Optically Tunable Diffraction Efficiency in Reflection Grating Written in Photomobile Polymers

In this work, we report the fabrication and optical characterization of a one-dimensional reflection holographic volume phase grating recorded in a recently developed holographic photomobile composite polymer mixture. The reflection grating recorded on the photomobile material was a periodic one-dimensional arrangement of hard polymeric walls and viscous regions. The reflection notch was located in the near-infrared region of the electromagnetic spectrum. The transmission efficiency of the grating was modulated by an external CW laser light source operating at λ = 532 nm. The transmission efficiency increased with the increase in the power of the external laser source, and in the range of the used power values, the phenomenon was completely reversible. At the highest power levels, a 48% increase in the diffraction efficiency was achieved. The increase in the diffraction efficiency was related to the growth of the refractive-index contrast of the grating. In particular, under illumination, the viscous material escaped from the irradiated area. This feature explains the experimentally observed changes in the values of the grating’s refractive index

Synchrotron characterization of hexagonal and cubic lipidic phases loaded with azolate/phosphane gold(I) compounds: a new approach to the uploading of gold(I)-based drugs

none9Gold(I) phosphane compounds have recently attracted a renewed interest as potential new protagonists in cancer therapy. A class of phosphane gold(I) complexes containing azolate ligands has been successfully tested against several cancer cell lines and, in particular, against basal-like breast (BLB) cancer, a form characterized by strongly severe diagnosis and short life lapse after classic chemotherapy. Even though the anticancer activity of gold(I) phosphane compounds is thoroughly ascertained, no study has been devoted to the possibility of their delivery in nanovectors. Herein, nonlamellar lyotropic liquid crystalline lipid nanosystems, a promising class of smart materials, have been used to encapsulate gold(I) azolate/phosphane complexes. In particular, ((triphenylphosphine)-gold(I)-(4,5-dichloroimidazolyl-1H-1yl)) (C-I) and ((triphenylphosphine)-gold(I)-(4,5-dicyanoimidazolyl-1H-1yl)) (C-II) have been encapsulated in three different lipid matrices: monoolein (GMO), phytantriol (PHYT) and dioleoyl-phosphatidylethanolamine (DOPE). An integrated experimental approach involving X-ray diffraction and UV resonant Raman (UVRR) spectroscopy, based on synchrotron light and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, has been employed to establish the effects of drug encapsulation on the structure and phase behavior of the host mesophases. The results indicate that gold(I) complexes C-I and C-II are successfully encapsulated in the three lipid matrices as evidenced by the drug-induced phase transitions or by the changes in the mesophase lattice parameters observed in X-ray diffraction experiments and by the spectral changes occurring in UV resonant Raman spectra upon loading the lipid matrices with C-I and C-II.openPaola Astolfi, Michela Pisani, Elisabetta Giorgini, Barbara Rossi, Alessandro Damin, Francesco Vita, Oriano Francescangeli, Lorenzo Luciani, Rossana GalassiAstolfi, Paola; Pisani, Michela; Giorgini, Elisabetta; Rossi, Barbara; Damin, Alessandro; Vita, Francesco; Francescangeli, Oriano; Luciani, Lorenzo; Galassi, Rossan

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

Layered ω-Substituted Alkylpyridinium Salts with Inorganic Anions: Effects of H-Bonding Patterns on the Layer Thickness

The synthesis and characterization of a carboxy-substituted alkylpyridinium cation with inorganic counterions is reported. Structural evidence points to the formation of a layered structure with mutual recognition of cations through strong O-(HO)-O-... bonding when halides X- (X = Cl, Br) are chosen. Variation of the anionic component to complex metal ions of [MX4](2-) type affords a different layer motif with weaker cation-anion O-(HX)-X-...-M interactions and interdigitation of functionalized alkyl chains

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

Polar order in bent-core nematics: An overview

The possible existence of a ferroelectric nematic phase has been challenging liquid crystal scientists since it was first envisaged about 30 years ago. At present, an undisputable proof of proper ferroelectricity in low-molecular weight thermotropic nematics is still missing. However, over the last decade several groups have reported the observation of a ferroelectric-like switching behavior in the nematic phase of a number of bent-core mesogens. This effect is generally ascribed to polar clusters of molecules, known as cybotactic groups, permeating the nematic phase. In the unperturbed state the cluster dipoles are randomly oriented, so that the phase is macroscopically uniaxial and apolar; however, an external field exceeding a threshold is able to align the cluster dipoles, inducing the transition to a switchable polar and biaxial state. Even though this behavior clearly differs from that expected in a proper ferroelectric liquid crystal, it still deserves considerable interest for its potential implications from both a fundamental and a technological point of view. Here we review the studies devoted to this extraordinary effect, both experiments and simulations, and discuss the open questions that still remain unanswered

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