Denis Heissler

Combining fluorescence lifetime and polarization microscopy to discriminate phase separated domains in giant unilamellar vesicles.

Using fluorescence lifetime microscopy we study the structure of lipid domains in giant unilamellar vesicles made from sphingomyelin, 1,2-dioleoyl-sn-glycero-3-phosphocholine, and cholesterol. Lifetimes and orientation of a derivative of the fluorescent probe DPH embedded in the membrane were measured for binary and ternary lipid mixtures incorporating up to 42 mol % of cholesterol. The results show that adding cholesterol always increases the lifetime of the probe studied. In addition, the analysis of the probe orientation indicates that cholesterol has little influence on the ordering of the sphingomyelin alkyl chains whereas it has a noticeable effect on the structure of the 1,2-dioleoyl-sn-glycero-3-phosphocholine chains. The measurements made on the orientation and lifetime of the probe show the structure of the membrane in its liquid ordered and liquid disordered domains.

Influence of the length of the spacer on the partitioning properties of amphiphilic fluorescent membrane probes

Four fluorescent diphenylhexatriene derivatives were considered as membrane probes, namely two ammonium compounds, 3-(diphenylhexatrienyl)propyltrimethylammonium (TMAP-DPH) and 22-(diphenylhexatrienyl)docosyltrimethylammonium (LcTMA-DPH), and two phospholipids, 1-palmitoyl-2-[3-(diphenylhexatrienyl)propanoyl]-sn-glyc ero-3-phosphocholine (DPHpPC) and 1-palmitoyl-2-[21-(diphenylhexatrienyl)henicosanoyl]-sn-phos phocholine (LcDPHpPC). For each pair, the molecules differ by the length of the polymethylenic spacer between the fluorescent moiety and the polar head, so one pair comprises two short chain molecules (C3 spacer) and the other two long chain molecules (C21 or C22 spacer). The partitioning of these probes between gel and liquid crystalline phases of multilamellar vesicles with binary composition (DEPC and DSPC) was measured by a method based on fluorescence anisotropy. The partitioning was shown to depend strongly on the length of the spacer. Short chain probes preferably partition into fluid phases (Kf/s = 1.7 +/- 0.3 for TMAP-DPH; 2.6 +/- 0.11 for DPHpPC), whereas long chain probes show a strong preferential partitioning for gel phases of the vesicles (Kf/s = 0.12 +/- 0.06 for LcTMA-DPH; 0.22 +/- 0.11 for LcDPHpPC). This strong partitioning may be explained by the interdigitation of the long polymethylenic chains across the mid-point of the lipid bilayer (I.E. Mehlhorn et al. (1988) Biochim. Biophys. Acta 939, 151-159), which is enhanced by the better packing provided by a gel phase.

Dependence of the cellular internalization and transfection efficiency on the structure and physicochemical properties of cationic detergent/DNA/liposomes.

Control of the structure and physicochemical properties of DNA complexed with nonviral vectors is essential for efficient biodistribution and gene delivery to cells. Cationic liposomes interact with DNA giving transfection competent but large and heterogeneous aggregates. On the other hand, cationic detergents condense DNA into small homogeneous but reversible complexes inefficient for transfection.

Identification of long-chain tricyclic terpene hydrocarbons (C21–C30) in geological samples

The structure of a series of long-chain tricyclic terpene hydrocarbons occurring in sediments and petroleums has been confirmed by synthesis of the C21–C30 members; these compounds could result from a yet unknown cyclisation of polyprenols in micro-organisms.

Synthesis of (+)-tricyclohexaprenol, a possible precursor of a family of tricyclic geoterpanes, and synthesis of an isomer

Abstract A synthesis of (+)-tricyclohexaprenol 2 starting from isocopalenol 8 and asynthesis of its isomer 4 starting from ent -(14αH)-isocopalenol 26 are described.

SYNTHESIS OF TRICYCLOPOLYPRENOLS VIA A RADICAL ADDITION AND A STEREOSELECTIVE ELIMINATION. PART I : METHODOLOGY

Abstract The feasibility of a synthesis of tricyclopolyprenols based on the addition of the isocopalen-15-yl radical either to a 2-methylene-3-hydroxy alkenenitrile or to a methyl 2-methylene-3-hydroxy alkenoate - both prepared by a Baylis-Hillman reaction - is examined. When two model adducts, a β-acetoxy nitrile and a β-mesyloxy ester, were subjected to an elimination reaction, the former gave a trans α,β-unsaturated nitrile whereas the latter gave a cis α,β-unsaturated ester. The reduction of the ancillary cyano or methoxycarbonyl groups into a methyl is also described.

A radical-based synthesis of (Z,Z)-tricyclohexaprenol

Abstract Addition of the isocopal-12-en-15-yl radical to a methyl 3-hydroxy-3-methylene alkenoate and stereoselective elimination of methanesulphonic acid from the mesylated adducts are the key steps of this synthesis of (Z,Z)-tricyclohexaprenol.

Tricyclohexaprenol and an octaprenediol, two of the “primitive” amphiphilic lipids do improve phospholipidic membranes

Abstract Unilamellar vesicles were prepared from tricyclohexaprenol and dimyristoylphosphatidylcholine or a di-tertiary-octaprenediol and Halobacterium total polar lipids. Both tricyclohexaprenol and the octaprenediol were well incorporated in the membrane (up to 30mol% and 25mol% respectively). Effects of tricyclohexaprenol or the octaprenediol on the mechanical properties of the bilayer were investigated by the osmotic swelling method in a stopped-flow apparatus. These substances do not show a marked effect on the elasticity of the bilayer, but they do lower the water permeability through the membrane. Therefore, it was confirmed, at least in model systems, that these postulated phylogenetic precursors of cholesterol and carotenoids are membrane reinforcers.

Synthesis of the trans-syn-trans perhydrobenz[e]indene moiety of the stellettins and of the stelliferins

Abstract The perhydrobenz[ e ]indene moiety of the stellettins and of the stelliferins, two families of isomalabaricane-type triterpenes with trans-syn-trans ring junctions, has been built from a bicyclic γ,δ-unsaturated aldehyde by a reaction sequence including a Lewis acid catalysed ene cyclisation to form a cyclopentanol, a hydroxyl-directed cyclopropanation, and the ring opening of a cyclopropyl ketone with trimethylsilyl iodide.

Synthesis of fluorescent probes for localized membrane fluidity measurements

Abstract The synthesis of two long-chain homologues of the fluorescent membrane probes TMA-DPH and DPHpPC is described. The long-chain phosphatidylcholine could be synthesized from palmitoyl-lysophosphatidylcholine and 21-(diphenylhexatrienyl) henicosanoic acid only when the promoting agent was 1,1′-thionyldiimidazole.