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71.
72.
The application of hydrolases in organic solvents for synthetic purposes is a procedure routinely adopted in organic chemistry, especially for the preparation of chiral building blocks. Numerous studies have shed light on several aspects of the mechanism of hydrolase action in low-water environments. Procedures suitable to improve the catalytic efficiency of enzymes and productivity of the synthetic processes have been reported. These fundamental and applied investigations have made hydrolase-catalyzed reactions in organic solvents of industrial interest. In this article we describe and discuss various approaches adopted to optimize the performance of hydrolases in organic media, with special emphasis on the formulation of the biocatalysts which, under proper conditions, can display an activity equal to that displayed in aqueous buffers. 相似文献
73.
Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation
Photodegradation of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) in hexane solution was studied under controlled near-UV light exposure in the spectral region from 325 to 269 nm. GC-MS was used to detect the amount of unreacted dioxin and to characterize the relevant degradation products. Irradiation experiments carried out at a constant light energy (700 mJ) showed that the percentage of 1,2,3,4-TCDD left in the solution after irradiation changed from about 55 to 75%, with a minimum of 55% at 310 nm. Further irradiation experiments carried out at two wavelengths, namely 310 and 269 nm, and light energy ranging from 0 to 4000 mJ, showed that the photodegradation reaction of the TCDD always followed a pseudo-first-order kinetic, with a rate constant of 8 × 10−4and 5 × 10−4mJ−1, respectively. These experiments also showed that trichloro- and dichloro-dibenzo-p-dioxins were produced with less than 15% of the initial quantity of TCDD, leading to the conclusion that the dechlorination process is a minor photolysis pathway. 相似文献
74.
Cubadda F 《Journal of AOAC International》2004,87(1):173-204
Inductively coupled plasma-mass spectrometry (ICP-MS) has definitely emerged as a powerful technique for total element determination and as a sensitive and selective detector in hyphenated methods for speciation analyses of elements in foods. In this review, the analytical challenges of elemental analysis of food and agricultural matrixes are discussed and several applications are examined. Selected examples illustrate the analytical approaches being used so far to address specific issues in various areas of food and nutrition research. The applications discussed include studies on dietary intake, element metabolism in man, transfer of elements through the food chain, effects of food processing and domestic preparation, and authenticity and origin assessment. The use of ICP-MS in the field of analytical quality assurance, food control, evaluation of food contact materials, and radionuclide contamination is also examined. Finally, the hyphenated techniques with ICP-MS detection used for elemental speciation in food are reviewed, and an overview of the main applications currently in the literature is presented. Throughout, recent trends and analytical developments likely to have a major impact on food-related areas are highlighted. 相似文献
75.
Muzzalupo R Trombino S Iemma F Puoci F La Mesa C Picci N 《Colloids and surfaces. B, Biointerfaces》2005,46(2):78-83
Vesicular formulations (liposomes and niosomes) play an increasingly important role since they can be used as drug delivery and targeting systems. We described the formation of two niosomal systems based on synthetic bolaform surfactants (4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecanedioc acid diamide (BD-16) and alpha,omega-(4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecane (BC-16). Systems containing BD-16 or BC-16 and different amount of cholesterol (CH) were prepared by aqueous dispersion of films, followed by examination of methylene blue (MB) entrapment, particle size and morphology. Indeed, we also studied the hydration in the distilled water and physiological solution, in order to investigate the complexing ability on vesicle formation. The results obtained in this study show a high encapsulation capacity and this ability and the size depends on cholesterol content. 相似文献
76.
Francesco De Sarlo Roberto Cencioni Ciovanni Renzi Letizia Bausi 《Journal of heterocyclic chemistry》1977,14(2):181-184
Carbethoxy-substituted 12-methylisoxazolin-5-ones and several functional derivatives have been prepared. Spectral properties of the corresponding carboxylic acids are discussed. These acids ant stronger when the carboxy group is in position 3 than when in position 4 of the heterocycle. 相似文献
77.
Graziano Guella Ines Mancini Giuseppe Chiasera Francesco Pietra 《Helvetica chimica acta》1992,75(1):310-322
78.
Reported here are two novel quasi-racemic (bis)indole alkaloids, cycloaplysinopsin A (5) and cycloaplysinopsin B (6), isolated from tropical Indo-Pacific (Comoros, Philippines) scleractinian corals of the family Dendrophylliidae. Although their structures suggest a Diels-Alder cycloaddition origin from aplysinopsin-type precursors, neither experiments, nor theory allowed us to clearly distinguish an enzymatic process with scarce enantioselection from the intrusion of an adventitious catalyst in the coral extracts, where the chiral environment caused a slight asymmetric induction. 相似文献
79.
Francesco Malatesta Giacomo Carrara Maria Perla Colombini Ambrogio Giacomelli 《Journal of solution chemistry》1993,22(8):733-749
The activity coefficients of Co(en)3Cl3 and K2SO4 were measured by means of a cell with ion-exchange liquid membranes following the method described in paper I. The results prove that this method is even more valuable with multicharged salts than with 1-1 electrolytes. The values obtained are precise and reliable down to dilution limits never before accessible, e.g., 4×10–5 mol-kg–1 in Co(en)3Cl3. High dilution levels are of particular importance when dealing with highly charged electrolytes since the trend at higher concentrations often leads to errors both in extrapolation to infinite dilution and in the absolute activity coefficients. As an application, the activity coefficients of [Co(en)3]2(SO4)3-suspected to be wrongly evaluated in past literature-were measured, and their values at low concentrations were actually lower than those quoted before. 相似文献
80.
It is shown that strains of the marine ciliate Euplotes raikovi are subtly variable in their production of secondary metabolites. Strains GA8 and 39W from Mediterranean and SB8 from Californian coasts produce the sesquiterpenoid epiraikovenal ( 3 ), while strains GA8 and SB8 also produce secoepiraikovenal ( 4 ), which play an instrumental niche-exploitation role and have also taxonomic significance. Comparison of 3 and 4 with raikovenal ( 2 ) and its putative biogenetic precursor 1 , which have similar roles in the conspecific strain Morl from Casablanca coast in the Atlantic Ocean, inspired us the first case of intramolecular tele-dienone-olefin [2+2] photocycloaddition, exemplified here by the transformation of 1 into ent- 3 . This served also to unequivocally clarify the stereochemical relationship between 3 and 2 . 相似文献