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Foram estudados os efeitos da presença de surfatantes aniônicos (dodecilsulfato de sódio - SDS e dodecilbenzenosssulfonato de sódio - SDBS) e catiônico (cloreto de dodecilamônio - DAC) em diferentes interfases metal/cloreto de sódio, em valores de pH iguais a 5,8 e 3,0 . Platina, cobre e níquel foram utilizados como substratos. Técnicas eletroquímicas (polarizações potenciostáticas catódicas e anódicas; voltametria cíclica; cronoamperometria; impedância eletroquímica, com eletrodo parado e com eletrodo de disco rotativo - EDR) foram empregadas, bem como técnicas não eletroquímicas (espectroscopia Raman \"in situ\" SERS; microscopia eletrônica de varredura (MEV) / espectroscopia de dispersão de energia - EDS) a fim de caracterizar a ação destes surfatantes em processos anódicos e catódicos que ocorrem nas interfases citadas. DAC apresentou ação inibidora acentuada para as reações de oxidação e redução da água, na interfase Pt/NaCl 0,1 mol.L1 , não sendo eletroativo na faixa de potenciais compreendida entre estes dois processos. Utilizando-se eletrodo parado, o surfatante mostrou ação inibidora mais acentuada para os processos anódicos do que para os catódicos. Com convecção forçada empregando EDR, o surfatante apresentou graus de inibição da ordem de 90 % para ambos os processos, sugerindo que o transporte de massa favorece a adsorção do DAC sobre a platina. Tal comportamento pôde também ser comprovado quando se utilizou cobre e níquel como substratos, -1 em meio de pH igual a 5,8. Para a interfase Cu / NaCl 0,1 mol.L-1 pH = 3, com EDR, os três surfatantes tiveram seus efeitos estudados na região catódica, a fim de se verificar a sua atuação na reação de desprendimento de hidrogênio. Os surfatantes aniônicos não apresentaram efeito inibidor sobre a referida reação, aumentando a sua velocidade para potenciais mais negativos + do que -1,0 V / ECS. DAC, ao contrário, inibiu a reação H+ / H2 , com valores de grau de cobertura 2 da ordem de 50 %. A adsorção dos surfatantes sobre cobre foi caracterizada por espectroscopia Raman (SERS), cujos estudos mostraram que os três surfatantes são adsorvidos através da cadeia carbônica (hidrofóbica), no potencial de corrosão (Ecorr ) e a valores de potencial mais positivos e Ecorr . Os resultados espectroscópicos sugerem a presença da parte polar do SDS na interfase, enquanto que, no no caso do DAC, não foi possível caracterizar, por esta técnica, a adsorção do grupamento amônio Foram realizados também estudos sobre o efeito destes surfatantes em processo de eletrodeposição de níquel sobre cobre. SDS apresentou aumento de rendimento de 28% para 43% a um potencial de -1,10 V / ECS, em relação ao processo efetuado em ausência de surfatante. Os depósitos obtidos em presença de SDS e SDBS apresentaram-se mais brilhantes e visualmente mais homogêneos do que aquele obtido em ausência de surfatante, confirmando a ação abrilhantadora destes aditivos utilizados em banhos comerciais de deposição. A presença de DAC inibiu a reação Ni2+ /Ni, obtendo-se depósito de níquel apenas nas bordas do eletrodo de cobre. As superfícies de cobre niqueladas foram caracterizadas por medidas de potencial de circuito aberto, polarização anódica, cronoamperometria, impedância eletroquímica e por MEV / EDS. Os resultados obtidos, empregando as diferentes técnicas, indicaram que a deposição de níquel sobre cobre em meio de NaC1 0,1 mol.L-1, pH = 3, contendo 1,0X10-3 mol.L-1 de SDS foi a apresentou melhores características tanto em relação ao rendimento quanto à qualidade do depósito formado. / The effect of anionic (sodium dodecylsulphate - SDS and sodium dodecylbenzenesulphonate - SDBS) and cationic (dodecylammonium chloride - DAC) surfactants has been studied in different metal / sodium chloride interfaces, at pH = 5.8 and pH = 3.0 . Platinum, copper and nickel have been used as substracts. Electrochemical (anodic and cathodic potentiostatic polarisation, cyclic voltammetry, chronoamperometry, and electrochemical impedance, using stationary and rotating disk electrodes - RDE) and non-electrochemical techniques (\"in situ\" Raman spectroscopy / SERS ; scanning electronic microscopy - SEM / energy dispersion spectroscopy - EDS) have been used to study the action of these surfactants on anodic and cathodic reactions that occur in the interfaces. DAC has shown strong -1 inhibitory action on reduction and oxidation water reactions, on Pt / 0.1 mol.L-1 NaCl interfhace, without electroactivity in all the potential range studied. Stationary electrode, has shown that DAC is more effective as inhibitor for the anodic processes than for the cathodic one. Using rotating disc electrode (RDE), surfactant presents about 90 % of inhibitory efficiency in both processes, suggesting that mass transport favours DAC adsorption on Pt. Furthermore the inhibitory action is the same when using copper and nickel as substract , at pH = 5.8. The three surfactants (SDS, SDBS and DAC) were studied on cathodic potential range, in order to verify their action on hydrogen evolution reaction, in Cu / NaCl 0.1 mol.L-1 , pH = 3.0, using RDE. Anionic surfactants have not shown inhibitory action on the mentioned reaction, increasing its rate at more negative potentials than -1.0 V / ECS. On the other hand, DAC inhibits the same reaction, showing 50 % inhibitory efficiency. Surfactants adsorption on copper have been studied by Raman Spectroscopy (SERS) \"in situ\". These studies have shown the adsorption of DAC, SDS and SDBS through carbonic chain (hydrophobic) at corrosion potential (Ecorr) and at more negative and more positive potentials. The presence of the polar head at the interface have been confirmed for SDS and SDBS. For DAC, however, it was not possible to characterize the ammonium group adsorption from Raman spectra. The effect of these surfactants have also been studied for nickel electrodeposition process on copper. SDS increased the process yield (28 % to 43 %, at E = -1.1 V / ECS), when compared to the results obtained without surfactant. Deposits were brighter and more homogeneous than those obtained in the absence of SDS and SDBS surfactants, confirming the brightening action of these additives in commercial deposition baths. DAC also inhibits Ni /Ni2+ reduction, producing nickel deposit just on the edge of copper electrode. The results, obtained from different techniques, have shown that nickel deposition on copper, in 0.1 mol.L-1 NaC1, pH = 3, containing 1.0X10-3 mol.L-1 SDS, presented the best performance, if it is considered the yield values and the quality of the deposit.

