Controlling supramolecular structures in iron tetrasulfonated phthalocyanine films through pH variation: implications for thin-film device performance.

Improving the performance of thin film-based devices is a crucial factor for their successful application, mainly for organic electronic semiconductors. The adjustment of supramolecular structuring of thin films plays a role in the optical and electrical properties. In this sense, we investigated how various pH values, such as 2.5, 6.0, and 9.0, of the solutions influenced the growth of iron tetrasulfonated phthalocyanine (FeTsPc) Layer-by-Layer (LbL) films and their respective supramolecular structures as well as their electrochemical properties. The supramolecular structures were evaluated via UV-vis absorption spectroscopy, quartz crystal microbalance (QCM), micro-Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and cyclic voltammetry. The different pH values of the solution induce different degrees of molecular aggregation for FeTsPc (monomer, dimer, and aggregate formation). For instance, the higher the pH, the higher the aggregation. Films produced at pH 2.5 were organized preferentially with the molecules perpendicular to the substrate, while films at pH 6.0 and 9.0 were organized preferentially with the molecules parallel to the substrate. Besides, the film produced at pH 2.5 results in higher film thickness, higher stability, and better electrocatalytic behavior for the electrochemical detection of catechol. The results presented here enhance the understanding of nanostructured films, helping to harness supramolecular organization to improve the performance of thin-film devices.

Lipid-matrix effects on tyrosinase immobilization in Langmuir and Langmuir-Blodgett films.

The immobilization of the enzyme tyrosinase (Tyr) in lipid matrices can be explored to produce biosensors for detecting polyphenols, which is relevant for the food industry. Herein, we shall demonstrate the importance of the lipid composition to immobilize the enzyme tyrosinase in Langmuir-Blodgett (LB) films. Tyr could be incorporated into Langmuir monolayers of arachidic acid (AA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG), having as the main effect an expansion in the monolayers. Results from polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) pointed to electrostatic interactions between the charged residues of Try and the lipid headgroups, in addition to changes in the order of lipid chains. The interaction between Tyr and DPPC in Langmuir monolayers can be correlated with the superior performance of DPPC/Tyr LB films used as biosensors to detect catechol by cyclic voltammetry. The molecular-level interactions assessed via PM-IRRAS are therefore believed to drive an immobilization process for Tyr in the lipid LB matrix and may serve as a general criterion to identify matrices that preserve enzyme activity.

Supramolecular architecture and electrical conductivity in organic semiconducting thin films.

Organic thin films are an essential component of the structure of optical and electronic devices. However, the optical and electrical properties of these films depend on their supramolecular architecture, which may vary according to the techniques used to manufacture them. Here, the correlation between conductivity and supramolecular architecture was investigated. The supramolecular architecture was analyzed in terms of the molecular organization and J- or H-aggregation established during the fabrication of perylene tetracarboxylic diimide (PTCD) nanometric films. Three deposition techniques, Langmuir-Schaefer (LS), Langmuir-Blodgett (LB), and Physical Vapor Deposition (PVD), were evaluated. The UV-vis absorption spectra indicated that LS, LB, and PVD films grow homogeneously. Also, the presence of J and H aggregates was observed for all films, the H aggregates prevailing for the LB film. The FTIR measurements suggested that the molecular organization is similar for LS and LB films, with a tendency to form head-on organization onto a solid substrate. For the PVD film, the perylene macrocycles are inclined approximately 45° relative to the substrate. AFM measurements indicated a homogenous surface for all films. In terms of electrical conductivity, the highest conductivity was found for LS, followed by LB and PVD. The conductivity values were interpreted in terms of molecular organization and J- or H-aggregate formation.

Metallic Phthalocyanines: impact of the film deposition method on its supramolecular arrangement and sensor performance.

This short review gives a concise overview of the impact of deposition methods on the supramolecular arrangement of metallic phthalocyanine films and their applications. Primarily, an introduction about the possible phthalocyanine molecular structures and derivatives obtained from modification on the phthalocyanine rings was presented. The possibility of perfecting/improving the supramolecular arrangement of metallic phthalocyanine (MPcs) films by using different deposition techniques such as Langmuir-Blodgett (LB), Langmuir-Schaefer (LS), Layer-by-Layer (LbL), physical vapor deposition (PVD) and electrodeposition was discussed in further details. Herein, we highlighted some techniques used on the characterization of supramolecular arrangement (morphology, optical properties, and molecular organization), including the impact on sensing applications. The main scope of this short review is focused on the advances made in this research field in the last five years.

