The reactivity of chemical warfare agents (CWAs) and CWA simulants on organic and oxide surfaces is not currently well understood, but is of substantial importance to the development of effective sensors, filters and sorbent materials. Polyurethane coatings are used by the armed forces as chemical agent resistive paints to limit the uptake of CWAs on surfaces, while the use of metal oxides has been explored for decontamination and protection purposes. To better understand the chemical nature of the interactions of organophosphonate simulants with these surfaces, an ultra-high vacuum environment was used to isolate the target interactions from environmental gaseous interferences. The use of highly-characterized surfaces, coupled with molecular beam and dosing capabilities, allows for the elucidation of adsorption, desorption, and reaction mechanisms of CWA simulants on a variety of materials. Model urethane-containing organic coatings were designed and applied toward the creation of well-ordered thin films containing carbamate linkages. In addition, novel trisilanolphenyl-polyhedral oligomeric silsesquioxane (POSS) molecules were used to create Langmuir-Blodgett films containing reactive silanol groups that have potential use as sensors and coatings. The uptake and reactivity of organophosphonates and chlorophosphates on these surfaces is the focus of this study. Surfaces were characterized before and after exposure to the phosphates using a number of surface sensitive techniques including: contact angle goniometry, reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) measurements. In conjunction with surface probes, uptake coefficients were monitored according to the King and Wells direct reflection technique. The integration of these analytical techniques provides insight and direction towards the design of more effective chemical agent resistant coatings and aids in the development of more functional strategies for chemical warfare agent decontamination and sensing. / Ph. D.

Developing methods to detect, adsorb, and decompose chemical warfare agents (CWAs) is of critical importance to protecting military and civilian populations alike. The sorption of dimethyl methylphosphonate (DMMP), a CWA simulant, into trisilanolphenyl-POSS (TPP) films has previously been characterized with reflection absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and uptake coefficient determinations [1]. In our study, the quartz crystal microbalance (QCM) is used to study the sorption phenomena of DMMP into highly ordered Langmuir-Blodgett (LB) films of TPP. In a saturated environment, DMMP sorbs into the TPP films, binding to TPP in a 1:1 molar ratio. Although previous work indicated these DMMP-saturated films were stable for several weeks, DMMP is found to slowly desorb from the TPP films at room temperature and pressure. Upon application of vacuum to the DMMP-saturated films, DMMP follows first-order desorption kinetics and readily desorbs from the film, returning the TPP film to its original state. [1] Ferguson-McPherson, M.; Low, E.; Esker, A.; Morris, J. J. Phys. Chem. B. 2005, 109, 18914. / Master of Science

O crescente número de bactérias resistentes é devido principalmente ao número limitado de modos de ação dos antibióticos, contra os quais bactérias criam mecanismo de resistência. Há, portanto, necessidade de terapias com espectro de ação mais amplo, atingindo diferentes alvos moleculares. A inativação fotodinâmica (IFD) pode ser uma dessas terapias, pois baseia-se na geração de espécies reativas que atacam diversas moléculas, e não um alvo específico. Fotossensibilizadores (FSs) absorvem luz em comprimento de onda específico e a energia absorvida pode ser transferida a um oxigênio molecular, gerando espécies reativas de oxigênio (EROs). Tais espécies são altamente citotóxicas e produzem reações de oxidação que levam à morte celular. Um dos alvos das EROs são fosfolipídios insaturados das membranas biológicas. O objetivo desta dissertação é investigar a interação dos FSs curcumina e azul de metileno com fosfolipídios e o efeito da foto-ativação desses FSs em um mimético de membrana bacteriana. Para tanto, foram usados filmes de Langmuir do extrato lipídico de Escherichia coli e dos lipídios sintéticos isolados DOPE, POPG e cardiolipina. As isotermas de pressão com o extrato de E coli indicam interação entre os FSs e os lipídios do filme, aumentando a área ocupada. A irradiação do filme na presença de curcumina aumenta sua estabilidade, o que sugere formação de hidroperóxidos de lipídio, mais hidrofílicos, pela ação do oxigênio singleto. Nos filmes dos lipídios isolados só a curcumina é incorporada, havendo aumento na área ocupada pelo filme, e redução no potencial de superfície. Nenhum efeito decorrente da irradiação desses filmes foi detectado. Um filme Langmuir-Blodgett (LB) de extrato de E. coli com curcumina foi submetido a quatro ciclos de fotoclareamento seguido de recuperação da fluorescência visualizados num microscópio confocal. A intensidade da fluorescência aumentou após o primeiro ciclo, indicativo de mudança conformacional para alocar maior quantidade de curcumina, o que corrobora a hipótese da formação de hidroperóxidos. / The growing number of resistant bacteria is mainly due to the limited number of modes of action of antibiotics, against which bacteria create resistance. There is, therefore, a need for therapies with broader action spectrum, reaching different molecular targets. Photodynamic inactivation (PDI) may be one of these therapies, because it is based on the generation of reactive species that attack several molecules, not a specific target. Photosensitizers (FSs) absorb