Ab initio and DFT Study on 2H-Isoxazol-5-one: Consequences of Strong Intermolecular Hydrogen-Bond Formation in Supramolecular Structures

Ab initio and density-functional-theory (DFT) calculations on 2H-isoxazol-5-one (A), its linear dimer (LD), cyclic dimer (CD), and cyclic trimer (CT), have been performed with several basis sets in the gas phase, including electron correlation by second-order Møller-Plesset perturbation theory. The calculated complexation energy for the intermolecular H-bonded trimer as well as the corresponding geometric changes are in good agreement with the notion of resonance-assisted intermolecular H-bond formation. Bond distances and angles of the optimized geometry of CT are in accordance with the X-ray-diffraction data found on a trimeric supramolecular complex of parent compound 4-(2-methoxybenzyl)-3-phenyl-4H-isoxazol-5-one. Ab initio and DFT geometry optimizations are also reproducing exactly the large asymmetry in bond angles around the CO group that is systematically present in all literature available X-ray data for analogous heterocyclic penta-atomic compounds.     

Nonlinear pair population analysis: The study of basis‐set dependence

The nonlinear pair population analysis recently introduced as a new means of visualization of bonding in molecules with complex bonding patterns was tested for the assumed sensitivity of calculated populations to the quality of the basis set. The testing was performed on a series of several simple molecules ranging from systems well represented by the classical Lewis model of localized two‐center two‐electron (2c–2e) bonds to electron‐deficient boranes containing three‐center bonding. It has been shown that even if this basis‐set sensitivity is slightly greater than for the closely related linear population analysis the dependence is not important enough to question the usefulness of this new approach for the analysis and visualization of bonding molecular systems. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 127–137, 1999     

Dynamics of macromolecules and nuclear magnetic relaxation: Application of mode-coupling diffusion theory to DNA,proteins and their complexes

A mode-coupling approach has been used to solve the Smoluchowski diffusion equation describing the correlation functions relevant in nuclear magnetic relaxation experiments on biological molecules like protein and DNA. A good reproduction of relaxation patterns for molecules that are fluctuating about three-dimensional structures imposed by secondary motives has been found. Important differences can be explained with the poor statistics collected by numerical simulations that do not contain fluctuations contributing to rates in the ns time-scale, therefore comparable with rotational rates.     

Biodegradation of PVA-based formulations

Investigation of the biodegradability of water soluble poly(vinyl alcohol) (PVA) based blown films was carried out under different lab-scale environmental conditions. In particular respirometric tests were utilized in order to evaluate the biodegradability of PVA films in composting, in modified Sturm test and in soil burial simulation tests. Several microbial inocula present in river water, mature compost, forest and farm soils as well as sewage sludge from municipal and paper mill wastewater treatments plants were utilized for the relevant tests. A mixed PVA-degrading microbial culture was obtained by a common enrichment procedure by using sewage sludge from paper mill as inoculum; this culture was tentatively utilized for the isolation of single PVA-degrading microorganisms. As a first result we can stress that significant biodegradation extent in fairly low incubation time can be obtained only in the presence of acclimated microbial populations such as those deriving from paper mill sewage sludge, in liquid cultures. Nevertheless separation of single degrading microbial species was impossible most likely due to the establishment of symbiotic or commensal interactions between the single components of the PVA-degrading mixed cultures. On the other hand, limited mineralization rates were recorded in solid cultures in the presence of soil or compost. Finally, a mechanism of degradation of polymer chains unlike random or unzipping was suggested in the presence of either PVA-degrading mixed culture and its filtrate by means of viscometric determinations of molecular weight within the time.     

Quantum histories without contrary inferences

In the consistent histories formulation of quantum theory it was shown that it is possible to retrodict contrary properties. We show that this problem do not appear in our formalism of generalized contexts for quantum histories.