Purification results

Prior to the kinetic experiments, possible deactivation phenomena of the catalytic system were checked by recycling experiments with prenal and citral as substrates. These results provide not only important hints on the form of the rate equation, but also on which reaction is convenient for long-term investigations in the loop reactor. After the reaction, the aqueous and organic phases were separated and the catalyst phase was reused without further purification. Results on the hydrogenation of prenal are shown in Fig. 7. The reaction rate clearly decreases if the catalyst phase is reused. According to GC analysis and H-NMR studies, this can be attributed to the fact that the product of the reaction, prenol, is highly soluble in water. Consequently, a simple phase... 

Thermolysis of aryl chloro diazirine (18) in the presence of acetone and a trapping agent such as A -phenylmaleimide gave rise to cycloadducts such as 41. The unstable adduct hydrolyzed during purification resulting in synthesis of bicyclic hemiacetals 42 and 43 as a mixture of endo and exo adducts in 37 and 8% yield, respectively. The exclusive generation of the singlet carbene was confirmed by low-temperature electron spin resonance (ESR) study of the irradiated diazirine. 

A stirred mixture of 94 (798 mg, 2 mmol), ethyl (acetylamino)(cyano)acetate (701 mg, 4.12 mmol), K2C03 (382 mg, 2.76 mmol), and KI (8.3 mg, 0.05 mmol) in acetone was refluxed in the dark under argon for 20 h. After cooling, the solid precipitate was filtered and washed with acetone. The crude product was purified by preparative TLC (fy0.24, CHCIs/EtOH 94 6) to give 95 as a glassy solid yield 360 mg (47%). [TLC purification resulted in loss of material, apparently because the crude material also contained the phenolic ester of A-acetyl-2-cyano-4-(4-hydroxybenzoyl)phenylalanine.]... 

Nitrones.1 O-Trimethylsilyloximes undergo N-methylation on reaction with Meerwein s reagent or methyl trifluoromethanesulfonate. The products are converted into nitrones on addition of KF or Bu4NF. Although both (E)- and (Z)-nitrones are formed initially, purification results in isolation of the more stable (Z)-nitrones. 

It has been suggested that GTF is not a chromium complex.1091 This arises from the failure to isolate a biologically active Crm complex from extracts of brewers yeast grown in a medium containing added Crm. Two fractions showed biological activity, but further purification resulted in the loss of chromium and the isolation of biologically active chromium-free compounds. One of these was largely tyramine (formed from tyrosine residues), but pure tyramine does not show GTF-type properties. The activity of this fraction must therefore be due to the minor component... 

Successful protein purification results from the exploitation of one or more of the many characteristics responsible for the wide diversity within the protein population, such as charge, size, hydro-phobicity, or biological affinity. Fortunately, in some properties immunoglobulins are distinctive and as a consequence an acceptable degree of purity can often be achieved using relatively straightforward procedures. 

An earlier procedure reported from this laboratory for the isolation of sulfides was based on the selective oxidation of the sulfides to the sulfoxides with photoexcited singlet oxygen followed by silica gel chromatographic separation of the sulfoxides (9). Reduction of the isolated sulfoxides back to the sulfides and a subsequent chromatographic purification resulted in the isolation of the sulfides as a pale yellow oil. However, when the sulfur is in a five-membered ring, the photooxidation may lead to side reactions (22). Therefore, other oxidation methods had to be explored. 

Once it was established that pheromone biosynthesis was regulated by a peptide produced in the SEG, the next goal was to identify the peptide. In the purification of any biologically active factor, each purification step requires a sensitive bioassay to measure the active material. In the purification of PBAN, the bioassay consisted of head ligated females that were injected with bioactive fractions. After a 1-3 h period of incubation, the pheromone gland was excised and titers of pheromone determined by gas chromatography (GC). The first PBAN was purified and identified from H. zea (Raina el ah, 1989). Dissection of about 5000 brain-SEG complexes followed by several steps of HPLC purification resulted in a pure peptide that could be sequenced. It was found to be a 33 amino acid peptide with a C-terminal amide (Table 5.1). The peptide was synthesized and was shown to be active in the bioassay in a dose as low as 2 pmol (Raina et al., 1989). In the same year, a PBAN from B. mori was purified and sequenced (Kitamura et al.,... 