light at a specific wavelength and the absorbed energy can be transferred to a molecular oxygen, generating reactive oxygen species (ROS). Such species are highly cytotoxic and produce oxidation reactions that lead to cell death. One of the targets of ROS are unsaturated phospholipids from biological membranes. The objective of this dissertation is to investigate the interaction of the FSs curcumin and methylene blue with phospholipids and the effect of photoactivation of these FSs on a bacterial membrane mimetic. For this purpose, Langmuir films of the lipid extract of Escherichia coli and the synthetic lipids DOPE, POPG and cardiolipin were used. The surface pressure isotherms with the E. coli extract indicate interaction between the FSs and the lipids of the film, increasing the occupied area. The irradiation of the film in the presence of curcumin increases its stability, which suggests the formation of more hydrophilic lipid hydroperoxides by the action of singlet oxygen. In the synthetic lipid films only curcumin is incorporated, with increase in the area occupied by the film, and reduction in surface potential. No effect from irradiation of these films was detected. A Langmuir-Blodgett (LB) film of E. coli extract with curcumin was submitted to four cycles of photobleaching followed by fluorescence recovery visualized in a confocal microscope. The intensity of the fluorescence increased after the first cycle, indicative of conformational change to allocate a larger amount of curcumin, which corroborates the hypothesis of hydroperoxide formation.

O crescente número de bactérias resistentes é devido principalmente ao número limitado de modos de ação dos antibióticos, contra os quais bactérias criam mecanismo de resistência. Há, portanto, necessidade de terapias com espectro de ação mais amplo, atingindo diferentes alvos moleculares. A inativação fotodinâmica (IFD) pode ser uma dessas terapias, pois baseia-se na geração de espécies reativas que atacam diversas moléculas, e não um alvo específico. Fotossensibilizadores (FSs) absorvem luz em comprimento de onda específico e a energia absorvida pode ser transferida a um oxigênio molecular, gerando espécies reativas de oxigênio (EROs). Tais espécies são altamente citotóxicas e produzem reações de oxidação que levam à morte celular. Um dos alvos das EROs são fosfolipídios insaturados das membranas biológicas. O objetivo desta dissertação é investigar a interação dos FSs curcumina e azul de metileno com fosfolipídios e o efeito da foto-ativação desses FSs em um mimético de membrana bacteriana. Para tanto, foram usados filmes de Langmuir do extrato lipídico de Escherichia coli e dos lipídios sintéticos isolados DOPE, POPG e cardiolipina. As isotermas de pressão com o extrato de E coli indicam interação entre os FSs e os lipídios do filme, aumentando a área ocupada. A irradiação do filme na presença de curcumina aumenta sua estabilidade, o que sugere formação de hidroperóxidos de lipídio, mais hidrofílicos, pela ação do oxigênio singleto. Nos filmes dos lipídios isolados só a curcumina é incorporada, havendo aumento na área ocupada pelo filme, e redução no potencial de superfície. Nenhum efeito decorrente da irradiação desses filmes foi detectado. Um filme Langmuir-Blodgett (LB) de extrato de E. coli com curcumina foi submetido a quatro ciclos de fotoclareamento seguido de recuperação da fluorescência visualizados num microscópio confocal. A intensidade da fluorescência aumentou após o primeiro ciclo, indicativo de mudança conformacional para alocar maior quantidade de curcumina, o que corrobora a hipótese da formação de hidroperóxidos. / The growing number of resistant bacteria is mainly due to the limited number of modes of action of antibiotics, against which bacteria create resistance. There is, therefore, a need for therapies with broader action spectrum, reaching different molecular targets. Photodynamic inactivation (PDI) may be one of these therapies, because it is based on the generation of reactive species that attack several molecules, not a specific target. Photosensitizers (FSs) absorb light at a specific wavelength and the absorbed energy can be transferred to a molecular oxygen, generating reactive oxygen species (ROS). Such species are highly cytotoxic and produce oxidation reactions that lead to cell death. One of the targets of ROS are unsaturated phospholipids from biological membranes. The objective of this dissertation is to investigate the interaction of the FSs curcumin and methylene blue with phospholipids and the effect of photoactivation of these FSs on a bacterial membrane mimetic. For this purpose, Langmuir films of the lipid extract of Escherichia coli and the synthetic lipids DOPE, POPG and cardiolipin were used. The surface pressure isotherms with the E. coli extract indicate interaction between the FSs and the lipids of the film, increasing the occupied area. The irradiation of the film in the presence of curcumin increases its stability, which suggests the formation of more hydrophilic lipid hydroperoxides by the action of singlet oxygen. In the synthetic lipid films only curcumin is incorporated, with increase in the area occupied by the film, and reduction in surface potential. No effect from irradiation of these films was detected. A Langmuir-Blodgett (LB) film of E. coli extract with curcumin was submitted to four cycles of photobleaching followed by fluorescence recovery visualized in a confocal microscope. The intensity of the fluorescence increased after the first cycle, indicative of conformational change to allocate a larger amount of curcumin, which corroborates the hypothesis of hydroperoxide formation.

