Phytotoxic metabolites by nine species of Botryosphaeriaceae involved in grapevine dieback in Australia and identification of those produced by Diplodia mutila,Diplodia seriata,Neofusicoccum australe and Neofusicoccum luteum

Botryosphaeria dieback is one of the main trunk diseases of grapevine caused by several species of Botryosphaeriaceae. Twenty-four fungal isolates representing the eight most widespread and most virulent Botryosphaeriaceae were tested for their ability to produce phytotoxic metabolites. The chromatographic profiles of their culture filtrates organic extracts showed the ability of all isolates to produce several and different metabolites. When tested on grapevine leaves and tomato cuttings the organic extracts phytotoxicity varied among isolates and species. To our knowledge, this is the first study on phytotoxic compounds produced by Botryosphaeriaceae species found in Australian vineyards. The phytotoxic metabolites produced by Diplodia seriata, Diplodia mutila, Neofusicoccum australe and, for the first time, by Neofusicoccum luteum were isolated and chemically identified essentially by spectroscopic methods.

     

Understanding the orientation and dynamic motion of planar heterocyclic N-donor ligands by exploiting the symmetry properties of mixed-ligand mu-oxorhenium(V) dinuclear complexes

Factors influencing the orientation and dynamic motions of planar N-donor heterocyclic ligands (L) are of interest since such features have broad relevance in metallobiochemistry [Marzilli, L. G.; Marzilli, P. A.; Alessio, E. Pure Appl. Chem. 1998, 70, 961-968]. We found that mu-oxorhenium(V) dinuclear complexes [ReOCl2LsLt]-O-[ReOCl2LsLt] bearing either symmetrical (L = py = pyridine; 3,5-lut = 3,5-lutidine) or lopsided (L = Me3-Bzm = 1,5,6-trimethylbenzimidazole) cis L ligands are particularly useful for studying these factors. NMR data showed that terminal (Lt) and stacked (Ls) ligands were exchanged by approximately 180 degrees rotation about the Re-O-Re bond system. Such exchange occurred, however, between degenerate chiral conformers. Here we report a combined X-ray structural and solution NMR investigation of the AA + CC (racemic) and AC (meso) forms of two mixed-ligand mu-oxorhenium dimers that bear one lopsided and one symmetrical ligand on each Re atom, namely, Re2O3-Cl4(py)2(Me3Bzm)2 (1rac and 1meso) and Re2O3Cl4(3,5-lut)2(Me3Bzm)2 (2rac and 2meso). The presence of two different cis L ligands in 1 and 2 breaks the local symmetry at each Re atom, so that, in the racemic dimers, the exchange of terminal and stacked ligands leads to nondegenerate conformers. Overall, NMR data showed that the unsymmetrical dimers 1 and 2 undergo two dynamic processes contemporaneously, namely, 180 degrees rotation about the Re-N(py or 3,5-lut) bond and coupled rotation about the Re-O-Re/Re-N bonds. Both processes reach the slow exchange limit below -80 degrees C. Rotation of py in 1 occurs faster than that of 3,5-lut in 2; this difference is attributed to the higher steric demands of 3,5-lut compared to py. For both dimers NMR data provided compelling evidence of the preferred conformers in solution, including ligand orientations. The low-T solution structure of 1meso and 2meso is chiral, the same as that found in the solid state for 2meso, where the Me3Bzm on one Re atom is stacked with the 3,5-lut on the other Re atom. The remaining Me3Bzm and 3,5-lut, one on each Re atom, are both terminal. In solution the coupled Re-O-Re/Re-N rotations interconvert the two halves of each meso dimer to yield the same overall stable chiral conformation. For the racemic dimers, however, this process does not interconvert one enantiomer into the other, but instead interconverts two rotamers, R1 and R2, each of which is chiral. We found that, in the case of both 1rac and 2rac, the conformer with stacking symmetrical ligands (R1) is roughly 1 order of magnitude more stable than that with stacking Me3Bzm ligands (R2). Moreover, the solution conformation of R1 is the same as that found in the solid state of 1rac. Solution- and solid-state data indicate that the key interaction favoring the observed conformations is very likely the electrostatic attraction between the delta+ H2 atoms on the Me3Bzm ligands and the negative O and Cl groups in the core of the dimers. Finally, for both meso and racemic dimers we were also able to elucidate the preferred pathways of the coupled dynamic motions and establish that, very likely, the two halves of the dimers swing back and forth by approximately 130 degrees through the anti eclipsed form.     

