Giovanni Tabbì

University of Catania, Catania, Sicily, Italy

Are you Giovanni Tabbì?

Claim your profile

Publications (35)100.25 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The heptapeptide Semax is an analog of the adrenocorticotropic hormone (ACTH) 4-10 fragment. This study shows the metal binding ability and protective activity of Semax against copper induced cytotoxicity.
    Journal of Inorganic Biochemistry. 01/2015; 142:39–46.
  • Source
    Dataset: SI JIB
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Formal redox potentials in aqueous solution were determined for copper(II) complexes with ligands having oxygen and nitrogen as donor atoms. All the chosen copper(II) complexes have well-known stereochemistries (pseudo-octahedral, square planar, square-based pyramidal, trigonal bipyramidal or tetrahedral) as witnessed by their reported spectroscopic, EPR and UV-visible (UV-Vis) features, so that a rough correlation between the measured redox potential and the typical geometrical arrangement of the copper(II) complex could be established. Negative values have been obtained for copper(II) complexes in tetragonally elongated pseudo-octahedral geometries, when measured against Ag/AgCl reference electrode. Copper(II) complexes in tetrahedral environments (or flattened tetrahedral geometries) show positive redox potential values. There is a region, always in the field of negative redox potentials which groups the copper(II) complexes exhibiting square-based pyramidal arrangements. Therefore, it is suggested that a measurement of the formal redox potential could be of great help, when some ambiguities might appear in the interpretation of spectroscopic (EPR and UV-Vis) data. Unfortunately, when the comparison is made between copper(II) complexes in square-based pyramidal geometries and those in square planar environments (or a pseudo-octahedral) a little perturbed by an equatorial tetrahedral distortion, their redox potentials could fall in the same intermediate region. In this case spectroscopic data have to be handled with great care in order to have an answer about a copper complex geometrical characteristics.
    Journal of inorganic biochemistry 08/2013; 128C:137-145. · 3.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Many neurodegenerative proteinopathies are characterized by ubiquitin (Ub)-containing intraneuronal inclusion bodies. Recent reports have shown that Ub is able to bind Cu(II) and Zn(II), the dyshomeostasis of which is a hallmark of neurodegeneration. Here we use complementary techniques like potentiometry, circular dichroism-visible, and electron spin resonance to unveil the Ub/metal species that form, at neutral pH, their binding constants and structural features. Next, we show that both Zn(II) and Cu(II) ions hinder the interactions between Ub and Ub-conjugating E2 enzymes and inhibit significantly both Lys48 and Lys63 self-polyubiquitination reactions in a cell-free medium. The effects of Zn(II) and Cu(II) on Lys63 and Lys48 polyUb chain synthesis are compatible with the hypothesis that metal binding to His68 modifies the Ile44 hydrophobic patch of Ub and makes the protein less available for polyUb. These findings contribute to further arguments for a close relationship between metal dyshomeostasis and abnormal protein degradative pathways in the upstream events, triggering neurodegeneration.
    Inorganic Chemistry 07/2013; · 4.59 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A simple experiment was devised to let students determine the solubility and solubility product, Ksp, of calcium sulfate dihydrate in a first-level laboratory. The students experimentally work on an intriguing equilibrium law: the constancy of the product of the ion concentrations of a sparingly soluble salt. The determination of solubility is proposed either in an equimolar precipitation of CaSO4·2H2O, from which the Ksp is obtained, or working with an excess of one of the two reagents.