Die vorliegende Arbeit widmete sich unter grundlagenorientierten und praxisrelevanten Aspekten der Entwicklung maßgeschneiderter, multifunktionalisierter Tenside mit potenziellen Sammler- und Filmbildungseigenschaften im Zusammenhang mit der mineralischen Flotation. Auf der Basis supramolekularer Konstruktionsprinzipien gelang die Synthese dendritisch verzweigter Amphiphile, die relevante Unterschiede in der Hydrophilie-Hydrophobie-Balance aufweisen und in der Flexibilität des Spacersegmentes sowie der peripheren Alkylkettenlänge im hydrophoben Molekülbereich variieren. Im Hinblick auf die Struktur-Wirkungs-Beziehungen der neuartigen Amphiphile fanden Versuche zur Ermittlung der tensidchemischen Parameter sowie Untersuchungen zu ihrem Filmbildungsverhalten statt. Des Weiteren wurden die synthetisierten Tenside im Mikroflotationsversuch auf ihre Eignung als Sammlerkomponenten am Modellmineral Fluorit getestet. Generell führt eine Erweiterung der polaren Haftgruppen zu einer wesentlich besseren Fixierung der amphiphilen Moleküle sowohl an der Phasengrenzfläche Wasser/Luft als auch an der mineralischen Fluoritoberfläche. Darüber hinaus begünstigt eine starre Geometrie die Ausbildung stabilerer monomolekularer Adsorptionsschichten. Im Flotationsprozess bewirken die präorganisierten, dendritisch verzweigten Sammlermoleküle gegenüber konventionellen Reagenzien eine deutliche Effizienzsteigerung.

The functionalization of surfaces has received attention because the process allows the design and tailoring of substrate surfaces with a new or improved function. "Host-guest" thin film complexes are composed of "host" molecules attached the substrate surface, either through physisorption or covalent bonds, with cavities for the inclusion of desired "guest" molecules for the functionalization of the surface. Two methods for fabricating functional "host-guest" thin films were investigated: Langmuir-Blodgett (LB) deposition and self-assembly monolayer (SAM). Langmuir films were created at the air-water interface using octadecanesulfonic acid (C18S) as the amphiphilic "host" molecules separated by hydrophilic guanidinium (G) spacer molecules, which created a cavity allowing the inclusion of desired "guest" molecules. Surface pressure-area isotherms of the (G)C18S, with and without guests, are characterized by the lift-off molecular areas and are use to determine the proper deposition surface pressure. "Host-guest" Langmuir films are deposited onto silicon substrates using the LB deposition technique. The LB films were then subjected to stability testing using different solvents over increasing periods of time. Grazing-angle incidence X-ray diffraction (GIXD), specular X-ray reflectivity (XRR) and transfer ratio measurements were used to characterize the crystallinity, film thickness, overall film stability and film coverage. The GIXD data revealed that the crystallinity of the deposited film varies with the "guest" molecules and can be disrupted by the functional group on the "guest" molecule through hydrogen bonding. After modeling the XRR data using StochFit, it was discovered that the more polar solvent, tetrahydrofuran (THF), removed the film completely while the nonpolar solvent, hexane, compacted the thin film and increased the electron density. With transfer ratios around 0.95 to 1.05, the deposited films were homogenous. The second method used was self-assembly monolayers, which differs from Langmuir films in that they are created by a spontaneous chemical synthesis from immersing a substrate into a solution containing an active surfactant. Octadecyltrichlorosilane (OTS) was used initially as a molecule to study the self-assembled monolayer procedure. To study a "host-guest" self-assembled monolayer system, a compound is being synthesized from 9-bromoanthracene. This compound would already contain the cavity necessary for the inclusion of "guest" molecules. The solution that contained OTS was composed of a 4:1 mixture of anhydrous octadecane: chloroform. Silicon substrates with a deposited oxide layer were hydroxylated for the surfactant binding chemical reaction to occur. The OTS SAMs were exposed to the same stability tests as the LB films. Surface contact angle measurements were taken of the OTS SAMs before and after the stability tests. The contact angle prior to the stability tests was 110° (±2°). The contact angle after immersion in THF was 101° (±2°) while the contact angle resulting from immersion in hexane was 105° (±2°). From the contact angle measurements, the degradation of the OTS SAMs was less extensive than that of the (G)C18S LB films. / Master of Science

