Cubic and Hexagonal Mesophases for Protein Encapsulation: Structural Effects of Insulin Confinement

Monoolein-based cubic and hexagonal mesophases were investigated as matrices for insulin loading, at low pH, as a function of temperature and in the presence of increasing amounts of oleic acid, as a structural stabilizer for the hexagonal phase. Synchrotron small angle X-ray diffraction, rheological measurements, and attenuated total reflection-Fourier transform infrared spectroscopy were used to study the effects of insulin loading on the lipid mesophases and of the effect of protein confinement in the 2D-and 3D-lipid matrix water channels on its stability and unfolding behavior. We found that insulin encapsulation has only little effects both on the mesophase structures and on the viscoelastic properties of lipid systems, whereas protein confinement affects the response of the secondary structure of insulin to thermal changes in a different manner according to the specific mesophase: in the cubic structure, the unfolding toward an unordered structure is favored, while the prevalence of parallel β-sheets, and nuclei for fibril formation, is observed in hexagonal structures

On the Limits of Validity of the Two-Wave Approximation in the Dynamical Theory of Electromagnetic Scattering by Periodic Dielectric Media

We investigate the accuracy and limits of validity of the two-wave approximation in the dynamical theory of electromagnetic scattering by periodic dielectric media. The errors ensuing from the approximation are estimated by applying the dynamical theory to a scattering problem for which an alternative exact electromagnetic solution is available and comparing results. The conditions for applying the approximate theory and its accuracy are discussed in terms of concepts peculiar to the classical dynamical theory of the scattering of X-rays in crystals, such as the Ewald sphere in the reciprocal space and the resonance error. After introducing the basic equations of the dynamical theory of electromagnetic scattering by three dimensional periodic dielectric media, the theory is applied to the scattering by one-dimensional periodic layered structures where a rigorous analytical solution is available. The analysis of the errors involved in the two-wave approximation indicates that, in the general case, the quality of the approximation cannot be quantified in terms of just the resonance error but it is also strongly affected by the dielectric contrast. Simple formulae are reported yielding a reliable error estimate in many practical cases. an extension of the results to the two and three dimensional case is also provided. Finally, it is suggested that a modification of the boundary conditions which are usually enforced in the dynamical theory when solving the propagation equation could improve its accuracy and extend the limits of validity of the two-wave approximation

Insights into the cybotactic nemaic phase of bent-core mesogens

We present X-ray diffraction evidence for clusters exhibiting a skewed cybotactic supramolecular structure in the nematic phase of the butyloxy-phenyl diester, ODBP-Ph-OC4, a bent core mesogenic diester of the nonlinear diol 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). The temperature dependence of the off-meridional four-spot pattern shows that the tilt angle in the cybotactic clusters changes with temperature. The correlation lengths exhibit no evidence of critical behavior but there is no underlying smectic C phase in ODBP-Ph-OC4. The tilted cybotactic clusters persist throughout the 85 C wide nematic phase, and even remain evident in the supercooled nematic. This inherently biaxial supramolecular structure—clusters of stratified and tilted mesogens—embedded in an otherwise translationally disordered nematic host medium may account for the NMR biaxiality observed in nematic phases of ODBP mesogens

Elliptical Small-Angle X-Ray Scattering Patterns from Aligned Lamellar Arrays

Semicrystalline polymers aligned by drawing into films or fibers produce small-angle X-ray scattering patterns with two or four spots. Some liquid crystalline materials, cybotactic nematics, produce extremely similar patterns when oriented in magnetic fields. A structure of stacked lamellae, tilted for four point patterns, explain the basic features. However, the peak intensity positions of the broadened reflections lie not on a layer line or on the arc of a circle, but very close to an ellipse. Specific structural explanations of this feature have been suggested, but models using an equilibrium distribution of molecular orientations and lamellar tilts can predict elliptical shapes for the reflections. The model parameters are chosen by fitting the entire 2D intensity distribution of the scattering pattern. Assumptions required for modeling make some fitted parameters uncertain, but it is clear that the elliptical form can emerge from a statistical distribution of the properties of the stacks of lamellae, without a directly assignable structural cause

Mesomorphic Behaviour of Some 4-n-Pentanoyl-4'-n-Alkanoyloxy Azobenzenes (PPAPE). A New Series of Liquid-Crystal Compounds

In this paper we present the synthesis and the study of the homologous series {Mathematical expression} whith m=3 and n ranging from zero to sixteen. Transition temperatures, enthalpies and entropies have been determined making use of optical methods, differential scanning calorimetry and X-ray diffraction. Smectic and/or nematic phases have been observed for all the homologues with a complex polymorphism in some cases. A comparison with the series m=0, m=1 and m=2, precedently studied, is also reported

High resolution polarization gratings in liquid crystals

Efficient recording of polarization gratings in dye-doped liquid crystals is reported. By exploiting the effect of light-induced anchoring of the molecular director, it has been possible to write stable holographic gratings with a diffraction efficiency of 8% at a resolution of 1000 lines/mm. The required surface energy density of 0.3 J/cm(2) sets these materials among the most sensitive for optical storage

Dimensional Sensitivity of End-to-End Phase Difference in Ring Terminated Ramsey Cavities

A transmission line analysis is reported of a long Ramsey cavity for a primary Cesium beam frequency standard, terminated at the extremities with two waveguide rings for distributed phase shift minimization. The purpose of this effort is to understand the effect of the rings on end-to-end phase shift. Contributions to the latter from asymmetries in the Ramsey cavity long arms, in the similarity of the rings, and in the two coupling junctions between rings and Ramsey cavity, are separately analyzed as a function of frequency. It is shown that this third asymmetry source may be a cause of phase shift instability because of its linear dependence on frequency. The slope of this sensitivity to operating frequency is reduced by almost an order of magnitude if the rings are designed to be antiresonant instead of resonant