Toward the complete prediction of the 1H and 13C NMR spectra of complex organic molecules by DFT methods: application to natural substances

The NMR parameters (1H and 13C chemical shifts and coupling constants) for a series of naturally occurring molecules have been calculated mostly with DFT methods, and their spectra compared with available experimental ones. The comparison includes strychnine as a test case, as well as some examples of recently isolated natural products (corianlactone, daphnipaxinin, boletunone B) featuring unusual and/or crowded structures and, in the case of boletunone B, being the subject of a recent revision. Whenever experimental spectra were obtained in polar solvents, the calculation of NMR parameters was also carried out with the Integral Equation-Formalism Polarizable Continuum Model (IEF-PCM) continuum method. The computed results generally show a good agreement with experiment, as judged not only by statistical parameters but also by visual comparison of line spectra. The origin of the remaining discrepancies is attributed to the incomplete modeling of conformational and specific solvent effects.     

A miniaturized kit for ozone biomonitoring

A new miniaturized kit based on very young supersensitive tobacco Bel-W3 plantlets, which can be easily used to detect phytotoxic levels of ozone in ambient air in large scale surveys, is described. It has been developed in laboratory as well as field studies. The optimal sampling time is 5–7 d. The advantages of the kit are its user-friendliness, low cost, and reliability. The kit may be integrated by a passive sampling tube set and may be also proposed for educational programs.     

Ecological assessment of Santa Giusta Lagoon (Sardinia,Italy)

The general environmental conditions of Santa Giusta Lagoon, an important Sardinian coastal lagoon often affected by dystrophic crises, are examined. The study considers both the monitoring data collected over the past ten years on the relevant water quality parameters and the preliminary results on the structure and heavy metal content of the surface sediments of the lagoon. These data emphasised its elevated trophic level, due to the excessive presence of plant nutrients in water, and a relative low level of heavy metal contamination. At the moment, the eutrophy--brought about the urban and industrial wastes from Oristano and Santa Giusta--can be considered the main environmental issue of the lagoon.     

Computer simulation of solid and liquid benzene with an atomistic interaction potential derived from ab initio calculations

Molecular dynamics atomistic simulations of solid and liquid benzene have been performed, employing a model intermolecular potential derived from quantum mechanical calculations. The ab initio database includes approximately 200 geometries of the benzene dimer with interaction energies computed at the MP2 level of theory. The accuracy of the modeled force field results is satisfactory. The thermodynamic and structural properties, calculated in the condensed phases, are compared with experimental data and previous simulation results. Single particle and collective dynamical properties are also investigated through the calculation of translational and rotational diffusion coefficients, reorientational dynamics, and viscosities. The agreement of these data with experimental measurements confirms the reliability of the proposed force field.     

Kinetics of chalcone oxidation by peroxide anion catalysed by poly-l-leucine

An insight into the kinetics, mechanism and optimum reaction conditions of the Julia-Colonna epoxidation has been gained using a soluble polyleucine catalyst.     

From linear to nonlinear PGD-based parametric structural dynamics

The present paper analyzes different integration schemes of solid dynamics in the frequency domain involving the so-called Proper Generalized Decomposition – PGD. The last framework assumes for the solution a parametric dependency with respect to frequency. This procedure allowed introducing other parametric dependences related to loading, geometry, and material properties. However, in these cases, affine decompositions are required for an efficient computation of separated representations. A possibility for circumventing such difficulty consists in combining modal and harmonic analysis for defining an hybrid integration scheme. Moreover, such a procedure, as proved in the present work, can be easily generalized to address nonlinear parametric dynamics, as well as to solve problems with non-symmetric stiffness matrices, always operating in the domain of low frequencies.     

