Mafalda Rodrigues

Gemini Imidazolium Amphiphiles for the Synthesis, Stabilization, and Drug Delivery from Gold Nanoparticles

Gold nanoparticles (AuNPs) are considered useful vehicles for medical therapy and diagnosis. Despite the progress made in this field, there is need to find direct, reliable, and versatile synthetic procedures for their preparation as well as new multifunctional coating agents. In this sense, we have explored the use of imidazolium amphiphiles to prepare new AuNPs designed for anion recognition and transport. Thus, in this work we describe (a) the synthesis, by a phase transfer method, of new gold nanoparticles using gemini-type surfactants as ligands based on imidazolium salts, those ligands acting as transfer agents into organic media and also as nanoparticle stabilizers, (b) the examination of their stability in solution, (c) the chemical and physical characterization of the nanoparticles, using a variety of techniques, including UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), (d) toxicity data concerning both the imidazolium ligands and the imidazolium coated nanoparticles, (e) the assessment of their molecular recognition ability toward molecules of biological interest, such as anions and carboxylate containing model drugs, such as ibuprofen, (f) the study of their toxicity and those of their coating ligands, as well as their ability for cell internalization, and (g) the study of their ability for delivering anionic pharmaceuticals. The structurally governed triple role of those new gemini-type surfactants is responsible for the preparation, remarkable stability, and delivery properties of these functional AuNPs.

Supramolecular gels based on a gemini imidazolium amphiphile as molecular material for drug delivery

A novel physical gel was obtained using a gemini imidazolium-based amphiphilic molecule dissolved in ethanol-water mixtures. The structure of the gel is comprised of intertwining nanofibres with widths of approximately 80 nm. The ethanol/water ratio has an important influence on the gelation process: the gelator is sparingly soluble in water and soluble in ethanol. The gelator is capable of incorporating anionic drugs in its fibrillar network easily; sodium ibuprofenate, indomethacin and the sodium salt of methotrexate were used as model drugs that were incorporated into the quickly forming gels. The characterization of these composite xerogels was made by different microscopy techniques as well as X-ray powder diffraction. The ability of the amphiphile to form a gel is largely maintained in the presence of the different model drugs and the overall morphology of the gels (that present a fibre like structure in all cases with intertwined ribbons) is very similar. Furthermore the in vitro release of the drugs from the gel and the in vivo anti-inflammatory efficacy was studied. The overall results show better release profiles and anti-inflammatory efficacy for indomethacin, and prove the promise of this molecular gel in controlled drug release, in the present case dermatological application.

Water-soluble gold nanoparticles based on imidazolium gemini amphiphiles incorporating piroxicam

Water soluble gold nanoparticles were synthesized in a single step using a double layer of a gemini imidazolium-based amphiphile as both reagent and stabilizer. The synthetic strategy exploits the amphiphilic nature of the ligand, and different ratios of ligand to Au(III) precursor were tested in order to favour the formation of amphiphile bilayer-coated nanoparticles, as indicated by their solubility and the thermogravimetric analysis, which proved the gold/organic ratio. The approximately 10 nm nanoparticles display cytotoxicity on Caco-2 cells similar to gold nanomaterials coated with other cationic surfactants, mainly because of their bilayer coating. Instead, genotoxicity was proven to be low, and the gold nanoparticles showed cell internalization being able to leave endosomes and without entering the nuclei. The incorporation of piroxicam, a poorly water soluble drug that has anti-inflammatory and antitumoral activity, was achieved thanks to anion binding by the amphiphile. Subsequently in vitro release of piroxicam from these nanoparticles was demonstrated, indicating their potential in combined chemotherapy.

