Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide.

Polyimides are a polymer class that has been extensively investigated as a membrane material for gas separation owing to its interesting permselective properties in a wide range of operation temperatures and pressures. In order to improve their properties, the addition of different filler types is currently studied. p-tert-Butylcalix[n]arene macrocycles (PTBCs) with different cavity sizes (PTBC4, PTBC6, PTBC8) were used as fillers in a commercial thermoplastic polyimide, with a concentration in the range 1-9 wt%, to develop nanocomposite membranes for gas separation. The selected macrocycles are attractive organic compounds owing to their porous structure and affinity with organic polymers. The nanocomposite membranes were prepared in the form of films in which the polymeric matrix is a continuous phase incorporating the dispersed additives. The preparation was carried out according to a pre-mixing approach in a mutual solvent, and the solution casting was followed by a controlled solvent evaporation. The films were characterized by investigating their miscibility, morphology, thermal and spectral properties. The gas transport through these films was examined as a function of the temperature and also time. The results evidenced that the incorporation of the chosen nanoporous fillers can be exploited to enhance molecular transport, offering additional pathways and promoting rearrangements of the polymeric chains.

A novel cationic ß-cyclodextrin decorated with a choline-like pendant exhibits Iodophor, Mucoadhesive and bactericidal properties.

Iodine is a vital microelement and a powerful antiseptic with a rapid and broad spectrum of action. The development of iodophor compounds to improve the solubility and stability of iodine is still challenging. Here, we report the synthesis of a novel cationic ß-cyclodextrin bearing a choline-like pendant (ß-CD-Chol) designed to complex and deliver iodine to bacterial cells. The characterization of ß-CD-Chol and the investigation of the inclusion complex with iodine were performed by NMR spectroscopy, mass spectrometry, UV-vis spectrophotometry, isothermal titration calorimetry, and dynamic light scattering. The functionalization with the positively charged unit conferred improved water-solubility, mucoadhesivity, and iodine complexation efficiency to the ß-CD scaffold. The water-soluble ß-CD-Chol/iodine complex efficiently formed both in solution and by solid-vapor reaction. The solid complex exhibited a significant stability for months. Iodine release from the inclusion complex was satisfactory and the bactericidal activity was proved against a Staphylococcus epidermidis strain. The absence of cytotoxicity tested on human keratinocytes and the improved mucoadhesivity make ß-CD-Chol a promising drug delivery system and an appealing iodophor candidate for iodine-based antisepsis including mucosa disinfection.

Calix[4]arene Derivative for Iodine Capture and Effect on Leaching of Iodine through Packaging.

A hydrophobic calix[4]arene derivative was investigated for its iodine (I2) capture efficiency from gaseous and liquid phase. The iodine uptake was followed by UV-vis spectroscopy. Additionally, the influence of the calix[4]arene derivative-polyolefin system on the leaching of iodine through packaging from a povidone-iodine-based (PVP-I) formulation was evaluated. In fact, iodine is a low-cost, multi-target, and broad-spectrum antiseptic. However, it is volatile, and the extended storage of I2-based formulations is challenging in plastic packaging. Here, we investigated the possibility of reducing the loss of I2 from an iodophor formulation by incorporating 4-tert-butylcalix [4]arene-tetraacetic acid tetraethyl ester (CX) and its iodine complex in high-density polyethylene (HDPE) or polypropylene (PP) via a swelling procedure. Surface and bulk changes were monitored by contact angle, thermogravimetric analysis (TGA), and UV-vis diffuse reflectance spectra. The barrier effect of the different polymeric systems (embedded with CX, iodine-CX complex, or I2) was evaluated by monitoring the I2 retention in a buffered PVP-I solution by UV-vis spectroscopy. Overall, experimental data showed the capability of the calix[4]arene derivative to complex iodine in solution and the solid state and a significant reduction in the iodine leaching by the PP-CX systems.

p-Sulfonato-Calix[4]arene Micelles Stabilize a Povidone Iodine Solution: Supramolecular Interactions, Iodine Retention, and Bactericidal Activity.

Povidone iodine (PVPI) is an antiseptic widely used against a broad spectrum of pathogens. However, undesired side-effects are still associated with PVPI treatment due to the irritant effect of iodine. Reducing the concentration of a PVPI formulation could provide safer and more friendly formulations, for routine use and applications in very delicate organs such as the eye. However, managing the storage of a low-concentration solution of PVPI is challenging due to the high iodine volatility. In this study, we demonstrated that an amphiphilic p-sulfonato-calix[4]arene derivative forming micelles (SC4OC6) improves the stability of a 0.1% PVPI aqueous buffered solution. UV-vis and NMR spectra as well as dynamic and electrophoretic light scattering measurements showed that SC4OC6 establishes non-covalent supramolecular interactions with PVPI, resulting in the formation of nanoaggregates with a negatively charged surface. Isothermal titration calorimetry provided the aggregation parameters and evidenced that the formation of the supramolecular assembly is an enthalpically favored process. The interaction of SC4OC6 with PVPI enhances the iodine retention and stability of the solution without affecting the rapid and effective bactericidal activity of PVPI, as demonstrated by a time-killing assay with Staphylococcus epidermidis.

