Partially Fluorinated Thioethers at the Water/Air Interface. Langmuir Monolayer Characterization and X-ray Scattering Studies

Abstract

A series of partially fluorinated aliphatic thioethers of the following formula: CF(3)-(CF(2))(7)-(CH(2))(10)-S-C(n)H(2n+1), where n = 1, 2, 4, 8, 12, and 18, were synthesized and spread from chloroform solution onto the water/air interface in a Langmuir trough. Upon compression of the film, the surface pressure-mean molecular area isotherms were recorded. It turned out that all the investigated compounds are capable of stable Langmuir monolayers formation. The electrical properties of the studied monolayers have been investigated by monitoring the change in the surface potential (ΔV) upon film compression. The performed experiments proved that regardless of the length of the C(n)H(2n+1) chain, the orientation of the film molecules is very similar. The investigated monolayers have been visualized applying Brewster angle microscopy. The monolayers of the shorter homologues turned out to be homogeneous until their collapse, whereas for longer homologues, the formation of multilayer aggregates was observed. The methods of grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR) have also been applied for the characterization of the organization of thioether molecules in their monolayers. The GIXD experiments proved that the films of the studied thioethers possess a periodical in-plane structure. They are collectively tilted toward the next neighbor (NN tilt), and their packing within the monolayer (xy) plane can be described by the 2-dimentional rectangular centered lattice. Interpretation of the XR results indicate that only the partially fluorinated chain of the thioether molecule is periodically organized at the water/air interface, whereas the hydrocarbon chain is disordered and has a liquid character.

Lupane-Type Pentacyclic Triterpenes in Langmuir Monolayers: A Synchrotron Radiation Scattering Study

“…The L z values are interpreted as the length of the fragment of a filmforming molecule which scatters X-rays coherently; it can be the whole hydrophobic tail or a shorter fragment if there is disorder in this moiety. 44 The values of 13−14 Å observed for the investigated terpenes are in good agreement with the CSD crystallographic data. 4 The length of 13.5 Å is exactly the length of the hydrophobic moiety, which is close to the length of the whole molecule.…”

“…Lupeol and betulinic acid have very similar values of L z . The L z values are interpreted as the length of the fragment of a film-forming molecule which scatters X-rays coherently; it can be the whole hydrophobic tail or a shorter fragment if there is disorder in this moiety . The values of 13–14 Å observed for the investigated terpenes are in good agreement with the CSD crystallographic data .…”

Comparative Characteristics of Membrane-Active Single-Chained Ether Phospholipids: PAF and Lyso-PAF in Langmuir Monolayers

“…The best results (the lowest value of χ 2 ) were obtained for the two-slab model in which the first box refers to the region of the hydrophobic tail (lower value of electron density), whereas the second contains the polar headgroup with hydrating water molecules (higher ρ values). Such a division of phospholipid molecules into two boxes was successfully applied in our previous studies , as well as also frequently applied by the other authors. ,− The parameters derived from such a model were listed in Table .…”

“…GIXD experiments were performed using the same apparatus, as described above in the case of the XR method. The comprehensive theoretical description of the GIXD technique as well as the procedure of data processing were described in detail both in our previous papers − and in several other articles. ,,, GIXD measurements provide high resolution information about the lateral organization of a monolayer on the Å scale. The quantitative information can be obtained only if there is a periodical ordering of surfactant molecules in a monolayer.…”

Ion-Specific Induced Charges at Aqueous Soft Interfaces

“…The results can be used to predict the effect of other trivalent and divalent ions such as in recent results for DMPC monolayers [8] and for fatty acids [5], respectively, as briefly discussed in the Supplementary Material. Our approach can also be expanded to crystal growths at biomimetic interfaces [24] and to ionic effects at cell membranes [25,26].…”