Polarization-modulated Reflection Absorption Spectroscopy Research Articles

Antitrypanosomal activity of epi-polygodial from Drimys brasiliensis and its effects in cellular membrane models at the air-water interface

Epi-polygodial, a drimane sesquiterpene was isolated from Drimys brasiliensis (Winteraceae). This compound demonstrated high parasite selectivity towards Trypanosoma cruzi trypomastigotes (IC50 = 5.01 μM) with a selectivity index higher than 40. These results were correlated with the effects observed when this compound was incorporated in cellular membrane models of protozoans, represented by Langmuir monolayers of dipalmitoylphosphoethanolamine (DPPE). Surface pressure-area isotherms showed that epi-polygodial expands DPPE monolayers at higher areas and condenses them at lower areas, which was attributed to the preferential interaction with the polar heads of the lipid. This mechanism of action could be corroborated with Polarization-Modulation Reflection-Absorption Spectroscopy and Brewster Angle Microscopy. These results pointed to the fact that the interaction of epi-polygodial with DPPE monolayers at the air-water interface affects the physical chemical properties of the mixed film, which may be important to comprehend the interaction of this drug with cellular membranes at the molecular level.

Polarization Modulation Reflection-Absorption Spectroscopy applied in ultrathin films of algal biomacromolecules may explain the mechanism associated to the removal of pollutant metals

The current work investigates the action of extracts of exopolysaccharides and proteins (EPS) from the microalgae Cryptomonas tetrapirenoidosa immobilized on Langmuir-Blodgett films (LB) of the lipid dioctadecyldimethylammonium bromide (DODAB). The main objective of this paper was to evaluate the changes provided in the structure of the lipid-algal biomolecules composite film by Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) when these supramolecular structures are immersed in solutions with metallic ions of environmental interest. EPS was incorporated at DODAB monolayer as analyzed with surface pressure-area isotherms, PM-IRRAS and Brewster Angle Microscopy. The mixed films were transferred to solid supports as LB films and amide bands related to proteins present in the extract were analyzed since they are highly sensitive to molecular conformation. The films were put in contact with selected ions of environmental interest, such as lead, cooper, iron, and mercury, and changes in the protein structure were investigated with PM-IRRAS. The results showed a specific interaction of each ion with the LB films, which may be promising for building biosensors with specificity for metallic ions.

Langmuir and Langmuir-Blodgett films of di-ureasil hybrid compounds containing phosphotungstic acid

The search for new molecular architectures to improve the efficiency of sensors and optoelectronic devices is fundamental to enhance the effectiveness of nanostructured materials. In this present work, a di-ureasil hybrid compound (DUPTS) was spread at the air-water interface in order to form Langmuir monolayers. Phosphotungstic acid, H3PW12O40, PWA inserted in the aqueous subphase stabilized the formation of DUPTS as a stable Langmuir film, as showed with surface pressure and surface potential-area isotherms, rheological measurements, polarization modulation reflection-absorption spectroscopy, and Brewster angle microscopy. The monolayers were transferred to solid supports as Langmuir-Blodgett films and presented different patterns of heterogeneity as observed with atomic force microscopy, with the morphology dependent on the presence of PWA and on the kind of solid support surface.

Interaction of non-aqueous dispersions of silver nanoparticles with cellular membrane models

In this work, silver nanoparticles (AgNPs) dispersed in non-aqueous media and stabilized with polyether block polymers amide (PEBA) were incorporated in Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC), which served as a cell membrane model. The AgNPs presented surface activity, disturbing the viscoelastic properties of the floating film. They expanded the monolayers decreasing their surface elasticity as observed with surface pressure-area isotherms. Polarization modulation reflection-absorption spectroscopy showed that the permanence of AgNPs at the air-water interface is favored by PEBA, affecting both the hydrophilic and the hydrophobic groups of the phospholipid. Brewster angle microscopy showed that the AgNPs lead to the formation of aggregates at the air-water interface, establishing domains that shear with each other due to the low lateral viscosity of irregular and non-monomolecular domains. These data can be correlated to the possible toxicity and microbicide effect of AgNPs in lipidic surfaces such as in mammalian and microbial membranes.

