Electrospray mass spectrometric studies of L-carnosine (beta-alanyl-L-histidine) complexes with copper(II) or zinc ions in aqueous solution

Electrospray ionization mass spectrometry (ESI-MS) was used for the speciation of supramolecular assemblies formed between equimolar amounts of carnosine and copper or zinc ions in dilute aqueous solutions. In the case of pure carnosine and carnosine/copper systems, the effect of pH changes, in the range 2-9, on the complexes surviving in solution was also explored. ESI data, besides supporting previous reported results on the formation of dimeric carnosine/copper and carnosine/zinc complexes, allowed a more complete speciation of the examined systems, bringing to light the existence of bis-complex species and, in the zinc case, the formation of oligomeric species. The data obtained for the systems investigated show that ESI-MS is not only a reliable and fast technique for the analysis of the metal/ligand systems, but also an interesting tool to obtain stoichiometric information on metal complexes formed in very low concentration solutions

Copper(II) assisted self-assembly of functionalized beta-Cyclodextrins with beta-alanyl-L-histidine

A combined UV–visible, CD and ESI-MS spectroscopic approach has been followed to obtain the speciation and the bonding details of copper(II) complexes with beta-cyclodextrins functionalized by means of the bio-active peptide beta-alanyl-L-histidine (carnosine). A new metal-assisted self-assembled system of bifunctionalized beta-cyclodextrins has been shown to exist

Coordination features of difunctionalized beta-cyclodextrins with carnosine: ESI-MS and spectroscopic investigations on 6A,6D-di-(beta-alanyl-L-histidine)-6A,6D-dideoxy-beta-cyclodextrin and 6A,6C-di-(beta-alanyl-L-histidine)-6A,6C-dideoxy-beta-cyclodextrin and their copper(II) complexes

The synthesis and characterization of two beta-cyclodextrins (beta-CD) functionalized with two units of carnosine (beta-alanyl-L-histidine) through the amino group, 6A,6C-(beta-alanyl-L-histidine)-6A,6C-dideoxy-beta-cyclodextrin (ACCDAH) and 6A,6D-(beta-alanyl-L-histidine)-6A,6D-dideoxy-beta-cyclodextrin (ADCDAH), are reported. NMR and C.D. data of the ligands indicate a different interaction of dipeptide chains with upper rim and cavity of beta-CD. Analogously, spectroscopic and electrospray ionization mass spectrometry data show different copper(II) complex species formed by the two regioisomers. The ability of carnosine-cyclodextrin derivatives to bind copper ions in a head-to-tail fashion induces the formation of oligomeric species (up to hexamers) in the case of ACCDAH, where the two carnosine moieties are adjacent, while in the ADCDAH case the mutual interaction between the peptidic chains of two ADCDAH molecules allows the almost exclusive formation of a copper-assisted self-assembled dimeric species

Thermally reversible highly cross-linked polymeric materials based on furan/maleimide Diels-Alder adducts

A novel thermally reversible cross-linked polymer has been synthesized by a Diels-Alder (DA) reaction between bis(4-maleimido-phenyl)fluorene (cBMI) and tetrakis-furan monomers (4F) under microwave (MW) irradiation. The ultimate aim of this work was the preparation of a thermosetting material recyclable by a simple thermal treatment. The use of the MW irradiation was necessary because under thermal conditions the DA polymerization could lead to materials only partially cross-linked for a not desired equilibrium between DA and retro-DA processes induced by the high temperature. The easy thermal degradation of this cross-linked material was ascertained by appropriate experiments. Moreover, to better study the involved reactions of formation and decomposition, a more simple model-compound was also synthesized. The reported data confirm the recyclability of the synthesized cross-linked polymer by simply heating with the possibility of a regeneration of the polymer network by a further MW irradiation

Copper(II) complexes with beta-cyclodextrin-homocarnosine conjugates and their antioxidant activity

Copper(II) complexes of the b-cyclodextrin (b-CD) functionalized with homocarnosine (HC) in the primary (CDHC6) and secondary rim (CDHC3) were characterized by means of different spectroscopic techniques such as UV–Vis absorption, circular dichroism, electron paramagnetic resonance and electron-spray mass spectrometry. Taken together, all the spectroscopic parameters indicate the formation of different copper(II) complex species at various pH values. In the CDHC3 copper(II) complex species, a direct involvement of the secondary hydroxyl group 2 of functionalized b-CD’s ring has been pointed out. The antioxidant activity of the copper(II) complexes of the two derivatives was determined through pulse radiolysis measurements. The results obtained provide direct evidence for a high catalytic activity of both complexes towards the dismutation of the superoxide anion radical. It is also demonstrated that the complex formation is not detrimental to the excellent scavenger activity exhibited by the ligands alone towards hydroxyl radicals. These copper complexes then represent very intriguing antioxidant agents against well known toxic reactive oxygen species