Antibacterial Nanoassembled Calix[4]arene Exposing Choline Units Inhibits Biofilm and Motility of Gram Negative Bacteria.

The high incidence of antibiotic resistance and biofilm-associated infections is still a major cause of morbidity and mortality and triggers the need for new antimicrobial drugs and strategies. Nanotechnology is an emerging approach in the search for novel antimicrobial agents. The aim of this study was to investigate the inherent antibacterial effects of a self-assembling amphiphilic choline-calix[4]arene derivative (Chol-Calix) against Gram negative bacteria. Chol-Calix showed activity against Escherichia coli and Pseudomonas aeruginosa, including antibiotic-resistant strains, and affected the bacterial biofilm and motility. The activity is likely related to the amphipathicity and cationic surface of Chol-Calix nanoassembly that can establish large contact interactions with the bacterial surface. Chol-Calix appears to be a promising candidate in the search for novel nanosized nonconventional antimicrobials.

A novel facile one-pot synthesis of photothermally responsive carbon polymer dots as promising drug nanocarriers.

Luminescent and photothermic carbon polymer dots (CPDs-PNM), composed of a carbonized core and cross-linked chains of poly(N-isopropylacrylamide), were synthetized by a novel, simple, solvent- and reagent-free method. The formation of CPDs-PNM was controlled by both temperature and heating time. The CPDs-PNM exhibited LCST behaviour, high photothermal conversion efficiency, curcumin loading capacity and no toxicity to eukaryotic cells. Proof of concept experiments confirmed an excellent thermally induced drug release activity to be used for photothermally controlled drug release.

Novel Peptide-Calix[4]arene Conjugate Inhibits Aß Aggregation and Rescues Neurons from Aß's Oligomers Cytotoxicity In Vitro.

Alzheimer's disease (AD) is a progressive neurodegenerative condition affecting people in the elderly. Targeting aggregation of ß-amyloid peptides (Aß) is considered a promising approach for the therapeutic treatment of the disease. Peptide based inhibitors of ß-amyloid fibrillation are emerging as safe drug candidates as well as interesting compounds for early diagnosis of AD. Peptide conjugation via covalent bond with functional moieties enables the resultant hybrid system to acquire desired functions. Here we report the synthesis, the structural characterization, and the Aß42 interaction of a p-amino-calix[4]arene derivative bearing a GPGKLVFF peptide pendant at the lower rim. We demonstrate that the p-amino-calix[4]arene-GPGKLVFF conjugate alters the Aß42 aggregation pathways by preventing Aß42's conformational transition from random coil to ß-sheet with concomitant changes of the aggregation kinetic profile as evidenced by circular dichroism (CD), thioflavin T (ThT), and dynamic light scattering (DLS) measurements, respectively. High resolution mass spectrometry (HR-MS) confirmed a direct interaction of the p-amino-calix[4]arene-GPGKLVFF conjugate with Aß42 monomer which provided insight into a possible working mechanism, whereas the alteration of the Aß42's fibrillary architecture, by the calix-peptide conjugate, was further validated by atomic force microscopy (AFM) imaging. Finally, the herein proposed compound was shown to be effective against Aß42 oligomers' toxicity in differentiated neuroblastoma cells, SH-SY5Y.

Injectable supramolecular nanohydrogel from a micellar self-assembling calix[4]arene derivative and curcumin for a sustained drug release.

In the search for soft and smart materials for nanomedicine, which is a present challenge, supramolecular nanohydrogels built on self-assembling low-molecular-weight building blocks attract interest for their structural, mechanical and functional properties. Herein, we describe a supramolecular nanohydrogel formed by a biofriendly micellar self-assembling choline-calix[4]arene derivative in the presence of curcumin, a natural and multitarget pharmacologically relevant drug. Morphology and mechanical properties of the nanohydrogel were investigated, and theoretical simulation performed to model the nanohydrogel structure. The self-healing and injectable nanohydrogel easily formed in PBS medium at physiologic pH, without using additives and organic solvents. The micellar nanohydrogel protected curcumin from rapid chemical and photochemical degradation, and slowly dissolved in curcumin-loaded micelles sustaining the drug release in a low rate. The nanohydrogel which combines the mechanical properties of a hydrogel and the benefits of a nanoscale micelle in drug delivery, appears a promising novel material for drug delivery.

Binding Affinity and Driving Forces for the Interaction of Calixarene-Based Micellar Aggregates With Model Antibiotics in Neutral Aqueous Solution.

