New (1R,4R)-2-arylidene-p-menthan-3-ones with a bridging ester group in the arylidene fragment. Synthesis and behavior in liquid-crystalline systems

(1R,4R)-2-(4-Hydroxybenzylidene)- and (1R,4R)-2-(4′-hydroxybiphenyl- 4-yl)methylene-p-menthan-3-ones were synthesized by condensation of (-)-menthone with O-tetrahydropyran-2-yl derivatives of 4-hydroxybenzaldehyde and 4′-hydroxy-4-formylbiphenyl, respectively, in a DMSO - base medium followed by the removal of the protective group. The reactions of these hydroxy derivatives with 4-alkylbenzoic, 4-alkyloxybenzoic, trans-4-alkylcyclohexane-4- carboxylic, and 4′-alkylbiphenyl-4-carboxylic acids afforded three series of new chiral esters. Compounds containing the arylidene moiety with three benzene rings were found to exhibit liquid-crystalline properties. The characteristic features of these compounds are discussed based on the results of studies by polarizing microscopy, differential scanning calorimetry, and small-angle X-ray scattering. It was found that the mesomorphic compounds under study can form a smectic A mesophase, twist grain boundary mesophases (TGBA), and blue phases in a wide temperature range. Upon dissolution of certain of chiral compounds in 4′-cyano-4-pentylbiphenyl, a rather high twisting power and the thermal stabilizing effect on mesophases were observed.

Evaluation of Preservative Effectiveness of Liquid Crystalline Systems with Retynil Palmitate by the Challenge Test and D-value

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evaluation of preservative effectiveness of liquid crystalline systems with retinyl palmitate by the challenge test and D-value

The objective of this work was to evaluate the preservative effectiveness of liquid crystalline systems containing retynil palmitate (RP) by the challenge test (CT) and D-value. A system was developed containing water, silicon glycol copolymer, and polyether functional siloxane with 1% RP added. The analyses were carried out by methods in the U.S. Pharmacopeia (USP 31, 2008) using the microorganisms Escherichia coli, Staphylococcus aureus,Pseudomonas aeruginosa, Candida albicans, and Aspergillus niger. The CT showed that after 7 days, all microorganisms were eliminated except A. niger, which maintained viability for at least 28 days after inoculation. Moreover, the microorganisms E. coli, P. aeruginosa, S. aureus, C. albicans and A. niger presented different growth behaviors, evidenced by differences among the D-values calculated. It was concluded that the CT and D-value were efficient methods for evaluation of the preservative property of these formulations.

Modeling and simulations of nanoparticles in liquid crystalline systems

The aim of this work is to investigate, using extensive Monte Carlo computer simulations, composite materials consisting of liquid crystals doped with nanoparticles. These systems are currently of great interest as they offer the possibility of tuning the properties of liquid crystals used in displays and other devices as well as providing a way of obtaining regularly organized systems of nanoparticles exploiting the molecular organization of the liquid crystal medium. Surprisingly enough, there is however a lack of fundamental knowledge on the properties and phase behavior of these hybrid materials, making the route to their application an essentially empirical one. Here we wish to contribute to the much needed rationalization of these systems studying some basic effects induced by different nanoparticles on a liquid crystal host. We investigate in particular the effects of nanoparticle shape, size and polarity as well as of their affinity to the liquid crystal solvent on the stability of the system, monitoring phase transitions, order and molecular organizations. To do this we have proposed a coarse grained approach where nanoparticles are modelled as a suitably shaped (spherical, rod and disk like) collection of spherical Lennard-Jones beads, while the mesogens are represented with Gay-Berne particles. We find that the addition of apolar nanoparticles of different shape typically lowers the nematic–isotropic transition of a non-polar nematic, with the destabilization being greater for spherical nanoparticles. For polar mesogens we have studied the effect of solvent affinity of the nanoparticles showing that aggregation takes places for low solvation values. Interestingly, if the nanoparticles are polar the aggregates contribute to stabilizing the system, compensating the shape effect. We thus find the overall effects on stability to be a delicate balance of often contrasting contributions pointing to the relevance of simulations studies for understanding these complex systems.

