Biological Transformations

Sections Most of the steroids in animals are formed by biological transformations 26 12-26 15 of cholesterol... 

The biological transformations that involve ATP are both numerous and funda mental They include for example many phosphorylation reactions m which ATP trans fers one of its phosphate units to the —OH of another molecule These phosphoryla tions are catalyzed by enzymes called kinases An example is the first step m the metabolism of glucose... 

See if you can come up with an extensive range of possible applications of biological transformations that may facilitate separation and use of the racemates. (Think of the application of enzymatically mediated transformations which we describe earlier, this should help you to come up with several ideas). 

Fig. 12-1 Biological transformations of nitrogen compounds. The numbers refer to processes described in the text.

Even if organocatalysis is a common activation process in biological transformations, this concept has only recently been developed for chemical applications. During the last decade, achiral ureas and thioureas have been used in allylation reactions [146], the Bayhs-Hillman reaction [147] and the Claisen rearrangement [148]. Chiral organocatalysis can be achieved with optically active ureas and thioureas for asymmetric C - C bond-forming reactions such as the Strecker reaction (Sect. 5.1), Mannich reactions (Sect. 5.2), phosphorylation reactions (Sect. 5.3), Michael reactions (Sect. 5.4) and Diels-Alder cyclisations (Sect. 5.6). Finally, deprotonated chiral thioureas were used as chiral bases (Sect. 5.7). 

Biodegradation Partly Some near-surface bacteria appear capable of entering and surviving in the deep-well environment. However, in general, temperature and pressure conditions in the deep-well environment are unfavorable for microbiota that are adapted to near-surface conditions. Biological transformations are primarily anaerobic. 

Descriptions of the Major Types of Biological Transformation Processes... 

The biological cycle — that may encompass processes of biological transformation, plant uptake, bioaccumulation, soil organisms transformations and others. 

In all of the workshops, but especially in the FAT and Exposure Assessment workshops, the need for better understanding and model representation of soil systems, including both unsaturated and saturated zones, was evident. This included the entire range of processes shown in Table II, i.e., transport, chemical and biological transformations, and intermedia transfers by sorption/desorption and volatilization. In fact, the Exposure Assessment workshop (Level II) listed biological degradation processes as a major research priority for both soil and water systems, since current understanding in both systems must be improved for site-specific assessments. 

Simple models are used to Identify the dominant fate or transport path of a material near the terrestrial-atmospheric Interface. The models are based on partitioning and fugacity concepts as well as first-order transformation kinetics and second-order transport kinetics. Along with a consideration of the chemical and biological transformations, this approach determines if the material is likely to volatilize rapidly, leach downward, or move up and down in the soil profile in response to precipitation and evapotranspiration. This determination can be useful for preliminary risk assessments or for choosing the appropriate more complete terrestrial and atmospheric models for a study of environmental fate. The models are illustrated using a set of pesticides with widely different behavior patterns. 

Bollag J-M, Liu S-Y (1990) Biological transformation processes of pesticides. In Cheng HH (ed) Pesticides in the soil environment processes, Impacts and Modeling. Soil Science Society of America, Madison, Wisconsin, pp 169-211. 

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