Bile salts form lyotropic liquid crystals

Condensed Supramolecular Helices: The Twisted Sisters of DNA

Condensation of DNA helices into hexagonally packed bundles and toroids represents an intriguing example of functional organization of biological macromolecules at the nanoscale. The condensation models are based on the unique polyelectrolyte features of DNA, however here we could reproduce a DNA-like condensation with supramolecular helices of small chiral molecules, thereby demonstrating that it is a more general phenomenon. We show that the bile salt sodium deoxycholate can form supramolecular helices upon interaction with oppositely charged polyelectrolytes of homopolymer or block copolymers. At higher order, a controlled hexagonal packing of the helices into DNA-like bundles and toroids could be accomplished. The results disclose unknown similarities between covalent and supramolecular non-covalent helical polyelectrolytes, which inspire visionary ideas of constructing supramolecular versions of biological macromolecules. As drug nanocarriers the polymer-bile salt superstructures would get advantage of a complex chirality at molecular and supramolecular levels, whose effect on the nanocarrier assisted drug efficiency is a still unexplored fascinating issue.

Novel transdermal bioadhesive surfactant-based system for release and solubility improvement of antimalarial drugs artemether-lumefantrine

Artemether (ART) and lumefantrine (LUM) are the gold standard antimalarial drugs used for the treatment of malaria in children and pregnant women. Typically, ART and LUM are delivered orally in the form of a combined tablet, however, the appropriateness of this route of administration for these drugs is questionable due to the poor absorption and therefore bioavailability observed unless administered alongside lipid-rich foods. Transdermal drug delivery in the form of a patch-type system has been identified as a viable alternative to the conventional tablet-based therapy. A novel, surfactant-based ART-LUM formulation (S3AL), developed for transdermal delivery, may eliminate the shortcomings associated with oral delivery; namely poor drug absorption which is caused by the inherently low solubility of ART and LUM. Moreover, by successfully delivering these antimalarials transdermally, first-pass metabolism will be avoided leading to enhanced drug bioavailability in both cases. The S3AL formulation contained ART and LUM at equal concentrations (2.5% w/w of each) as well as Procetyl® AWS (30% w/w), oleic acid (10% w/w), 1-methyl-2-pyrrolidone (10% w/w), and water (45% w/w). The addition of LUM to the formulation changed the system from a striae structure to a dark field structure when visualized by a polarized light microscope. Additionally, this system possessed higher viscosity and superior skin bioadhesion, as evidenced by mechanical characterization, when compared to a similar formulation containing ART alone. S3AL was also proven to be biocompatible to human keratinocyte cells. Finally,in vitrostudies demonstrated the propensity of S3AL for successful delivery via the transdermal route, with 2279 ± 295 µg cm^-2of ART and 94 ± 13 µg cm^-2of LUM having permeated across dermatomed porcine skin after 24 h, highlighting its potential as a new candidate for the treatment of malaria.

Self-Assembly of a Bile Acid Dimer in Aqueous Solutions: From Nanofibers to Nematic Hydrogels

A mixture of a cholic acid dimer with a secondary amine group and formic acid at a molar ratio of 1/1 is regarded as an organic salt, and it self-assembles in aqueous solutions to form monodisperse nanofibers. The nanofibers are separated at low concentrations of the mixture but entangle with each other at high concentrations to form well-dispersed and randomly arranged 3D fibrous networks. Above the minimum gelation concentration of the dimer, the fibrous network is strong enough to gelate the aqueous solutions to form a hydrogel. Hydrogels obtained from the dimer salt at a lower concentration are isotropic and show extinction between crossed polarizers in the polarizing microscope, whereas they become anisotropic (i.e., nematic hydrogels) upon increasing the dimer salt concentration or under physical stirring. The parallel arrangement of nanofibers from randomly directed fibrous networks may be responsible for the formation of such nematic hydrogels.

On the stability of lithocholate derivative supramolecular tubules

Solubility and calorimetry data provide the description of a phase map for metastable supramolecular nanotubes of biological origin.

Supramolecular hydrogelation with bile acid derivatives: structures, properties and applications

Bile acid derivatives can form molecular hydrogels that may be useful for drug delivery, tissue engineering and nanotemplating.

Unique lamellar lyotropic liquid crystal phases of nonionic phytosterol ethoxylates in glycerol

As one type of biocompatible surfactant, phytosterol ethoxylates (BPS-n, n is the oxyethylene chain length) have attracted more and more attention for their characteristic molecular structure.

Formation and dynamics of "waterproof" photoluminescent complexes of rare earth ions in crowded environment

Understanding behavior of rare-earth ions (REI) in crowded environments is crucial for several nano- and bio-technological applications. Evolution of REI photoluminescence (PL) in small compartments inside a silica hydrogel, mimic to a soft matter bio-environment, has been studied and explained within a solvation model. The model uncovered the origin of high PL efficiency to be the formation of REI complexes, surrounded by bile salt (DOC) molecules. Comparative study of these REI-DOC complexes in bulk water solution and those enclosed inside the hydrogel revealed a strong correlation between an up to 5×-longer lifetime of REIs and appearance of the DOC ordered phase, further confirmed by dynamics of REI solvation shells, REI diffusion experiments and morphological characterization of microstructure of the hydrogel.