    Journal of chemical education 03/2012; 89(4):545-547. · 0.82 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Metallated meso-tetrakis(N-methyl-4-pyridyl)porphyrin (MTMPyP) and 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis-(hydroxylcarbonylmethoxy)-calix[4]arene (C(4)TsTc) were used as key components for building up discrete supramolecular entities starting from the formation of the template species MTMPyP:C(4)TsTc (1 : 4, M = Cu, Zn). The stepwise addition of further amount of porphyrin allows the facile non-covalent synthesis of discrete supramolecular entities (2 : 4 and 3 : 4) which can be built up just by programming the right stoichiometric addition of the proper porphyrin. The redox potentials of these supramolecular complexes in aqueous media, as well as those of the parent metalloporphyrins, have been characterized by using square wave voltammetry technique. The use of the simulation procedure leads us to establish the electrochemical steps involved in the redox processes for each supramolecular species, evidencing multistep electron reductions which were not experimentally resolved clearly because of their closeness. The most striking result is that the electrochemistry of each of these supramolecular complexes is different from that of the parent components. This "anomalous" behavior can be explained only considering each of these supramolecular complexes as a unique entity, in which such an internal electronic communication might occur. The formation of the 1 : 4 supramolecular complex produces a negative shift as to the metallated porphyrin redox potentials of about 30 mV. In the case of 2 : 4 and 3 : 4 species, the redox potentials progressively shifts towards more positive values by about 10-15 mV for each complexation step.
    Dalton Transactions 03/2011; 40(16):4223-9. · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A spectroscopic (UV-Vis, CD and EPR), thermodynamic and voltammetric study of the copper(ii) complexes with the Ac-PHPGGSNWGQ-NH(2) polypeptide (L), a fragment of the opossum PrP protein N-terminal four-repeat region, was carried out in aqueous solution. It suggests the formation of a highly distorted [Cu(L)H(-2)] complex species in the neutral region, the stereochemistry of which is ascribable to a square base pyramid and a CuN(3)O(2) chromophore, resulting from the coordination of a histidine imidazole and two peptide nitrogen atoms and probably oxygen atoms from water molecules. At basic pH values a [Cu(L)H(-3)](-) species with a pseudo-octahedral geometry was also obtained, with four nitrogen donor atoms in its equatorial plane, coming from the histidine residue and from peptidic nitrogen atoms. Interestingly, at pH values relatively higher than the neutrality, the coordination sphere of the copper complex in the [Cu(L)H(-2)] species changes its stereochemistry towards a pseudo-octahedron, as suggested by the change in the parallel copper hyperfine coupling constant of the EPR spectra at low temperature. A slight difference in the redox potentials between this two-faced [Cu(L)H(-2)] complex species seems to confirm this behaviour. Both potentiometric and spectroscopic data were compared with the analogous species obtained with the Ac-PHGGGWGQ-NH(2) peptide, belonging to the octarepeat domain of the human prion protein (hPrP) N-terminal region. The [Cu(L)H(-2)] species formed by the Ac-PHPGGSNWGQ-NH(2) decapeptide, having a slightly lower stability, turned out to be less abundant and to exist within a narrow pH range.
    Dalton Transactions 01/2011; 40(11):2441-50. · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra high molecular weight polyethylene (UHMWPE) is a component of mobile prostheses. The irradiation performed to sterilize and cross-link the polymer limits its life because of the free radicals originated during this process. In this work, a UHMWPE was electron-beam irradiated under high vacuum and annealed. Mechanical tests were performed on the UHMWPE samples before and after the annealing treatment. The results were compared with a study of radical species type and amount and the crystalline degree changes. Experimental results show that the annealing treatment prevents degrading reactions, favors intermolecular and/or intramolecular chemical rearrangements, and improves wear resistance without compromising the typical elasto-plastic mechanical behavior.
