Sonia B. Díaz

Lysophosphatidylcholine-arbutin complexes form bilayer-like structures.

Arbutin is known to suppress melanin production in murine B16 melanoma cells and inhibit phospholipase action. This encourages the possibility to stabilize it in lipid aggregates for its administration in medical applications. Thus, it was of interest to demonstrate that monomyristoylphosphatidylcholine (14:0 lysoPC) and arbutin may form association complexes. This was studied by Electron Microscopy (EM), 31P Nuclear Magnetic Resonance (31P NMR), Electronic Paramagnetic Resonance (EPR) and Fourier Transform Infrared Spectroscopy (FTIR). EM images show the formation of particles of c.a. 6 nm in diameter. For a 1:1 lysoPC-arbutin molar ratio 31P NMR shows a spectrum with a shoulder that resembles the axially symmetric spectrum characteristic of vesicles. The addition of La3+ ions to the arbutin-lysoPC complex allows one to distinguish two phosphorous populations. These results suggest that arbutin-lysoPC forms vesicles with bilayers stabilized in an interdigitated array. FTIR spectroscopy shows that arbutin interacts with the hydrated population of the carbonyl groups and with the phosphates through the formation of hydrogen bonds. It is interpreted that hydrophobic interactions among the phenol group of arbutin and the acyl chain of lysoPC are responsible for the decrease in acyl chain mobility observed at the 5th C level by EPR. A model proposing the formation of interdigitated bilayers of arbutin-lysoPC could explain the experimental results.

Interaction of S-methyl methanethiosulfonate with DPPC bilayer

The present study is a first step towards the investigation of S-methyl methanethiosulfonate (MMTS) interaction with membrane model systems like liposomes. In this paper, the interaction of MMTS with dipalmitoylphosphatidylcholine (DPPC) bilayers was studied by FTIR and SERS spectroscopy. Lysolipid effect on vesicle stability was studied. The results show that MMTS interacts to different extents with the phosphate and carbonyl groups of membranes in the gel and the liquid crystalline states. To gain a deeper insight into MMTS properties that may be potentially helpful in the design of new drugs with therapeutic effects, we performed theoretical studies that may be the basis for the design of their mode of action.

Vibrational and structural behavior of (L)-cysteine ethyl ester hydrochloride in the solid state and in aqueous solution.

The aim of this work is to evaluate the vibrational and structural properties of l-cysteine ethyl ester hydrochloride (CE), and its electronic behavior mainly in relation to the action of the thiol and amine groups at different degrees of solvation. The crystal structure of CE was determined at room temperature by X-ray diffraction methods. Infrared and Raman spectra were collected to compare the behavior of different functional groups in the molecule, both in the solid phase and in aqueous solution. Its UV and circular dichroism spectra were also measured in aqueous solution. The influence of an aqueous environment on the CE spectra was simulated by means of implicit (polarizable continuum model) and explicit (molecular dynamics, solute-solvent clusters) methods. Calculations in explicit and continuous solvent are of interest to explain the behavior of bioavailable sites in this medium. The study was completed by natural bond orbital analysis to determine the presence of hyperconjugative interactions.

Reorganization of Hydration Water of DPPC Multilamellar Vesicles Induced by l-Cysteine Interaction

The aim of this study is to analyze the consequences of water redistribution on the structure and stability of phospholipid bilayers induced by cysteine (Cys). This interaction is studied with 1,2-dipalmitoyl- sn-glycero-3-phosphatidylcholine (DPPC) multilamellar vesicles in gel (30 °C) and liquid crystalline (50 °C) state; experimental studies were performed by means of Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and differential scanning calorimetry (DSC). The polar head sites of the lipid molecules to which water can bind are identified by competition with compounds that form hydrogen bonds, such as Cys. FTIR spectroscopy results revealed that there is a Cys interaction with the phospholipid head groups in the gel and liquid crystalline phases. Raman spectra were measured in the gel state. They were dominated by vibrations of the fatty acyl chains, with superposition of a few bands from the head group, and clearly showed that the S-H stretching band of Cys shifted to lower frequencies with a decrease in its force constant. DSC disclosed an overview of the behavior of the multilamellar vesicles in the working temperature range (30-50 °C) and showed how the increase of the molar ratios modified the environment of the polar head and the hydrocarbon chains. A loss of the pretransition ( TP) and an increase in the temperature of main transition ( Tm) with increasing Cys/DPPC molar ratio were observed.