Among the classic cases in this group are the aspirin cases where a particular degree of purification resulted in effectively a new product because as so purified the material had medicinal uses not previously known. The claim of the Hoffman patent (23) is ... 

Before describing these enzymes (see the examples in Table 1), it is necessary to make a broad division of metal interactions in enzymes. In one case, the metal ion is firmly attached to the protein so that like a nonmetal of an amino acid it does not exchange within days. In snch a sitnation, the isolation of the metallo-protein, correctly named, can be followed through all steps of purification until further purification procedures fail to alter the stoichiometry of the metal/protein, and this is a whole number. At the same time, if the metallo-protein is an enzyme, activity will become optimal. This approach to metallo-enzymes was first developed by Professor B. L. Vallee of Harvard. A different extreme is one in which the metal ion is loosely attached to the protein when isolation procedures may well result in an apoprotein, and if it was an enzyme, it would then be devoid of activity. The problem in such a case is to know which metal ion was intrinsically involved in activity in vivo. Now a great number of metal ion/protein interactions are intermediate in character between extremes so that purification results in the discovery of fractional stoichiometry and can be beset by contamination. Confusion is increased because many enzymes have several metal ion centers when it may require astute experimentation to reveal the nature of the original metal ion complement. We must be aware of both binding constants of metal ions to proteins of different kinds and of their rates of exchange so as to establish their nature correctly as it is related to function (1-4). 

Processes whereby purification results by the use of an electrical field, which is not accompanied by decomposition or destruction of the pollutant, can be divided into four different groups electrodialysis (ED), electrofiltration, electrosorption, and electroremediation. The main electrochemical reaction in these types of processes is decomposition of water. 

Table 3.35 Summary of the purification results for an API and its impurities on different stationary phases.

The olefin 157 was epoxidized to an equimolar mixture (158a,b). Both epoxides opened with lithium di-/t-propy]amide to the desired allylic alcohols (159). Expoxide 158a also yielded unwanted tertiary alcohol 160 (40%). Reaction of the crude epoxide mixture with lithium di-/i-propylamide followed by oxidation (Ct03-py2) and purification resulted in a 71 29 mixture of enones 152 and 161, with an overall yield of 152 from 155 of 16%. The oxidation of 160 to 161 occurs by allylic rearrangement of the intermediate chromate ester. The reduction product from 154 was resolved into its enantiomers via the brucine salt of the hydrogen phthalate 162. The levorotatory enantiomer was found to have the absolute configuration corresponding to that of the pentacyclic triteipenes. 

S. V. Karnik, M. K. Hatalis, M. V. Kothare, Towards a palladium micromembrane for the water gas shift reaction Microfabrication approach and hydrogen purification results,... 

Triaryl isocyanurates are useful as activators for the continuous anionic polymerization and postpolymerization of c-caprolactam to nylon-6 possessing a low unreacted monomer content and a highly stable melt viscosity [93]. Although a wide variety of catalysts for the trimerization of aryl isocyanates to triaryl isocyanurates are known, purity of trimerized product (a requirement for nylon of good quafity) is problematic and purification results in product... 

Table 1.1 presents information on the effect of additives upon the adhesion strength of an adhesive based on ED-20 resin cured hy polyethylene polyamine (PEPA). It is evident that the lowest adhesion strength is exhibited by the adhesive based on the unpurified resin. The sorption of low-molecular weight fractions of an epoxy resin from the interphase boundary caused by addition of alcohols to this adhesive, i.e. resin purification, results in increase of the adhesion strength. Adding further alcohol to a purified resin results in formation of a weak layer on the interphase boundary, producing some decrease of the adhesion strength. 

The challenge is to purify microbially produced protein-based polymers to adequate levels for use as biomaterials. The pharmaceutical use of microbially prepared insulin requires that impurities be less than 10 parts per million (ppm). Repeated use of the phase separation property for purification results in a... 

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