Lipase-catalyzed synthesis of geranyl acetate in n-hexane with membrane-mediated water removal.

The esterification of geraniol with acetic acid in n-hexane was investigated. A commercial lipase preparation from Candida antarctica was used as catalyst. The equilibrium conversion (no water removal) was found to be 94% for the reaction of 0.1 M alcohol and 0.1 M acid in n-hexane at 30 degrees C. This was shown by both hydrolysis and esterification reactions. The activation energy of reaction over the temperature range 10 degrees to 50 degrees C was found to be 16 kJ/mol. The standard heat of reaction was -28 kJ/mol. Membrane pervaporation using a cellulose acetate/ceramic composite membrane was then employed for selective removal of water from the reaction mixture. The membrane was highly effective at removing water while retaining all reaction components. Negligible transport of the solvent n-hexane was observed. Water removal by pervaporation increased the reaction rate by approximately 150% and increased steady-state conversion to 100%.

[The vitamin B 12 serum level at various ages]. / Der Vitamin-B12-Spiegel im Serum in verschiedenen Altersstufen.

A report is presented on the determination of the vitamin B12 content by means of radioassay in the serum of 402 healthy persons aged between 14 to 98 years. With increasing age a significant decrease of the vitamin B12 content could be observed in both sexes after the sixtieth year of age. In the age group between 21 to 30 only the low values of women made an exception, which may be due to the administration of contraceptives.

PIP: 275 women and 127 men between 14 and 98 years of age were tested for Vitamin B-12 serum levels by radioassay. Median values, standard deivation; and the standard deviation from the medium were calculated according to age and sex, in order to determine if these factors were significant for Vitamin B-12 serum levels. Women 21-30 years of age had significantly lower Vitamin B-12 serum levles than men of the same age (p .001), which may be due to the use of oral contraceptives. Both men and women showed a significant decrease in the Vitamin B-12 level after the 60th year of age (p .001). This finding supports studies based on biological methods for determining Vitamin B-12 levels.