Transformation of an organism

The transformation of an organic compound by a microorganism that is unable to use the substrate or one of its constituent elements as a source of energy is termed co-metabolism. The active microbial populations thus derive no nutritional benefit from the substrates they co-metabolize. The energy sufficient to sustain growth fully is not acquired even if the conversion is an oxidation and releases energy, and the C, N, S, or P that may be in the molecule is not used as a source of these elements for biosynthetic purposes [93-95,185,188-190,202]. 

The other process is the transformation of an organic precursor into a continuous thin ceramic fiber. In the spinning process, polycarbosilane, a high molecular weight polymer containing Si and C, is obtained by thermal decomposition and polymerization of polydimethylsilane. The fiber thus produced consists of a mixture of P-SiC, carbon crystallite and SiO. The presence of carbon crystallite suppresses the growth of SiC crystals. Yajima and coworkers (Yajima et al., 1976, 1978, 1979) were the first to produce fine (10-30 pm in diameter), continuous and flexible fibers, which are commercialized with the trade name of Nicalon (Nippon Carbon Co.). 

Examination of the behaviour of a dilute solution of the substrate at a small electrode is a preliminary step towards electrochemical transformation of an organic compound. The electrode potential is swept in a linear fashion and the current recorded. This experiment shows the potential range where the substrate is electroactive and information about the mechanism of the electrochemical process can be deduced from the shape of the voltammetric response curve [44]. Substrate concentrations of the order of 10 molar are used with electrodes of area 0.2 cm or less and a supporting electrolyte concentration around 0.1 molar. As the electrode potential is swept through the electroactive region, a current response of the order of microamperes is seen. The response rises and eventually reaches a maximum value. At such low substrate concentration, the rate of the surface electron transfer process eventually becomes limited by the rate of diffusion of substrate towards the electrode. The counter electrode is placed in the same reaction vessel. At these low concentrations, products formed at the counter electrode do not interfere with the working electrode process. The potential of the working electrode is controlled relative to a reference electrode. For most work, even in aprotic solvents, the reference electrode is the aqueous saturated calomel electrode. Quoted reaction potentials then include the liquid junction potential. A reference electrode, which uses the same solvent as the main electrochemical cell, is used when mechanistic conclusions are to be drawn from the experimental results. 

Transformation of an organic polymer into a material that consists largely of carbon. 

Before we take a look at some typical rate laws encountered with chemical reactions in the environment, some additional comments are necessary. It is important to realize that the empirical rate law Eq. 12-10 for the transformation of an organic compound does not reveal the mechanism of the reaction considered. As we will see, even a very-simple-looking reaction may proceed by several distinct reaction steps elementary molecular changes) in which chemical bonds are broken and new bonds are formed to convert the compound to the observed product. Each of these steps, including back reactions, may be important in determining the overall reaction rate. Therefore, the reaction rate constant, k, may be a composite of reaction rate constants of several elementary reaction steps. 

As discussed in Section 14.2, the oxidative or reductive transformation of an organic compound commonly requires two electrons (or, more generally, an even number of electrons) to be transferred to yield a stable product. In many cases, however, the two electrons are transferred in sequential steps (Eberson, 1987). With the transfer of the first electron, a radical species is formed which, in general, is much more reactive than the parent compound. Hence, the overall transformation rate will often be determined by the rate of transfer of the first electron from or to the organic compound. Therefore, we should be particularly interested in those compound-specific properties that are relevant for this first one-electron reaction. 

A broader definition of fermentation is "an enzymatically controlled transformation of an organic compound" according to Webster s New College Dictionary (A Merriam-Webster, 1977) that we adopt in this text. 

All oxidations meet criteria (1) and (2), and many meet criterion (3), but this is not always easy to demonstrate. Alternatively, an oxidation can be described as a transformation of an organic substrate that can be rationally dissected into steps or primitive changes. The latter consist in removal of one or several electrons from the substrate followed or preceded by gain or loss of water and/or hydrons or hydroxide ions, or by NUCLEOPHILIC substitution by water or its reverse and/or by an intramolecular molecular rearrangement. 

Lastly, the word fermentation needs to be discussed due to the confusion caused by different definitions of the word. Traditionally, fermentation was defined as the process for the production of alcohol or lactic acid from glucose. A broader definition of fermentation, which has been adopted in this handbook, is an enzymatically controlled transformation of an organic compound. 

One of the most general and frequently applied indirect methods is the transformation of an organic compound into a nitrocompound. The method is applied to hydrocarbons and other aromatic compounds, mainly those bearing a phenyl ring, e.g. phenols, substituted anilines, phenyl-bearing amino acids etc. The nitrating mixture consists of nitric acid, either pure or... 

Breakdown Products Compounds resulting from transformation of an organic substance through chemical, photochemical, and/or biochemical reactions. 

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