C13 Nuclear-Magnetic-Resonance study of poly(trans-4-methacryloyloxyazobenzene)

The 50.3 MHz 13C NMR of radically initiated poly(trans-4-methacryloyloxyazobenzene) was studied in CDCl3 solution at room temperature. Resonance assignments were made by comparison with low molecular weight structural analogs and from dynamic measurements. Restricted internal rotation of the side chain azobenzene group was found to be responsible for the splitting of some aromatic carbon signals. The carbonyl, methyl and main chain quaternary carbons gave rise to multiplets attributable to pentad and triad stereosequences. Their intensity distribution closely fitted a Bernoullian statistics (Pm=0.257) consistent with a predominantly syndiotactic structure of the polymer backbone. Molecular dynamics in solution was investigated by 13C T1 and NOEF measurements

Photomodulation of the hydrophilic properties of acrylic polymers containing side-chain azobenzene chromophores

Partially hydrophilic polymers have been prepared by free-radical copolymerization of trans-4-acryloyloxyazobenzene with N-tert-butylacrylamide and N-isopropylacrylamide. A turbidimetric method has been adapted to investigate the dependence of the polymer hydrophilic-hydrophobic balance on chemical composition and extent of photoisomerization of side-chain azobenzene chromophores. Irradiation at 366 nm of polymer suspension in THF-water induces the isomerization of azobenzene groups from the planar apolar trans form to the nonplanar polar cis form. Correspondingly, the solution turbidity is appreciably modified. Experimental results are discussed in terms of polymer structural parameters. Suspension stability and the possibility of carrying out photochemical cycles have been also investigated

Novel Antiproliferative Biphenyl Nicotinamide: NMR Metabolomic Study of its Effect on the MCF-7 Cell in Comparison with Cisplatin and Vinblastine

A 1H-NMR-based metabolomic study was performed on MCF-7 cell lines treated with a novel nicotinamide derivative (DT-8) in comparison with two drugs characterized by a well-established mechanism of action, namely the DNA-metalating drug cisplatin (cis-diamminedichloridoplatinum(II), CDDP) and the antimitotic drug vinblastine (vinblastine, VIN). The effects of the three compounds, each one at the concentration corresponding to the IC50 value, were investigated, with respect to the controls (K), by the 1H-NMR of cells lysates and multivariate analysis (MVA) of the spectroscopic data. Relevant differences were found in the metabolic profiles of the different treatments with respect to the controls. A large overlap of the metabolic profiles in DT-8 vs. K and VIN vs. K suggests a similar biological response and mechanism of action, significantly diverse with respect to CDDP. On the other hand, DT8 seems to act by disorganizing the mitotic spindle and ultimately blocking the cell division, through a mechanism implying methionine depletion and/or S-adenosylmethionine (SAM) limitationThis research was funded by PRIN, Grant 201744BN5T_004S

13C NMR study of poly[(-)-menthyl methacrylate]

The 13C NMR spectrum of a radically initiated sample of poly[(-)-menthyl methacrylate] was studied in different solvents at different field strengths. Resonance assignments were made by comparison with suitable high and low molecular weight model compounds and from 13C dynamic measurements. The splittings of the carbonyl signal were attributed to pentad stereosequences, thus allowing us to demonstrate a slightly predominating syndiotactic arrangement of monomeric units. 13C dynamic measurements are in agreement with an isotropic overall tumbling model

Bis(h5-Cyclopentadienyl)bistriphenylsilanolatozirconium(IV) : a new precursor for ethylene polymerization catalyst

Trialkylsilanols were reported to modify and also to improve the catalytic performance in ethylene polymerization when added to zirconocene/methylaluminoxane (MAO) systems. In order to obtain more information about the chemistry involved, a new stable catalytic precursor was investigated in this work. The precursor bis(eta5-cyclopentadienyl)bistriphenylsilanolatozirconium(IV) [ZrCp2(OSiPh3)2] was compared to ZrCp2(CH3)2 and ZrCp4, which can generate ZrCp2(OSiPh3)2 in situ on triphenylsilanol addition. In ethylene polymerization, ZrCp2(OSiPh3)2 exibits a comparable activity and a larger stability than dicyclopentadienylzirconium complexes. On addition of triphenylsilanol to zirconocenes, the productivity increased and the molecular weight sharply decreased, thus suggesting the occurrence of ligand substitution in solution. The reported results are discussed with reference to the proposed mechanism of ethylene polymerization with the conventional ZrCp2Cl2/MAO system

Methacrylic polymers containing permanent dipole azobenzene chromophores spaced from the main chain: synthesis and characterization

Three photochromic monomers containing a permanent dipole photochromic azobenzene group separated from the methacryloyl moiety by a polymethylene spacer, namely 4-(4-oxy-4'-cyanoazobenzene)but-1-yl methacrylate, 6-(4-oxy-4'-cyanoazobenzene)hex-1-yl methacrylate, and 8-(4-oxy-4'-cyanoazobenzene)oct-1-yl methacrylate, were synthesized in three steps starting from 4-cyanoaniline. These monomers were homopolymerized and copolymerized with an optically active monomer, (-)-menthyl methacrylate, in the presence of AIBN as a radical initiator. The polymeric materials, having a molar content of photochromic units comprised between 5 and 100% and molecular weights of about 15000, were characterized by an almost random distribution of monomeric units and a glass transition temperature ranging from 35 to 131 degrees C. Polymer samples having a content of aromatic units larger than 75% were characterized by a thermotropic liquid crystalline structure, as evidenced by optical microscopy, X-ray diffraction and DSC measurements. Two-dimensional correlations spectroscopy (COSY) allowed an appreciable contribution by intramolecular charge transfer mesomers to the electronic distribution of the azobenzene chromophore to be highlighted