(Bis(1,2,4-triazol-1-yl)methane)silver(I) phosphino complexes: structures and spectroscopic properties of mixed-ligand coordination polymers

Adducts of the ligand bis(1,2,4-triazol-1-yl)methane (tz(2)(CH(2))) of the form AgX:tz(2)(CH(2)):ER(3):MeCN (1:1:1:x) (X = NO(3), R = Ph, E = P, As, or Sb, x = 1 or 2; X = NO(2), ClO(4), O(3)SCF(3), E = P, R = Ph, x = 0, 1 or 2; X = NO(3), ClO(4), E = P, R = cy, x = 1; X = ClO(4), E = As, R = Ph, x = 2) and AgNO(3):tz(2)(CH(2)):P(o-tolyl)(3) (2:2:1) have been synthesized and characterized in the solid state and in solution by analyses, spectral (IR, far-IR, (1)H and (13)C NMR, ESI MS data) data, and conductivity measurements. In the one-dimensional polymers (characterized by X-ray studies) AgNO(3):tz(2)(CH(2)):PPh(3):CH(3)CN (1:1:1:1), AgClO(4):tz(2)(CH(2)):PPh(3):CH(3)CN (1:1:1:2), AgNO(3):tz(2)(CH(2)):AsPh(3): CH(3)CN (1:1:1:2), and AgNO(3):tz(2)(CH(2)):SbPh(3):CH(3)CN (1:1:1:2), the silver atom can be regarded as four-coordinate, the tz(2)(CH(2)) ligands behaving as bridging groups rather than chelates, with no pair of ligands being dominant, quasi-trans, in their interactions. The AgNO(3):tz(2)(CH(2)):P(o-tolyl)(3) (2:2:1) adduct is a two-dimensional polymer containing two independent silver atoms, one four-coordinated unsymmetrically by a pair of triazolyl rings, one P(o-tolyl)(3), and a unidentate nitrate and the second by a quasi-symmetrical O(2)NO chelate and a pair of equivalent triazolyl rings.     

Reversal of Clar's Aromatic-Sextet Rule in Ultrashort Single-End-Capped [5,5] Carbon Nanotubes

The three-fold HOMO-LUMO gap oscillation, typical of finite length armchair carbon nanotubes (CNT), has a major effect on the magnetic response of ultrashort, single-end-capped [5,5] carbon nanotubes to a perturbing magnetic field parallel to the main symmetry axis. For the CNT's containing 40, 70, and 100 carbon atoms, for which 100 % of the C=C double bonds can be grouped into aromatic-sextets, i. e., fully or complete Clar networks, large paratropic (antiaromatic) global circulations around the cylindrical axis are predicted at the DFT level of calculation. Local and semi-global diatropic (aromatic) currents of strengths not larger than that of the benzene molecule are determined for a perpendicular perturbing magnetic field. CNTs of intermediate lengths do not display this enhanced antiaromatic response. The paratropic current flow clearly shows that these complete Clar networks can be viewed as stacked cycloparaphenylene belts, each providing a double annulene circuit as a consequence of the quinoidal resonance structure that results from their closure. Paradoxically, the fully aromatic Clar structure itself is responsible for the enhanced global antiaromaticity.     

Some advances in the knowledge of grape, wine and distillates chemistry as achieved by mass spectrometry

Mass spectrometry plays a very important role in acquiring knowledge of the chemistry of grape and its derivative products. By liquid mass spectrometry, anthocyanins of grape were studied, and in hybrid grape extracts, delphinidin, cyanidin, petunidin and malvidin 3-O-(6-O-p-coumaroyl)-5-O-diglucosides were found. A semiquantitative procedure to estimate the amounts and percentages of monoglucoside and diglucoside anthocyanins without chromatography was developed. By gas chromatography mass spectrometry (GC/MS), aroma compounds of grape, wine and the distillate Italian grappa were studied, and molecular structures characterized. The representative aroma profile of Muscat grape was characterized by 23 terpenols, present in both free and bonded form, and direct correlation between aroma and genetic profile permitted to distinguish between different Muscat grape varieties. Aroma of Italian grappa resulted from and was characterized by several compounds linked to the grape variety, such as vitispiranes, terpenols, ethyl cinnamate, salicylic esters, benzaldehyde and farnesol. Synthesis of O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) derivatives and GC/MS analysis resulted in a sensitive and selective method to study carbonyl compounds at the low levels occurring in wine.     

