Analysis of the structure of nanocomposites of triglyceride platelets and DNA

DNA-complexes with platelet-like, cationically modified lipid nanoparticles (cLNPs) are studied with regard to the formation of nanocomposite structures with a sandwich-like arrangement of the DNA and platelets. For this purpose suspensions of platelet-like triglyceride nanocrystals, stabilized by a mixture of two nonionic (lecithin plus polysorbate 80 or poloxamer 188) and one cationic stabilizer dimethyldioctadecylammonium (DODAB), are used. The structure of the platelets in the native suspensions and their DNA-complexes, ranging from the sub-nano to the micron scale, is investigated with small- and wide-angle scattering (SAXS, SANS, WAXS), calorimetry, photon correlation spectroscopy, transmission electron microscopy and computer simulations. The appearance of strong, lamellarly ordered peaks in the SAXS patterns of the DNA-complexes suggests a stacked arrangement of the nanocrystals, with the DNA being partially condensed between the platelets. This finding is supported with computer simulated small-angle scattering patterns of nanocrystal stacks, which can reproduce the measured small-angle scattering patterns on an absolute scale. The influence of the choice of the nonionic stabilizers and the amount of the cationic stabilizer DODAB on the structure of the native suspensions and the inner structure of their DNA-complexes is studied, too. Using high amounts of DODAB, lecithins with saturated acyl chains and polysorbate 80 instead of poloxamer 188 produces thinner nanocrystals, and thus decreases their repeat distances in the nanocomposites. Such nanocomposites could be of interest as DNA carriers, where the triglyceride platelets protect the sandwiched DNA from degradation

X-ray Studies on the C12EO2\mathrm{C_{12}EO_2}/Water System

Binary mixtures of the poly(oxyethylene) surfactant C12EO2 and water have been investigated using optical microscopy and time-resolved X-ray diffraction during temperature scans. At concentrations in the range from 48 to 70 wt % of surfactant a thermal sequence from lamellar Lα to cubic Ia3d to cubic Pn3m to L2 was found upon heating. The geometrical parameters of the phases such as thickness of the hydrocarbon core of the lamellar phase and length and diameter of the rods forming the cubic structures were calculated for such conditions. In the lamellar Lα phase the surface area per molecule and the thickness of the hydrocarbon core showed little sensitivity to concentration. The thickness of the ethoxy groups was estimated to 1 nm. At high concentrations and temperatures near the cloud point, equilibrium conditions are difficult to reach, leading to the formation of cubic phases with apparently the same structure but different thermal behavior. One is insensitive to temperature changes while the other shrinks upon heating. The transition between the Ia3d and Pn3m cubic phases has the characteristics of a Bonnet transformation

Cubic topology in surfactant and lipid mixtures

Ternary systems of palmitoyl-oleoyl-phosphatidylcholine (POPC) and the non-ionic surfactant C12EO2 (di-ethylene-oxide-mono-dodecyl-ether) in water have been studied with optical microscopy, NMR, DSC and X-rays from ambient temperatures to 45 °C. Below 29 °C the system is in the lamellar liquid crystalline state. Between 30 and 32 °C it transforms into a cubic Ia3d structure which converts into the cubic Pn3m phase at 39 °C. The transitions are fully reversible. An epitaxial relationship between all three phases was found, which is an elegant and convenient way to rearrange molecules from lamellar bilayers to a network of curved surfaces. The la3d (Q230) to Pn3m (Q224) transition occurs without measurable enthalpy change. This, together with the metric relation of 1.60 between the cubic lattice constants is strong evidence for a Bonnet transformation, where the structural changes occur without change in curvature. The potential significance of the cubic phases as intermediate structures for biological processes, e. g. transport across a bilayer or fusion of membranes, are discussed

Modification of Phospholipid Bilayers Induced by Sulfurated Naphthoquinones

New thionaphthoquinones and their hydroxyl derivatives, bearing alkyl side chains that match the phospholipids POPC and POPE, were synthesized in order to investigate their interactions with lipids. It was observed that, in general, these additives destabilize the lipid bilayer and induce less organized structures with higher curvature, in particular the induction of an hexagonal phase on aqueous POPC mixtures. Moreover, cubic phases, not normally observed in the pure lipids when fully hydrated, were detected. Coexistence of lamellar phases was interpreted as a consequence of microsegregation of the components in the mixtures. These results are in line with previous observations on the effect of structurally similar (hydro)quinones in phase behavior of these lipids

Comparative SAXS and DSC study on stratum corneum structural organization in an epidermal cell culture model (ROC):Impact of cultivation time

Cell cultured skin equivalents present an alternative for dermatological in vitro evaluations of drugs and excipients as they provide the advantage of availability, lower variability and higher assay robustness compared to native skin. For penetration/permeation studies, an adequate stratum corneum barrier similar to that of human stratum corneum is, however, a prerequisite. In this study, the stratum corneum lipid organization in an epidermal cell culture model based on rat epidermal keratinocytes (REK organotypic culture, ROC) was investigated by small-angle X-ray scattering (SAXS) in dependence on ROC cultivation time and in comparison to native human and rat stratum cornea. In addition, the thermal phase behavior was studied by differential scanning calorimetry (DSC) and barrier properties were checked by measurements of the permeability of tritiated water. The development of the barrier of ROC SC obtained at different cultivation times (7, 14 and 21 days at the air–liquid interface) was connected with an increase in structural order of the SC lipids in SAXS measurements: Already cultivation for 14 days at the air–liquid interface resulted overall in a competent SC permeability barrier and SC lipid organization. Cultivation for 21 days resulted in further minor changes in the structural organization of ROC SC. The SAXS patterns of ROC SC had overall large similarities with that of human SC and point to the presence of a long periodicity phase with a repeat distance of about 122 Å, e.g. slightly smaller than that determined for human SC in the present study (127 Å). Moreover, SAXS results also indicate the presence of covalently bound ceramides, which are crucial for a proper SC barrier, although the corresponding thermal transitions were not clearly detectable by DSC.Due to the competent SC barrier properties and high structural and organizational similarity to that of native human SC, ROC presents a promising alternative for in vitro studies, particularly as it can be obtained under overall rather straightforward cell culture conditions and thus low assay costs

Cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) by simultaneous measurements of X-ray scattering and dielectric spectroscopy

The isothermal cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) was investigated by simultaneous small and wide angle X-ray scattering and dielectric spectroscopy (DS). By this experimental approach, simultaneously collected information was obtained about the specific changes occurring in both crystalline and amorphous phases during crystallization, namely about the chain ordering through wide angle X-ray scattering, about the lamellar crystals arrangement by means of small angle X-ray scattering, and about the amorphous phase evolution by means of DS. The results indicate that average mobility of the amorphous phase suffers a discontinuous decrease upon passing from the primary to the secondary crystallization regime. We interpret these results assuming that the restriction to the mobility of the amorphous phase occurs mainly in the amorphous regions between the lamellar stacks and not in the amorphous regions within the lamellar stacks. © 2002 Elsevier Science Ltd. All rights reserved.MCYT (grant FPA2001-2139) Spain. The experiments at HASYLAB (Hamburg, Germany) have been funded by the IHP-Contract HPRI-CT-1999-00040 of the European Commission (EC(ERBFMGEDT 950059) and II-00-015 EC).Peer Reviewe