    International Journal of Polymer Analysis and Characterization 10/2010; 15(7):424-437. · 1.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Spectroscopic (UV-Vis and EPR) and voltammetric studies have been carried out on the copper(II) complexes with the Ac-PEG11-(PHGGGWGQ)4-NH2 (L) polypeptide. In the ratios Cu : L 3 : 1 and 4 : 1, the two [Cu3(L)H(-6)] and [Cu4(L)H(-8)] complex species have been characterized at neutral pH values. All the copper atoms occupy similar coordination sites formed by imidazole, peptidic nitrogen atoms and carbonyl oxygen atoms in a square base pyramidal geometry. Voltammetric measurements on these systems point out the cooperativity in the electron transfer processes among the copper(II) sites during their reduction. NO interaction with these polynuclear copper species is characterized by the reduction of the copper sites through the formation of two different intermediate complex species. When an excess of the Ac-PEG11-(PHGGGWGQ)4-NH2 ligand is considered, frozen solution EPR parameters and UV-Vis spectroscopic data identify the [Cu(N(im))4]2+ chromophore, which does not interact with NO.
    Dalton Transactions 05/2009; · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The interaction of nitric oxide with copper(ii) complexes of two octarepeat sequences belonging to the prion protein was studied, considering both mononuclear and dinuclear systems, i.e. Cu-Ac-(PHGGGWGQ)(2)-NH(2) and Cu(2)-Ac-(PHGGGWGQ)(2)-NH(2), respectively. The NO interaction with both systems was followed in aqueous solutions at physiological pH value, by using UV-Vis and EPR spectroscopic techniques as well as cyclic voltammetry. The mechanism of NO interaction with the mononuclear copper complex can be considered similar to that previously observed for the analogous copper systems with Ac-HGGG-NH(2) and Ac-PHGGGWGQ-NH(2). A more complicated behaviour was found with the copper dinuclear system, in which the involvement of two different intermediate complex species was evidenced. A positive cooperativity between the two copper ions, in the reduction process was inferred. When working with a large excess of the Ac-(PHGGGWGQ)(2)-NH(2) ligand, the frozen-solution EPR parameters pertain to the well characterized [Cu(N(im))(4)](2+) unit, which did not exhibit any interaction with NO. The presence of a free coordination site is the necessary requirement for the NO interaction to occur, as found only in the square-pyramidal geometry of [Cu(L)H(-2)] or [Cu(2)(L)H(-4)] complex species, which form when copper and ligand concentrations are similar.
    Dalton Transactions 08/2008; · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 6-Deoxy-6-{4-[N-(2-aminoethyl)propaneamide]imidazolyl}cyclohepta amylose (CDcarc) and 6-{3-amine-N-[2-(imidazol-4-yl)ethyl]propaneamide}-6-deoxycyclohepta amylose (CDcrac) were synthesized with the aim to obtain copper(II) complexes able to scavenge superoxide radical. The copper(II) complexes were studied by means of UV–Vis, ESR, CD, ESI-MS spectroscopies to gain information about the species present in solution as function of the pH. The antioxidant activity was assayed against superoxide enzymatically generated and compared with that obtained from copper(II) complex with underivatized carcinine. The hydroxyl radical scavenging ability of these new ligands was also tested.
    Inorganica Chimica Acta - INORG CHIM ACTA. 01/2008; 361(6):1705-1714.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The interaction between NO and copper(II) complexes formed by peptides coming from the N-terminal prion protein octa-repeat region was studied. Aqueous solutions of the Cu-Ac-HGGG-NH(2) and the Cu-Ac-PHGGGWGQ-NH(2) systems around pH 7.5 were tested after the addition of NONOates as a source of NO. UV-Vis, room temperature and frozen solution EPR spectra showed the occurrence of copper(ii) reduction in all these complexes. The reduction of these complexes is probably mediated by the formation of a labile NO adduct, which, after re-oxidation, leads to a relatively stable NO(2)(-) adduct through the apical coordination along the void site of their square pyramidal structure. In fact, the most significant shifts in EPR magnetic parameters (g(||) and A(||) or g(iso) and A(iso)) as well as in the optical parameters (lambda(max) and epsilon(max)) gave a reason for geometrical changes of the copper coordination polyhedron from a distorted square pyramid to a pseudo-octahedron. The presence of oxygen in the aqueous solution hindered the reduction ability of NO towards copper, but it made it easier to return to the original species. In order to elucidate the possible mechanism of this interaction, the reduction of copper complexed by these ligands was followed by means of zinc powder addition. The further addition of nitrite to the solution containing reduced copper led to the conclusion that nitrite could easily form an adduct, which after re-oxidation presented the same spectral features of the species obtained when the NO interaction was followed. The complexity of this interaction could involve both an inner or an outer-sphere electron transfer mechanism.
