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Mixed monolayers were prepared using phospholipids in order to mimic cell membranes and fractions of capsaicinoids (extracted from Malagueta, Caps-M, and Bhut Jolokia, Caps-B, peppers). According to their surface-pressure isotherms and polarization-modulated infrared reflection absorption spectra (PM-IRRAS), weak molecular-level interactions were observed between Caps and phospholipids. Both Caps-M and Caps-B penetrated into the alkyl tail region of the monolayer, interacted with the phosphate group of the phospholipids and affected hydration of their C O groups. Since the physiological activity of Caps is not governed solely by interaction with cell membranes, it should require participation of a neuronal membrane receptor, e.g. vanilloid receptor (TRPV1).

FAPESP (Brazil) CNPq (Brazil) CAPES (Brazil) nBioNet (Brazil) We report on the interaction between mer-[RuCl3(dppb)(VPy)] (dppb = 1,4-bis(diphenylphosphine)-butane and VPy=4-vinylpyridine) (RuVPy) and dipalmitoyl phosphatidyl serine (DPPS), in Langmuir and Langmuir-Blodgett (LB) films. Interaction of RuVPy with DPPS, which predominates in cancer cell membranes, should be weaker than for other phospholipids since RuVPy is less toxic to cancer cells than to healthy cells. Incorporation of RuVPy induced smaller changes in electrochemical properties of LB films of DPPS than for other phospholipids, but the same did not apply to surface pressure isotherms. This calls for caution in establishing correlations between effects from a single property and phenomena on cell membranes. (C) 2014 Elsevier B.V. All rights reserved. Univ Estadual Ponta Grossa, Appl Chem Program, BR-84035900 Ponta Grossa, PR, Brazil Univ Sao Paulo, Sao Carlos Inst Phys, BR-13560970 Sao Carlos, SP, Brazil Univ Fed Sao Paulo, Dept Exact Sci, BR-09972270 Diadema, SP, Brazil Univ Fed Sao Paulo, Dept Exact Sci, BR-09972270 Diadema, SP, Brazil Web of Science

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) rede nBioNet (Brazil) This study shows the incorporation of ibuprofen, an anti-inflammatory drug, in Langmuir monolayers as cell membrane models. Significant effects were observed for dipalmitoyl phosphatidyl choline (DPPC) monolayers with relevant changes in the elasticity of the monolayer. Dipalmitoyl phosphatidyl glycerol (DPPG) monolayers were affected by small concentrations of ibuprofen, from 1 to 5 mol%. for both types of monolayer, ibuprofen could penetrate into the hydrophobic part of the monolayer, which was confirmed with polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). Brewster angle microscopy (BAM) images showed that ibuprofen prevents the formation of large domains of DPPC. the pharmacological action should occur primarily with penetration of ibuprofen via electrically neutral phospholipid headgroups of the membrane. (c) 2013 Elsevier B.V. All rights reserved. Univ São Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP, Brazil Universidade Federal de São Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Diadema, SP, Brazil Universidade Federal de São Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Diadema, SP, Brazil Web of Science

Polymer light-emitting devices (PLEDs) have been produced with Langmuir–Blodgett (LB) films from poly(2-methoxy-5-hexyloxy)-p-phenylenevinylene (OC1OC6–PPV) as the emissive layer and an ionomer of a copolymer of styrene and methylmethacrylate (PS/PMMA) as an electron-injection layer. The main features of such devices are the low operating voltages, obtainable firstly due to the good quality of the ultrathin LB films that allows PLEDs to be produced reproducibly and secondly due to the improved electrical and luminance properties brought by the electron-injection layer. Also demonstrated is the superior performance of an all-LB device compared to another one produced with cast films of the same materials.

Light emission control is reported in anisotropic Langmuir–Blodgett films from a poly( p -phenylene vinylene) derivative. The films are considered as containing long conjugated segments in the dipping direction, which are efficient emitters, with the short conjugated segments perpendicular to the dipping direction. Because the latter mainly transfer energy to adjacent chains, an interplay between light emission and energy transfer is exploited in further controlling emission, which depends on the polarization of the light.

