Degradation experiments

Flambamycin. Flambamycin, produced by Streptomjces hjgroscopicus DS 23230, also has undergone substantial chemical degradative experiments during stmcture elucidation (22,23,25). Nmr interpretation of the stmcture was reported later (20,26). The stmcture, shown in Table 2, chemical reactions, and biological properties have been thoroughly reviewed (22) it melts at 202—203°C. 

Leonard and Elderfield have also carried out degradation experiments with alstonine and its tetrahydride. On fusion with potassium hydroxide at 300-350° in nitrogen, alstonine furnishes barman (p. 490) and indefinite basic and acidic fractions. Tetrahydroalstonine on like treatment produces barman, worharman, and three unidentified bases, each of which fluoresces blue in alcoholic hydrochloric acid Base A, C4,H4gN2, m.p. 171-5 to 172-5°, forms a picrate, m.p. > 267° is probably a substituted -carboline. Base B, or 18 3, gives apicrate, m.p. 261° (dec.). Base C,... 

The most interesting product arising from more drastic degradation experiments is a base, C Hi ONa, m.p. 115-120°, obtained by distilling mitragynine with zinc dust. It contains a methoxyl and a methylimino group, and has a reactive methylene group, since it forms a p-nitrobenzyl-idene derivative, m.p. 255°. This base closely resembles both ind- and jM/r-iV-methylharmine, but is not identical with either. 

The explanation proposed involved sequential inter- and intramolecular addition steps. The presence of cyclic structures within the polymer chain was soon confirmed by degradation experiments.106 However, these experiments did... 

At least 90 percent of free-radical-polymerized 2,3-dimethylbutadiene consists of 1,4 units according to ozone degradation experiments. Successive substitution of the methyl groups on carbons 2 and 3 of butadiene is seen to increase the proportion of 1,4 units formed. In polychloroprene no less than 97 percent of the structure consists of 1,4 Cl... 

In order to obtain solutions with the desired flow properties, shear-induced degradation should be avoided. From mechanical degradation experiments it has been shown that chain scission occurs when all coupling points are loose and the discrete chains are subjected to the velocity field. Simple considerations lead to the assumption that this is obtained when y) is equal to T sp(c-[r ]) (Fig. 18). The critical shear rate can then easily be evaluated [22]. 

Enzymatic Degradation of H214/03. The degradation experiments were carried out with molecular mixtures of H214/03 or LVP and MO. These were obtained from mixtures of the peptide and MO dissolved in 99.5% ethanol, from which the ethanol was evaporated under reduced pressure at room temperature for about two days. Appropriate amounts of melted mixtures were then weighed in small Erlenmeyer flasks. Care was taken to insure that the bottom of each flask was covered with the mixture, which was then left to freeze. In this way the area and the thickness of the lipid/peptide layer was comparable in the flasks. Typically five flasks were used in each experiment... 

Not long ago this could have been determined only by extremely laborious, and often equivocal, selective degradation experiments but the coming of carbon n.m.r. spectroscopy has now made all the difference. Neither the 12C nor the 14C carbon isotopes produce an n.m.r. signal but the 13C isotope, which occurs in ordinary carbon to... 

Fig. 1 Concentration profiles of (a) BP3, (b) BP1 and (c) 4-MBC concentration during 24 h degradation experiment by T. versicolor at Erlenmeyer scale and at 10 mg/L initial concentration. Treatments (filled circle) uninoculated controls (UNI), (open circle) experimental bottles (EB) and (filled inverted triangle) heat-killed controls (HK). Laccase activity in EB is also plotted in long dashes. Values plotted are means standard error for triplicates. Modified from [44, 49]...

Fungal degradation of BP1 resulted in the formation of 4HB and 4DHB. The levels of these metabolites found after 3 and 6 days of treatment were similar to those achieved in BP3 degradation experiments. Likewise in BP3 degradation tests, THB and DHMB were not detected in any of the collected samples. The levels found of these metabolites were quite low therefore, these products cannot be considered as major degradation products. 

Degradation experiments were performed with [13C]-deca-BDE to measure the pollutant mineralization degree by the fungus. 

Before degradation experiments were performed, a characterization of the composition of both mixtures, which is summarized in Table 4, was carried out. Note that in the case of penta-BDE mixture, due to the lack of analytical standards, it was only possible to quantify 6 of the 27 compounds present in the mixture. These compounds correspond to BDE-47, BDE-100, BDE-99, BDE-154, BDE-153 and BDE-183. These compounds are the major components of penta-BDE mixture, representing the 92.5% of the total composition, and they are usually detected in the environment. Respect octa-BDE mixture, two compounds were detected, BDE-153 and BDE-183, which correspond to the major components of the mixture according to the reviewed literature [4], and probably the other compounds present in the mixture were not detected due to the lack of the corresponding analytical standards. 

Fungal degradation of these mixtures in aqueous phase was carried out under the same conditions as deca-BDE degradation experiments performed previously, except for the initial mixture concentration, which was 5 mg L 1 for both mixtures, and the extension of the degradation period, which corresponded to 14.5 days in both cases. 

All of the DBDPO and HBCD thermal degradation experiments reported here were carried out isothermally with a nitrogen purge in a thermal gravimetric analyzer (TGA) at temperatures between 390 and 410° C for DBDPO and 240° C for HBCD, respectively. 

Fig. 38. A Degradation experiments with pregel polymers isolated prior to the onset of macrogelation in 1,4-DVB polymerization [209] Variation of Mw ( ) and dz (O) with the time of ultrasonic degradation. The polymer sample was prepared at 5 g/100 mL monomer concentration and its initial Mw was 2.2 X106 g/mol. The dotted horizontal line shows Mw of zero conversion polymers ( individual microgels ). B Variation of Mw with the polymerization time t and monomer conversion x in 1,4-DVB polymerization at 5 g/100 mL monomer concentration. The region 1 in the box represents the limiting Mw reached by degradation experiments. [Reprinted with permission from Ref. 209,Copyright 1995, American Chemical Society].

Fig. 5.1.4. (— )-LC-ESI-MS chromatogram of an FBBR degradation experiment on LAS taken after 8 days. Peak numbering (1)...

Fig. 5.1.7. Concentration profile of C12-LAS on FBBR during adsorption and degradation experiments at a surfactant concentration of 100 mgL. ...

In degradation experiments of radiolabelled LAS in soil columns, Branner et al. [29] observed that microbial transformation products, believed to be SPC, were virtually not retained on the column at all. Conversely, the results from the waterworks Rhine study [23] show that the subsequent slow sand filtration leads to a nearly total elimination of the SPC homologues. The residues detected in the water after this step... 

From these considerations there evolved the concept of "primary valence chains" in cellulose, held together in bundles, or micelles (crystallites) by secondary forces, as propounded by Meyer and Mark (5). This view was then extended to encompass other high polymers as well. It should be noted however, that Freudenberg had already proposed a chain structure for cellulose, based on degradation experiments (6). If the micelles were to... 

It is also the starting point for the fundamental degradation experiments which have paved the way to the synthesis of this important substance (Nencki, Kuster, Piloty, Willstatter, H. Fischer). 

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