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The utilization of ionic liquids as versatile reaction media and catalysts has garnered significant attention in the field of green and sustainable chemistry. In this study, sum frequency generation vibrational spectroscopy (SFG-VS) is employed to investigate the interactions between l-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) and styrene oxide (SO) at the air/liquid interface. Spectral analysis in the range of 1000 cm−1 to 3700 cm−1 reveals that only vibrational modes of C–H bonds are observed. Notably, the orientation of the epoxy ring of SO is found to be towards the bulk phase, while the three C–H groups on the imidazolium ring of the cation are parallel to the surface. Consequently, there are no observed interactions between the cation and SO. However, in the vibrational spectra of C–H bonds, interactions between the anion BF4- and the CH2 group of the epoxy ring result in blue shifts in the vibrations of CH (SO) and CH3 (cation). These findings support a proposed reaction mechanism where the ionic liquid catalyzes SO first and subsequently reacts with CO2 providing valuable insights into intermolecular interactions and molecular orientations at reaction interfaces. [ABSTRACT FROM AUTHOR]

Investigating the effects of electrolyte ions on the adsorption configuration of methanol at a charged interface is important for studying the interface structure of electrolyte solutions and the oxidation mechanism of methanol in fuel cells. This study uses sum frequency generation (SFG) and heterodyne-detected second harmonic generation (HD-SHG) to investigate the adsorption configuration of methanol at the air/aqueous interface of 0.1 M NaClO4 solution, 0.1 M HClO4 solution and pure water. The results elucidate that the ion effect in the electrolyte solution affects the interface's charged state and the methanol's adsorption conformation at the interface. The negatively charged surface of the 0.1 M NaClO4 solution and the positively charged surface of the 0.1 M HClO4 solution arise from the corresponding specific ionic effects of the electrolyte solution. The orientation angle of methyl with respect to the surface normal is 43.4° ± 0.1° at the 0.1 M NaClO4 solution surface and 21.5° ± 0.2° at the 0.1 M HClO4 solution surface. Examining these adsorption configurations in detail, we find that at the negatively charged surface the inclined orientation angle (43.4°) of methanol favors the hydroxymethyl production by breaking the C–H bond, while at the positively charged surface the upright orientation angle (21.5°) of methanol promotes the methoxy formation by breaking the O–H bond. These findings not only illuminate the intricate ion effects on small organic molecules but also contribute to a molecular-level comprehension of the oxidation mechanism of methanol at electrode interfaces. [ABSTRACT FROM AUTHOR]

We conduct a molecular study on the structural chirality in Langmuir monolayers composed of dipalmitoylphosphatidylcholine (DPPC) using in situ nonlinear optical spectroscopies, including second harmonic generation (SHG) and sum frequency generation (SFG). Chiral SHG response is observed from L-DPPC monolayers at moderate surface pressures and almost vanishes at a high surface pressure. SFG spectra of L-DPPC monolayers show chiral features that can be assigned to the terminal CH3 groups and the CH2 groups attached to the chiral center atom. This means that these achiral moieties form chiral superstructures at the interface. Along with increasing surface pressure, the structural chirality of CH3 groups shows a similar trend as that of chiral SHG, but CH2 chirality increases monotonically. Furthermore, in a racemic DPPC monolayer with a moderate surface pressure, both chiral SHG and chiral SFG of CH3 groups are absent, whereas chiral SFG of CH2 groups is clearly present, indicating that L- and D-DPPC are diastereomers at the air/water interface and interfacial CH2 prefers a certain orientation regardless of the molecular handedness. A molecular mechanism is proposed to explain the origin of the structural chirality in DPPC monolayers. [ABSTRACT FROM AUTHOR]