Due to the essential demands for novel anti-tuberculosis treatments for global tuberculosis control, this research investigated the antimycobacterial activity of Hypericum perforatum herb (commonly known as St. John’s wort, SJW), including a SJW methanol extract, purified major bioactive constituents of SJW: hypericin (Hpn), pseudohypericin (Phn) and hyperforin (Hfn). The SJW acidified methanol extract showed bactericidal activity against Mycobacterium JLS at 0.05 mg/ml culture. Purified compounds were tested at similar concentrations contained in the SJW methanol extract treatment. Among three purified bioactive compounds, only Hfn was bactericidal at 12 μg/ml. The other two compounds Phn and Hpn were not inhibitory or bactericidal at concentrations corresponding to the SJW methanol extract treatments. The Polysorbate surfactant Tween 80, which is commonly added to the mycobacterial cultures to prevent cell clumping, was found to have inhibitory effects on the antimycobacterial activities of SJW extract and hyperforin. The addition of Tween 80 (0.05% v/v) increased the minimum bactericidal concentration (MIC) of SJW methanol extract from 0.05 to 0.33mg /ml and from 12 to 80 μg/ml for Hfn. This inhibitory effect of Tween 80 on SJW is opposite to the effect of Tween 80 on the antimycobacterial activity of rifampin and isoniazid. These observations are also in conflict with the existing permeability barrier hypothesis. A hypothesis that hyperforin molecules were sequestered in the core of Tween 80 micelles was given out to explain the repression effect of Tween 80 on hyperforin activity. The effectiveness of Tween 60, Tween 40 and Tween 20 on SJW activity was also tested. Tween 60 and Tween 40 showed the similar dose-dependent inhibitory effect on SJW extract activity with Tween 80, while the inhibitory effect of Tween 20 is much weaker. A preliminary test was performed to detect the activity of SJW acidified MeOH extract and hyperforin on M. tuberculosis H37Rv strain. Results showed the MIC was 0.67mg SJW extract/ml and 200 μg Hfn /ml. In all, M. tuberculosis H37Rv stain is not that sensitive to SJW and hyperforin as other non-pathogenic strains tested in the present and previous studies.

In recent years there has been increasing interest in novel forms of surfactants. Of particular interest are gemini surfactants, which consist of two conventional surfactants joined by a spacer at the head groups, as they exhibit lower critical micelle concentrations than can be achieved by conventional surfactants. In this work, the self-assembly behaviour of several nonionic gemini surfactants with polyethylene oxide head groups (GemnEm, where n (= 20) is the number of carbons per tail and m (= 10, 15, 20 and 30) is the number of ethylene oxides per head group) were investigated. The Critical Micelle Concentrations (CMCs) were measured using a fluorescence probe technique. The CMCs are all ~2 x 10?7 M, with almost no variation with m. The CMCs are several orders of magnitude lower than conventional C12Em nonionic surfactants. The mixing behaviour of the gemini surfactants with conventional surfactants was also studied. They obeyed ideal mixing behaviour with both ionic and nonionic surfactants. Micelle morphologies were studied using Small Angle Neutron Scattering. The gemini surfactants with the larger head groups (i.e. Gem20E20 and Gem20E30) formed spherical micelles. Gem20E15 showed strong scattering at low Q, characteristic of elongated micelles. As the temperature was increased towards the cloud point, the scattering approached the Q-1 dependence predicted for infinite, straight rods. The existence of anisotropic micelles was supported by the viscosity of Gem20E15, which increases by several orders of magnitude on heating towards its cloud point. Phase behaviour was determined using Diffusive Interfacial Transport coupled to near-infrared spectroscopy. Much of the behaviour of these systems is similar to conventional nonionic surfactants. For example, Gem20E10 forms a dilute liquid isotropic phase (W) coexisting with a concentrated lamellar phase (La) at around room temperature and forms a sponge phase at higher temperatures. This is similar to the behaviour of C12E3 and C12E4. The other surfactants studied are all quite soluble in water and form liquid isotropic and hexagonal phases from room temperature. At higher concentrations Gem20E15 formed a cubic and then a lamellar phase while Gem20E20 formed a cubic phase and then an intermediate phase. This is also comparable to the phase behaviour of conventional nonionic surfactants except the intermediate phase, which is often only observed for surfactant systems with long alkyl tails.