We report on the two-photon absorption (2PA) cross-section for eight azoaromatic compounds in dimethyl sulfoxide solutions, using the Z-scan technique with femtosecond laser pulses at 775 nm. The 2PA cross-sections of these molecules are of the order of (1–6)×10 −50 cm 4 s photon −1 . A correlation was established between the molecular structure and the two-photon absorption process, which makes it possible to develop molecular design strategies to create structures with suitable two-photon absorption coefficients.

The use of an effective surface charge density has allowed the Gouy–Chapman (GC) theory to explain surface potential isotherms of Langmuir monolayers of dioctadecyldimethylammonium bromide (DODAB). The effective surface charge density of DODAB monolayer increases with the electronegativity of the counterions in the subphase. The pressure–area isotherms indicate a very condensed monolayer for DODAB spread on an I−-containing subphase, which exhibits the lowest surface charge density, whereas the monolayer on a F−-containing subphase is extremely expanded owing to the high surface charge density or electrostatic repulsion between headgroups.

The three-layer capacitor model proposed by Demchak and Fort [J. Colloid Interface Sci. 46 (1974) 191] is employed to relate measured surface potentials of Langmuir monolayers from a series of polyphenyl carboxylic acids to molecular dipole moments calculated using semiempirical quantum methods. The effective dielectric constant at the air/monolayer interface is 3.0±0.6, very close to that estimated for aliphatic compounds. Good agreement between theory and experiment is obtained by adopting a dielectric constant of 6.4 for the monolayer/water interface and a contribution from the water reorientation of −0.064±0.006 D, which shows that the parameters in the DF model are essentially the same as for aliphatic amphiphiles, such as esters, acids, alcohols and ethers.

Dynamic optical nonlinearities of ytterbium bis-phthalocyanine (YbPc 2 ) dissolved in chloroform were characterized using the Z-scan technique with pulse trains. Two contributions of opposite signs were observed for the nonlinear refraction: a fast process related to the singlet population, and a slow accumulative contribution arising from the triplet population and thermal lensing. As the fluence increases, the nonlinear absorption first presents a weak saturation, followed by a reverse saturable absorption process. We used a six-energy-level diagram to explain these results and to obtain spectroscopic parameters such as the excited state cross-sections and the intersystem crossing lifetime.

A simple model of electron transfer is adapted to explain fluorescence quenching in self-assembled films of poly(p-phenylene vinylene) (PPV) alternating with poly(thiophene acetic acid) (PTAA). Quenching is caused by a photo-induced electron transfer between the excited PPV (donor, D) and the PTAA (acceptor, A). The electron-transfer process can be mediated by insertion of electronically inert spacing bilayers between the D and A layers. As the number of bilayers is increased, the fluorescence is gradually recovered which is explained theoretically by assuming that the electron-transfer rate can be described as k=Z exp (−βr) where r is the distance between D and A.

Aggregation of azobenzene chromophores in Langmuir–Blodgett films of stearoyl ester of Disperse Red-13 (DR13St) and cadmium stearate (CdSt) hampers the trans–cis photoisomerization that normally leads to optical storage capabilities, since the required free volume around the chromophore is not available. Such aggregation has been inferred by UV–VIS. spectroscopy and X-ray diffraction. Optical storage properties could still be obtained if DR13St was mixed in a guest–host system with a polycarbonate matrix.

Surface potential measurements on stearic acid monolayers formed on dilute NaCl solutions and ultrapure water show that the double-layer potential, ψ 0 , obeys the simple Gouy-Chapman theory only if account is taken of the effect of subphase ion concentration on monolayer dissociation. It is concluded that the enhanced lateral conductance observed during compression of stearic acid monolayers cannot arise from the higher proton concentration in the diffuse double-layer but rather from a H-bonded network at the monolayer/water interface as described previously for phospholipid monolayers.

Evidence for two-dimensional protonic charge transport along a monolayer/water interface is presented, supporting the concept of localised charge transport along membrane surface. Charge transport proceeds only at and above a critical molecular packing density, and probably occurs via a network of hydrogen-bonded water molecules and lipid headgroups.