Structural characterization and in vivo evaluation of retinyl palmitate in non-ionic lamellar liquid crystalline system

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A New Class Of Photo-Cross-Linkable Side-Chain Liquid Crystalline Polymers Containing Bis(Benzylidene)Cyclohexanone Units

This paper reports a new class of photo-cross-linkable side chain liquid crystalline polymers (PSCLCPs) based on the bis(benzylidene)cyclohexanone unit, which functions as both a mesogen and a photoactive center. Polymers with the bis(benzylidene)cyclohexanone unit and varying spacer length have been synthesized. Copolymers of bis(benzylidene)cyclohexanone containing monomer and cholesterol benzoate containing monomer with different compositions have also been prepared. All these polymers have been structurally characterized by spectroscopic techniques. Thermal transitions were studied by DSC, and mesophases were identified by polarized light optical microscopy (POM). The intermediate compounds OH-x, the monomers SCLCM-x, and the corresponding polymers PSCLCP-x, which are essentially based on bis(benzylidene)cyclohexanone, all show a nematic mesophase. Transition temperatures were observed to decrease with increasing spacer length. The copolymers with varying compositions exhibit a cholesteric mesophase, and the transition temperatures increase with the cholesteric benzoate units in the copolymer. Photolysis of the low molecular weight liquid crystalline bis(benzylidene)-cyclohexanone compound reveals that there are two kinds of photoreactions in these systems: the EZ photoisomerization and 2 pi + 2 pi addition. The EZ photoisomerization in the LC phase disrupts the parallel stacking of the mesogens, resulting in the transition from the LC phase to the isotropic phase. The photoreaction involving the 2 pi + 2 pi addition of the bis(benzylidene)cyclohexanone units in the polymer results in the cross-linking of the chains. The liquid crystalline induced circular dichroism (LCICD) studies of the cholesterol benzoate copolymers revealed that the cholesteric supramolecular order remains even after the photo-cross-linking.

Effect of Polymer Grafting on the Bilayer Gel to Liquid-Crystalline Transition

Grafted polymers oil the surface of lipid membranes have potential applications in liposome-based drug delivery and Supported membrane systems. The effect of polymer grafting on the phase behavior of bilayers made up of single-tail lipids is investigated using dissipative particle dynamics. The bilayer is maintained in a tensionless state using a barostat. Simulations are carried Out by varying the grafting fraction, G(f), defined as the ratio of the number of polymer molecules to the number of lipid molecules, and the length of the lipid tails. At low G(f), the bilayer shows I sharp transition from the gel (L-beta) to the liquid-crystalline (L-alpha) phase. This main melting transition temperature is lowered as G(f) is increased, and above a critical value of G(f), the interdigitated L-beta I phase is observed prior to the main transition. The temperature range over which the intermediate phases are observed is a function of the lipid tail length and G(f). At higher grafting fractions, the presence of the L-beta I, phase is attributed to the increase in the area per head group due to the lateral pressure exerted by the polymer brush. The areal expansion and decrease in the melting temperatures as a function of G(f) were found to follow the scalings predicted by the self-consistent mean field theories for grafted polymer membranes. Our study shows that the grafted polymer density can be used to effectively control the temperature range and occurrence of a given bilayer phase.

Synthesis and characterization of photo-crosslinkable main-chain liquid-crystalline polymers containing bis(benzylidene)cycloalkanone units