Designing Silver Nanoparticles for Detecting Levodopa (3,4-Dihydroxyphenylalanine, L-Dopa) Using Surface-Enhanced Raman Scattering (SERS).

Detection of the drug Levodopa (3,4-dihydroxyphenylalanine, L-Dopa) is essential for the medical treatment of several neural disorders, including Parkinson's disease. In this paper, we employed surface-enhanced Raman scattering (SERS) with three shapes of silver nanoparticles (nanostars, AgNS; nanospheres, AgNP; and nanoplates, AgNPL) to detect L-Dopa in the nanoparticle dispersions. The sensitivity of the L-Dopa SERS signal depended on both nanoparticle shape and L-Dopa concentration. The adsorption mechanisms of L-Dopa on the nanoparticles inferred from a detailed analysis of the Raman spectra allowed us to determine the chemical groups involved. For instance, at concentrations below/equivalent to the limit found in human plasma (between 10-7-10-8 mol/L), L-Dopa adsorbs on AgNP through its ring, while at 10-5-10-6 mol/L adsorption is driven by the amino group. At even higher concentrations, above 10-4 mol/L, L-Dopa polymerization predominates. Therefore, our results show that adsorption depends on both the type of Ag nanoparticles (shape and chemical groups surrounding the Ag surface) and the L-Dopa concentration. The overall strategy based on SERS is a step forward to the design of nanostructures to detect analytes of clinical interest with high specificity and at varied concentration ranges.

Supramolecular Arrangement of Iron Phthalocyanine in Langmuir-Schaefer and Electrodeposited Thin Films.

The supramolecular arrangement in thin film technology has been explored through different deposition techniques aiming to control the film properties at the molecular level. We report on the formation of iron phthalocyanine (FePc) films using both Langmuir-Schaefer (LS) and electrodeposition methods. The multilayer formation was monitored with ultraviolet-visible absorption spectroscopy (UV-vis) and electrochemical measurements. According to Raman spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM), the surface morphology of electrodeposited films is more homogeneous than LS films at micro and nanometer scales. From FTIR spectroscopy, the FePc molecules in the electrodeposited films are oriented preferentially with the macrocycle parallel to the substrate surface (flat-on), while a slight tilt is suggested in LS films, being both films crystalline. Therefore, the use of different deposition techniques allowed the fabrication of thin films from FePc with distinct supramolecular arrangements, leading to distinct electrochemical properties. For instance, the electrodeposited films show higher surface coverage, suggesting a more compact structure, which favors the charge transfer and smaller energy gap. The possibility of tuning some properties according to deposition technique for the same material can help the development of technological applications such as electronic or sensing devices.

Surface Plasmon Resonances in Silver Nanostars.

The recent development of silver nanostars (Ag-NSs) is promising for improved surface-enhanced sensing and spectroscopy, which may be further exploited if the mechanisms behind the excitation of localized surface plasmon resonances (LSPRs) are identified. Here, we show that LSPRs in Ag-NSs can be obtained with finite-difference time-domain (FDTD) calculations by considering the nanostars as combination of crossed nanorods (Ag-NRs). In particular, we demonstrate that an apparent tail at large wavelengths ( λ ≳ 700 nm) observed in the extinction spectra of Ag-NSs is due to a strong dipolar plasmon resonance, with no need to invoke heterogeneity (different number of arms) effects as is normally done in the literature. Our description also indicates a way to tune the strongest LSPR at desired wavelengths, which is useful for sensing applications.

Influence of the Supramolecular Arrangement in the Electrical Conductivity of Poly(thiophene) Thin Films.

Thin films of regioregular polythiophene derivatives have had their optical, structural and morphological properties characterized, but there is still a lack of comparative studies to determine the effect from deposition techniques, especially on the electrical properties. In this study, we produced Langmuir-Schaefer and spin-coated films of regioregular alkyl-substituted polythiophene derivatives (P3AT) to investigate how distinct supramolecular arrangements can affect their properties. The Langmuir-Schaefer films deposited on indium-tin oxide substrates were observed to grow linearly with the number of layers, according to UV-visible absorption spectroscopy. Atomic force microscopy and Brewster angle microscopy were carried out for morphological characterization. From electrical transport measurements, the DC electrical conductivity of Langmuir-Schaefer films of P3AT was higher than the corresponding spin-coated films, which can be related to the dissimilar roughness and molecular-level organization provided by the Langmuir-Schaefer technique.