Este trabalho visa ao entendimento da interação de capsaicinóides com membranas celulares utilizando sistemas modelo. Dentre os alcalóides derivados de plantas do gênero Capsicum, a capsaicina e a dihidrocapsaicina respondem por 90% dos capsaicinóides, que são usados como analgésicos e antiinflamatórios, devido a sua interação específica com receptores. O mecanismo neurofarmacológico já foi bastante estudado, mas o modo de ação não neural ainda não foi elucidado. Usamos extratos brutos (EBs) de pimenta malagueta e de dedo-de-moça, que têm atividade superficial, e afetaram monocamadas de Langmuir de fosfatidil colina de dipalmitoíla (DPPC) e fosfatidil glicerol de dipalmitoíla (DPPG). Tais efeitos não tiveram dependência expressiva com a carga, pois o EB de dedo-de-moça interagiu mais fortemente com o DPPC do que com o DPPG, ao passo que o contrário se verificou para o EB de malagueta. Também não houve diferença significativa entre os EBs das duas pimentas. Nas monocamadas de Langmuir representativas para a bactéria S. aureus, ambos os EBs tiveram efeito, tanto nas isotermas de pressão quanto nos resultados de espectroscopia de absorção e reflexão no infravermelho com modulação de polarização (PM-IRRAS), sem distinção significativa entre malagueta e dedo-de-moça. No entanto, as medidas de vazamento com lipossomos mostraram maior interação com o EB de dedo-de-moça, o que é consistente com a atividade bactericida para S. aureus. De fato, a concentração inibitória mínima (MIC) foi 0,13 mg mL-1 para o EB da pimenta dedo-de moça e 4,0 mg mL-1 para o EB de malagueta. Para a E. coli, os EBs interagiram com as monocamadas de Langmuir sem diferenças dignas de nota para as duas pimentas, e nas medidas de vazamento o efeito maior foi para a dedo-de-moça. Não houve efeito bactericida para nenhum dos extratos. Isso se explica porque bactérias gram-negativas, como a E. coli, têm uma camada externa protetora de lipossacarídeos (LPS). Das medidas de monocamadas de Langmuir representativas da camada de LPS, observou-se pouca incorporação dos EBs. Conclui-se, assim, que os EBs não conseguem causar rompimento da camada de LPS. Do conjunto dos resultados, infere-se que o mecanismo de ação para a S. aureus envolve solubilização parcial da membrana, e não há relação entre pungência e atividade bactericida, pois a pimenta dedo-de-moça, que é menos pungente, teve maior efeito do que a malagueta. Depreende-se, também, que a ação de extratos de pimenta deve depender da interação com receptores na membrana, o que explica porque o uso de tais extratos tem sido principalmente em aplicações tópicas. / This study is aimed at understanding the interaction of capsaicinoids with cell membranes using model systems. Among the alkaloids derived from plants of the genus Capsicum, capsaicin and dihydrocapsaicin account for 90% of capsaicinoids, which are used as analgesic and anti-inflammatory due to their interaction with specific receptors. The neuropharmacological mechanism has been well studied, but the non-neural mode of action has not been elucidated. Here, we use crude extracts (EBs) of malagueta and dedo-de-moça chilli peppers, which are surface active, and affected Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG). Such effects did not depend on the charge, since EB from dedo-de-moça interacted more strongly with DPPC than with DPPG, while the opposite applied for malagueta. In addition, there was no significant difference between the two EBs. For Langmuir monolayers representing the bacteria S. aureus, both EBs affected the surface pressure isotherms and the polarizationmodulated infrared reflection-absorption spectroscopy (PM-IRRAS) data, without significant distinction between dedo-de-moça and malagueta. However, in the leakage measurements with liposomes the EB from dedo-de-moça was more efficient in rupturing the liposome, which is consistent with the bactericidal activity for S. aureus. In fact, the minimum inhibitory concentration (MIC) was 0.13 mg mL-1 for dedo-de-moça and 4.0 mg mL-1 for malagueta. For the Langmuir monolayers mimicking the E. coli membrane, the EBs interacted much in the same way, while the EB from dedo-de-moça caused larger leakage in liposomes. There was no bactericidal effect of the EBs. This is explained by the fact that gram-negative bacteria, such as E. coli, have a protective outer layer of liposaccharides (LPS). In monolayers representing LPS, there was little incorporation of EBs, from which one infers that the EBs cannot cause disruption of the LPS layer. Taking all these results together, it appears that the mechanism of action for S. aureus involves partial solubilization of the membrane. Furthermore, there is no relationship between pungency and bactericidal activity because dedo-de-moça, which is less pungent, had greater effect than malagueta. It seems also that the action of pepper extracts must depend on the interaction with membrane receptors, which explains why the use of such extracts has been essentially in topical applications.

