids to produce epoxidized lipids and cobalt-adducted lipids at different voltages. These lipids are then fragmented upon low-energy collision-induced dissociation (CID), generating diagnostic fragments to indicate C═C locations and sn-positions that cannot be achieved by the low-energy CID of native lipids. We have demonstrated that lipid structural isomers show significantly different profiles in the analysis of healthy and cancerous mouse prostate samples using this strategy. The application of divergent cascade reactions in lipid identification allows the four-in-one analysis of lipid headgroups, fatty acyl chains, C═C locations, and sn-positions simply by tuning the nESI voltages within a single experiment. This feature as well as its low sample consumption, no need for an extra apparatus, and quantitative analysis capability show its great potential in lipidomics.

Investigation on the binary ionization choices for large conjugated amines during electrospray ionization

RATIONALE

Generally, amines form protonated cations ([M + H]⁺ ) in positive polarity during electrospray ionization (ESI). However, it was found that large conjugated amines (LCAs) had binary ionization choices of generating either radical cations (M^•+ ) or [M + H]⁺ during ESI. Investigation on the mechanism would further our understanding of ESI.

METHODS

In this work, the binary ionization behavior of LCAs was reported and studied. Internal factors (functional groups and sizes of conjugated systems) and external factors (solvent type, flow rate, and electrode position) were systematically investigated and discussed.

RESULTS

For the internal factors, electron-donating groups and large conjugated structures of LCAs were conducive to the generation of M^•+ . For the external factors, aprotic solvent, higher flow rate, and shorter distance from the electrode to the spray cone facilitated the formation of M^•+ but hampered the generation of [M + H]⁺ .

CONCLUSION

The present study illustrated that the formations of M^•+ and [M + H]⁺ for LCAs were two independent processes. The M^•+ cations of LCAs were formed on the surface of the electrode through electrochemical oxidation, whereas the [M + H]⁺ cations were generated following the typical ESI evolution process. By regulating the external factors, the ionization results of LCAs could be well modulated.

High Electric Field on Water Microdroplets Catalyzes Spontaneous and Ultrafast Oxidative C-H/N-H Cross-Coupling

Oxidative C-H/N-H cross-coupling has emerged as an atom-economical method for the construction of C-N bonds. Conventional oxidative C-H/N-H coupling requires at least one of the following: high temperatures, strong oxidizers, transition metal catalysts, organic solvents, light, and electrochemical cells. In this study, by merely spraying the water solutions of the substrates into microdroplets at room temperature, we show a series of oxidative C-H/N-H coupling products that are strikingly produced in a spontaneous and ultrafast manner. The reactions are accelerated by six orders of magnitude compared to the same reactions in the bulk. It has been previously proposed by fluorescence microscopy and theory that the spontaneously generated electric field at the microdroplets peripheries can be in the ∼10⁹ V/m range. Based on mass spectrometric analysis of key radical intermediates, we opine that the ultrahigh electric field catalytically oxidizes the substrates by removing an electron, which further promotes C/N coupling. Taken together, we anticipate that microdroplet chemistry will be an avenue rich in green opportunities of constructing C-heteroatom bonds.

Investigation of Tryptic Protein Digestion in Microdroplets and in Bulk Solution

Recent studies have shown that ultrafast enzymatic digestion of proteins can be achieved in microdroplet within 250 μs. Further investigation of peptides resulting from microdroplet digestion (MD) would be necessary to evaluate it as an alternative to the conventional bulk digestion for bottom-up and biotherapeutic protein characterization. Herein we examined and compared protein tryptic digestion in both MD and bulk solution. In the case of MD of β-lactoglobulin B, the preservation of long peptides was observed due to the short digestion time. In addition, MD is applicable to digest both high- and low-abundance proteins in mixture. In the case of digesting NIST 8671 mAb antibody containing a low level of commonly encountered host cell protein (HCP) PLBL2 (mAb:PLBL2 = 100:1 by weight), MD produced lower levels of digestion-induced chemical modifications of asparagine/glutamine deamidation, compared with overnight digestion. No significant difference between MD and bulk digestion was observed in terms of trypsin digestion specificity based on examination of semi- and unspecific-cleaved peptides. Our study suggests that MD, a fast digestion approach, could be adopted for bottom-up proteomics research and for peptide mapping of mAbs to characterize site-specific deamidation and glycosylation, for the purpose of development of biopharmaceuticals.

