Revealing the Impact of pH on Lipase Structure and Surface Propensity at the Air–Water Interface and in Aqueous Aerosols

Sea spray aerosols (SSAs), generated through oceanic bubble bursting, are chemically complex particles that significantly influence climate processes and ecosystem health. These aerosols are enriched with biological macromolecules such as enzymes and proteins, whose structure and activity at the air-water interface remain poorly understood, particularly under the highly variable pH conditions of SSAs. In this study, we investigate the pH-dependent surface activity of <i>Burkholderia cepacia</i> lipase (BCL), a model extracellular enzyme commonly found in marine environments. Using surface tension and infrared reflection-absorption spectroscopy (IRRAS) measurements, we observe that BCL exhibits increased surface propensity at higher pH compared to acidic conditions. All-atom molecular dynamics simulations further reveal molecular-level insight into these observations, showing structural changes in BCL at the interface in acidic environments with new, highly atmosphere exposed conformations. Additionally, we explore the heterogeneous reactivity of BCL-containing aerosol particles with gaseous nitric acid to identify potential reactive sites relevant to interactions with atmospheric trace gases. Understanding these heterogeneous reaction pathways of biological macromolecules not only may be relevant for SSAs but also has broad implications for the atmospheric reactivity of bioaerosols.