Abstract

Olefin trimers can be prepared selectively from α‐olefins with n‐alkyl‐substituted triazacyclohexane–CrCl3 complexes as catalysts in the presence of methyaluminoxane (MAO).

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The effect of microbial pectin esterases (Aspergillus foetidus) and higher plants (tomatoes, alfalfa) on high-esterified pectin was investigated. Pectin derivatives of esterification degree E 42-66% were prepared by a partial deesterification catalyzed by the above-mentioned enzymes. The distribution pattern of free and esterified carboxyl groups in the linear pectin macromolecule was determined on the basis of activity coefficients of counterions γCa2+ as found in solutions of the proper calcium pectinates. The activity coefficients γCa2+ were compared with the corresponding γCa2+ values determined in pectins partially deesterified with alkali, with a random distribution pattern of free carboxyl groups. The plant pectin esterases under investigation lead to a block-wise arrangement of the free carboxyl groups in the pectin molecule, whereas A. foetidus pectin esterase cleaves randomly the ester groups in the same mode as do the alkali hydroxides. Significant differences were observed with final products of enzyme deesterification of pectin even in the selectivity of Ca2+ 2K+ cation exchange, as documented by the change of electrostatic free enthalpy of exchange of these cations. The different mechanism of action of plant and A. foetidus pectin esterases was thus unambiguously proved by a physico-chemical method.

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The Cr‐catalyzed trimerization of 1‐decene and 1‐dodecene is a highly selective method to synthesize C30 and C36 olefins. After hydrogenation, these products display very attractive viscosity indices (VI's). Due to the high trimer selectivity of the reaction no additional work‐up is needed to separate C20, C24 or C40+ oligomers from the product prior to a potential use of these products in synthetic lubricants for automotive applications.

Summary. Trichoderma reesei pectinesterase (isoelectric point 8.3-9.5; pH-optimum 7.6) catalyzes deesterification of pectin by giving rise to blocks of free carboxyl groups in the macromolecule; a mode similar to that observed with higher plant pectinesteruses which also have |p and pH-optima in the alkaline region.Pectinesterases of higher plants (tomato 1-3, orange 4-7 and alfalfa 3) catalyze deesterification of pectin linearly along the chain of the molecule, giving rise to blocks of free carboxyl groups. On the other hand, deesterification of pectin by alkali and acids results in a statistical distribution of free and esterified carboxyl groups 4, 5. The present study reports the mode of deesterification of pectin catalyzed by Triehoderma reesei pectinesterase, which has its pH-optimum and isoelectric point in the alkaline region. Material and methods. Pectinesterase was prepared from culture filtrate of the fungus Trichoderma reesei QM 9414 cultivated on pectin as a carbon source, after ammonium sulfate precipitation and chromatography on Sephadex G-25 and G-100 columns ~~ This preparation included 5 multiple forms of pectinesterase with isoelectric points in the range 8.3-9.5 and pH-optimum 7.6. Preparation and characterization of pectin samples deesterified by pectinesterase. Purified citrus pectin (Genu Pectin, Medium Rapid Set, Kobenhavns Pektinfabrik, Denmark) was esterified to 94.7% with methanolic 1 M HzSO 4 at 3 ~ This pectin contained 88.2% of highly esterified D-galacturonan and exhibited a limit viscosity number tidus ; O, AspergiUus niger ; 9 tomato ; ~, orange ; I% alfalfa 3.was deesterified by Trichoderma reesei pectinesterase at pH 7.3 under continuous titration with 0.1 M NaOH at 25~ a Radiometer pH-stat and autotitrator set (Denmark). The 1% pectin solution (250 ml) was treated with I ml enzyme (total activity 1.2 x 10 -3 tool sec -~) until the required degree of esterification (d.c.) was obtained. The enzyme was inactivated by 10 min heating on a boiling water bath and after cooling the pectin was precipitated with acidified ethanol (final concentration 0.33 M HC1 in 60% ethanol) and washed several times with 60% ethanol to remove chloride ions. The content of free carboxyl groups of pectin was determined by potentiometric titration with 0.05 M KOH, and the overall content of carboxyl groups by precipitation of insoluble copper pectates ~ ~. lz. The amount of copper bound to pectin carboxyl groups was determined chelatometrically. The limit viscosity number [11] of pectin solutions adjusted to pH ~ 7 with KOH and containing 0.15 mol NaC1 -0.005 tool sodium oxalate in 1 t was measured using an Ubbelohde viscometer at 25.0 -4-0.1 ~ Determination of calcium ion activities in Ca-pectinate solutions. Solutions of pectinic acids (4-5 mmol COOH 1-1) were centrifuged at 20,000 • g for 20 min and the supernatants neutralized with a saturated calcium hydroxide solution (0.021 M Ca(OH)2 ) to pH ~ 7.2. Single-ion activity coefficients 7c,2+ of calcium ions bound to carboxyl groups of pectin were determ...