Antonio Rojas

Rate constants and equilibria of monochelate formation of iron(III) with 2-acetylcyclohexanone

Kinetics and equilibria in aqueous 1:1 chelation of iron(III) by 2-acetylcyclohexanone have been investigated spectrophotometrically in aqueous solution at 25°C and 0.5 mol dm-3 NaClO4. In conjunction with earlier work, the results suggest that the deprotonation rate of the keto tautomer of 2-acetylcyclohexanone has a minimum value when compared with 1,3-dicarbonylic ligands of similar structure. The mechanism proposed to account for the kinetic data involves pathways in which both Fe3+ and Fe(OH)2+ react with the enol tautomer of the ligand. The relative rates of complex formation are shown to depend not only on the metal species involved but also on ligand structure factors such as steric hindrances, ring strain and intramolecular hydrogen bonding.

Innovations in the brewing industry: light beer

Abstract The demand for light beers has led brewers to innovate by developing light beer. However, these products are not widely accepted in Europe compared to North America and Australasia because of their lack of fullness in the taste and low bitterness compared with conventional beer. The lower levels of some important compounds, present in light beer, can explain these features since they are responsible for the characteristics of the beer. These include alcohol soluble proteins, oligosaccharides, glycerol, polyphenols, iso-α-acids, fusel alcohols and trihydroxy fatty acids. Light beer is produced by several methods, the most commonly used is the addition of glucoamylase to the wort before or during fermentation. This enzyme metabolizes residual carbohydrates (mainly dextrins) transforming them into fermentable sugars and reducing the caloric and alcohol content in this type of beer. Recently pilot studies have been carried out with genetically engineered yeast strains in which amylolytic genes are introduced into the yeast genome in order to metabolize carbohydrate residues. When introducing amylolytic genes, a better fermentability occurs although the fullness of flavor still becomes reduced.