Correction of wandering smoothing effects on static measurements of a wing-tip vortex

Wandering is a typical feature of wing-tip vortices and it consists in random fluctuations of the vortex core. Consequently, vortices measured by static measuring techniques appear to be more diffuse than in reality, so that a correction method is needed. In the present paper statistical simulations of the wandering of a Lamb-Oseen vortex are first performed by representing the vortex core locations through bi-variate normal probability density functions. It is found that wandering amplitudes smaller than 60% of the core radius are well predicted by using the ratio between the RMS value of the mean cross-velocity and its slope measured at the mean vortex center. Furthermore, the principal axes of wandering can be accurately evaluated from the opposite of the cross-correlation coefficient between the spanwise and the normal velocities measured at the mean vortex center. The correction of the wandering smoothing effects is then carried out through four different algorithms that perform the deconvolution of the mean velocity field with the probability density function that represents the wandering. The corrections performed are very accurate for the simulations with wandering amplitudes smaller than 60% of the core radius, whereas errors become larger with increasing wandering amplitudes. Subsequently, the whole procedure to evaluate wandering and to correct the mean velocity field is applied to static measurements, carried out with a fast-response five-hole pressure probe, of a tip vortex generated from a NACA 0012 half-wing model. It is found that the wandering is predominantly in the upward-outboard to downward-inboard direction. Furthermore, the wandering amplitude grows with increasing streamwise distance from the wing, whereas it decreases with increasing angle of attack and free-stream velocity.     

Optical co-ordinates in general relativity 2 — the problem of distance

Summary Let denote the congruence of null geodesics associated with a given optical observer inV ₄. We prove that determines a unique collection of vector fieldsM₍₎ ( =1, 2, 3) and ₍₀₎ overV ₄, satisfying a weak version of Killing's conditions.This allows a natural interpretation of these fields as the infinitesimal generators of spatial rotations and temporal translation relative to the given observer. We prove also that the definition of the fieldsM₍₎ and ₍₀₎ is mathematically equivalent to the choice of a distinguished affine parameter f along the curves of, playing the role of a retarded distance from the observer.The relation between f and other possible definitions of distance is discussed.

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Sommario Sia la congruenza di geodetiche nulle associata ad un osservatore ottico assegnato nello spazio-tempoV ₄. Dimostriamo che determina un'unica collezione di campi vettorialiM₍₎ ( =1, 2, 3) e ₍₀₎ inV ₄ che soddisfano una versione in forma debole delle equazioni di Killing. Ciò suggerisce una naturale interpretazione di questi campi come generatori infinitesimi di rotazioni spaziali e traslazioni temporali relative all'osservatore assegnato. Dimostriamo anche che la definizione dei campiM₍₎, ₍₀₎ è matematicamente equivalente alla scelta di un parametro affine privilegiato f lungo le curve di, che gioca il ruolo di distanza ritardata dall'osservatore. Successivamente si esaminano i legami tra f ed altre possibili definizioni di distanza in grande.

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Work performed in the sphere of activity of: Gruppo Nazionale per la Fisica Matematica del CNR.     

On the carrier properties of perfluoropolyether-betaine mixed vesicles: the contribution of electron spin resonance spectroscopy

The carrier properties of mixed unilamellar vesicles of fluorocarbon-hydrocarbon surfactants built up with the ammonium salt of a perfluoropolyether and n-dodecylbetaine were investigated by electron spin resonance spectroscopy (ESR). The ESR-active lipophilic nitroxide 5-doxylstearic acid (5-DSA) was used as a model of a lipophilic drug to be carried and delivered into cell membranes. Healthy and malignant colorectal tissues were used as the target cells. Cell suspensions of living tissues were studied in physiological conditions. For the maintenance of the surgically removed tissues, McCoy’s 5A culture medium was used. 5-DSA probe was rapidly delivered from perfluoropolyether (PFPE)/betaine mixed vesicles to the membranes of both healthy and malignant colorectal cells. The analysis of the computed 5-DSA ESR line shapes ensured that no spectral differences occurred when 5-DSA was either introduced directly into the cells or through the intervention of vesicles. This well agreed for an unmodified physical status of the membranes where the probe was mainly localized.