Accelerated Zymonic Acid Formation from Pyruvic Acid at the Interface of Aqueous Nanodroplets.

To explore the role of the liquid interface in mediating reactivity in small compartments, the formation kinetics of zymonic acid (ZA) is measured in submicron aerosols (average radius = 240 nm) using mass spectrometry. The formation of ZA, from a condensation reaction of two pyruvic acid (PA) molecules, proceeds over days in bulk solutions, while in submicron aerosols, it occurs in minutes. The experimental results are replicated in a kinetic model using an apparent interfacial reaction rate coefficient of = (0.

A Detailed Reaction Mechanism for Thiosulfate Oxidation by Ozone in Aqueous Environments.

The ozone oxidation, or ozonation, of thiosulfate is an important reaction for wastewater processing, where it is used for remediation of mining effluents, and for studying aerosol chemistry, where its fast reaction rate makes it an excellent model reaction. Although thiosulfate ozonation has been studied since the 1950s, challenges remain in developing a realistic reaction mechanism that can satisfactorily account for all observed products with a sequence of elementary reaction steps. Here, we present novel measurements using trapped microdroplets to study the pH-dependent thiosulfate ozonation kinetics.

Infrared Reflection Absorption Spectroscopy (IRRAS) of Water-Soluble Surfactants: Is it Surface-Specific?

Infrared reflection absorption spectroscopy (IRRAS) is commonly used to study the structure and chemistry of molecules residing at surfaces, including water surfaces, which has far-reaching applications including atmospheric chemistry and food science. However, there is some debate regarding the surface-specificity of IRRAS when examining soluble surfactants on aqueous solutions, and there is some evidence that the surface-specificity may differ between IRRAS of ionic surfactants and soluble organic acids. This paper presents infrared reflection absorption (IRRA) spectra of soluble organic acids underneath monolayers of insoluble surfactants, where the contributions from the insoluble surfactants are subtracted from the spectra to capture "subsurface effects".

Infrared Reflection-Absorption Spectroscopy of α-Keto Acids at the Air-Water Interface: Effects of Chain Length and Headgroup on Environmentally Relevant Surfactant Films.

A variety of organic surfactants are found at air-water interfaces in natural environments, including on the surfaces of aqueous aerosols. The structure and morphology of these organic films can have profound impacts on material transfer between the gas and condensed phases, the optical properties of atmospheric aerosol, and chemical processing at air-water interfaces. Combined, these effects can have significant impacts on climate via radiative forcing, but our understanding of organic films at air-water interfaces is incomplete.

Oxygen Effect on the Ultraviolet-C Photochemistry of Lactic Acid.

Lactic acid, a small α-hydroxyacid, is ubiquitous in both indoor and outdoor environments. Recently, the photochemistry of lactic acid has garnered interest among the abiotic organic chemistry community as it would have been present in abiotic settings and photoactive with the high-energy solar radiation that would have been available in the low oxygen early Earth environment. Additionally, we propose that the photochemistry of lactic acid is relevant to modern Earth during indoor ultraviolet-C (UVC) sterilization procedures as lactic acid is emitted by humans and is thus prevalent in indoor environments where UVC sterilization is increasingly being used.

Infrared Reflection-Absorption Spectroscopy of α-Hydroxyacids at the Water-Air Interface.

Organic molecules, including α-hydroxyacids, are ubiquitous in the natural environment. Often found at water-air interfaces, organic molecules can alter the structure of the interface or participate in interfacial chemistry. Despite their prevalence in the environment, the structure and ordering of α-hydroxyacids have not been widely investigated at water-air interfaces, and the impact of the hydrophobic tail length on structure has not been explored.

Water-Air Interfaces as Environments to Address the Water Paradox in Prebiotic Chemistry: A Physical Chemistry Perspective.

The asymmetric water-air interface provides a dynamic aqueous environment with properties that are often very different than bulk aqueous or gaseous phases and promotes reactions that are thermodynamically, kinetically, or otherwise unfavorable in bulk water. Prebiotic chemistry faces a key challenge: water is necessary for life yet reduces the efficiency of many biomolecular synthesis reactions. This perspective considers water-air interfaces as auspicious reaction environments for abiotic synthesis.

Chemistry and Photochemistry of Pyruvic Acid at the Air-Water Interface.

Interfacial regions are unique chemical reaction environments that can promote chemistry not found elsewhere. The air-water interface is ubiquitous in the natural environment in the form of ocean surfaces and aqueous atmospheric aerosols. Here we investigate the chemistry and photochemistry of pyruvic acid (PA), a common environmental species, at the air-water interface and compare it to its aqueous bulk chemistry using two different experimental setups: (1) a Langmuir-Blodgett trough, which models natural water surfaces and provides a direct comparison between the two reaction environments, and (2) an atmospheric simulation chamber (CESAM) to monitor the chemical processing of nebulized aqueous PA droplets.

Lactic Acid Spectroscopy: Intra- and Intermolecular Interactions.

Lactic acid, a relevant molecule in biology and the environment, is an α-hydroxy acid with a high propensity to form hydrogen bonds, both internally and to other hydrogen-bond-accepting molecules. This work includes the novel recording of infrared spectra of gas-phase lactic acid using Fourier transform infrared spectroscopy, and the vibrational absorption features of lactic acid are assigned with the aid of computationally simulated vibrational spectra with anharmonic corrections. Theoretical chemistry methods are used to relate intramolecular hydrogen-bond strengths to the relative stability of lactic acid conformers.