Controlled release of folic acid through liquid-crystalline folate nanoparticles

The present study explores folate nanoparticles as nano-carriers for controlled drug delivery. Cross-linked nanoparticles of liquid crystalline folates are composed of ordered stacks. This paper shows that the folate nanoparticles can be made with less than 5% loss in folate ions. In addition, this study shows that folate nanoparticles can disintegrate in a controlled fashion resulting in controlled release of the folate ions. Release can be controlled by the size of nanoparticles, the extent of cross-linking and the choice of cross-linking cation. The effect of different factors like agitation, pH, and temperature on folate release was also studied. Studies were also carried out to show the effect of release medium and role of ions in the release medium on disruption of folate assembly.

Sustained release of methotrexate through liquid-crystalline folate nanoparticles

To make chemotherapy more effective, sustained release of the drug is desirable. By controlling the release rates, constant therapeutic levels can be achieved which can avoid re-administration of drug. This helps to combat tumors more effectively with minimal side effects. The present study reports the control release of methotrexate through liquid-crystalline folate nanoparticles. These nanoparticles are composed of highly ordered folate self-assembly which encapsulate methotrexate molecules. These drug molecules can be released in a controlled manner by disrupting this assembly in the environment of monovalent cations. The ordered structure of folate nanoparticles offers low drug losses of about 4-5%, which is significant in itself. This study reports the size-control method of forming methotrexate encapsulated folate nanoparticles as well as the release of methotrexate through these nanoparticles. It has been demonstrated that methotrexate release rates can be controlled by controlling the size of the nanoparticles, cross-linking cation and cross-linking concentration. The effect of different factors like drug loading, release medium, and pH of the medium on methotrexate release rates was also studied.

Formation and properties of gels based on lipo-plexes

Aqueous systems containing sodium taurodeoxycholate and, eventually, soybean lecithin were investigated. Depending on the relative amounts of two such species, molecular, micellar, vesicular, liquid crystalline, and solid phases were formed. In the presence of bovine serum albumin, micellar and vesicular systems form lipo-plexes. The latter self-organize into gels, depending on composition and thermal treatments. According to scanning electron microscopy, vesicle-based gels obtained from lipo-plexes form sponge-like entities, whereas micelle-based ones self-arrange in fibrous organizations. Gels are characterized by a significant viscoelasticity in a wide temperature and frequency range. Rheological data were interpreted by assuming strict relations between the system response and the self-organization of the lipo-plexes into gels. It was inferred that differences in the gel properties depend on the different self-assembly modes of the aggregates formed by the mentioned lipo-plexes. Use of the above systems in biomedical applications, mostly in the preparation of matrices requiring the use of smart and biocompatible gels, is suggested.

Supra-molecular association and polymorphic behaviour in systems containing bile acid salts

A wide number of supra-molecular association modes are observed in mixtures containing water and bile salts, BS, (with, eventually, other components). Molecular or micellar solutions transform into hydrated solids, fibres, lyotropic liquid crystals and/or gels by raising the concentration, the temperature, adding electrolytes, surfactants, lipids and proteins. Amorphous or ordered phases may be formed accordingly. The forces responsible for this very rich polymorphism presumably arise from the unusual combination of electrostatic, hydrophobic and hydrogen-bond contributions to the system stability, with subsequent control of the supra-molecular organisation modes. The stabilising effect due to hydrogen bonds does not occur in almost all surfactants or lipids and is peculiar to bile acids and salts. Some supra-molecular organisation modes, supposed to be related to malfunctions and dis-metabolic diseases in vivo, are briefly reported and discussed.

Polymorphic Behavior in Protein−Surfactant Mixtures: The Water−Bovine Serum Albumin−Sodium Taurodeoxycholate System

Mixtures containing water, bovine serum albumin (BSA), and sodium taurodeoxycholate (NaTDC), a component of the bile in mammals, have been investigated in a wide range of composition and pH. Depending on the concentration of both solutes and the pH, solutions, precipitates, and gels are formed. Under spontaneous pH conditions, the transport properties in dilute solutions indicate the occurrence of significant interactions between BSA and the surfactant. Conversely, acidic media favor the formation of nonsoluble protein-surfactant complexes, with subsequent precipitation. The nucleation kinetics of the protein-surfactant complexes in solid form and the related precipitation processes can be slow or fast, depending on the overall solute content and the mole ratio. At high concentrations, a gel, extending on both sides of the charge neutralization line, and two-phase regions are observed. Gels shrink in open air and swell in the presence of excess water. Depending on concentration and temperature, the gels transform from an essentially liquidlike behavior to that peculiar to true gels (when G' > or = G''). The thermal gelation threshold, the temperature above which G' > or = G'', depends on BSA and NaTDC content and is concomitant to moderate heat effects, inferred by differential scanning calorimetry (DSC). The above data also indicate that the protein thermal denaturation in the gel is shifted to higher temperatures compared to water. Such a stabilizing effect is presumably related to the occurrence of both electrostatic and hydrophobic interactions with NaTDC. Water self-diffusion in the gels is slightly slower than that in the bulk and poorly sensitive to composition: it is about 65% the value of neat H2O in a wide concentration range, irrespective of the BSA, or NaTDC, concentration. A peculiar behavior is also observed in 23Na longitudinal and transverse relaxation rates. The T1 and T2 values, measured at 105.75 MHz on BSA-NaTDC gels, indicate that the motions determining the NMR relaxation of the sodium ions in the hydration layer of the protein-surfactant aggregates are not slow, having frequencies comparable with the Larmor one. The above properties, especially the rheological and the spectroscopic ones, are important for understanding the behavior of gels based on protein-surfactant mixtures.