Interaction of Sodium Dodecyl Sulfate with Lipid Monolayer Studied by Sum-Frequency Generation Spectroscopy at Air–Water Interface

Abstract

We employed vibrational sum-frequency generation (VSFG) spectroscopy to obtain molecular-level understanding of interaction of anionic surfactant sodium dodecyl sulfate (SDS), in low bulk concentration at the micromolar level, with lipid monolayer zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at the air–water interface. These results are different from those reported at higher bulk concentration of SDS at millimolar level. At very low concentration neither DPPC nor SDS produces any VSFG signal in the CH stretch region in the water subphase, but with the same concentration DPPC produces typical VSFG spectra at the SDS subphase due to interaction between these two molecules. The interaction leads to polar ordering of DPPC molecules with enhancement of VSFG intensity in the CH vibrational region of the hydrophobic tails. The interaction between the lipid and SDS molecules is influenced by concentrations of both lipid and SDS. Hydrophobic interactions between long alkyl chains of SDS and DPPC are responsible for an increase in the conformational order of the alkyl chain of DPPC with a decrease in the gauche defect and increase in trans conformer. Similarly, the orientation and concentration of interfacial water molecules of DPPC monolayer at SDS subphase are controlled by concentration of both SDS and DPPC. The VSFG results are complemented by the surface-pressure measurements.

Solvent Isotopic Effects on a Surfactant Headgroup at the Air–Liquid Interface

“…It has recently been reported that analyzing PPP is beneficial compared to analyzing SSP and PPP polarization combinations because one can avoid difficulties resulting from the CH 3 SS split caused by Fermi interaction with an overtone of the bending mode and interference of the CH vibrational modes with the OH stretch of the interfacial water. 27,64 A range of 30.8−40.5°was found for the average tilt angle (θ) of the terminal methyl group of the alkyl tail. In an all-trans methylene configuration, the difference in tilts between methyl groups and the overall alkyl chain is 41.5°.…”

Einfluss von Tensiden auf die molekulare Struktur der Öl/Wasser‐Grenzfläche

“…Mit Erreichen eines Grenzwertes der SDS-Konzentration führen die Va n-der-Waals-Wechselwirkungen (vdW) zwischen den hydrophoben Ketten der SDS-Moleküle zu einer gewissen Ordnung der SDS-Moleküle an der Flüssigkeit/Luft-GF.D ie Methyl-und Methylen-Schwingungen in den SFG-Spektren sind im Einklang mit früheren Studien. [20] Die Existenz des Methylen-Signals (bei 2860 cm À1 )w eist auf gauche-Defekte in der adsorbierten SDS-Schicht hin.…”

Revealing Molecular-Level Interaction between a Polymeric Drug and Model Membrane Via Sum Frequency Generation and Microfluidics

“…Indeed, in recent years, SFG has widely been applied to study the molecular-level interfacial structures between model cell membranes and different drugs, such as peptides, proteins, DNA, nanoparticles, and polymers. − Interfacial features, including molecular position, orientation, and conformation after interaction with model cell membranes, can be acquired by analyzing the SFG spectra, which are useful for drug design. For instance, a number of antimicrobial peptides have been studied to understand the mechanism on how the cell membranes are disrupted. , It should be noted that the SFG studies were normally performed with no control of the interfacial flow.…”