Chemical manipulation

R. M. Sacher, "Strategies to Discover Plant Growth Regulators for Agronomic Crops," in Chemical Manipulation of Crop Growth and Development 1982, p. 167. 

Japan held 37.5% of the world antibiotic market ki 1988, the USA 23.2%, Italy 8.0%, the United Kingdom 5.4%, Germany 3.6%, and other countries 22.3% (20). The disproportionate size of the Japanese market is in part a consequence of the inherent strengths of Japanese industry which include expertise in fermentation technology and intensive chemical manipulation of known stmctures. In addition, antibiotic prescribing in Japan is extremely popular among doctors as a result of the Japanese reimbursement system. 

Although soaps have many physical properties in common with the broader class of surfactants, they also have several distinguishing factors. First, soaps are most often derived direcdy from natural sources of fats and oils (see Fats and fatty oils). Fats and oils are triglycerides, ie, molecules comprised of a glycerol backbone and three ester-linked fatty oils. Other synthetic surfactants may use fats and oils or petrochemicals as initial building blocks, but generally require additional chemical manipulations such as sulfonation, esterification, sulfation, and amidation. 

AH cephalosporins found in nature (Tables 1 and 2) have the D-a-aminoadipic acid 7-acyl side chain (21). AH of these compounds can be classified as having rather low specific activity. A substantial amount of the early work in the cephalosporin area was unsuccessfiiHy directed toward replacing the aminoadipic acid side chain or modifying it appropriately by fermentation or enzymatic processes (6,22). A milestone ia the development of cephalosporins occurred in 1960 with the discovery of a practical chemical process to remove the side chain to afford 7-ACA (1) (1). Several related processes were subsequendy developed (22,23). The ready avaHabHity of 7-ACA opened the way to thousands of new semisynthetic cephalosporins. The cephalosporin stmcture offers more opportunities for chemical modification than does that of penicillins There are two side chains that especiaHy lend themselves to chemical manipulation the 7-acylamino and 3-acetoxymethyl substituents. 

These studies trace the evolution of penicillin investigations from microbiological curiosity through the development of increasing therapeutic utility to increasingly sophisticated chemical manipulations. This chapter will focus primarily on the chemical aspects of this area. Because of the vast amount of relevant literature, it has been possible to discuss only selected studies which hopefully are representative of the different investigative directions. The reader is urged to consult the cited references for more detailed discussion and for references to related studies. 

Some of the more obvious sources of contamination of solvents arise from storage in metal drums and plastic containers, and from contact with grease and screw caps. Many solvents contain water. Others have traces of acidic materials such as hydrochloric acid in chloroform. In both cases this leads to corrosion of the drum and contamination of the solvent by traces of metal ions, especially Fe. Grease, for example on stopcocks of separating funnels and other apparatus, e.g. greased ground joints, is also likely to contaminate solvents during extractions and chemical manipulation. 

SOME HAZARDS OF CHEMICAL MANIPULATION IN PURIFICATION AND RECOVERY OF RESIDUES... 

However, in rare cases, crystallisation is not a satisfactory method of purification, especially if the impurity forms crystals that are isomorphous with the material being purified. In fact, the impurity content may even be greater in such recrystallised material. For this reason, it still remains necessary to test for impurities and to remove or adequately lower their concentrations by suitable chemical manipulation prior to recrystallisation. 

These iiicchanisnis can affect the near-term and ultimate fate of a chemical hazard. Recognition of these inechanisms can significantly assist in the identification of a chemical agent as a health hazard. In recent years, the understanding of chemical transport, chemical manipulation in the body, and response by animals luid humans to cheniicals has advtmccd to a point where it is possible to determine whether a chemical is indeed a health hazard. 

Besides the above-mentioned titration methods, some special instrumentical analytical ones were established in recent years. A big advantage lies in the fact that single components can be detected even in complex mixtures by using chromatographic methods. Gas chromatography fails to analyze nonvolatile surfactant molecules. To get volatile components, chemical manipulations have to be... 

The groundwork has now been laid for the exploitation of f.a.b.-m.s. by all carbohydrate chemists involved with the structural analysis of novel compounds. There is no reason why f.a.b.-m.s. should not take its place alongside g.l.c.-m.s., e.i.-m.s., and c.i.-m.s. as a relatively routine, analytical procedure. It is important, however, that f.a.b.-m.s. be integrated into sensible structural strategies, and that it be very closely linked to the chemical manipulations that are also being conducted as part of the structural program. 

Chemical manipulation of phenolic allelochemical production in plants has two potential values 1) for study of the role of phenolic allelochemicals in plant interactions with other organisms and 2) to alter such interactions for agricultural purposes. The first of these uses has already been accomplished on a limited scale (21, 22, 50, 51, 84, 86), however, there is no published evidence of the latter. This does not mean that herbicide and growth regulator-influences on plant secondary metabolism do not affect agricultural ecosystems by changing allelochemic compositions of plants. It is likely that this is the case, but it... 

Chemical manipulation of secondary compound composition of crop plants offers several advantages over genetic control of their production. Chemical manipulation allows for timing the manipulation as well as possibly determining the quality and quantity of the desired response. 

Several matrix modifiers, which alter the drying or charring properties of the sample matrix, have been tested [374-378] to reduce nonspecific absorption. However, the matrix modification methods do not permit determinations of the indigenous lead in seawater because of the relatively high detection limit and poor precision, and yet gross chemical manipulations of the samples should be avoided to prevent contaminations which can be dramatic when the analyte is present at p,g/l or sub- xg/l level. 

Chen S (2004) Chemical manipulations of nanoscale electron transfers. J Electroanal Chem 574 153-165... 

For example, X-ray fluorescence spectrometry may provide rapid but rather imprecise quantitative results in a trace element problem. Atomic absorption spectrophotometry, on the other hand, will supply more precise data, but at the expense of more time-consuming chemical manipulations. 

---