Heats of vaporization of esters by the gas chromatography–calorimetry method

A recently developed gc–calorimetry procedure involving a combination of gas chromatography and heat of solution measurements has been used to measure heats of vaporization of 17 esters, including methyl 2,2-dimethylpropanoate, butyl acetate, glyceryl triacetate, diethyl phthalate, methyl 9-octadecenoate, and 12 methyl esters of C3- to C15-fatty acids. Comparison with measurements of ΔHv reported in the literature indicates that the gc–calorimetry method often has smaller uncertainties in measurements (0.25 to 1.00 kJ mol−1) and more consistent methylene increments for the series of fatty acid methyl esters. Two of the experimental ΔHv measurements which differ appreciably from recent literature values have been verified by vaporization calorimetry.

Isolierung und Charakterisierung einer Acetylester-Hydrolase aus Aspergillus rtiger / Isolation and Characterization of an Acetylester-Hydrolase from Aspergillus niger

The characteristic features of an acetic acid esters hydrolyzing enzyme (acetylesterase, EC 3.1.1.16) are described. The pH- and temperature optimum were 7.0 and 40 °C respectively. The stability of the enzyme regarding different pH- and temperature conditions was investigated. The molecular weight of the acetylesterase could be determined to 160000. A small acetic ester hydrolyzing activity was found too with a molecular weight of about 25000. The activity was not inhibited by addition of di-isopropylphosphorofluoridate (DFP) or physostigmine. The KM-value for glyceryl triacetate was about 90 mM. Concentration of the enzyme was done by ultrafiltration and column-chromatography. The enzymatic activity tests were performed titrimetrically using glyceryl triacetate for substrate.

Some Enzymatic Properties of Plasma Esterases from Channel Catfish (Ictalurus punctatus)

Rates of ester hydrolysis by plasma enzymes from five fish species ranged from 12 8 to 46.6 μmoles acetylcholine hydrolyzed/ml plasma per hr. Enzymes in channel catfish (Ictalurus punctatus) plasma hydrolyzed the substrates acetylcholine, phenyl acetate, and glyceryl triacetate at rates of 28.1, 96.7, and 6.8 μmoles substrate hydrolyzed/ml plasma per hr, respectively. Esterolytic activity was attributed, in part, to an acetylcholinesterase-like enzyme. In vitro organophosphate inhibition of enzymes in channel catfish plasma was similar to that previously reported for catfish brain acetylcholinesterase (EC 3.1.1.7, acetylcholine acetyl-hydrolase).