Investigating layer-by-layer films of carbon nanotubes and nickel phthalocyanine towards diquat detection.

The indiscriminate use of pesticides makes us susceptible to the toxicity of these chemical compounds, which may be present in high quantities in our food. It is crucial to develop inexpensive and rapid methods for determining these pesticides for government control or even for the general population. In this study, we investigated the fabrication of self-assembled LbL films using multi-walled carbon nanotubes (MWCNT) and nickel tetrasulphonated phthalocyanine (NiTsPc) as an electrochemical sensor for the herbicide Diquat (DQ). The Layer-by-Layer (LbL) assembly of the (MWCNT/NiTsPc) film was examined, along with its structural and morphological characteristics. The effect of the number of layers in DQ detection was evaluated by cyclic voltammetry, followed by the detection through differential pulse voltammetry. The achieved limit of detection was 9.62 × 10-7 mol L-1. A ~ 30% decrease in sensitivity was observed in the presence of Paraquat, a banned herbicide and electrochemical interferent due to the structural similarities, which is regularly neglected in the most published studies. The sensor was tested in real samples, demonstrating a recovery of 98.5% in organic apples.

Exploring the synergistic effects of amoxicillin and methylene blue on unsaturated lipid structures: A study of Langmuir monolayers and giant unilamellar vesicles.

The potentially toxic effects of emerging pollutant mixtures often deviate from the individual compound effects, presenting additive, synergistic, or agonistic interactions. This study delves into the complex world of emerging pollutants' mixtures, with a particular focus on their potential impact on unsaturated lipid DOPC (1,2-dioleoyl-sn-glycerol-3-phosphocholine) structured as both monolayers and bilayers, which are valuable tools for mimicking cell membranes. Specifically, we examine the effects of two common types of pollutants: antibiotics (amoxicillin) and dyes (methylene blue). Utilizing Langmuir monolayers, our research reveals a synergistic effect within the pollutant mixture, as evidenced by pressure-area isotherms and polarization-modulated infrared reflection absorption spectroscopy. We identify the specific chemical interactions contributing to this synergistic effect. Furthermore, through contrast phase microscopy experiments on giant unilamellar vesicles (bilayer system), we find that the individual pollutants and the mixture exhibit similar molecular effects on the bilayer, revealing that the molecular size is a key factor in the bilayer-mixture of pollutant interaction. This highlights the importance of considering molecular size in the interactions with bilayer systems. In summary, our research dissects the critical factors of chemical interactions and molecular size concerning the effects of pollutants on DOPC, serving as simplified models of cell membranes. This study underscores the significance of comprehending the molecular effects of emerging pollutants on human health and the development of models for exploring their intricate interactions with cell membranes.

Selective Detection of Paraquat in Adulterated and Complex Environmental Samples Using Raman Spectroelectrochemistry.

Growing demand for pesticides has created an environment prone to deceptive activities, where counterfeit or adulterated pesticide products infiltrate the market, often escaping rapid detection. This situation presents a significant challenge for sensor technology, crucial in identifying authentic pesticides and ensuring agricultural safety practices. Raman spectroscopy emerges as a powerful technique for detecting adulterants. Coupling the electrochemical techniques allows a more specific and selective detection and compound identification. In this study, we evaluate the efficacy of spectroelectrochemical measurements by coupling a potentiostat and Raman spectrograph to identify paraquat, a nonselective herbicide banned in several countries. Our findings demonstrate that applying -0.70 V during measurements yields highly selective Raman spectra, highlighting the primary vibrational bands of paraquat. Moreover, the selective Raman signal of paraquat was discernible in complex samples, including tap water, apple, and green cabbage, even in the presence of other pesticides such as diquat, acephate, and glyphosate. These results underscore the potential of this technique for reliable pesticide detection in diverse and complex matrices.

Molecularly designed layer-by-layer (LbL) films to detect catechol using information visualization methods.

