Efeitos de terpenos nas membranas de estrato córneo estudados por ressonância paramagnética eletrônica / Effects of terpenes on the stratum corneum membranes studied by electron paramagnetic resonance


IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia




The interaction of the skin penetration enhancers DL-menthol, -terpineol, 1,8-cineole and (+)-limonene with membranes of the uppermost skin layer, the stratum corneum (SC) and with multilamellar vesicles from 1,2-dipalmitoyl-sn-glycero-3-phosphaticylcholine (DPPC)is investigated by electron paramagnetic resonance (EPR) spectroscopy using spin-labeled analogs of androstanol ASL),stearic acid (5-DSA), methyl stearate (5-DMS) and a small spin label 2,2,6,6-tetramethylpiperedine-1-oxyl (TEMPO). The terpenes were added to SC samples using ethanol as a co-solvent (20% ethanol in the buffer), the effect of ethanol on the SC also was investigated. The spectra of spin labels ASL, 5-DSA and 5-DMS in the membranes of SC are characterized by the presence of two spectral components differing in mobility.Component 1 was attributed to the spin labels H-bonded to the headgroups, while component 2 was assigned to the spin labels H-bonded to water molecules or temporally non-hydrogen-bonded. EPR results showed that ethanol in the range 0-70% did not alter the fluidity in SC membranes or the relative fractions of these two components. Instead, ethanol only caused a selective extraction of spin labels, indicating that ethanol acts as extractor and not as fluidizer when facilitates molecular permeation in the skin. Addition of 1% DLmenthol to the solvent containing 20% ethanol increases both the mobility and the fraction of spin labels in the component 2 (more mobile spectral component). Similarly, with the addition of 1,8-cineole, the spin probes were gradually transferred from the motionally more restricted component 1 to the more mobile component 2. The spectrum of the spin label TEMPO in the membranes of SC allows for the determination of the actual partition coefficient and rotational diffusion rates of the spin probe in the aqueous and hydrocarbon environments. The enthalpy changes,H,to transfer the spin probe from the aqueous to the hydrocarbon phase, as well as the activation energies associated to its rotational motion, were considerably smaller for SC when compared to DPPC, indicating less pronounced thermal reorganizations for SC samples. For DPPC,all terpenes increased both the partition coefficient and the rotational diffusion rate of the spin label in the membrane, except in the liquid-crystalline phase. These results suggest that the terpenes,effectively acting as spacers in the membrane,fluidize the lipids and cause ruptures in the hydrogen-bonded network of the membrane-water interface, with consequent displacements of spin probes towards the hydrophobic core. The EPR spectra of maleimide derivative spin label (6-MSL)covalently attached to stratum corneum proteins indicate that 1,8-cineole does not alter the dynamics of protein backbones.Instead, this terpene only increases the solvents ability to dissolve and mobilize the nitroxide side chain, which is in agreement with its low irritation response. OBS:= significa um símbolo que o programa não copia


fisica estrato córneo rpe marcadores de spin terpeno espectroscopia de resson paramagnétic eletrônic; terpenos stratum corneum epr spin label terpene

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