Roberto Centore

The Anti-Proliferative Effect of L-Carnosine Correlates with a Decreased Expression of Hypoxia Inducible Factor 1 alpha in Human Colon Cancer Cells

In recent years considerable attention has been given to the use of natural substances as anticancer drugs. The natural antioxidant dipeptide L-carnosine belongs to this class of molecules because it has been proved to have a significant anticancer activity both in vitro and in vivo. Previous studies have shown that L-carnosine inhibits the proliferation of human colorectal carcinoma cells by affecting the ATP and Reactive Oxygen Species (ROS) production. In the present study we identified the Hypoxia-Inducible Factor 1α (HIF-1α) as a possible target of L-carnosine in HCT-116 cell line. HIF-1α protein is over-expressed in multiple types of human cancer and is the major cause of resistance to drugs and radiation in solid tumours. Of particular interest are experimental data supporting the concept that generation of ROS provides a redox signal for HIF-1α induction, and it is known that some antioxidants are able to suppress tumorigenesis by inhibiting HIF-1α. In the current study we found that L-carnosine reduces the HIF-1α protein level affecting its stability and decreases the HIF-1 transcriptional activity. In addition, we demonstrated that L-carnosine is involved in ubiquitin-proteasome system promoting HIF-1α degradation. Finally, we compared the antioxidant activity of L-carnosine with that of two synthetic anti-oxidant bis-diaminotriazoles (namely 1 and 2, respectively). Despite these three compounds have the same ability in reducing intracellular ROS, 1 and 2 are more potent scavengers and have no effect on HIF-1α expression and cancer cell proliferation. These findings suggest that an analysis of L-carnosine antioxidant pathway will clarify the mechanism underlying the anti-proliferative effects of this dipeptide on colon cancer cells. However, although the molecular mechanism by which L-carnosine down regulates or inhibits the HIF-1α activity has not been yet elucidated, this ability may be promising in treating hypoxia-related diseases.

New NLO active cyclopalladated chromophores in main-chain polymers

Abstract Four new OH-functionalized orthopalladated complexes bearing an electron-donor and an acceptor group in a trans -like arrangement with respect to the metal have been prepared and characterized. The ligands are Schiff bases, bound as C,N- or N,O-chelating moieties. Four new polyesters were obtained by polycondensation from the monomeric complexes and pentyloxyterephthaloyl chloride. Two “model” complexes, each one related to one monomer, were also synthetized, in order to obtain further and more detailed characterization data, and in particular to perform measurements of μβ .

A series of compounds forming polar crystals and showing single-crystal-to-single-crystal transitions between polar phases

Condensation of 4-hydroxybenzohydrazide with a variety of non-chiral aliphatic ketones, methylethylketone, acetone, cyclohexanone and cyclobutanone, affords imine compounds crystallizing in polar space groups (Pna21 or Cc). For all the compounds synthesized, the crystal structure was determined by single crystal X-ray analysis and second harmonic generation experiments were performed on powder samples. The imine obtained using acetone shows solid state polymorphism with unusual behaviour; three different crystal phases have been identified (phases I, II and III), all having the same polar space group Pna21, and the transitions from I to II and from III to II are topotactic, i.e. single-crystal-to-single-crystal. During the irreversible transition from phase I to II, the polar axis undergoes a strong compression (about 15%) and single crystals of the parent phase are violently shattered into single crystal fragments of the new phase, while in the reversible transition from phase III to II, the polar axis expands (about 14%) and the integrity of single crystals is preserved.

Structure and Electronic Properties of Extended Chromophores for Applications in Second-Order Nonlinear Optics

A structural and theoretical analysis of new 2-[(4-phenylazo)phenyl] benzoxazole chromophores of potential interest in the field of second-order nonlinear optics is presented. Computations predict comparatively high hyperpolarizabilities for most of the compounds in their equilibrium nuclear configuration, with a significant dependence upon some conformational degrees of freedom and independence upon some others. This behavior is rationalized in the frame of the two-level model and sheds light on the conjugation pattern of these new chromophores.

Synthesis and characterisation of polyesters with nonlinear optical properties

Eight new homo- and copolymers have been obtained by polycondensation of terephthalic acid and propyloxyterephthalic acid with two different second order NLO-active chromophores derived from 4-[N,N-bis(2-hydroxyethyl)amino]-benzaldehyde. Polymers exhibit good optical clarity, satisfactory thermal stability above the glass transition temperature and most of them are soluble in common organic solvents. Second order nonlinear optical properties of two corona poled polymer films were evaluated by second harmonic generation (SHG) measurements with an incident radiation of 1542 nm.