CdSe magic-sized quantum dots incorporated in biomembrane models at the air–water interface composed of components of tumorigenic and non-tumorigenic cells

Cadmium selenide (CdSe) magic-sized quantum dots (MSQDs) are semiconductor nanocrystals with stable luminescence that are feasible for biomedical applications, especially for in vivo and in vitro imaging of tumor cells. In this work, we investigated the specific interaction of CdSe MSQDs with tumorigenic and non-tumorigenic cells using Langmuir monolayers and Langmuir–Blodgett (LB) films of lipids as membrane models for diagnosis of cancerous cells. Surface pressure-area isotherms and polarization modulation reflection-absorption spectroscopy (PM-IRRAS) showed an intrinsic interaction between the quantum dots, inserted in the aqueous subphase, and Langmuir monolayers constituted either of selected lipids or of tumorigenic and non-tumorigenic cell extracts. The films were transferred to solid supports to obtain microscopic images, providing information on their morphology. Similarity between films with different compositions representing cell membranes, with or without the quantum dots, was evaluated by atomic force microscopy (AFM) and confocal microscopy. This study demonstrates that the affinity of quantum dots for models representing cancer cells permits the use of these systems as devices for cancer diagnosis.

Mechanism of Action of Thymol on Cell Membranes Investigated through Lipid Langmuir Monolayers at the Air-Water Interface and Molecular Simulation.

A major challenge in the design of biocidal drugs is to identify compounds with potential action on microorganisms and to understand at the molecular level their mechanism of action. In this study, thymol, a monoterpenoid found in the oil of leaves of Lippia sidoides with possible action in biological surfaces, was incorporated in lipid monolayers at the air-water interface that represented cell membrane models. The interaction of thymol with dipalmitoylphosphatidylcholine (DPPC) at the air-water interface was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), polarization-modulation reflection-absorption spectroscopy (PM-IRRAS), and molecular dynamics simulation. Thymol expands DPPC monolayers, decreases their surface elasticity, and changes the morphology of the lipid monolayer, which evidence the incorporation of this compound in the lipid Langmuir film. Such incorporation could be corroborated by PM-IRRAS since some specific bands for DPPC were changed upon thymol incorporation. Furthermore, potential of mean force obtained by molecular dynamics simulations indicates that the most stable position of the drug along the lipid film is near the hydrophobic regions of DPPC. These results may be useful to understand the interaction between thymol and cell membranes during biochemical phenomena, which may be associated with its pharmaceutical properties at the molecular level.

The effect of the electrode material on the electrodeposition of zinc from deep eutectic solvents

The voltammetric behaviour of the ZnCl2 containing deep eutectic solvent choline chloride/ethylene glycol 1:2 was investigated on glassy carbon, stainless steel, Au, Pt, Cu, and Zn electrodes. While cyclic voltammetry on glassy carbon and stainless steel showed a cathodic peak for zinc electrodeposition only in the anodic reverse sweep, a cathodic peak was found also in the cathodic forward sweep on Au, Pt, Cu, and Zn. This behaviour is in agreement with the proposed mechanism of zinc deposition from an intermediate species Z, whose formation depends on the cathodic reduction potential of the solvent. The voltammetric reduction of the electrolyte involves hydrogen evolution and as a result the formation of Z and its reduction to zinc depend on the hydrogen overpotential for each electrode material. On Au, Pt, and Cu also the anodic stripping was different from that on glassy carbon and steel due to the formation of surface zinc alloys with the three former metals. The morphology of the zinc layers on Cu has been characterised by scanning electron microscopy and focussed ion beam. X-ray diffraction confirmed the presence of crystalline zinc and a Cu4Zn phase. Spectroelectrochemistry by means of polarization modulation reflection-absorption spectroscopy (PM-IRRAS) on a glassy carbon electrode in the ZnCl2 containing deep eutectic solvent showed characteristic potential dependent changes. The variation of band intensities at different applied potentials correlate with the voltammetry and suggest the formation of a compact blocking layer on the electrode surface, which inhibits the electrodeposition of zinc at sufficiently negative potentials.