Macrocyclic imidazolium-based amphiphiles for the synthesis of gold nanoparticles and delivery of anionic drugs

In the present work, we have explored the use of amphiphilic bis-imidazolium based macrocycles and an open chain analog for the successful synthesis of gold nanoparticles (AuNPs). The macrocyclic ligands incorporate hydrophobic chains of different lengths, and the newly synthesized ligands were further used for the synthesis of AuNPs in a biphasic system. The successfully synthesized AuNPs were thoroughly characterized. The sizes of the AuNPs were ca. 8 nm, using macrocyclic ligands bearing two 10 carbon atoms alkyl chains, ca. 5 nm in the case of macrocyclic ligands with two 18 carbon atoms alkyl chains, and ca. 7 nm for the open chain ligand with two 18 carbon atoms alkyl chains. Their possible application as vehicles to load and release anionic drugs (such as sodium ibuprofenate) was also assessed and compared with previously described open chain analogs. In this case, it was observed that the AuNPs had high efficiency in extracting sodium ibuprofenate from an aqueous solution. The application as a drug delivery vehicle was confirmed by in vitro release experiments at different pH values.

Novel nanostructured supramolecular hydrogels for the topical delivery of anionic drugs

A bis-imidazolium-based amphiphilic molecule was used to form novel supramolecular gels in ethanol-water mixtures. The proportion of solvents, the concentration of gellant and the temperature are factors that strongly influence the gelling process. The physical gels that are formed comprise entangled fibers of around 100nm in diameter, able to incorporate anionic drugs, whose morphology varies depending on the drug they incorporate. These hydrogels are soft and therefore optimum for skin application. They show good stability when compared to previously reported gels. Suitable drug release and skin permeation profiles were obtained, and, moreover, they seem to promote the retention of the drug inside the skin. Finally, effective in vivo anti-inflammatory activity was observed, especially with the indomethacin-incorporated gel, which indicates that these supramolecular hydrogels are a good option for the delivery of poor water soluble drugs for the treatment of acute inflammation or other skin diseases.

Nanostructured materials for photodynamic therapy: synthesis, characterization and in vitro activity

Three nanostructured vehicles are proposed as potential carriers for photosensitizers to be used in photodynamic therapy: spherical nanoparticles, hexahedral microparticles and cylindrical magnetic nanorods. A comparative study of their photodynamic properties was performed, and the influence of their size and the amount of loaded porphyrin was considered to discuss their effects in the observed photodynamic activity. All the vehicles have a gold surface, allowing functionalization with a disulfide-containing porphyrin as the photosensitizer, as well as with a PEG-containing thiol to improve their biocompatibility and water solubility. The activity of the porphyrin loaded in each vehicle was assessed through in vitro photocytotoxicity studies using HeLa cells. A synergic effect for the porphyrin toxicity was observed in all of the vehicles. The zinc-containing porphyrin showed better production of singlet oxygen, and proved more photocytotoxic both in solution and loaded in any of the vehicles. The magnetism of the nanorods allows targeting with a magnetic field, but causes their aggregation, hampering the porphyrins activity. Microparticles showed lower cell internalization but their bigger size allowed a high porphyrin loading, which translated into high photocytotoxicity. The highest cell internalization and photocytotoxicity was observed for the porphyrin-loaded nanoparticles, suggesting that a smaller size is favored in cell uptake.

Au( i ) N-heterocyclic carbenes from bis-imidazolium amphiphiles: synthesis, cytotoxicity and incorporation onto gold nanoparticles

A gold(I) N-heterocyclic carbene 4 from a bis-imidazolium-amphiphile was synthesized and characterized. The cytotoxicity against HT-29 colon carcinoma and MDA-MB-231 breast adenocarcinoma cells was assessed for the NHC complex 4, the imidazolium salt precursor 2, and its methyl analogue 3, indicating that compounds 2–4 are promising cytotoxic agents. Furthermore, the ability of these compounds to be associated with gold nanoparticles was also explored, in order to develop an anticancer drug delivery system. The free ligands displayed more activity when compared with the ligands immobilized on the gold nanoparticles. The synthesized gold particles incorporating the bis-imidazolium salts either 2 or 3 showed monodisperse spherical shape with sizes of approximately 5 nm.

In situ template synthesis of gold nanoparticles using a bis-imidazolium amphiphile-based hydrogel.

