Availability to organisms

The natural world is one of eomplex mixtures petroleum may eontain 10 -10 eomponents, while it has been estimated that there are at least 150 000 different proteins in the human body. The separation methods necessary to cope with complexity of this kind are based on chromatography and electrophoresis, and it could be said that separation has been the science of the 20th century (1, 2). Indeed, separation science spans the century almost exactly. In the early 1900s, organic and natural product chemistry was dominated by synthesis and by structure determination by degradation, chemical reactions and elemental analysis distillation, liquid extraction, and especially crystallization were the separation methods available to organic chemists. 

Nuclear magnetic resonance (NMR) spectroscopy is the most valuable spectroscopic technique available to organic chemists. It s the method of structure determination that organic chemists turn to first. 

The content of astaxanthin in the aplanospores is about 1 to 2% of dry weight and their thick walls require physical breakage before the astaxanthin can be extracted or become available to organisms consuming the alga. ... 

Hazard evaluation posed by organotin compounds to natural resources is predicated partly on their chemical composition, partly on their concentration and persistence in abiotic materials and diet items, and partly on their availability to organisms. In each of these areas, key data are missing for promulgation of effective regulations. It seems that additional research is needed in eight areas to acquire these data ... 

While it is one of the most important and versatile transformations available to organic chemists, there is no unequivocal example of a biological counterpart. Hence, attempts to generate antibodies which could catalyse this reaction were seen as an important target. The major task in producing a Diels-Alderase antibody lies in the choice of a suitable haptenic structure, because the transition state for the reaction resembles product more closely than reactants (Fig. 12). The reaction product itself is an inappropriate hapten because it is likely to result in severe product inhibition of the catalyst, thereby preventing turnover. 

Remember, however that CHAOS does not intend to be a database of "synthetic methods" presently available to organic chemists. CHAOS is aimed at finding the intermediate precursors of the "synthesis tree" by means of selected basic disconnections (either "consonant" or "dissonant"). In the author s view, it is of minor importance, for instance, how a "carbene" -resulting from a -(2 + 1) cycloelimination- is generated, or whether a double bond is the direct result of a Wittig reaction or the dehydration of an alcohol formed in a Grignard reaction. In... 

The principle of solvent extraction—the distribution of chemical species between two immiscible liquid phases—has been applied to many areas of chemistry. A typical one is liquid partition chromatography, where the principle of solvent extraction provides the most efficient separation process available to organic chemistry today its huge application has become a field (and an industry ) of its own. The design of ion selective electrodes is another application of the solvent extraction principle it also has become an independent field. Both these applications are only briefly touched upon in the chapter of this book on analytical applications (Chapter 14), as we consider them outside the scope of... 

In the 1970s a new technique, low temperature (5-20 K) isolation, became available to organic chemists that allowed the preparation and isolation of highly reactive species which previously could not be directly observed. Typically a precursor was condensed in a matrix of an inert substance (e.g., argon) and then... 

Given that the Fe and P bound to the DOM in humic lakes are probably not directly available to organisms, the DOM-Fe-P complex would have to undergo some form of transformation to yield bioavailable Fe and P species. In terms of biological uptake, in general it can be said that Fe is preferred in the dissolved free ionic form and P as orthophosphate (P04). Several known processes result in the transformation of Fe and P from the DOM-Fe-P complex into biologically available species. Two of the mechanisms are physical-chemical processes (1) UV-mediated photoreduction and (2) DOM-mediated chemical reduction or dark reduction. Other mechanisms are... 

Morgan, J.J. 2000. Manganese in natural waters and earth s crust Its availability to organisms. Met. Ions Biol. Syst. 37 1-34. 

The finite resources available to organisms must be allocated to several life processes including growth, reproduction, maintenance, defense, and further resource acquisition. It is often assumed that a resource allocated to one process incurs a cost to the remaining processes because the resource is diverted away from them.7 8 It is also assumed that natural selection acts to optimize the allocation of resources to best suit the life history and environment for a particular organism, of course, within evolutionary and ecological constraints. 

As only a small fraction of a substance in the soil is likely to be available to organisms, total concentrations of substances in soils are generally poor predictors... 

The oxidation of phenols and other organic substrates by MnP Is dependent on Mnll (23,30). Apparently the enzyme first oxidizes Mnll to Mnlll, and Mnlll subsequently oxidizes the organic substrates (30,31,47). As shown In Figure 3, addition of one equivalent of Mnll rapidly reduces MnP compound I to compound II (41). A second equivalent of Mnll reduces MnP compound II to the native ferric enzyme. Similarly, MnP compound I Is reducible by phenolic substrates, albeit at a slower rate. However, phenolic substrates are not able to reduce MnP compound II efficiently (41). Thus the enzyme Is unable to complete Its catalytic cycle efficiently In the absence of Mnll. This would seem to explain the absolute Mnll requirement for catalytic activity. In the conversion of MnP compound I to compound II, the porphyrin tt-cation Is reduced back to a normal porphyrin. This suggests that the porphyrin radical Is exposed In a peripheral site as recently suggested for HRP (48) and that this site may be available to organic substrates and to Mnll. In contrast, the FeIV 0 center of MnP compound II may be partially burled and only available to Mnll Ions. 

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