Microfluidic synthesis as a new route to produce novel functional materials

By geometrically constraining fluids into the sub-millimeter scale, microfluidics offers a physical environment largely different from the macroscopic world, as a result of the significantly enhanced surface effects. This environment is characterized by laminar flow and inertial particle behavior, short diffusion distance, and largely enhanced heat exchange. The recent two decades have witnessed the rapid advances of microfluidic technologies in various fields such as biotechnology; analytical science; and diagnostics; as well as physical, chemical, and biological research. On the other hand, one additional field is still emerging. With the advances in nanomaterial and soft matter research, there have been some reports of the advantages discovered during attempts to synthesize these materials on microfluidic chips. As the formation of nanomaterials and soft matters is sensitive to the environment where the building blocks are fed, the unique physical environment of microfluidics and the effectiveness in coupling with other force fields open up a lot of possibilities to form new products as compared to conventional bulk synthesis. This Perspective summarizes the recent progress in producing novel functional materials using microfluidics, such as generating particles with narrow and controlled size distribution, structured hybrid materials, and particles with new structures, completing reactions with a quicker rate and new reaction routes and enabling more effective and efficient control on reactions. Finally, the trend of future development in this field is also discussed.

Direct Phosphonylation of N-Phenyltetrahydroisoquinolines in Microdroplets

Because of their unique properties and high biological activities, organophosphorus compounds have been used worldwide in agricultural, industrial, medicinal, and veterinary applications. Conventional strategies for direct phosphonylation suffer from the usage of stoichiometric or excessive metallic or nonmetallic catalysts and long reaction times under harsh conditions, leading to a strong desire for environment-friendly protocols for phosphonylation. A protocol for the accelerated phosphonylation of N-phenyltetrahydroisoquinolines in minutes was developed without the use of any catalyst in microdroplets. The phosphonylation process was completed (>85% yields) in 10 min at 40 °C using 0.8 equiv 2,3-dicyano-5,6-dichlorobenzoquinone as the oxidant and acetonitrile as the solvent. The microdroplet phosphonylation strategy showed good suitability to alkyl phosphites and N-phenyltetrahydroisoquinolines bearing electron-withdrawing and electron-donating substitutes, and the yields of the microdroplet reaction were much greater than those of the bulk (accelerated by two orders of magnitude from the ratio of the rate constants using the microdroplet and the bulk method). Furthermore, microdroplet phosphonylation can be scaled up to a 1-phenyl-2-dimethylphosphonite-1,2,3,4-tetrahydroisoquinoline amount of 510 mg h^-1 by spraying 0.1 mol L^-1 N-phenyltetrahydroisoquinoline at 300 μL min^-1. These figures of merit make it a promising alternative to classic organic methodologies for the synthesis of organophosphorus compounds.

Accelerated synthesis of energetic precursor cage compounds using confined volume systems

Confined volume systems, such as microdroplets, Leidenfrost droplets, or thin films, can accelerate chemical reactions. Acceleration occurs due to the evaporation of solvent, the increase in reactant concentration, and the higher surface-to-volume ratios amongst other phenomena. Performing reactions in confined volume systems derived from mass spectrometry ionization sources or Leidenfrost droplets allows for reaction conditions to be changed quickly for rapid screening in a time efficient and cost-saving manner. Compared to solution phase reactions, confined volume systems also reduce waste by screening reaction conditions in smaller volumes prior to scaling. Herein, the condensation of glyoxal with benzylamine (BA) to form hexabenzylhexaazaisowurtzitane (HBIW), an intermediate to the highly desired energetic compound 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), was explored. Five confined volume systems were compared to evaluate which technique was ideal for forming this complex cage structure. Substituted amines were also explored as BA replacements to screen alternative cage structure intermediates and evaluate how these accelerated techniques could apply to novel reactions, discover alternative reagents to form the cage compound, and improve synthetic routes for the preparation of CL-20. Ultimately, reaction acceleration is ideal for predicting the success of novel reactions prior to scaling up and determining if the expected products form, all while saving time and reducing costs. Acceleration factors and conversion ratios for each reaction were assessed by comparing the amount of product formed to the traditional bulk solution phase synthesis.

Incorporating Electro-Epoxidation into Electrospray Ionization Mass Spectrometry for Simultaneous Analysis of Negatively and Positively Charged Unsaturated Glycerophospholipids

In this study, we develop an alternating current (AC)-induced electro-epoxidation reaction and incorporate it into nanoelectrospray ionization for locating carbon-carbon double-bonds in positively and negatively charged forms of lipids simultaneously. An AC voltage plays multiple roles in this method, including initiation of the electro-epoxidation of carbon-carbon double-bonds in both charged states of lipids and protonation/deprotonation of lipids for detection in both ion modes. Moreover, the rapid switch between native lipids and their electro-epoxidation products can be achieved at different AC voltages. The efficacy of the present method was demonstrated in mixtures of lipid standards and in a biological polar lipid extract. The advantages of simultaneous detection of negatively and positively charged unsaturated lipids, the low sample consumption, and on-demand electro-epoxidation should allow its wide applications in lipid-related research.