Une nouvelle méthode de détection sans marquage des interactions biomoléculaires a été développée. Elle est basée sur la conception d’une couche sensible supportée innovante réalisée par la technique de Langmuir‐Blodgett. Cette couche est composée d'un lipide à tête polaire immobilisant un cation métallique divalent capable (i) de chélater une molécule possédant une affinité pour ce type de cation et (ii) de catalyser la réaction de chimiluminescence du luminol. L'intensité du signal chimiluminescent est modulée par la présence de biomolécules fixées en surface de la couche sensible, qui modifient l'environnement immédiat du cation métallique. La variation du signal chimiluminescent (issu de la catalyse par le cation immobilisé) a pu être quantifiée et corrélée à une gamme de concentration d’histamine et d’anticorps. Les potentialités de cette approche ont finalement été exploitées pour développer une puce de PMMA de type macropuce immobilisant la monocouche de lipides. / A new label‐free detection method for biomolecular interactions was developed. It is based on the development of an original sensitive layer performed with the Langmuir‐ Blodgett technique. This layer is composed of a lipid which immobilized a bivalent metallic cation on his polar head, able (i) to chelate a molecule which has an affinity for this cation and (ii) to catalyze the luminol chemiluminescent reaction. The chemiluminescent signal intensity is modulated by the presence of immobilized biomolecules on the sensitive layer surface, which modifies the immediate environmentof the metallic cation. The chemiluminescent signal variation (from catalysis by the metallic cation) has been quantified and correlated to a histamine and antibody concentration range. The potentialities of this approach have finally been employed to achieve a PMMA chip (macroarray type), immobilizing the lipid monolayer.

Gegenstand der vorliegenden Arbeit ist die Entwicklung, Synthese und Charakterisierung neuartiger oligofunktionalisierter Amphiphile mit potentiellen Sammler- und LB-Filmbildungseigenschaften. Basierend auf dem entwickelten Konzept der supramolekularen Strukturbildung zum Aufbau präorganisierter und gebündelter Sammleraggregate wurden zwei Typen neuartiger oligofunktioneller Tenside synthetisiert, die sich insbesondere in ihrer konformativen Flexibilität und Hydrophilie-Lipophilie-Balance unterscheiden. Ausgeprägte oberflächenaktive Eigenschaften wurden bei den bi-, tri- und tetrafunktionellen Aminosäure-analogen Zielverbindungen (Typ II) mit linearer, trigonaler und tetragonaler Molekülstruktur gefunden. Diese Verbindungen bilden auch stabile monomolekulare Filme geringer Heterogenität aus. Im mineralischen Flotationsprozess ergeben diese präorganisierten Tenside mit geometrisch kontrollierter Positionierung der lateralen Funktionseinheiten im Vergleich zu konventionellen Sammlern bei spezifischem Verhalten eine bemerkenswerte Steigerung der flotativen Effizienz.

