Properties of unusual phospholipids. III: Synthesis, monolayer investigations and DSC studies of hydroxy octadeca(e)noic acids and diacylglycerophosphocholines derived therefrom

Structure-function relationships of antifungal monohydroxy unsaturated fatty acids (HUFA) of plant and bacterial origin

This study investigated the relationships between the structures of hydroxy unsaturated fatty acids (HUFA) and their antifungal activities. Structurally diverse HUFA, including four monohydroxy-18:1 isomers, two monohydroxy 18:2 isomers and two monohydroxy 18:2 isomers were extracted from seeds of plants (Coriaria nepalensis, Thymus vulgaris, Mallotus philippensis and Dimorphotheca sinuata) for which information was available on PlantFAdb database, and from culture supernatants of lactobacilli. They were purified by high-speed counter current chromatography (HSCCC) and identified by LC-MS/MS. The minimum inhibitory concentrations of HUFA were tested against a panel of five yeasts and five mycelial fungi. The membrane phase changes under HUFA treatment and the content of ergosterol were both measured to differentiate HUFA-sensitive and HUFA-resistant fungi. HUFA with a hydroxyl group near the center of the 18-carbon fatty acid chains were found to contribute strongly to HUFA antifungal activity. Antifungal HUFA targeted filamentous fungi but not yeasts. HUFA didn't alter the overall membrane fluidity of sensitive fungi, but the most HUFA-sensitive fungi had a lower average ergosterol content compared to the resistant yeasts. This indicates the possible interaction of HUFA with fungal membrane with low sterol content, which partially support the previous proposed mode of action. Findings here provide insight on further development of HUFA application in food products.

Enantioselective Organocatalysis-Based Synthesis of 3-Hydroxy Fatty Acids and Fatty γ-Lactones

3-Hydroxy fatty acids have attracted the interest of researchers, since some of them may interact with free fatty acid receptors more effectively than their non-hydroxylated counterparts and their determination in plasma provides diagnostic information regarding mitochondrial deficiency. We present here the development of a convenient and general methodology for the asymmetric synthesis of 3-hydroxy fatty acids. The enantioselective organocatalytic synthesis of terminal epoxides, starting from long chain aldehydes, is the key-step of our methodology, followed by ring opening with vinylmagnesium bromide. Ozonolysis and subsequent oxidation leads to the target products. MacMillan’s third generation imidazolidinone organocatalyst has been employed for the epoxide formation, ensuring products in high enantiomeric purity. Furthermore, a route for the incorporation of deuterium on the carbon atom carrying the hydroxy group was developed allowing the synthesis of deuterated derivatives, which may be useful in biological studies and in mass spectrometry studies. In addition, the synthesis of fatty γ-lactones, corresponding to 4-hydroxy fatty acids, was also explored.

Effect of the fluorination degree of hydrophobic chains on the monolayer behavior of unsaturated diacylphosphatidylcholines bearing partially fluorinated 9-octadecynoyl (stearoloyl) groups at the air-water interface

The effect of the fluorination degree of hydrophobic chains on the monolayer behavior of unsaturated diacylphosphatidylcholines (PCs) was examined by employing a series of PCs bearing partially fluorinated 9-octadecynoyl (stearoloyl) groups (DFnStPCs, n: the number of fluorinated carbon atoms in a stearoloyl group; n=1, 2, 4, 8), including their hydrophobic parts--partially fluorinated stearolic acids (FnStAs)--at the air-water interface. π-A isotherm measurements and Brewster angle microscope observations revealed: (i) all DFnStPCs including FnStAs form monolayers of liquid character at 25 °C; (ii) they form more expanded monolayers than their non-fluorinated counterparts, distearoloyl-PC (DStPC) and stearolic acid, while the monolayer stability increases with n; (iii) compared with DStPC and DF8StPC, DFnStPCs (n=1, 2, 4) in the low-π region tend to show a weakening in their self-aggregation property and an increase in the work required for monolayer compression; (iv) although DF8StPC forms the most expanded monolayer, the behavior of DF8StPC resembles that of DStPC rather than that of DFnStPCs (n=1, 2, 4). The monolayer behavior of DFnStPCs (n=1, 2, 4) is explained by postulating a flatly-lying conformation of hydrophobic chains, in which three polar parts (ester group, triple bond, CF2-CH2 linkage) in chains are immersed in the subphase at large areas. DStPC and DF8StPC lacking a CF2-CH2 linkage, however, do not likely adopt such a conformation.

Membrane potential-dependent binding of polysialic acid to lipid monolayers and bilayers

Polysialic acids are linear polysaccharides composed of sialic acid monomers. These polyanionic chains are usually membrane-bound, and are expressed on the surfaces of neural, tumor and neuroinvasive bacterial cells. We used toluidine blue spectroscopy, the Langmuir monolayer technique and fluorescence spectroscopy to study the effects of membrane surface potential and transmembrane potential on the binding of polysialic acids to lipid bilayers and monolayers. Polysialic acid free in solution was added to the bathing solution to assess the metachromatic shift in the absorption spectra of toluidine blue, the temperature dependence of the fluorescence anisotropy of DPH in liposomes, the limiting molecular area in lipid monolayers, and the fluorescence spectroscopy of oxonol V in liposomes. Our results show that both a positive surface potential and a positive transmembrane potential inside the vesicles can facilitate the binding of polysialic acid chains to model lipid membranes. These observations suggest that these membrane potentials can also affect the polysialic acid-mediated interaction between cells.

Surface properties of unsaturated non-oxidized and oxidized free fatty acids spread as monomolecular films at an argon/water interface

The interfacial properties of monomolecular films of stearic acid (SA) oleic acid (OA), linoleic acid (LA), ricinoleic acid (RA), 13(S)-hydroperoxyoctadeca-9Z,11E-dienoic acid (13-HPODE) and 13(S)-hydroxyoctadeca-9Z,11E-dienoic acid (13-HODE) were studied by recording the changes occurring in response to monomolecular film compression in their surface pressure and surface potential at the argon/water interface. The oxidized free fatty acids are more expanded than the parent non-oxidized free fatty acids, reflecting a higher hydrophilic-lipophilic balance. The lift-off values of the molecular area of 13-HODE, 13-HPODE and RA were 68, 74 and 106 A2 molecule(-1), respectively, as compared to 47 and 40 A2 molecule(-1) in the case of LA and OA, respectively. Variations in the molecular orientation of free fatty acids can result in large changes in the dipole moment which are not accompanied by appreciable changes in the surface pressure. In the case of the oxidized free fatty acids, the spontaneous desorption into the aqueous phase was found to increase at increasing surface pressures. The desorption rates of OA and LA increased dramatically in the presence of beta-cyclodextrin (beta-CD); whereas the presence of beta-CD only slightly increased the desorption rates of the oxidized free fatty acids.