New phases induced by sucrose in saturated phosphatidylethanolamines: an expanded lamellar gel phase and a cubic phase

AbstractA new lamellar gel phase (Lβ) with expanded lamellar period was found at low temperatures in dihexadecylphosphatidylethanolamine (DHPE) and dipalmitoylphosphatidylethanolamine (DPPE) dispersions in concentrated sucrose solutions (1–2.4 M). It forms via a cooperative, relatively broad transition upon cooling of the Lβ gel phase of these lipids. According to the X-ray data, the transformation between Lβ and Lβ is reversible, with a temperature hysteresis of 6–10°C and a transition width of about 10°C. No specific volume changes and a very small heat absorption of about 0.05 kcal/mol accompany this transition. The Lβ−Lβ transition temperature strongly depends on the disaccharide concentration. From a value of about 10°C below the melting transition of DHPE, it drops by 25°C with decrease of sucrose concentration from 2.4 M to 1 M. The low-temperature gel phase Lβ has a repeat spacing by 8–10 Å larger than that of the Lβ gel phase and a single symmetric 4.2 Å wide-angle peak. It has been observed in 1. 1.25, 1.5 and 2.4 M solutions of sucrose, but not in 0.5 M of sucrose. The data clearly indicate that the expanded lamellar period of the Lβ phase results from a cooperative, reversible with the temperature, increase of the interlamellar space of the Lβ gel phase. Other sugars (trehalose, maltose, fructose, glucose) induce similar expanded low-temperature gel phases in DHPE and DPPE. The Lβ phase is osmotically insensitive. Its lamellar period does not depend on the sucrose concentration, while the lattice spacings of the Lα, Lβ and HH phases decrease linearly with increase of sucrose concentration. Another notable sugar effect is the induction of a cubic phase in these lipids. It forms during the reverse HH−Lα phase transition and coexists with the Lα phase in the whole temperature range between the HH and Lβ phases. The cubic phase has only been observed at sucrose concentrations of 1 M and above. In accordance with previous data, sucrose suppresses the Lα phase in both lipids and brings about a direct Lβ−HH phase transition in DHPE. A rapid, reversible gel-subgel transformation takes place at about 17°C in both DPPE and DHPE. Its properties do not depend on the sucrose concentration. The observed new effects of disaccharides on the properties of lipid dispersions might be relevant to their action as natural protectants

Fullerene up-take alters bilayer structure and elasticity: A small angle X-ray study.

The coupling of fullerene (C60) to the structure and elasticity of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers has been explored by synchrotron small angle X-ray scattering. Multilamellar vesicles were loaded with 0, 2 and 10mol.% of C60 and studied in a temperature range from 15 to 65°C. The addition of C60 caused an increase in the bilayer undulations (∼20%), in the bilayer separation (∼15%), in the linear expansion coefficient and caused a drop in the bending rigidity of the bilayers (20-40%). Possible damaging effects of fullerene on biomembranes are mainly discussed on the basis of altered bilayer fluidity and elasticity changes

Development of a two-dimensional virtual pixel X-ray imaging detector for time-resolved structure research

An interpolating two-dimensional X-ray imaging detector based on a single photon counter with gas amplification by GEM (gas electron multiplier) structures is presented. The detector system can be used for time-resolved structure research down to the microsecond-time domain. The prototype detector has been tested at the SAXS beamline at ELETTRA synchrotron light source with a beam energy of 8 keV to test its capabilities in the rough beamline environment. The imaging performance is examined with apertures and standard diffraction targets. Finally, the application in a time-resolved lipid temperature jump experiment is presented.Comment: 10 pages, 14 figures, accepted for publication in J. Synchrotron Rad, revised version, paper shortened, minor change

A synchrotron X-ray scattering study of the crystallization behavior of mixtures of confectionary triacylglycerides: effect of chemical composition and shear on polymorphism and kinetics

Cocoa butter equivalents (CBE) are mixtures of triglycerides from multiple sources (e.g., sunflower oil, mango kernel and sal), which resemble cocoa butter (CB) in both physical and chemical properties. Despite being widely used to replace CB in chocolate products, the crystallization behavior of many CBEs is still poorly understood. The aim of this work was to develop a fundamental understanding, at the molecular level, of the crystallization behavior of selected CBEs, and compare it with that of CB. Chromatography was used to determine the composition of CBEs, in terms of fatty acids and triacylglycerides (TAGs), while their thermodynamic behavior and crystallization kinetics were studied using polarized microscopy, differential calorimetry and three different synchrotron X-ray scattering setups. CBEs of different origin and chemical composition (e.g., different ratios of the main CB TAGs, namely POP, SOS and POS) crystallized in different polymorphs and with different kinetics of nucleation, growth and polymorphic transformation. SOS rich CBEs presented showed more polymorphs than CB and POP rich samples; whereas, CBEs with high concentration of POP showed slow kinetic of polymorphic transformation towards the stable β(3L) form. Additionally, it was observed that the presence of small amounts (<1% w/w) of specific TAGs, such as OOO, PPP or SSS, could significantly affect the crystallization behavior of CBEs and CBs in terms of kinetics of polymorphic transformation and number of phases detected (multiple high melting β(2L) polymorphs were identified in all samples studied). Finally, it was found that, regardless of the CBE composition, the presence of shear could promote the formation of stable β polymorphs over metastable β’ and γ forms, and reduced the size of the crystal agglomerates formed due to increased secondary nucleation

Bile Salts Caught in the Act: From Emulsification to Nanostructural Reorganization of Lipid Self-Assemblies

