Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.
The present study aimed to estimate school recess moderate-vigorous intensity physical activity (MVPA). Methods: A systematic review was carried out in MEDLINE and SportDiscus to identify observational studies where MVPA had been measured objectively during school recess. Study quality was assessed formally. Results: Twenty-four eligible studies in primary school pupils (N= 5,778 individuals), revealed a weighted mean of 12 minutes MVPA per school day. Only two eligible studies were identified in high school pupils (N= 399 individuals). The evidence was generally of moderately high quality. Conclusions: Recess makes a small contribution to daily MVPA. Substantial policy effort is likely to be needed if recess is to make a more useful contribution to MVPA among children and adolescents.
A series of water insoluble dyes for the measurement of pH in an inaccessible water phase in water immiscible solvents have been designed and synthesised based upon the fluorescein system. The solubilities of the anionic forms of the dyes depend strongly upon the nature of the ester substituent and the degree of substitution of the aromatic rings. For dye molecules with long chain alkyl esters and with bromine substituents in the rings, the sodium or potassium salts are soluble in organic solvents such as diethyl ketone or ethyl acetate and the anions do not partition measurably into aqueous solution. Other less highly substituted dyes can be solubilised as their anions by the addition of quaternary ammonium salts or crown ethers. Titration curves for the dyes show that they are able to respond reproducibly to the pH of a water phase in contact with the organic phase although the detailed physical chemistry of the ion exchange is complex. Certain of the dyes are suitable for monitoring the pH in reaction systems using enzymes as catalysts in water immiscible solvents.
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