Dissecting the Flash Chemistry of Electrogenerated Reactive Intermediates by Microdroplet Fusion Mass Spectrometry

A novel mass spectrometric method for probing the flash chemistry of electrogenerated reactive intermediates was developed based on rapid collision mixing of electrosprayed microdroplets by using a theta-glass capillary. The two individual microchannels of the theta-glass capillary are asymmetrically or symmetrically fabricated with a carbon bipolar electrode to produce intermediates in situ. Microdroplets containing the newly formed intermediates collide with those of the invoked reactants at sub-10 microsecond level, making it a powerful tool for exploring their ultrafast initial transformations. As a proof-of-concept, we present the identification of the key radical cation intermediate in the oxidative dimerization of 8-methyl-1,2,3,4-tetrahydroquinoline and also the first disclosure of previously hidden nitrenium ion involved reaction pathway in the C-H/N-H cross-coupling between N,N'-dimethylaniline and phenothiazine.

Glass surface as strong base, 'green' heterogeneous catalyst and degradation reagent

Systematic screening of accelerated chemical reactions at solid/solution interfaces has been carried out in high-throughput fashion using desorption electrospray ionization mass spectrometry and it provides evidence that glass surfaces accelerate various base-catalyzed chemical reactions. The reaction types include elimination, solvolysis, condensation and oxidation, whether or not the substrates are pre-charged. In a detailed mechanistic study, we provide evidence using nanoESI showing that glass surfaces can act as strong bases and convert protic solvents into their conjugate bases which then act as bases/nucleophiles when participating in chemical reactions. In aprotic solvents such as acetonitrile, glass surfaces act as 'green' heterogeneous catalysts that can be recovered and reused after simple rinsing. Besides their use in organic reaction catalysis, glass surfaces are also found to act as degradation reagents for phospholipids with increasing extents of degradation occurring at low concentrations. This finding suggests that the storage of base/nucleophile-labile compounds or lipids in glass containers should be avoided.

Recent Advances of In-Source Electrochemical Mass Spectrometry

Hyphenation of electrochemistry (EC) and mass spectrometry has become a powerful tool to study redox processes. Approaches that can achieve this hyphenation include integrating chromatography/electrophoresis between electroinduced redox reactions and detection of products, coupling an EC flow cell to a mass spectrometer, and performing electrochemical reactions inside the ion source of a mass spectrometer. The first two approaches have been well reviewed elsewhere. This Minireview highlights the inherent electrochemical properties of many mass spectrometry ion sources and their roles in the coupling of electrochemistry and mass spectrometric analysis. Development of modified ion sources that allow the compatibility of electrochemistry with ionization processes is also surveyed. Applications of different in-source electrochemical devices are provided including intermediate capturing, bioanalytical studies, nanoparticle formation, electrosynthesis, and electrode imaging.

Microdroplet Ultrafast Reactions Speed Antibody Characterization

Recently, microdroplet reactions have aroused much interest because the microdroplet provides a unique medium where organic reactions could be accelerated by a factor of 10³ or more. However, microdroplet reactions of proteins have been rarely studied. We report the occurrence of multiple-step reactions of a large protein, specifically, the digestion, reduction, and deglycosylation of an intact antibody, which can take place in microseconds with high reaction yields in aqueous microdroplets at room temperature. As a result, fast structural characterization of a monoclonal antibody, essential for assessing its quality as a therapeutic drug, can be enabled. We found that the IgG1 antibody can be digested completely by the IdeS protease in aqueous microdroplets in 250 microseconds, a 7.5 million-fold improvement in speed in comparison to traditional digestion in bulk solution (>30 min). Strikingly, inclusion of the reductant tris(2-carboxyethyl)phosphine in the spray solution caused simultaneous antibody digestion and disulfide bond reduction. Digested and reduced antibody fragments were either collected or analyzed online by mass spectrometry. Further addition of PNGase F glycosylase into the spray solution led to antibody deglycosylation, thereby producing reduced and deglycosylated fragments of analytical importance. In addition, glycated fragments of IgG1 derived from glucose modification were identified rapidly with this ultrafast digestion/reduction technique. We suggest that microdroplets can serve as powerful microreactors for both exploring large-molecule reactions and speeding their structural analyses.