Bile salts (BSs) are important for the digestion and absorption of fats and fat-soluble vitamins in the small intestine. In this work, we scrutinized, with small-angle X-ray scattering (SAXS), the crucial functions of bile salts beyond their capacity for the interfacial stabilization of submicrometer-sized lipid particles. By studying a wide compositional range of BS-lipid dispersions using two widely applied lipids for drug-delivery systems (one a monoglyceride being stabilizer-sensitive and the other an aliphatic alcohol being relatively stabilizer-insensitive), we identified the necessary BS to lipid ratios to guarantee full emulsification. A novel ad hoc developed global small-angle-X-ray scattering analysis method revealed that the addition of BS hardly changes the bilayer thicknesses in bicontinuous phases, while significant membrane thinning is observed in the coexisting fluid lamellar phase. Furthermore, we show that a BS strongly decreases the average critical packing parameter. At increasing BS concentration, the order of phases formed is (i) the bicontinuous diamond cubic ( Pn3 m), (ii) the bicontinuous primitive cubic ( Im3 m), and (iii) the fluid lamellar phase ( L ). These distinctive findings on BS-driven "emulsification" and "membrane curvature reduction" provide new molecular-scale insights for the understanding of the interfacial action of bile salts on lipid assemblies

Divalent cations affect chain mobility and aggregate structure of lipopolysaccharide from Salmonella minnesota reflected in a decrease of its biological activity

AbstractThe physicochemical properties and biological activities of rough mutant lipopolysaccharides Re (LPS Re) as preformed divalent cation (Mg2+, Ca2+, Ba2+) salt form or as natural or triethylamine (Ten+)-salt form under the influence of externally added divalent cations were investigated using complementary methods: Differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopic (FT-IR) measurements for the β↔α gel to liquid crystalline phase behaviour of the acyl chains of LPS, synchrotron radiation X-ray diffraction studies for their aggregate structures, electron density calculations of the LPS bilayer systems, and LPS-induced cytokine (interleukin-6) production in human mononuclear cells. The divalent cation salt forms of LPS exhibit considerable changes in physicochemical parameters such as acyl chain mobility and aggregate structures as compared to the natural or monovalent cation salt forms. Concomitantly, the biological activity was much lower in particular for the Ca2+- and Ba2+-salt forms. This decrease in activity results mainly from the conversion of the unilamellar/cubic aggregate structure of LPS into a multilamellar one. The reduced activity also clearly correlates with the higher order – lower mobility – of the lipid A acyl chains. Both effects can be understood by an impediment of the interactions of LPS with binding proteins such as lipopolysaccharide-binding protein (LBP) and CD14 due to the action of the divalent cations

Comparative study of the AT1 receptor prodrug antagonist candesartan cilexetil with other sartans on the interactions with membrane bilayers

AbstractDrug–membrane interactions of the candesartan cilexetil (TCV-116) have been studied on molecular basis by applying various complementary biophysical techniques namely differential scanning calorimetry (DSC), Raman spectroscopy, small and wide angle X-ray scattering (SAXS and WAXS), solution 1H and 13C nuclear magnetic resonance (NMR) and solid state 13C and 31P (NMR) spectroscopies. In addition, 31P cross polarization (CP) NMR broadline fitting methodology in combination with ab initio computations has been applied. Finally molecular dynamics (MD) was applied to find the low energy conformation and position of candesartan cilexetil in the bilayers. Thus, the experimental results complemented with in silico MD results provided information on the localization, orientation, and dynamic properties of TCV-116 in the lipidic environment. The effects of this prodrug have been compared with other AT1 receptor antagonists hitherto studied. The prodrug TCV-116 as other sartans has been found to be accommodated in the polar/apolar interface of the bilayer. In particular, it anchors in the mesophase region of the lipid bilayers with the tetrazole group oriented toward the polar headgroup spanning from water interface toward the mesophase and upper segment of the hydrophobic region. In spite of their localization identity, their thermal and dynamic effects are distinct pointing out that each sartan has its own fingerprint of action in the membrane bilayer, which is determined by the parameters derived from the above mentioned biophysical techniques

Thermal, dynamic and structural properties of drug AT1 antagonist olmesartan in lipid bilayers

It is proposed that AT1 antagonists (ARBs) exert their biological action by inserting into the lipid membrane and then diffuse to the active site of AT1 receptor. Thus, lipid bilayers are expected to be actively involved and play a critical role in drug action. For this reason, the thermal, dynamic and structural effects of olmesartan alone and together with cholesterol were studied using differential scanning calorimetry (DSC), 13C magicangle spinning (MAS) nuclear magnetic resonance (NMR), cross-polarization (CP) MAS NMR, and Raman spectroscopy as well as small- and wide angle X-ray scattering (SAXS and WAXS) on dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles. 13C CP/MAS spectra provided direct evidence for the incorporation of olmesartan and cholesterol in lipid bilayers. Raman and X-ray data revealed how both molecules modify the bilayer&apos;s properties. Olmesartan locates itself at the head-group region and upper segment of the lipid bilayers as 13C CP/MAS spectra show that its presence causes significant chemical shift changes mainly in the A ring of the steroidal part of cholesterol. The influence of olmesartan on DPPC/cholesterol bilayers is less pronounced. Although, olmesartan and cholesterol are residing at the same region of the lipid bilayers, due to their different sizes, display distinct impacts on the bilayer&apos;s properties. Cholesterol broadens significantly the main transition, abolishes the pre-transition, and decreases the membrane fluidity above the main transition. Olmesartan is the only so far studied ARB that increases the gauche:trans ratio in the liquid crystalline phase. These significant differences of olmesartan may in part explain its distinct pharmacological profile