The search for novel surfactants or drug delivery systems able to improve the performance of old-generation antibiotics is a topic of great interest. Self-assembling amphiphilic calix[4]arene derivatives provide well-defined nanostructured systems that exhibit promising features for antibiotics delivery. In this work, we investigated the capability of two micellar polycationic calix[4]arene derivatives to recognize and host ofloxacin, chloramphenicol, or tetracycline in neutral aqueous solution. The formation of the nanoaggregates and the host-guest equilibria were examined by nano-isothermal titration calorimetry, dynamic light scattering, and mono- and bi-dimensional NMR. The thermodynamic characterization revealed that the calix[4]arene-based micellar aggregates are able to effectively entrap the model antibiotics and enabled the determination of both the species and the driving forces for the molecular recognition process. Indeed, the formation of the chloramphenicol-micelle adduct was found to be enthalpy driven, whereas entropy drives the formation of the adducts with both ofloxacin and tetracycline. NMR spectra corroborated ITC data about the positioning of the antibiotics in the calixarene nanoaggregates.

Synthesis of a calix[4]arene derivative exposing multiple units of fucose and preliminary investigation as a potential broad-spectrum antibiofilm agent.

Calix[4]arene derivative (1), bearing four α-l-C-fucosyl units linked via a flexible spacer, and a monomeric analogous (2) bearing a single moiety of fucose, were synthesized. Compounds 1 and 2 were assayed for antibiofilm activity against Pseudomonas aeruginosa (Gram-) and Staphylococcus epidermidis (Gram+). The macrocyclic compound 1 showed very high percentage of biofilm inhibition against two different bacterial strains while compound 2, which does not possess a macrocyclic structure, showed only moderate biofilm inhibition against P. aeruginosa and no biofilm inhibition against S. epidermidis. The fucose multivalent derivative could be a new broad-spectrum antibiofilm agent.

Essential oils encapsulated in polymer-based nanocapsules as potential candidates for application in food preservation.

The aim of this work is the encapsulation of essential oils (EOs) in polymeric nanocapsules (NCs), in order to enhance their antimicrobial activity against food-borne pathogens. Thymus capitatus and Origanum vulgare EOs were selected for their different chemical composition, carvacrol (73%) and thymol (44%) being the major constituent, respectively. Polymeric poly(ɛ-caprolactone) (PCL) nanocapsules loaded with EOs were prepared by a nanoprecipitation method. The EO-NCs showed monomodal distribution with diameter size 171 and 175 nm, high efficiency of encapsulation and stability with high retention of EOs at both 4 °C and 40 °C, for a period of at least 30 days. The antimicrobial activity of EO-NCs against food-borne pathogens was higher than that of the corresponding pure essential oils and the NCs loaded with Thymus capitatus EO were the most active. Interestingly EO-NCs showed a bactericidal activity even at the minimum inhibitory concentrations (MICs). It makes them appealing as natural food preservatives.

Design and synthesis of a multivalent fluorescent folate-calix[4]arene conjugate: cancer cell penetration and intracellular localization.

A novel fluorescently labeled folate conjugate in which four folic acid units are covalently conjugated with a 7-nitro-benzofurazan fluorophore by means of a calix[4]arene platform was synthesized by using a Cu-catalyzed azide-alkyne cycloaddition reaction (click chemistry). The synthesized construct (FA-C4-NBD) was characterized by mass spectrometry, NMR and fluorescence spectroscopy. Confocal fluorescence microscopy experiments were carried out to evaluate the cell penetration ability of FA-C4-NBD on normal and cancer cells. The cellular uptake of FA-C4-NBD proceeds via folate receptor-mediated endocytosis. FA-C4-NBD is internalized into HeLa cancer cells which express high levels of folate receptors, whereas the uptake into fibroblast NIH3T3 cells which have very low expression levels of folate receptors is negligible. The involvement of the folate receptor was corroborated by competition tests with free folic acid. Co-localization analysis with different organelle markers indicated that FA-C4-NBD is not eliminated by recycling towards the outside of the cell, but accumulates intracellularly in the endo-lysosomal system.

The KDEL receptor couples to Gαq/11 to activate Src kinases and regulate transport through the Golgi.

Membrane trafficking involves large fluxes of cargo and membrane across separate compartments. These fluxes must be regulated by control systems to maintain homoeostasis. While control systems for other key functions such as protein folding or the cell cycle are well known, the mechanisms that control secretory transport are poorly understood. We have previously described a signalling circuit operating at the Golgi complex that regulates intra-Golgi trafficking and is initiated by the KDEL receptor (KDEL-R), a protein previously known to mediate protein recycling from the Golgi to the endoplasmic reticulum (ER). Here, we investigated the KDEL-R signalling mechanism. We show that the KDEL-R is predicted to fold like a G-protein-coupled receptor (GPCR), and that it binds and activates the heterotrimeric signalling G-protein Gα(q/11) which, in turn, regulates transport through the Golgi complex. These findings reveal an unexpected GPCR-like mode of action of the KDEL-R and shed light on a core molecular control mechanism of intra-Golgi traffic.