Interaction of galacto-oligosaccharides and lactulose with dipalmitoylphosphatidilcholine lipid membranes as determined by infrared spectroscopy

Lactulose and galacto-oligosaccharides (GOS) have been recognized as health promoting compounds due to their recognized prebiotic capacity. In addition, because of their polyhydroxilated nature, they are effective protectants during processes involving dehydration of lactic acid bacteria. The protective effects of sugars have been associated with their capacity to replace water molecules from lipid membranes and/or to form glassy matrices. Although this latter property has been previously investigated for GOS and lactulose, the capacity of these sugars to replace water molecules was not. Furthermore, it must be considered that GOS are usually mixtures of oligo-saccharides with different degrees of polymerization (DP) including or excluding different amounts of mono and disaccharides, and the effect of their composition on the GOS-membrane interaction has not been addressed so far. The aim of the present work was to study the interaction of lactulose and GOS of different compositions with dipalmitoylphosphatidilcholine (DPPC) membranes both in the gel (Lβ) and in the liquid crystalline phase (Lα) by using infrared spectroscopy. Both GOS and lactulose interacted with the phosphate groups of the polar head region, but only lactulose (disaccharide) penetrated into the lipid bilayers and decreased the membrane phase transition (Tm). In contrast, GOS containing no mono and disaccharides were excluded from the hydrophobic region, leading to an increase of the Tm. In turn, GOS containing mono and disaccharides showed a concentration-dependent effect. The results obtained shed light on the mechanisms involved in protection mediated by GOS and lactulose, thus providing support to improve the stabilization of lactic acid bacteria.

Characterization of interactions of eggPC lipid structures with different biomolecules

In this paper we study the interactions of two biomolecules (ascorbic acid and Annonacin) with a bilayer lipid membrane. Egg yolk phosphatidylcholine (eggPC) liposomes (in crystalline liquid state) were prepared in solutions of ascorbic acid (AA) at different concentration levels. On the other hand, liposomes were doped with Annonacin (Ann), a mono-tetrahydrofuran acetogenin (ACG), which is an effective citotoxic substance. While AA pharmacologic effect and action mechanisms are widely known, those of Anns are only very recently being studied. Both Fourier Transformed Infrared (FTIR) and Raman spectroscopic techniques were used to study the participation of the main functional groups of the lipid bilayer involved in the membrane-solution interaction. The obtained spectra were comparatively analyzed, studying the spectral bands corresponding to both the hydrophobic and the hydrophilic regions in the lipid bilayer. Electrochemical experiments namely; impedance spectroscopy (EIS) and cyclic voltamperometry (CV) were used as the main characterization techniques to analyse stability and structural changes of a model system of supported EggPC bilayer in connection with its interactions with AA and Ann. At high molar ratios of AA, there is dehydration in both populations of the carbonyl group of the polar head of the lipid. On the other hand, Ann promotes the formation of hydrogen bonds with the carbonyl groups. No interaction between AA and phosphate groups is observed at low and intermediate molar ratios. Ann is expected to be able to induce the dehydration of the phosphate groups without the subsequent formation of H bonds with them. According to the electrochemical analysis, the interaction of AA with the supported lipid membrane does not alter its dielectric properties. This fact can be related to the conservation of structured water of the phosphate groups in the polar heads of the lipid. On the other hand, the incorporation of Ann into the lipid membrane generates an increase in the number of defects while changes the dielectric constant. This, in turn, can be associated with the induced dehydration of the phosphate groups.