A series of new photo-crosslinkable main-chain liquid-crystalline polymers containing bis(benzylidene)cycloalkanone units have been studied. These units in the polymers function as mesogens as well as photoactive centres. Polyesters with three different bis(4-hydroxybenzylidene)cycloalkanones corresponding to three cycloalkanones, namely cyclopentanone, cyclohexanone and cycloheptanone, have been prepared. Three dicarboxylic acids with ether linkages, which were derived from oligoethylene oxides, namely triethylene glycol, tetraethylene glycol and pentaethylene glycol, have been used as spacers in these polymers. Polymerization was carried out by both solution and interfacial polycondensation; the latter method gave high-molecular-weight polymers. Structural characterizations were done by ultra-violet, infra-red and H-1 nuclear magnetic resonance spectroscopy. Liquid-crystalline properties were studied by differential scanning calorimetry and polarized-light optical microscopy. These polymers show a nematic mesophase. Liquid-crystalline transition temperatures were correlated with polymer structure. The decrease in transition temperature with increase in cycloalkanone ring size was explained in terms of the change in geometrical anisotropy of bis(benzylidene)cycloalkanone units. MNDO (modified neglect of differential overlap) calculations were performed on the model compounds, bis(4-acetyloxybenzylidene)cycloalkanone to elucidate the geometrical variation of the mesogenic units with cycloalkanone ring size. Studies of photolysis reveal the two kinds of photoreactions that proceed in these polymer systems, namely photoisomerization and photo-crosslinking. The former reaction disrupts the parallel stacking of the chromophores and is reflected as an increase in the ultra-violet spectral intensity. The favourability of these two reactions depends on the mobility of the polymer chains. When the photolysis was done below T-g, photo-crosslinking dominates over photoisomerization. Above T-g, photoisomerization is followed by photo-crosslinking. The photosensitivity of the polymers decreases with increase in size of the cycloalkanone ring.

New 4-(2-(4-alkoxyphenyl)-6-methoxypyridin-4-yl) benzonitriles: synthesis, liquid crystalline behavior and photo physical properties

A new series of luminescent 4-(2-(4-alkoxyphenyl)-6-methoxypyridin-4-yl) benzonitriles containing three ring systems, viz. methoxy pyridine, benzonitrile and alkoxy benzene with variable alkoxy chain length, with bent-core structures were synthesized as potential mesogens and characterized by spectral techniques. Their liquid crystalline behavior was investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and variable temperature powder X-ray diffraction (PXRD) measurements. The study reveals that compounds with shorter chain lengths i.e. m = 4] exclusively exhibit the nematic phase while compounds with longer chain lengths i.e. m = 6-14 (only even)] show predominantly the orthorhombic columnar phase. Single crystal X-ray analysis of 4-(2-(4-butyloxy/octyloxyphenyl)-6-methoxypyridin-4-yl) benzonitriles reveals that they possess slightly non-planar unsymmetrical bent structures and their molecular packing consists of nonconventional H-bond interactions; it also explains the observed liquid crystalline phase. An optical study indicates that the title compounds are good blue emitting materials showing absorption and emission bands in the range 335-345 nm and 415-460 nm, respectively. An electrochemical study of 4-(2-(4-octyloxyphenyl)-6-methoxypyridin-4-yl) benzonitrile shows a band gap of 1.89 eV with HOMO and LUMO energy levels of -5.06 and -3.17 eV, respectively. Also, density functional theory (DFT) calculations confirm its optimized geometry, electronic absorption and frontier molecular orbital distributions.

Electric-field-induced molecular alignment of side-chain liquid-crystalline polyacetylenes containing biphenyl mesogens

Electric-field-induced molecular alignments of side-chain liquid-crystalline polyacetylenes [-{HC=C[(CH2)(m)OCO-biph-OC7H15]}-, where biph is 4,4'-biphenylyl and m is 3 (PA3EO7) or 9 (PA9EO7)] were studied with X-ray diffraction and polarized optical microscopy. An orientation as high as 0.84 was obtained for PA9EO7. Furthermore, the molecular orientation of]PA9EO7 was achieved within a temperature range between the isotropic-to-smectic A transition temperature and 115 degreesC, and this suggested that the orientational packing was affected by the thermal fluctuation of the isotropic liquid and the mobility of the mesogenic moieties. The maximum achievable orientation for PA9EO7 was much greater than that for PA3EO7. This was the first time that the electric-field-induced molecular orientation of a side-chain liquid-crystalline polymer with a stiff backbone was studied.

Rheological properties in blends of poly(aryl ether ether ketone) and liquid crystalline poly(aryl ether ketone)

Rheological properties of the blends of poly(aryl ether ether ketone) (PEEK) with liquid crystalline poly(aryl ether ketone) containing substituted 3-trifluoro-methylbenzene side group (F-PAEK), prepared by solution precipitation, have been investigated by rheometer. Dynamic rheological behaviors of the blends under the oscillatory shear mode are strongly dependent on blend composition. For PEEK-rich blends, the systems show flow curves similar to those of the pure PEEK, i.e., dynamic storage modulus G' is larger than dynamic loss modulus G", showing the feature of elastic fluid. For F-PAEK-rich systems, the rheological behavior of the blends has a resemblance to pure F-PAEK, i.e., G" is greater than G', showing the characteristic of viscous fluid. When the PEEK content is in the range of 50-70%, the blends exhibit an unusual rheological behavior, which is the result of phase inversion between the two components. Moreover, as a whole, the complex viscosity values of the blends are between those of two pure polymers and decrease with increasing F-PAEK content. However, at 50% weight fraction of PEEK, the viscosity-composition curves exhibit a local maximum, which may be mainly attributed to the phase separation of two components at such a composition.