    Dalton Transactions 05/2007; · 3.81 Impact Factor
  • Source
    Angewandte Chemie International Edition 02/2007; 46(42):7993-5. · 11.34 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Due to their ballistic precision, apoptosis induction by protons could be a strategy to specifically eliminate neoplastic cells. To characterize the cellular and molecular effects of these hadrons, we performed dose-response and time-course experiments by exposing different cell lines (PC3, Ca301D, MCF7) to increasing doses of protons and examining them with FACS, RT-PCR, and electron spin resonance (ESR). Irradiation with a dose of 10 Gy of a 26,7 Mev proton beam altered cell structures such as membranes, caused DNA double strand breaks, and significantly increased intracellular levels of hydroxyl ions, are active oxygen species (ROS). This modified the transcriptome of irradiated cells, activated the mitochondrial (intrinsic) pathway of apoptosis, and resulted in cycle arrest at the G2/M boundary. The number of necrotic cells within the irradiated cell population did not significantly increase with respect to the controls. The effects of irradiation with 20 Gy were qualitatively as well as quantitatively similar, but exposure to 40 Gy caused massive necrosis. Similar experiments with photons demonstrated that they induce apoptosis in a significantly lower number of cells and in a temporally delayed manner. These data advance our knowledge on the cellular and molecular effects of proton irradiation and could be useful for improving current hadrontherapy protocols.
    APOPTOSIS 02/2006; 11(1):57-66. · 3.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An aqueous solution spectroscopic (Vis and EPR) study of the copper(II) complexes with the Ac-HGGG-NH2 and Ac-PHGGGWGQ-NH2 polypeptides (generically designated as L) suggests square base pyramids ascribable to [Cu(L)H(-2)] complex species, which contain three nitrogen donor atoms, arising from imidazole and peptide groups, in the equatorial plane and for a pseudo-octahedral geometry in the case of [CuLH-3]- and [Cu(L)H-4]2- which have four nitrogen donor atoms in their equatorial plane. The coordination sphere of the copper complex in the [Cu(L)H(-2)] species, which is present at neutral pH values, is completed by two oxygen donor atoms. ESI-MS spectra ascertained that water molecules are not present in the coordination equatorial plane of this latter species, in comparison with other copper(II) complexes with ligands bearing nitrogen and oxygen donor atoms and surely having equatorial water molecules. This indicates the coordination of a carbonyl oxygen atom in the equatorial plane has to be invoked. However, no direct proof about the involvement of a carbonyl group oxygen donor atom apically linked to copper was obtained, due to the flexibility of these structures at room temperature. Additionally, the low A(ll) value leads one to consider another oxygen atom of a carbonyl group being involved in the apical bond to copper in a fast exchange fashion. This apical interaction, which may also involve a water molecule, is more pronounced in the Cu-Ac-HGGG-NH2 than in the analogous Cu-Ac-PHGGGWGQ-NH2 system, probably because of the presence of tryptophan and proline in the polypeptide sequence.
    Dalton Transactions 02/2005; · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Dipyridyl pendants, suitably attached onto a calix[4]arene fixed in its 1,3-alternate conformation, form stable complexes with copper(ii) in acetonitrile. Both the mononuclear and the homobinuclear species ([Cu(1)](2+) and [Cu(2)(1)](4+)), previously detected through a UV-Vis investigation, have been studied by ESR, UV-Vis and cyclic voltammetry. ESR and UV-Vis data clearly indicate that in the [Cu(1)](2+) species the nitrogen atoms of dipyridyl pendants are tetrahedrally arranged around copper(II). Computer models, optimised through molecular mechanics methods, further support these spectroscopic findings. The tetrahedral arrangement, achieved thanks to the anchoring of the dipyridyl moieties onto the calixarene platform, accounts for the easy reversible reduction of this species. The aspects associated with the reduction-oxidation of the homobinuclear species are also discussed.
