Conformational features and coordination properties of functionalized β-cyclodextrins. Formation, stability and structure of proton and copper(II) complexes of 3A-[1-(2-amino)ethylamino]-3A-deoxy-2A(S),3A(R)-β-cyclodextrin

Synthesis, characterization and sorption properties of silica modified with some derivatives of β-cyclodextrin

Nanoporous β-cyclodextrin-containing silicas which differ by functional substituents of wide edge of attached cyclic oligosaccharide molecules (alcohol, bromoacetyl, thiosemicarbazidoacetyl groups) have been synthesized. The structure and chemical composition of the surface, porosity of obtained materials, their chemical and thermal stability have been characterized by scanning electron microscopy, IR spectroscopy, thermogravimetry, nitrogen ad-desorption, elemental and chemical analyses of solid surface. Sorption of trace amounts of cadmium (II) in the presence of ten- and hundred-fold excess of hardness salts by synthesized organosilicas has been studied. It has been demonstrated that the sorption equilibrium is reached after 30 min. The sorption of trace amounts of cadmium (II) from multi-component solutions does not decrease, but even increases in the presence of hardness salts, simulating soft and hard water. Coefficients of distribution and selectivity as well as the sorption parameters of Langmuir and Freundlich equations have been calculated. It was found that the driving force of cadmium (II) sorption on the surface of functional β-cyclodextrin-containing silicas is the formation of inclusion complexes "β-cyclodextrin-nitrate-anion". It has been proved the formation of supramolecular structures on the surface of synthesized organosilicas as a result of cadmium (II) sorption. Chemical composition of supermolecules depends on the structure of surface active centers.

Selectively functionalized cyclodextrins and their metal complexes

Cyclodextrins (CDs) are cyclic oligomers of alpha-1,4-linked D-glucopyranose. Due to their unique structure, marked by a chiral and hydrophobic cavity, CDs have been extensively used as chiral selectors and drug delivery systems. The functionalization both improve the CD applications and widen their use in many other fields, such as molecular recognition and enzyme mimicking. Moreover, the functionalization highly increases the metal binding properties of the CDs. This critical review is a report of recent applications concerning the CD derivatives and their metal complexes. The metal ion assists the host-guest interaction often increasing the properties of CDs to act as chiral receptors. Furthermore, it can act as a catalytic center in the mimicking of metalloenzymes based on functionalized CDs (164 references).

New glycosidic derivatives of histidine-containing dipeptides with antioxidant properties and resistant to carnosinase activity

Synthesis, antioxidant properties and resistance to carnosinase hydrolysis of histidine-containing dipeptides are reported in this study. Carnosine (beta-alanyl-l-histidine), homocarnosine (gamma-aminobutyryl-l-histidine) and anserine (beta-alanyl-3-methyl-l-histidine) were covalently derivatized with beta-cyclodextrin to form different OH- or NH-bound conjugates. Mass spectroscopic and (1)H NMR data were used to determine the structure and the purity of the various beta-cyclodextrin derivatives. The inhibitory effect towards oxidation of human LDL induced by Cu(2+) ions, was estimated by measuring malondialdehyde formation as a function of increasing concentrations of these newly synthesized compounds (the beta-cyclodextrin-anserine conjugated in 3 had the highest antioxidant effect). All derivatives had higher antioxidant effects than those of the corresponding free histidine-containing dipeptides. Resistance to rat brain carnosinase hydrolysis of the most active derivatives indicated that these compounds are good candidates for further studies in more complex cellular and animal models. Their possible applications for remedies in neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, are discussed.

Synthesis and antioxidant activity of new homocarnosine beta-cyclodextrin conjugates

Several in vitro and in vivo studies have suggested that carnosine (beta-alanil-L-histidine) and homocarnosine (beta-aminobutyril-L-histidine) can act as scavengers of reactive oxygen species. beta-Cyclodextrin was functionalized with homocarnosine, obtaining the following new bioconjugate isomers: 6(A)-[(4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}-4-oxobutyl)amino]-6(A)-deoxy-beta-cyclodextrin and (2(A)S,3(A)R)-3A-[(4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}-4-oxobutyl)amino]-3(A)-deoxy-beta-cyclodextrin. Pulse radiolysis investigations show that the beta-cyclodextrin homocarnosine bioconjugates are scavengers of (*)OH radicals because of the formation of stable imidazole-centered radicals and the scavenger ability of glucose molecules of the macrocycle. The ability of these new beta-cyclodextrin derivatives to inhibit the copper(II) driven LDL oxidation was determined in comparison with that displayed by the analogous carnosine derivatives. Both the beta-cyclodextrin carnosine isomers show a higher protective effect than that of free dipeptide and homocarnosine derivatives, bringing into light the role of the beta-CD cavity. The ability of these new beta-cyclodextrin derivatives to inhibit the copper(II) driven LDL oxidation was determined in comparison with that displayed by the analogous carnosine derivatives. Both the beta-cyclodextrin carnosine isomers show a higher protective effect than that of free dipeptide and homocarnosine derivatives, bringing into light the role of the beta-CD cavity.

Ligand exchange capillary electrophoresis by cyclodextrin derivatives, a powerful tool for enantiomeric separations

Five pure CD derivatives synthesized in our laboratory were used as chiral selectors in the presence of copper(II) ion. Three enantiomeric pairs of amino acids were submitted to separation experiments in CE, by exploiting the ligand exchange mechanism. The results obtained in the investigated systems, together with those of the analogous systems previously studied, clearly show the usefulness of this technique in chiral separations. By comparing the ligand exchange CE results with potentiometric results, either reported elsewhere or studied here for the first time (system Cu/CDampy/tyrosine), it has been possible to rationalise the separation results. The importance of the availability of pure selectors, and to characterise them both spectroscopically and thermodynamically is discussed.

Coordination properties of 3-functionalized β-cyclodextrins. Thermodynamic stereoselectivity of copper(ii) complexes of the A,B-diamino derivative and its exploitation in LECE

The bis-amino AB derivative of beta-cyclodextrin on the secondary rim was synthesised and spectroscopically characterised by different techniques. Its binary systems both with protons and copper(II) were thermodynamically characterised by pH-metric potentiometry. In addition the ternary systems with each of the enantiomers of tryptophan and alanine were investigated. A thermodynamic stereoselectivity was observed for the tryptophan enantiomers and this was exploited to separate them by capillary electrophoresis through a ligand exchange mechanism (LECE). LECE separation of racemates of phenylalanine and tyrosine was also obtained.