The control of molecular architectures has been exploited in layer-by-layer (LbL) films deposited on Au interdigitated electrodes, thus forming an electronic tongue (e-tongue) system that reached an unprecedented high sensitivity (down to 10(-12) M) in detecting catechol. Such high sensitivity was made possible upon using units containing the enzyme tyrosinase, which interacted specifically with catechol, and by processing impedance spectroscopy data with information visualization methods. These latter methods, including the parallel coordinates technique, were also useful for identifying the major contributors to the high distinguishing ability toward catechol. Among several film architectures tested, the most efficient had a tyrosinase layer deposited atop LbL films of alternating layers of dioctadecyldimethylammonium bromide (DODAB) and 1,2-dipalmitoyl-sn-3-glycero-fosfo-rac-(1-glycerol) (DPPG), viz., (DODAB/DPPG)5/DODAB/Tyr. The latter represents a more suitable medium for immobilizing tyrosinase when compared to conventional polyelectrolytes. Furthermore, the distinction was more effective at low frequencies where double-layer effects on the film/liquid sample dominate the electrical response. Because the optimization of film architectures based on information visualization is completely generic, the approach presented here may be extended to designing architectures for other types of applications in addition to sensing and biosensing.

The Role of Cholesterol in the Interaction of the Lipid Monolayer with the Endocrine Disruptor Bisphenol-A.

Among pollutants of emerging concern, endocrine disruptors (ED) have been shown to cause side effects in humans and animals. Bisphenol-A (BPA) is an ED by-product of the plastic industry and one of the chemicals with the highest volume produced yearly. Here, we studied the role of cholesterol in the BPA exposure effects over membrane models. We used Langmuir films of both neat lipid DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and cholesterol (Chol) and a binary mixture containing DPPC/Chol, exposing it to BPA. We evaluate changes in the π-A isotherms and the PM-IRRAS (polarization modulation-infrared reflection adsorption spectroscopy) spectra. BPA exposure induced changes in the DPPC and Chol neat monolayers, causing mean molecular area expansion and altering profiles. However, at high surface pressure, the BPA was expelled from the air-water interface. For the DPPC/Chol mixture, BPA caused expansion throughout the whole compression, indicating that BPA is present at the monolayer interface. The PM-IRRAS analysis showed that BPA interacted with the phosphate group of DPPC through hydrogen bonding, which caused the area's expansion. Such evidence might be biologically relevant to better understand the mechanism of action of BPA in cell membranes once phosphatidylcholines and Chol are found in mammalian membranes.

Consequences of the exposure to bisphenol A in cell membrane models at the molecular level and hamster ovary cells viability.

The inadequate disposal and the difficulty in its removal from water treatment systems have made the endocrine disruptor bisphenol A (BPA) a significant hazard for humans and animals. The molecular-level mechanisms of BPA action are not known in detail, which calls for systematic investigations using cell membrane models. This paper shows that BPA affects Langmuir monolayers and giant unilamellar vesicles (GUVs) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) used as membrane models, in a concentration-dependent manner and with effects that depend on BPA aggregation. BPA increases DPPC monolayer fluidity in surface pressure isotherms upon interacting with the headgroups through hydrogen bonding, according to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). In DPPC GUVs, BPA induced wrinkling and distortion in the spherical shape of the vesicles, but this was only observed for fresh solutions where it is not aggregated. BPA also decreased the viability of hamster ovary cells (CHO) in in vitro experiments. In contrast, aged, aggregated BPA solutions did not affect the GUVs and even increased CHO viability. These results may be rationalized in terms of size-dependent effects of BPA, which may be relevant for its endocrine-disrupting effects.

Coupling surface-enhanced resonance Raman scattering and electronic tongue as characterization tools to investigate biological membrane mimetic systems.

The surface-enhanced Raman scattering (SERS) effect and sensor and biosensor analyses are widely applied to investigate drug-biomolecule interactions or to detect trace amount of analytes. In this work, surface-enhanced resonance Raman scattering (SERRS) and an electronic tongue system using impedance spectroscopy were brought together, combining sensitivity and structural level information. Taking advantage of the use of layer-by-layer (LbL) films of phospholipids as biological membrane mimetic systems, cardiolipin (CLP) and dipalmitoyl phosphatidyl glycerol (DPPG) were applied as transducers onto Pt interdigitated electrodes forming an array of sensing units. This e-tongue system was able to detect the phenothiazine methylene blue (MB) below nanomolar concentrations. SERRS was applied to investigate the MB molecular arrangement (monomers or aggregates) when in contact with the phospholipids at trace levels of concentration. The key point was the adsorption of Ag nanoparticles (AgNPs) within the phospholipid LbL films. This approach did not compromise the e-tongue performance and allowed the recording of in situ SERRS spectra for the LbL films after immersion into MB aqueous solutions. The detection of MB through SERRS gave similar results to those reported in the literature but now with an unprecedented sensitivity.

