Unnatural processes

A thermodynamic process is said to have taken place if a change is observed to have taken place in any macroscopic property of the system. An infinitesimal process is a process in which there is only an infinitesimal change in any macroscopic property of the system. A natural process is an infinitesimal process that occurs spontaneously in real systems an unnatural process is one that cannot occur spontaneously in real systems. Reversible processes are either natural or unnatural processes which can occur in either direction between two states of equilibrium... 

There is a need to gain this energy (entropy) and it is possible within such an isolated system by an unnatural process of transformation of heat to mechanical energy. But, this process is "running" at a background of a natural process of the heat transfer in accordance with the II. Principle of Thermod5mamics. 

A characteristic feature of thermoplastics shaped by melt processing operations is that on cooling after shaping many molecules become frozen in an oriented conformation. Such a conformation is unnatural to the polymer molecule, which continually strives to take up a randomly coiled state. If the molecules were unfrozen a stress would be required to maintain their oriented conformation. Another way of looking at this is to consider that there is a frozen-in stress corresponding to a frozen-in strain due to molecular orientation. 

A central focus in modem organic synthesis has been the development of highly efficient catalytic processes for the syntheses of natural and unnatural compounds of medicinal interest or intermediates useful for functional materials. A particularly attractive approach is to apply transition metal catalysed cyclisation reactions for the transformation of simple starting materials into monocyclic, bicyclic and polycyclic scaffolds that can be further elaborated into specific targets. 

If an aromatic compound reacts with an OH radical to form a specific set of hydroxylated products that can be accurately identified and quantified in biological samples, and one or more of these products are not identical to naturally occurring hydroxylated species, i.e. not produced by normal metabolic processes, then the identification of these unnatural products can be used to monitor OH radical activity therein. This is likely to be the case if the aromatic detector molecule is present at the sites of OH radical generation at concentrations sufficient to compete with any other molecules that might scavenge OH radical. 

McDaniel, R., Licari, P. and Khosla, C. (2001) Process development and metabolic engineering for the overproduction of natural and unnatural polyketides in Metabolic Engineering, vol. 73 (ed. 1. Nielsen), Springer, Berlin, pp. 31-52. 

The ether linkage is a major structural motif found in a broad range of natural and unnatural structures. Due to the biomedical and industrial importance of these molecules, the efficient and selective construction of ether bonds has been a topic of long-standing interest. While numerous etherification processes have been developed ever since the discovery of the Williamson ether synthesis,1 an increasingly large number of examples have employed transition... 

This article provides a brief overview of several recent total syntheses of natural and unnatural products that have benefited from the use of catalytic asymmetric processes. The article is divided by the type of bond formation that the catalytic enan-tioselective reaction accomplishes (e.g C-C or C-0 bond formation). Emphasis is made on instances where a catalytic asymmetric reaction is utilized at a critical step (or steps) within a total synthesis however, cases where catalytic enantioselective transformations are used to prepare the requisite chiral non-racemic starting materials are also discussed. At the close of the article, two recent total syntheses are examined, where asymmetric catalytic reactions along with a number of other catalyzed processes are the significant driving force behind the successful completion of these efforts (Catalysis-Based Total Syntheses). 

It is an exciting prospect that catalysts of this nature may lead to artificial enzymes capable of processing natural and unnatural polyisoprenoids to generate various useful terpenes. 

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