    Dalton Transactions 11/2004; · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 6A,6B-Dideoxy-6A,6B-di[(N-salicylidene)amino]-beta-cyclodextrin was synthesized and characterized by NMR, UV and CD spectroscopy in order to prepare a N,N(')-bis-(salicylidene)ethane-1,2-diamine (SalenH(2)) type ligand. The manganese(III) complex was synthesized and characterized by UV and cyclic voltammetry and compared to EUK-8. The superoxide dismutase (SOD)-like and catalase-like activities were tested by indirect assay. The cyclodextrin complex shows a larger solubility than EUK-8 and good SOD-like activity. Catalase activity is also shown.
    Journal of Inorganic Biochemistry 07/2004; 98(6):969-76. · 3.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this chapter is to summarize the knowledge on the ability of metal complexes to act as catalysts of the dismutation of superoxide radicals to hydrogen peroxide and dioxygen. The focus will be on the critical evaluation of this knowledge, and to suggest future developments. No attempt is made to be exhaustive in this very large body of literature [1–4]. This field has grown so vast that discussing or even citing most of the important contributions is virtually impossible; therefore, important aspects might, and will, remain uncovered. Rather, the authors focus particularly on specific copper compounds, for which, to the best of our knowledge, the most recent review was published in 1989 [4].
    01/2003;
  • Source
    G Tabbì, S C Fry, R P Bonomo
    [Show abstract] [Hide abstract]
    ABSTRACT: Xyloglucan is degraded by a mixture of copper(II), hydrogen peroxide and ascorbate. In the presence of ascorbate and/or hydrogen peroxide, copper(II) species were rapidly reduced to copper(I), which react with hydrogen peroxide. Spin-trapping experiments showed that hydroxyl radicals formed and attacked xyloglucan causing its degradation. The formation of a carbon-centred ascorbyl (C-ascorbyl) radical and its degradation with the formation of oxalate, was also caused by hydroxyl radicals. As a consequence, the features of the bis(oxalate) copper(II) complex clearly appeared in the frozen solution ESR spectra. The formation of carbon-centred radicals on the xyloglucan is the trigger for a series of possible molecular rearrangements which led to its oxidative scission.
    Journal of Inorganic Biochemistry 05/2001; 84(3-4):179-87. · 3.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The N-terminal octapeptide repeat region of human prion protein (PrPc) is known to bind Cu(II). To investigate the binding modes of copper in PrPc, an octapeptide Ac-PHGGGWGQ-NH2 (1), which corresponds to an octa-repeat sequence, and a tetrapeptide Ac-HGGG-NH2 (2) have been synthesised. The copper(II) complexes formed with 1 and 2 have been studied by circular dichroism (CD) and electron spin resonance (ESR) spectroscopy. Both peptides form 1:1 complexes with Cu(II) at neutral and basic pH. CD, ESR and visible absorption spectra suggest a similar co-ordination sphere of the metal ion in both peptides, which at neutral pH consists of a square pyramidal geometry with three peptidic nitrogens and the imidazole nitrogen as donor atoms. Cyclic voltammetric measurements were used to confirm the geometrical features of these copper(II) complexes: the observation of negative redox potentials are in good agreement with the inferred geometry. All these results taken together suggest that peptide 1 provides a single metal binding site to which copper(II) binds strongly at neutral and basic pH and that the binding of the metal induces the formation of a stiffened structure in the HGGG peptide fragment.
    Chemistry 12/2000; 6(22):4195-202. · 5.83 Impact Factor