Hydration, Orientation, and Conformation of Methylglyoxal at the Air–Water Interface

Abstract

Aqueous-phase processing of methylglyoxal (MG) has been suggested to constitute an important source of secondary organic aerosol (SOA). The uptake of MG to aqueous particles is higher than expected because its carbonyl moieties can hydrate to form geminal diols, as well as because MG and its hydration products can undergo aldol condensation reactions to form larger oligomers in solution. MG is known to be surface active, but an improved description of its surface behavior is crucial to understanding MG-SOA formation. These studies investigate MG adsorption, focusing on its hydration state at the air-water interface, using a combined experimental and theoretical approach that involves vibrational sum frequency spectroscopy, molecular dynamics simulations, and density functional theory calculations. Together, the experimental and theoretical data show that MG exists predominantly in a singly hydrated state (diol) at the interface, with a diol-tetrol ratio at the surface higher than that for the bulk. In addition to exhibiting a strong surface activity, we find that MG significantly perturbs the water structure at the interface. The results have implications for understanding the atmospheric fate of methylglyoxal.

Bulk Contributions Modulate the Sum-Frequency Generation Spectra of Water on Model Sea-Spray Aerosols

“…23,41,44,49,61,70,71,73,79,80,92,94 More recent efforts have focused on gaining molecular-level insights into complex interfaces by determining specific hydrogen-bonding patterns, surface propensity and binding motifs of dissolved species, and effects of interfacial electric fields. 15,33,38,65,66,72,91,99,107 These studies demonstrated that interfacial water molecules reorient to point their hydrogen atoms toward negatively charged surfaces and away from positively charged surfaces. 73 Zwitterionic headgroups of phospholipid monolayers on aqueous subphases reorient water molecules to a lesser extent, but along the same direction as negatively charged headgroups.…”

Bulk Contributions Modulate the Sum-Frequency Generation Spectra of Interfacial Water on Model Sea-Spray Aerosols

“…[25][26][27][28][29][30][31][32][33][34][35][36] More recent efforts have focused on gaining molecular-level insights into complex interfaces by determining specific hydrogen bonding patterns, surface propensity and binding motifs of dissolved species, and effects of interfacial electric fields. [37][38][39][40][41][42][43][44][45] These studies demonstrated that interfacial water molecules reorient to point their hydrogen atoms toward negatively charged surfaces and away from positively charged surfaces. 29 Zwitterionic headgroups of phospholipid monolayers on aqueous subphases reorient water molecules to a lesser extent, but along the same direction as negatively charged headgroups.…”

De Novo Determination of Molecular Orientation at Interfaces through Multimode Polarization-Dependent Sum-Frequency Generation Spectroscopy

“…SFG signals recorded with different polarization combinations for the SFG, visible and infrared fields further contain the orientational information of interfacial molecular groups, accessible through their vibrations. [7][8][9][10][11][12][13][14][15][16][17] For example, Shen and Wang groups explored the orientation of the free O-H groups of the interfacial water molecules. [8][9][10][11]18,19 Tyrode, Johnson, and co-workers investigated the molecular orientation of several organic molecules at the air-water interface.…”