Doctor of Philosophy (PhD) / Oligomeric surfactants, sometimes referred to as gemini surfactants, consist of two or more amphiphilic ‘monomer’ units linked together by spacer groups. The chemical identity of the spacer group is unconstrained, and it joins the individual units at or near the hydrophilic headgroups. Oligomeric surfactants display a range of interesting properties, including very low critical micelle concentrations, high surface activity and unusual rheology and self-assembly. Consequently they have many potential applications, both scientific and industrial. Until now, their use has been limited by the cost of their synthesis, which in some cases involve long and difficult procedures. This project developed from the idea that a synthesis based on polymerization could prove a useful and versatile method for producing these surfactants. The chemical starting point for this project was a series of polymerizable surfactants (‘surfmers’), upon which polymerization was performed. Two families of surfmers were investigated, both cationic and based on methacrylate and vinylpyridinium moieties respectively. The physical behaviour of these surfactants – a number of which are new – was investigated using standard techniques; these included the determination of the critical micelle concentration, characterization of phase behaviour, neutron scattering and surface adsorption. In producing oligomers, the initial focus was on free-radical polymerization, with control of molecular weight to be achieved by chain-transfer techniques. Due largely to analysis problems, this work proved unsuccessful. In its place a new reaction, not based on conventional polymerization methods, has been developed. The vinylpyridinium surfmers mentioned above readily undergo addition across the double bond to produce alkyl ring substituents. Under basic conditions, these alkylpyridiniums undergo an elimination/addition reaction in which they link together to form oligomers. This reaction can be started or stopped by raising or lowering the pH of the reaction solution, and has been performed in both organic and aqueous solutions. It is referred to in this thesis as LELA(Linkage by ELimination/Addition). The LELA reaction was used to produce mixtures of oligomers, the phase behaviour and surface adsorption of which were examined. Small-angle neutron scattering was used to monitor the reaction in real time and identify changes in self-assembly as the average oligomer length increased. Progress was also made towards a chromatographic protocol that would allow mixtures to be separated into their components and the pure oligomers to be studied. Finally, some of the compounds studied display interesting pH-dependent chromophoric properties which were also found to occur with other simple alkylpyridinium species. They are tentatively ascribed to inter- and intramolecular charge-transfer complexes, and evidence towards this conclusion was collected and is presented along with relevant calculations.

The accurate prediction of a complex fluid's equilibrium microstructure and corresponding thermodynamic properties relies on the capability to describe both the molecular level architecture and specific governing physics. This thesis makes key contributions to furthering the application and understanding of molecular models for complex bulk and inhomogeneous fluids with a specific interest in mixtures involving trace components. Such developments have potential for wide-ranging application to fields from consumer goods and medicine to energy and targeted specialized material design. In the bulk, the perturbed-chain statistical associating fluid theory (PC-SAFT), an equation of state based on Wertheim's first order thermodynamic perturbation theory (TPT1) is used to demonstrate the robustness and performance of intrinsic molecular parameters determined for a complex fluid (water) with a new fitting strategy. Experimental solubility data at ambient conditions was used to find the PC-SAFT parameters for water which where capable of reproducing water content for binary mixtures with liquid and vapor n -alkanes under a myriad of physical conditions. The model gave excellent qualitative and very good quantitative agreement without the need of a binary interaction parameter. For inhomogeneous fluids, the application of a density functional theory (DFT) also based on TPT1, is extended to model the self-assembly of amphiphilic molecules at a liquid-liquid interface. This DFT, interfacial SAFT ( i SAFT), is validated against molecular simulation results for the microstructure and interfacial tension of a simple diatomic surfactant based on the continuum oil-water-surfactant model of Telo da Gama and Gubbins. A comprehensive systematic study is conducted for characterizing the affects of part of the vast parameter space governing the fluid microstructure and observed interfacial tension. The role of surfactant structure, oil structure, surfactant concentration, nonionic cosurfactant mixtures, and temperature play in altering molecular level phenomena such as surfactant aggregation, solvent depletion, and surfactant chain conformation as a result of the balance between enthalpic and entropic driving forces are described.

Reproduction de : Thèse de doctorat : Chimie organique : Reims : 2006. / Titre provenant de l'écran titre. Bibliogr. f.

Thèse de doctorat : Sciences du bois : Nancy 1 : 2008. / Titre provenant de l'écran-titre.