Headgroup-Specific Interaction of Biological Lipid Monolayer/Water Interface with Perfluorinated Persistent Organic Pollutant (f-POP): As Observed with Interface-Selective Vibrational Spectroscopy

Abstract

Perfluoro compounds are widely used in various manufacturing processes, which leads to their bioaccumulation and subsequent adverse effects on human health. Using interface-selective vibrational spectroscopy (heterodyne-detected vibrational sum frequency generation (HD-VSFG)), we have elucidated the molecular mechanism of the perturbation of lipid monolayers on the water surface using a prototype perfluorinated persistent organic pollutant, perfluoroheptanoic acid (PFHA). PFHA disrupts the well-ordered all-trans conformation of a cationic lipid (1,2-dipalmitoyl-3-trimethylammonium propane (DPTAP)) monolayer and reduces the interfacial electric field at the lipid/water interface. In contrast, the hydrophobic packing of an anionic lipid (1,2-dipalmitoyl-sn-glycero-3-phospoglycerol (DPPG)) monolayer remains largely unaffected in the presence of PFHA, though the interfacial electric field is reduced. For a zwitterionic lipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC))/water interface, both alkyl chain ordering and interfacial electric field are fairly perturbed by PFHA. Lipid headgroup-specific interaction of PFHA and the repulsive interaction of oleophobic fluoroalkyl chain with the lipid alkyl chains govern these distinct perturbations of the lipid monolayers on the water surface.

Momentum-dependent sum-frequency vibrational spectroscopy of bonded interface layer at charged water interfaces

“…However, the zeta potential for liposomes of PC lipids has been reported to be negative at pH 7 ( 37 ). It was also argued that the PC monolayers on neat water were positively charged due to partial deprotonation of the phosphate groups with p K a in the range of 1 to 3 ( 38 ). Whether it is valid to presume negligible normalχDLfalse(2false)false(normalω2false) in interpreting the SF spectra appears to be questionable.…”

Comparative Thermodynamic and Structural Analysis of Polyfluorinated Dodecylphosphonic Acid Adsorption to Distilled and River Water Interfaces

“…To study F 21 -DDPA adsorption to the neutral WR-H 2 O surface, F 21 -DDPA was dissolved in a 1:3 methanol:CHCl 3 mixture (final concentration of 0.375 mg/mL) to overcome the solubility issues observed for the neutral WR-H 2 O solution. The organic solvated F 21 -DDPA solution was then added dropwise to the surface of a neutral WR-H 2 O solution, similar to how lipid monolayers are constructed at the air–water interface. , The results of these measurements are shown in Figure c, where the surface pressure is plotted against the added surface concentration (assuming no F 21 -DDPA dissolves into the subphase). The surface pressure seems to be quite insensitive to the presence of F 21 -DDPA until a concentration of ∼7 × 10 –7 mol/m 2 is reached, where a sudden decrease and then a plateau in the surface tension is observed.…”

Sixty Years of Surface-Specific Spectroscopy

“…The surface selectivity of SHG and VSFG allows the study of molecular partitioning at membranes, and air–liquid and liquid–liquid interfaces, and provides information about the orientation and structure of molecules at these interfaces. For example, Foster et al used vibrational sum-frequency scattering to study the adsorption of charged surfactants onto droplet surfaces, and the way the solvent affects these measurements was investigated by Carpenter et al The competition between surfactant and ion adsorption at saline water/air interfaces was elucidated with SFG, tensiometry, and atomistic simulations by Nguyen et al Mondal and co-workers used VSFG to study the penetration of the “forever chemical” perfluoroheptanoic acid into cationic lipid monolayers, and Haber and co-workers used temperature dependent SHG measurements to obtain information about the free energy of adsorption and transport of a dye molecule across phospholipid bilayers . Heterodyne-detected vibrational sum-frequency generation spectroscopy was used by Moll et al to study the properties of acetic acid and formic acid surfaces .…”