HYPOTHESIS Gemini-type bis-imidazolium amphiphiles are able to stabilize gold nanoparticles (GNPs) and also form hydrogels. It should be possible to obtain GNPs synthesized within these hydrogels and stabilized by the bis-imidazolium molecules. EXPERIMENTS Hydrogels containing a gold salt were formed using 1,3-bis[(3-octadecyl-1-imidazolio)methyl]benzene dibromide. After aging of the gel, upon addition of the reducing agent in a solvent the formation of GNPs was assessed. The gel was characterised and the GNPs were observed using High Resolution Transmission Electron Microscopy (HRTEM). FINDINGS Monodisperse GNPs with an average size of ca. 5 nm and well defined icosahedral geometry were formed in situ using the bis-imidazolium amphiphile-based hydrogel as template. Furthermore the gelator is also the stabilizing ligand of the GNPs, allowing the recovery of the GNP by disassembling the gel without aggregation of the inorganic colloid.

Amphiphilic gemini pyridinium-mediated incorporation of Zn(II)meso-tetrakis(4-carboxyphenyl)porphyrin into water-soluble gold nanoparticles for photodynamic therapy

Zn-containing porphyrins are intensely investigated for their ability to form reactive oxygen species and thereby being potent photosensitizers for use in photodynamic therapy (PDT). Some of the drawbacks of the PDT approach, such as unspecific distribution, could be addressed by means of photosensitizer drug delivery systems. In this work, we synthesize and characterize new water-soluble gold nanoparticles (GNP) stabilized by a mixture of a polyethyleneglycol-containing thiol (to improve water solubility) and a new amphiphilic gemini-type pyridinium salt, which also acts as promotor of the incorporation of the anionic photosensitizer Na-ZnTCPP into the GNP. The obtained GNP have sizes between 7 and 10nm, as observed by Transmission Electron Microscopy. The incorporation of the photosensitizer caused an increase in the hydrodynamic size, detected by Dynamic Light Scattering, as well as a shift in the Surface Plasmon Resonance peak on the GNP UV-vis absorption spectra. The presence of the photosensitizer in the GNP was corroborated using Fluorescence Spectroscopy. The amount of Na-ZnTCPP was found to be 327 molecules per GNP. The porphyrin-containing Na-ZnTCPP-1·GNP showed good enhanced ability to produce singlet oxygen, compared to free Na-ZnTCPP. Their cytotoxicity and phototoxicity were investigated in vitro using two different human breast cell lines, one of tumoral origin (SKBR-3) and another of normal epithelium origin (MCF-10A). SKBR-3 cells showed higher sensitivity to Na-ZnTCCP and Na-ZnTCPP-1·GNP in dark conditions. After irradiation, no significant differences were observed between both cell lines except for 1μM Na-ZnTCCP-1·GNP where SKBR-3 cells were also more sensitive.

Cationic supramolecular hydrogels for overcoming the skin barrier in drug delivery

Abstract A cationic bis‐imidazolium‐based amphiphile was used to form thermoreversible nanostructured supramolecular hydrogels incorporating neutral and cationic drugs for the topical treatment of rosacea. The concentration of the gelator and the type and concentration of the drug incorporated were found to be factors that strongly influenced the gelling temperature, gel‐formation period, and overall stability and morphology. The incorporation of brimonidine tartrate resulted in the formation of the most homogeneous material of the three drugs explored, whereas the incorporation of betamethasone resulted in a gel with a completely different morphology comprising linked particles. NMR spectroscopy studies proved that these gels kept the drug not only at the interstitial space but also within the fibers. Due to the design of the gelator, drug release was up to 10 times faster and retention of the drug within the skin was up to 20 times more effective than that observed for commercial products. Experiments in vivo demonstrated the rapid efficacy of these gels in reducing erythema, especially in the case of the gel with brimonidine. The lack of coulombic attraction between the gelator–host and the guest–drug seemed particularly important in highly effective release, and the intermolecular interactions operating between them were found to lie at the root of the excellent properties of the materials for topical delivery and treatment of rosacea.