Nonlinear optical properties of some side chain copolymers based on benzoxazole containing chromophores

Acrylate-methylmethacrylate copolymers have been synthesized for nonlinear optical applications. Acrylate monomer units are characterized by the presence in the side chain of phenylbenzoxazole groups containing electron donor-electron acceptor substituents. The phase behavior of all polymers has been investigated by DSC, X-ray diffraction and polarizing microscopy: two of them exhibit liquid crystalline behavior of smectic type. For four polymers, nonlinear optical properties have been examined by second harmonic generation measurements on thin films (∼ 1 μm thickness) electrically poled by corona discharge. Second order susceptibility coefficients d33 and average relaxation times 〈τ〉, relative to the time stability of the chromophore poling, have been measured.

Polymers containing substituted 2-phenyl-benzoxazole side-chain groups: Synthesis and phase behavior

SYNOPSIS The synthesis of substituted 2-phenyl-benzoxazoles has been accomplished by ring closure of Schiff bases. The compounds have been used as precursors of acrylic derivatives displaying LC properties : formula chem. R 1 = NO 2 , CN ; R 2 = -OOC-pC 6 H 4 -O(CH 2 ) 6 OOCCH=CH 2 ; R 1 = - OOC - pC 6 H 4 - O(CH 2 ) 6 OOCCH=CH 2 , -N(CH 3 )(CH 2 ) 6 OOCCH =CH 2 ; R 2 = NO 2 Four comb-like homopolymers have been obtained by radical catalysis from the acrylic monomers. The polymers have been characterized by 1 H-NMR, DSC, x-ray diffraction, viscometry, and polarizing microscopy. Three of the polymers exhibit liquid crystalline properties of smectic type.

Strong and Anomalous Thermal Expansion Precedes the Thermosalient Effect in Dynamic Molecular Crystals.

The ability of thermosalient solids, organic analogues of inorganic martensites, to move by rapid mechanical reconfiguration or ballistic event remains visually appealing and potentially useful, yet mechanistically elusive phenomenon. Here, with a material that undergoes both thermosalient and non-thermosalient phase transitions, we demonstrate that the thermosalient effect is preceded by anomalous thermal expansion of the unit cell. The crystal explosion occurs as sudden release of the latent strain accumulated during the anisotropic, exceedingly strong expansion of the unit cell with αa = 225.9 × 10−6 K−1, αb = 238.8 × 10−6 K−1 and αc = −290.0 × 10−6 K−1, the latter being the largest negative thermal expansivity observed for an organic compound thus far. The results point out to the occurence of the thermosalient effect in phase transitions as means to identify new molecular materials with strong positive and/or negative thermal expansion which prior to this work could only be discovered serendipitously.

Nickel(II) and copper(II) complexes of allyl 2-(thiophen-2-ylmethylene)hydrazinecarbodithioate: synthesis, X-ray crystal structures, and theoretical study

We report allyl 2-(thiophen-2-ylmethylene)hydrazine-carbodithioate (HL) and its Ni(II) and Cu(II) complexes, [ML2]. The compounds were fully characterized by elemental analysis, IR, 1H-NMR, UV-Vis, and molar conductivity. The crystal structure analysis indicates that the metal is four-coordinate square planar and that a parallel stacking of the molecular planes is present in the crystals, with stacking distances of 3.642 and 3.676 Å for the Ni(II) and Cu(II) complexes, respectively. Gas phase DFT computations indicate that the thione tautomeric form of the free ligand is more stable than the thiol form by 14.52 kJ mol–1. For HL and ML2, comparison between the computed and experimental data shows good agreement.

Mesophase behaviour of some semiflexible trimeric compounds

The synthesis and the phase behaviour of a class of semiflexible mesogenic compounds, containing two terminal α-methylstilbene and one central p-biphenyl groups, linked each other by flexible spacers, is reported. Their phase behaviour has been investigated by DSC, X-ray diffraction and optical methods. All compounds show liquid crystalline polymorphism; in particular all but one exhibit a highly ordered smectic phase whose nature is discussed. The occurrence of enthalpic and entropic changes at the nematic-isotropic phase transition, which are sensibly higher than those reported for monomeric and dimeric model compounds of semiflexible polymers, is also discussed