Semifluorinated thiols in Langmuir monolayers – A study by nonlinear and linear vibrational spectroscopies

A series of semifluorinated thiols of the general formula CmF2m+1CnH2nSH (abbr. FmHnSH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F10) and variable length of the hydrogenated part (H6, H10, H12), and having identical hydrogenated segment (H12) connected to a fluorinated moiety of different lengths (F6, F8, F10). For the sake of comparison, an alkanethiol (H18SH) was also examined, and F10H10COOH and F10H10OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF3 group, while PM-IRRAS was used to probe CF2 groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perfluorinated part. SFG measurements recorded at three polarization combinations (ppp, ssp, sps) enabled us to estimate the tilt angle of the terminal CF3 group in semifluorinated thiol molecules as ranging from 35° to 45°, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region.

The interaction of eugenol with cell membrane models at the air–water interface is modulated by the lipid monolayer composition

Eugenol, a natural phenylpropanoid derivative with possible action in biological surfaces as microbicide, anesthetic and antioxidant, was incorporated in lipid monolayers of selected lipids at the air–water interface, representing cell membrane models. Interaction of eugenol with the lipids dipalmitoylphosphatidylcholine (DPPC), dioctadecyldimethylammonium bromide (DODAB), and dipalmitoylphosphatidylserine (DPPS) could be inferred by means of surface pressure-area isotherms and Polarization–Modulation Reflection–Absorption Spectroscopy. The interaction showed different effects on the different lipids. A higher monolayer expansion was observed for DPPS and DODAB, while more significant effects on the polar groups of the lipids were observed for DPPS and DPPC. These results pointed to the fact that the interaction of eugenol with lipid monolayers at the air–water interface is modulated by the lipid composition, which may be important to comprehend at the molecular level the interaction of this drug with biological surfaces.

In situ PM-IRRAS of a glassy carbon electrode/deep eutectic solvent interface.

The interface of a 1 : 2 molar choline chloride/ethylene glycol deep eutectic solvent with a glassy carbon electrode has been investigated by polarization modulation reflection-absorption spectroscopy (PM-IRRAS). Temporal spectral changes at open circuit potential show the experiments to be surface sensitive and indicate slow adsorption of electrolyte molecules on the electrode surface. In situ spectroelectrochemical PM-IRRAS measurements reveal characteristic potential-dependent changes of band intensities and wavenumber-shifts in the surface spectra. The potential dependent spectral changes are discussed in terms of adsorption, reduction, desorption and reorientation of choline cations at the interface. Analogies are drawn to the ionic layer structure proposed for the architecture of electrode/ionic liquid interfaces. The results show that in situ PM-IRRAS is generally applicable to glassy carbon electrodes and to electrode interfaces with deep eutectic solvents.

Crystallinity measurements of polyamides adsorbed as thin films

The crystallinity degree of thin polyamide films (PA66, 610 and 612) spin coated on four types of substrates are estimated. Two original methods based on the analysis of infrared spectra are proposed. The high sensitivity of polarization modulation reflection-absorption spectroscopy for the study of thin polymer films leads to quantitative results. These two methods offer the possibility to estimate the degree of crystallinity by using infrared spectroscopy, independently of any other technique, if the crystallinity degree in the isotropic bulk state is known. Polyamides are spin coated, on the one hand, on inert and highly reflecting gold substrates, and on the other hand, on the same gold substrates grafted with different chemical functionality. Our calculations show a lower crystallinity degree for inert substrate and higher values for functionalized systems with respect to the bulk. These results suggest that the surface chemical grafts not only play the role of nucleation seeds, but also affect the crystalline morphology as seen by atomic force microscopy.

Evaluation of Molecular Orientation in a Polymeric Monolayer at the Air−Water Interface by Polarization-Modulated Infrared Spectroscopy

Polarization-modulated reflection-absorption spectroscopy (PM-IRRAS) is employed to record infrared spectra of a monolayer of(dodecyl)cellulose spread at the air-water interface. Methylene symmetric and antisymmetric stretches of the alkyl side chains are clearly visible in the monolayer spectra as positive peaks at 2852 and 2922 cm -1 . It is thus concluded that the side chains possess a net orientation perpendicular to the water surface. Bands characteristic of the cellulose backbone are also observed as positive PM-IRRAS peaks, in the region 1160-980 cm -1 . This result indicates that the rigid polysaccharide chain lies essentially parallel to the water surface. Spectra recorded as a function of molecular area reveal little change in molecular orientation during monolayer compression. Significant differences in orientation are however evident between dense films obtained by the compression of disperse monolayers and those prepared by direct spreading at low surface areas.