A quantitative approach to the recycling of alpha-tocopherol by coantioxidants

A systematic investigation is reported on the regeneration of alpha-tocopherol (alpha-TOH) in homogeneous solution by coantioxidants in order to better understand the mechanism and the factors responsible for the effectiveness of this process. The current availability of thermochemical data concerning the reactants involved in the regeneration reactions, as well as a large number of the kinetic constants for the various reactions involved, allowed us to rationalize the experimental observations collected so far. Three limiting cases have been considered. The first case is that of a coantioxidant irreversibly regenerating alpha-TOH, where the effectiveness of the recycling process depends on the magnitude of the rate constant k(r). The second case is that of a coantioxidant reversibly recycling alpha-TOH, where regeneration can only be observed if the bond dissociation enthalpy value of the coantioxidant is lower or at least close to that of the O-H bond of alpha-tocopherol. The third case is that of a catechol derivative (chosen as a model compound for polyphenolic antioxidants), where recycling of alpha-TOH is feasible even though the BDE value is significantly higher than that of vitamin E. In this case, the driving force for the recycling process is the removal of the semiquinone radical from the catechol derivative by the alpha-tocopheroxyl radical, which makes the regeneration of alpha-TOH practically irreversible.     

Synthesis of 4,5-dihydro-2,4-benzoxazepin-3( 1H)ones and 1,3,4,5-tetrahydro-2,4-benzoxazepines

o- Aminomethylbeiizyl alcohols (X) easily cyclize with phosgene in an aqueous alkaline medium to form 4,5-dihydro-2,4-benzoxazepin-3(1H)ones (IV) and with aldehydes in acidic conditions to yield 1,3,4,5-tetrahydro-2,4-benzoxazepines (V). The characteristics and chemical behaviour of these new heterocyclic ring systems are reported.     

Comparison of thermodynamic properties of coarse-grained and atomic-level simulation models.

Thermodynamic data are often used to calibrate or test amomic-level (AL) force fields for molecular dynamics (MD) simulations. In contrast, the majority of coarse-grained (CG) force fields do not rely extensively on thermodynamic quantities. Recently, a CG force field for lipids, hydrocarbons, ions, and water, in which approximately four non-hydrogen atoms are mapped onto one interaction site, has been proposed and applied to study various aspects of lipid systems. To date, no extensive investigation of its capability to describe salvation thermodynamics has been undertaken. In the present study, a detailed picture of vaporization, solvation, and phase-partitioning thermodynamics for liquid hydrocarbons and water was obtained at CG and AL resolutions, in order to compare the two types or models and evaluate their ability to describe thermodynamic properties in the temperature range between 263 and 343 K. Both CG and AL models capture the experimental dependence of the thermodynamic properties on the temperature, albeit a systematically weaker dependence is found for the CG model. Moreover, deviations are found for solvation thermodynamics and for the corresponding enthalpy-entropy compensation for the CG model. Particularly water/oil repulsion seems to be overestimated. However, the results suggest that the thermodynamic properties considered should be reproducible by a CG model provided it is reparametrized on the basis of these liquid-phase properties.     

Value at Ruin and Tail Value at Ruin of the Compound Poisson Process with Diffusion and Efficient Computational Methods

We analyze the insurer risk under the compound Poisson risk process perturbed by a Wiener process with infinite time horizon. In the first part of this article, we consider the capital required to have fixed probability of ruin as a measure of risk and then a coherent extension of it, analogous to the tail value at risk. We show how both measures of risk can be efficiently computed by the saddlepoint approximation. We also show how to compute the stabilities of these measures of risk with respect to variations of probability of ruin. In the second part of this article, we are interested in the computation of the probability of ruin due to claim and the probability of ruin due to oscillation. We suggest a computational method based on upper and lower bounds of the probability of ruin and we compare it to the saddlepoint and to the Fast Fourier transform methods. This alternative method can be used to evaluate the proposed measures of risk and their stabilities with heavy-tailed individual losses, where the saddlepoint approximation cannot be used. The numerical accuracy of all proposed methods is very high and therefore these measures of risk can be reliably used in actuarial risk analysis.