Multivariate analysis of the polyphenol composition of Tempranillo and Graciano red wines

Vitis vinifera L. cv Graciano is often used as a blending partner of Tempranillo based wines because it is considered to contribute significantly to the quality. The aim of this study is to discriminate between Tempranillo and Graciano monovarietal wines, and those made by the incorporation of 20% of Graciano variety in two different stages (at the end of malolactic fermentation and mixing the two grape varieties in the pre-fermentative maceration stage) of the winemaking process of the Tempranillo variety. To achieve this, supervised and unsupervised pattern recognition tools were applied to the data obtained in the study of the detailed polyphenolic composition, colour and other oenological parameters (143 variables). Patterns related to stages in the winemaking and ageing process, different wines and vintages can be observed using principal component analyses. Furthermore, linear discriminant analysis has been applied in order to characterise the wine samples. From the 143 variables, flavan-3-ols have exerted a profound influence on wine differentiation.     

Nickel‐Catalyzed Chemo‐, Regio‐ and Diastereoselective Bond Formation through Proximal CC Cleavage of Benzocyclobutenones

The first catalytic intermolecular proximal C1? C2 cleavage of benzocyclobutenones (BCB) without prior carbonyl activation or employing noble metals has been developed. This protocol operates at room temperature and is characterized by an exquisite chemo‐, regio‐ and diastereoselectivity profile, constituting a unique platform for preparing an array of elusive carbocyclic skeletons.     

Phase transfer catalysis using chiral catalysts. V. Asymmetric nucleophilic substitutions with C,O, N and S-anions

Several asymmetric nucleophilic substitutions with C, N, O and S-anions have been performed under PTC conditions using chiral quaternary ammonium salts as PT catalysts.     

Cross-coupling reactions of organosilicon compounds in the stereocontrolled synthesis of retinoids

This paper presents a full account of the use of Hiyama cross-coupling reactions in a highly convergent approach to retinoids in which the key step is construction of the central C10-C11 bond. Representatives of two families of oxygen-activated dienyl silanes (ethoxysilanes and silanols) and of all reported families of "safety-catch" silanols (siletanes, silyl hydrides, allyl-, benzyl-, aryl-, 2-pyridyl- and 2-thienylsilanes) were regio- and stereoselectively prepared and stereospecifically coupled to an appropriate electrophile by treatment with a palladium catalyst and a nucleophilic activator. Both all-trans and 11-cis-retinoids, and their chain-demethylated analogues, were obtained in good yields regardless of the geometry (E/Z) and of the steric congestion in each fragment. This comprehensive study conclusively establishes the Hiyama cross-coupling reaction, with its mild reaction conditions and stable, easily prepared, ecologically advantageous silicon-based coupling partners, as the most effective route to retinoids reported to date.     

On the Structure and Stability of the Set of Solutions of a Nonlocal Problem Modeling Ohmic Heating

In this work we analyze the existence, structure and stability of the set of positive solutions of a nonlocal elliptic boundary value problem modeling Ohmic heating. By regarding the total electric current flowing through the device by unit of cross-sectional area as the continuation parameter, we show that the set of steady states is constituted by a finite number of differentiable curves. Moreover, the instability index of a steady state changes by 1 when we pass through by a turning point and does not change if we pass through an hysteresis point. Some sufficient conditions so that the model admit a positive steady state for each value of the parameter, as well as for uniqueness and non-existence, will be also given.