Doubling Down: Delving into the Details of Diacid Adsorption at Aqueous Surfaces

Abstract

The behavior of complex interfacial systems is central to an ever-increasing number of applications. Vibrational sum frequency (VSF) spectroscopy is a powerful technique for obtaining surface specific structural information. The coherent nature of VSF that provides surface specificity, however, also creates difficulty in spectral interpretation especially as the system complexity increases. Computations of VSF spectra shed light on the molecular level source of the experimental VSF signal, allowing for the analysis of more complicated systems. Unfortunately, the majority of calculations of VSF spectra look at the response of the solvent or of rigid molecules and therefore often poorly reflect the experimental environment of most VSF spectroscopic measurements. In this work, flexible solute molecules at interfaces are investigated by doubling down, obtaining and comparing experimental and theoretical spectra, to determine a more accurate computational treatment. The surface behavior and VSF spectra of glutaric acid and adipic acid at the air/water interface are determined experimentally and calculated using a combination of classical molecular dynamics and density functional theory. Both diacids are found to be surface active. At high concentrations, glutaric acid forms dimers altering its VSF response and acidic properties. Calculated VSF spectra are found to be sensitive to vibrational mode frequencies, with ordering and spacing affecting relative intensities, as well as molecular conformation. A proper description requires consideration of multiple conformers and anharmonic effects on the molecular vibrational energies.

A means to an interface: investigating monoethanolamine behavior at an aqueous surface

“…78 The minimum average surface area per molecule has been calculated to be B126 Å 2 per molecule. This large interfacial footprint is characteristic of other doubly functionalized molecules 53 and indicates MEA is on average largely isolated from itself at the surface, even at high concentrations. Additionally, the overall surface mole fraction of a 10 M MEA solution has been calculated to be B0.3, roughly equivalent to B9.8 M. For a 5 M solution, the surface mole fraction has been calculated to be B0.1, roughly equivalent to B4.9 M. These surface mole fractions indicate a fairly large surface density of MEA that roughly mirrors the bulk solution concentration.…”

“…The computational methodology used in this study has been outlined in previous publications, 13,49,[51][52][53] and is discussed here as it applies to this work.…”

“…Ultimately B2PLYP/6-311++G(2d,2p) was found to provide the best agreement between calculated and experimental VSF spectra with respect to both peak positions and relative intensities; a discussion of these tested methodologies is found in the ESI. † VSF intensities were calculated using in-house code 53 that probes the second-order linear susceptibility tensor via eqn (3).…”

Hierarchical Structure Formation and Effect Mechanism of Ni/Mn Layered Double Hydroxides Microspheres with Large-Scale Production for Flexible Asymmetric Supercapacitors

“…The best tool to accomplish this task is SFG vibrational spectroscopy (SFG-VS). The fundamental principle of SFG-VS technique is demonstrated in Figure a, which is a second-order nonlinear optical process that oscillates at the sum of the two incoming laser frequencies: one visible (ω 1 , incident angle β 1 ) and one IR (ω 2 , incident angle β 2 ) laser beams overlap in an interfacial region of broken symmetry to generate a third beam (the SFG signal, ω = ω 1+ ω 2 , emergence angle β). In this study, the LDHs paste covering the Cu foil and Pt slice were chosen as the active electrodes, respectively, and all components were sealed in a transparent crystal cover together with 6 M KOH electrolyte or pure water.…”

Mitophagy in Parkinson’s Disease: From Pathogenesis to Treatment

“…It has been estimated that GBA1 mutations lead to a 20-fold to 30-fold increased risk of PD, and at least 7–10% of PD patients have a GBA1 mutation [118]. Autophagy defects have been confirmed in iPSC-derived neurons from GBA1-associated PD patients [119], and mitochondrial function was also impaired in GD patients [120]. Additionally, GBA1 deficiencies resulted in α-syn aggregation in PD or GD models and patients [121,122,123], indicating that GBA1 is involved in α-syn pathology and PD pathogenesis, likely by impairing autophagy and mitochondrial function.…”