Metalloporphyrins as chemical shift reagents: the unambiguous NMR characterization of the cis- and trans-isomers of meso-(bis)-4′-pyridyl-(bis)-4′-carboxymethylphenylporphyrins

The condensation of pyrrole with 4-pyridylcarboxyaldehyde and methyl 4-formyl benzoate under Adler-Longo conditions yielded the series of meso-(4′-pyridyl)/(4′-carboxymethylphenyl)porphyrins as a mixture. Careful column chromatography afforded each isomer in pure form. In this paper we focus on the two bis-substituted isomeric meso-porphyrins, 5,10-bis(4′-pyridyl)-15,20-bis(4′-carboxymethylphenyl)porphyrin and 5,15-bis(4′-pyridyl)-10,20-bis(4′-carboxymethylphenyl)porphyrin, respectively, 4′-cis and 4′-transDPyDMeP. The assignment of the geometry of the two isomers was performed by ¹H NMR spectroscopy on the trinuclear adducts [(4′-cisDPyDMeP){Ru(TPP)(CO)}₂] and [(4′-transDPyDMeP){Ru(TPP)(CO)}₂], obtained by selective coordination of [Ru(TPP)(CO)(EtOH)] (TPP=tetraphenylporphyrin) to the peripheral nitrogen atoms. The axially bound ruthenium porphyrins act as chemical shift reagents on the central porphyrin, allowing a clear distinction of the pyrrole proton resonances and consequent unambiguous assignment of the geometry of each isomer based upon symmetry considerations.     

Optimization of membrane area and catalyst distribution in a permeative-stage membrane reactor for methane steam reforming

Methane steam reforming to produce high purity hydrogen is conveniently carried out in membrane reactors. The interest on this process has led to several studies about the influence of the key operating variables on the system performances. In the present paper we focus on the optimization of the catalyst and membrane area axial distribution by computer simulation. To this purpose, a numerical model of a permeative-stage membrane reactor (PSMR), a system composed of traditional reactive and membrane permeative stages laid out in alternated series, has been developed. This is based on 1D mass, momentum and energy balances including thermal effects on all the system properties. First, an equi-sized nine-stage PSMR is analyzed at various temperatures and membrane thicknesses, in comparison with a conventional membrane reactor, showing that improved performances, especially in terms of methane conversion, can be obtained. Then, considering the stage lengths as design variables, the optimal system performances are determined by maximizing two objective functions, namely the methane conversion and the hydrogen recovery factor. Different optimal length distributions are found utilizing the two criteria, corresponding to privileged kinetic or permeative aspects. In comparison to the conventional MR, the PSMR leads to a higher conversion and lower recovery factor when the conversion is maximized, whilst the opposite situation occurs when maximizing the recovery factor. Furthermore, the role of the heat exchange area between the furnace and the reactor is studied, considering a PSMR with adiabatic permeative stages. From this case, it is possible to see that the greater advantage of this apparatus (having the same membrane area, catalyst amount and heat-exchange area as the MR) consists in a much higher recovery factor (+21% ca.), which at the end demonstrates to be the most convenient objective function by means of the introduction of an overall performance index, identified as the hydrogen recovery yield. Therefore, the analysis proposed in the present paper shows that the reactive/permeative stage distribution has to be considered an important reactor design parameter, which can be opportunely modified to improve the performances of the process.     

Effects of multiple-stage membrane process designs on the achievable performance of automatic control

There is limited information from literature on the dynamic operability of membrane processes with multiple stages or loops. Such information is useful for assessing the performance achievable by an automatic controller proposed for a process design before the actual controller is implemented. Based on dynamic modeling of an industrial whey ultrafiltration process with an increasing number of stages up to a maximum of 12, the dynamic responses of the flowrate and concentration of the retentate were obtained. Features of the dynamic responses were used to determine the performance, in terms of quality and speed, that can be achieved by automatic controllers. In particular, limitations on the performance are indicated by features of dynamic responses such as effective time delay and inverse responses. Changes in effective time delay and inverse responses with the number of stages in the whey ultrafiltration process demonstrate a trade-off between process performance and control performance. This trade-off should be considered during process and controller design to maximize the economic return from the production of whey protein concentrates.     

Sample covariance shrinkage for high dimensional dependent data

For high dimensional data sets the sample covariance matrix is usually unbiased but noisy if the sample is not large enough. Shrinking the sample covariance towards a constrained, low dimensional estimator can be used to mitigate the sample variability. By doing so, we introduce bias, but reduce variance. In this paper, we give details on feasible optimal shrinkage allowing for time series dependent observations.     

An exact approach to sparse principal component analysis

We show a branch and bound approach to exactly find the best sparse dimension reduction of a matrix. We can choose between enforcing orthogonality of the coefficients and uncorrelation of the components, and can explicitly set the degree of sparsity. We suggest methods to choose the number of non-zero loadings for each component; illustrate and compare our approach with existing methods through a benchmark data set.     

Probabilistic approach for break-up and coalescence in bubbly-flow and coupling with CFD codes

In this paper, a CFD model for bubbly-flow including break-up and coalescence is discussed. The probabilistic method, developed according to this model, is tested for an industrial configuration: numerical bubble-size distributions are compared with those derived by experiments.