Detection of catechol using mixed Langmuir-Blodgett films of a phospholipid and phthalocyanines as voltammetric sensors.

The combination of metallic phthalocyanines (MPcs) and biomolecules has been explored in the literature either as mimetic systems to investigate molecular interactions or as supporting layers to immobilize biomolecules. Here, Langmuir-Blodgett (LB) films containing the phospholipid dimyristoyl phosphatidic acid (DMPA) mixed either with iron phthalocyanine (FePc) or with lutetium bisphthalocyanine (LuPc(2)) were applied as ITO modified-electrodes in the detection of catechol using cyclic voltammetry. The mixed Langmuir films of FePc + DMPA and LuPc(2) + DMPA displayed surface-pressure isotherms with no evidence of molecular-level interactions. The Fourier Transform Infrared (FTIR) spectra of the multilayer LB films confirmed the lack of interaction between the components. The DMPA and the FePc molecules were found to be oriented perpendicularly to the substrate, while LuPc(2) molecules were randomly organized. The phospholipid matrix induced a remarkable electrocatalytic effect on the phthalocyanines; as a result the mixed LB films deposited on ITO could be used to detect catechol with detection limits of 4.30 × 10(-7) and 3.34 × 10(-7) M for FePc + DMPA and LuPc(2) + DMPA, respectively. Results from kinetics experiments revealed that ion diffusion dominated the response of the modified electrodes. The sensitivity was comparable to that of other non-enzymatic sensors, which is sufficient to detect catechol in the food industry. The higher stability of the electrochemical response of the LB films and the ability to control the molecular architecture are promising for further studies with incorporation of biomolecules.

Iron phthalocyanine in non-aqueous medium forming layer-by-layer films: growth mechanism, molecular architecture and applications.

The application of organic thin films as transducer elements in electronic devices has been widely exploited, with the electrostatic layer-by-layer (LbL) technique being one of the most powerful tools to produce such films. The conventional LbL method, however, is restricted in many cases to water soluble compounds. Here, an alternative way to produce LbL films containing iron phthalocyanine (FePc) in non-aqueous media (chloroform) is presented. This film fabrication was made possible by exploiting the specific interactions between Fe and NH(2) groups from PAH, poly(allylamine hydrochloride) used as the supporting layer, leading to the formation of bilayers structured as (PAH/FePc)(n). We have also incorporated silver nanoparticles (AgNPs) in LbL films with (PAH/FePc/AgNP)(n) trilayers, making it possible to achieve the surface-enhanced Raman scattering (SERS) phenomenon. The molecular architecture of the LbL films was determined through different techniques. The growth was monitored with UV-Vis absorption spectroscopy, their morphology characterized by optical and scanning electron (SEM) microscopes, and their molecular organization determined using FTIR. The electrochemical properties of the LbL films were successfully applied in detecting dopamine in KCl aqueous solutions at different concentrations using cyclic voltammetry. The results confirmed that the LbL films from FePc in non-aqueous media keep their electroactivity, while showing an interesting electrocatalytic effect. The SERS phenomenon suggested that FePc aggregates might be directly involved in the maintenance of the electroactivity of the LbL films.

Molecular architecture of thin films fabricated via physical vapor deposition and containing a poly(azo)urethane.

Organic thin films are widely applied as transducers in devices whose performance is determined by the optical and electrical properties of the films. In this context, the molecular architecture of the thin films plays an important role. In this work we report the fabrication and characterization of a poly(azo)urethane synthesized fixing CO2 in bis-epoxide followed by a copolymerization reaction with an azodiamine without using isocyanate. The poly(azo)urethane thin films were fabricated by physical vapor deposition (PVD) technique using vacuum thermal evaporation. The molecular architecture of the PVD films was investigated under control growth at nanometer level of thickness, as well as the surface morphology at micro and nanometer scales and the molecular organization. The thermal stability of the poly(azo)urethane molecules, which is a challenge in itself considering the thermal evaporation process, was followed by thermogravimetric analysis (TG) and also by both Fourier transform infrared absorption (FTIR) and ultraviolet-visible (UV-vis) absorption spectroscopies. The UV-vis absorption spectra showed a linear growth of the absorbance of the PVD films with the mass thickness measured by a quartz crystal balance. A random distribution of the poly(azo)urethane molecules in the PVD films was revealed by FTIR spectra. The film morphology was investigated at microscopic level combining chemical and topographical information through micro-Raman technique. At nanoscopic scale, the morphology was investigated by atomic force microscopy (AFM) for films fabricated using distinct evaporation rates. As a proof of principle (for potential applications), the film luminescence was measured over a wide range of temperature. Interestingly, an unusual increase of fluorescence intensity was observed at +150 degrees C after a monotonic decrease from -150 degrees C.

