Pluronic P123/DMSO Lyotropic Liquid Crystal for Incorporating Bioactive Substances for Topical Application.

Lyotropic liquid crystals (LLCs) have attracted considerably growing interest in drug delivery applications over the last years. The structure of LLC matrices is complementary to cell membranes and provides an efficient, controlled, and selective release of drugs. In this work, a complex of experimental methods was used to characterize binary LLCs Pluronic P123/DMSO and triple LLC systems Pluronic P123/DMSO/Ibuprofen, which are interesting as transdermal drug delivery systems. Liquid crystalline, thermal, and rheological properties of LLCs were studied. Concentration and temperature areas of the lyomesophase existence were found, and phase transition enthalpies were evaluated. Intermolecular interactions among the components were studied by infrared (IR) spectroscopy. In vitro studies of Ibuprofen (Ibu) release from various LLCs allow differentiation of its release depending on the polymer content. Atomic force microscopy and contact angle methods were used to characterize the surface morphology of the hydrophobic membrane, which was used as a stratum corneum model, and also evaluate the adhesion work of the LLCs. A complex analysis of the results provided by these experimental methods allowed revealing correlations between the phase behavior and rheological characteristics of the LLCs and release kinetics of ibuprofen. The proposed biocompatible systems have considerable potential for a transdermal delivery of bioactive substances.

Concentration-dependent dielectric and electro-optical properties of composites based on nematic liquid crystals and CdS:Mn quantum dots.

Composites in a wide concentration range of 0-0.6 wt% based on a nematic liquid crystal mixture and CdS quantum dots doped with manganese ions (Mn 6%) are presented. The effect of the CdS:Mn quantum dots on the phase diagram and electronic structure of composites was studied using differential scanning calorimetry and fluorescence analysis. Nonmonotonic concentration-dependent changes in the clearing point, which correlate with the fluorescence quenching behavior of the main CdS:Mn peak, were found. Dielectric spectroscopy and electro-optic studies revealed a corresponding increase in the dielectric permittivity anisotropy and birefringence in the 0.2-0.4 wt% range, where thermodynamic changes occur. The initiating factors behind this effect are supposed to be the self-assembly of quantum dots, and the distortion of the orientation order of liquid crystal molecules at a higher mass concentration of quantum dots.

Chitosan/Lactic Acid Systems: Liquid Crystalline Behavior, Rheological Properties, and Riboflavin Release In Vitro.

Chitosan or its derivatives exhibit lyotropic liquid crystalline mesophases under certain conditions due to its semi-rigid structures. This work describes the development of chitosan-based biocompatible systems that include new components: lactic acid and non-ionic surfactants. Polarized optical microscopy studies revealed that these systems are capable of forming gels or lyotropic liquid crystals (LLCs) in a certain range of chitosan and lactic acid concentrations. According to the viscosity studies, the rheological flow of the LLCs can be accurately described by the Casson flow model. The intermolecular interactions of the LLC components were studied by FTIR spectroscopy. According to the FTIR data, hydrogen bonding is supposed to be responsible for the formation of the LLCs. In the studied systems, this LLC complex exists as the [ChitH+·CH3-CH(OH)-COO-] ion pair. The studied gel and LLCs were shown to possess the most prolonged release capabilities for riboflavin among similar binary LLC systems. The supramolecular organization and rheological characteristics of the studied chitosan-based systems were found to affect the release of riboflavin.

Effect of Magnetic and Electric Field on the Orientation of Rare-Earth-Containing Nematics.

We report rare-earth-containing metallomesogens with newly synthesized ligands represented by the ß-diketone 1-(4-(4-propylcyclohexyl)phenyl)octane-1,3-dione (CPDk3-5) and the Lewis base 5,5'-bis(heptadecyl)-2,2'-bipyridine (bpy17-17). The stoichiometry of the complexes is [Ln(CPDk3-5)3bpy17-17], where Ln is a trivalent rare-earth ion (La, Sm, Eu, Gd, Tb, Dy, Ho, Tm, and Yb). Although the ligands themselves do not form any mesophase, the respective metal complexes produce nematic and smectic A phases. The mesogenic rare-earth complexes were characterized by NMR, MS, POM, DSC, X-ray diffraction, magnetic susceptibility measurements, and dielectric spectroscopy. The metal complexes display a remarkably large magnetic anisotropy in the mesophase. These nematic liquid crystals can, therefore, be easily aligned by an external low-threshold magnetic field.

Incorporating a Tetrapeptide into Lyotropic Direct Hexagonal Mesophase.

An approach to incorporate a bioactive hydrophobic substance, C22H32N4O7 tetrapeptide (TP), into the structure of the hexagonal mesophases C12EO10/H2O and C12EO10/La(III)/H2O was proposed. Concentration and temperature ranges of mesophases in the C12EO10/H2O/TP and C12EO10/La(III)/H2O/TP systems were established. The analysis of the X-ray diffraction data revealed a change in the structural characteristics of mesophases in the presence of tetrapeptide. Formation of a denser packing of molecules in the mesophases with TP was detected. Based on the FTIR spectroscopy data, intermolecular changes in the systems were examined. Pulsed-gradient spin-echo NMR self-diffusion experiments were performed to characterize the structure of lyomesophases depending on system composition and temperature. The degree of hydration of water molecules in lyomesophases was analyzed. The data confirmed successful incorporation of tetrapeptide into the structure of lyomesophase and, therefore, the possibility of using hexagonal mesophases for both incapsulation and delivery of biomolecules.

Influence of Eu(III) Complexes Structural Anisotropy on Luminescence of Doped Conjugated Polymer Blends.

Europium(III) complexes that are the anisometric analogues of a well-known Eu(DBM)3Phen (DBM = dibenzoylmethane; Phen = 1,10-phenanthroline) complex were synthesized. Quantum-chemical calculations of the excited states of new Eu(III) complexes and some conjugated polymers showed that poly(N-vinylcarbazole) provides the most efficient energy transfer in polymer films doped with synthesized Eu(III) complexes. These new composite films were prepared, and their luminescence properties were studied. The results of experimental data confirmed theoretical prediction about significant influence introduced in molecular structure long terminal alkyl chains and cyclohexane on the luminescence efficiency of "Ln(III)-polymer" composite. As the result a substantial contribution of complex anisometry to the luminescence efficiency of composite was revealed due to the increase of the complex limit concentration before self-quenching more than twofold.

Influence of structural anisotropy on mesogenity of Eu(III) adducts and optical properties of vitrified films formed on their base.

A new series of europium adducts with the general formula Eu(CPDk3-CnH2n+1)3Phen, where CPDk3-CnH2n+1 denotes ß-diketones and Phen is 1,10-phenanthroline, was synthesized. The obtained mesogenic complexes were heated to the temperatures of the isotropic liquid state and then cooled. The complexes having short CH3 and C2H5 substituents crystallized upon cooling, and the complexes with longer substituents from C3H7 to C6H13 underwent a glass transition with the formation of optically transparent amorphous films. Inside the series the complexes with C7H15 and C8H17 substituents exhibited a unusual smectic C mesomorphism for lanthanidomesogens. On the basis of quantum-chemical simulations and the results of small-angle X-ray scattering the dependence between the anisotropy of Eu(III) complexes with various ligand environments and their supramolecular organization was found. The synthesized Eu(III) complexes in the solid state show intense red photoluminescence upon irradiation by ultraviolet light (λmax - 337 nm).