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In order to make a preliminary study of substituent effects on the rate and enantioselectivity obtained in esterolytic reactions catalyzed by a lipase from Candida rugosa, a series of racemic esters, derived from some α-alkyl and α-halo phenylacetic acids, were prepared. The reactions were studied at pH 6.0 and 50°C under which conditions uncatalyzed hydrolysis was relatively slow. Reaction samples were studied at different points of time by means of analytical chiral reversed-phase liquid chromatography, which permitted the simultaneous determination of product enantiomeric excess and of the degree of total ester hydrolysis. These data were then used to calculate initial rates as well as enantioselectivity. An increase of the steric bulk of the α-substituent was found to highly decrease the rate of the reaction. On the other hand, rates were higher for the p-nitrophenyl esters than for the corresponding 2-chloroethyl esters. Consistently, the enantioselectivity was found to be higher for the latter type of ester. The esters of the α-halo (bromo and chloro) phenylacetic acids gave mandelic acid as the final product. This was caused by a rapid solvolysis of the α-halo phenylacetic acid initially formed. © 1993 Wiley-Liss, Inc. 相似文献
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Abstract Kiwifruit plants, Actinidia sp., are native to subtropical China. The flower-bud gall of A. valvata, which is induced by an undescribed gall midge in the genus Pseud as phond ylia, is valued by the pharmaceutical industry. When studying the biology of the Actinid ia/Pseud as phond ylia interaction in Central-south China we found evidence suggesting that under certain circumstances the gall insect modifies the reproductive mode of the dioecious host plant. Surveys and field experiments in the National Hupingshan Natural Reserve showed a high frequency of galled trees. The density of galled trees varied among valleys and among trees within the valleys. In two valleys, 92% and 75%, respectively, of all trees were attacked, while in a third valley no trees were attacked. When infested, staminate tree only produced galls, whereas pistillate plants produced normal fruits as well as galls. Gall shape differed between male and female trees. Trees with galls tended to produce more fruits than treea without galls. We speculate that this is one of a few documented examples of an insect that induces androdioecy in an otherwise functionally dioecious plant. 相似文献
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Three endocyclic sulfoximides of the 1-aryl- and 1-alkyl-3-oxo-benzo[d]-isothia (IV)-azole 1-oxide type (1-substituent = 2′-carboxyphenyl, 2′-carbethoxyphenyl, and octyl, respectively) were found to be well resolved on a chiral phase derived from bovine serum albumin (BSA). Selectivities (α) of 1.74, 1.12, and 1.44, respectively, were obtained. The retention behaviour of 1-octyl-3-oxo-benzo[d]isothia(IV)-azole 1-oxide was further investigated in some detail as a function of the mobile phase composition and the elution order was established from optically active material obtained from the enantiopure sulfoxide precursor. An enantiomeric excess of 85.4% was obtained in the cyclocondensation reaction of the octyl-substituted sulfoxide precursor with hydrazoic acid to the corresponding endocyclic sulfoximide. © 1995 Wiley-Liss, Inc. 相似文献
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Nineteen patients (11 women and eight men) aged 20-68 received long-term parenteral nutrition, mostly at home, for six to 63 months (mean 19 months). Indications for LTPN were extensive, active Crohn''s disease in three patients, intestinocutaneous fistulas in three, and short-bowel syndrome in the remaining 13 patients. Subclavian or intra-atrial (Broviac) catheters were most commonly used, for which the average life was four and seven months respectively. Complications of long-term parenteral nutrition included pneumothorax in four out of 48 subclavian vein punctures. Catheter-induced thrombosis of central veins was shown by phlebography 17 times in nine patients, and eight episodes of total occlusion occurred. Two of these patients had pulmonary infarction. Nineteen episodes of catheter sepsis occurred in 11 patients, but only one was fatal. Complications related to intestinal disease included intra-abdominal abscesses and intestinal fistulas, and disturbances of liver function. Five patients died, though in only two was death related to long-term parenteral nutrition. One of these patients died from catheter sepsis, the other had subdural haematoma possibly caused by anticoagulant treatment. Eight of the 14 surviving patients still needed parenteral nutrition. All received a disability pension, but six had an acceptable quality of life with almost normal social activities.Despite problems such as difficulties in maintaining standardised infusion programmes, it was concluded that long-term parenteral nutrition at home is practicable and consistent with an acceptable quality of life. 相似文献
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Abstract. Woody biomass production in natural forests of arid and semi-arid regions is low. The fuelwood demand of settlements often exceeds the sustained yield and regeneration capacity of natural forests, which results in deforestation. Regeneration and woody biomass development was studied in cleared Acacia zanzibarica bushland in Bura, eastern Kenya. The area was cleared in 1982 and studied in 1988. The site had been colonized primarily by Acacia zanzibarica and A. reficiens. Mean density was 1333 trees/ha, mean total woody biomass (dry weight) 1954 kg/ha, equal to 2.53 m3/ha. Mean annual increment was 293 kg/ha, or 0.3 8m3/ha. Expressed as rain use efficiency, the natural dry matter productivity of the woody component equals 0.83 kg ha-1 yr-1 mm-1. The regeneration potential and some management implications are discussed. 相似文献
8.