Shear induced molecular alignments of a side-chain liquid crystalline polyacetylene containing biphenyl mesogens

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4'-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity.

High order liquid crystalline structure of poly(11-{[(4 '-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne)

Liquid crystalline properties of a mesomorphic polyacetylene {-[HC=C(CH2 )(9)OOC-Biph-OC7H15](n)- (PA9EO7), Biph=4-4'-biphenylyl} are investigated by X-ray diffraction, polarizing optical microscope, and transmission electron microscope. Polyacetylene PA9EO7 from solution adopts a sandwich structure, which is a high order smectic phase. The biphenylyl pendants pack in a hexagonal fashion and the distance between two appendages is 4.51 Angstrom. The heptyloxy tails on one polymer backbone overlap with those on the neighboring chain. The nonyl spacer and the heptyloxy tail exhibit a hexagonal packing arrangement with intermolecular distance of 3.24 Angstrom.

Theranostic applications of fluorescent liquid crystalline nanoparticles

Lipid liquid crystalline nanoparticles can find application as nanocarriers in several fields of the daily life but, very likely, the pharmaceutical arena is the most relevant. Indeed, several problems encountered in drugs administration (e.g. critical sideeffects from antitumor drugs) require alternative, less invasive, but simultaneously efficient therapeutic routes to be explored. Novel fields of personalized nanomedicine are developing in this direction. One of the most interesting is theranostic, which calls for the design of platforms capable of combining therapeutic and diagnostic functionalities. In this optic, we explored the potential of monoolein-based cubosomes and hexosomes as nanocarriers for theranostic purposes. Our work focussed on the design of lipid nanoparticles able to deliver antineoplastic drugs and imaging probes for fluorescent optical in vitro and in vivo imaging. We developed cubosome formulations loaded with antineoplastic drugs and useful for the fluorescence imaging of cells. Such formulations were also actively targeted to cancer cells and coupled with a NIR-emitting fluorophore, which was the promise for in vivo applications. We also investigated hexosomes with encouraging results encapsulating in their lipid matrix a BODIPY derivative with solvatochromic properties, helpful for the understanding of the dye localization. Importantly, we reported (manuscript submitted) the first proof-of-principle for in vivo fluorescence optical imaging application using monoolein-based cubosomes in a healthy mouse animal model. Finally, since relatively little is known about the interaction of cubosomes with biological systems, their effects on lipid droplets, mitochondria and lipid profile of HeLa cells were deeply studied. This thesis is divided in two main parts. The introduction section reports on the essential background of the research field, and it is followed by the publications (published or submitted) resulting from these three years of work.

A rheological and SAXS study of the lamellar order in a side-on liquid crystalline block copolymer

We study the structure and shear flow behavior of a side-on liquid crystalline triblock copolymer, named PBA-b-PA444-b-PBA (PBA is poly(butyl acrylate) and PA444 is a poly(acrylate) with a nematic liquid crystal side-on mesogen), in the self-assembled lamellar phase and in the disordered phase. Simultaneous oscillatory shear and small-angle X-ray scattering experiments show that shearing PBA-b-PA444-b-PBA at high frequency and strain amplitudes leads to the alignment of the lamellae with normals perpendicular to the shear direction and to the velocity gradient direction, i.e., in the perpendicular orientation. The order-to-disorder transition temperature (T-ODT) is independent of the applied strain, in contrast to results reported in the literature for coil-coil diblock copolymers, which show an increase in T-ODT with shear rate. It is possible that in our system, T-ODT does not depend on the applied strain because the fluctuations are weaker than those present in coil-coil diblock copolymer systems.