Liesegang patterns: Effect of dissociation of the invading electrolyte

The effect of dissociation of the invading electrolyte on the formation of Liesegang bands is investigated. We find, using organic compounds with known dissociation constants, that the spacing coefficient, 1+p, that characterizes the position of the n-th band as x_n ~ (1+p)^n, decreases with increasing dissociation constant, K_d. Theoretical arguments are developed to explain these experimental findings and to calculate explicitly the K_d dependence of 1+p.Comment: RevTex, 8 pages, 3 eps figure

Formation of Liesegang patterns: A spinodal decomposition scenario

Spinodal decomposition in the presence of a moving particle source is proposed as a mechanism for the formation of Liesegang bands. This mechanism yields a sequence of band positions x_n that obeys the spacing law x_n~Q(1+p)^n. The dependence of the parameters p and Q on the initial concentration of the reagents is determined and we find that the functional form of p is in agreement with the experimentally observed Matalon-Packter law.Comment: RevTex, 4 pages, 4 eps figure

Rhodococcus opacus B4: a promising bacterium for production of biofuels and biobased chemicals

Bacterial lipids have relevant applications in the production of renewable fuels and biobased oleochemicals. The genus Rhodococcus is one of the most relevant lipid producers due to its capability to accumulate those compounds, mainly triacylglycerols (TAG), when cultivated on different defined substrates, namely sugars, organic acids and hydrocarbons but also on complex carbon sources present in industrial wastes. In this work, the production of storage lipids by Rhodococcus opacus B4 using glucose, acetate and hexadecane is reported for the first time and its productivity compared with Rhodococcus opacus PD630, the best TAG producer bacterium reported. Both strains accumulated mainly TAG from all carbon sources, being influenced by the carbon source itself and by the duration of the accumulation period. R. opacus B4 produced 0.09 and 0.14 g L1 at 24 and 72 h, with hexadecane as carbon source, which was 2 and 3.3 fold higher than the volumetric production obtained by R. opacus PD630. Both strains presented similar fatty acids (FA) profiles in intact cells while in TAG produced fraction, R. opacus B4 revealed a higher variability in fatty acid composition than R. opacus PD630, when both strains were cultivated on hexadecane. The obtained results open new perspectives for the use of R. opacus B4 to produce TAG, in particular using oily (alkane-contaminated) waste and wastewater as cheap raw-materials. Combining TAG production with hydrocarbons degradation is a promising strategy to achieve environmental remediation while producing added value compounds.This work was financially supported by the Portuguese Science Foundation (FCT) and European Social Fund (ESF, POPH-QREN) through the Grant given to A.R. Castro (SFRH/BD/64500/2009), the FCT Strategic Project of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684) and project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462)

Metabolic constituents of grapevine and grape-derived products

The numerous uses of the grapevine fruit, especially for wine and beverages, have made it one of the most important plants worldwide. The phytochemistry of grapevine is rich in a wide range of compounds. Many of them are renowned for their numerous medicinal uses. The production of grapevine metabolites is highly conditioned by many factors like environment or pathogen attack. Some grapevine phytoalexins have gained a great deal of attention due to their antimicrobial activities, being also involved in the induction of resistance in grapevine against those pathogens. Meanwhile grapevine biotechnology is still evolving, thanks to the technological advance of modern science, and biotechnologists are making huge efforts to produce grapevine cultivars of desired characteristics. In this paper, important metabolites from grapevine and grape derived products like wine will be reviewed with their health promoting effects and their role against certain stress factors in grapevine physiology

The annealing of alkaline‐earth metal polymetaphosphate powders (I). Crystallisation and sintering processes

Amorphous barium, strontium, calcium and magnesium polymetaphosphate powders (MP2O6)n, n = 20 were prepared by dehydration of the corresponding polymetaphosphate hydrate precipitates. These powders were annealed by different continuous and isothermal heat treatments over the temperature range 450° to 700 °C, the glass transition temperatures Tg to above (Tg + 120) °C. The morphologies at different degrees of crystallisation were studied by scanning electron microscopy. For the main crystallisation process (ten to sixty‐seventy percent crystallisation), the powder particles retained their original pea‐pod form; then after seventy percent crystallisation, these crystallised particles sintered laterally to lozenge‐shaped twin‐hexagonal crystals of lengths 0.5 to 3 μm. Differential thermal analysis confirmed that a markedly exothermic crystallisation process (overall enthalpy changes from about 30 to 45 kJ mol−1) was occurring within the powder particles. Crystallisation rates varied from −1 at temperatures near Tg to > 0.5 min−1 at higher temperatures; the activation energies for this process varied from 360 to 560 kJ mol−1. The completely annealed crystals were studied by scanning electron microscopy, X‐ray diffraction and further differential thermal analysis to 1000 °C. The X‐ray diffraction d value patterns, the fusion temperatures and the enthalpies of fusion were all in close agreement with the literature values for the corresponding beta alkaline‐earth metal polymetaphosphates prepared by melt crystallisation.</p

The precipitation of alkaline‐earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes, final precipitate compositions and crystal sizes

The precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline‐earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra‐red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X‐ray powder diffraction. Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 1014 to 1015 at the critical concentrations to above 1017 per 1. solution. Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular‐weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular‐weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri‐ and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions. The precipitates from aqueous (NaPO3(I))n (n = 12) solutions had the compositions (BaP2O6 · 2.5 H2O)6, (SrP2O6 · 3 H2O)n and (CaP2O6 · 4 H2O)n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP2O6 · 4 H2O)n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO3(II))n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26. The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.</p

The crystallisation of alkaline‐earth metal phosphates from alkaline‐metal halide and alkali metal phosphate melts: Some preliminary solubility‐temperature phase diagram studies

The solubility v temperature phase diagrams, for magnesium and calcium meta‐, pyroand orthophosphate solutions in the alkalineearth metal halide melts and in different alkali metal phosphate melts, have been analysed: these are the pseudo‐binary sections of the ternary P2O5MOMX2 and P2O5MONa(K)2O systems at MO/P2O5= 1, 2, and 3, respectively. The temperature ranges and yields for crystallisations of alkalineearth, metal phosphates from these melt solutions are discussed.</p