Free Fatty Acids in the Rat Brain in Moderate and Severe Hypoxia 总被引:20,自引:16,他引:4
Mark Gardiner Bengt Nilsson Stig Rehncrona Bo K. Siesjö 《Journal of neurochemistry》1981,36(4):1500-1505
Abstract: The effects of mild, moderate, and severe hypoxia on cerebral cortical concentrations of free fatty acids (FFAs) were investigated in artificially ventilated rats under nitrous oxide anaesthesia. No change occurred during either mild (arterial Po2 35–40 mm Hg) or moderate (Po2 25–30 mm Hg) hypoxia. The effects of severe hypoxia (Po2 about 20 mm Hg) combined with hypotension (mean arterial blood pressure 80–85 mm Hg) varied with the EEG pattern and the tissue energy state. Thus, a major increase in total as well as in individual FFAs occurred first when EEG was severely depressed (almost isoelectric) and energy homeostasis disrupted. On a relative basis the greatest change occurred in free arachidonic acid. It is concluded that hypoxia is associated with an increase in the concentrations of FFAs in brain tissue, provided that tissue oxygen deficiency is severe enough to cause tissue energy failure. However, an increase in FFAs does not invariably accompany minor reductions in the adenylate energy charge (EC) of the tissue. 相似文献
9.
CNDO/2 studies on the conformation of the chain of lecithin indicated a strong preference for a gauche-gauche arrangement about the phosphodiester group. Folding the chain about and 4 was energetically very favorable. Hydration of the same segment revealed three levels of water-binding energies. The ion-dipole interactions of water and the choline moiety were energetically non-substantial. In contrast, binding of water to the unesterified phosphate oxygens produced the highest enthalpies. Attachment of water to the esterified phosphate oxygens or the ester oxygens of the chain resulted in intermediate binding strengths. By investigating complete incorporation of nine water molecules into a chosen lipid structure, a plausible lecithin-water geometry was deduced for a liquid crystalline system. 相似文献
10.
dsRNA-mediated resistance to Beet Necrotic Yellow Vein Virus infections in sugar beet (Beta vulgaris L. ssp. vulgaris) 总被引:1,自引:0,他引:1
Britt-Louise Lennefors Eugene I. Savenkov Jan Bensefelt Elisabeth Wremerth-Weich Petra van Roggen Stig Tuvesson Jari P. T. Valkonen Jan Gielen 《Molecular breeding : new strategies in plant improvement》2006,18(4):313-325
Rhizomania, one of the most devastating diseases in sugar beet, is caused by Beet Necrotic Yellow Vein Virus (BNYVV) belonging to the genus Benyvirus. Use of sugar beet varieties with resistance to BNYVV is generally considered as the only way to maintain a profitable yield on rhizomania-infested fields. As an alternative to natural resistance, we explored the transgenic expression of viral dsRNA for engineering resistance to rhizomania. Transgenic plants expressing an inverted repeat of a 0.4 kb fragment derived from the BNYVV replicase gene displayed high levels of resistance against different genetic strains of BNYVV when inoculated using the natural vector, Polymyxa betae. The resistance was maintained under high infection pressures and over prolonged growing periods in the greenhouse as well as in the field. Resistant plants accumulated extremely low amounts of transgene mRNA and high amounts of the corresponding siRNA in the roots, illustrative of RNA silencing as the underlying mechanism. The transgenic resistance compared very favourably to natural sources of resistance to rhizomania and thus offers an attractive alternative for breeding resistant sugar beet varieties. 相似文献