Dissociation Energy Computations for Saline Bonds Implied in Interactions Mediated by Peptidoglicans

Summary: Dissociation energy and hydration energy calculations, in water solution, are presented for saline bonds mediated by Ca²⁺ and Mg²⁺ ions with Brőnstedt type bases ( COO ,  OSO₃ ,  OH). A computationally intensive method, Polarisable Continuum Model (PCM) using 6-31G^* basis set, was applied. Hydration energies were computed by various methods, as well as dissociation energies of some L₂M complexes. L₂Ca complexes result as more stable against dissociation than L₂Mg complexes. Hydration energy calculation results, for some of the methods, here used, seem rather reliable as compared to experimental results.     

Sorption-desorption behavior of bispyrazolato-copper(II) 1D coordination polymers

A new polycrystalline vapochromic polymorph of the one-dimensional copper bispyrazolate polymer reversibly and selectively absorbs a number of small molecules; the crystal structures of the anhydrous and fully hydrated species, determined by powder diffraction methods, are markedly different despite their simple, fast, and reversible interconversion.     

Kinematic Viscosities of Binary Liquid Mixtures of 2-Butanone with 1,2-Propanediol

Kinematic viscosities of the binary 2-butanone (1) + 1,2-propanediol (2) solvent system have been measured for mixtures covering the whole miscibility range expressed by 0 x _i 1, at 19 temperatures in the range –10 t/°C 80. The measured values have been used to test empirical equations that express the kinematic viscosities as functions of the composition and temperature. Excess kinematic viscosities (^E) have also been calculated. Sign and magnitude of these quantities are discussed in terms of type and nature of specific intermolecular interactions. Furthermore, derived quantities such as thermodynamic parameters of viscous flow (G, H and S), are analyzed on the basis of Eyring's model. All the investigated excess mixing properties indicate the probable existence of stable two-component adducts in this binary solvent system.     

Model studies toward the synthesis of dihydropyrimidinyl and pyridyl alpha-amino acids via three-component Biginelli and Hantzsch cyclocondensations

A novel and versatile strategy for the synthesis of heterocyclic alpha-amino acids has been described. The use of components (aldehyde or beta-ketoester) bearing a masked glycinyl moiety in Biginelli and Hantzsch cyclocondensations allowed access to the 4-dihydropyrimidinyl-alpha-glycines, 4-dihydropyrimidinyl-alpha-alanines, 4-pyridyl-alpha-alanines, and 2-pyridyl-alpha-alanines classes. Dihydropyrimidinyl-amino acids were obtained as a mixture of diastereoisomers due to the formation of the stereocenter at C4 of the dihydropyrimidinone ring. Individual stereoisomers were isolated as pure compounds and their structures were assigned with the aid of X-ray crystallography and chiroptical properties. The enantiomeric purity of a representative selection of the above amino acids was greater than 96% as verified by derivatization to the corresponding Mosher's amides and subsequent (1)H and (19)F NMR spectroscopy. Incorporation of the 4-pyridyl-alpha-alanine derivative into a peptide chain is also described.     

A counterintuitive, yet efficient synthesis of bis(indenyl)zirconium dihalides

The use of bisindenyl zirconium dimethyl in the synthesis of the corresponding dihalides is described. The synthesis of Ind₂ZrCl₂ has been carried out, cleanly and quantitatively, by chlorination of Ind₂ZrMe₂ (2) with a variety of inorganic chlorides, including BCl₃, SCl₂ in either toluene or methylene chloride, and HCl in Et₂O. The latter method is the preferred one, since it produces methane as the only byproduct, and the formed Ind₂ZrCl₂ precipitates quantitatively from the Et₂O solvent: a simple filtration then gives the analytically pure product in quantitative yield. Ind₂ZrBr₂ and Ind₂ZrI₂ are obtained by reacting 2 with Br₂ and I₂, respectively. The ‘inverse’ synthesis of metallocene dichlorides by chlorination of their dimethyl ‘derivatives’ has advantages compared to the classic method: first, Ind₂ZrCl₂ is obtained in higher yield (90-96%); second, it is easier to purify (at the dimethyl stage) and is obtained free from LiCl. Five bisindenyl zirconium complexes with different sigma ligands have been investigated in solution propylene polymerizations: it is found that the σ-ligands have no relevant influence on the catalyst activity, nor on the polymer properties.     