Este trabalho visa ao entendimento da interação de capsaicinóides com membranas celulares utilizando sistemas modelo. Dentre os alcalóides derivados de plantas do gênero Capsicum, a capsaicina e a dihidrocapsaicina respondem por 90% dos capsaicinóides, que são usados como analgésicos e antiinflamatórios, devido a sua interação específica com receptores. O mecanismo neurofarmacológico já foi bastante estudado, mas o modo de ação não neural ainda não foi elucidado. Usamos extratos brutos (EBs) de pimenta malagueta e de dedo-de-moça, que têm atividade superficial, e afetaram monocamadas de Langmuir de fosfatidil colina de dipalmitoíla (DPPC) e fosfatidil glicerol de dipalmitoíla (DPPG). Tais efeitos não tiveram dependência expressiva com a carga, pois o EB de dedo-de-moça interagiu mais fortemente com o DPPC do que com o DPPG, ao passo que o contrário se verificou para o EB de malagueta. Também não houve diferença significativa entre os EBs das duas pimentas. Nas monocamadas de Langmuir representativas para a bactéria S. aureus, ambos os EBs tiveram efeito, tanto nas isotermas de pressão quanto nos resultados de espectroscopia de absorção e reflexão no infravermelho com modulação de polarização (PM-IRRAS), sem distinção significativa entre malagueta e dedo-de-moça. No entanto, as medidas de vazamento com lipossomos mostraram maior interação com o EB de dedo-de-moça, o que é consistente com a atividade bactericida para S. aureus. De fato, a concentração inibitória mínima (MIC) foi 0,13 mg mL-1 para o EB da pimenta dedo-de moça e 4,0 mg mL-1 para o EB de malagueta. Para a E. coli, os EBs interagiram com as monocamadas de Langmuir sem diferenças dignas de nota para as duas pimentas, e nas medidas de vazamento o efeito maior foi para a dedo-de-moça. Não houve efeito bactericida para nenhum dos extratos. Isso se explica porque bactérias gram-negativas, como a E. coli, têm uma camada externa protetora de lipossacarídeos (LPS). Das medidas de monocamadas de Langmuir representativas da camada de LPS, observou-se pouca incorporação dos EBs. Conclui-se, assim, que os EBs não conseguem causar rompimento da camada de LPS. Do conjunto dos resultados, infere-se que o mecanismo de ação para a S. aureus envolve solubilização parcial da membrana, e não há relação entre pungência e atividade bactericida, pois a pimenta dedo-de-moça, que é menos pungente, teve maior efeito do que a malagueta. Depreende-se, também, que a ação de extratos de pimenta deve depender da interação com receptores na membrana, o que explica porque o uso de tais extratos tem sido principalmente em aplicações tópicas. / This study is aimed at understanding the interaction of capsaicinoids with cell membranes using model systems. Among the alkaloids derived from plants of the genus Capsicum, capsaicin and dihydrocapsaicin account for 90% of capsaicinoids, which are used as analgesic and anti-inflammatory due to their interaction with specific receptors. The neuropharmacological mechanism has been well studied, but the non-neural mode of action has not been elucidated. Here, we use crude extracts (EBs) of malagueta and dedo-de-moça chilli peppers, which are surface active, and affected Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG). Such effects did not depend on the charge, since EB from dedo-de-moça interacted more strongly with DPPC than with DPPG, while the opposite applied for malagueta. In addition, there was no significant difference between the two EBs. For Langmuir monolayers representing the bacteria S. aureus, both EBs affected the surface pressure isotherms and the polarizationmodulated infrared reflection-absorption spectroscopy (PM-IRRAS) data, without significant distinction between dedo-de-moça and malagueta. However, in the leakage measurements with liposomes the EB from dedo-de-moça was more efficient in rupturing the liposome, which is consistent with the bactericidal activity for S. aureus. In fact, the minimum inhibitory concentration (MIC) was 0.13 mg mL-1 for dedo-de-moça and 4.0 mg mL-1 for malagueta. For the Langmuir monolayers mimicking the E. coli membrane, the EBs interacted much in the same way, while the EB from dedo-de-moça caused larger leakage in liposomes. There was no bactericidal effect of the EBs. This is explained by the fact that gram-negative bacteria, such as E. coli, have a protective outer layer of liposaccharides (LPS). In monolayers representing LPS, there was little incorporation of EBs, from which one infers that the EBs cannot cause disruption of the LPS layer. Taking all these results together, it appears that the mechanism of action for S. aureus involves partial solubilization of the membrane. Furthermore, there is no relationship between pungency and bactericidal activity because dedo-de-moça, which is less pungent, had greater effect than malagueta. It seems also that the action of pepper extracts must depend on the interaction with membrane receptors, which explains why the use of such extracts has been essentially in topical applications.