Taking advantage of electrostatic interactions to grow Langmuir-Blodgett films containing multilayers of the phospholipid dipalmitoylphosphatidylglycerol.

The use of phospholipids as mimetic systems for studies involving the cell membrane is a well-known approach. In this context, the Langmuir and Langmuir-Blodgett (LB) methods are among the main techniques used to produce ordered layers of phospholipids structured as mono- or bilayers on water subphase and solid substrates. However, the difficulties of producing multilayer LB films of phospholipids restrict the application of this technique depending on the sensitivity of the experimental analysis to be conducted. Here, an alternative approach is used to produce LB films containing multilayers of the negative phospholipid dipalmitoylphosphatidylglycerol (DPPG). Inspired by the electrostatic layer-by-layer (LbL) technique, DPPG multilayer LB films were produced by transferring the DPPG Langmuir monolayers from the water subphase containing low concentrations of the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) onto solid substrates. Fourier transform infrared (FTIR) absorption spectroscopy revealed that the interactions between the NH(3)(+) (PAH) and PO(4)(-) (DPPG) groups might be the main driving forces that allow growth of these LB films. Besides, ultraviolet-visible (UV-vis) absorption spectroscopy showed that the multilayer LB films can be grown in a controlled way in terms of thickness at nanometer scale. Cyclic voltammetry showed that DPPG and PAH are more packed in the LB than LbL films. The latter finding is related to the distinct molecular architecture of the films since DPPG is structured as monolayers in the LB films and multilamellar vesicles in the LbL films. Despite the interaction with PAH, cyclic voltammetry also showed that DPPG retains its biological activity in LB films, which is a key factor since this makes DPPG a suitable material in sensing applications. Therefore, multilayer LB films were deposited onto Pt interdigitated electrodes forming sensing units, which were applied in the detection of a phenothiazine compound [methylene blue (MB)] using impedance spectroscopy. The performance of DPPG in single-layer and multilayer LB films was compared to the performance of sensing unities composed of DPPG in single-layer and multilayer LbL films, showing the importance of both the thickness and the molecular architecture of the thin films. As found in a previous work for LbL films, the high sensitivity reached by these sensing units is intimately related to changes in the morphology of the film as evidenced by the micro-Raman technique. Finally, the interaction between MB and the (DPPG+PAH) LB films was complemented by pi-A isotherms and surface-enhanced resonance Raman scattering (SERRS).

Interaction between 17 α-ethynylestradiol hormone with Langmuir monolayers: The role of charged headgroups.

The persistence of steroid hormones disposed of in the environment may pose risks to the health of humans and wildlife, which brings the need of understanding their mode of action, believed to occur in cell membranes. In this study, we investigate the molecular-level interactions between the synthetic hormone 17 α-ethynylestradiol (EE2) and Langmuir monolayers that represent simplified cell membranes. In surface pressure isotherms, EE2 was found to expand the monolayers at low surface pressures of the positively charged dimethyldioctadecylammonium bromide (DODAB), zwitterionic 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), negatively charged 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), and partially anionized stearic acid (StAc). The largest effects were observed for the charged DODAB and DPPG. At the pressure (30mN.m-1) corresponding to the molecular packing of a cell membrane, EE2 caused the compressibility modulus to decrease, again with the largest changes occurring for DODAB and DPPG. The effects from EE2 on the packing of the lipid molecules at this high pressure depended essentially on the size of the headgroups, with EE2 contributing to the area per lipid for StAc and DODAB, whose headgroups are small. EE2 interacted with the headgroups of all lipids and StAc, also affecting the ordering of the tails for DODAB, DPPG and DPPC, according to in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Based on the analysis with the two characterization methods, we propose a model for the EE2 positioning and molecular groups involved in the interaction, which should be relevant to unveil the endocrine disrupting action of EE2.