Annalinda Contino

Complexation of native L-α-aminoacids by water soluble calix[4]arenes

The aromatic or aliphatic residue of native L-α-aminoacids is selectively included into the hydrophobic cavity of water soluble calix[4]arene receptors. The association constants values are determined by 1H NMR titration experiments and the binding process is further elucidated by preliminary Molecular Mechanics calculations, which give results fully consistent with the NMR data.

Complexation of small neutral organic molecules by water soluble calix[4]arenes

Abstract The inclusion of small neutral organic guests (alcohols, ketones and nitriles) by water-soluble calix[4]arene receptors was studied by 1 H NMR spectroscopy at neutral pH. The guests are included into the host hydrophobic cavity by their apolar aliphatic residues. The binding constants, determined by 1 H NMR titrations, confirm the importance of charge assistance in the apolar binding of guests inside calixarene cavities and highlight the role played by the conformational properties of the receptors in the recognition process.

Application of charged single isomer derivatives of cyclodextrins in capillary electrophoresis for chiral analysis

The review focuses on the role of ionic or ionisable single isomer derivatives (SIDs) of cyclodextrins on the separation of chiral analytes in capillary electrophoresis (CE), covering the period since the year 2000. The advantages of using pure compounds are discussed, as well as the ways to optimise the separations in the context of a rational approach to these techniques. Specific attention is paid to the modulation of the selector-analyte interaction. The advantage due to a detailed knowledge of equilibria occurring in solution during the CE run is underlined, particularly in the case of the presence of metal complexes, as occurs in chiral ligand exchange capillary electrophoresis (CLECE).

Inclusion of naturally occurring amino acids in water soluble calix[4]arenes: a microcalorimetric and 1H NMR investigation supported by molecular modeling

The thermodynamic parameters for the inclusion of some naturally occurring amino acids into a series of p-sulfonated calix[4]arenes, were determined via both 1H NMR and calorimetric titrations in buffered aqueous solution at 25 degrees C. The calorimetric data show that inclusion is enthalpically driven in all cases, regardless of flexibility of the host and the nature of the guest. The most efficient receptor is the calix[4]arene tetrasulfonate 1, which exists in solution at pH 7 in a cone conformation, stiffened by H-bonding at the lower rim. Molecular mechanics data help in the understanding of why some hosts do not form inclusion complexes at all. The comparison of our data with literature reports shows that there are dramatic buffer-dependent changes in the binding affinities.

Barbituric and thiobarbituric acids: a conformational and spectroscopic study

A conformational study on Barbituric (BA) and Thiobarbituric (TBA) acids was performed at ab initio MP2/6-31G** level on the neutral, protonated, mono- and di-anionic forms. Acid-base equilibria were studied by comparing the electronic transitions evaluated for the most stable conformations and the experimental spectra at different pH values. The electronic transitions were obtained through the ZINDO approach.

Recent advances in chiral separation of amino acids using capillary electromigration techniques.

This review highlights recent progresses in the chiral recognition and separation of amino acid enantiomers obtained by capillary electromigration techniques, using different chiral selectors and especially cyclodextrins, covering the literature published from January 2010 to March 2014. Sections are dedicated to the use of derivatization reagents and to the possibility to enantioseparate underivatized amino acids by using either ligand exchange capillary electrophoresis (LECE) and capillary electrophoresis (CE) coupled on line with mass spectrometry. A short insight on frontier nanomaterials is also given.

Water-soluble calix[6]arenes. Characterization of 5,11,17,23,29,35-hexasulphonate-37,38,39,40,41,42-hexahydroxycalix[6]arene and thermodynamic study of proton complex formation

Abstract The title compound, synthesized by modifying the procedure described in literature, was characterized by NMR, IR, TG, LSIMS, ICP-AES and potentiometry, and found to be an octasodium salt. Its protonation constants were determined in aqueous solution at 25°C and I = 0.1 mol dm −3 (NaNO 3 ) and compared with literature data determined under similar conditions. Enthalpy and entropy values, determined calorimetrically under the same experimental conditions employed for the potentiometric measurements, together with NMR results, provide a detailed picture of the processes taking place in aqueous solution.

Coordination properties of dialkyltin (IV) in aqueous solution. Thermodynamic study of dimethyltin (IV) complexes with l-amino acids

Abstract The complex formation of dimethyltin (IV) ([SnMe2]2+) with alanine, phenylalanine, triptophane and valine has been investigated by means of potentiometry at 25 °C and I = 0.1 mol dm−3 (KNO3). The selection of the models and the calculation of stability constants have been performed collecting a large amount of data points and using three different computer programs. This procedure has made it possible to detect the species forming in low percentages. A comparison with monodentate and bidentate systems previously studied gives an indication as to the number and the nature of the donor atoms involved in the coordination.

Probing archaeological and artistic solid materials by spatially resolved analytical techniques

The study of ancient works-of-art and archaeological remains requires the use of analytical methods which minimise the impact on the integrity of the object. Spatially resolved analytical methods have significantly enhanced our capacity to study ancient material since they cause minimal and at times no damage to the studied object. They have also amplified the range of analytical information we can extract from ancient and valuable objects. Here we provide an overview of the recent achievements in the knowledge of the past obtained thanks to the use of a variety of spatially resolved analytical methods.

Charge assisted hydrophobic binding of ethanol into the cavity of calix[4]arene receptors in aqueous solution

Abstract Ethanol is included into the hydrophobic cavity of the water soluble calixarenes 1 and 2 in aqueous solution, with the alkyl residue pointing towards the cavity and the hydroxyl group facing the bulk of the solvent. No inclusion is detected for 3 , and this suggests that the sulphonate groups serve as anchoring points.