Sprayed water microdroplets containing dissolved pyridine spontaneously generate pyridyl anions

Area of Science:

• Physical Chemistry
• Chemical Physics
• Surface Chemistry

Background:

• The pyridine anion (C5H5N−) was previously considered a transient species in the gas phase, observed only indirectly.
• In condensed phases, C5H5N− stability is attributed to solvation effects.
• Understanding the behavior of ions at interfaces is crucial for various chemical processes.

Purpose of the Study:

• To investigate the formation and stability of isolated pyridine anions (C5H5N−) in water microdroplets.
• To determine the gas-phase lifetime of C5H5N− generated under microdroplet conditions.
• To explore the chemical reactivity and potential applications of C5H5N− formed in microdroplets.

Main Methods:

• Generation of isolated C5H5N− from pyridine-dissolved water microdroplets.
• Analysis using negative ion mass spectrometry to detect C5H5N− and its complexes.
• Positive ion mass spectrometry to identify oxidation products, supporting the proposed mechanism.

Main Results:

• Striking observation of isolated C5H5N− in the gas phase, with an estimated lifetime of at least 50 ms.
• Formation of a stable (Py-CO2)− complex, confirming the existence and stability of C5H5N−.
• Evidence for electron transfer from OH− to pyridine at the air-water interface, generating C5H5N− and •OH radicals.

Conclusions:

• Water microdroplets enable the formation of surprisingly stable gas-phase pyridine anions, significantly extending their known lifetime.
• The high electric field at the microdroplet interface facilitates unique electron transfer reactions.
• This study highlights the distinct chemical properties of microdroplets compared to bulk water and suggests a green chemistry approach for synthesizing valuable chemicals.