Preparation of highly dispersed CuO catalysts on oxide supports for de-NO(x) reactions

CuO based catalysts dispersed on silica-alumina supports at low (0.56 wt.%) and high (13 wt.%) Al(2)O(3) content were prepared by adsorption method with or without ultrasound treatment. The catalysts obtained were studied in their bulk (atomic absorption, X-ray diffraction, temperature programmed reduction) and surface (N(2) adsorption and X-ray photoelectron spectroscopy) properties. Significant differences between the series of catalysts prepared over the two supports in terms of size of the CuO aggregates and of their redox properties were evidenced. All the catalysts were tested in the selective catalytic reduction of NO(x) using C(2)H(4) as reducing species (HC-SCR process) in highly oxidant atmosphere. The CuO-catalysts prepared using ultrasounds were the most active. Moreover, they displayed a peculiar activity being able to activate NO both by reducing it to N(2), in larger extent, and by oxidizing it to NO(2).     

New interpretation of local dynamics of poly(dimethyl siloxane) observed by quasielastic neutron scattering

Synthetic and natural polymers have complex dynamic behavior with distinct motions taking place on a wide range of time and length scales. For poly(dimethyl siloxane) we show that, at temperatures above the melting point, the reorientation of the CH3 groups provides a non-negligible contribution to the incoherent dynamic structure factor. Analysis of the quasielastic neutron scattering data is carried out using a model function that includes fast rotational motion of the CH3 groups and local conformational transitions between isomeric states. By using this model, detailed comparison between experimental data and theoretical predictions at distances where deviations from the traditional Rouse model are expected becomes possible.     

Secondary ion mass spectrometry and X-ray photoelectron spectroscopy investigation on chemical vapor deposited CeO(2-)ZrO(2)-TiO(2) thin films

Mixed CeO(2)-ZrO(2) systems have attracted widespread interest for their use in three-way catalyst (TWC) technology for automotive exhaust conversion to non-toxic products. In this work, CeO(2)-ZrO(2) thin films were deposited, via chemical vapor deposition, in order to obtain nanoscale materials with a high surface-to-volume ratio, with precise control of system properties. The addition of TiO(2) as buffer layer was also investigated. Cordierite was chosen as substrate, being the usual refractory material for catalytic mufflers. The multilayers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). In particular, the combination of SIMS and XPS allowed us to investigate both surface and in-depth chemical composition, studying also film-intermixing phenomena induced by annealing processes.     

The synthesis of pyrazolo[1,2-a]pyrazoles. Regio- and stereo-selective 1,3-dipolar cycloadditions of (1Z)-rel-(4R,5R)-1-arylmethylene-4-benzoylamino-5-phenyl-3-pyrazolidinon-1 -azomethinimines

Reaction of rel-(4R,5R)-4-benzoylamino-5-phenyl-3-pyrazolidinone (4) with aromatic aldehydes 5a-f gave the corresponding (1Z)-rel-(4R,5R)-1-arylmethylene-4-benzoylamino-5-phenyl-3-pyrazolidinon-1-azomethinimines 6a-f . 1,3-Dipolar cycloadditions of azomethinimines 6a-f to various dipolarophiles, which were found to proceed regio- and stereo-selectively, afforded the corresponding pyrazolo[1,2-a]-pyrazoles 8a-f, 10 , and 13–16 . Reaction of azomethinimine 6a with hydrogen cyanide gave rel-(5R,6R)-6-benzoylamino-5,6-dihydro-3,5-diphenyl-1-oxo-1H,7H-pyrazolo[1,2-a][1,2,3]triazole (18) as a representative of a new ring system.