Sabina Licen

Size-dependent cation transport by cyclic α-peptoid ion carriers

N-Benzyloxyethyl macrocyclic peptoids 3 and 4 were synthesized and subjected to alkali metal binding studies; these compounds, plus the known 1 and 2, when subjected to ion transport studies, demonstrated size-dependent selectivity for the first group alkali metals cation transport.

CyPLOS: a new family of synthetic ionophores

The ion transport properties of a new family of synthetic ionophores based on cyclic phosphate-linked oligosaccharide (CyPLOS) macrocycles are described.

Design, Synthesis and Characterisation of a Fluorescently Labelled CyPLOS Ionophore

A novel fluorescently labelled synthetic ionophore, based on a cyclic phosphate-linked disaccharide (CyPLOS) backbone and decorated with four tetraethylene glycol tails carrying dansyl units, has been synthesised in 12 steps in 26% overall yield. The key intermediate in the synthetic strategy is a novel glucoside building block, serving through its 2- and 3-hydroxy groups as the anchor point for flexible tetraethylene glycol tentacles with reactive azido moieties at their ends. To test the versatility of this glucoside scaffold, it was preliminarily functionalised with a set of diverse probes--as fluorescent, redox-active or hydrophobic tags--either by reduction of the azides followed by condensation with activated carboxylic acid derivatives, or by a direct coupling with a terminal alkyne in a Cu(I)-promoted 1,3-dipolar cycloaddition. Tagging of the monomeric building block with dansyl residues allowed us to prepare a fluorescent, amphiphilic macrocycle, which was investigated for its propensity to self-aggregate in CDCl(3)--studied by means of concentration-dependent (31)P NMR spectroscopy experiments--and in aqueous solution, in which combined dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements provided a detailed physico-chemical analysis of the self-assembled systems, mainly organised in the form of large vesicles. Its ion-transport properties through phospholipid bilayers, determined by HPTS fluorescence assays, showed this compound to be more active than the previously synthesised CyPLOS congeners. Solvent-dependent fluorescence changes for the labelled ionophore in liposome suspension established that the dansyl moieties are dispersed in environments with polarity intermediate between those of CH(2)Cl(2) and propan-2-ol, suggesting that the CyPLOS tentacles infiltrate the mid-polar region of the membranes.

Anion transport across phospholipid bilayers promoted by a guanidinium calix[4]arene conjugate

The ionophoric activity of a calix[4]arene guanidinium conjugate (4G4Oct) has been investigated in bulk chloroform membrane and mainly in liposomes. In both membrane models 4G4Oct shows high activity in the transport of chloride. The mechanistic evidence suggests a carrier mechanism in which the calixarene binds the anions through electrostatic interactions and hydrogen bonds with the guanidinium moieties. Studies on anion transport in liposomes indicate a peculiar selectivity sequence inverse to the most commonly observed lyotropic series with chloride transported faster than bromide and iodide virtually non-transported. This selectivity sequence together with competitive inhibition of chloride transport by the non-transported ions suggests a strong anion binding to the guanidinium moieties in the membrane environment. The complex formed is lipophilic and is able to shuttle the ion across the membrane. The origin of the observed anion selectivity is suggested to be related to a less favourable ion exchange at the membrane interface of iodide with respect to chloride with OH− , which is the antiported ion in the transport process in liposome. These studies complement the reported ability of 4G4Oct to condensate plasmid DNA and to transfect cells, showing that the calixarene derivative is also able to efficiently transport chloride across a phospholipid bilayer.

Artificial anion transporters in bilayer membranes.

Anion transport across phospholipid membrane is a typical supramolecular function involving dynamic recognition of the substrate during the whole translocation process. Supramolecular chemists, taking inspiration by the natural anion transporters, have designed artificial systems able to mimic, at the functional level, several features of the natural ion channels. The scope of this research is twofold: on one hand to get insight on the molecular basis of recognition and transport, and on the other hand to get control of the biomedical relevant processes. The present review focuses on the synthetic systems promoting anion transport, covering both artificial channels and carriers that operate in phospholipid membrane. The design principles of such systems will be discussed together with the potential biomedical applications.

Characterization of dried and freeze-dried sea fennel ( Crithmum maritimum L. ) samples with headspace gas-chromatography/mass spectrometry and evaluation of an electronic nose discrimination potential

Processed samples (air-dried @ 40 and @ 60 °C and freeze-dried) of sea fennel (Crithmum maritimum L.), an autochthonous spice with interesting market potential, were analyzed by headspace gas-chromatography/mass spectrometry and classification capabilities of an electronic nose in discriminating between samples with stepwise forward statistics were evaluated as well. Freeze-drying process was the most preservative in terms of limiting darkening without compromising appearance of the final product, providing weight loss of about 85% and water activity below the limit for mold growth issues. Headspace analysis of samples highlighted the presence of 35 volatiles grouped as terpene hydrocarbons, oxygenated terpenes, sesquiterpen hydrocarbons, phenyl propanoids, not-terpenic aldehydes and not-terpenic ketones. Correlations emerged between selected sensors and some detected volatile organic compounds. Stepwise linear discriminant analysis and simple K-nearest neighbors obtained a 100% overall correct classification rate in cross-validation of the electronic nose in classifying samples, whereas stepwise quadratic discriminant analysis and Naive-Bayes gave 93.3%. The sea fennel could be a new interesting spice to launch in the food market and the electronic nose showed the potential to be used in monitoring the industrial process aimed at extending its shelf-life.